UNIVERSITY OF NAIROBI

Review of Grout Material in Difficult Dam Foundations with

Emphasis on

Cement-Bentonite Material

BY

MBIYU MEDLIN NJOKI

F16/2341/2009

SUPERVISOR: ENG. J. R. RUIGU

A project submitted as a partial fulfillment

for the requirement for the award of the degree of

BACHELOR OF SCIENCE IN CIVIL ENGINEERING

MARCH 2014

F16/2341/2009 i

ABSTRACT

Grouting is a popular ground treatment technique, but not well known to most in the engineering

industry. A lot of misconceptions surround this subject. This dissertation presents the research on

grouting in an attempt to clarify the basic parameters involved such as permeability, to provide a

full coverage on the practices in use in the recent past to help aid in its use currently and to report

on their effects to the environment.

Cement based grout is the main material in focus and with the use of documented case studies,

this paper provides a brief discussion of the effectiveness in foundation treatment.

The application of cement based permeation grouting is still largely a trial and error process in

the current practice, especially in the local construction industry.

F16/2341/2009 ii

DEDICATION

I would like to dedicate this project to my family for their contribution in my life and steadfast

support which can never be repaid.

F16/2341/2009 iii

ACKNOWLEGEMENT

Without help, support and encouragement from lecturers, engineers and colleagues among

others, the author would never have been able to finish this work.

The author wishes to express their deep gratitude to their supervisor, Eng. J. R. Ruigu for his

tireless efforts, wise advice and constant guidance.

In the same breath, the author is grateful to Eng. Dedan Otiato for taking the time to expose a

student to the little known field of Grouting and going further as to expect feedback and

recommendations on the subject.

Many thanks to the entire Civil engineering department staff for their helpful advice. The author

is indebted for their resilient effort which made this work fruitful.

This project may never have been accomplished without the support of family and friends who

raised one‘s spirits when headway in the project seemed improbable. To the class of 2014, thank

you all for the hard work, co-operation and level-headed constructive criticism.

The author wishes to express their sincere gratitude to the following institution: Norken (I) Ltd..

This is in recognition for their support and informative data.

Most importantly, glory be to God for His grace which knows no bounds.

F16/2341/2009 iv

CONTENTS

ABSTRACT ..................................................................................................................................... i

DEDICATION ................................................................................................................................ ii

ACKNOWLEGEMENT ................................................................................................................ iii

LIST OF FIGURES ....................................................................................................................... vi

LIST OF TABLES ....................................................................................................................... viii

ABBREVIATIONS ....................................................................................................................... ix

1. INTRODUCTION ................................................................................................................... 1

1.1 DEFINITION OF GROUTING ............................................................................................ 1

1.2 PROBLEM STATEMENT ................................................................................................... 2

1.3 OBJECTIVES OF RESEARCH ........................................................................................... 2

1.4 SCOPE AND RESEARCH METHODOLOGY ................................................................... 3

2. LITERATURE REVIEW ........................................................................................................ 4

2.1 BACKGROUND INFORMATION ON DAM FOUNDATIONS ....................................... 4

2.1.1. DAM FOUNDATION TYPES ..................................................................................... 4

2.1.2. TREATMENT OF NON-IDEAL DAM FOUNDATIONS .......................................... 5

2.2 GROUTING ........................................................................................................................ 11

2.2.1 FACTORS TO CONSIDER DURING GROUTING .................................................. 11

2.3 CLASSIFICATION OF GROUT........................................................................................ 13

2.3.1 EMULSION TYPE...................................................................................................... 13

2.3.2. SOLUTION TYPE GROUT ....................................................................................... 13

2.3.3. SUSPENSION TYPE GROUT ................................................................................... 16

2.3.4 CEMENT-BENTONITE GROUTS ............................................................................. 17

2.4 GROUTING PROCEDURE ............................................................................................... 17

2.4.1 METHODS ................................................................................................................... 17

2.4.2. COMMON EQUIPMENT USED ............................................................................... 19

2.4.3. CLOSURE GROUTING ............................................................................................. 20

2.5 SPACING OF GROUT HOLES ......................................................................................... 23

2.6 GENERAL SIZE AND DEPTH OF GROUT HOLES ...................................................... 24

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2.7. TESTS ASSOCIATED WITH GROUTING ..................................................................... 24

2.7.1. UNCONFINED COMPRESSIVE STRENGTH TEST (UCS) ................................... 24

2.7.2 WATER PRESSURE TESTS/ PERMEABILITY TESTS .......................................... 28

2.7.3 SECONDARY PERMEABILITY INDEX (SPI)......................................................... 32

2.8 TECHNICAL SPECIFICATIONS FOR CEMENT BENTONITE SLURRY ................... 33

3. CASE STUDIES.................................................................................................................... 34

3.1. THETA DAM, KENYA .................................................................................................... 34

3.1.1 BACKGROUND INFORMATION ............................................................................. 34

3.1.2 GEOLOGY OF THE SITE ........................................................................................... 34

3.1.3 GEOPHYSICAL INVESTIGATIONS ........................................................................ 35

3.1.4 DESIGN, METHODS AND CONSTRUCTION ......................................................... 36

3.1.5 RESULTS ..................................................................................................................... 37

3.2 TURTLE CREEK DAM, USA ........................................................................................... 39

3.2.1 BACKGROUND INFORMATION ............................................................................. 39

3.2.2. SUBSURFACE CONDITIONS ............................................................................. 40

3.2.3 DESIGN, METHODS AND MATERIALS OF CONSTRUCTION ........................... 40

3.2.4 SAMPLING AND TESTING ...................................................................................... 42

3.2.5 RESULTS AND FINDINGS........................................................................................ 43

3.3 KARKHEH DAM, IRAN ....................................................................................................... 45

3.3.1 BACKGROUND INFORMATION ............................................................................. 45

3.2.2 GEOLOGY ................................................................................................................... 45

3.3.3 DESIGN, METHODS AND CONSTRUCTION ......................................................... 46

3.3.4 RESULTS ..................................................................................................................... 50

4. DISCUSSION ........................................................................................................................ 51

5. CONCLUSION AND RECOMMENDATION .................................................................... 54

5.1 CONCLUSION ................................................................................................................... 54

5.2 RECOMMENDATIONS .................................................................................................... 55

REFRENCES ................................................................................................................................ 56

F16/2341/2009 vi

LIST OF FIGURES

Figure 2.1. Cutoff trench in an embankment dam.

Figure 2.2. Sheet piling as seen on site.

Figure2.3. Types and arrangement of grouting equipment used.

Figure2.4. positions of primary and secondary grout holes.

Figure 2.5 positions of multiple grout holes.

Figure 2.6. (a) Grout permeation within first two stages.

Figure 2.6. (b) Grout permeation within subsequent stage.

Figure2.7. Grouting required for ideal foundation.

Figure 2.8. Failure pattern typical of brittle specimens.

Figure 2.9. Soil consistency in relation to ultimate strength.

Figure 2.11. Mohr‘s circle for Unconfined Compression Test.

Figure 2.12. Layout of the constant head packer test.

Figure 3.1. A geographic map of Theta dam site.

Figure3.2. Resistivity values within the different strata located at different depths along dam

axis.

Figure 3.3. Turtle creek as is seen today.

Figure 3.4. Plan view of transverse shear walls.

Figure 3.5. Side view of transverse shear walls.

Figure 3.6. Table showing average UCS values for samples.

Figure 3.7. UCS values with time for sample collected.

F16/2341/2009 vii

Figure 3.8. Aerial view of Karkheh dam.

Figure 3.9. Longitudinal cross section of Karkheh dam.

Figure 3.10. Karkheh dam cutoff walls and the location of the probable chemical grouting

curtain.

Figure 3.11. Sketch showing the triangular placement of shallow test holes in phase 1 of test

chemical grouting.

Figure 3.12. Material arrangement within grout hole.

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LIST OF TABLES

Table 2.1. Comparison of chemical grouts as to their technical aspects and their effects on

human health and the environment.

Table 2.2. Spacing of grout holes.

Table 2.3. Relative consistency as a function of unconfined compressive strength.

Table 2.4. Pressure magnitudes for each stage in Lugeon Test.

Table 2.5. A graphic summary of the five behavior groups defined by Houlsby (1976), as

well as the representative Lugeon value that should be reported for each group.

Table 2.6. Properties of rock masses according to lugeon range.

Table 2.7. Rock mass classification based on the SPI and ground treatment considerations.

Table 3.1. Grout holes made along dam axis.

Table 3.2 Lugeon values attained before and after grouting.

Table 3.3. Summary of grouting in phase 1 test holes.

Table 3.4. Summary of grouting records in the test hole S4.

F16/2341/2009 ix

ABBREVIATIONS

AA - acrylic acid

MAA - methacrylic acid

PAH - polycyclic aromatic hydrocarbons

TDI - toluene di-isocyanate

BDP- di-n-butylphthalate

DFG - Deutsche Forschungsgesellschaft (German Research Society)

1 F16/2341/2009

1. INTRODUCTION

1.1 DEFINITION OF GROUTING

Grouting is defined as the procedure of filling or injecting fluid with pressure into structural and

lithological defects or cavities between ground layer and base rock, generally via boreholes.

Grouting was first used in 1802 by the French engineer Charles Berigny using water and

pozzolanic cement mixture in ground grouting.

The purpose of injecting a grout may be any one or more of the following:

To decrease permeability of foundation ground.

To increase shear strength of foundation.

To decrease compressibility of the foundation.

Nowadays, it extends to alleviate settlement of ground caused by basement and tunnel

excavation works, to strengthen ground so that it can be used as a structural member or as a

retaining structure in solving geotechnical problems.

Later, with the development of cement and hydraulic binders, the use of grouting in construction

and mining engineering has become widespread. (Johan Lagerlund, 2009)

Grouting proves especially effective in the following cases:

When the foundation has to be constructed below the ground water table. The deeper the

foundation, the longer the time needed for construction, and therefore, the more benefit

gained from grouting as compared with dewatering.

When there is difficult access to the foundation level. This is very often the case in city

work, in tunnel shafts, sewers, and subway construction.

When the geometric dimensions of the foundation are complicated and involves many

boundaries and contact zones.

When the adjacent structures require that the soil of the foundation strata should not be

excavated (extension of existing foundations into deeper layers).

F16/2341/2009 2

Grouting has been extensively used primarily to control ground water flow under earth and

masonry dams, where rock grouting is used. Since the process fills soil voids with some type of

stabilizing material, grouting is also used to increase soil strength and prevent excessive

settlement.

Grouting, instead of being an old and obsolete ground treatment technique, is still developing in

both methodology as well as hardware engineering. Its application is extending in the civil

engineering field, from small-scale remedial work site to very large-scale project site. It is still

the most popular ground treatment method used today ( V.N.S. Murthy).

1.2 PROBLEM STATEMENT

Backfill for a borehole instrument is a material that receives a disproportionate lack of

attention despite having a great amount of significance in a construction project.

The area of study is mostly unfamiliar to many engineers since actual drilling and

grouting is done by specialists. Most difficulties and disputes in this phase of work arise

when an inexperienced firm is sub-contracted.

1.3 OBJECTIVES OF RESEARCH

To provide comprehensive information on grouting in relation to cement based grout

material used in dam foundations.

To clarify misconceptions that may exist in connection with grouting.

It is an attempt to weigh the pros and cons of the methods involved thus bringing the

industry one step closer to perfecting methods used.

F16/2341/2009 3

1.4 SCOPE AND RESEARCH METHODOLOGY

General foundation properties will be considered in connection to techniques used to improve on

them. Materials for grouting will be discussed as well as their advantages and disadvantages.

This project also involves data discussions on analysis of geophysical data collected, properties

used for parameters developed for grouting and sensitivity analysis carried out to ascertain

effectiveness of procedure the procedure with due regard to the material in use.

The properties of grout material will be investigated as well as specifications for such design.

Collection of information will be mainly through internet research as well as through library

books, e-books and review of case study reports.

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2. LITERATURE REVIEW

2.1 BACKGROUND INFORMATION ON DAM FOUNDATIONS

2.1.1. DAM FOUNDATION TYPES

It is important to consider the suitability of the various types of rock and soil as foundation and

construction materials when proposing to construct a dam.

The foundation geology at a dam site often dictates the type of dam suitable for that site. The

strength, thickness, and inclination of strata; permeability; fracturing; and faulting are all

important considerations in selecting the dam type be it earthfill, rockfill or concrete. Some of

the different foundations commonly encountered are discussed below.

(a) Rock Foundations -Competent rock foundations, which are free of significant geologic

defects, have relatively high shear strengths and are resistant to erosion and percolation.

In addition they offer few restrictions as to the type of dam that can be built upon them.

The economy of materials or the overall cost should be the ruling factor.

The removal of disintegrated rock together with the sealing of seams and fractures by

grouting is frequently necessary. Weaker rocks such as clay shales, some sandstones,

weathered basalt, etc., may present significant problems to the design and construction of

a dam and may heavily influence the type of dam selected.

(b) Gravel Foundations.-Gravel foundations, if well compacted, are suitable for earthfill or

rockfill dams. Because gravel foundations are frequently subjected to water percolation at

high rates, special precautions just be taken to provide adequate seepage control or

effective water cutoffs or seals.

(c) Silt or Fine Sand Foundations.-Silt or fine sand foundations can be used for low concrete

gravity dams and earthfill dams if properly designed, but they are generally not suitable

for rockfill dams. Design concerns include non uniform settlement, potential soil collapse

upon saturation, uplift forces, the prevention of piping, excessive percolation losses, and

protection of the foundation at the downstream embankment toe from erosion.

(d) Clay Foundations.-Clay foundations can be used for the support of earthfill dams, but

require relatively flat embankment slopes because of relatively lower foundation shear

strengths. Clay foundations under dams can also consolidate significantly.

F16/2341/2009 5

Because of the requirement for flatter slopes and the tendency for clay foundations to

settle a lot, it is usually not economical to construct a rockfill dam on a clay foundation.

Clay foundations are also ordinarily not suitable for concrete gravity dams. Tests of the

foundation material in its natural state are usually required to determine the consolidation

characteristics of the foundation strata and their ability to support the superimposed load.

(e) Non-uniform Foundations.-Occasionally, situations occur where reasonably uniform

foundations of any of the types described above cannot be found and where a non-

uniform foundation of rock and soft material must be used if the dam is to be built.

Nevertheless, such conditions can often be counterbalanced by special design features.

Even dam sites that are not highly unusual present special problems requiring the

selection of appropriate treatment by experienced engineers.

Foundations are not actually designed. Rather, certain provisions for treatment are made in

designs to ensure that the essential requirements are met. No two foundations are exactly alike;

each foundation presents its own separate and distinct problems requiring corresponding special

treatment and preparation. The importance of adequate foundation treatment is emphasized by

the fact that approximately 40 percent of all earthfill dam accidents and 12 percent of all failures

are attributed to foundation failures.

2.1.2. TREATMENT OF NON-IDEAL DAM FOUNDATIONS

Different treatments are appropriate for different conditions. Foundations are grouped into three

main classes according to their predominant characteristics:

1. Foundations of rock.

2. Foundations of coarse-grained material (sand and gravel).

3. Foundations of fine-grained material (silt and clay).

The character of a foundation, as revealed by exploration, can usually be safely generalized for

the design of dams to fit into one of the classes given above. Once the class is determined, the

nature of the problem requiring treatment will be evident. Ordinarily, coarse-grained, pervious

foundations present no difficulties in the matter of settlement or stability for a small dam;

conversely, fine grained, weak foundations subject to settlement or displacement usually present

no seepage problems.

F16/2341/2009 6

2.1.2.1 Rock foundations

Rock foundations are generally considered as the best foundation condition. However, dam sites

with good rock foundations are becoming increasingly rare hence engineers are being forced to

use foundations that are far from ideal because of the growth and shifting of population centers

that cause increased emphasis on water conservation for domestic, agricultural, and industrial use

in new locations.

Treatment of deficient foundation zones is especially critical for the areas beneath the

impervious core and the filter and drainage zones immediately downstream of the impervious

zone.

Rock foundation treatment includes grouting as a measure to counter erosive leakage, excessive

uplift pressure, or high water losses occurring through joints, fissures, crevices, permeable strata,

or along fault planes within the foundation.

The grouting of a dam foundation is usually performed along a single line of grout holes spaced

10 to 20 feet (3m – 6 m) centre to centre. This creates some tightening deep in the foundation

and some reduction in permeability. However, multiple lines of grout holes are necessary when

severely fractured or highly permeable rock is encountered. Only multiple-line curtains improve

the degree of reliability, but even then results are speculative because it is impossible to

thoroughly grout all fractures or pores in the foundation. A grout curtain should not be relied on

as the single provision to reduce seepage and related uplift pressures so that downstream seepage

control features are reduced or eliminated. In cases where large zones of fractured rock lie at the

foundation contact or where the zone of broken rock within a fault has great width, it may be

possible to grout the zone by grouting to a shallow depth, usually 10 to 30 feet (3m-9m), by

using a grid pattern. This type of grouting is referred to as ―blanket grouting.‖ It reduces leakage

in the fractured zone and provides a more firm foundation for the dam. In most cases, the

foundation directly beneath the impervious zone requires some blanket grouting.

F16/2341/2009 7

2.1.2.2. Sand and Gravel Foundations

Often the foundations for such dams consist of recent alluvial deposits composed of relatively

pervious sands and gravels overlying impervious geologic formations. The pervious materials

may range from fine sand to openwork gravels, but more often they consist of stratified

heterogeneous mixtures. Generally, sand and gravel foundations have sufficient strength to

adequately support loads caused by the embankment and reservoir, although this must be verified

by adequate exploration, testing and analysis.

Knowledge of the geologic deposition process can help determine the potential occurrence of

low strength zones.

Two basic problems are found in pervious foundations; one pertains to the amount of

underseepage, and the other is concerned with the forces exerted by the seepage.

The type and extent of treatment justified to decrease the amount of seepage should be

determined by the purpose of the dam, the streamflow yield in relation to the reservoir

conservation capacity, and the necessity for making constant reservoir releases to serve senior

water rights or to maintain a live stream for fish or for other conservation purposes. Loss of

water through underseepage may be of economic concern for a storage dam.

Various methods of seepage and percolation control can be used in combination to reduce the

flow and to control seepage forces.

The methods include:

(a) Cutoff trenches

Pervious foundation should be cut off by a trench extending to bedrock or other impervious

stratum. This is the most positive means of controlling the amount of seepage and ensuring that

no difficulty will be encountered by piping through the foundation or by uplift pressures at the

downstream toe.

F16/2341/2009 8

Figure 2.1. Cutoff trench in an embankment dam. (ikonet.com)

(b) Sheet piling

This is an earth retention technique that retains soil using steel sheet piles. Steel sheet piling is

relatively expensive and where cobbles or boulders are present, or where the material is highly

resistant to penetration, driving or jetting becomes difficult and costly. It is highly doubtful that

an effective cutoff can be obtained because of the tendency of the piling to wander and become

damaged by breaks in the interlocks or tearing of the steel. A heavy structural section with strong

interlocks should be used if the foundation contains gravel.

Under the best conditions, including the use of compound to seal the interlocks and good contact

of the bottom of the piling with an impervious foundation, it can be expected that the piling will

be only 80 to 90 percent effective in preventing seepage.

F16/2341/2009 9

Figure 2.2. Sheet piling as seen on site.(Donegan.co.uk)

(c) Mixed-in-place concrete pile curtains

The mixed-in-place cement-bound curtain is another means of establishing a cutoff in pervious

foundations. The curtain is constructed by successively overlapping individual piles. Each

mixed-in-place pile consists of a column of soil intimately mixed with mortar to form a pile like

structure within the soil. Such a pile is constructed by injecting mortar through a vertical rotating

hollow shaft, the lower end of which is equipped with a mixing head for combining the soil with

the mortar as the latter is injected. The mortar is introduced into soil that has been loosened by

the mixing head as the bit is simultaneously rotated and advanced into, or withdrawn from, the

soil. The piles may be reinforced as required.

(d) Slurry trenches

This is an effective method of constructing positive cutoffs when wet conditions or deep cutoffs

in alluvial valleys make conventional construction methods uneconomical is the slurry trench

method. The technique was adapted from well drilling methods used by the oil industry.

Bentonite clay suspensions are used to support holes cut in soft soils. The slurry trench method

uses water bentonite slurry to seal and support the trench wall during the excavation process.

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2.1.2.3. Silt and Clay Foundations.

Foundations of fine grained soils are usually impermeable enough to avoid the necessity of

providing design features for underseepage and piping.

The main problem with these foundations is stability. In addition to the obvious danger of

bearing failure of foundations of saturated silts and clays, the designs must take into account the

effect of foundation saturation of the dam and of connected works next to the reservoir.

Methods of foundation treatment are based on the soil type, the location of the water table, and

the density of the soil.

(a) Saturated foundations

The methods of treatment applicable to these conditions are;

1. To remove the soils with low shear strength.

2. To provide drainage of the foundation to permit the increase of strength during

construction.

3. To reduce the magnitude of the average shear stress along the potential sliding surface by

flattening the slopes of the embankment.

Removing soft foundation soils is sometimes practicable. Relatively thin layers of soft soils

overlying firm material may be removed when the cost of excavation and refill is less than the

combined cost of special investigations and the flatter embankment slopes required. The most

practicable solution for foundations of saturated fine-grained soils is flattening the embankment

slopes. This means the critical sliding surface will lengthen, thereby decreasing the average shear

stress along its path and increasing the factor of safety against sliding.

(b)Relatively Dry Foundations.

Unsaturated impermeable soils are generally satisfactory for foundations of dams because the

presence of air in the soil voids permits appreciable volume change, increase of normal effective

stress, and mobilization of frictional shear resistance without drainage of the pore fluid.

That is, for a given void ratio, an impervious soil has greater bearing capacity in the unsaturated

condition than in the saturated condition. Also, in a situation where water gets to the foundation,

appreciable settlement would occur thus compromising dam stability.

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Therefore, the foundation in this area should be thoroughly wetted to raise the average water

content to saturation. This ensures voids are filled with water hence settlement that would occur

would be negligible. (United States Department of the Interior Bureau of Reclamation, 1987)

2.2 GROUTING

It is a fact that all dams leak thus the main objective in this regard is to reduce the amount of

leakage so that;

The structure can serve its purpose throughout its design life without compromising on

safety requirements.

The rate of leakage can be reduced to an economically viable level.

The goal is to reduce leakages to 0.03 cumecs but in some cases it is justifiable to allow leakage

of up to 2.3 cumecs. In the case where grouting is done to reduce permeability, tests are usually

carried out to ascertain if grout works must be carried out. (Ramakrishnana et al, 1989)

2.2.1 FACTORS TO CONSIDER DURING GROUTING

Conditions requiring grouting include;

High porosity observed in underground material during site investigation through

scanning and exploratory cores drilled and recovered.

Presence of faults which can also be determined by geophysical mapping.

Foundation conditions often can be determined from a visual inspection of erosion effects, of

outcrops, and of excavations such as highway or railroad cuts, building excavations, abandoned

pits, and quarries in the general area of the dam site. Information on ground-water conditions

often can be obtained from local wells.

Subsurface exploration of the foundation is needed to determine;

1. The depth to bedrock at the dam site.

2. The character of both the bedrock and the soils under the dam and under accompanying

structures.

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A number of drill holes are usually required at a dam site to determine the bedrock profile along

the proposed axis. The number of drill holes required for foundation exploration of dams should

be determined by the complexity of geologic conditions, but the depth of the drill holes should

be greater than the height of the dam.

Tests normally carried out on site comprise geological mapping, geophysical survey, and

recovery of core samples from site for laboratory tests as well as field tests on site.

2.2.1.1 Geological mapping

Geological mapping describes the exercise of representing the earth‘s surface of a specified area

with particular emphasis on the contours and demarcation of overburden and rock outcrops and

their classification according to colour, grain size, origin and estimated depth. Rock units better

known as geologic strata are shown by colours or symbols where they are exposed to the surface.

The rock outcrops are described according to the following: lithological or Petrographic name,

Colour, Hardness and estimated uni-axial compressive or strength (UCS) using Schmidt Hammer,

indicative block or bedding thickness.

2.2.1.2. Geophysical survey

This is simply the collection of sub-surface data for purposes of design. These tests give a picture

of the nature and quality of material under the site in question. Methods that can be used are;

N Seismic methods such as seismic refraction and seismic tomography.

N Siesmoelectrical methods.

N Geodesity and gravity techniques.

N Magnetic techniques.

N Electrical techniques.

N Elecromagnetic techniques such as ground penetrating radar.

N Remote sensing techniques.

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2.3 CLASSIFICATION OF GROUT

The most accepted form of classifying grout is according to material used. The main types

include;

2.3.1 EMULSION TYPE

These kinds of grout are bituminous. Asphalt grouting has sometimes been used successfully,

particularly in sealing watercourses in underground rock channels. Asphalt grout has also been

used to plug leaks in cofferdams and in natural rock foundations. Asphalt is a brown-to-black

bituminous substance belonging to a group of solid or semisolid hydrocarbons. It occurs

naturally or is obtained as a comparatively nonvolatile residue from the refining of some

petroleums. It melts between 150° F and 200° F. When used for grouting it is generally heated to

400° or 450° F before injection. Asphalt emulsions have also been used for grouting. These are

applied cold. In the emulsion the asphalt is dispersed in colloidal form in water.

After injection the emulsion must be broken so that the asphalt can coagulate to form an

effective grout. Special chemicals are injected with the emulsion for this purpose. Coal-tar pitch

is not a desirable material for grouting since it melts more slowly and chills more quickly than

asphalt grout. When heated above its melting point, coal-tar pitch also emits fumes that are

dangerous to personnel. (Defense Agencies, U.S.A., 1990)

2.3.2. SOLUTION TYPE GROUT

Solution type grout entails chemical grouting which is the process of injecting a chemically

reactive solution that behaves as a fluid but reacts after a predetermined time to form a solid,

semisolid, or gel. Several kinds of chemical grouts are available. The most common are sodium

silicate, acrylate, lignin, urethane, and resin grouts. Chemical grouting requires specially

designed grouting equipment in that the reactive solution is often formed by proportioning the

reacting liquids in an on-line continuous mixer. Typically, chemical-grout plants do not have

particulate materials/filler suspended in a liquid. Further, the materials used in the pumps and

mixers are specifically selected to be nonreactive with the chemicals being mixed and pumped.

The primary advantages of chemical grouts are their low viscosity which enables them to seal

small pores hence providing a low degree of permeability and good control of setting time.

F16/2341/2009 14

Unfortunately, chemical grouts are more expensive than suspension type grouts and can have

toxic effects in some circumstances. (U.S. Army Corps of Engineers, 1995).

Chemical grouts are relatively low viscosities which cause a higher rate of bleeding when used.

This is unsafe especially in dam foundations if the material contaminates the water in the

reservoir.

Chemical grouts are an ever present source of concern as they are not compatible with the

environment hence could negatively affect the ecosystem of the site creating problems which

may never be fully dealt with.

2.3.2.1. Environmental Considerations

Regarding the environmental compatibility of chemical grouts most concern has arisen in

connection with releases of contaminants during their use. Grouts containing mutagenic (altering

the cell structure of a living thing), cancerogenic(causing cancer) or teratogenic(causing

malformations of a foetus) substances or substances with a high toxicity to aquatic organisms

should be avoided .

Degradation of organic contaminants in the ground can result in reducing foundation conditions

and presence of heavy metal compounds. Acids may dissolve compounds and increase mineral

content and water hardness. After saturation is achieved precipitation can occur and influence

local permeability of the ground.

In the following page is a tabulation of chemical grouts used and effects on humans and the

environment. (European Union, 2002)

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Table 2.1. Comparison of chemical grouts as to their technical aspects and their effects on human health and the environment.

16 F16/2341/2009

2.3.3. SUSPENSION TYPE GROUT

Refers to material in suspension within a mixture and comprise clay, cement and lime.

The behavior of the backfill, a material in explicit contact with the formation is critical for

obtaining measurements. Instrument observations may indicate unstable backfill, lack of backfill

or backfill that is too soft or too stiff. Cement-bentonite grout is the most universally applicable

material for successfully backfilling a borehole.

2.3.3.1. Bentonite

Bentonite is a form of clay consisting of mostly montmorilonite(a clay mineral) interlayered with

calcium or sodium and minor amounts of quartz, feldspar, kaolinite, carbonates, sulphides,

sulphates and organic matter and may be chemically classified as absorbent aluminium

phyllosilicate. It expands while absorbing water hence is a good sealant. There are different

types of bentonite in existence named after the dominant element contained. Common kinds are:

Calcium bentonite; It is the main active ingredient of Fuller’s earth which is highly

plastic sedimentary clay used by military and civil service to decontaminate clothing

exposed to radiation.

Also used to decolorize, filter and purify animal, mineral and vegetable oils.

In addition it is used in the film industry for special effects to create large dust clouds

after creating explosions.

Potassium bentonite; It is formed from an alteration of volcanic ash and is used as pet

litter and in mud-drilling (helps to lubricate and cool cutting tools, remove cutting and

prevent blowouts during drilling).(www.wikipedia.com)

2.3.3.2 Sodium bentonite

Its most notable feature is the ability to swell when wet, absorbing several times it‘s dry mass in

water. By swelling it creates a low permeability barrier which is most appropriate for use in

grout works hence sealing dam foundations. Sodium Bentonite has the ability to absorb small

amounts of water and to prevent the penetration of more water and generates the internal

pressure when it gets wet necessary to form a waterproof seal. This creates a confining expansion

of wet bentonite also gives it the capability to prevent water migration, to self-repair damaged

F16/2341/2009 17

areas and to reseal cracks that will occur from time to time in most concrete. Bentonite‘s

capacity to ―self repair‖ and a potential life span measured in centuries (it is already up to 90

million years old) makes it the major sealing component of virtually all toxic waste and landfill

projects.

Bentonite grouts are of low permeability which is ideal but unfortunately they are sensitive to

overmixing leading to a flash set and can be difficult to pump down small (3/4 inch) grout pipes.

2.3.4 CEMENT-BENTONITE GROUTS

Bentonite used on its own is generally unstable since one cannot control its volumetric changes

thus creates uncertainty concerning locally introduced pore water pressures caused by hydration

process.

Cement-bentonite grouts are much easier to use since they allow more working time and can

withstand a wider range of margin in mix ratios in comparison to bentonite grouts.

Most grouts allow for up to 6% of bentonite in the mixture but this design can be altered in

certain cases depending on difficulty encountered in the dam foundation. (Mikkelsen,

P.Erik,2002)

2.4 GROUTING PROCEDURE

2.4.1 METHODS

Many different materials have been injected into soils to produce changes in the engineering

properties of the soil.

In one method a casing is driven and injection is made under pressure to the soil at the

bottom of the hole as the casing is withdrawn.

In another method, a grouting hole is drilled and at each level in which injection is

desired, the drill is withdrawn and a collar is placed at the top of the area to be grouted

and grout is forced into the soil under pressure.

Another method is to perforate the casing in the area to be grouted and leave the casing

permanently in the soil.

F16/2341/2009 18

Penetration grouting may involve portland cement or fine grained soils such as bentonite or other

materials of a nature. These materials penetrate only a short distance through most soils and are

primarily useful in very coarse sands or gravels. Viscous fluids, such as a solution of sodium

silicate, may be used to penetrate fine grained soils. Some of these solutions form gels that

restrict permeability and improve compressibility and strength properties. Displacement grouting

usually consists of using a grout like portland cement and sand mixture which when forced into

the soil displaces and compacts the surrounding material about a central core of grout. Injection

of lime is sometimes used to produce lenses in the soil that will block the flow of water and

reduce compressibility and expansion properties of the soil. The lenses are produced by

hydraulic fracturing of the soil. The injection and grouting methods are generally expensive

compared with other stabilization techniques and are primarily used under special situations.

(V.N.S. Murthy)

Bleeding is a term that refers to the instance where the grout mix seeps out of the ground at other

locations nearby the site during pumping in of the grout mix. This could be due to high pressures

used causing fissures that lead to the ground surface or prior presence of fissure which are

difficult to seal at existing pressure. It could also be due to low viscosity of grout material.

Grouting pressures are influenced by the following factors:

Type of rock.

Degree to which rock is fractured.

Jointing system within the rock.

Stratification of rock.

Depth of zone being grouted.

Location of hole being grouted.

Weight of overlying material at time of grouting.

F16/2341/2009 19

2.4.2. COMMON EQUIPMENT USED

Cement-Bentonite (CB) Mixing Plant: The plant for making cement bentonite slurry normally

consists of colloidal mixer(s), with valves, hoses, supply lines, pumps, scales, meters, tools, and

other equipment required to prepare slurry and deliver it in a continuous supply from the plant to

the grout holes.

The most common procedure for cement-bentonite grout is done in parts. First, the bentonite is

mixed in a colloidal mixer then let to hydrate. Thereafter it is mixed with cement in a high

velocity mixer.

The resulting grout mix is then transferred to an agitator then pumped in the grout holes at a

specific pressure determined from hydraulic testing (Dugnani 2006).

Figure2.3.Types and arrangement of grouting equipment used.

F16/2341/2009 20

2.4.3. CLOSURE GROUTING

This is a procedure in which grouting is done in an area fairly wide apart. The first grout holes

are equidistant and along the plane then the second set of grout holes are done in midway

between the first ones and so on until the grouting is deemed satisfactory.

Figure2.4. positions of primary and secondary grout holes.

The first grout holes are known as primary while the second set of grout holes are called

secondary and the third set are tertiary. If further closure is required the sets of grout hole are

known as quaternary, quinary, quinary, sextary, septenary, octary and so forth.

Figure 2.5 positions of multiple grout holes.

F16/2341/2009 21

The grout in the primary hole is meant to penetrate and occupy void space as shown in the

illustration below. The subsequent holes contain grout which seals the voids as well as

connecting with the grout from holes adjacent thus creating a chain of grout to act as a barrier.

2.6(a)

2.6(b)

Figure 2.6. Grout permeation within first two stages (a) and subsequent stage (b)

Actual penetrations may be very different and nonsymmetrical. The extent of grout travel from

grout holes depends on many factors, such as Crack size, Grout mix, Mixing methods, Injection

methods, Pressure, Crack configuration, Stage method, Rock movements, Connections between

holes e.t.c.

Closure methods are particularly useful for grout curtains; the grouting is closed down to the

required standard of tightness or to some appropriate spacing.

F16/2341/2009 22

By comparing water test results and grout takes in the holes as the closure proceeds, a measure is

obtained of the grouting's level of success (or lack of it). This comparison may indicate that

changes to techniques are necessary; it also helps with decisions about when to stop grouting.

For grouting in several stages, the layout below is common. Primary holes run deepest and

subsequent series of grout holes are made to be shallower each time. It usually combines

economy with quality work and avoids doing needless grouting. While at the same time it

enables extra grouting to be given to bad spots found while the work is in progress.

The foundation is, in effect, probed and checked more thoroughly than scattered investigation

holes can provide.

Figure 2.7. Grouting required for ideal foundation.

F16/2341/2009 23

The layout applies to foundations where permeabilities reduce with depth. There are many

variations on site one extreme is where permeabilities remain high for the full depth of the

curtain coupled with short penetration distance, - in such a case it would probably be fairly

evident at the start that tertiary and possibly even subsequent holes will need to go to the full

depth.

The distance between primaries in a curtain should be as regular as possible in order to simplify

setting out and thus minimize errors. Primary holes should not be so close that they connect with

each other; connections at this juncture can jeopardize the quality of grouting and interfere with

proper evaluation of takes. On the other hand, primary holes should not be so wide apart that it is

necessary to routinely close down to such remote sequences as sextary or septenary in order to

get a reasonable spacing of final holes.(Burk Look, 2007)

2.5 SPACING OF GROUT HOLES

Spacing of grout holes is done according to preference to an adopted method within a certain

country. A general observation is that three kinds of holes are grouted i.e. primary, secondary

and tertiary. Each individual kind is done in a straight line but staggered in relation to the rest.

Below is a table showing examples of preferences in a couple of countries. Dimensions are in

metres.

Table 2.2. Spacing of grout holes.

Country Primary Secondary Tertiary

India 12 6 3

Kenya 8 4 2

F16/2341/2009 24

2.6 GENERAL SIZE AND DEPTH OF GROUT HOLES

General size and depth of grout holes depend on the design requirements and nature of

foundation material.

According to IS: 11293 (Part2)-1993 ―Guidelines for the design of grout curtains‖, the following

empirical criteria may be used as a guide:

D= (2/3) H + 8

Where;

D is the depth of the grout curtain in meters and

H is the height of the reservoir water in meters.

This can be altered if the cavities are below the depth well known.

The grout holes may be either vertical or inclined. The orientation, plan and inclination of grout

holes depend upon the type of joints and the other discontinuities in the foundation rock. The

most common practice is to drill holes inclined towards the upstream at 5 to 10 degrees to the

vertical.

2.7. TESTS ASSOCIATED WITH GROUTING

2.7.1. UNCONFINED COMPRESSIVE STRENGTH TEST (UCS)

This is a quick test to obtain the shear strength parameters of cohesive(fine grained) soils either

in undisturbed or remolded state. The method is used primarily for saturated, cohesive soils and

is inappropriate for dry sands or crumbly clays because these materials would fall apart without

lateral confinement.

The test is strain controlled and when the soil sample is loaded rapidly, the pore pressures (water

within the soil) undergo changes and do not have enough time to dissipate. The test is thus a

representative of soils in construction sites where the rate of construction is very fast and the

pore waters do not have enough time to dissipate. (University of Texas)

F16/2341/2009 25

Applications

• The test results provide an estimate of the relative consistency of the soil.

• Almost used in all geotechnical engineering designs (design and stability analysis of

foundations, retaining walls, slopes and embankments) to obtain a rough estimate of the soil

strength and viable construction techniques

• To determine Undrained Shear Strength or Undrained Cohesion (Su or Cu) = 𝑞𝑢

2

Equipment

• Unconfined compression testing machine (Triaxial Machine)

• Specimen preparation equipment

• Sample extruder

• Balance

Figure 2.8. Failure pattern typical of brittle specimens.

F16/2341/2009 26

Figure 2.9. Soil consistency in relation to ultimate strength.

Table 2.3. Relative consistency as a function of unconfined compressive strength.

F16/2341/2009 27

Test Procedure

To perform an unconfined compression test, the sample is extruded from the sampling tube. A

cylindrical sample of soil is trimmed such that the ends are reasonably smooth and the length-to-

diameter ratio is on the order of two. The soil sample is placed in a loading frame on a metal

plate; by turning a crank, the operator raises the level of the bottom plate. The top of the soil

sample is restrained by the top plate, which is attached to a calibrated proving ring. As the

bottom plate is raised, an axial load is applied to the sample. The operator turns the crank at a

specified rate so that there is constant strain rate. The load is gradually increased to shear the

sample, and readings are taken periodically of the force applied to the sample and the resulting

deformation. The loading is continued until the soil develops an obvious shearing plane or the

deformations become excessive. The measured data are used to determine the strength of the soil

specimen and the stress-strain characteristics. Finally, the sample is oven dried to determine its

water content.

Interpretation of data

The material is supposed to follow the stress relationship plotted below.

Figure 2.11. Mohr’s circle for Unconfined Compression Test.

Axial strain, 𝜀𝑎=

∆𝐻

𝐻×100

Where H is the height of the specimen and ΔH is the change in height of the specimen.

F16/2341/2009 28

Stress 𝜎 =𝐹

𝐴𝑐

Where F - Force recorded at material failure.

𝐴𝑐 =𝐴𝑖

1−𝜀 ; Ai is the initial area of the specimen.

Area correction (Ac) is applied in the interpretation of the results as the cross section of the

sample doesn‘t remain constant as the load is increased. There will be an observed bulge at the

middle of the specimen due to which it is almost presumptive to consider uniform stress

throughout the specimen length. However, the volume of the specimen is assumed constant.

The maximum load per unit area is defined as the unconfined compressive strength, qu.

2.7.2 WATER PRESSURE TESTS/ PERMEABILITY TESTS

Packer test is a commonly used permeability test also known as Lugeon test; a name derived

from Maurice Lugeon (1933). It is a constant head test that takes place in an isolated portion of

the hole. Water at a constant pressure is injected into a rock mass through a slotted pipe bounded

by pneumatic packers. A pneumatic packer is an inflatable rubber sleeve that expands radially to

seal the annulus space between the drill rods and the boring walls.

F16/2341/2009 29

Figure 2.12. Layout of the constant head packer test.

At the beginning of the test a maximum test pressure (PMAX) is defined. PMAX is chosen such that

it does not exceed the confinement stress (σ3) expected at the depth where the test is being

conducted in order to avoid the development of hydraulic fracturing or hydraulic jacking.

PMAX = D ×1psi

ft

Where;

D is equal to the minimum ground coverage – depth in the case of a vertical boring in a

flat site or minimum lateral coverage in the case of a test conducted in a hillside.

F16/2341/2009 30

The test is conducted in five stages. The first three done with ascending pressures while the last

two pressures are the same as the first two hence creating a pressure loop. These pressures are a

fraction of PMAX as presented in the table below;

Table 2.4. Pressure magnitudes for each stage in Lugeon Test.

Description Pressure Step

1st

stage Low 0.5 PMAX

2nd

stage Medium 0.75 PMAX

3rd

stage Maximum PMAX

4th

stage Medium 0.75 PMAX

5th

stage low 0.5 PMAX

Lugeon values; during the execution of each stage, both water pressure (P) and flow rate (q)

values are recorded every minute. Subsequently, average values for P and q are then used to

compute the hydraulic conductivity for each stage. The hydraulic conductivity is expressed in

terms of the Lugeon value, which is empirically defined as the hydraulic conductivity required to

achieve a flow rate of 1 litre/minute per meter of test interval under a reference water pressure

equal to 1 Megapascal (MPa)

Where α is a constant for SI unit conversion.

Po is the atmospheric pressure.

L is the depth tested.

Assuming homogenous and isotropic conditions, 1 Lugeon is equivalent to 1.3 × 10-5

cm/s.

For each test section, results obtained for each pressure stage are interpreted based on typical

behaviours observed. There are five typical behaviours as follows;

F16/2341/2009 31

Table 2.5. A graphic summary of the five behavior groups defined by Houlsby (1976), as well as

the representative Lugeon value that should be reported for each group.

Table below describes conditions associated with different Lugeon values, as well as the typical

precision used to report these values. ( Houlsby, A. 1976)

Table 2.6. Properties of rock masses according to lugeon range.

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2.7.3 SECONDARY PERMEABILITY INDEX (SPI)

This test applies to jointed rock where there is presence of fractures. To describe and estimate the

permeability of jointed rock, the result of water pressure test should be transferred to k-value

instead of lugeon value. Much more effort had been done to find correlation between the result

of water pressure test and k-value. This problem was solved by using Secondary Permeability

Index method (SPI). The Secondary Permeability Index (SPI) usually, expressed from the

conversion of the take of water pressure test into a permeability coefficient analogous to porous

mass (Foyo et al 2005). Usually, the grouting of the dam foundation requires that the rock mass

be previously divided in zones with different ground treatment. The Secondary Permeability

Index (SPI), based on water flow trough fissures, allows zoning the dam foundation regarding

different quality classes. The importance of the SPI method is possibility of distinguishing

difference between dilation and hydraulic fracturing. The dilation is occurred at elastic manner,

but the hydraulic fracturing is occurred at plastic manner (Ajalloeian and Moein 2009 ).

Therefore, the Secondary Permeability Index (SPI) is defined as follows:

SPI = CLn

2ler

+ 1

2πle

Q

Ht

Where:

SPI (Secondary Permeability Index) - l/s per m2 of borehole test surface.

C - constant depending upon viscosity for an assumed temperature of rock at 100

C ,

1.49×10-10 (Snow, 1968).

le- length of the test section (m),

r- borehole radius (m)

Q- water flow absorbed by fissured rock mass (litres),

T - duration of each pressure level (seconds)

H- total pressure expressed as water column (metres).

The SPI establishes a new permeability based rock mass classification (Table 2.5.3.a.). Based on

this classification, different considerations regarding ground treatment are proposed (Foyo et al.

2005). The proposed classification differs from classical geomechanical classifications.

F16/2341/2009 33

Most critically, it does not reflect the strength of the intact rock. Instead, the classification

defines the quality of the rock mass based on the permeability of the discontinuities (Foyo et al.

2005).

Table 2.7. Rock mass classification based on the SPI and ground treatment considerations (Foyo

et al. 2005)

Secondary Permeability Index, SPI (1/s m2)

< 2.16 ×10-14 2.16 ×10-14 1.72× 10-13 1.72 ×10-12

Rock mass Class A Class B Class C Class D

Classification Excellent Good–Fair Poor Very poor

Ground

Treatment

Needless Local Required Extensive

2.8 TECHNICAL SPECIFICATIONS FOR CEMENT BENTONITE SLURRY

The technical specifications are used as a guide to Cement-Bentonite(CB) Slurry manufucture

for a specific site.

In general, there are two types of CB: CB slurry walls made from Portland cement and Bentonite

and CB slurry walls made from Portland cement, Bentonite, and Blast Furnace Slag cement. In

part, the performance specifications will determine the type of CB. These types can be called

CB/PC and CB/BFS.

CB/PC has a fully-cured UCS (unconfined compressive strength) of about 5 to 35

psi and a permeability of about 5 x 10-6 cm/sec

CB/BFS has a cured UCS of about 50 to 200 psi and a permeability of about 1

x10-7cm/sec.

CB is said to have dynamic properties and improves as it cures.

CB properties are also said to be influenced by its ―shear history‖ so consistent

sampling is critical

―Fully cured‖ is usually assume to be 90 days, but CB cures over a long period.

F16/2341/2009 34

3. CASE STUDIES

3.1. THETA DAM, KENYA

3.1.1 BACKGROUND INFORMATION

Theta dam was constructed on Theta Basin within Kikuyu escarpment located about 80 km from

Nairobi, Kenya. The dam site is at a confluence of two streams and was constructed for the

purposes of providing domestic water supply to approximately 50,000 people near the vicinity.

This dam is 17 m high with an axis which was 63 metres in length.

Figure 3.1. A geographic map of Theta dam site.

3.1.2 GEOLOGY OF THE SITE

The project area has a shallow, red volcanic soil which is locally sticky when wet and a high

fertility rate. The geology of the area is described by Thompson A.O (1964) in his description of

the Geology of the Kijabe Area. The dam site is covered by middle and upper Tertiary volcanics

consisting of basalts, phonolites and trachytes intercalated with their pyroclastic equivalents

F16/2341/2009 35

which are predominantly tuffs and are divided into upper, middle and lower Kerichwa valley

tuffs. The volcanics overlie the Basement rocks at a relatively greater depth. Although the area is

characterised by minor faults, no major fault has been positively identified. (Athi water Services

Board, 2010)

3.1.3 GEOPHYSICAL INVESTIGATIONS

Geophysical investigations were carried out using Vertical Electric Sounding (VES) which

captured sub-surface changes by use or Electrical Resistivity Tomoghraphy (ERT). The profile

of interest was along the dam axis for a length of 65m. Findings were as shown in the diagram.

Figure 3.2. Resistivity values within the different strata located at different depths along dam

axis.

High resistivity values indicate areas of high density or compact material which have low

permeability while low values imply high permeability. It is clear from the profile that a region

of high permeability existed below the dam axis and core drilling as well as permeability tests

were conducted to confirm this.

Four exploratory holes were drilled along the dam axis with cores being recovered. Recovery of

cores confirmed the geophysical survey.

The permeability of the soil material at the site ranged between 4.6 x 10-6

to 4.9 x

10-8

cm/s (low to very low) and the percentage of fines is at least 80%.

F16/2341/2009 36

There was a zone of high porosity which could have been due to rock fissures or presence of an

aquifer. However due to lack of significant faulting activity in the area the particular zone was

probably an aquifer.

3.1.4 DESIGN, METHODS AND CONSTRUCTION

The zone of low resistivity was a cause for concern since water would seep under the dam unless

measures were taken. It was proposed to construct a curtain grout along the dam axis. Primary

holes were 9 spaced 8m apart with Secondary holes 8 in number placed in between the primary

holes. Two raking holes were also done at each end of the axis; one inclined at 55 degrees and

the other inclined at 63 degrees from the horizontal.

The accepted formula for highest pressure used in Kenya is:

P= (2/3) H where P is pressure and H is the depth to be grouted.

Grout mix comprised 100 litre of water for 1 bag of cement (50 kg) and 2.5 kg of bentonite.

This translated to 5% bentonite in cement grout for the primary holes.

The table below shows the summary of the proposed grout holes and to which depth they were

made. Grout holes with the prefix ‗P‘ are primary in nature while those with the prefix ‗S‘ are

secondary.

Table 3.1. Grout holes made along dam axis.

Chainage along dam axis (m) Grout hole label Depth of grout hole(m)

0 + 000 P1 10

0 + 005 S1 10

0 + 010 P2 60

0 + 015 S2 20

0 + 020 P3 60

0 + 022.5 S3 60

0 + 025 P4 50

0 + 027.5 S4 50

0 + 030 P5 60

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0 + 035 S5 50

0 + 040 P6 60

0 + 044 S6 20

0 + 048 P7 30

0 + 052 S7 10

0 + 056 P8 10

0 + 060 S8 10

0 + 063 P9 10

3.1.5 RESULTS

Eight primary holes were grouted with the exception of P3 which was used as a test hole. The

results of the lugeon test are tabulated below

Table 3.2 Lugeon values attained before and after grouting.

Borehole chainage Depth of test section

(m)

Lugeon values before

grouting.

Lugeon values after

grouting

0+ 020 (P3) 0-5 10.42 1.681

5-10 11.68 2.643

10-15 10.75 1.678

15-20 1.75 1.595

20-25 1.24 6.657

25-30 0.28 0.089

30-35 9.17 2.530

35-40 89.95 27.458

40-45 23.23 5.056

45-50 12.32 2.509

50-55 0.16 0.432

55-60 1.59 0.205

F16/2341/2009 38

The results above prove that grouting was effective. However, not all Lugoen values were below

5. The zone 35-40 which recorded the largest values was assumed to be where resistivity was

lowest.

Unfortunately Packer tests done at the secondary holes showed Lugeon values greater than 5.

The main cause for this was cited as high pressure used during grouting as well as the aquifer

which transported the grout mix downstream (bleeding) hence significant setting of the material

had not occurred. There were also instances of borehole collapse due to the weak nature of

underground material.

This prompted design mix alteration to up to 20% bentonite in cement grout and reduction of

pressures used in grouting of the secondary grouting holes.

Grouting of the secondary grout holes was conducted so that lugeon values would be less than 5.

The two raking holes were then drilled and water pressure tests conducted. Grout material was

recovered in the cores and the Lugeon values were found out to be less than 2.

F16/2341/2009 39

3.2 TURTLE CREEK DAM, USA

3.2.1 BACKGROUND INFORMATION

Turtle Creek Dam is located in Manhattan, Kansas city and acts as a reservoir on the Big Blue

River 8km North of Manhattan. It is a catchment area of about 25,000 km2 with a shoreline of

160 km.

Figure 3.3. Turtle creek as is seen today.

The Corps of Engineers-Kansas City District conducted extensive seismic evaluations for Tuttle

Creek Dam. These evaluations revealed that an earthquake with a magnitude of 5.7 or greater

would cause liquefaction of the foundation sand and result in large deformations or collapse of

the embankment. The maximum credible earthquake (MCE) from the nearby Humboldt Fault

Zone is a magnitude 6.6 earthquake. Slope stability analysis confirmed these findings. To reduce

the risk of deformation and slope instability during and after the MCE, cement bentonite slurry

walls were constructed in the foundation sands through the downstream portion of the

embankment.

F16/2341/2009 40

3.2.2. SUBSURFACE CONDITIONS

The soil in the alluvial foundation of Tuttle Creek Dam consists of 8 to 27 ft of silt and low

plasticity clay underlain by sand, silty sand, and gravelly sand. The sand deposits vary in

thickness from about 25 to 60 ft and can be separated into two distinct zones. The upper zone

consists of a 15 to 20-ft-thick layer of loose fine to medium sand and the lower zone consists of a

25 to 30-ft-thick layer of dense coarse to gravelly sand that increases in grain size with depth.

Due to the alluvial Due to the alluvial nature of the foundation deposits, multiple lenses of

cohesive soil exist within the coarse grained layers. Bedrock consists of alternating layers of

shale and limestone. The silt and clay form a natural cohesive soil blanket over the more-

permeable sands.

The upper sand zone was determined to be potentially liquefiable during large earthquake

motions. The upper silts and clays were also expected to suffer significant strength loss due to

large strains caused by liquefaction of the underlying sand. It was therefore proposed that a

grout curtain be constructed to increase the bearing strength of the dam.

3.2.3 DESIGN, METHODS AND MATERIALS OF CONSTRUCTION

The Kansas City District found that rehabilitation of the liquefiable foundation sands is required

to prevent an uncontrolled release of the reservoir during or after the design earthquake.

Transverse shear walls were constructed through the embankment and underlying foundation

soils in the downstream slope and toe of the dam.

The walls were 1.22 m wide, 13.72 m long, and generally about 21 m deep. A 3.05 m clearspace

exists between them. Design of the clear-spacing considered requirements for unimpeded

seepage between the walls in both the pervious drain and foundation sands, while also

considering soil displacement between the walls using limit equilibrium methods. These

transverse shear walls are self-hardening cement bentonite slurry walls. (Paul J. Axtell et all)

F16/2341/2009 41

Figure 3.4. Plan view of transverse shear walls (units in ft, 1m=3.28ft)

Figure 3.5. Side view of transverse shear walls (units in ft, 1 m=3.28 ft)

F16/2341/2009 42

In order to install the walls, a working platform was constructed on the downstream slope of the

dam. The working platform was constructed of predominantly sand with an aggregate surface.

Two kinds of mixes were used; cement consisting of a 50/50 mixture of Portland cement and

ground granulated blast furnace slag (slag). Additionally, a 25/75 Portland cement to slag cement

mix-ratio was used in a small number of walls.

Both mixes included a 5 percent bentonite component. A laboratory investigation was conducted

on recovered samples obtained from production walls (initially they were test walls) to determine

the large-strain, or post-peak, shear strength of the hardened cement-bentonite material.The

results of the laboratory investigation were required for use in limit-equilibrium slope stability

analyses used to design the shear walls and numerical deformation modeling to assess the

earthquake induced permanent deformation of the dam and foundation materials. For the

majority of the production work, unconfined compression tests were used to validate the design.

Construction of the Cement Bentonite wall was done by simultaneously excavating material and

replacing with Walls were constructed by excavating and simultaneously placing self hardening

cement bentonite slurry in the trenches. By continuously placing slurry into the excavation, the

trench would remain open during construction of the wall. Walls were oriented transverse to the

axis of the dam. Walls were typically 3 or 4 feet wide, 45 feet long, and approximately 65 feet

deep.

The slurry level in the walls was observed to drop during cure. The observed drop was a

combination of slurry permeation into the adjacent soil and slurry bleed during curing. The walls

were topped off with fresh slurry daily to account for drop during curing. Total slurry drop was

typically 10% of wall depth.

3.2.4 SAMPLING AND TESTING

This was performed on an onsite batching plant, on the fluid slurry as well as on hardened

material via core drilling. Fluid slurry samples were cast in 3-in by 6-in cylinders. The samples

were originally stored in a 100-percent humidity curing room until being tested for unconfined

compressive strength (UCS) stored submerged under water until UCS testing.

F16/2341/2009 43

Coring was conducted on 92% of walls in the test section, and approximately 40% of walls in the

remainder of construction. Walls were typically cored between 60 and 90 days after construction,

but some were cored as early as 28 days and as late as 200 days to observe strength changes with

time.

3.2.5 RESULTS AND FINDINGS

In general, wall strength and specific gravity increased with increasing cement water ratio. Based

on an independent laboratory investigation of the proposed mixes, and verified by full-scale field

measurements, relatively minor strength increases can be expected beyond 90 days for these

materials.

Figure 3.6. Table showing average UCS values for samples.

F16/2341/2009 44

Figure 3.7. UCS values with time for sample collected.

The majority of the tests occurred within the 90 day time frame. Walls constructed with 75%

slag content exhibited significantly higher strength than walls of the same cement water (c/w)

ratio constructed with 50% slag content. Strength generally increased with increase in depth and

this was attributed to the increase in specific gravity of the zone examined. (Amod K. Koirala et

all, 2011)

F16/2341/2009 45

3.3 KARKHEH DAM, IRAN

3.3.1 BACKGROUND INFORMATION

Karkheh dam is constructed on Karkheh river located 200 kilometers northwest of the Persian

Gulf southwest of Iran. It is an earth-fill dam with a reservoir capacity of 5600Mm3 constructed

for hydropower production. Karkheh earthfill dam is the largest one in Iran.

The dam height over foundation is 127m and the crest length is 3030m. The project includes the

embankment placed across the Karkheh River, a powerhouse with total installed capacity of

400MW, at the left abutment and a gate-controlled chute type spillway with a crest width of 10m

and length of 955m located at right abutment.

Figure 3.8. Aerial view of Karkheh dam.

3.2.2 GEOLOGY

Geology of the sites consists mainly of conglomerate layers with the overall permeability of the

conglomerate estimated to be in the relatively high range of about 4-9

×10-4

m/s this is primarily

caused by the zones of discontinuity and open framework gravels. The conglomerate is stratified

by mudstone layers 3 to 9 m thick, and nearly horizontal.

F16/2341/2009 46

The mudstone layers at levels below the river have been given negative numbers (-1, -2 and -3)

and those above the river have been attributed positive values (+1, +2, +3 and +4)

Figure 3.9. Longitudinal cross section of Karkheh dam. Hatched area represents the extension

of cutoff wall. The figure is exaggerated in the vertical direction.

The composition of mudstone layers is also variable between the clay rock and sandy-silty rock.

The estimated permeability of the mudstones is between 10-7

and 10-10

m/s. Geotechnical

investigations and observations indicated that these layers are continuous enough at the location

of dam to provide different strata for each conglomerate layer confined by mudstone layers

Due to the high permeability of conglomerate layers, a vertical foundation water sealing system

was required to control water flow to downstream, to reduce exit hydraulic gradient, to prevent

high measure of leakage, to decrease the uplift pressure, and finally to provide associate stability

of the dam body and its hydraulic structures.

3.3.3 DESIGN, METHODS AND CONSTRUCTION

Different water sealing alternatives were considered for the Karkheh dam foundation. The first

alternative was grout curtain, a selection of which was favored by the availability and lower cost

of grouting technology within the country and anticipating suitable performance speed on the

one hand, and lack of other suitable technologies on the other hand. However, theoretical

advantages of grout curtain proved false by test grouting and economical studies. Hence, cutoff

wall was taken into consideration as the second alternative.

F16/2341/2009 47

Enormous studies and investigations were carried out leading to design of a plastic concrete

cutoff wall as the main part of the dam foundation water-tightening system.

Therefore a plastic concrete cutoff wall with thickness of 0.8 to 1.0 meter was performed

throughout the dam axis. At different locations of dam, the depth of wall was determined

regarding seepage analysis, construction ability and economical factors

Figure 3.10. Karkheh dam cutoff walls and the location of the probable chemical grouting

curtain.

The dam monitoring data indicated that the cutoff wall rerouted the seepage flow into

preferable paths (sufficiently far) and as a result reduction in the seepage discharge, hydraulic

gradient and pore pressure in the rock masses was obtained which all together provide more

suitable conditions for the stability of the powerhouse slopes.

But in the access gallery 950, the situation was not as successful. Observations showed water

leakage in this section to be higher than anticipated. To remedy the problem of seepage in this

part of dam foundation, the other existing alternative was chemical grouting.

F16/2341/2009 48

As the permeability of the formation is around 10-5

cm/sec, a silicate-base chemical grout was

assessed to be a suitable type of grouting of the conglomerate formation. (Heidarzadeh et all)

However, there was no experience of chemical grouting in the country as well as a lack of any

published work on chemical grouting of conglomerate formations. Therefore, ambiguities were

associated with the design and construction of the Karkheh dam chemical grout curtain. To

overcome part of these ambiguities, prior to the main chemical grouting, testing programs were

performed to evaluate the performance of the method in the water sealing of the area using a

combination of field and laboratory tests. At first, extensive site trials and laboratory tests were

carried out to develop an effective grout mix. In these laboratory tests the chemical grouts alone

were examined with regard to viscosity-time behavior, gelation time, temperature-influence,

stability, and deformability. These laboratory tests, led to the selection of the final chemical

grout which was a solution of sodium silicate, water, and ethyl acetate as reactant. This grout

system widely known as sodium silicate system is the most popular chemical grout system

because of its safety and environmental compatibility.

The only concern was that sodium salts can leach from gelled silicate and raise the pH of the

surrounding environment. This was considered to be a relatively small issue.

The second step tested grout-soil interaction: The ease of injection and permeability reduction of

the selected chemical grout was examined in field injection tests. In this step two field tests were

performed including shallow test holes without hydrostatic pressure and full scale tests under

dam real hydrostatic pressure head.

The concentration of the silicate solution which was selected for use in Karkheh dam

ranged between 37%. Such grouts would have viscosity of up to 3 cP(0.003Ns/m2), which was

suitable for the encountered formation.

In phase 1 of test chemical grouting, shallow test holes with depths ranging between 4 to 5

meters were used which did not undergo any hydrostatic pressure. These grouting holes each

having 101 mm diameters were drilled in the corners and side midpoints of an equilateral

triangle located near gallery 950.

As can be seen in the figure 3.11, a test hole named CH (Control Hole) was drilled in the center

of the triangle to be used for water pressure test to assess the effectiveness of the process.

F16/2341/2009 49

Figure 3.11. Sketch showing the triangular placement of shallow test holes in phase 1 of test

chemical grouting.

The Complex Curtain Method(CCM)

Cement-bentonite grouting was done followed by sodium silicate chemical grouting in alternate

sections of the holes. At first all grouting sections would be injected by cementitious grouts. In

the next stage, the remaining section would then be treated by the injection of chemical grouts.

(A.A. Mirghasemi et all)

Figure 3.12. Material arrangement within grout hole.

F16/2341/2009 50

3.3.4 RESULTS

Chemical grout from design grout mix was injected into holes S1, S2 and S3. In this stage, the

permeability test was taken in the intermediate holes S5, S6 and S7 indicated that the

permeability varied from 70 to 102.5 Lugeons. Finally, after injection of chemical grouts in all

test holes, the permeability at the Control Hole (CH) showed the value of 73 Lugeons, which was

more than the acceptable limit of about 5 Lugeons. Results of performed chemical grouting in

triangular test holes indicated that improvement of conglomerate formation was not satisfactory.

It can be inferred that some cavities or perforations remained untapped or untreated.

Table 3.3. Summary of grouting in phase 1 test holes (che.gro. –chemical grouting).

The technique of chemical grouting was effective for clogging of small voids and the

developed silica gels could not resist against water flow in large openings. In other words,

it was found that for treatment of a medium having both large and small voids like conglomerate

formations, a combination of chemical and cementitious grouting was employed in order to fill

small and large openings respectively.

Water pressure test was conducted on test hole S4 and the results attained are tabulated below.

Table 3.4. Summary of grouting records in the test hole S4.

F16/2341/2009 51

4. DISCUSSION

As more development takes place in the world, it has become increasingly hard to find an ideal

site for projects. An ideal site would have a sound foundation such that a project could be

constructed and function as expected. Unfortunately this is not always the case and more

important factors such as available land and resources required for operation and maintenance

override the need to have a sound foundation on site.

As a consequence, a site with a weak foundation may be chosen and that foundation improved to

achieve the standards and specifications needed to construct a dam. While other methods such as

sheet piling and cutoff trenches are suitable, grouting offers the least disruptive method of

dealing with weak foundations.

Data obtained from Theta dam show that grouting in primary holes using cement bentonite

sealed the pores in the foundation and reduced permeability from 89.95 lugeons to 27.46 lugeons

in the most permeable zone.

Bentonite in the grout mix was then increased to improve its sealing characteristics. The second

stage of grouting in secondary holes reduced permeability to values below 2 Lugeons which was

within the accepted range of less than 5 Lugeons.

This indicated that grouting using cement bentonite was successful. Grouting in subsequent

stages reduces the amount of material used. Such a technique initiates a self-checking

mechanism to ensure the permeability sought is attained since tests were done after each stage to

confirm permeability achieved before proceeding.

In Turtle Creek dam, grouting using cement bentonite material was done using walls rather than

grout holes. This ensured that the foundation would be strong enough to provide support and

resistance to the dam in the event of an earthquake. Results from Unconfined Compressive

Strength(UCS) tests showed sample material to have achieved sufficient strength to withstand

the Maximum Credible Earthquake expected(6.7). This was due to the increased strength of the

foundation which also made it more stable.

F16/2341/2009 52

The cement bentonite grouts were considered highly effective for conglomerate foundations such

as in Karkheh dam thus it was used. Test results confirmed that Lugeon values dropped from 70

to 29 in control hole 4. This is a difference in 41 Lugeon values which was a lot but still not

within the acceptable range.

Sodium Silicate grouts were used to seal small pores hence offered more effective hydraulic

resistance to seepage within the foundation. Water pressure tests conducted showed a change in

Lugeon values from 29 to 1.2 in control hole 4. This Lugeon value was within the accepted range

thus grouting was successful.

The use of sodium silicate solutions are generally considered to be non-toxic and noncorrosive.

They are considered to be free of health hazards and environmental effects. However, sodium

salts can leach from gelled silicate and raise the pH of the surrounding environment.

Combining different kinds of grouts was ideal since cement bentonite sealed the large pores

found in conglomerate foundations. The remaining pores were small hence a lower rate of

bleeding would occur during grouting which was economical. These pores were sealed with

chemical grout which through which reduced permeability hence seepage was negligible.

However cementitous grouts supposedly degrade at a faster rate than the other kinds of material

available and are a relatively short term solution to problems including seepage and stability.

In respect to dams it may be theorized that this degradation may have little effect on the

functionality as:

Sediments will fill up the dam and reduce its capacity to the point where the dam is not

useful. By this point, degradations will not matter since the project lifespan will have

ended.

After a period of time, earth movements and compressibility of sediments will cause

stratification. This may in turn retard the increase in permeability caused by degradation

to levels that are acceptable.

With the exception of sodium silicate grouts, most kind of chemical grouts provide potentially

harmful and irreversible side effects. It is this nature that requires specialized technology in its

use. . This especially applies to developing nations which may not have the correct technology to

successfully and safely conduct chemical grouting. Lowered viscosity and longer time to gel

F16/2341/2009 53

increases risk of water contamination. Workers suffer risk from exposure and there is no exact

way to quantify the exact risks involved.

Emulsion grouts require greater expertise to use since the bitumen in the mix must be heated to

high temperatures (120o

Celsius- 140o Celsius). Unfortunately the fumes emitted during this

exercise are harmful if inhaled thus endanger workers and pollute the air. In addition, the world‘s

petroleum reserves are finite thus;

Bitumen becomes more expensive to attain due to becoming high demand. Financial

project constraints which are a feature in most projects could eliminate emulsion grout as

a material to be used.

Bitumen has other uses such as in road construction which may unfortunately take

priority over the field of grouting.

As with most engineering, a balance is sought such that the project under construction may be as

useful as possible while creating the least damage possible.

F16/2341/2009 54

5. CONCLUSION AND RECOMMENDATION

5.1 CONCLUSION

Grouting using cement bentonite in Theta dam construction reduced permeability to acceptable

levels thus was effective. Grouting in stages enabled permeability to be checked before

proceeding to the secondary stage which could prove to be economical since process can be

stopped once specifications are attained.

Foundations can be made strong enough to withstand undesirable loads by use of cement

bentonite grout which is currently the best material available. This case was seen in Turtle creek

dam where grouting walls in foundation using cement bentonite increased the design strength of

the foundation.

Grout material may be used in combination to get optimum use of their properties. In Karkheh

dam, Cement bentonite grout sealed pore within its conglomerate foundation while the chemical

grout was used to effectively reduce seepage by sealing the remaining small pores.

Chemical grouts are effective in sealing small pores but have side effects on the environment.

There may be more than one grouting technique that can solve one particular geotechnical

problem, but precautions to take during the construction work, progress and cost level maybe

quite different.

Emulsion grouts contain bitumen which is harmful when inhaled and a finite resource hence it is

rarely considered as a material for continuing and future use in grouting.

F16/2341/2009 55

5.2 RECOMMENDATIONS

New materials should be considered to deal with the challenges surrounding grouting. While the

advancements made so far are impressive, more must be done.

Use of new techniques in grouting should be encouraged of instead of purely relying on the tried

methods. Although new methods are risky, they could provide better advantages.

Information should be made more readily available on such procedures since with increase in

population more sites are made to be ideal instead of searching for the ideal site.

Research on projects involving new techniques and material used should be encouraged. Testing

on different kinds of grouts and their variants should be considered. This will increase improve

options available for consideration on grouting.

Probable measures to reduce side effects of chemical grouting should be investigated to ensure

safety for future generations.

Ambiguity in projects involving grouting should be avoided in order to increase accountability

and credibility. It will also help to effectively monitor any changes and effects(both long-term

and short-term) that occur.

F16/2341/2009 56

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