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MicropileInstallation

MethodsandSelection

Dr.DonaldA.Bruce

Agenda

1. DrillinginRockandOverburden

1.1 Methods

1.2 FlushingCharacteristics

1.3 MonitoringWhileDrilling

2. Grouting

2.1 ClassificationofMicropilesBasedonGroutingMethod

2.2 Means,MethodsandMaterials

2.3 QA/QC

3. StorageHandlingandPlacementofReinforcement

4. GrowthoftheMicropileMarketintheU.S.

5. FinalRemarks

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Scope Typically3to12inchdiameter.

Typically200footdepth.

Typicallywithin30 ofverticalorhorizontal.

Mostlybeneaththewatertable.

Requiredinalltypesofground,naturalorplaced,unconsolidated

orlithified,andwilloftenencounterobstructions.

MayfaceFederalregulations,e.g.,USACE1997.

Mustcauseminimaldamagetothegroundorexistingstructures.

Mustallowcompletionoftheholeinoneday.

Mustbeconsistentandabletobecontrolledandmonitored.

Generallycontractordriven(performancespecification).

ScopeandCommonalities

1. DrillinginRockandOverburden

1.1Methods

Continuous,straightpenetration Constantdiameter,stableandcleanbore Consistentwiththepurposeofthedrill

hole(e.g.,groutholevs.anchorhole)

Appropriatecombinationsofthrust,torque,rotation,percussion,flush

Costeffective

Dictatedbyground,nothistoricalbias Environmentallycompatible

ScopeandCommonalities(continued)

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EvolutionofRockDrillingMethods

DawnoftheADSCAge

Basicdrillingmethodselectionguideforrockusingnoncoring methods,

LittlejohnandBruce,1977(adaptedfromMcGregor1967).

Rotary Highrpm,lowtorque,lowthrust(blindorcore)

Lowrpm,hightorque,highthrust

RotaryPercussive TopHammer

DowntheHoleHammer

Directcirculation

Reversecirculation

Dualfluiddrilling

Waterhammers

RotaryVibratory(Sonic)

RockDrilling

Methods

(Disco

Era)

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OverburdenDrillingMethods

OVERBURDENDRILLING METHODS

Overburden isSTABLE*

Overburden isUNSTABLE*

Solid

StemAuger

Open Hole(with Rock

DrillingMethods)

HollowStem

Auger

CombinationMethods

SlurrySupported

Methods

CasedMethods

LOW ----- Presence of -- SEVERE

Obstructions

HIGH --Environmental ---- LOW

Concerns

Sonic Single

TubeRotaryDuplex

Rotary

PercussiveDuplex

(Eccentric)

Double

HeadDuplex

Bentonite Polymer Self

Hardening Rotary

PercussiveDuplex

(Concentric)

OVERBURDENDRILLING METHODS

Overburden isSTABLE*

Overburden isUNSTABLE*

Solid

StemAuger

Open Hole(with Rock

DrillingMethods)

HollowStem

Auger

CombinationMethods

SlurrySupported

Methods

CasedMethods

LOW ----- Presence of -- SEVERE

Obstructions

HIGH --Environmental ---- LOW

Concerns

Sonic Single

TubeRotaryDuplex

Rotary

PercussiveDuplex

(Eccentric)

Double

HeadDuplex

Bentonite Polymer Self

Hardening Rotary

PercussiveDuplex

(Concentric)

VERY HIGH ------------------------------------------------------------------------------------ Instantaneous Penetration Rate Potential ---------------------------------------------------------------------------------- LOWER

LOW -------------------------------------------------------------------------Technological Sophistication ----------------------------------------------------------------------- HIGH

LOW --------------------------------------------------------------------------- Presence of Obstructions --------------------------------------------------------------------- SEVERE

*Stability refers to the overburdens ability to maintain the shape and size of the drilled hole without detriment to thesurrounding ground after withdrawal of the drilling system.

Basic drill method selection guide foroverburden (Bruce, 2003).

Mostoverburdenisunstable especiallywhenholesarelongandindifficulturbansettings.

Unstablemethodsaresubdividedinto4categories:1. HSA butbecareful.

2. Combinationmethods canofferoriginalandeffective

projectsolutions.3. Slurrysupportedmethods organicpolymersoffer

considerableadvantagesoverbentonite.

4. Casedmethods now5.

Notesonthe2003Classification

Basicsubdivisionisstablevs.unstable. Stableoverburdencanbe

drilledwithSSCFAorrockdrilling

methods(e.g.,rotarywithair).

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MoreRecentDevelopments

AtlasCopcoElemexsystem aringonthecasingredirectstheairflushawayfromtheDTHbitfaceandsomakesiteasierto

control.

CenterRockRotolocsystem featuresapatentedmethodofextending,lockingandretractingcuttingwingsonthecentral

pilotbit,inaverysimpleandreliablefashion. Doesnotrelyondownwardspressureonthefaceandleavesnothingbehindin

theground.

Theseinclude:

NumaSuperjaws featuring24wingswhichopenbypressureon

thefaceofthehole. Direct

descendentofoldAckerCasing

UnderreamerSystem.

RotoLock(retracted) RotoLock(extended)

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Upholevelocity(UHV)>sinkingvelocity Inwater,sinkingvelocity(Vz)isVz 106 xd2 m/swheredisthediameteroftheparticles.

Abilityofflushtocarryorsuspendcuttingsdependenton: rateofflowoffluid

Viscosityoffluid

sizeandshapeofcuttings

s.g.offluidandcuttings

UHV(m/min)=1274xFlushPumpRate(Liters/min)

D2 d2 (mm)

where D= drillholediameter(inmm)d = drillstringdiameter(inmm)

1.2 FlushingCharacteristics

AcceptableUpholeVelocities.

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DrillingFlush

Characteristics

Airvs.Water Rotaryvs.RotaryPercussion

Guidelineforselection:

Providecleanhole

Enhancepenetrationrate

Minimizetoolwear

Consistentwithpurposeofhole

Minimal

damage

to

formation

and/or

structures Environmentallycompatible

Reconsideroptionsiflostflushoccurs

FundamentalConcept

ManualMonitoring

AutomatedMonitoring

BenefitstoOwnerandContractor(notcoveredinthispresentation)

1.3 MonitoringWhileDrilling

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FundamentalConcept

Everyholethatisdrilledinthegroundisapotentialsourceof

informationonthepropertiesandresponseoftheground. This

obviouslyappliestodesignatedsiteinvestigationholes,butis

equallytrueofeveryproductionhole,suchasdrilled

foranchors,micropiles,nailsorgrout

holes. Suchinformationcanbe

collectedbytwobasicmethods:

manualandautomatic. Thedatamust

be

studied

in

real

time

to

be

useful.

BasicPrinciplesofMonitoringWhileDrilling(MWD)

Examples:

1. Helpsdetermineorverify

appropriatebondzonehorizonsfor

anchors andmicropiles.

2. Secondaryandhigherorderholes

willdemonstrateprogressive

densificationofgroundin

compactiongrouting projects.

3. Helpsselectappropriatejetgrouting

parameters.

4. Willprovideamechanicaland

hydraulicpictureoftherockmass

ateachphaseofagroutcurtain

project.

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Manual Monitoring

Basic Principles of Monitoring While Drilling (MWD)

The value of routine drillers logs can begreatly enhanced by periodic recordingof: penetration rate thrust torque flush return characteristics (cuttings,

volume) drill action interconnections between holes hole stability groundwater observations

These data can easily be recorded by agood driller who has been briefed aboutthe overall purpose of the project andso understands what to look for.

These data should be recorded at 5 ft maximum intervals.

AutomatedRecordingofDrillingProgressandParameters

Value of real time continuousmonitoring for design purposes(manual vs. automatic)

Look for exceptions andunexpecteds [Weaver, 1991]

Indication of progressiveimprovement (e.g., denser, lesspermeable conditions)

Concept of specific energy Several generations/evolutions as software and hardwareevolve

BasicPrinciplesofMonitoringWhileDrilling(MWD)

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AutomatedMonitoring

CalculationofSpecificEnergy

e = F + 2NT

A AR

where

e = specificenergy(kJ/m3)

F = thrust(kN)

A = crosssectionalareaofhole(m2)

N = rotationalspeed

(revolutions/second)T = torque(kNm)

R = penetrationrate(m/sec)

GroutingandGroutFunction

Transfers loads from reinforcement to surroundingground

May be load-bearing portion of pile

Protects steel reinforcement from corrosion

May be used as drill fluid during initial drilling Secondary/Post grout enhances soil/grout bond further

Basis for Micropile Classification

2. Grouting

2.1 ClassificationofMicropilesBasedonGrouting

Method

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Classification Based on Grouting Method

Type A: Gravity

Type B: Pressuregrouting throughcasing

Type C: Single, globalpost grout

Type D: Multiple,repeatable post grout

Type E: Injection borebars

Grout introduced into the drill hole through a tremie pipeexiting at the bottom of the hole

No excess pressure is applied

This type and phase of grouting is referred to as theprimary treatment

Typically only used when pile is founded in rock, or whenlow-capacity piles are being installed in stiff or hardcohesive soils

Gravity Filling Techniques (Type A)

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Pressure Grouting Through the Casing(Type B)

Grout injected under controlled pressure throughpressure cap on top of drill casing (often the drillinghead itself)

Additional grout injected under pressure after primarygrout has been tremied (as temporary casing iswithdrawn)

Enhances grout/soil bond characteristics

Can be limited to the load transfer length within thedesign-bearing stratum, or extended to the full length ofthe pile

Post-Grouting (Types C and D)

Additional grout injected via grout tubes after placingof primary grout

Higher water content grout used

(w/c ratio = 0.5 to 0.75)

High pressures used (> 1 MPa)

Type C only used in France to date

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Basics: Design of Neat Cement Grout

RelationshipofGeotechnicalBondValue

toGroutingPressure

0.7 1.4 2.1 2.8 3.530

60

90

120

150

180

210

240

270

300

330

360

390

420

450

Grouting Pressure [N/mm2]

Ultima

teCapac

ityo

fAnc

hor

[kN/m]

Influence of GroutingPressure on Ultimate Load

Holding Capacity

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Grouting Equipment

Mixers

High-speed, high-shear colloidal mixers essential

Low-speed, low-energy mixers (paddle mixers) areoccasionally still used, but should not be

Pumps

Constant pressure, rotary-screw type pumps (Moyno)

Fluctuating pressure piston or ram pumps

Agitation Tanks

Combined Units

Batching and Injection Monitoring Equipment

Keys to Good Grouting

Grout Batching

Water added to mixer using calibrated tank or flowmeter

Cement is batched by weight, either in bags or bulk froma silo

Additives are proportioned in relation to weight of cement

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Keys to Good Grouting

Grout Mixing

Grout mixing sequence: water, cement, additives

Grout colloidally mixed for a maximum of 2 minutes andthen held in a paddle agitation tank until needed

Safe workability time typically not in excess of 1 hour

Grout Monitoring

Electronic Pressure and Flow Recorder

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Limiting Excessive Takes of Primary Grout

Injecting excessive quantities may be dangerous as wellas wasteful

Remedies include:

changing the rheology of the primary grout (e.g. addsand; reduce water/cement ratio; use appropriateadditives)

changing the hydration characteristics of the primarygrout (e.g. use accelerator)

in extreme conditions consider pretreatment of theentire area with an economic controllable grout (e.g.low mobility grout/concrete)

2.3 Grouting Quality Assurance and Quality Control

(QA/QC)

Critical importance

Plans and specification development stage through finalconstruction

Implementation of all requirements

Enforcement of qualifications

Submittal reviews Installation

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Site Organization and Leadership

Mission Control

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Preproduction Testing

Maintaining Good Photographic Records inReal Time

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ConstructionMonitoring

Grouting Mixing and Pumping

Ensure continuous grout placement

Ensure cement is colloidally mixed and grout iscontinuously agitated

Prevent presence of air in the grout lines

Do not draw down the level of grout in the agitation tankbelow the crown of the exit pipe

Ensure exclusion of foreign matter during groutplacement

Construction Monitoring

Grouting Placement

Prevent heaving or ground distress

Prevent soil in bottom of hole from blowing in

Grout as soon as possible after drilling the bond zone

Use tremie to ensure complete filling of hole

Tie tremie tube loose enough for removal during/or after

tremie grouting

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Construction Monitoring

Grouting Placement (continued)

Observe suitable grout return

Maintain a positive head at the grout holding tank

Measure grout pressures close to the point of injectionto account for line losses

Monitor grout pressures and volumes throughout bothtremie grouting and pressure grouting (if used)

processes

Typical post-grouting pressures are typically 200-600 psi- safety issue

Cubes practically useless as a routineQA/QC tool

Grout Testing

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Real time testing of fluid groutproperties is far superior

Baroid Mud Balance (SG)

Marsh Cone (Fluidity)

3.Storage, Handling and Placement ofReinforcement

Types

Reinforcing steel bars (rebar)

Continuous-thread solid steel bars

Continuous-thread hollow-coresteel bars (injection bore)

Steel pipe casing

Composite reinforcement

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Placed either before or after initialtremie grouting (but always beforethe temporary casing is withdrawn)

Reinforcement must be clean ofsurface soil and mud

Centralizers used to maintain thespecified grout cover

HandlingandStorage

Store in a protected location

Inspect steel when delivered tosite

Reject steel that exhibits flakycorrosion or pitting

Extra care with corrugated

protected/epoxy-coated bars

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Installation

Install either before or afterinitial grout placement butbefore temporary casing(if used) is withdrawn

Record the total pile lengthand bond zone length

Insert to the prescribedlength without the use offorce

Do not damage corrosionprotection or centralizersduring installation

Ensure reinforcement is clean of any surface soil, oil, mudetc.

Check attachment and intervals (typically 2.5 to 3 meters)of centralizers and spacers

Center reinforcement in borehole

Ensure full engagement of successive bar or pipesections

Installation (continued)

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Annu

alEs

tima

tedMarke

t($m

illions

)

Universities

Professional

EngineeringSocieties

ISM

FederalGovernment

TradeAssociations

Annual Market

Contractors/Suppliers

$210

$180

$150

$120

$90

$60

$30

StateGovernments

Huge

Degreeo

fInfluence

None1970 19901975 1980 1985 1995 2000 2005

4. Growth of the Micropile Market in the U.S.

5. Final Comments

Profile of a Driller

Drillers are as diverse a group ofpeople as the industry in whichthey work. Every drillingoperation is different and requiresa highly skilled person to ensurethat the drilling process issuccessful.

Australian Drilling Industry

Technical Training Committee Ltd.

(1997)

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Micropiles in karst. (Owners must recognize needfor pregrouting and/or remedial grouting.)

Decline in standards (familiarity breeds contempt).

Continued support for DFI, ADSC and ISMmicropile activities.

Areas of Concern

Dedicated to the Vision of

Dr. Fernando Lizzi(1914-2003)

The Godfather of Micropiles

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MicropileInstallation

MethodsandSelection

Dr.DonaldA.Bruce