Ground Ground Improvement Improvement

Issues & Issues & TechniquesTechniques

CE1203 Geotechnical CE1203 Geotechnical Properties & Construction Properties & Construction

MethodsMethods

Definition of Ground Definition of Ground ImprovementImprovement

• Ground treatment is the Ground treatment is the controlled controlled alterationalteration of the state, nature or of the state, nature or mass mass behaviour of ground materialsbehaviour of ground materials in in order to achieve an intended satisfactory order to achieve an intended satisfactory response to existing or projected response to existing or projected environmental and engineering environmental and engineering actions.actions.

Mitchell, J M and Jardine, F M (2002) Mitchell, J M and Jardine, F M (2002)

‘‘A Guide to ground treatment’A Guide to ground treatment’

CIRIACIRIA

Main Improvement Main Improvement Techniques:Techniques:

• • temporarytemporary

e.g. dewatering or ground freezing, where e.g. dewatering or ground freezing, where the improvement is only during the the improvement is only during the applicationapplication

• • short-term short-term

e.g. some forms of grouting, or use of e.g. some forms of grouting, or use of diaphragm walls for ease of construction diaphragm walls for ease of construction with longer term benefitswith longer term benefits

• • long-term long-term

e.g. soil nailing, vibro-replacement, curtain e.g. soil nailing, vibro-replacement, curtain grouting of a dam, where the treatment is grouting of a dam, where the treatment is integral to the permanent works.integral to the permanent works.

Benefit to the Benefit to the Construction WorkConstruction Work

• Reduction and control of Reduction and control of deformation & settlementdeformation & settlement

• Reduction, control and exclusion of Reduction, control and exclusion of groundwater to aid safety and groundwater to aid safety and buildabilitybuildability

• Reduction of susceptibility to erosion Reduction of susceptibility to erosion and improving life-span.and improving life-span.

Effect on the GroundEffect on the Ground• • Change of state; Change of state;

i.e. the same ground but made stronger, i.e. the same ground but made stronger, stiffer, denser, more durablestiffer, denser, more durable

• • Change of nature; Change of nature;

i.e. the ground becomes a different i.e. the ground becomes a different material by inclusion of other materialsmaterial by inclusion of other materials

• Change of response; Change of response;

i.e. through the incorporation of other i.e. through the incorporation of other materials, the ground becomes a materials, the ground becomes a composite material with enhanced load-composite material with enhanced load-carrying or deformation characteristics.carrying or deformation characteristics.

• • by vibration by vibration

• • by adding load by adding load

• • by structural reinforcement by structural reinforcement

• • by structural fill by structural fill

• • by admixtures by admixtures

• • by groutingby grouting

• • by specialist dewatering by specialist dewatering

Main Improvement Main Improvement Techniques:Techniques:

◊◊◊ ◊◊◊ = Main benefit= Main benefit

◊ ◊ = Secondary = Secondary benefitbenefit

Benefit

Technique Higher BearingCapacity

Less/ moreEven settlement

FasterSettlement

Ground water

control

ReducedLiquefactio

npotential

IncreasedErosionresistance

Improvedslope / facestability

Vibro-replacement ◊◊◊ ◊◊◊ ◊ ◊◊◊ ◊

Dynamic Compaction ◊◊◊ ◊◊◊ ◊◊◊ ◊

Pre compression ◊◊◊ ◊◊◊

Vertical Drainage ◊◊◊ ◊◊◊ ◊◊◊ ◊

Reinforcing soil / soil nailing ◊ ◊ ◊ ◊◊◊

Structural fill ◊ ◊◊◊ ◊

Lime/cement admixture ◊◊◊ ◊ ◊ ◊◊◊ ◊ ◊

Permeation grouting ◊ ◊ ◊◊◊ ◊ ◊◊◊

Cavity grouting ◊ ◊◊◊ ◊

Ground freezing ◊◊◊ ◊◊◊

Slurry cut off trench & pumping ◊◊◊ ◊ ◊

Well pointing ◊◊◊ ◊◊◊ ◊

VibroflotatVibroflotation Plantion Plant

Mitchell, J M and Jardine, F M Mitchell, J M and Jardine, F M (2002)(2002)

Use of Vibration Use of Vibration TechniquesTechniques

Mitchell, J M and Jardine, F M Mitchell, J M and Jardine, F M (2002)(2002)

Vibro-ReplacementVibro-Replacement

1. Vibrator penetrates

weak soils under action

of vibrations and

‘compressed air’ jetting

medium and forms a

hole to design depth,

usually a competent

bearing stratum

2. After being held at

depth for a short time,

the vibrator is

withdrawn and a

charge of stone is

placed into the hole

3. The vibrator is

reintroduced into the

hole, the stone is

compacted, forced out

and tightly interlocked

with the surrounding

ground

4. By adding

successive charges of

stone and compacting

each one, a column of

very compact stone is

built up to ground level

Principles of column construction using the dry top-feed process

Animation Clip

Palm Island Dubai

Specialist Rig to reduce noise and environmental disturbance

Dynamic Compaction Dynamic Compaction PlantPlant

Dynamic CompactionDynamic Compaction

• It involves the repeated dropping of a It involves the repeated dropping of a large weight (15 tonnes or so) from a large weight (15 tonnes or so) from a height of up to 15 metres. height of up to 15 metres.

• The site is usually covered at first with a The site is usually covered at first with a wide grid, followed by a smaller grid using wide grid, followed by a smaller grid using a lighter weight or a reduced fall. a lighter weight or a reduced fall.

• This technique can effectively compact the This technique can effectively compact the ground down to a depth of a few metres  ground down to a depth of a few metres 

• Not suitable for small sites or sites where Not suitable for small sites or sites where vibration, impact etc can affect adjacent vibration, impact etc can affect adjacent buildings or building service in the groundbuildings or building service in the ground

• Video ClipVideo Clip

Summary – Summary – Factors Effecting Ground Factors Effecting Ground

ImprovementImprovement• Suitability of existing geotechnical Suitability of existing geotechnical

materials?materials?• Size of improvement area?Size of improvement area?• Availability of specialist plant / Availability of specialist plant /

equipment?equipment?• Proximity to existing habitation / Proximity to existing habitation /

buildings?buildings?• Access & safety considerations?Access & safety considerations?• Cost effective cf: traditional methods?Cost effective cf: traditional methods?

ActivityActivityExamine the following situations and state what Examine the following situations and state what

ground improvement method would be ground improvement method would be suitable & why:suitable & why:

1.1. A deep vertical shaft construction in an A deep vertical shaft construction in an area of high ground water.area of high ground water.

2.2. An area of ground with shallow soft man-An area of ground with shallow soft man-made fill materials, such as mining waste, made fill materials, such as mining waste, for housing development. for housing development.

3.3. An area of previously drained and An area of previously drained and reclaimed silt with low bearing capacity for reclaimed silt with low bearing capacity for road construction. road construction.

4.4. The stabilisation of a rock face The stabilisation of a rock face overhanging a busy railway.overhanging a busy railway.

5.5. A previous land fill tip used for domestic A previous land fill tip used for domestic waste.waste.

Ground Freezing

Dynamic Compaction / vibro-flotation

Pre-compression

Cement grouting / nailing

Importing structural fill