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SPECIALIST CIVIL AND GEOTECHNICAL CONSULTING ENGINEERS
Concerns on Grouting in Soils
Dr Indrayogan Yogarajah GeoEng Consultants (S) Pte Ltd
Scope of Presentation
Methods/Forms of grouting Grouting for Deep Excavation Effects of Grouting Overcoming effects Weed out some misconceptions
Various forms of grouting
Jet grouting Deep Soil Mixing Deep Cement Mixing Jet Mechanical Mixing Wet Soil Mixing Chemical grouting Compaction grouting Fissure grouting In fill grouting
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Grouting
Grouting of soils is a process of injecting a cementitious compound/mixture into the ground to minimise one or more of the following
Ingress of water (eg. Chemical grouting) Stiffening/strengthening of soils (eg. Jet grouting, deep soil mixing, deep cement mixing etc.) Lifting of structures (compaction grouting) Sealing of gaps in rocks (permeation grouting, fissure grouting)
Grouting
Soil fracturing Soil strengthening Soil compaction Soil permeation
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Grouting of soils
Sealing of CBP, Retaining Wall Service Gap
Grouting of soils
Soil improvement for tunnelling
Grouting of soils
Underpinning
Grouting of soils
Uses of Grouting
Improved soil base for excavations, especially in soft soils (most common use). - Improve overall stability - Reduce ground movements and subsidence - Reduce forces on retaining wall and strut loads
Improved soil
Grouting of soils
Grouting for Deep Excavation
High pressure grouting
Jet Grouting (JGP)
Mixing only
Deep Soil Mixing (DSM) High PressureGrouting Deep Cement Mixing (DCM) Wet Soil Mixing (WSM) Grout Mixed Piles (GMP)
Mixing Methods
Grouting
Mixing and pressures
Enhanced Grout Mixed Piles (EGMP) Turbo Jet (TJ) Jet Mechanical Mixing (JMM)
RANGE OF SOIL PARAMETERS FOR VARIOUS GROUTING METHODS
Organic Clay Silt JGP DSM DCM WSM Enh_d GMP Turbo
Sand Gravel
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Concerns of grouting
Design Stage
Strength and Stiffness Performance of grouting methods Behaviour of Earth Retaining Structures during Excavation
Construction Stage
Quality of grouting Heave/settlement and lateral movements of the ground and/or Earth Retaining Structures Performance of Earth Retaining Structures during Excavation
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Jet Grouting
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Overview
Jet grouting used in Singapore for more than 20 years extensive experience. We should not under-estimate local experience. Jet grout consist of high pressure water/grout jets that cuts the soil by disintegrating the soil matrix. The cut soil is mixed and partially replaced by the cement grout. As drill string is rotated and withdrawn, a column of cement mixed soil is formed.
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Overview
Mechanical properties of jet grouted soil is much like that of sedimentary rocks (e.g. mudstone, siltstone, sandstone depending of soil jet grouted). To understand and apply jet grouting - Good understanding of soils - Knowledge of basic fluid mechanics - Knowledge of basic mechanical engineering
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JET GROUTING PROCESS
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Jet Grout Pile
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Jet Grout Pile
Variants of Jet Grouting
3 basic variants Single tube/fluid Double tube / fluid Triple tube / fluid At present, double tube system is most widely used in Singapore.
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Jet Grout Pile
SINGLE,DOUBLE & TRIPLE FLUID/TUBE JET GROUTING
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Jet Grout Pile
Typical Jet Grouting Parameters Singapore Experience
Parameters
Flow Rates Water Jet Grout Jet Air Shroud Jet Fluid pressures Water Jet Grout Jet Air Shroud Jet Cement and Grout Water / cement Lifting Parameters Withdrawal Rate Rotation Speed Size of Collumns In Marine Clay m 0.5 to 0.8 up to 2.5 up to 2.0 up to 4.5 min/m rpm varies 8 - 30 5-10 6 -1 2 5-10 16 8 -12 W:C 0.9 - 1.4 0.9 - 1.4 0.8 - 1.0 2 - 2.5 bars bars bars NA 200-300 NA NA 200-400 7 -12 350-400 100-200 7 -12 NA 300-400 7 -12 l/min l/min cfm NA 60-70 NA NA 60-200 175-500 60 -120 80-160 175-500 NA 600 175-500
Unit
Single Tube
Double Tube
Triple Tube
Super Jet
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Jet Grout Pile
Jet Grouting
Diameter of columns formed 1.0m to 4.5m diameter The large diameters are formed by high grout flow. Diameter of rods approx 90mm to 120mm
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Believe
Strength of Grout columns cannot be ascertained mathematically Large diameters = Large pressures Large pressures = Large movements Large wall movements = Damage
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Strength Design of Jet Grouted Marine Clay
Most commonly jet grouted soil in Singapore is in marine clay. Strength of jet grouted marine clay can be estimated by determining the various contents of clay soil, water and cement. The relative amounts of the three constituents in the jet grout can be estimated by mass balance.
Refer: Lee Y. (1998) A Framework for the Design of Jet Grout Piles in Singapore Marine Clay. MEng Thesis, Civil Engineering, NUS.
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Jet Grout Pile
Believe
Large diameters = Large pressures Large pressures = Large movements Large wall movements = Damage Strength of Grout columns cannot be ascertained mathematically
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Energy decay of submerged jets
PQ
no air shroud
air shrouded
Distance from nozzle
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Jet Grouting
Water jet impinge on soil wall. Pore pressure increases rapidly in soil mass. Bonds between soil particles overcome by pore pressure. Soil particles disintegrates. Therefore, ease of disintegration depends on particle to particle bond.
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Jet Grout Pile
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High pressure water jet impact on marine clay sample : note the total disintegration i.e. no pieces of intact clay (LeeYeong 1998) Jet Grout Pile
WATER JET CUTS SOIL (NOT PUSH)
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Jet Grout Pile
CASE STUDY
RL 103.5
Diaphragm wall 1.2m thick Grout thickness 4m to 5m Cu= 300kPa E= 150 MPa
Fill
RL 86.5
RL 86.0 JGP top
UMC
F1/F2
LMC OA
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RL 82.0 JGP bottom
TYPICAL SECTION
W2
IW 3
IW 4
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27th Dec 2007 W2 IW 3 IW 4 Approx 6m width
Time vs Displacement
100 0 -100 0 -200 -300 -400 No of Days from 1st Dec
IW 4 IW 3
Max inclinometer displacements
30
60
90
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27th Dec 2007 W2 IW 3 IW 4 Approx 6m width
3rd Jan 2008
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Inclinometer Records for IW3 and IW4
Time vs Displacement
Jan 1st
100 Max inclinometer displacements 0 -100 0 -200 -300 -400 No of days from 1st Dec IW 4 IW 3 30 60
Feb 1st
Introduction of relief wells
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7th Jan 2008 IW 3 IW 4
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Inclinometer Records for IW3 and IW4
Time vs Displacement
Jan 1st
100 Max inclinometer displacements 0 -100 0 -200 -300 -400 Time from 1st Dec 30 60
Feb 1st
IW 4
IW 3
Introduction of relief wells
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-400 -300 -200 -100 0 0
100 200 300 400
RL 103.5
10
Fill
15 20
RL 86.5
RL 86.0
25
(m)
UMC
F2
30
DEPTH
35
LMC OA
RL 82.0
40
45
50
55
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60
DEFLECTION (m m )
Typical wall movement mode
If annulus is not maintained
Discharge is minimised Causing increased ratio of soil to cement and water to cement
Drilling to the point Of Soil Improvement
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When soil improvement commence slurry is discharged
Start of volume build up in cavity causing heave or lateral disp
Flow of slurry out of casing
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Jet Grouting
Grout pressures are not the main cause of wall movements. Wall movements can be controlled by allowing slurry to be discharged Relief wells at the location of each grout point would be best Controlled grouting volume is required
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Jet Grouting
Avoid relief wells away from the point of installation Relief wells need to be cleaned If volume of grout is mixed with the slurry, the strength would be reduced If proper relief wells are provided, chances are the volume of cement can be reduced allowing some savings
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Grout Mixed Pile/ Deep Soil Mixing/ Deep Cement Mixing
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Grout Mix Pile
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Grout Mix Pile
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Grout Mix Pile
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Grout Mix Pile
Grout Mix Pile
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Typical three shaft system
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Typical DSM/DCM/GMP parameters
Single double- triple-quadruple shafts Diameter of columns up to 2000mm per shaft leading to approx 3.5m2 treated area per 4 shaft configuration (0.8m per shaft) Strengths up to 1MPa in MC Can be used for stiff soils depending on the machine torque Pressures applied are slightly higher than that required to over come the overburden pressures
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Typical DSM/DCM layout - four shafts
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Enhanced GMP/ Jet & Mechanical Mixing
Jet Mechanical Mixing
Enhanced GMP/JMM
Similar to GMP/DSM/DCM With the addition of a jet nozzle to cater for larger diameter A cross between the jet grout method and the GMP/DSM/DCM methods Used for wide ranged of soil types
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Jet Mechanical Mixing
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Enhanced GMP
Jet Mechanical Mixing
Enhanced Grout Mixed Piles
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TYPICAL EGMP/JMM LAYOUT
Diameter by Jet pressures Blade diameter
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Concerns of grouting -DCM/DSM/EGMP/JMM
Design Stage
Strength and Stiffness Performance of grouting methods Behaviour of Earth Retaining Structures during Excavation
Construction Stage
Quality of grout cores Properties of soils which have been disturbed Heave and lateral movements of the Earth Retaining Structures
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Change of soil properties due to Deep Mixing Methods
GL
CPT-1
QC (Mpa) 0 0 1 2 3 2 4 6 8 10
Fill
4 5 6 7 8 9 Depth (m)
UMC
F2
10 11 12 13 14
LMC OA
15 16 17 18 19 20 21
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Change of soil properties due to Deep Mixing Methods
GL
CPT-5
QC (Mpa) 0 0 5 10 15 20 25
Fill
Depth (m)
MC
10
12
14
16
18
OA
20
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DSM/DCM
Method of grouting can cause disturbance to existing soil layers. Wall movements could be larger than predicted if the lower strengths are not considered Controlled grouting at the upper layers may be required
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DSM/DCM
More analysis and tests required to understand the sensitivity of the various grouting methods Wall stiffness may be a variation that needs to be considered Mixing of soft clays can cause it to be remoulded sensitivity of Singapore Marine Clay is about 5.
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Concerns of grouting
Design Stage
Strength and Stiffness Performance of grouting methods Behaviour of Earth Retaining Structures during Excavation
Construction Stage
Quality of grouting cores Heave and lateral movements of the Earth Retaining Structures Performance of Earth Retaining Structures during Excavation
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Correlation of SPT N with UCS or Cu
Occasionally we see CPT as a test requirement. CPT can only provide the determination of the top of grout layer Strength of soil improvement not obtainable
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Correlation of SPT N with UCS or Cu
Very often we see SPT and Coring tests to be carried out in specifications Core strength is commonly mentioned but not N value to achieve So consultants/contractors treat it as clay and use Cu= 5-6N So to achieve 300kPa, we need nearly SPT N of 50 to 60
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Correlation of SPT N with UCS or Cu
Plot of Cu to SPT 'N' Values of Jet Grouted Areas
3 Undrained Shear Strength, Cu(N/mm2) 2.7 2.4 2.1 1.8 1.5 1.2 0.9 0.6 0.3 0 0 20 40 60 SPT 'N' Value 80 100 120
y = 0.0167x
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Correlation of SPT N with UCS or Cu
More data and statistical analysis needed to be carried out to allow a better representation of SPT N SPT N and coring methods of obtaining strength have their own pit falls and data should be carefully analysed. Care has to be taken to ensure that the soil type is considered in any analytical model
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Discussions
Grouting of soils is still considered an Art as opposed to being a science Grouting in soils seems to be still the domain of specialist sub contractors Consultants always would like to leave the issues to the contractors
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Discussions
More research and conscientious grouting works is still required for more systematic grouting procedures to be developed Jet grouting is known to cause movements to earth retaining structures if not done correctly soil mixing methods remoulds the upper soil layers and causes strength reduction and needs to be considered at design stage
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Moving Forward
More needs to be done to mitigate movements caused by JGP. This has to be part of the MS and trial test process Present Advisory notes require critical control levels to be developed for grouting. How do we do that if we are unsure of the process?
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Moving Forward
For all grouting methods, more data collection still required for a better understanding of grouting strengths etc. Contractors and Consultants need to work more closely to have a better understanding of the grouting methods
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Thank you
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