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Improving the capacity of bored piles by shaft grouting shaft grouting

Presentation · March 2018

DOI: 10.13140/RG.2.2.11111.39847

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 SHAFT GROUTING
Improving the capacity of bored piles by shaft grouting
Tran Nguyen Nhat Nam
Management Associate Program
March 2018
1. Introduction
Shaft grouting, a relatively new technique, is carried out by injecting grout at discrete points around
a pile shaft, assuming that the grout spreads along it. Researchers and practising engineers have
reported an increase in the stiffness and capacity of deep bored piles. (Morrison et al, 1987 )

Q
u
Basic concept:
The ultimate load-bearing capacity of a drilled shaft is:
Qu= Qp + Qs
Q Where Qu = Ultimate load
s
Qp = Ultimate load-carrying capacity at the base
Qs = Frictional (skin) resistance
𝐿
Qs = 0 𝐹𝑠 𝑑𝑧 = 𝑈 𝒒𝒔𝒊 . 𝑙𝑖
High pressure grout will flow up the sides of the shaft increasing resistance
Q
b
FIGURE 1-1. Ultimate load-
bearing capacity of a drilled shaft

01 SHAFTGROUTING
1. Grouting Mechanism

The mechanisms proposed by Stocker

and Troughton & Stocker as follows:
FIGURE 1-2. Schematic Diagram of the
Impregnation Mechanism for TAM Grouting

 The concrete on the perimeter pile is cracked and pushed out against the surrounding soil with the
grout bracing the pile against the soil
 The increased lateral pressure causes a local increase in soil density in the interface zone of the
pile bore which has become softened or loosened by the pile construction process.
 In granular soils, cementation of the soil particles in the interface zone may occur due to the
infiltration grout into the pores of the soil.
 Voids, fissures, cavities or wash outs may be filled with grout providing an improved contact
between the pile and the soil.

02 SHAFTGROUTING
2. Back - analysic
τu = fs × N

where, τu = Ultimate skin friction (kPa),

fs = Correlation factor with SPT N-value
N = Uncorrected mean blow count of SPT.
Table 1. Summary of Typical Design Parameters
Soi Pile type Correlation Limiting ultimate
factor, fs friction, (kPa)
Alluvial Deposits Plain 0.8 - 1.0 100
Shaft grouted 3.5 - 6.0 200
Completely Plain 0.8 - 1.2 160 - 200
Shaft grouted 2.5 200
Weathered Plain 0.6 - 1.2 120-160
Sedimentary Rocks Shaft grouted 1.6 - 5.0 120-200

It can be seen that typically shaft grouting is able to enhance the shaft friction by two to three folds

03 SHAFTGROUTING
2. Back - analysic
 The Hongkong shaft grout test result
for bored pile constructed under
water show a maximum friction
mobilized of 210 kPa. A two or three
fold increase in friction capacity is
realized.
 In Bangkok, test result show
enhanced friction value in the range
150 to 300 kPa and a correlation of
5N up to 250 kPa, respectively. This
is more than a 100% increase form
the average shaft resistance values.
FIGURE 2-1. Hongkong and Bangkok shaft grout result

04 SHAFTGROUTING
2. Back - analysic

FIGURE 2-2. Littlechild, Plumbridge, and Free (1998)

FIGURE 2-3. Dương Minh Trí and Phạm Quốc Dũng (Bachy Soletanche Việt Nam)

05 SHAFTGROUTING
2. Back - analysic
Figure 2-4 presents the KCRC test data
for shaft grouted piles with published
results for plain piles in Hong Kong,
Suraj De Silva et al (1998); and Geo
(1996). Again, the shaft grouting
technique has substantially improved the
friction capacity over normal plain pile
construction techniques in Hong Kong

FIGURE 2-4. Comparison with Ungrouted Pile Tests in Hong Kong

06 SHAFTGROUTING
2. Back - analysic

FIGURE 2-5. Shaft resistance versus average vertical effective FIGURE 2-6. Shaft resistance versus average SPT N value in sand
stress in sand layer for plain and shaft grouted pile. layer for plain and shaft grouted pile.

The shaft resistance values for plain piles Figure 2-6 provides a summary of these
fall in the range 65 to 170 kPa while the results in terms of shaft resistance versus
shaft grouted pile show enhanced value in SPT N value, For both the plain and shaft
the range 150 to 300 kPa grouted piles the shaft resistance value in
sand appears to be independent of the
SPT N value over the range N = 27 to 60
07 SHAFTGROUTING
2. Back - analysic

Table 2. Recommended range of beta  Skin friction capacity for shaft-grouting piles, based
on effective stress method (Bjerrum-Burland)
Soil type Friction Beta
Angle (f) coefficient 𝑹𝒔 = 𝒑. ∆𝑳. 𝜷. 𝒒′ 𝒛
Clay 25-30 0.2-0.35
Where 𝑞 ′ 𝑧: effective overburden at the center
Silt 28-34 0.25-0.50
of depth increment
Sand 32-40 0.30-0.90 𝛽: Bjerrum-Burland beta coefficient
Gravel 35-45 0.35-0.80

 Ultimate shaft grouted friction:

Sand: 250 – 400 kPa
Clay: 200 – 270 kPa

08 SHAFTGROUTING
3. Construction sequences
After 24 hours of casting the piles, a small amount of water is injected at high pressure to crack the
concrete surrounding the grout pipes. This creates an injection path for subsequent bentonite-
cement grouting. In both grouting stages, a double packer is inserted into the TaM to control the
cracking and grout intake at specific depth

Casing installation -> Drilling -> 1st Desanding ->

Steel cage installation -> 2nd Desanding ->
Concreting -> Water cracking -> Shaft grouting

FIGURE 3-1. Construction sequences

09 SHAFTGROUTING
4. Grout mix design
Requirement:

 Grout consists of Ordinary Portland Cement and plasticizer

additive with water complying to BSEN 934.
 Typical grout proportion: 50 litres of water + 100 kg cement
+ 1 litre Plasticizer additive.
 Grout to have a Marsh Cone Viscosity of 30-50 second and
maintain workability of 30-40 minutes.
 Grout mix component shall be measured individually by
weight or volume as appropriate. Required number of
sample cubes shall be taken from each pile or batch for
compressive strength testing. Sampling to have a minimum
of 4 cubes per day / pile.
 More than 20 Mpa compressive strength shall be achieved
after 28 days.
 Grout mix shall be submitted for Engineer’s approval.

FIGURE 4-1. Effect of Water Content on Grout

Properties (after Littlejohn, 1982)

10 SHAFTGROUTING
4. Grout mix design
Table 3. Typical Grout Mix (Baker and Broderick, 1997)
Description Quantity Standard Comment/Effect
Cement 110-225 kg ASTM C-150 Control strength of mix, increase density
of mix
Flyash * 90-310 kg ASTM C-618 Improve pumpability, increase density,
reduce cement content required for mix,
Class F or Class C
Water 60-160 L Control slump
Admixtures 1%-2% of cement Control set time, control shrinkage
(optional)
* Depending on the fines available from the sand.

Table 4. Sample w/c ratios design

Houlsby, 1982 The Chinese Code for Pile Foundations Sammy Cheung Bauer Bachy
w/c ratio 0.4 – 0.55 0.45 – 0.65 0.5 – 0.6 0.66 0.5 0.6
saturated soil loose soil

11 SHAFTGROUTING
5. Supervision of grouting
The following parameters will be recorded for each stage of grouting:
 Date and time of beginning and ending of the stage
 Pump number
 Grout hole number, stage number and depth
 Accummulative volume of the stage
 Pressure during the open sleeve process and final pressure
 Total grout volume
 The causes of pump stop, automatic or manual

There are 3 stop criteria for the grouting:

 Maximum volume is reached following design values based on void ratio of soil (35 – 40%)
 Limited pressure is reached
 Resurgence (grout flowing back up to the ground surface) is identified.

12 SHAFTGROUTING
5. Supervision of grouting
SINNUS System
To achieve the required accuracy in recording the grout
volume and pressure, an automatic recorder, named the
SINNUS System, will be used. In this system, each pump
window displays the instantaneous values of volume,
pressure and flow rate. The real-time pressure and flow
rate curves are also shown. Every value of volume,
pressure and flow rate is recorded for subsequent analysis.
(Hoa Binh’s statement for TAM Grouting, Saigon Centre
project).

FIGURE 5-1. SINNUS system

13 SHAFTGROUTING
5. Supervision of grouting
CINTAC 15 – JEANLUTZ system

Grouting
Transducers - Volume
pressure 2 grouting lines Computer
B2BA3 - Pressure
100 times/s Display
Flow meter Flow rate - Flow rate

Site
check Operator

FIGURE 5-2. CINTAC 15 Frame-work

14 SHAFTGROUTING
5. Supervision of grouting
Sample Grouting records:

FIGURE 5-3. Water cracking records. FIGURE 5-4. Grout mixing records FIGURE 5-5. Grout injection records.

15 SHAFTGROUTING
6. Strain Gauge Measurement
 The standard method of strain gauge measurement is based on the linear relationship
between electric resistance and strain of the gauge. They measure load, stress and
pressure in concrete foundations.
 Strain gauges should be placed near the shaft bottom, although the stress regime is
variable at the bottom. Strain gauges are typically installed on 18-feet (5.5 m) along the
shaft pile, at layer change, and readings are collected every 1 to 5 seconds.

16 SHAFTGROUTING
7. Problems and observations
Table 5. Problems and observations
Problems Reason / solution
sediment can be trapped under the grouting system
Base contamination
sediment can be swept to the pile perimeter by concrete flow from the tremie.
Common to piles constructed under bentonite. This phenomenon occurs with piles
Pile slippage at low where excavation exceeds 48 h and a thick filter cake forms at the soil interface.
grout pressures Uplift of the pile may be observed at grout pressures less than 10 bar.
In this event, grouting should be stopped and the pile regrouted after 24 h.
Hydrofracture occurs when the grout pressure is sufficiently high to fracture the
soil, creating flow paths away from the pile.
Hydrofracture is easily identified by a significant reduction in grout pressure and a
Hydrofracture corresponding increase in grout volume injected. To minimize hydrofracture it was
recommended that the rates of grout injection be limited to 2 l/min.
In the event of hydrofracture it is recommended that grouting is stopped and the
pile regrouted 24 h later

17 SHAFTGROUTING
8. Water cracking

 Pressure should be limited from 400 – 600 psi. There is a greater risk of clogging when grout pressure
exceeds 600 psi.
 Water cracking is an important process to facilitate the subsequent grouting. In order to ascertain the
timing of the cracking operation and its water pressure, a trial was carried out using concrete in drums
with same TAM arrangement. Figures 7-1 show crack trails at 24hrs and 51 hrs respectively.

The results of the trial show that cracking should

be taken place later than 24 hours after the
concrete casting (24 – 48h) as it was found that
early cracking (even after the initial setting, say in
12 hours) will create only hair cracks to the
concrete cover and there was a chance of closing
the crack again by the lateral soil pressure

FIGURE 8-1. Crack Trial at 24 hrs (left), 51 hrs (right)

18 SHAFTGROUTING
9. Recommend spacing of piles
The grouting planthus adopted calls for grouting over a horizontal distance of three times the radius of the
shaft from the center of the shaft. (Atlas of Oculoplastic and Orbital Surgery, Thomas C. Spoor, page 105 )

Table 6. Recommended range of beta

IS 2911-1-1 NBC, 1976 Indian Congress TCVN
(2010) 205:1998
Pile type (Sec. 6.6.1 6.6.2) (Sec. 13-132-120) (Sec 3.9.2)
Friction 3.0D 2D or 1:75 H > 760 mm 3.5D 3D
Point bearing 2.5D 2D or 1:75 H > 610 mm 3.0D 2D

where D: pile diameter;

H: diagonal distance for rectangular shaped piles.

19 SHAFTGROUTING
9. Recommend spacing of piles
The Norwegian Code of Practice on Piling, Den Norske Pelekomite (1973), give the following minimum pile
sapcing

Table 7. The Norwegian Code

Length of pile Friction pile in sand Friction piles in clay Point bearing piles
Less than 12 m 3D 4D 3D
12 to 24 m 4D 5D 4D
Greater than 24m 5D 6D 5D

where D: pile diameter;

H: diagonal distance for rectangular shaped piles.

20 SHAFTGROUTING
10. Group reduction factors
The AASHTO (1990) bridge specifications still give it as a "suggestion" for friction piles, shaft-grouting
pile (The Converse-Labarre).

𝑛−1 𝑚+ 𝑚−1 𝑛 d
𝐸 =1−𝜃 which 𝜃 = 𝑎𝑟𝑐𝑡𝑎𝑛
90𝑚𝑛 s

where: n number of piles in the x direction

m number of piles in the y direction
𝜃 angle having tangent, expressed in degrees
s axial spacing of piles
d diameter of piles FIGURE 10-1. Frictional piles (single pile and group
of three piles)

21 SHAFTGROUTING
10. Group reduction factors
In 1996, Troughton et al, after load-testing, they excavated the piles and their true dimensions measured,
The result indicated an increaser in the pile diameter of between 5.8% - 6.1% for cased shaft grouted
pile.
Table 8. Measured pile diameter
Pile No Theoretical drilling Measured pile diameter Enlargement of pile
diameter (mm) diameter (medium) %
Min (mm) Max (mm) Medium (mm)
1 570 580 640 605 6.1
2 570 580 660 603 5.8

B.D Little Child (1998) indicates: the volume of grout injected along the pile soil interface is equivalent to an
average thickness of approximately 25mm around the perimeter of the pile in the shaft grouted zone. This
equates to only a 3% increase in pile surface..

We have 2 theories:
- Consider grouting mixtures as concretes used in pile, the diameter increase so the reduce factor is
less than.
- Grouting is 50% water, 50% cement, can be eliminated in calculation, so reduce factor is the same as
the original one (non-shaft grouting)
22 SHAFTGROUTING
11. Tenderer’s Alternative Design
Items Bauer Bachy Fecon
1.Mixed design
- Cements (kG) 100 105 100
- Water (l) 55 66 66.6
2. The grade of grout required (MPa) 20 20 25
3.The grout volume per each
Manchettes
- Maximum (l/m2) 35 35 35
- Minimum (l/m2) N/A 25 25
4. The limiting pressure 40 (bar) ~ 4 (MPa) 40 (bar) ~ 4 (MPa) 40 (bar) ~ 4 (MPa)
5. Water cracking times 12h~24h after concreting 8h~24h after concreting 5h~24h after concreting
6. Injection times After water cracking Least 5 days after Least 5 days after
concreting concreting
7. Factor of improved skin friction 2 (for all layers) ~2.4 (for sand layer) ~2.4 (for sand layer)
8 Frictional resistance /Ultimate load 90% 85% 95%
9. Friction parameters :
- Sand (kPa) 300 300 -320 300
- Clay (kPa) 180 240 250 260
11. Tenderer’s Alternative Design
Items Bauer Bachy Fecon
10. Pile Diameter (mm) 1200 1000 1200
11. Pile Length (m) 40 59 58
12. Starting grout level (m) -2.75 -37.7 -29
13. Ending grout level -42.75 -55.7 -57
14. Length of shaft grouting (m) 40 18 28
15. Shaft grouting for (m) All layer Sand layer Sand layer
16. Rc,u (kN) 24881 18847 24814
17. Gammak 2.20 1.46 2.1
18. Rc,d (kN) 11300 12901 11816
19. Skin friction fs (kPa)
Layer 3a (Clay) 100 40 75
Layer TK3( Sand) 140 55 55
Layer 4a (Sand) 200 220 200
* Note: Ultimate shaft grouting friction:
 Sand: 250 – 400 kPa
 Clay: 200 – 270 kPa
24 SHAFTGROUTING
12. Owner’s concern:
Table 9. Improvement factor of side friction for different soil types
(Kai Fang, Zhongmiao Zhang 2012)

ms ns
Soil types Sand Clay Clay Silt Fine sand Coarse sand Gravel
Minimum 1.58 1.10 1.12 1.33 1.27 1.50 1.42
Maximum 3.70 1.72 1.9 1.69 1.85 1.98 2.18
Average 2.50 1.39 1.42 1.52 1.54 1.70 1.79
Coefficients of variation 0.31 0.15 0.18 0.09 0.13 0.11 0.16

ms is the improvement factor of the initial stiffness for shaft grouting

ns is the improvement factor of side friction at shaft-soil interface influenced by
base grouting

Bauer use factor of side friction 2.0 for Clay and Sand layers. Although all soils can be
improved by shaft grouting technique, the applicability and effectiveness of grouting will be
many times effective in cohesionless soil than other soil type (Baker and Broadrick, 1997). .

25 SHAFTGROUTING
12. Owner’s concern:
1. Some guidance on post-grouting is included in FHWA’s Geotechnical Engineering
Circular (GEC) No. 10 Drilled Shafts: Construction Procedures and LRFD Design
Methods (Brown et al., 2010). But guidance on shaft-grouting is lacking of reliable design
methods.
2. No Standards for Shaft Grouting
3. How many strain gauges (SG) per shaft? To measure displacement
4. It is important that net volume be specified and accurately measured. The calculation
method and acceptable % abundance?
5. Instrumentation Monitoring
- Top of Shaft Displacement (Precision)
- Strain Gages at Bottom of Rebar Cage
6. Base grouting and shaft grouting? Which is more efficient?
7. We currently measure volume, pressure and flow rate as part of acceptance criteria.
- What is most important?
- Does this combination lead to consistency in product?
8. Group action reduction (Converse-Labarre):
𝑛−1 𝑚+ 𝑚−1 𝑛 diameter
𝐸 =1−𝜃 where 𝜃 = 𝑎𝑟𝑐𝑡𝑎𝑛
90𝑚𝑛 spacing(center to center)
The shaft-grouting will reduce E factor?
26 SHAFTGROUTING
 References
1. Vahidoddin Fattahpour, Beatrice Anne Baudet, James Wang-Cho Sze (2014),
Laboratory investigation of shaft grouting, Geotechnical Engineering, Volume 168 Issue GE1
2. V.M. Troughton and M.Stocker Proc Instn, Base and Shaft Grouted Piles, Civil
Engineers, Geotechnical Engineering
3. Nguyen, H.M., Fellenius, B.H., Pupppala, A.J. Aravind, P., and Tran, Q.T.2016.
Bidirectional test on two Shaft-Grouted Barrette Piles in the Mekong Delta, Vietnam.
Geotechnical Engineering Journal of the SEAGS & AGSSEA 47(1) 15-25
4. Trần Nguyễn Hoàng Hùng: Công nghệ xói trộn vữa cao áp, NXB Đại học quốc
gia TP HCM, 2016
5. The Chinese Technical Code for Building Pile Foundations JGJ 94-94
6. ROBSONR J. and WAHBYA. Base and shaft grouted bored pile foundations for the
first residential complex, Giza, Egypt. Piling and deep foundations conference, Brussels, 1994

27 SHAFTGROUTING
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