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Effects of Jet Grouting on Adjacent Ground and Structures

Article  in  Journal of Geotechnical and Geoenvironmental Engineering · December 2001

DOI: 10.1061/(ASCE)1090-0241(2001)127:12(1076)

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Bin-Chen Benson Hsiung David F T Nash

National Kaohsiung University of Applied Sciences University of Bristol
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 Effects of Jet Grouting on Adjacent Ground and Structures
By Ing Hieng Wong and Teoh Yaw Poh
Journal of Geotechnical and Geoenvironmental Engineering, Vol. 126, No. 3, 247- 256

Discussed by
Hsiung, Bin- Chen, Benson, postgraduate student, Department of Civil Engineering,
University of Bristol, Bristol, BS8 1TR, UK
Nash, D. F. T., senior lecturer, Department of Civil Engineering, University of Bristol,
Bristol, BS8 1TR, UK
Lings, M. L., senior lecturer, Department of Civil Engineering, University of Bristol,
Bristol, BS8 1TR, UK
Hsieh, H. S., associate professor, Department of Construction Engineering, National
YunLin University of Technology and Science, YunLin, 640, Taiwan

The authors' contribution is a welcome addition to the observational record on jet-

grouting reinforced deep excavations in soft clay. The discussers share similar research

interests and are now studying several excavation cases in Taipei, Taiwan. In the paper

the authors describe how large cantilever-shaped lateral wall deflections were observed

following a 3m to 9m-thick jet-grout treatment. This behaviour is in contrast with our

own observations in Taiwan.

Figure 1a and 1b show the observed behaviour of diaphragm walls after jet grouting as

well as a typical undrained shear strength profile of clay in Taipei. At two sites, 3-4m-

thickness high pressure jet grouting had been carried out to replace the soil beneath the

final excavation level completely. At the first site (CN257), double- tube jet grouting

(JSG system) was used to form a grout zone from 18.8m to 22.8m below ground level,

and the maximum lateral wall deflection (nearly 60mm) is comparable to that observed

by the authors. However, the lateral deflection profile was characterised by bulging, quite

different from the cantilever shape reported by the authors, with very small movements at

the top of the wall. The difference may partly be explained by the greater undrained
strength of Taipei clay, and partly by the greater depth of the grout zone. At the second

site (CN258), double- tube jet grouting with a rotating blade (SWING system) was used

to form a grout zone from 16.7m to 19.7m in depth in very similar ground conditions.

Here the lateral movements were much smaller, presumably because of the different technique

used, but again the lateral deflection profile was characterised by bulging. At this site, the top of

the diaphragm wall may have been restrained by the presence of adjacent buildings on raft

foundations.

It is not uncommon for jet grouting to result in considerable ground heave, although

large lateral movements appear to be less common. Such movements result from high

grouting pressures developed at depth due to restriction of the return flow. Under these

circumstances, particularly in clays, it is likely that the ground will fracture preferentially

perpendicular to the smallest total stress. Thus, in normally consolidated clays where

Ko<1, one would expect the initial formation of fractures filled with grout which would

result in lateral displacement of the ground and walls. Subsequently, as the lateral stresses

build up to exceed the vertical stresses, the fracturing would be horizontal, and the

movement vertical. In contrast, in over-consolidated clays where Ko>1, the fractures

would always be horizontal and the associated movements vertical. The data presented by

the authors suggests that at their site there was insufficient lateral resistance for the lateral

stresses to build up significantly.

After such large lateral movements during jet grouting it might be expected that the jet

grout slab would be very effective in reducing the inward movement of the wall during

main excavation. Are the authors able to present data to show how effective the jet

grouting was in restricting lateral movements?

 Chang et al. (1999) mention that, as a standard design procedure, both bending

moment and shear force distribution on the wall are calculated without taking into

account the effects of soil improvement. The discussers would be most interested to hear

the authors' opinion on the need to include such effects as well as wall installation in the

design procedures.

Reference:

Chang, C. J., Wang, F. G. and Huang, C. C., (1998), Soil Improvement of Deep

Excavation in Soft Ground, Construction News, No. 189, pp. 34- 49, Taipei, Taiwan

(In Chinese)

Moh and Associates Inc., (1995) Final Report for the Ground Monitoring Data for

Lot CN257 in Nankang Line, Taipei MRT System, Moh and Associates Inc., Taipei,

Taiwan. (In Chinese)

Moh and Associates Inc., (1998) Final Report for the Ground Monitoring Data for

Lot CN258 in Nankang Line, Taipei MRT System, Moh and Associates Inc., Taipei,

Taiwan. (In Chinese)

 Undrained Shear Strength (kPa)
Lateral wall movement (mm)

-80.0 -60.0 -40.0 -20.0 0.0 20.0 0 20 40 60 80 100 120

0 0

10 10
Soft to Firm Silty
Clay

20 20
SID7 in lot CN257,
treated soil at

Depth (m, bgl)

Depth (m, bgl)

18.8m bgl to 22.8m

bgl
30 30

SID2 in lot
CN258,Ttreated Clayey Silt
40 soil at 16.7m bgl to 40
19.7m bgl

Sand
50 50
SID4 in lot
CN258,Treated soil
at 16.7m bgl to
19.7m bgl Gravel
60 60

Figure 1a: Lateral wall movements Figure 1b: Typical design profile of
observed after jet grouting at two sites undrained shear strength in Eastern
on the Nankang Line of Taipei MRT Taipei
System

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