Field Measurements in Geomechanics, Leung, Tan & Phoon (eds)© 1999 Balkema, Rotterdam, ISBN 90 5809 066 3

Effect of different jet-grouting installations on neighboring structures

J.G.Wang Irzstitute of High Performance Computing, Singapore

B.Oh & S.W.Lim BBR Ground Engineering Pte Limited, Singapore

G.S.Kumar Kajima Overseas Asia Pte Limited, Singapore

ABSTRACT: This paper presents a case study to compare the effects of two methods of jet grouting installa­tion, triple-tube jet grouting and the Superjet, for a two-level basement structure in soft marine clay. Firstly, the jet-grouting parameters (discharge, pressures, withdrawal time, rotation speed and installation '.process) are . compared. Secondly, sizes of jet-grouting columns are compared. Superjet can get the jet~.grouting column up to 5m in diameter. Thirdly, the impact on neighboring structures is compared from field monitoring data. Fourth, the mechanism of such impact is simply analyzed by two dimensional Finite Element Method.

1 INTRODUCTION

Jet grouting is widely used in Singapore as a tool to stabilize very soft soils like upper marine clay. The jet grouting layer is used as a pre-located strut in the ground or as a .working platform for basement con­struction. Three main problems which pertain to jet grouting application are: a) strength of jet grout, b) size of jet grout pile (JGP), and c) ground movement associated with jet grouting. Installation of jet grout­ing will cause significant soil movement and deflec­tion to adjacent buildings like diaphragm wall I sheetpile which usually enclose the grouting area. These movements or deflections are usually not ac­ceptable in densely constructed area like the down­town area of Singapore. Thus the control of soil dis­placement during jet grouting should be studied carefully (Wang et al. 1998).

This paper presents a case study to compare the ef­fects of two methods of jet grouting installation, Le., Triple tube method and Superjet method. The above methods have been used in the construction of a two level basement structure in Singapore. The structure is located in soft marine clay conditions.

In this paper, we look into the following items: Firstly, the jet-grouting parameters are compared. Secondly, the sizes of jet-grouting columns are com­pared. Thirdly, the impact of grouting process on the neighboring structures is compared through field in­clinometer monitoring data. Fourth, the mechanism of such an impact is simply analyzed by two dimen­sional Finite Element Method. Jet grouting pressure and surcharge due to upheaval are studied. The nu-

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merical results on the deflections of Diaphragm wall and Sheetpile are compared with the in-situ readings. It is found that the jet-grouting pressure will cause deflection to a maximum. This maximum deflection depends on the in-situ soil conditions, jet grouting type and overburden pressure. The upheaval effect varies with installation method and construction consequence.

2 TRIPLE TUBE AND SUPERJET

2.1 Operation Parameters

Operation parameters are the most important pa­rameters that will determine the character of the soilcrete column. The operation parameters need to be changed as per the in-situ soil conditions. Table I gives the comparison of two installation methods in this project.

Table 1 Comparison of Operation Parameters

Item Triple Tube Superjet Water-cut pressure 300 - 400

bars Air pressure 6 - 7 bars 6 - 7 bars Air flow Grouting discharge 150-200 I/min 500 - 600 I/min rate Grouting Pressure 40 + 20 bars 200 - 300 bars Number of nozzles 3 2 Rotation rate 8-lOrpm 2.5 to 5 rpm Withdrawal speed 6-12 minim 12-16 minim Water/cement ratio 0.9 - 1.1 1.5 : 1 to 2.0: 1

2.2 Installation Process

The installation for Triple tube is as described in the literature (Bell and Burke 1992) and the following construction sequences are used for Superjet installa­tion:

1. Pre-bore hole with 300 mm in diameter and install steel casing if necessary.

2. Position the drill and jetting tools on the pro­posed location.

3.

4.

5.

6.

7.

8.

9.

Activate high-pressure pump with water to check nozzle and grout line clearance.

Lower the tube into the ground to the re­quired depth.

On reaching the desired depth, activate ce­ment slurry line; adjust rotation and with­drawal rate, discharge value etc. as per pre­determined operational parameter from the test.

Continue withdrawal while forming the col­umn using the auto valve until the nozzle reaches the design thickness.

Shut off cement slurry line and quickly with­draw the grouting tube while switching over to the water line for flushing.

Casing is then fully withdrawn.

Maintain the spoil level at pre-excavated slurry pit around the jetting point. The slurry is left to harden and is removed out the fol­lowing day.

10. Relocate installation rig to next location and start the Step 1 to Step 9.

Comparing Triple tube to Superjet, following characteristics vary from each method. SUPERJET grouting requires only 200----300 bars which is less than what Triple tube system uses. As we always assume that bigger jet grout column requires higher pressure. However, research has shown that not only the flow velocity but also flow rate from the nozzle has an effect on the size of the jet-grouted column. This is because cutting force is the product of veloc­ity and flow rate. It is important to highlight that how far the cutting jet radius depends on how much

512

-- .lttat,_.t cll1taace .......... Pro&kl::t of pceuure and f109 rata

( P • Q /1000 ) ( taf•ca•eia ') -.. ,.....,.~_.......,...._...-...-----------~ .... .I $00

--~-------..._..A..;J ....... ..-..~.-..........a.--~~ M no a• i.• • ,.

Floe r•t• Q (ltr/wln)

Fig. 1 Diameter with flow rate and pressure

energy is emitted from the nozzle. Following ex­perimental results gives the relationship of the two parameters and cutting diameter (Yoshida et al. 1996).

In triple tube jet grouting, grouting pipe is in­serted into a pre-drilled hole of 120 mm to 150 mm. This hole has about 25mm-annulus space to allow spoil to escape. Practice proves that this opening is too narrow for soft adhesive clay to flow out. There­fore, soil is usually pre-treated with water to reduce its adhesive effect. This can prevent the hole from clogging and casting overpressure in the ground, thus preventing heaving.

All of these disadvantages are overcome in SU­PERJET. It uses a much bigger pre-drilled hole up to 300mm diameter as stated in the installation se­quences. Much bigger annulus clearance will ensure continuous spill of sticky spoil. In case the clay is too sticky,· pre-water treatment concept can be ap­plied as well before the grouting takes place. To fa­cilitate smoother flow, water-cement ratio may be increased to 2: 1. In general the 28-day soilcrete strength (Cu) is about 300kPa or more. Operational parameters however are subjected to changes per in­situ soil conditions.

It is important to ensure continuous flow of spoil because clogging of the spoil escaping will result in ground heaving. Monitoring device for this over­pressure is developed in SUPERJET system. This monitoring device, which is mounted near the noz­zle, is an airflow sensor, which is also used for regu­lating air pressure injected into the ground. When there is a surge or change from the regular meter reading, hole clearance is necessarily checked to see if it's choke. The major difference in the SUPERJET equipment lies in its design of the tube and nozzle (also known as monitor). This monitor is developed over years from numerous experimental findings from its cutting distance using several types of pa­rameters such as pressure, flow rate, number of passes and rotating rate.

~9.'1!i I WfC=15 I

A ----1'--+-T-- A A ___. ____ _.....,_

Fig. 2 Layout of Test Point

The monitor is built with two nozzles mounted at the same level. Jet pressure and flow rate are speci­fied to be 300 bars and 600 lit/min, respectively. This flow rate is spilt into two 300-lit/min jets di­rected horizontally opposing each other so as to make horizontal momentum minimum.

2.3 Size of Jet Grouting Columns

As the specified in the Superjet specifications, the size of jet grouting column varies with ground con­ditions. An in-situ trail is usually required to deter­mine the operation parameters. For this project, the trial arrangement is given in Fig. 2 whose result is used in Phase II of this project. Jet grout pile was in­stalled between -11 m and -l 4m from ground level. Site soil is typical upper marine clay (Yong et. al 1990). Its physical properties are listed as follows: water content: over 90%~ liquid limit: 105% and bulk unit weight: 14 kN/m .

The trial test was done for 14-day and 28-day sam­ples. Mazier type sampling is employed and tested in an accredited laboratory. Pressuremeter test on 28-day deformation modulus is carried out on site. This test is to obtain the distribution of deformation modulus (E) of improved soilcrete column and soil masses. Results are summarized in Table 2. Their spatial distributions of strength and deformation modulus are shown in Fig. 3. The sample water con­tent is approximate 80% and its bulk unit weight is almost the same as before (14 kN/m3

).

In order to compare the difference between Triple tube and Superjet, a trial test is also carried out for Triple tube. Table 3 gives the comparison for strength. The average strength of Triple tube is usu-ally lower than that of Superjet. . We can draw following findin~s from the compari­son:

a) Compared to Triple tube, Superjet has more uniform shear strength. The deformation modulus, E, has homogeneous results even at the joint part of two columns.

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Table 2 Cu test and E for Superjet Column

Col. 14-day sample 28-day sample 28-day E 4m 5m 4m 4.5m Pressuremeter

point point point point (MPa) 1 268 511 167 2 58 124 177 3 1315 1811 216 4 266 105 448 177

1&2 274 380 166 3&4 803 948 175

Table 3 Cu (kPa) between Triple Tube and Superjet

Days Triple Tube Days Superiet 15 198 7 205 15 242 9 248 15 252 9 298 12 199 10 350 12 152 10 378 12 180 8 301 10 169 10 320

Aver. 198 Aver. 300

1.2

1 ----· --........

' io.s r\A

1 . .......Strength

' ~ ~0.6 -.-Modulus ~

a ;o.4 . ..

I-"1. 0.2

0

0 0.5 1 1.5 2 2.5 3 Distance from Column Center (m)

Fig. 3 Strength and Deformation Modulus Distribution

b) Triple tube has weaker shear s~ren~h th~n Superjet even though the cunng tn~e ~s longer. The average strength of SuperJet ts more uniform than Triple tube. The bigger column can improve the soil more homogene- : ously.

c) Trial test indicates that the diameter of Super­jet column can reach as big as 411_1. Even for shown diameter of 4.5,...,5m, the sotl has some improvement. Therefore, we can co.nclude that the effective diameter of the SuperJet col­umn is 4m and its effect range is approxi­mately 5m.

d) The equivalent deformation modulus (E) for Superjet can reach 175 MPa from pressureme­ter test. This value is almost homogeneous for different test points. Triple tube results are scattered (Lee 1998). Furthermore, our theo­retical analysis has shown that the bigger the

4/15/98 6/4/98 7/24/98 9/12/98 1111/98 12/21/98 is--~~~~~~~~~~~~~~~~~

Observation Date

Fig. 4 Inclinometer readings for two installations

column, the higher equivalent deformation modulus (Wang & Leung 1997).

2.4 Replacement Ratio

The replacement ratio of soilcrete column is an interesting topic. Based on the discharge rate, with­drawal speed, water/cement ratio, effective diameter and wastage of cement milk (10% for Superjet and 20% for Triple Tube are assumed), following re­placement ratios of cement are estimated: The col­umn weight ratios are 358 kg/m3 for Triple tube 284 kg/m3 for Superjet. If only soilcrete column is con­sidered, the volume replacement ratios are 52% for Superjet and 48% for Triple Tube. If the whole soil mass is regarded as improved mass, the volume re­placement ratios are 49% for Superjet and 44% for Triple Tube, respectively. Therefore, cement is more uniformly distributed for Superjet.

3 IMPACT ON NEIGHBORING STRUCTURES

3 .1 Inclinometer Readings during Installations

Fig. 4 gives the inclinometer readings during instal­lations of Superjet and Triple Tube when Phase II of this project was treated (Note that Phase I and Phase II are shown in Fig. 8). The deviation of local soil profile is not vast, hence inclinometer readings are comparable. From the figure 4, the impact of Super­jet on diaphragm wall is much less than that caused by Triple Tube.

3.2 FEM Model for Mechanism Analysis

As pointed out in our early paper (Wang et al. 1998), the impact of jet grouting on diaphragm wall comes from jet grouting pressure, surcharge due to ground heave and activity on the ground. A simple two­dimensional Finite Element Model as shown in Fig. 5 is proposed to study the impact mechanism.

For simplicity, only jet grouting pressure and sur­charge due to ground heave will be studied here.

Machine Uphmral Surchllrp

er rl 5 kN'ml E•2025kPa ip-ISo

Dia hr m Wall

JGP y-16 kN/ml E-2.6E5 kPa µ.-0.30 cp-18° c-125 kPa

Cover

Fill

y-16kNJml E-4050 kPa µ.-<l. 35 cp-220 c-5 kPa

MRT Zone

T"' 16 kN'm3 E•17000 kPa µRl 35 cp-25° c-5 kPa

Mud stone (completely weathered)

Mud stone y-20lcN/m1 r20 kN'ml E-7. 2E4 kPa µ-<l. 20 E-1.2E6 kPa ~- 20 cp-300 c-5 kPa cp-35° c-5 kPa

SUrclarge .,..20 kN'ni' E•l.3E3k:Pa µ.-0.30 cp-30° c-5 kPa

Fig. 5 FEM Model for Numerical Analysis

3.3 Jet Grouting Pressure

Fig. 6 shows the effect of jet grouting pressure on diaphragm wall. The equivalent jet grouting pressure is obtained by the same method as our early paper (Wang et. al. 1998). This figure shows that even the equivalent jet grouting pressure increases from 50 kPa to 150 kPa, the maximum deflection only in­creases from 5mm to 25mm. In this case the maxi­mum deflection is near the jet grouting zone. Super­jet uses lower pressure and causes lesser deflection.

3 .4 Ground Heave Effect --- Surcharge

As pointed out in our early paper (Wang et al. 1998), the ground heave will cause a lot of troubles to the neighboring building I structure. In order to under­stand this problem, the surcharge effect is analyzed here. Fig. 7 gives the comparison for different sur­charges.

r-.. E '-' --as ~

} ~ ·-Q

<-..-. 0

~ > c1)

.....:l '"Cl

c1) (.)

.g c1)

~

514.

110

100

90

80

70 ---- Jet pressure P=SO kPa

-+-- Jet pressure P=BO kPa

-ik-- Jet pressure P=l 1 O kPa

60 -+- Jet pressure p .. JSO kPa

50...__._~......___._~_._____.~---~---~

-10 0 10 20 30 Deflection of Diaphragm Wall (mm)

Fig.6 Effect of Jet Grouting Pressure On Diaphragm Wall

110

,,....., 5 100

....... 0

70

60

_._ Surcharge i.om

-+-- Surcharge I.Om

~ Surcharge O.Sm

50---'--~'--~~~---L-~L-----L-__J

0 20 40 60 80 Deflection (mm)

Fig. 7 Effect of Surcharge due to Heave

In Triple Tube system where effective release hole is absent, (1---2) m of ground upheaval is always ob­served in construction site. Fig. 7 shows that if the surcharge increases from 0.5m to 2.0m, the deflec­tion of the wall may increase 1---2 times. Of course, the w~igJl.t of this upheaval .will resist further up­heaval. For the site without neighboring buildings I structures, the upheaval is beneficial to further installation due to higher over-burden pressure. But for site constraint, this upheaval will cause a lot of problems for the surrounding structures even delay the project process. This conclusion does not con­sider the degradation of soil mechanical properties during installation. This degradation will apply more lateral force on the wall. This is another topic to be studied in the future.

3 .5 Uplift Effect for Sheetpiles

This project is divided into two parts (Phase I and II). Grouting at Phase I is all by Triple Tube method and is excavated during the installation of Phase II. Phase II us.es a combination of Superjet and Triple Tube. The interface of Phase I and II is divided by a row of 15-m sheetpile as a temporary support. It is observed that the Triple tube grouting installation near to the sheetpile had uplifted the sheetpile as much as 40mm. The movement damages the second ~nd third layer struts in Phase I. Subsequently Super­Jet method was employed and it was observed that the movement is much lesser (almost negligible). He~ce, in the remaining portion near sheetpile, Su­perJ et was used and the damaged struts were strengthened. There was no further damage of strut subsequently.

3.6 Photo After excavation

Fig.9 gives us a direct feeling on how big a Superjet column is. This photo was taken after the excavation of basement. During excavation, we found that the soil 0.5--- lm over the column top is of low water

515

Phase II

Superjet & Triple Tube

Diaphragm Wall

Q) -·-a-Q) Cl)

..r:: VJ

Phase I

Triple Tube

Fig. 8 Location for temporary Support, Sheetpile

content and likes improved soil, but there is no trace of cement in the soil. The soil out of the range does not improve any more.

4 CONCLUSION

We had comparatively studied the installations of Triple Tube and Superjet from operation parameters and the column test results. The size of soilcrete col­umn was studied through a trial test. The impact of installations on the neighboring buildings I structures was studied by using Finite Element results and field inclinometer readings. Based on these studies, we can draw our understandings as followings:

a) Superjet uses lower jet grouting pressure and high flow rate (discharge) while Triple tube uses high jet grouting pressure and low flow rate.

b) Superjet can achieve as big as 4m of soil­crete column. Its influence range can reach 4.5,....,5m in diameter.

c) Superjet has more homogeneous shear strength than Triple tube. This case study shows that the deformation modulus for the improved soil mass is almost homogeneous.

d) Superjet has lesser impact on surrounding buildings than Triple tube. The impact source comes from jet grout pressure and surcharge due to ground upheaval.

e) Because of the big diameter of soilcrete col­umn, Superjet is more suitable for large area

Fig. 9 Superjet Column after Excavation

improvement whereby it can act as a pre­located strut and as a dry working platform for basement slab construction.

5 REFERENCE

Bell, A.L. and Burke, G.K. 1992. The compressive strength of ground treated using Triple system jet grouting. Proceed­ings of Conference on Grouting in the Ground, (eds) by In­stitute of Civil Engineers, London, pp525-53 8.

Lee Yeong. 1998. A Framework for the Design of Jet Grout Piles in Singapore Marine Clay. Master Thesis, National University of Singapore.

Yong, K.Y., Karunaratne G.P. and Lee, S.L. 1990. Recent de­velopment in soft clay engineering in Singapore. In Soft Seabed Deposit, Kansai Int. Geotech Forum '90 on Com­parative Geotechnical Engineering. 3-10. Japan.

Yoshida, H., Jimo S. and Uesawa, S. 1996. Development and practical applications of large diameter soil improvement method. In R. Yonekura, M. Terashi & M. Shibazaki (eds), Grouting and Deep Mixing: 721-726. Rotterdam: Balkema.

Wang J.G., and Leung, C.F., 1997. A constitutive law for sof­tening of lumpy balls. Report to Department of Civil Engi­neering, National University of Singapore.

Wang J.G., Oh B., Lim S.W. and Kumar G.S., 1998. Studies on soil disturbance caused by grouting in treating Marine clay. 2"d Int. Conf. On Ground Improvement Techniques: 8-9 Oct. Singapore, 521-528.

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PROCEEDINGS OF THE 5TH INTERNATIONAL SYMPOSIUM ON FIELD MEASUREMENTS IN GEO MECHANICS - FMGM99 I SINGAPORE/ 1 - 3 DECEMBER/ 1999

Field Measurements in Geomechanics Edited by

C.F.Leung, S.A.Tan & K.K.Phoon Department of Civil Engineering, National University of Singapore

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A.A. BALKEMA/ROTIERDAM/BROOKFIELD/ 1999