CASE STUDY AND NUMERICAL MODELING FOR SOIL IMPROVEMENT WITH VACUUM CONSOLIDATION METHOD PDF

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rd Proceedings of Softsoils 2014, October, 21-23 2014 CASE STUDY AND NUMERICAL MODELING FOR SOIL IMPROVEMENT WITH VACUUM CONSOLIDATION METHOD R.Karlinasari 1, M. Djunaidy 2 and M.R.Fakhrurrozy 3 ABSTRACT: The use of vacuum consolidation method in Indonesia, currently was being developed enough to ov...

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Proceedings of Softsoils 2014, October, 21-23 2014

CASE STUDY AND NUMERICAL MODELING FOR SOIL IMPROVEMENT WITH VACUUM CONSOLIDATION METHOD R.Karlinasari 1, M. Djunaidy 2 and M.R.Fakhrurrozy 3

ABSTRACT: The use of vacuum consolidation method in Indonesia, currently was being developed enough to overcome the problems of soft soil. A power plant project located in Muara Bakti, Bekasi, West Java, Indonesia using a vacuum consolidation method for the preparation of Power Building, Passive Storage, Coal Crusher and Coal Storages area. Numerical modeling with the ability to model suction pressure as the effect of vacuum process were used to analyze the soil improvement. The phenomenon of horizontal shrinkage were successfully modeled, so that it can explain the differences in settlement resulting from vacuum consolidation method, compared to another method of soil improvement. Keywords: vacuum consolidation, suction pressure, numerical modeling, horizontal shrinkage

INTRODUCTION To overcome problem of soft soil, especially in constructing structure in low land area of sediment zone, vacuum consolidation method currently was being developed in Indonesia. A number of project have been succesfully constructed in a soft soil with this kind improvement method. Since the method produce settlement behaviour which was different from the traditional one, this paper is intended to imitate the settlement phenomenon with a numerical model.

- GWL is located 0.8 m below existing ground surface or GWL at + 0.2000. - Layer (1) about 4 m thickness (0 – 4) is soft (sandy) clay with SPT values between 2 – 4. - Layer (2) about 6 m thickness (4 – 10) is very soft clay with SPT values 2 - 4. - Layer (3) about 3 m thickness (10 - 13) is soft (organic) clay with SPT value 4. - Layer (4) below level 13. Stiff clay with underlying silty sand with SPT value more than 3. The soil layer parameters is defined as in the table below : Table 1. Soft soil parameters

THE SOFT SOIL The Power Plant Project is located in Muara Bakti, Bekasi, West Java, Indonesia. The vaccuum consolidation method has been applied to the preparation of soil under Power Building, Passive Storage, Coal Crusher and Coal Storages area. The area is ... ha, devided by 4 zone ; A1, A2, B1 and C. The soil investigation result indicated that there is 12.0 m – 12.5 m depth of soft soil, with consistency of very soft to soft soil. The vaccuum method has been used with the apllication of 80 kPa of suction and a 1.95 m of preload, to simulate the working load of 11.25 ton/m2. The vacuum consolidation was done at October 2013 to January 2014. The very soft to soft soil layer is defined as follow : - Average existing ground surface is +1.000. 1

Lecture, Sultan Agung Islamic University, Semarang, INDONESIA Director, PT. GEOTEKINDO, INDONESIA 3 Engineer, RK Engineering Consultant, INDONESIA 2

Items Compressibility Index (Cc) Coefficient of Consolidation (Cv) Coefficient of Consolidation (Ch) Void ratio eo Unit weight γw

Units

Average Values 0.65

m2/year

15

m2/year

36

ton/m

3

1.57 1.54

THE MODEL The numerical model was build by Geostudio Program SEEP/W and SIGMA/W. The parameters is defined base by soft soil parameters in Table 1, as follow :

Table 2. SEEP/W parameters Items Saturated permeability Ksat Volumetric water content at saturation θ Coef. of volume compressibility mv

Units m/day

Average Values 2.16E-3 0.61

m2/kN

3.41E-06

Table 3. SIGMA/W parameters Items Modulus of Elasticity E Cohesion c Shear angle φ Shear angle due to suction φb

Units kN/m kN/m2 deg deg

Average Values 5600 25 8 8

The stage of vacuum method at site is as follow : - Stripping and sand backfill for platform - Install PVD and horizontal drainages. - Install geomenbrane and geotextile. - Install vacuum pumps and keep the pumps running for 3 ~ 4 month. - Backfill 1.95 m thickness soil - Unload vacuum pressure based on the settlement monitoring or calculated consolidation degree by Asaoka method. - Remove surcharge soil in the center part to meet the final level requirement. An initial model were build base on the initial ground water elevation. The maximum negative pressure head = 100 kPa. The pressure head contour is as follow :

Figure 1. Initial pressure head condition The suction application to the soft soil layer, was modelled by an aplication of head pressure equal to – 80 kPa, to the border of the model. The border of vaccuum head boundary condition is applied at the right, left and upper side of the model.

Figure 2. Suction application boundary condition The pressure head contour become as follow, the upper layer of soil have a pressure head - 92 kPa.

Figure 3. Suction contour after vacuum apllied From the pressure head contour above we can observed that the negative pressure also become higher at the right and left side of the model. The SIGMA/W analysis of coupled consolidation, than performed, deformation due to the application of vacuum pressure is as follow :

Figure 4. Deformation due to the application of vacuum pressure From Figure 4. the phenomenon of so called horizontal shrinkage were successfully modeled, the deformation not only vertical deformation but also lateral deformation towards the centre of the model. This is because the vacuum pressure work not only vertically, but it is work as a plane pressure on soil layers.

COMPARATION TO REAL MEASUREMENT The actual measurement at site we had the vacuum pressure is as follow :

Figure 5. Lateral deformation contour , max at 0.55 m Figure 9. Measured vacuum pressure vs time The maximum vacuum pressure is 95 kPA, it is in confirmity to the model, which is produce the pressure head of 92 kPa (Figure 3.) The vertical settlement due to settlement plate measurement is as follow :

Figure 6. Vertical deformation contour, max at 1.16 m The applied preload 35 kN/m2 than modelled at SIGMA/W program with coupled consolidation, saturated zone only, the final result is as follow : Figure 10. Measured vertical settlement The maximum vertical settlement is 1.102 m, it is in confirmity to the model, which is produce the vertical settlement of 1.16 m (Figure 6.)

Figure 7. Vertical deformation contour, max at 1.16 m

.

Figure 8. Lateral deformation contour , maximum at 0.76 m

Figure 11. Measured lateral deformation The lateral deformation due to inclinometer measurement are 6.7 cm at inclinometer 1 and 25.5 cm

at inclinometer 2. This is lower than lateral deformation produce by model, which is maximum at 76.0 cm (Figure 5.) CONCLUSION The numerical model has been successfully in confirmity represented the phenomenon of horizontal shrinkage (onward lateral deformation), which is observed during construction. That is explained why the in vacuum consolidation method, the value of vertical settlement were less than the vertical settlement usually observed from the tradisional preload soil improvement, because the lateral deformation tend to retain the vertical settlement. REFERENCES GEOTEKINDO, 2013, Ground Improvement Proposal For PT. Cikarang Listrindo Coal Fired Power Station Power Plant Site At Muara Bakti, Bekasi, West Java. GEOTEKINDO, 2014, Final Vacuum Monitoring Record A1-R1, PT. Cikarang Listrindo Coal Fired Power Station Power Plant Site At Muara Bakti, Bekasi, West Java. Karlinasari,R.,Rahardjo,P.P., 2010, Unsaturated Shear Strength Parameters of Tropical Volcanic Residual Soils, UNSATURATED SOILS, Eduardo E. Alonso, Technical University of Catalonia (UPC) Barcelona, Spain; Antonio Gens, Technical University of Catalonia (UPC), CRC PRESS, Barcelona, Spain....