case study

1. 1
Case Study: Ground Improvement of
Yangtze River Floodplain Soils with
Combined Vacuum and Surcharge
Preloading Method
Presentation By-
Girish S. Gaikwad
FY M. Tech Geotech
MIS 712221007

2.  CONTENTS
 Introduction
 Instrumentation
 Procedure
 Tests
 Results & Discussion
 Conclusion
 References

3.  INTRODUCTION
 Coal Storage at the bank of Yangtze river
 In situ soil
 Necessity of Ground Improvement
 PVD
 VPM
 CV-SPM

5.  INSTRUMENTATION
Vacuum Probe Piezometer
Inclinometer Vacuum Pressure

6. Plan View of Instrumentation

7.  PROCEDURE
Preliminary
Loading
Sand
Cushion
PVD
Installation
Corrugated
Pipes
Network
Sealing
Membrane
Applying
Vacuum
Pressure

8. Additional Steps for CV-SPM
VPM
Combined
Surcharge
Stage I
Stage II
Stage III
Total
Surcharge

10.  TESTS
Field Vane Shear Test
• Introduction
• Apparatus
• Set-up
• Procedure
• Observations
• Calculations
• Results

11. Plate Load Test
• Introduction
• Apparatus
• Set-up
• Procedure
• Observations
• Calculations
• Results

12.  RESULTS & DISCUSSION

19. Lateral displacement of
soils on the edge of the
site during preloading: (a)
Point IN; (b) Point IE; and
(c) Point IS

22.  CONCLUSION
 Vacuum pressure below the sealing membrane could reach 90 kPa when the sealing
membrane and the jet vacuum pump worked well. Vacuum pressure decreased along the
depth during its vertical transmission, and the decrease rate was higher through the sand
cushion and the upper unsaturated fill layer.
 The decrease rate of vacuum pressure is nearly 20 kPa=m in the top 2 m of PVDs, and
only about 3 kPa=m from 1.5 to 9 m in depth. The higher decrease rate in top ground
soils may be partially due to the high permeability of loose and unsaturated fill layer, and
partially because the vacuum load dissipated radially.
 The total loads in Section A were larger than those in Section B; as a result, the average
settlement in Section A (530 mm) is significantly higher than that in Section B (277 mm),
demonstrating that ground settlement was remarkably affected by the applied loads.

23.  locations, and this may be attributed to the spatial effect in the field. Moreover, soils in
some sections of the site underwent consolidation under the load of the Yangtze River
levee and civil constructions in the past, which led to a smaller settlement during
preloading.
 In VPM, pore-water pressure was stable after 30 days of vacuum preloading and the
dissipation of excess pore-water pressure was notably affected by vacuum load in PVDs.
In CV-SPM, both the vacuum load and filling load influence pore-water pressure. It
decreased with mere vacuum pressure and it increased after the application of filling
surcharge.
 Both water content and compressibility of soils decreased after preloading. The undrained
shear strength of soils reached 55–77 kPa from the initial 20–30 kPa along the depth
after treatment. All the shallow plate bearing test results met the design capacity
requirements, which indicated VPM and CV-SPM are effective for ground improvement of
the thick muddy-silty clay in the Yangtze River floodplain.

24. THANK
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