Geomechanics and Engineering

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Shallow ground treatment by a combined air booster and straight-line vacuum preloading method: A case study

  • Feng, Shuangxi (Department of Civil Engineering, Tianjin University) ;
  • Lei, Huayang (Department of Civil Engineering, Tianjin University) ;
  • Ding, Xiaodong (China Zhonghua Geotechnical Engineering Co., Ltd.) ;
  • Zheng, Gang (Department of Civil Engineering, Tianjin University) ;
  • Jin, Yawei (Jiangsu Xintai Geotechnical Technology Co. Ltd.)
  • Received : 2019.12.16
  • Accepted : 2021.01.06
  • Published : 2021.01.25
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Abstract

The vacuum preloading method has been used in many countries for soil improvement and land reclamation. However, the treatment time is long and the improvement effect is poor for the straight-line vacuum preloading method. To alleviate such problems, a novel combined air booster and straight-line vacuum preloading method for shallow ground treatment is proposed in this study. Two types of traditional vacuum preloading and combined air booster and straight-line vacuum preloading tests were conducted and monitored in the field. In both tests, the depth of prefabricated vertical drains (PVDs) is 4.5m, the distance between PVDs is 0.8m, and the vacuum preloading time is 60 days. The prominent difference between the two methods is when the preloading time is 45 days, the injection pressure of 250 kPa is adopted for combined air booster and straight-line vacuum preloading test to inject air into the ground. Based on the monitoring data, this paper systematically studied the mechanical parameters, hydraulic conductivity, pore water pressure, settlement and subsoil bearing capacity, as determined by the vane shear strength, to demonstrate that the air-pressurizing system can improve the consolidation. The consolidation time decreased by 15 days, the pore water pressure decreased to 60.49%, and the settlement and vane shear strengths increased by 45.31% and 6.29%, respectively, at the surface. These results demonstrate the validity of the combined air booster and straight-line vacuum preloading method. Compared with the traditional vacuum preloading, the combined air booster and straight-line vacuum preloading method has better reinforcement effect. In addition, an estimation method for evaluating the average degree of consolidation and an empirical formula for evaluating the subsoil bearing capacity are proposed to assist in engineering decision making.

Keywords

Acknowledgement

The authors are grateful for the supports from financial support: National Key Research and Development Program of China (Grant No. 2017YFC0805402), National Natural Science Foundation of China (NSFC) (Grant No. 51578371), Open Project of State Key Laboratory of Disaster Reduction in Civil Engineering (Grant No. SLDRCE17-01), Incentive Fund for Overseas Visits of Doctoral Students of Tianjin University in 2019 (070-0903077101), China Scholarship Council (CSC. 201906250153).

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