Geomechanics and Engineering

Techno-Press (테크노프레스)
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Shear behavior of foam-conditioned gravelly sands: Insights from pressurized vane shear tests

  • Shuying Wang (School of Civil Engineering, Central South University) ;
  • Jiazheng Zhong (School of Civil Engineering, Central South University) ;
  • Qiujing Pan (School of Civil Engineering, Central South University) ;
  • Tongming Qu (Department of Civil & Environmental Engineering, The Hong Kong University of Science and Technology) ;
  • Fanlin Ling (School of Civil Engineering, Central South University)
  • Received : 2022.09.09
  • Accepted : 2023.08.12
  • Published : 2023.09.25
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Abstract

When an earth pressure balance (EPB) shield machine bores a tunnel in gravelly sand stratum, the excavated natural soil is normally transformed using foam and water to reduce cutter wear and the risk of direct muck squeezing out of the screw conveyor (i.e., muck spewing). Understanding the undrained shear behavior of conditioned soils under pressure is a potential perspective for optimizing the earth pressure balance shield tunnelling strategies. Owing to the unconventional properties of conditioned soil, a pressurized vane shear apparatus was utilized to investigate the undrained shear behavior of foam-conditioned gravelly sands under normal pressure. The results showed that the shear stress-displacement curves exhibited strain-softening behavior only when the initial void ratio (e0) of the foam-conditioned sand was less than the maximum void ratio (emax) of the unconditioned sand. The peak and residual strength increased with an increase in normal pressure and a decrease in foam injection ratio. A unique relation between the void ratio and the shear strength in the residual stage was observed in the e-ln(τ) space. When e0 was greater than emax, the fluid-like specimens had quite low strengths. Besides, the stick-slip behavior, characterized by the variation coefficient of measured shear stress in the residual stage, was more evident under lower pressure but it appeared to be independent of the foam injection. A comparison between the results of pressurized vane shear tests and those of slump tests indicated that the slump test has its limitations to characterize the chamber muck fluidity and build the optimal conditioning parameters.

Keywords

Acknowledgement

The financial support from the National Outstanding Youth Science Fund Project of the National Natural Science Foundation of China (No. 52022112), the National Natural Science Foundation of China (No. 52108388) and the Hunan Provincial Innovation Foundation for Postgraduate of China (No. 2020zzts152) are acknowledged and appreciated.

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