JOURNAL OF YANGTZE RIVER SCIENTIFIC RESEARCH INSTI ›› 2020, Vol. 37 ›› Issue (4): 168-174.DOI: 10.11988/ckyyb.20191118


Theoretical Solution to Borehole Contraction Caused by Unloading in Anisotropic Sandy Soil

FEI Yi1, LI Wang-hui2, ZHAO Chun-feng1, WANG You-bao1, WU Yue1   

  1. 1.Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China;
    2.School of Civil Engineering and Transportation,South China University of Technology,Guangzhou 510640,China
  • Received:2019-09-16 Online:2020-04-01 Published:2020-05-21

Abstract: Radial unloading-induced borehole contraction is caused in the drilling process of bored pile. On the basis of the SMP yield criterion and the non-correlated flow rule, the solution for the stress and displacement fields in two stress-state conditions of plastic zone around the vertical borehole is deduced with the coefficient K0 of lateral earth pressure considered. Parameter analysis shows that the K0 and internal friction angle φ of soil have a great influence on the emergence and development of plastic zone as well as the radius re and rp of plastic zone. The relative displacement and stress of borehole wall increase linearly along with the increase of drilling depth with different values of K0 and mud's unit weight rmud. The relative displacement of borehole wall intensifies with the growth of K0, while declines with the rising of rmud. However, the radial and circumferential stresses of borehole wall do not change with K0. In addition, the range of plastic zone around the vertical borehole hardly changes along the depth in sandy soil, and the plastic radius rp has a remarkable influence on the circumferential stress. The theoretical solution presented in this paper is of theoretical significance for the unloading problem of borehole in initial in-situ stress field of sandy soil.

Key words: sand, cast-in-place pile, coefficient of lateral earth pressure, vertical drilling, radial unloading, theoretical solution

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