Borehole contraction and depth analysis based on Extended SMP criterion. Issue 4 (October 2021)

• Record Type: Journal Article
• Authors: Zhang, Jiaqi; Zhao, Chunfeng; Zhao, Cheng; Gong, Xin; Wu, Yue; Liu, Fengming
• Is Part Of: IOP conference series. Volume 861:Issue 4(2021)
• Publication Date: 2021-10
• Subjects: Borehole drilling -- Cylindrical cavity -- Extended SMP criterion -- Three-dimensional solution -- Radius -- Intermediate principal stress -- Slurry wall protection; Earth sciences -- Periodicals; Environmental sciences -- Congresses; Environmental sciences -- Periodicals; 550.5
• DOI: 10.1088/1755-1315/861/4/042105
• Languages: English
• ISSNs: 1755-1307

Abstract

Abstract: The excavation of vertical boreholes is involved in several geotechnical engineering constructions. Earth pressure in the soil is released during the drilling process, resulting in soil stress redistribution and borehole contraction along the excavation surface. The stress and displacement responses tend to increase with soil depth, which may degrade the quality of hole formation and cause collapse. Therefore, the concerns of three-dimensional (3-D) stress and displacement states of the soil around the borehole should be addressed during the design and construction of associated engineering. This study proposes exact and simplified analytical solutions based on the Extended Spatially Mobilized Plane criterion to obtain a more accurate borehole contraction law and depth in drained soil. The 3-D stress and displacement values along the borehole depth are obtained by combining the derived plane solution of cylindrical cavity contraction with the classical earth pressure formula. The proposed solution can reasonably consider the influence of the intermediate principal stress and explicitly state its value. The contraction degree of the proposed solution is 7.76% less than the Mohr–Coulomb solution at a depth of 80 m with the specified soil parameters. A parametric analysis shows that the contraction will be reduced by 21.4% and 36.8% if the unloading ratio increases from 0.4 to 0.5 and 0.6, respectively. The borehole can be supported by a high unit weight of slurry in an elastic state. A decrease in soil shear strength impairs borehole stress state and hole formation quality, and internal friction angle affects more than cohesion in deep soil. The effect of dilatancy on borehole contraction is insignificant. Further, the proposed approximate solution, which ignores the elastic strain in the plastic zone, has a slight error in borehole displacement but is convenient for engineering calculation.