3D Evolution of soil arching during shield tunnelling in silty and sandy soils: A comparative study

Abstract

AbstractDuring earth pressure balance (EPB) shield tunnelling, a three‐dimensional stress redistribution occurs, which leads to development of soil arching. In this paper, development of soil arching by stress redistribution in two types of soils, silty and sandy soil is studied. A three‐dimensional numerical model was first developed and validated using the case study of the extension of Dwaraka Najafgarh Metro Corridor of Phase‐III of Delhi MRTS. Using the validated model numerous simplified numerical analyses were carried out to determine the evolution of soil arching in both silty and sandy soil. The variation in stresses (σxx, σyy and σzz), deformation and shear strain were evaluated and, on this basis, the extent of the loosened region and soil arching region was determined for both soil types. Furthermore, impact of different parameters (i.e., face pressure, grout pressure, C/D ratio and diameter of tunnel) on the evolution of loosened region above tunnel crown was assessed. Based on the numerical analysis, the extent of loosened region in the vertical direction for silty soil was determined to be 1.21D from the tunnel crown and the extent for the sandy soil was determined to be only 0.73D. While in the horizontal direction, the loosened region extends up to 0.72D and 0.37D for silty and sandy soils respectively. An optimal range of different parameters which must be adopted at the time EPB shield tunnelling in silty and sandy soil is recommended.