Investigation on the macro‑ and microdeformation characteristics of silty clay under different shield construction stress paths

摘要

Geotechnical investigation and design show that when evaluating the settlement of ground with soft soil ground, the use of a single stress path results in a larger error than in the case of a multistress path. To understand the influence of a multistress path on the deformation properties and microstructure characteristics of soil, a two-stage stress path (corresponding to three stress states: the in situ state, unloading-loading state, and grouting pressure state) of soil was examined by analytical solution. Then, a series of triaxial tests was conducted to analyze macroscopic deformation properties considering four influencing factors, i.e., the relative distance between the soil and tunnel, stress paths, type of silty clay, and drainage conditions. The results show that axial strain of silty clay caused by the two-stage stress path increases by 31.6% with the relative distance decreasing from 1.67R (R means tunnel radius) to 1.25R on tunnel side, while the volume strain increases by 80% with the relative distance decreasing from 1.21R to 1.06R on tunnel bottom. In addition, the deformation caused by the two-stage stress path (or reconstituted soil or undrained condition) is larger than that caused by the one-stage stress path (or undisturbed soil or drained condition). Finally, through scanning electron microscopy and mercury intrusion porosimetry, the pore size, distribution, shape, and arrangement of silty clay on the bottom and sides of the tunnel were investigated. The research shows that under the two-stage stress path, the number of large pores decrease and that of small pores increase. The probability entropy of pore orientation ranges from 0.834 to 0.971 when silty clay is subjected to a two-stage stress path. This illustrates that the pore order of the soil on tunnel side is better than that on the tunnel bottom.