Study on Mechanical Behaviors of Unsaturated Remolded Collapsed Loess

A series of physical-mechanical tests and statistical analysis are conducted to investigate the mechanical behavior of unsaturated remolded collapsible loess, which includes deformation and strength behavior at different moisture capacity, degree of compaction, and confining pressure in order to assess stability of tunnel foundation base in loess. Results indicate that collapsible loess is easy to be compacted and the residual deformation potential can be controlled. At optimum moisture capacity of 14.5%,when the degree of compaction is not less than 0.95, the stress-strain curves of loess transform from strain softening to strain hardening as the confining stress increases, but the curves are always strain hardening when the compacting factor is 0.92,regardless of the change of the confining pressure. Increasing moisture capacity, confining pressure, or decreasing the degree of compaction will make the loess more strain hardening. There is a positive correlation between internal friction angle, cohesion and degree of compaction, contrary to the above, the correlation between those and moisture capacity is negative. Power-exponent function y=A.x^B can fit the relationship precisely. The concept of ultimate shear strength indexes, including ultimate internal friction angle ∅_m and ultimate cohesion c_m, is established, and the statistical analysis indicates that as the moisture capacity increases, ∅_m and c_m increases firstly and then decrease. The aforesaid relationship can be fitted precisely with Gaussian function ∅_m(c_m)=a.exp(-((ω-b)/c)²). Based on the concept and relationship above, an easy and fast method, involving only moisture capacity, is provided to judge if the strength can meet the design requirement, and verify the suitability through field experiment.