Based on the necessary relationship between the strength and the water content of unsaturated soil, combined with real foundation pit in unsaturated soil, firstly, physical and mechanical parameters of soil samples with different water content are obtained through triaxial test. Secondly, the computation model is built by using PLAXIS, and numerical analyses of deformation characteristic in deep foundation pit are performed, then, the relation curves between water content and deformation values are plotted, which include ground deformation, support pile deformation and upheaval deformation at pit bottom, meanwhile, the influence laws of soil water content on deformation characteristic are summed up. The case study show that soil water content is a key influence factor for deformation characteristic of deep foundation pit in unsaturated soil, and the research results have some theoretical meaning and practical value for design and construction of deep foundation pit.

Aiming at the phenomenon of empirical selection in CFG pile compound foundation's design parameters, the computational models considering different pile length were built by numerical simulation software PLAXIS, whose background came from an actual highway engineering. The relation curves were plotted and analyzed concerning pile length with subgrade horizontal deformation, subgrade settlement, integral stability of embankment and end bearing force of pile, in the light of deformation and stress cloud graphs from post-processing results. The feasibility of pile length optimization in conventional design was judged synthetically according to above mentioned curves, and the optimized pile length was 2m shorter than the one of conventional design, which cut down construction cost. The construction practice indicates that there are not abnormal occurrence in subgrade treatment section during period of traffic operation.