Abstract: The structural and mechanical properties of the soil foundations on the construction site are critical for the investigation on the deformation and failure of structures in the goaf region. A series of true triaxial tests on the unconsolidated soils from Nanpiao mining area was conducted using TSW-40 apparatus. The variations of stress ratio and structural parameters of unconsolidated layers soil under true 3D stress state were measured under different conditions of the confining pressure, the moisture content and the intermediate principal stress ratio. A mathematical model of the structural parameters was established. The results show that undisturbed soil present three types of relationships between q and???s, i.e., strain softening, ideal elastoplasticity, and strain hardening. However, the remolded soil and saturated soil exhibit strain-hardening type of q???s relationship. The structural parameters m? decrease with increasing the shearing strain, moisture content, confining pressures, and intermediate principal stress ratio. In the initial stage of shearing, the structural parameter m? decreases significantly. Then mh tends to be stable gradually as ?s is equal to 5%. The m? equals to 1 when ?s equals 15%. The proposed mathematical model shows that of the number of mh is significantly dependent on confining pressures, whereas less sensitive to the moisture content, and the intermediate principal stress ratio. The proposed model describes well on the structural parameter of unconsolidated soils under different experimental conditions, and compares well with the experimental measurements.

Key words: comprehensive structure potential, stress ratio structural parameters, unconsolidated soil layers, the generalized shear strain, mining subsidence