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 co

nditions 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 ε

s

i.e.

strain softening

ideal elastoplasticity

and strain hardening.However

the remolded soil and saturated soil exhibit strain-hardening type of q-ε

s

relationship.The structural parameters mηdecrease with increasing the shearing strain

moisture content

confining pressures

and intermediate principal stress ratio.In the initial stage of shearing

the structural parameter mη decreases significantly.Then m

η

tends to be stable gradually as εs is equal to 5%.The m

η

equals to 1 when ε

s

equals 15%.The proposed mathematical model shows that of the number of m

η

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.