Unsaturated loess with large pores

large void ratio and under-consolidation has significantly structural behavior

affecting its mechanical properties. Based on the discussion of researching approaches on soil structural mechanics characteristics

the structural index reflecting the initial structure behavior and structural parameters reflecting the variation of structure behavior under loading and watering is expressed by the comprehensive structure potential concept

which reflecting the stability to maintain soil structure unchanging and variability to perform structural property after breakage. The compression deformation structural parameters stress structural parameters and stress ratio structural parameters of loess

and its structural index being corresponding to the structural character of soil physical properties are also discussed respectively. Through the confining compressive experiment

unsaturated soil direct shearing test

triaxial test and true triaxial test

three structural parameters changing with water content and shear strain and structural index changing with water content

as well as the structural strength and compressive characteristics are determined by the loess experimental results. The structural equivalence critical state concept is proposed by the Mohr-Coulomb criterion considering the strength index changing with structural parameter under wetting and shear action. Because of the shear strength of normal consolidation soil being uniquely corresponding to its effective stress and density

the normal consolidation soils can be considered as the special soil without structural behavior and its structural parameter or structural index identically equal to 1. On the basis of modified Cam-clay model

the structural shear yield surface equation is established by considering the critical state line and isotropic compression yield stress changing with the structural parameters

so as to lay the solid foundation to study the structural elastoplastic constitutive model. At the same time

it is also discussed how to apply the strength law considering structural behavior of loess in the stability analysis of loess mass surrounding tunnel

supporting force determination of lining structure

settlement and bearing capacity analysis of loess foundation

so as to deepen loess mechanics theory