Strength Reduction Study Based On Unified Strength Theory

The Mohr-Coulomb criterion commonly used in slope stability analysis by strength reduction method does not consider the influence of intermediate principal stress on the strength of geotechnical materials,which makes the calculation of stability coefficient safer and does not fully exert the strength reserve of the slope.The unified strength theory can consider the influence of intermediate principal stress on the strength of geotechnical materials through the influence of intermediate principal stress parameter b.However,at present,the strength reduction method for the unified strength theory is not systematic enough,and the relevant results are not perfect.In this paper,based on the finite difference method of FLAC3D software,the unified elastoplastic constitutive model of finite difference is derived,which is expressed by cohesion c₀,internal friction angle ?₀,uniaxial tensile strength ?_t and uniaxial compressive strength ?_c.In visual studio 2010,the corresponding dll file is written in c++language and loaded into FLAC3D,which is preliminarily validated with the Mohr-Coulomb constitutive model.The influence of boundary conditions and slope size on slope stability is discussed.For two different constitutive models of unified strength theory,four reduction schemes are adopted to calculate slope stability coefficients by reducing c₀,?₀ and ?_t,?_c,the intermediate principal stress influence parameter b respectively.The stability calculation results of four reduction schemes are compared.The strength effect of the intermediate principal stress parameter b at the same reduction coefficient is studied by means of the maximum shear strain increment,the maximum displacement in X direction and the development range of the plastic zone.Combining the two-parameter strength reduction method with the strength reduction scheme?1?,the influence of strength parameter reduction ratio R and intermediate principal stress parameter b on comprehensive stability coefficient and potential sliding surface of slope is studied.The results show that the boundary constraints of the side boundary in the fixed y direction are more realistic when the slope is extended in the y direction for 60m.Synchronous reduction of c₀ and ?₀ is more practical.The calculation results of stability coefficient for ?_t and ?_c synchronous reduction are too large.The results do not accord with reality.Whether the intermediate principal stress influence parameter b should be synchronous reduction needs further study.The intermediate principal stress parameter b should be increased to increase the intrinsic strength of geotechnical materials,which makes the slope more difficult to destroy.The maximum shear strain,the maximum displacement in x direction and the range of plastic zone decrease with the increase of b value.In the two-parameter strength reduction method,the wider the b value is,the wider the selection range of reduction path is;with the increase of reduction ratio R,the sliding surface of the slope deepens and develops towards the interior of the slope,and the comprehensive stability coefficient increases accordingly.