Damage Constitutive Model Of Pores Rock Under Freezing-Thawing And Load

Along with the development of China's economic construction and the implementation of the strategy of "One Belt and One Road",the quality and scale of cold engineering construction constantly increased,and the freezing and thawing disasters will be primary problem of cold engineering construction,as a result,it is important to study the damage characteristics and damage mechanism of rock under freeze-thaw condition,which has important theoretical and engineering significance for the safety of engineering construction.As the aggregate of various mineral particles formed under the geological action,the inter-granular pores of rock must be exist.Due to external factors,particle fragmentation and internal pore pressure density?expansion,resulting in constant changes of rock volume,thus showing different mechanical properties.Therefore,it is necessary to fully consider the influence of rock volume change when exploring damage characteristics and constitutive relation of rock.In this paper,macroscopic phenomenological damage mechanics and non-equilibrium statistical methods are combined,the rock was abstracted as pore,damage and not damage three parts based on the deformation and failure characteristics of porous rock,however,the pore and damage parts do not bear the residual strength.Using Weibull distribution to describe the random behavior of the strength of rock infinitesimal,based on D-P strength criterion,and by the dynamic porosity under load reflects the change of rock volume,establish contain rock pores damage constitutive model.Base on the geometric conditions of the peak point,the expression of the model parameters is pushed by using the whole differential method of multiple function.Finally,the rationality of the model is verified through the mechanical properties test of the sandstone,and the mechanical properties of rock damage are analyzed.Base on the influence of the freeze-thaw factors on the lotus rock,respectively from the aspects of damage area and micro-element destruction degree consideration,the total damage variables under freeze-thaw and load are obtained,therefore,the damage constitutive model of porous rock is established by considering the coupling effect of freeze-thaw and load.The rationality of the model is verified by the freezing-thawing cycle and triaxial compression test data of sandstone.The variation of damage variables and total damage evolution rate with confining pressure and freeze-thaw cycles was discussed.Results shows that:the confining pressure is constant,the increase of freeze-thaw cycle aggravate rock damage,resulting in compressive strength decreases,plastic reinforcement;when the freezing and thawing times are certain,rock internal damage is inhibited with the increase of confining pressure,the rock shows that ductility continuous enhancement,brittleness gradually weakens.On the basis of analyzing the whole process of rock strain softening deformation,the damage constitutive model of porous rock based on residual strength under normal temperature and freeze-thaw-load were established by introducing damage factor,and compare with that the experimental curves and reference theoretical curves.The effects of model parameters m and F0 on the constitutive model and damage variables were discussed and its physical significance was clarified.Finally,the influence of freeze-thaw cycle and confining pressure on the softening property of rock strain is discussed.