Deformation Behavior And Theoretical Research Of Rock Subjected To Complex Environment Of Freeze-Thaw And Dry-Wet

In recent years,numerous rock mass projects have been built with the accelerated constructions in cold regions,particularly in the construction of tunnels at high altitudes and latitudes.During the cold season,rock mass is obviously frozen and its freeze-thaw cycles（FTCs）is intense.Furthermore,the repeated dry-wet cycles（DWCs）of rock mass are also caused due to the dry climate and the low rainfall.Based on this,the damage deterioration of rock properties is caused,and it is essential to establish a mechanical damage model that accurately reflect the deformation process of rock.However,the current mechanical damage constitutive models used to simulate rock deformation often overlook its initial compacted stage,which makes it difficult to accurately simulate the whole deformation process.The long-term FTCs also directly affect the surrounding rock of tunnel,resulting in the deterioration of their mechanical properties and deformation behaviors,leading to the obvious frost heaving characteristics of tunnel in cold regions.Hence,it is necessary to develop a frost heave solution of the tunnel in cold regions affected by FTCs.In this paper,a novel mechanical damage constitutive model（MDCM）and brittleness index(BI _new)of rock were established based on the statistical damage theory.We conducted experiments to study the mechanical properties of red sandstones under low temperature,FTCs,DWCs and the rationality of the MDCM for frozen rocks,frozen-thawed rocks and dried-wetted rocks We systematically studied the damage evolution and brittleness indexes of the rocks.Furthermore,we applied the novel MDCM and brittleness index to the Yushuchuan tunnel in Northeast China and proposed the elastoplastic solution of frost heaving force for tunnel in cold regions considering the long-term freeze-thaw damage deterioration,intermediate principal stress effect and non-uniform frost heave of surrounding rock.The main research contents and conclusions are as follows:（1）The exponential function of strain difference was established using the existing triaxial compression deformation curves of rocks.Then,two novel MDCM simulating the whole deformation process of rock were proposed based on the maximum tensile strain theory and Hoek-Brown criterion,and a novel brittleness index BI _new was established on account of the proposed MDCM and energy calculation method.The novel MDCMs can well simulate the deformation test curves of rocks,and BI _new can effectively improve the shortcoming of the existing brittleness indexes.（2）The mechanical properties,strength characteristics and failure characteristics of frozen rocks were analyzed based on the triaxial compression results of red sandstones under low temperature,and its prediction model of rock strength considering temperature characteristics were explored.The MDCM describing the whole deformation process of frozen rocks was established based on the Hoek-Brown criterion and statistical damage theory,and the rationality of that was proved compared with the existing ones.（3）The initial damage of rock caused by FTCs or DWCs was determined by conducting the P-wave velocity and CT scanning tests.The damage and deterioration of rock mechanical properties caused by FTCs and DWCs were analyzed based on the triaxial compression tests of frozen-thawed rocks and dried-wetted rocks.Then,a novel MDCM of rock was proposed considering the continuous damage theory,statistical element strength theory and coupled damage theory,which can well simulate the whole deformation process of rocks with initial damage.（4）Compared with the contrast models I～III,the novel MDCM was well agreement with the experimental curves and can be applicable to all types of rocks.Compared with contrast models I and II,contrast model III can well simulate the pre-peak deformation behavior of rock,and that has a good agreement with the experimental curves in the shorter range of residual deformation stage.（5）With increasing the low temperature,the brittleness index BI_new increases and the rock brittleness was enhanced.With the increase of the number of FTCs or DWCs,the brittleness index BI’_new decreases and rock ductility was improved.Under the condition of multiple factors,the variation trends of D’_m-max and D_f-D_i/ε_r-ε_i were consistent with that of BI _new and BI’_new,and it was applicable that the brittleness characteristics of rocks can be evaluated by the dual indexes of damage evolution and brittleness index.（6）The degradation rate of linear elastic modulus of surrounding rock of the Yushuchuan tunnel reaches 67.413%after 600 FTCs.Based on that,the damage deterioration curve of mechanical parameters of surrounding rock was obtained.Then,the elastoplastic solution of frost heaving force for tunnel surrounding rock in cold regions was proposed considering FTCs,the intermediate principal stress effect,and the non-uniform frost heave of surrounding rock,and that was verified by comparing with the existing solutions.Finally,the variation trend of frost heave force for surrounding rock of the Yushuchuan tunnel was predicted considering the influence of different factors.