Study Of The Damage And Creep Properties Of Frozen Soft Rock Of Cretaceous Formation

Along with the implementation of west development strategy in our country and the growth of energy demand, the focus of coal mine construction is also moved to the west. The cretaceous strata of western mine is given priority to sandstone and mudstone which have many engineering characteristics such as argillaceous cementation, low strength, and they belong to soft rock. With shaft sinking by freezing method in the cretaceous strata, the deformation and stability of the frozen wall directly depend on mechanics properties of the soft rock after freezing. Through a large number of Instantaneous and creep experiments, the constitutive model which could describe the mechanics law of frozen soft rock of cretaceous formation is built combined with damage and rheological mechanics. This work is as follows:Many triaxial compression tests are conducted under different temperatures about soft rocks of cretaceous strata, by which the relationship between the instantaneous mechanic parameters and the temperature and confining pressure is acquired. At the same temperature, both the peak intensity and elasticity modulus of soft rock improve with the increasing of the confining pressure. At the same confining pressure,they increase with the decreasing of temperature.In order to correctly describe the stress-strain process of five stages for soft rock, damage recovery variable is established and damage expression of fracture pressure section is obtained presuming initial damage exists in soft rock. Supposing the infinitesimal strength is coincided with the weibull probability distribution,and considering the strength of material damage part as residual strength,an incremental statistical damage constitutive model describing the frozen soft rock is established. In order to conduct numerical simulation for triaxial test,the model is embedded in ABAQUS finite element program and correctness of the model is verified.Many triaxial creep tests under different temperatures are conducted. Through the analysis, the creep deformation curve of frozen soft rock of cretaceous formation has very obvious character of three stages. With the decreasing of the temperature, the total creep value reduces and the long-term strength increases.By introducing Mohr-Coulomb yield criterion, the viscoplastic element of XiYuan-model is improved, and creep damage constitutive model that can describe three stages of creep characteristics is established with the introduction of improved Kachanov creep damage rate.Finite element analysis method of the creep damage model is derived,and the constitutive model is embedded into ABAQUS finite element program.The simulation for the digging of tube of Bojianghaizi mine is conducted,by which the stress and displacement field distribution of frozen wall are abtained under different section high,and the relationship between maximum radial displacement of well sidewall and time is determined. Compared with the measured value, the results of simulation of displacement are coincident which proved the correctness of the creep damage constitutive model of this paper, and it could provide guidance for the design and construction of the frozen wall.