Creep Characteristics Of Argillaceous Red Sandstone Under Different Water Content And Its Influence On Stability Of Tunnel Surrounding Rock

Argillaceous red sandstone,as a kind of soft rock widely distributed in China,has high mud content and obvious creep effect,which is aggravated by water.The creep of soft rock leads to instability and failure of geotechnical and underground engineering during construction.Therefore,it is of great engineering significance to study the creep characteristics of argillaceous red sandstone under different water-bearing states and its influence on the stability of surrounding rock of tunnel,which is closely related to water for the construction safety of soft rock tunnel.Relying on Ganzhou city Rongjiang four road river-crossing tunnel project,in engineering field of argillaceous sandstone as the research object,has carried out dry,natural and saturated state strength and creep test,the creep features,different moisture state argillaceous sandstone and through macro mesoscopic analysis,reveals the different water-bearing states the difference of argillaceous sandstone creep damage mechanism.Then according to the creep test results Burgers was not selected model of argillaceous sandstone creep test result analysis and parameter inversion,will test the physical and mechanical parameters and the inversion of the creep model parameters are used to numerical simulation of land research and analysis of the tunnel excavation supporting within 15 days of the distribution of the stress and deformation,the paper main research work and achievements are as follows:(1)According to the actual working conditions,the rock is taken from the engineering site for processing,and the sample is made.In order to reduce the dispersion of test results,longitudinal wave velocity test was carried out on the samples with small wave velocity difference.The basic physical parameters of argillaceous red sandstone are obtained by testing the physical indexes of argillaceous red sandstone.Then,uniaxial compression and triaxial compression tests are carried out on argillaceous red sandstone in different water-bearing states,and the mechanical parameters,stress deformation and strength characteristics of argillaceous red sandstone under corresponding conditions are obtained after finishing and calculating.At the same time,the differences of strength and deformation characteristics between natural and saturated muddy red sandstone are clarified.(2)Uniaxial creep tests were carried out on argillaceous red sandstone under dry,natural and saturated conditions,and the long-term strength of argillaceous red sandstone under dry,natural and saturated conditions was calculated by steady-state creep method.The results show that the limit deformation of creep failure in saturated state is smaller than that in dry state.The long-term strength of argillaceous red sandstone is greatly affected by water,so the reduction of surrounding rock strength should be considered in the construction stage with water action.(3)Triaxial unloading and confining pressure creep tests are carried out on natural and saturated muddy red sandstone,and the excavation process is simulated by unloading confining pressure to obtain the law of surrounding rock deformation.The results show that the change of confining pressure has a greater effect on transverse strain,and the deformation of arch waist should be paid more attention to during tunnel excavation.(4)The macroscopic analysis of creep failure mode of argillaceous red sandstone under dry and saturated conditions is carried out,and it is found that the compression failure of argillaceous red sandstone belongs to compression shear failure;Microscopic analysis of the damaged section by scanning electron microscope shows that the dry argillaceous red sandstone has a compact structure,while the saturated argillaceous red sandstone has a large number of pores and small particles,and the structure is loose.The difference between the dry and saturated argillaceous red sandstone under compression and its mechanism are summarized.(5)By introducing Burgers model to fit creep curves of argillaceous red sandstone with different water content states,creep parameters of argillaceous red sandstone are obtained by inversion.The average correlation coefficient between test results and fitting results is about0.93,which proves that Burgers can describe the creep of argillaceous red sandstone well.It can also provide creep parameters for later numerical simulation.(6)According to the general situation of the project,the tunnel model of the land segment is established,and FLAC3 D software is used to assign values and calculate the model based on the parameters obtained in the test based on FISH language.The analysis results show that the deformation of surrounding rock in saturated state is much larger than that in natural state.During the 5 days of tunnel excavation and support,there is stress concentration in the arch foot,which should be paid close attention to.The deformation of surrounding rock is close to the measured data,which proves that Burgers model is reasonable and correct to describe the creep of muddy red sandstone.