Study On The Mechanical Properties Of Single Non-through Centric Jointed Sandstone Under The Conditions Of Dry And Wet Cycle

Because of long-term geological activities and human engineering activities,there are often many discontinuous structural planes within the natural rock mass,and there are many different forms and different numbers of joint fractures.It is obvious that the presence of joints will affect the mechanical properties of rock masses.In particular,the reservoir bank slope is located in the rock mass of the falling belt.Not only is there a joint structure,but it is also affected by the reservoir water's repeated circulation of the wet and dry rock mass.At the same time,the rock mass also bears the confining pressure of the surrounding rock mass.Under the multiple influences of different form joints,wet and dry cycles,and confining pressure,it is bound to have a great impact on the mechanical properties of the rock mass and produce a significant deterioration of the rock.Therefore,it is necessary to study the mechanical properties of jointed rock under the action of dry-wet cycle.At present,most researches on jointed rocks are focused on the characteristics of joints themselves,and the joints in most joint researches are relatively fixed.The rock bridges are generally located inside the rock masses.This paper takes into account the wideness and diversity of joints and their production.In the non-through-joint center joint rock sample,the joint surface passes through the center of the rock sample,and the rock bridge is located at both ends of the joint surface.This article chooses the sandstone of Xizhen Town in Shagui Town,Zigui County as the research object.The mechanical properties of the sandstone are studied through laboratory tests.The main research contents are as follows:1)According to the test content,make uniform requirements for the connectivity of rock samples(k=0.25)without considering the influence of joint connectivity on the test.According to the connectivity requirements,cut and make non-through joints and joint rock samples.Before and after making the joints,the wave speed variation test was performed.2)Experiments on the physical properties of sandstones and SEM electron microscopy scans of rock specimens after wet and dry cycles have found that wet and dry cycles have a significant effect on the wave speed,water absorption,and mass loss rate of sandstones.In the early stages of the wet and dry cycle,The physical indexes of the rock samples decreased more obviously,but with the increase of the number of dry and wet cycles,the physical characteristics of rock samples gradually stabilized.The scanning electron microscopy(SEM)scanning shows that with the gradual accumulation of the number of cycles,the accumulated damage effect of water on the pores within the rock is also gradually obvious.The pores of the microscopic fractures on the surface of the rock sample develop progressively and gradually grow into macroscopic fracture pores.3)Complete triaxial compression tests of intact sandstones after different cycles of drywet cycles.The Mohr-Coulum criterion and Brown-Hoek criterion were used to fit the peak intensities,and the deformation parameters and failure characteristics of the rock samples were analyzed.Conduct the analysis.It is found that the Mohr-Coulum criterion is more accurate in fitting the rock sample strength and provides an analysis basis for the triaxial damage test after the joint-dry-wet cycle of jointed rock samples.4)Completion of the triaxial compression test with a single non-interpenetrated central jointed sandstone subjected to various cycles of dry-wet cycles,and studies the influence of loading confining pressure,joint dip,and wet-dry cycles on the mechanical properties of jointed rock samples.It was found that the dry-wet cycle effect significantly degrades the non-penetrating joint rock samples,and the mechanical parameters generally decrease.The influence of confining pressure and joint dip angle on the mechanical properties of the core joint rock samples is similar to that of ordinary joint rock sample tests.5)Based on the results of sandstone wet-and-dry cycle tests mentioned above,the damage constitutive relations of rocks are described by means of continuous damage mechanics and statistical theory.Among them,the wet-dry cycle damage can be directly coupled to the statistical damage constitutive model.The damage evolution equation is established through the Weibull distribution of the rock micro-intensity,and the damage constitutive equation of the sandstone under the wet-dry cycle is deduced.According to the constitutive equation,the fitting data of the previous experiment was introduced into the constitutive equation to derive the empirical formula of the constitutive equation for the noncontinuous central joint under the effect of the wetting and drying cycle.