Analysis On Mechanical Test And Mesoscopic Model Of Limestone Under Seepage Pressures

With the high-speed development of China economy,a large number of tunnel projects have emerged,and the number of high water pressure tunnels is also increasing.The pressure of permeate water has a deteriorating effect on the mechanical properties of tunnel surrounding rock and also has an adverse effect on its stability.Therefore,it is very important to study the influence law of seepage water pressure on rock mechanical properties to ensure the stability of the project.In this paper,water injection penetration tests under different pressures,uniaxial compression and acoustic emission tests under high water pressure were carried out on limestone,which taken from the entrance area of the Maixi Tunnel in Guiyang City,Guizhou Province.Based on the experimental results,the effects of seepage water pressure on the microstructure and acoustic emission characteristics of limestone were analyzed,and the impact mechanism was revealed.The damage evolution model of limestone considering the effect of osmotic pressure was established.The main research contents of this paper are as follows:(1)Indoor microscopic tests(SEM,X-ray diffraction)and macroscopic tests(saturation test,mass inspection test and acoustic emission characteristic test)of limestone specimens under different penetrating water pressures were conducted.The experimental results show that as the permeation pressure increases,the secondary pores number and mass loss rate of the limestone increase,while the amplitude of the acoustic emission spectrum decreases gradually.Based on Darcy's law and the capillary model,the pore development equation of rock was established.(2)The uniaxial compression and acoustic emission tests under different osmotic pressures were performed on the limestone specimens.The test results show that with the increase of permeate pressure,the uniaxial compressive strength and elastic modulusof the limestone decrease gradually,and the compaction phase of the stress-strain curve becomes more and more obvious.The number of acoustic emission rings and the corresponding stress during the active energy phase increases gradually.The size of rock fragments gradually became uniform.Based on the theory of fracture mechanics,the mechanism of crack initiation considering the effect of osmotic pressure was analyzed.(3)It is assumed that the constitutive relation of limestone in the elastic deformation stage conforms to Hooke's law.On this basis,based on the theory of continuous damage theory and statistical damage theory,the constitutive relation of limestone damage stage is established.Based on the variation law of the parameters of the fitting model with the osmotic pressure,the constitutive model of limestone damage with the influence of osmotic pressure was established.The results show that the theoretical results are consistent with the experimental results.