Study Of Lithology Influence On Relationship Between The Tectonic Stress And Ground Stress

There are two primary kinds of factors that can influence the relationship between tectonic stress and ground stress: physical and mechanical properties of the rock and tectonic deformation characteristics.By conducting laboratory tests,the influence of physical and mechanical properties of the rock on tectonic stress and ground stress was investigated.Specifically,unconfined compression tests(simulating the tectonic stresses)were performed on rock samples of certain size and various lithologies,water pressures were also applied on the rock samples through a specially designed hydraulic splitting apparatus.The rock samples were failed under different compression loadings,and the corresponding applied water pressures at failure,which were proportional to the induced internal stresses of the rock samples,were measured.By analyzing the relationship between compression loadings and the water pressures at failure for samples of various hardnesses,the influence of physical and mechanical properties of the rock on the tectonic stress and ground stress was studied.At present,the method to conduct hydraulic fracture experiment on rock samples in laboratory is not mature,and no simulation has been found about the hydraulic fracture experiment on small scale rock samples.In order to achieve the objectives of this research,an apparatus was designed to conduct the hydraulic fracture experiment on rock samples.Through the combination use of a hollow bolt and a seal disc,a hole of small diameter inside the sample was sealed and pore-water pressure can be applied in the hole.Water pressure kept increasing until the sample failed,and the applied water pressures during the failure process were monitored.Before conducting the experiment,in order to have a rough idea about the range of water pressures at failure for rock samples of various hardnesses and under different compression loadings,seepage analyses were conducted to simulate the failure processes of rock samples by using RFPA2D-Flow software.Numerical simulation was not only used to provide a basis to the test program,it was also used to partially check the test results.The main conclusions were listed as follows: 1.A set of experiment apparatus was designed to impose pore-water pressures on rock samples and to measure the pore-water pressures during the failure process.2.A test program was designed to investigate the influence of lithology on ground stress and tectonic stress.3.The data which describe the relationship between compression loadings and pore-water pressures for rock samples during the failure process were obtained.Positive correlation was found between pore-water pressures at failure and the hardness of rock,i.e.,the larger the Young’s modulus of the rock,the higher internal stress of the rock will be induced by the tectonic stress.