Experimental Study On Dynamic Mechanical Properties Of Water Content Sandstone Under Confining Pressure

The mechanical properties of underground engineering rock mass in a complex geological environment are greatly influenced by the factors such as ground water,ground stress and external load etc.Aiming at the shortcomings of the previous single experimental factors,experimental study on static and dynamic mechanical properties of sandstone under three coupling factors as water content,strain rate and confining pressure is carried out in this paper.The common red sandstone is taken as the research object,and aqueous sandstone samples are quickly prepared by vacuum extraction method.Uniaxial and triaxial compression tests on aqueous sandstone under low strain rates are carried out on the RMT301 rock and concrete mechanics test system,then dynamic compression tests on aqueous sandstone under high strain rates are carried out on SHPB test equipment with an active confining pressure device.The influence of confining pressure,strain rate and water content on the static and dynamic mechanical properties of rock is studied,and the interaction relationship between three factors is discussed through the tests.Then a sandstone dynamic damage constitutive model considering confining pressure,strain rate and water content is put forward on the basis of existing theory.The research results can be used to provide reference to mechanical properties research of other brittle materials.(1)By analyzing the uniaxial and triaxial compression test results of aqueous sandstone under low and medium strain rates,the performance that three factors influence the static mechanical properties of sandstone are water weakening effect,strain rate strengthening effect and confining pressure hardening effect.There is a certain fitting relationship between water content,strain rate and sandstone strength,the peak strain and elastic modulus under the uniaxial compression.There is an also certain fitting relationship between confining pressure and sandstone mechanical parameters.There is a certain interaction between the three factors.Overall,the increasing of confining pressure will reduce the water weakening effect and the strain rate hardening effect;the increasing of water content will increase the confining pressure hardening effect and reduce rate hardening effect;the increasing of strain rate will reduce the hardening effect of confining pressure and increase the water weakening effect.(2)By analyzing the SHPB test results of aqueous sandstone under high strain rates,the dynamic compressive strength and toughening effect of brittle materials like rocks increase as the confining pressure increases,and appear development trends to ductile characteristic,which reveals a strong confining pressure effect.Under the same range of confining pressure,the change of peak strength and strain of sandstones reveal significant strain rate dependence.The dynamic strength appears approximate linear increase as stain rate increases and the dynamic strength increase factor keeps an approximate linear relationship with the logarithm of strain rate.The dynamic strength of sandstones keeps a good linear relationship with water content.(3)By studying dynamic test results of sandstones and the existing constitutive theories,a sandstone dynamic damage constitutive model considering confining pressure,strain rate and water content is put forward,and the model is fitting well with the test curves.