Study On Fracture Toughness Characteristics Of Red Sandstone Under Water Environment

In practical engineering,water rock interaction is very common in nature.Water is one of the main factors causing various geological disasters.The fracture toughness of rock is greatly affected by water.A large number of studies have shown that the compressive strength,tensile strength and other mechanical parameters of rock are affected by water,but only a few of them focus on the study of rock fracture toughness under water conditions,and these studies mainly focus on the test of fracture toughness under dry or saturated conditions.Generally,the rock sample is immersed in water first,then its surface is sealed,and finally the load is measured in air Try.However,in many practical rock engineering,such as rock slope of hydropower station or pillar and mining chamber of deep mining engineering,rock saturation will change according to the development and use stage of power station or mine.Rock is not loaded in air,but in water.Therefore,in order to better understand the stability of the engineering structure and the fracture toughness of the rock under different saturation and different conditions(dry or water environment),the following experimental studies are carried out on the SCB red sandstone with the help of RMT-150 C digital controlled electro-hydraulic servo testing machine and self-developed testing device:(1)In order to understand the basic properties of red sandstone used in this paper,firstly,the water absorption test of red sandstone is carried out.According to the soaking time water content curve of red sandstone,the rock samples with soaking time of 0h,1H,6h and 24 h and other special time nodes are selected as the research objects.The basic mechanical properties of red sandstone,such as compressive strength,modulus of elasticity and Poisson's ratio,are obtained by uniaxial compression test;(2)In order to study the effect of water on fracture toughness,three-point bending tests were carried out on red sandstone with different fracture obliquity under different water content.The dry rock samples were soaked in distilled water for different time to represent different water content.Then,the samples were taken out and sealed with wax.The fracture toughness was tested under air condition.Some empirical relations between the fracture toughness and water content / soaking time were obtained.(3)In order to understand the fracture toughness of rock under the coupling action of load and water,three-point bending tests of red sandstone with different fracture obliquity were carried out.When the dried rock sample is immersed in water while the top load is applied,itwill continue to be loaded until it is damaged after a certain period of creep deformation under constant load,and the test results will be compared and analyzed.(4)Three point bending tests of red sandstone with different load levels are carried out.In this paper,the strength of red sandstone is 50%,60% and 75% after soaking for 1 hour.(5)In order to understand the influence of fracture length on fracture toughness,three-point bending tests of red sandstone with different fracture length were carried out.Three point bending tests were carried out on rock samples with crack length diameter ratio a / R of 0.2and 0.4 under the action of water and load and loading after immersion respectively.