EXPERIMENTAL STUDY OF STRENGTH CHARACTERS OF SATURATED RED SANDSTONE ON NEGATIVE TEMPERATURE UNDER TRIAXIAL COMPRESSION

Saturated red sandstones,as the research subjects from 500–600 meters deep of Meilinmiao mine in Ordos,in China,were tested respectively by triaxial compression in the condition of different temperatures(10 ℃,-5 ℃,-10 ℃,-15 ℃) and different confining pressures(0,4,8,12 MPa). Results show that:(1) When temperature range from 10 ℃–-15 ℃,the triaxial compressive strength of saturated red sandstones increase with the temperature dropping down,and present exponent relation. Elastic modulus increase and present linear relation;Friction angles increase while cohesive strengths c decrease,as temperature reduce.(2) When confining pressures change between 0–12 MPa,triaxial compressive strengths of saturated red sandstones increase with the confining pressures increasing,show the linear relation and still follow Mohr yield criterion. Elastic modulus,peak axial strain and peak radial strain increase with the increment of confining pressures.(3) Under the experimental conditions,the Poisson ratio are less affected by the confining pressure,but significantly affected by temperature,more attentions should be paid to the impact of temperature on Poisson ratio;The elastic modulus E is affected greatly by temperature and significantly by confining pressure. The temperature is the main factor affecting the elastic modulus and the confining pressure is the secondary consideration. Compared with Poisson ratio,the value of the elastic modulus is easily affected by external environment.(4) The failure modes of saturated red sandstone specimen are affected by temperature and confining pressure significantly. However,these are two different failure mechanism. Temperature decreases result in rock particles gravity reduction,and pore ice increases the pore friction area,then increases the friction;With the confining pressure increasing,it is due to the formation of micro-cracks inside the rock,that cohesive strength declines,at the same time,increases vertical component force,coming from rising confining pressure,on the fracture surface,thereby,increases the friction.