Frozen strength test on deep water-rich sandstone in Ordos

The rock mechanism under frozen condition has played down the significance on the design of frozen wall thickness and section height of the ultra-deep shaft in Western of China.This paper investigated the particle size and voids distribution principles using magnified image technique,which is on the typical medium size sandstone within the deep water-rich stratum during a coal mining construction with artificial freezing skill in Ordos of China.The frozen medium size sandstone have been studied with triaxial compression test under the temperature of -5℃,-10℃,-15℃,and Brazilian Split test at 26℃,-10℃ and -20℃.The test results indicated that the compressive strength improved linearly up to maximum of 27.29% when temperature dropped down,and this effect was weakened with the increase of the confining pressure.So did the internal frictional angle and cohesion,which ended up with the biggest rise of 12.54% and 18.69%.The tensile strength jumped from 0.73 MPa at 26℃ up to 1.59 MPa at -10℃,as of 118.18% extra,followed with declining when the temperature reduced more.The strength property of medium sandstones have been further improved with only certain extent during lowering the temperature,therefore the design criteria of frozen wall thickness should rather be governed by the purpose of sealing water than over cooling control.