Experimental Research On Loading Rate Effect Under Triaxial Compression

The mechanical properties of rocks are important to assess and maintain the stability of rock masses engineering.But the mechanical properties of rocks are often changed by the influence of extermal factors so that the stability of rock masses engineering is affected.Loading rate effect which is one of the extermal factors is important to affect the mechanical properties of rocks.Therefore,constant loading rate experiment and alternating loading rate experiment are performed on the Tage tuff and Jingkou standstone under different confining pressure.The confining pressure effect and loading rate effect at peak-loading and in the post-failure region are researched.The study results can provide theoretical basis to assess and maintain the stabilbity of hypogee.The main conclusions obtained are as follows:(1)The peak strength,strain at the peak point and elastic modulus of three kinds of rocks increase with the growth of the loading rates and show great loading rate effect.The peak strength and strain at the peak point increase with the growth of the confining pressure and show great confining pressure effect.(2)Failure mode of Tage tuff is singal ramp shear failure under low loading rate and transform to X-shaped conjugate ramp shear failure with the growth of the loading rates under uniaxial compression.But the failure mode of Tage tuff is plastic flow under triaxial compression.The failure mode of Jingkou standstone like Tage tuff under uniaxial compression.But its failure mode is singal ramp shear failure under triaxial compression.The relationship between fracturing shape and failure mode of Ogino tuff and loading rate is not obvious because the discreteness is large.But its failure mode transform to plastic flow with the growth of confining pressure.(3)Four kinds of loading rate effect coefficients n_a,n_b,n_c and n_d in the post-failure region all can be used to quantify the loading rate effect in the post-failure region of rocks.And n_d which is one of loading rate effect coefficients in the post-failure region is the most applicable to quantifying the loading rate effect in the post-failure region of rocks.(4)Under low confining pressure,loading rate effect of three kingds of rocks at peak-loading is more obvious than loading effect in the post-failure region.Then the loading rate effect of Tage tuff and Ogino tuff at peak-loading is similar to the loading rate effect in the post-failure region,but the relationship between loading rate effect in the post-failure and at peak-loading of Jingkou standstone under high confining pressure likes the relationship under low confining pressure.(5)The loading rate effect at peak-loading of three kinds rocks become more unobvious with the growth of confining pressure.And the relationship between confining pressure and the loading rate effect in the post-failure region of Jingkou standstone like the above-said pattern.But the relationship between confining pressure and the loading rate effect in the post-failure of Tage tuff and Ogino tuff is opposite to the relationship of Jingkou sandstone.