等增量循环荷载下砂岩的变形特征试验研究

Experimental study on the deformation behaviors of sandstone under equal increment cyclic loading

根据南京秦淮东河新开挖河道高边坡的受力情况,对该工程穿越地段的黄马青组(T_(2h))砂岩进行了应力水平不断提高的等增量单轴反复加载、卸载试验,并对其变形及破坏特性进行了研究。试验结果表明,岩块中不含明显结构面时,岩石可能发生拉裂和剪裂破坏。随着循环次数的增加,卸载后岩石中塑性变形逐渐增大,滞回环包络线在轴向应力较低时呈上凹型曲线。根据塑性变形速率随应力增大后的变化情况,可将岩石变形分为初始变形(空隙压密)、等速变形(微破裂稳定发展)、加速变形(裂隙贯通)后整体破坏三个阶段。岩石的变形模量随循环次数的增大先增大后减小,而阻尼比的变化规律与变形模量相反,但变形模量变化规律的转变较阻尼比滞后。岩块中包含明显的结构面时,变形模量随着循环次数的增大而不断降低,阻尼比的变化规律则较复杂,且循环加载导致岩石强度下降幅度显著,不含明显结构面的岩石强度受循环加载影响降幅较小。

According to the stress condition of the excavated high slope,the mechanical behavior of the rocks under cyclic loading should be studied.The uniaxial compression tests under equal increment loading conditions are carried out for the sandstone of the Huangmaqing Group (T2h)from the Qinhuai East River in Nanjing.The testing results indicate that the failure modes of the rock block have two types of the tensile and the shear.When the cycle number increases,the plastic deformation increases after unloading.The upward concave characteristics are presented for the enveloping lines of hysteresis loops. By the plastic strain rate,the compressive deformation of the rock block could be divided into three stages of the initial deformation (cracks closure),the stable deformation (development of micro fractures)and the accelerated deformation (fracture connection).The deformation modulus of the rock increases firstly and then decreases with the increase of cycle number,but the change laws of the damping ratio is opposite to the deformation modulus,and the law change of deformation modulus is slower than damping ratio. When the rock blocks contain obvious structural planes,the deformation modulus decreases with the increase of cycle times,but the change of damping ratio is more complex and the cyclic loading leads to a significant decrease in rock strength.