泥岩试件改性前后拉破坏实验研究

Experimental research on tensile failure of mudstone samples before and after modification

为了研究泥岩在拉应力作用下的变形破坏过程,采用巴西劈裂实验和白光数字散斑相关方法,对泥岩在拉应力作用下的破坏过程进行观测,利用水泥对泥岩进行改性,研究了改性泥岩拉破坏过程的变化规律,并从微观角度分析了改性前后泥岩的拉破坏过程。结果表明:(1)改性后的泥岩试件,经过24 h养护,抗拉强度随水泥含量的增加以线性趋势增加。(2)改性前,拉应力较小时,泥岩内部形成局部变形区;随着拉应力的逐渐增加,局部变形区的面积逐渐增加,相邻的局部变形区相互合并,形成更大的局部变形区;载荷为峰值载荷的58.2%时,局部变形区演化成应变局部化带;最终应变局部化带发展成宏观裂纹,试件发生破坏。(3)水泥改性泥岩时,泥岩中聚集体间孔隙大部分被填充,抗拉强度提高。(4)水泥改性泥岩后,随着水泥含量的增加,局部变形区演化成应变局部化带的位置逐渐向峰值载荷移动。(5)水泥提高了泥岩的胶结程度,拉应力超过抗拉强度时,弹性能短时间内释放出来,使宏观裂纹迅速扩展。

The tensile failure procedures of remoulded mudstone samples are experimentally studied using a designed deformation field inspection system. The samples are pulled to failure with the speed of 0.06 mm/min in the process of Brazilian split load. The mudstone is modified by Portland cement in order to enhance its tensile strength and the failure procedure of modified sample under tensile stress is researched. The fracture mechanism of mudstone before and after modification under tensile stress is investigated. The results show: (1) the tensile strength increases linearly with the Portland concrete content of modified samples after curing for 24 h at room temperature; (2) the deformation field localizes on the surface of unmodified samples at the early stage of loading, when the load is 58.2% of peak load, localization band occurs by means of merging deformation regions, and it forms macro crack that fails the sample; (3) the quantity and size of pores between aggregates decrease after modification with Portland cement, and the tensile strength of mudstone increases obviously because of the cementation of silicate; (4) with the increase of Portland concrete content, the position in which localization band occurs by means of merging deformation regions moves towards the load peak; (5) because of more elastic strain energy stored in modified samples, the macro crack extends rapidly when the load exceeds the peak load. © 2015, China Coal Society. All right reserved.