Experimental investigation on mechanical behaviors of granites after high-temperature exposure

Abstract

To investigate the influence of temperature on the physical, mechanical and acoustic emission characteristics of granites, uniaxial compression test, variable-angle shear test, acoustic emission signal monitoring and the measurement of physical parameters including mass, size and P-wave velocity were carried out on granite samples treated at temperatures T ranging from 25 to 900 ° C. The results show that the density and P-wave velocity decrease gradually with increasing T. As the temperature increases, the peak compressive stress decreases while the peak strain increases, due to the fact that a high temperature induces the escaping of waters within granites, the expanding of mineral grains and the generations of fractures. With the increment of T, both the peak shear stress and the cohesion decrease, whereas the frictional angle increases. During the compressing and shearing tests, the maximum acoustic emission counts show a decreasing trend when T increases from 25 to 900 °C. When T exceeds 573 °C, the crystal lattice structure of quartz changes from α-phase to β-phase, decreasing the mechanical behavior of granites to a great extent. In addition, the results also indicate that T=500–600 °C is the critical temperature ramge to characterize the influence of temperature on the physical, mechanical and acoustic emission characteristics of granites.

摘要

为了研究高温处理对花岗岩物理力学特性及声发射特征的影响, 本文对25~900 & deg; C 范围内高温处理后的花岗岩试样分别开展了单轴压缩和变角剪切试验, 同时监测了试验过程中的声发射信号, 此外, 还测量了高温处理前后花岗岩试样的质量、尺寸和纵波波速. 结果表明; 花岗岩的密度和波速随着温度的升高而逐渐降低; 随着温度的上升, 花岗岩单轴抗压强度减小而峰值应变增大, 这是因为高温致使岩石内部水分逸出、矿物颗粒不均匀膨胀及裂隙萌生、扩展; 当温度升高时, 花岗岩抗剪强度和黏聚力减小, 而内摩擦角增大; 在压缩和剪切试验过程中, 声发射计数最大值随温度的升高而呈现下降趋势. 当温度超过573 & deg; C 时, 花岗岩中石英的晶体结构由& alpha; 相转变为& beta; 相, 花岗岩力学性能急剧降低. 试验表明, 500~600 & deg; C 可视为花岗岩基本物理力学特性及声发射特征发生突变的临界温度区间.