高温层理砂岩劈裂力学特性及裂隙演化研究

Experimental studies on split mechanical properties and fracture evolution behavior of bedding sandstone after high-temperature treatment

对25~1 000℃处理后含垂直和水平层理砂岩开展巴西劈裂试验,采用数字图像相关技术(digital imagine correlation,DIC)记录劈裂过程高温层理砂岩水平应变场演化规律,同时通过电镜扫描(scanning electron microscopy,SEM)研究不同温度下砂岩微观结构损伤。研究结果表明:层理砂岩劈裂破坏前应变集中可以分为两种类型:圆盘两端应变集中型(≤400℃)和圆盘中央应变集中型(>400℃)。随着温度升高,垂直和水平层理砂岩的抗拉强度均呈现出先增大后减小的趋势,200℃时达到最大值;600~1 000℃时,层理对砂岩抗拉强度的影响随温度升高逐渐降低,800~1 000℃存在使得温度成为影响抗拉强度主要因素的阈值温度。微观结构损伤分析表明,热处理温度较低时,基质主要表现为裂纹增多、长度延展,但晶体仍相对完整;层理面表现为孔隙数量增多和尺度增大;温度对层理破坏更大。温度较高时,基质和层理破坏程度相近,这也是热处理后,砂岩应变演化和强度变化的主因。

The Brazilian test was conducted on sandstones containing vertical and horizontal laminations after 25 ℃ to 1 000 ℃treatment. Digital imaging correlation(DIC) was used to record the evolution of the horizontal strain field of high-temperature bedding sandstone during the splitting process. Meanwhile, microscopic structural damage characteristics of samples after different temperatures treatment were investigated using scanning electron microscopy(SEM). The results show that:(1) The strain concentration of the bedding sandstone before splitting can be divided into two types: the strain concentration at both ends of the disk(≤400 ℃) and the strain concentration at the center of the disk(>400 ℃).(2) With the increase of temperature, the tensile strength of vertical and horizontal bedding sandstone first increases and then decreases and reaches the maximum at 200 ℃. With the increase of temperature at 600~1 000 ℃, the effect of bedding on the tensile strength gradually decreases. Temperature becomes the main factor affecting the tensile strength after a threshold temperature of 800~1 000 ℃.(3) The microstructure damage analysis shows that the sandstone matrix is mainly characterized by increased cracks and extended length after the lower temperature treatment, while the crystal is still intact. Also, after this treatment, both the number and size of pores in the bedding plane increase and more damage in bedding occurs. However, when the temperature is higher, the damage of matrix and bedding is very similar, which is the main reason for the variations in strain and strength of the sample after heat treatment.