不同含水率红砂岩静动态劈拉试验及细观分析

Static-dynamic Split Tensile Tests and Micro Analysis on Red-sandstone with Different Moisture Contents

研究水-岩耦合作用下岩石力学特性及细观结构,对减少由地下水造成的深部岩体工程病害具有重要意义。采用直径为100 mm的分离式霍普金森压杆(SHPB)装置与电液伺服压力试验机,进行不同含水率下砂岩试件的动静态劈裂抗拉试验,而后对试件破坏断口进行电镜扫描观察,分析断口形貌特征,依靠SEM图像数字处理技术,进一步得出红砂岩拉伸破坏规律。试验结果表明:红砂岩的劈拉强度随含水率的增加而降低,有明显的遇水软化现象;相比于静态抗拉强度,动态抗拉强度大幅提升,且有显著的应变率强化效应;随着含水率的提高,砂岩试件拉伸破坏时,碎块数量逐渐增多,尺度逐渐减小;饱水岩样的动态劈裂拉伸破坏相比于干燥岩样表现出一定的塑性特征。对断口微裂隙的面积等信息进行定量化处理,分析动态劈拉破坏中的水-应变率效应,得出水在不同应变率下砂岩试样的动态劈拉破坏裂纹扩展中具有均衡作用;微裂隙数量与面积随应变率的提高有增加趋势,破坏断口细观形貌特征存在应变率相关性。

It is significant to study rock mechanical properties and mesostructure under water-rock interaction for reducing deep rock mass engineering diseases caused by groundwater. Using the hydraulic and servo-controlled pressure testing machine and the split Hopkinson pressure bar（ SHPB） with a diameter of 100 mm,splitting tensile tests of sandstone with different moisture contents were carried out to study the static and dynamic mechanical properties of sandstone. Then the mesostructure of fracture was analyzed by pictures obtained by scanning electron microscope（ SEM）,and dynamic tensile failure rules of red sandstone was acquired by digital image processing technique. Results indicate that,the tensile strength of red sandstone decreases with the increase of moisture content,and its water softening phenomenon is obvious. The dynamic tensile strength of red sandstone is substantially higher than the static tensile strength,and the strain rate effect is obvious. Meanwhile,increase of water content results in the increase of fragments and the decrease of size. Compared with the dry sample,the dynamic splitting tensile failure of sample which is full of water is featured by plastic in some extent. Based on the quantitatively processing of microcracks,water-strain rate effect was analyzed in dynamic splitting tensile damage,conclusion that water in different strain rates has a balance function in the crack growth of sand sample which is in the condition of dynamic splitting tensile damage was drawn. The mesostructure appearance of fracture such as area and number of microcracks exhibits strain rate hardening effect.