损伤破裂砂岩单轴蠕变特性试验研究

Uniaxial experimental study of creep properties of sandstone in damage and fracture states

深部岩体工程处于高应力环境中,开挖破裂后的工程岩体在持续的高地应力作用下具有很强的时间效应,深入研究其峰后蠕变特性,具有重要的理论和实际应用价值。先采用RMT-150B型岩石力学试验系统对完整岩样进行单轴峰前屈服、峰后破裂卸载试验,制备出具有不同破裂损伤程度的峰前屈服、峰后破裂的损伤岩样;再采用RLW-2000型微机伺服岩石三轴流变仪对其进行单轴蠕变试验,研究其单轴蠕变力学特性。研究结果表明:损伤岩样波速与完整岩样相比,均出现了不同程度的降低;损伤岩样各级应力水平下,瞬时应变量均是随着应力水平的增加而逐步增加,且均符合线性函数关系;相同应力水平下,峰后破裂损伤岩样瞬时应变明显大于峰前屈服损伤岩样;各级应力水平下,总体上各蠕变量随着应力水平的增加而逐步提高,且均符合指数函数关系;相同应力水平下,峰后破裂损伤岩样蠕变量明显大于峰前屈服损伤岩样,且随着荷载水平的进一步提高,两者差异程度增加;损伤岩样各瞬时变形模量随着应力水平的增加均逐步提高,两者之间符合线性函数关系;各应力水平下对应的瞬时变形模量存在明显差异,岩样损伤程度越高,瞬时变形模量越低;各损伤岩样在各级应力水平下,改进的西原模型能够较好地模拟其单轴蠕变特征。

Since engineering rock mass is under high stress conditions, it has strong time-dependent effect due to continuously high ground stress after excavation and rupture. The study of creep properties after its post-peak is significant in both theory and practice. Firstly, the uniaxial pre-peak yield and post-peak rupture unloading tests are conducted on the intact rock samples using RMT-150B rock mechanics test system. Then the rock samples with different damage degrees are prepared under conditions of pre-peak yield and post-peak rupture. Lastly, uniaxial creep tests on the prepared rock samples are conducted to obtain uniaxial creep mechanical properties by using RLW-2000 microcomputer servo rock triaxial rheology testing system. From experimental results, velocities of all damaged rock samples show different degrees of reduction by comparing with the velocities of intact rock samples. Under each stress level, instantaneous dependent variable of the damaged rock samples gradually increases with the increase of the stress level, and there is linear relationship between the instantaneous dependent variable and stress level. It is found that the instantaneous dependent variable of post-peak damaged and rupture rock sample is significantly greater than that of pre-peak yield and damaged rock sample under the same stress level. Generally, each creep deformation gradually increases with the increase of the stress level under all stress levels, which meets exponential function relationship. The creep deformation of post-peak damaged and rupture rock sample is substantially greater than the pre-peak yield and damaged rock sample under the same stress level, Moreover, the difference of the creep deformation between post-peak damaged rock sample and pre-peak yield and damaged rock sample increases with increasing the load. The instantaneous deformation modulus of damaged rock sample steadily improved with the increase of stress level, furthermore, the instantaneous modulus changes linearly with the stress level. The instantaneous modulus of deformation at each stress level is obviously different, the higher the degree of rock damage, the lower the instantaneous modulus of deformation. For the damaged rock samples under all levels, the improved Nishihara model can be used to simulate uniaxial creep characteristics.