开挖卸荷对砂岩力学特性影响试验研究

卸荷作用广泛存在于人类的工程活动和地质作用过程中,岩体在卸荷条件下的力学特性研究一直是工程界探讨的热点问题之一。根据实际边坡工程开挖后应力变化状态确定试验方案,进行了砂岩三轴卸荷破坏试验,研究了卸荷状态下岩体的应力应变特征、破坏特征及力学参数变化规律,并与加载破坏试验数据进行了对比分析。试验结果表明,卸荷破坏时岩样变形模量随着卸荷量的增加可降低5%～42%左右,二者之间的关系可用指数函数拟合;卸荷破坏时岩体的峰值应变随围压线性增长,残余应变与围压无明显关系;相比于加载破坏,卸荷破坏时岩体凝聚力c值降低了4%左右,内摩擦角?增加了12%左右;卸荷速率对岩样强度和变形参数有较大影响;卸荷条件下岩体破坏具有沿卸荷方向强烈扩容特征,主要表现为张剪破坏,并伴随有环向裂纹,初始围压越高,卸荷程度越强烈,岩体的破碎程度越高。

Experimental study of influence of excavation unloading on mechanical properties of sandstone

The phenomenon of unloading occurs widely in human project activities and the geological process. The research of rock mass mechanical properties under unloading conditions has been one of the hot topics of engineering all the time. Based on the results of three-dimensional unloading tests, the stress-strain characteristics, the destructions and the law of mechanical parameters variation of sandstone have been discussed and compared with the law of loading tests. It is shown that: the deformation modulus of rock mass can be reduced by 5%-42% at continued unloading condition; the higher the initial confining pressure, the greater the deformation modulus reduced; the relationship between them could be fitted by the exponential function; the peak strain increased linearly with the confining pressure when the rock mass damaged under unloading condition, and the residual strain had no significant relationship with the confining pressure; compared with loading destructions, cohesion c of rock mass damaged under unloading condition reduced by 4%, and internal friction angle ? increased by 12%; the speed ratio of unloading has great influence on the strength and deformation parameters of sandstone; the damage characteristics of rock samples indicate that strong expansion along the direction of unloading and circumferential cracks are presented in process of unloading; different from compression and shear failure under loading conditions, unloading damage is characterized by strong tensile and shear fracture; the higher the initial confining pressure, the stronger the degree of unloading and the higher the degree of fragmentation.