花岗岩高应力强卸荷作用下力学特性试验研究

Experimental Research On Mechanical Properties of Granites Under High Unloading Condition

在对花岗岩岩样进行常规三轴加载试验的基础上,进行了峰前高应力条件下卸围压并维持q=σ1-σ3不变的花岗岩卸荷破坏试验,研究卸荷条件下花岗岩的变形、破裂特征,强度准则.结果表明:1)常规三轴破坏以轴向变形为主,卸荷破坏以径向变形为主,卸荷破坏特征以向卸荷方向发生径向变形和体积扩容为主,卸荷状态下脆性特征较加载状态下明显.2)在加载试验中,岩石基本上表现为剪切破坏,张性破裂成分很少.卸荷破裂时各种级别的张裂隙发育,剪性破裂面以共轭X或局部剪切破坏为主.3)在初始围压相同情况下,卸荷点越大,岩样从卸围压至破坏的时间越短,说明高卸荷点更容易导致岩石破坏.4)Mogi-Coulomb强度准则适合描述花岗岩高应力强卸荷作用破坏下的岩石强度特征.

Based on conventional tri-axial load test of granite rock samples, the confining pressure under condition of high stress prior to the peak is unloaded and the destructive test of granite with invariable q=σ1-σ3 is maintained to study the granite deformation, breakage characteristics and strength criterion under unloading condition. The results show that：l ）The conventional tri-axial failure is predominantly axial deformation, whereas the unloading failure is predominantly radial deformation. The unloading failure characteristics are predominantly radial deformation and volume expansion in the unloading direction. At the unloading state the brittle characteristics are significantly higher than that at the loading state. 2）In the load test, the rock is essentially manifested as shear failure and there are rarely tensile rupture ingredients. During unloading rupture various levels of separation fracture is developed. The shear rupture plane is predominantly conjugation X or local shear failure. 3 ） With the same initial confining pressure, the greater the unloading point, the shorter the time from confining pressure unloading to damage of rock samples, indicating that high unloading point is more likely to cause damage to the rock. 4） Magi-Coulomb strength criterion is suitable for describing the rock strength characteristics of granite under high unloading action damage.