基于多级破坏方法确定岩石卸荷强度参数 的试验研究

 根据卸荷路径确定岩石卸荷强度参数时，为避免岩样本身离散性过大对强度的影响，采用了卸荷多级破坏试验方法。将卸荷应力路径与多级破坏方法有机结合，用单个岩样获取多个强度值，然后通过回归确定岩石卸荷强度参数。基于MTS 815.02岩石三轴试验机，研究荷载控制方式下多级破坏试验中峰值判断、破坏状态变形控制等几个问题，并提出相应的解决方案。最后成功开展了大理岩卸荷多级破坏试验，取得了与常规卸荷破坏试验较一致的结果。研究成果表明，卸荷应力路径中引入多级破坏的方法，既考虑了应力路径对强度的影响，又有效避免岩样离散性过大对强度的影响，是一种实用、有效的确定岩石卸荷强度参数方法。

EXPERIMENTAL STUDY OF ROCK UNLOADING STRENGTH PARAMETERS BASED ON MULTIPLE FAILURE METHOD

In analyzing excavation engineering，it is of great importance to determine rock strength parameters by unloading stress path. However，strength values determined by conventional unloading tests are often with great divergence. Obviously，among all the factors，divergence of rock specimens is important. To determine unloading strength parameters of rock by a single specimen，multiple failure state method is introduced into unloading stress path；and a special loading procedure based on unloading multiple failure method is put forward for triaxial tests. In conventional multiple failure state tests，it is believed that strain control is the only feasible way to carry out loading control. However，for some confining unloading tests，of which stress-controlled loading approaches are necessary，it is difficult to realize multiple failures by a stress-controlled loading approach. In stress-controlled tests performed by a MTS 815.02 triaxial testing machine for rock mechanics，several critical difficulties such as judging the peak strengths during the tests and controlling the axial deformation during each failure state are investigated；and solutions of these difficulties are proposed. Several multiple failure tests on marble specimens under confining unloading procedures are successfully conducted in the end. It is observed that strength values obtained from this approach matched well with those from conventional unloading tests. It is shown that the proposed approach is feasible and reliable，which not only considers the stress path，but also avoids the divergence of the specimens. It is a practicable and effective method for rock unloading strength parameters determination.