堆积软岩的强度及蠕变特性的三轴及平面应 变试验研究

 堆积软岩的力学特性是依存于应力条件的，但由于高强度岩土材料的试验难度较高，软岩的平面应变或真三轴试验比较少。采用新研制的仪器对堆积软岩进行三轴及平面应变剪切及蠕变试验。首先介绍新研制的平面应变试验仪，该试验仪可以实现初始等向固结，还可以测定试样剪切带内部或附近的孔压变化；然后介绍试验流程，包括试样的制作和饱和过程；最后对不同应力条件下软岩的应力–应变关系、应力比–剪涨比关系、蠕变破坏特性等试验数据进行详细分析。研究结果表明：平面应变状态下软岩的强度增加而剪涨量减少；相比于传统的八面体应力空间，建立在tij应力空间中的塑性势更适合软岩；无论三轴还是平面应变条件下，只有当荷载水平达到某一阈值之后软岩才会发生蠕变破坏；蠕变破坏所需时间与荷载相关。

EXPERIMENTAL RESEARCH ON STRENGTH AND CREEP BEHAVIOR OF SEDIMENTARY SOFT ROCK UNDER TRIAXIAL AND PLANE STRAIN CONDITIONS

It is recognized that the intermediate principal stress plays an important role in strength and stress- dilatancy relation of soft sedimentary rock. However，few plane strain/true triaxial experiments on soft rock have been referenced in literature due to the relatively high strength of geomaterials. By using new apparatuses，triaxial and plane strain tests of sedimentary soft rock have been conducted. An innovative plane strain test system is introduced firstly，which can obtain real isotropic consolidation before shear and measurement of inner pore water pressure within/near shear band. Then，testing procedures including issues related to specimen preparation，are introduced. Finally，the strength characteristics，stress-dilatancy relation and creep behavior are analyzed. The following conclusions have been drawn. The strength of the soft rock increases under plane strain conditions，while the dilatancy decreases. The plastic potential function based on concept of tij is suitable for soft rock. Creep failure occurs only when the creep load reaches a threshold value；and the failure time is related to magnitude of creep load.