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针对乌东德水电站地下厂房尾水洞薄层大理岩化白云岩进行原位真三轴试验,研究工程岩体卸荷条件下的变形和强度特性。试样为方柱体,长50 cm、宽50 cm、高100 cm,包含20~30条层面,制备时预加压力以减小卸荷松弛。先实施地应力水平下的变形试验,然后模拟洞室开挖时围岩应力调整情况,先加载轴向压力、然后卸载垂直层面方向的围压至试样破坏。试验结果表明:(1)变形具有正交各向异性。垂直层面方向变形模量与平行层面方向变形模量的比值为0.34~0.69。平行层面加载时层面张开,侧胀系数为0.52,反之,垂直层面加载时层面压密,侧胀系数为0.25;(2)塑性变形较大。在一个加卸荷循环中,卸荷残余变形与加载变形的比值为0.4~0.8;(3)加载变形模量与侧压正相关,垂直层面方向的卸荷回弹模量与侧压负相关;(4)卸荷变形具有非线性,卸荷回弹模量与卸荷应力差的相关关系可用负指数式描述;(5)垂直层面方向应力卸荷时,试样破坏型式为沿层面的剪切破坏,体积变形未经历压缩,而是持续、加速扩容;(6)基于沿层面剪切破坏的破坏模式,得到层面Mohr-Coulomb强度参数;视试样为均质岩体,得到岩体Mohr-Coulomb强度参数和Drucker-Prager强度参数。分析各类强度参数的适用性。
In-situ true triaxial tests of the thin marble dolomites in the tailrace tunnel at the Wudongde Hydropower Station are carried out to study the deformation and strength characteristics of the rock mass under unloading conditions. The sample is a square cylinder with a length of 50 cm, a width of 50 cm and a height of 100 cm. It contains 20 to 30 layers and is pre-stressed during preparation to reduce unloading and relaxation. First, the deformation test at the level of the ground stress is carried out. Then, the stress of the surrounding rock during the excavation of the cavern is modeled. The axial pressure is firstly loaded, and then the confining pressure in the vertical direction is unloaded to destroy the specimen. The experimental results show that: (1) the deformation has orthogonal anisotropy. The ratio of the vertical deformation modulus to the horizontal deformation modulus is 0.34 ~ 0.69. When the parallel plane is loaded, the horizontal expansion is 0.52. On the other hand, when the vertical plane is loaded, the horizontal plane is dense with the coefficient of expansion of 0.25; (2) The plastic deformation is large. In a loading-unloading cycle, the ratio of unloading residual deformation to loading deformation is 0.4 ~ 0.8. (3) The loading deformation modulus is positively correlated with the lateral pressure. The unloading elastic modulus in the vertical direction is negatively correlated with the lateral pressure ; (4) The unloading deformation is nonlinear, and the relation between the unloading resilience modulus and the unloading stress difference can be described by the negative exponential formula. (5) When the stress is unloaded vertically, the failure type of the specimen is along the layer (6) The Mohr-Coulomb strength parameters are obtained based on the failure mode of shear failure along the plane; the test sample is homogeneous rock mass, and the rock mass is obtained Mohr-Coulomb intensity parameters and Drucker-Prager intensity parameters. Analysis of the applicability of various types of strength parameters.