风化岩遇水软化的强度试验及力学特性研究

Strength test and mechanical characteristics of weathered rock softened by water

对深中通道沉管隧道段风化岩在天然和泡水两种状态下进行常规三轴不排水剪切试验,揭示了在不同条件下风化岩遇水后的强度变化规律。风化岩遇水后强度会有显著降低,表现出明显的遇水软化特性;在其他条件一定时,采用偏应力固结的试样剪切强度较等向固结时降低更为明显;随着围压、偏应力的增大,风化岩的应变软化现象逐渐减弱,峰值强度与残余强度逐渐趋同;将岩体在峰值强度前的弹性模量看作恒量,以内摩擦角和黏聚力达到残余值时的塑性内变量为变量,给出了黏聚力和内摩擦角与塑性内变量的拟合函数关系表达式,改进了考虑风化岩遇水后应变软化的本构模型;通过回归验证,模型的理论计算和试验结果具有一致性,说明该模型可描述风化岩遇水软化的变形特性。根据此模型得到了风化岩的软化模量,并提出了软化系数作为风化岩遇水后强度和刚度折减的参考,可为深中通道等类似工程设计与施工提供理论依据。

The conventional triaxial compression test was carried out on the weathered rock in immersed tunnel section of the Shenzhen-Zhongshan Bridge in natural and water-soaked states to reveal the strength change law of the weathered rock after encountering water under different conditions.The strength of weathered rock will decrease significantly when it encounters water,showing obvious softening behavior.When other conditions are certain,the shear strength of the specimen with deviator stress consolidation is significantly lower than that with isotropic consolidation.With the increases of confining pressure and deviator stress,the strain softening phenomenon of weathered rock gradually weakens,and the peak strength and residual strength gradually converge.The elastic modulus of the rock mass before the peak strength is regarded as a constant,and the plastic internal variable when the internal friction angle and cohesive force reach the residual values is used as the variable.The fitting of the cohesive force and internal friction angle to the plastic internal variable is given.The functional relationship expression improves the constitutive model considering the strain softening of weathered rock after encountering water;through regression verification,the theoretical calculation and test results of the model are consistent,indicating that the model can describe the deformation characteristics of weathered rock softened by water.Based on this model,the softening modulus of the weathered rock is obtained,and the softening coefficient is proposed as a reference for the strength and stiffness reduction of the weathered rock when it encounters water,which can provide a theoretical basis for the design and construction of similar projects such as Shenzhen-Zhongshan bridge.