全风化凝灰岩抗剪强度特性综合试验研究

Comprehensive Experimental Study on the Shear Strength Characteristics of Completely Weathered Tuff

北坑水库坝址区分布全风化凝灰岩,其作为大坝基础的可行性是项目投资与工程安全的重要影响因素。针对全风化凝灰岩开展了原位大型直剪、室内直剪和三轴压缩试验,以研究其抗剪强度特性,为坝基稳定分析提供抗剪强度参数取值的依据。对比分析不同试验方法、不同含水状态的试验值,揭示出全风化凝灰岩剪切变形、强度特征如下:(1)随剪应力增加,剪切刚度降低、剪应变加速增长;法向变形随剪应力增加而增长,呈剪缩特征。(2)内摩擦角随含水率增加而降低。(3)原位直剪实际为不固结不排水剪,其内摩擦角试验值低于室内固结快剪。(4)受原岩结构影响,原位直剪的黏聚力显著大于室内直剪和三轴剪。

The completely weathered tuff is encountered in the dam site area of Beikeng Reservoir,and its feasibility as a dam foundation is an important factor that affecting the project investment and the engineering safety.In-situ large-scale direct shear tests,laboratory direct shear tests and triaxial compression test are performed on the completely weathered tuff to study the shear strength characteristics and provide the basis of shear strength parameters for the dam foundation stability analysis.By comparing and analyzing the test results of different test methods and different water contents,the following shear deformation and strength characteristics of the completely weathered tuff are observed:1)With the increase of the shear stress,the shear stiffness decreases and the shear strain increases rapidly.The normal deformation increases with the increase of shear stress,indicating the shear shrinkage characteristics.2)The internal friction angle decreases with the increase of the water content.3)The in-situ direct shear is essentially unconsolidated undrained shear,and the test results of the internal friction angle is lower than that of the laboratory consolidated quick shear.4)Affected by the original rock structure,the cohesion of the in-situ direct shear is significantly greater than that of the laboratory direct shear and the triaxial shear tests.