基于结构信息的粗粒土抗剪强度模型研究

Study on shear strength model of coarse-grained soil based on structural information

结构特性是影响粗粒土抗剪强度发挥的重要因素之一,现阶段对土体结构特性的研究主要集中于细粒土,有关粗粒土组构和其宏观抗剪强度的研究还缺乏深入的探讨,暂时还未建立考虑结构信息的抗剪强度模型。为了研究粗粒土结构对抗剪强度的影响规律,首先以天然无胶结卵石颗粒为研究对象,按照不同粒径含量差异划分了4种结构类型,通过改进常规直剪设备,开展室内可视化直剪试验,验证粗粒土结构类型与强度特性之间的相关性和内在联系;其次,采用Matlab软件对剪切过程图像进行预处理,结合图像识别与分析技术提取不同结构类型土体扁平度、圆度、主定向角、配位数以及孔隙率等信息,并利用主成分分析法获取各个结构信息指标所占权重,从而建立表征粗粒土结构信息的综合量化指标K;最后,利用颗粒流离散元软件开展数值直剪试验,获取不同结构类型粗粒土抗剪强度参数,建立结构信息综合量化指标K与抗剪强度参数c,ψ的关系式,并以此构建嵌入结构信息综合参数的抗剪强度模型。研究结果表明:粗粒土抗剪强度指标与其结构信息综合参数指标存在非线性函数关系;通过将公式计算值、试验实测值分别与Mohr-Coulomb准则计算值进行对比分析,验证了嵌入初始结构信息的抗剪强度模型的可靠性,该模型能够较好地适用于低应力下粗粒土抗剪强度特性的表征。

Structural characteristics is one of the important factors affecting the shear strength of coarse-grained soil.At present,the research on the structural characteristics of soilmainly focuses on fine-grained soil.There is still a lack of in-depth discussion on the fabric and macro-shear strength of coarse-grained soil,and no shear strength model considering structural information has been established.In order to study the influence of coarse-grained soil structure on shear strength,uncemented pebble particles were first taken as the research object and divided into four typical structural types according to the content of different sizes.By improving the conventional direct shear equipment,the indoor visual direct shear test was carried out,and the correlation between the structural type and strength characteristics of coarse-grained soil was verified.Second,the Matlab software was used to preprocess the shear process image,and the Image recognition and analysis technology Image-Pro Plus(IPP)were used to extract the information of flatness,roundness,main orientation angle,coordination number and porosity of different structural types of soil.The principal component analysis method was used to obtain the weight of each structural information index so as to establish a comprehensive quantitative index K that characterizes the structural information of coarse-grained soil.Finally,The particle flow discrete element software(PFC2D)was used to simulate the direct shear test process,and the shear strength parameters of coarse-grained soil with different structural types were obtained.The relations between the comprehensive quantitative index K of structural information and the strength parameters c andψwere then established,and the shear strength model embedded with the comprehensive parameters of structural information was constructed.The results show that there is a nonlinear function relationship between the shear strength index of coarse-grained soil and the comprehensive parameter index of structural information.By analyzing the correlation between the calculated value of the formula and the measured value of the test and the calculated value of the Mohr-Coulomb criterion,it is verified that the shear strength model embedded with the initial structural information can be well applied to the characterization of the strength characteristics of coarse-grained soil under low stress.