珊瑚砂与土工格栅界面的剪切特性及本构模型

Shear Characteristics and Constitutive Model of Interface Between Coral Sand and Geogrid

摘要:

采用南海原位级配珊瑚砂和聚丙烯双向土工格栅，开展了不同法向应力下珊瑚砂和筋土界面大型直剪试验。试验结果表明，珊瑚砂和筋土界面剪应力—剪切位移曲线呈现明显的应变软化特征，峰值抗剪强度线呈现双折线形态，残余抗剪强度线则呈现较好的线性关系；各级法向应力下珊瑚砂与土工格栅界面摩擦比均值达到1.37左右，远高于石英砂与土工格栅界面摩擦比，说明在珊瑚砂中加筋能充分发挥加筋效果；珊瑚砂和筋土界面在剪切过程中总体上经历了相对剪缩—相对剪胀—相对剪缩的过程，对珊瑚砂加筋可显著减小其剪缩变形；珊瑚砂和筋土界面直剪试验试样的相对破碎率接近，均随法向应力的增大而增大，但增幅逐渐趋缓。采用邓肯—张模型和剪切软化模型分别描述南海原位级配珊瑚砂与聚丙烯双向土工格栅界面峰前和峰后剪应力—剪切位移曲线，所建立的筋土界面本构模型能够很好地反映其剪切特性。

Abstract:

Large direct shear tests were conducted on the in-situ graded coral sand in the South China Sea and the interface between the coral sand and polypropylene biaxial geogrid under different normal stresses. The test results show that the shear stress-shear displacement curves of coral sand and reinforcement-soil interface show obvious strain softening characteristics. The peak shear strength lines of both show a bilinear form， and the residual shear strength lines of both show a good linear relationship. The average interface friction ratio between coral sand and geogrid at all levels of normal stress is about 1.37， which is much higher than that between siliceous sand and geogrid， indicating that the reinforcement effect can be mobilized in the reinforced coral sand. During the shearing process of coral sand and reinforcement-soil interface， the samples generally experienced a “relative shear shrinkage-relative shear dilatancy-relative shear shrinkage”， and reinforced coral sand can significantly reduce the shear shrinkage deformation. The relative breakage rates of the samples in the direct shear test and the reinforcement-soil interface direct shear test are close and increase with the increase of the normal stress. The Duncan-Chang model and shear softening model are used to respectively describe the pre peak and post peak of shear stress-displacement curves of the South China Sea and polypropylene biaxial geogrid interface. The interface constitutive model established can well reflect its shear characteristics.