土工模袋砂界面摩擦特性试验研究

土工模袋砂界面特性指标对于各类模袋砂工程的设计至关重要。笔者开展了砂与土工模袋、土工模袋之间界面摩擦特性直剪试验;通过自制试验装置进行了模袋砂间界面摩擦试验,探讨了充填度对模袋砂间界面特性的影响;把试验结果用于典型工程实例变形和稳定性分析,并通过数值计算验证。研究结果表明:模袋与砂界面剪应力-位移关系表现出明显的非线性特征,剪应力峰值及其对应的位移随竖向压力的增大而增大,界面关系服从摩尔-库伦强度理论;砂与模袋间的摩擦角为30.3°,摩擦系数为0.58,黏聚力是3.1 kPa。土工模袋间界面关系也服从摩尔-库伦强度理论,摩擦角为21.3°,摩擦系数是0.39,黏聚力为1.29 kPa。模袋砂之间的摩擦特性指标则因充填度而异,受充填度影响显著,表现为充填度增大,摩擦角变大而粘聚力减小,抗剪强度增大,且竖向压力越大影响越明显。基于试验结果明确了洲头咀沉管隧道模袋砂围堰位移突变的原因及其稳定性,提出了设计控制指标;通过数值计算表明,基于界面摩擦试验结果分析所得结论合理。

Experimental Studies on Interface Friction Characteristics of Geotextile Bag with Sand

The interface friction characteristic index of the geotextile bag with sand is very important to the design of the geotextile bag with sand cofferdam. The direct shear test of friction characteristics between sand and geotextile bag was carried out and the test of friction characteristic between geotextile bags with sand was conducted by self-made test equipments as well as the influence of compactness on interface characteristics was analyzed. The test results finally were used to analyze deformation and stability of engineering example, and the rationality was verified by numerical calculation. The results show that the relationship between shear stress and displacement is obviously nonlinear, and the shear stress peak and its corresponding displacement increase with the vertical stress increases. The interface friction characteristic obeys Mohr-coulomb strength theory. The friction angle, friction coefficient and cohesion between the sand and geotextile bag with sand are respectively 30.3°, 0.58 and 3.1 kPa and the contact parameters between geotextile bags are respectively 21.3°, 0.39 and 1.29 kPa, while friction characteristic index between geotextile bag with sand are varied with different compactness. The influence of compactness on friction characteristics between the geotextile bags with sand is significant, which indicates that the friction angle increases and cohesion decreases, and shear strength increases with the vertical stress increases. The greater vertical stress is applied, the more significant effect it gives. The reasons of deformation and stability of Zhoutouzui tunnel cofferdam in Guangzhou was obtained based on test results and the control index was proposed for design of cofferdam. Numerical results show that the conclusion is feasible deduced by test results.