粗糙度对结构物-细砂界面剪切特性的影响

Effects of roughness on shear properties of structure-sands interface

下部基础与土体界面的剪切特性对于整个结构的安全施工至关重要,地基上部土层中多见砂土层,砂粒径大小和结构物表面粗糙程度会影响下部基础的受力特性,对于研究砂土层下部基础的侧摩阻力具有重要意义。利用改进后的直剪仪,进行粒组为0.075~0.150mm,0.150~0.300mm的砂与人造粗糙混凝土板、钢板的界面剪切试验,研究不同砂粒组、不同粗糙度、不同法向应力下的钢-砂和混凝土-砂界面抗剪强度和界面剪切强度指标。结果表明:界面剪切应力-剪切位移关系可用双曲线模型描述,试验峰值剪切应力与模型峰值剪切应力的比值为0.85~0.95;峰值剪切应力随法向应力和粗糙度的增大而增加,粒组Ⅰ的较粒组Ⅱ略大,混凝土-砂界面峰值剪切应力较钢-砂界面的大;对于未刻纹路的结构物-砂界面剪切面为一移动的水平面,刻有纹路的结构物-砂界面剪切面由间断的水平剪切面和动态曲形剪切面构成;界面摩擦角随粗糙度增大而增加,粒组Ⅰ的抗剪强度指标较粒组Ⅱ略大,钢-砂界面摩擦角集中在23°~28°,混凝土-砂界面摩擦角集中在25°~31°。研究成果可为砂土层桩侧摩阻力估计和数值模拟提供参考。

The shear properties of the interface between the underlying foundation and soil are very important for the safe construction of the entire structure. Sandy soil layers are common in the upper soil layer of the foundation, and the particle size of sand and surface roughness of the foundation will affect the mechanical properties of the pile foundation. It is very important to study the shaft resistance of the sand strata. In order to investigate the interface shear strength, interface shear strength index with different particle sizes of sands, different roughnesses and different normal stresses, the interface shear tests on sands having particle sizes of 0.075~0.150 mm and 0.150~0.300 mm with rough steel plate and concrete plate are performed by using an improved direct shear apparatus. The testing results indicate that the interface shear stress-displacement relationships can be described by a hyperbolic model. The ratio between the peak shear stress of the test and the peak shear stress of the model ranges from 0.85 to 0.95. The peak value of the measured shear stress increases with normal stress and roughness. The peak shear stress of the particle size I is slightly larger than that of the particle size II. The peak shear stress of the interface between concrete and sands is larger than that of the steel-sands interface. The shear surface for the sand-structure interface without engraved lines is a moving horizontal plane, while the shear surface for the sand-structure interface with engraved lines is composed of discontinuous horizontal shear planes and dynamic curved shear surfaces. The interface friction angle increases with roughness. The shear strength index of the particle size I is slightly larger than that of the particle size II. The friction angle for the sand-steel interface ranges from 23° to 28°, and the friction angle for the concrete-steel interface ranges from 25° to 31°. The research and analysis results can provide an experimental reference for shaft resistance estimation and numerical simulation of the sand strata.