Research on the Influence of Meso-Mechanical Characteristics of Medium Sand on the Stability of Cofferdam Foundation Pits
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摘要: 不同沉积深度的中砂的细观颗粒特征及其物理力学性质差异显著,研究其细观-力学特性差异对砂层中的围堰稳定性影响可辅助基坑设计及安全评估。以西安渭河中砂地层的某桥基围堰工程为例,基于室内直剪试验、渗透性试验、电子扫描显微镜(SEM)试验,开展了渭河中砂的细观结构-力学特征的研究;同时采用FLAC3D软件建立了中砂地层的基坑施工模型,系统分析了砂土的长宽比、磨圆度与粗糙度对内摩擦角、渗透系数和围堰稳定性变形的影响。结果表明:1)渭河中砂的颗粒形状不规则,且表面不光滑;颗粒长度多分布在0.1~0.3 mm,宽度多分布在0~0.2 mm;2)随着中砂长宽比和粗糙度的增加,内摩擦角逐渐增大,渗透性逐渐减弱,反之随着磨圆度的增加,内摩擦角逐渐降低,渗透性逐渐增强;3)随着中砂长宽比和粗糙度增加,围堰水平位移减小;磨圆度增加,围堰水平位移增大。本研究揭示了渭河中砂的细观结构与其物理力学性能之间的关系,以期为类似工程中的基坑围堰设计提供科学依据。Abstract: The microparticle characteristics and physical and mechanical properties of medium sand vary significantly with deposition depth. Studying how these micromechanical characteristics influence cofferdam stability in sand layers can provide valuable insights for foundation pit design and safety assessment. Taking a bridge foundation cofferdam project in the Wei River medium sand formation in Xi’an as an example, this study investigated the microstructural and mechanical characteristics of Wei River medium sand through direct shear tests, permeability tests, and SEM tests. Meanwhile, a foundation pit construction model for the medium sand stratum was established using FLAC3D software to systematically analyze the influence of sand particle length-to-width ratio, roundness, and roughness on internal friction angle, permeability coefficient, and cofferdam stability deformation. The results showed that: 1) the sand grains of the Wei River medium sand were irregular in shape with non-smooth surfaces; particle length was mainly distributed between 0.1 mm and 0.3 mm, and the width was mainly distributed from 0 to 0.2 mm. 2) As the length-to-width ratio and roughness of the medium sand increased, the internal friction angle gradually increased while permeability gradually decreased; conversely, with an increase in roundness, the internal friction angle gradually decreased and the permeability gradually increased. 3) The horizontal displacement of the cofferdam decreased with increasing length-to-width ratio and roughness of the medium sand, but increased with increasing roundness. This study revealed the relationship between the microstructure of Wei River sand and its physical and mechanical properties, aiming to provide a scientific basis for the design of foundation pit cofferdams in similar projects.
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Key words:
- medium sand /
- mesoscopic characteristics /
- cofferdam stability /
- laboratory test /
- numerical analysis
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