Application and research on large in-situ self-reacting direct shear apparatus owning two shear interfaces
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摘要:
原位直剪是测定土石混合料强度参数最为普遍也是最可靠的试验方法之一，但是现有原位直剪仪在试验过程中存在法向加压系统不合理、无法预留剪切缝等多方面的缺陷，影响试验结果的精度。本文对传统原位剪切仪进行有针对性的改造，研制出自反力双剪面大型剪切仪，该大型原位直剪仪有以下特点：（1）设备自身提供水平反力；（2）剪切过程中垂向加压系统固定，无需滚轴排；（3）剪切盒之间可预留可调节宽度的剪切缝，适用性更广；（4）装置模块化程度高，便于搬运、组装和拆卸。通过与单环剪切仪进行现场对比试验发现，与单环剪切仪得到的试验结果相比，自反力双剪面大型剪切仪得到的剪应力-剪切位移曲线为标准双曲线，并且可得到大剪切位移情况下的剪切曲线，通过大剪切位移曲线读取的最大剪应力更贴合实际。与单环剪切仪得到的抗剪强度值相比，内摩擦角低4.6°，而黏聚力高41.14 kPa。同时通过对两种剪切仪得到的剪切破坏面进行图像对照，可明显发现自反力双剪面大型剪切仪得到的剪切破坏面较为平整，未出现单环剪切仪对的剪切破坏面下凹现象。
Abstract:The in-situ shear test has been justified as one of the most reliable and common method used to test shear strength of soil-rock mixture. However, the existing in-situ shear test apparatuses show some shortcomings in practice that will influence the accuracy of the test results, including the unreasonable normal pressure system and unable to reserve shear opening, etc. A new self-reacting direct shear apparatus owning two shear interfaces is introduced. The apparatus is characterized by the followings: (1) it provides horizontal reaction force by itself; (2) the vertical pressure system is fixed during shearing without roller row; (3) the adjustable width of shear opening can be reserved between shear boxes; (4) it is of high modularity, and is easy to handle, assembly and disassembly. It is validated through comparison with the single-box direct shear test. Compared with the experimental results obtained by the single box shear apparatus, the shear stress-shear displacement curve obtained by the self-reacting direct shear apparatus is a standard hyperbolic curve, and the shear stress-displacement curve under large shear displacement can be obtained. The maximum shear stress read by shear stress-displacement curve under large shear displacement is more practical. Compared with the shear strength obtained by the single-ring shear apparatus, the internal friction angle is 4.6 degree lower and the cohesion is 41.14 kPa higher. At the same time, through the image comparison of the shear failure surface obtained by the two shear apparatuses, it can be obviously found that the shear failure interfaces obtained by self-reacting direct shear apparatus owning two shear interfaces is relatively flat, and there is no concave phenomenon of the shear failure surface on the single-ring shear instrument.
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Key words:
- in-situ test /
- large direct shear test /
- two shear interfaces
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