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摘要: 为了解决传统原位土体强度测试探测深度浅与过度依赖经验公式等问题，提出了钻孔原位剪切测试系统构想，并设计了样机，整个测试系统由孔内切削子系统和孔内变径剪切子系统组成，前者能够在钻孔内任意位置锚固并切削土环，后者能够对土环进行剪切试验，并通过传感器记录剪切力和剪切位移；基于模型箱钻孔剪切试验和室内直剪试验，进一步检验了钻孔原位剪切测试系统的可靠性。研究结果表明：模型箱钻孔剪切试验的剪切面平行于剪切力的方向，应力-应变曲线符合基本规律；黄土在模型箱钻孔剪切试验和室内直剪试验中均出现应变软化现象，且黄土的峰值剪切强度随含水率升高而下降；在室内直剪试验中黄土发生了脆性破坏，而在钻孔剪切试验中黄土表现出塑性破坏，在相同的孔隙比、含水率与加载压力下，钻孔剪切试验的峰值强度比室内直剪试验大，原因在于室内直剪试验剪切面的应力分布不均匀，而钻孔原位剪切试验的剪切面受力稳定且保持不变，与室内直剪试验相比，钻孔原位剪切测试系统具有更高的测试准度。Abstract: In order to solve the problems of shallow detection depth and over-reliance on empirical formulas in the traditional in-situ soil strength test, a borehole in-situ shear test system was proposed, and a prototype was developed. The whole test system consisted of an in-hole cutting subsystem, which could anchor and cut the soil ring at any position in the borehole, and an in-hole shear subsystem with a reducing wing, which could perform shear tests on the soil ring and record shear force and shear displacement through sensors. Based on the borehole shear test in the model box and the direct shear test in the laboratory, the reliability of the borehole in-situ shear test system was verified. Research results show that the shear plane of the borehole shear test in the model box is parallel to the direction of the shear force, and the stress-strain curve is found to be consistent with the expectation. The strain softening behavior occurs for loess in the borehole shear test in the model box and direct shear test in the laboratory, and the peak shear strength of the loess decreases with the increase in water content. The brittle failure is found in the direct shear test in the laboratory, while in the borehole shear test, the loess shows plastic failure. The peak strength is higher in the borehole shear test than in the direct shear test in the laboratory under the same void ratio, water content, and loading pressure. The above discrepancy is attributed to the fact that the stress distribution along the shear plane is not uniform in the direct shear test in the laboratory, while in the borehole in-situ shear test, the stress on the shear plane is stable and remains unchanged. Compared with the direct shear test in the laboratory, the borehole in-situ shear test system exhibits a higher test accuracy.
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图 1 土体强度原位测试技术发展历程
Figure 1. Development history of in-situ test technology for soil strength
表 1 试验黄土基本物理参数
Table 1. Basic physical parameters of test loess
含水率/% 颗粒比重 塑限/% 液限/% 粒径级配/% 黏粒(< 5 μm) 粉粒(5~75 μm) 砂粒(>75 μm) 11.6 2.65 16.1 27.8 10.5 83.2 6.3 
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表 2 试验概况
Table 2. Summary of tests
试验编号 孔隙比 剪切速率/(mm·min-1) 含水率/% 加载压力/kPa A-1 0.75 0.08 15 25 A-2 10 50 B-1 15 25 B-2 10 50 B-3 20
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