An experimental study of the unconfined compressive strength characteristics of the expansive soil with cracks
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摘要:
膨胀土易发育大量裂隙，对其工程性质影响显著。引入一种膨胀土试样预制裂隙方法，对特定裂隙形态下膨胀土试样开展无侧限抗压试验，研究了膨胀土强度特征受裂隙形态的影响，并揭示了裂隙的作用机制。研究结果表明：（1）裂隙形态显著影响试样破坏模式，垂直于受力方向裂隙越宽，破坏模式由剪切-拉伸破坏向张拉破坏转变；平行于受力方向裂隙条数越多，破坏模式由剪切破坏向鼓胀破坏转变。（2）垂直于受力方向裂隙形态对膨胀土试样应力-应变关系影响显著。裂隙越宽，闭合应变越大；裂隙越深，初始起裂应力越小，强度增量越大；平行于受力方向裂隙形态则对应力-应变关系无明显影响。据此划分多级上升型、波动上升型、多级下降型、标准型4种曲线形态。（3）裂隙方向显著影响含裂隙土的强度折减，含与受力方向平行裂隙试样的峰值强度接近无裂隙试样，含与受力方向垂直裂隙试样的峰值强度与变形模量随裂隙条数增加而降低，具有良好的对数函数关系，峰值应变受裂隙影响小。研究结果可为膨胀土边坡浅层性失稳机制提供一定的理论依据，为相应的裂隙土体工程设计与施工提供指导。
Abstract:Expansive soil is prone to develop a large number of cracks, which have a significant impact on its engineering properties. A prefabricated crack method of expansive soil samples is introduced to carry out the unconfined compression strength on the expansive soil samples under the specific crack morphology. The influence of the crack morphology on the strength characteristics of the expansive soil is examined, and the mechanism of crack action is revealed. The results show that: (1) The crack morphology has a significant effect on the failure mode of the samples. When the cracks become wider, which are perpendicular to the stress direction, the failure mode changes from shear-tensile failure to tensile failure. When the cracks parallel to the stress direction become more and more, the failure mode changes from shear failure to swelling failure. (2) The shape of the cracks perpendicular to the stress direction has a significant effect on the stress-strain relationship of the expansive soil samples. The wider the crack is, the greater the closed strain is. The deeper the crack is, the smaller the initial crack initiation stress is and the greater the strength increment is. The shape of cracks parallel to the stress direction has no obvious effect on the stress-strain relationship. Based on the results, four types of curves are divided, namely, the multi-level rise, fluctuation rise, multi-level decline and standard curve. (3) The direction of crack obviously affects the strength reduction of the cracked soil. The peak strength of the sample containing cracks parallel to the stress direction is close to that of the non-cracked sample. The peak strength and deformation modulus of the sample containing cracks perpendicular to the stress direction decrease with the increasing crack number, and have a good logarithmic function relationship. The peak strain is less affected by crack. This study can provide a theoretical basis for the shallow instability mechanism of the expansive soil slope, and a guidance for the design and construction of the corresponding cracked soil engineering.
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表 1 不同裂隙形态试样破坏过程及特征描述
Table 1. Description of the failure process and characteristics of the samples with different crack morphologies
试样编号 破坏模式 次生裂纹起裂、扩展 破坏形态 破坏特征描述 W1D6C2-1 剪切-拉伸破坏 
裂隙临空面拉应力最大，裂纹于裂隙两侧受拉起裂；裂隙闭合前，裂纹受拉垂向发育，闭合后，裂纹受剪应力作用偏转；破坏受拉-剪混合作用，剪切破坏面明显 W2D3C2-1 张拉破坏 
裂纹于裂隙两侧受拉起裂；裂隙闭合前后，裂纹受拉垂向扩展，并受拉-压应力作用侧向张开；破坏受拉应力作用显著 W2D3L1-1 剪切破坏 
裂纹受剪起裂，在裂隙处受约束作用偏转；破坏受剪应力作用，剪切破坏面明显 W2D6L4-1 鼓胀破坏 无 
裂隙约束作用明显，试样表面剪切裂纹不发育；破坏时，试样受压侧向鼓胀，裂隙受压侧向张开 
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