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基于侧限压缩试验的黏土动态力学性能研究

Study on dynamic mechanical properties of clay based on confined compression test

  • 摘要: 为研究斜井井筒采用冻结法施工穿过松软含水黏土层时,冻结壁失稳、冻结管破坏与黏土强度、黏土变形之间的关系,以黏土为试验对象,通过高压固结仪还原深部黏土受压变形过程,利用SHPB试验装置对无侧限、有侧限条件下的黏土试件进行不同应变率加载,借助高速摄影机拍摄黏土试件的变形破坏过程。研究结果表明:无侧限条件下,黏土试件变形大,被压成“薄饼状”,但仍具有一定的承载力,且存在透射信号差的问题;黏土试件以环刀作为侧限约束,环刀起到被动围压的作用,试件透射信号幅值明显增大,侧限条件下试件的峰值应力、应变与应变率呈正相关的关系;侧限条件下引入岩石类材料损伤变量D,通过分析损伤变量D随应变的演化规律,发现在相同应变比条件下,冲击速度越大,则D值越小,试件的压实程度越高;侧限条件下黏土具有明显的回弹现象,试件的回弹量随着平均应变率的增大而增大,黏土的回弹作用会对井筒、冻结管产生预压力,对其稳定性产生负面影响。

     

    Abstract: In order to study the existence of frozen wall instability and frozen pipe damage relations with clay strength and deformation when inclined shaft with ground freezing method construction through the soft water-bearing clay layer, this article taking clay as the test object, the compression deformation process of deep clay was reduced by high-pressure consolidation instrument, SHPB was used to load clay samples with different strain rates under unconfined and confined conditions. The deformation and failure process of clay samples was photographed by high-speed camera.The results show that under unconfined condition, the clay specimen deformation is large and is pressed into "pancake shape", but it still has a certain bearing capacity and the problem of poor transmission signal; with the ring cutter as the confined constraint, the ring cutter acts as the passive confined pressure, and the amplitude of the transmitted signal of the clay specimen increases significantly, under confined condition, the peak stress, strain and strain rate of the specimen are positively correlated with the strain rate; the damage variable D of rock material is introduced under confined condition, and the evolution law of damage variable D with strain is analyzed. It is found that under the condition of the same strain ratio, the higher the impact velocity, the smaller the D value and the higher the compacting degree of the specimen; under confined condition, clay has obvious rebound phenomenon, and the rebound amount of specimen increases with the increase of average strain rate. The rebound effect of clay will produce pre-pressure effect on shaft and frozen tube, and have negative influence on its stability.

     

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