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

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.