Analysis of water sensitivity and microstructure for silt in Zhengzhou area

In order to study the evolution mechanism of Zheng Han Gu Cheng, direct shear tests and disintegration test were carried out by using the scattered soil of Zheng Han Gu Cheng to prepare the samples with different water content, and the microscopic mechanism of water sensitivity characteristics for silt was analyzed by field emission scanning electron microscope. The test results show that the stress-strain curve of silt behaves as hardening type based on different water content, and with the increase of water content, the shear stress increases first and then decreases, and reaches the maximum at the optimum water content. The variation on shear strength with water content is consistent with that of shear stress. With the change of water content, the cohesion reaches its peak at the optimum water content, while the internal friction angle changes little, and the difference is about 1.7 degrees. With the increase in water content, the disintegrating rate of specimen decreases gradually due to the influence of water film. From the SEM images of different water content, it can be seen that silt has the least pore size, dense grain arrangement and mosaic structure under the optimum water content, which greatly improves the strength of soil samples. With the change of water content, the micro-structure of soil gradually develops from loose structure of dense structure, then to mosaic mechanism, and finally to directional arrangement structure. The above research results can provide a theoretical basis of the protection and reinforcement of ancient city walls.