Model test study on disturbance characteristics of surrounding rock inloess shield tunnel excavation

In order to explore the disturbance characteristics of loess shield tunnel excavation on surrounding rock under different water content and buried depth, similar model tests were carried out. Firstly, the physical parameters and strength indexes of undisturbed loess under different water content were measured by triaxial tests. Through a large number of tests, the test soil with similar strength indexes of undisturbed loess with different water content was obtained. Then, considering the characteristics of shield tail gap of shield tunnel, the simulation test of shield excavation under different water content and buried depth is carried out. The variation law of stratum deformation, surface settlement and surrounding rock stress under different working conditions is analyzed by means of monitoring components such as micro earth pressure sensor and dial indicator and digital image technology. It is found that the self-stabilizing ability of surrounding rock is strong when the water content is low; the higher the water content, the greater the buried depth ratio, the greater the disturbance of excavation to the stratum. The maximum ground settlement is positively correlated with water content and negatively correlated with buried depth ratio. The residual stress of surrounding rock increases with the increase of water content and buried depth, but when the water content increases to a certain value (26.6 %), the residual stress of surrounding rock decreases sharply. Based on the development law of surrounding rock stress and deformation under different water content, the water content of loess can be divided into self-stabilization, deformation and loosening water content. Based on the loosening of surrounding rock caused by water content and buried depth, the pressure action mode of surrounding rock of loess shield tunnel under different working conditions can be calculated according to deformation pressure and loosening pressure, so as to better adapt to the characteristics of loess strata.