Study On Mechanical Law And Design Theory Of Inclined Freezing Shaft Lining In Topsoil

In order to solve the problem that no reliable theory can be used in the design of inclined freezing shaft lining in topsoil, the research on the mechanical law of inclined freezing shaft lining in topsoil during the freeze sinking process was carried out in this paper with combination of theoretical analysis, numerical simulation and model experiment. Its design theory and method were also put forward.Firstly, the initial ground stress was decomposed into equivalent water pressure and equivalent soil skeleton pressure by the principle of stress balance. Then according to the different characteristics of water pressure and skeleton pressure and considering the unloading effect in excavation, the interaction models of circular inclined shaft lining, frozen wall and unfrozen strata under those two kinds of initial pressures were established separately. The analytical solutions of the stress and displacement of the shaft lining, frozen wall and unfrozen strata before and after frozen wall thawing were derived. The influence of some factors on the circular inclined shaft lining was obtained, including the different construction stages(freezing, sinking and thawing), the different separation and combination calculation method of soil and water pressure and the different parameter values. The design theory and method of circular inclined freezing shaft lining was put forward based on the ground-structure method, and the thickness calculation formula of shaft lining was deduced by the multi-axial strength criterion of concrete. The ground-structure method and separation calculation method of soil and water pressures were suggested to be adopted in the design of circular shaft lining.Secondly, a high precision and easy-implementation numerical simulation method of in-situ stress was proposed in this study. And the finite element model which could simulate the whole process of freezing inclined shaft construction was established. Through the numerical simulation, it was the first time to obtain the stress and deformation law of the inclined shaft lining formed by vertical sidewall, semicircular top arch and inverted arch before and after the frozen wall thawing. And the influence of various factors on t he stress in shaft lining was clarified. The research shows that the stress in shaft lining increases gradually during the thawing process. Generally, the tensile and compressive control points of the top arch are located in the centeral point of inner edge and the intersection point of inner sidewall and top arch respectively. For the inverted arch, the corresponding control points are separately the centeral points of inner and outer edge.Thirdly, an experiment system which could achieve the co-loading of unequal ground pressure and pore water pressure was developed, which could also realize the simulation of freezing and thawing process. The system was used to carry out the hydrostatic experiment of inclined shaft lining, the ground pressure experiment under different load combinations, the co-loading experiment of ground pressure and pore water pressure and the thawing experiment of frozen wall. And the deformation laws of shaft lining under these different loads were obtained. The results show that the deformation of top arch is significantly different under hydrostatic pressure and unequal ground pressure. Under the condition of constant boundary load, the stress of shaft lining is more unfavourable with the increase of pore water pressure. Therefore, for the strata with large porosity, the separation calculation method of soil and water pressures should be applied to reflect the different effects of skeleton pressure and pore water pressure on shaft lining structure.Finally, based on the above research results, the load calculation method for inclined shaft lining formed by vertical sidewall, semicircular top arch and inverted arch was put forward which could reflect the interaction between shaft lining and topsoil. The design theory and method were established based on the load-structure model. The detailed structure calculation formula were also presented.