Influence Of Shallow Covering Soil On Underwater Shield Tunnel’s Segment Floating Up And Research Of Damage Diagnosis Technique

When excavating shield tunnels in high water pressure area, developed underwater water system in particular, tunnel will be floating inevitably. segment’s floating up in such a situation always causes segment crack, segment surface’s exfoliation, segment deformation, leakage water, and even deformation of a whole section and other phenomena, while shallow covering soil’s influence on the floating up of segment is very prominent. Considering the huge influence on segment floating up caused by overlying covering soil, this thesis adopts the method of combing numerical simulation, field monitoring with theoretical calculation, carries out the study of the regularity of shallow covering soil’s influence on segment floating up and the research of the damage diagnosis technique of shield tunnel segment floating up. The main content and conclusion of the thesis are listed as follows:(1)Based on the analysis of both internal and external load of segment, relying on the case of Nanhu Road Shield Tunnel, the thesis, taken shield tunnel in situation of shallowest covering soil section and the state after impacting siltation unloading as simulation object, studies segment displacement, internal force’s variation regularity, and tunnel safeness. Meanwhile, comparing numerical simulation results with field monitoring data and minimum covering soil thickness, it shows that all results basically tally with each other, which conforms to design requirements.(2)On the basis of the simulation of segment floating up in the shallowest covering soil section, the thesis analyzes the variation regularity of shield tunnel segment displacement, soil mass displacement, and soil of plastic strain under different covering soil thickness and soil modulus. Shallow covering soil’s influence on shield tunnel’s segment floating up:the shallower the covering soil is, the bigger the segment floating up is; overlaying soil displacement increases when covering soil thickness decreases; when covering soil thickness decreases, soil of plastic strain amplitude increases. Properties of soil’s influence on shield tunnel segment floating up:the smaller soil modulus is, the bigger the segment floating up is; covering soil’s displacement increases when soil modulus decreases; when soil modulus decreases, plastic region is stable, plastic strain amplitude decreases.(3)According to the research of underwater shield tunnel segment floating up, the thesis analyzes the damage degree of underwater shield tunnel caused by segment floating up, and develops shield tunnel segment floating up damage diagnosis model. At last, based on the research achievement of the thesis, the thesis provides some technique measures to control segment floating up, such as determining covering soil thickness, improving soil properties, reducing covering soil’s and so on.