Study on numerical simulation of cup-shaped horizontal freezing reinforcement project near shield launching

Shield starting is an accident-frequent phase in the construction of shield tunnel. It is a key and urgent problem how to ensure the stability of reinforced soil in that phase. In this paper, the frequently adopted soil reinforcement methods at the shield tunnel end were summarized. Combining with the case of beginning project of shield acting at Suzhou Subway Yang Yu Xiang Station´s west end, in which the application of cup-shape horizontal freezing method was planned to reinforce soil, the ADINA program was run to analyze the shield starting project, followed by the strength checking calculation. In addition, a special attention was placed on the displacement field and stress field under variable thickness of cup bottom in this project. The conclusion is as follows: a) For the soft soil areas, the most frequently used reinforcement approach is cement-soil deep mixing pile + high pressure rotary jet grouting pile; b)When subject to the environmental constraints or ground sand level with water, the cup-shape level freezing method can be employed to reinforce the soil; c) Numerical simulation showed that the extent of displacement was increasing along the boring direction of tunnel toward the cave gate after removing the sealed door. The maximum displacement is by 8.1 mm, occurring in the center of tunnel face; The maximum deformation of the surface occurred over the sealed door, subsiding by 3.1 mm; d) The calculated strength of the cup-shaped reinforcement can meet the safety requirement. Difference of the displacement values and stress values from the variable effective thicknesses of the cup bottom is negligent. This reinforcement approach was feasible even if the effective thickness is 1.0 m. In the end, the parameter values of the reinforcement approach at the beginning project of shield acting in Suzhou subway construction were proposed.