Study On Ground Pretreatment Technology Of Pipe Curtain-Frozen Under Complex Conditions

ABSTRACT:This paper describes the characteristics of tunnel excavation under conditions of ultra-shallow buried, large section, offshore, unfavorable ground and complicated surrounding environment, introduces engineering measures usually taken, analyzes the role and characteristics of advanced formation pretreatment technology, comparative analyzes the advantages and disadvantages and the applicability of common ground pretreatment methods,, puts forward the integrated ground pretreatment technology of pipe curtain-frozen.This paper studies the mechanism of the integrated stratigraphic pretreatment technology of tube curtain-frozen, by theoretical analysis combined with field measurement data and by means of FLAC3D numerical simulation. It also analyzes the respective role of the pipe curtain and the frozen circle playing in the process of formation pretreatment and their combined effects. The following conclusions can be drawn:(1) Only pipe curtain circle can effectively integrated control surrounding rock deformation and maintain the stability of surrounding rock, ensure the safety of tunnel construction.(2)The disturbance of single pipe jacking is small; the latter pipe jacking has little disturbance for the former.(3) When using the strata pretreatment method of freezing, ground movement can be divided into three stages:freezing expansion stage, excavation and support stage and permafrost melting stage. The absolute value of strata displacement of excavation stage is smaller than the other two stages. The absolute value of strata displacement of permafrost melting stage is the biggest of the three stages.(4) With the increase of frost heaving ratio, soil displacement in the process of freezing increases,and so does the soil additional compressive stress generated in the soil.The effect of the frozen wall thickness increase for the control of ground settlement is obvious. Freezing method is not suitable for the soil whose frost heaving ratio is too large. The optimum thickness of frozen wall is about2.5m.(5) The combination of pipe curtain method and freezing method can make up with each other. Freezing method can use frozen circle to make every single pipes work as a whole, and improve the mechanics performance of pipe curtain, give full play to reinforce the surrounding rock, reduce the deformation; The pipe jacking method can reduce soil settlement in the process of melting and soil expansion in the process of freezing, reduce the ground disturbance.