MUCK IMPROVEMENT TEST FOR JACKING CONSTRUCTION OF LARGE RECTANGULAR CROSS-SECTION PIPE IN ANHYDROUS SAND LAYER

During the construction of large rectangular cross-section pipe corridor in anhydrous sand layer, due to the poor flow plasticity of sand, the bad phenomena such as "blocking", "gushing" and "cake forming" are easy to appear on the face of the pipe, which can affect the construction progress. This paper is based on the construction of rectangular pipe jacking with large section in Changhe West Road(Zhaoshan Street-Luyang Street), Tongzhou District, Beijing. It carries out the experimental study on the improvement of muck of front face. It uses different ratios of sodium base bentonite, polyacrylamide(PAM) and water as additives of sandy soil improvement. It uses viscosity test and filtration test of different ratios of modifying agent(bentonite added polyacrylamide) performance. It further uses the modified waste residue of the slump test, direct shear test and compression test, and evaluates the constraints of waste residue. The results show that the effect of adding polyacrylamide to bentonite on anhydrous sand is remarkable. According to the performance test of the improver, four good modifiers of bentonite:PAM:water: 60:2:1000, 70:1.5:1000, 70:2:1000 and 80:1.5:1000 are screened. The results show that the optimal ratio of modifier bentonite:PAM:water is 70:2:1000, and the optimal injection ratio of modifier is 15%. By adding the modifier, the slump of the modified soil is reduced by 30 mm, the cohesion is increased by 9.3 kPa, the internal friction angle is reduced by 6.5°, and the compression coefficient is increased by 0.090 MPa^-1. At this time, the anhydrous sand soil is close to the plastic-flow state, which effectively reduces the side wall resistance of large section rectangular pipe and improves the jacking efficiency.