OPTIMIZATION THIXOTROPIC SLURRY RATIO AND DRAG REDUC￣TION PERFORMANCE TEST FOR RECTANGULAR PIPE JACKING IN ANHY￣DROUS SAND LAYER

In pipe jacking construction, thixotropic mud plays the role of lubrication, drag reduction and supporting formation. The mud is an important material to ensure the safe and rapid pipe jacking construction. Its resistance reduction performance is an important factor affecting the pipe jacking construction. This paper is based on the comprehensive pipe gallery project of Lucheng Town, Tongzhou City, the vice center of Beijing City. It takes bentonite, CMC and soda as the raw materials of thixotropic slurry, carries out the orthogonal test of different material ratio, and optimizes the optimal ratio of thixotropic slurry. The drag reduction effect of thixotropic slurry is investigated by scale model test. In addition, the microstructure and drag reduction mechanism of thixotropic mud are studied by SEM. The results show that: the content of thixotropic slurry raw materials has a great influence on the performance of the mud. 10% bentonite, 0.2% CMC, 0.5% soda ash and 89.3% water are the optimal proportion of slurry raw materials. Under this ratio, the slurry has good fluidity and thixotropy, small water loss, dense "filter cake" and optimal comprehensive performance. In addition, the friction coefficient between the test block and sand can be effectively reduced by 40% with the thixotropic slurry, and the drag reduction effect is remarkable. The thixotropic slurry has a lamellar structure, and its main mineral component montmorillonite has micro characteristics such as lattice substitution and cation exchange, which makes the thixotropic slurry show thixotropy macroscopically and plays the role of drag reduction. Finally, the pipe and surrounding soil are fully isolated in the form of mud sleeve, so as to realize the drag reduction function.