Experimental study on the effect of injecting slurry inside a jacking pipe tunnel in silt stratum

Through a three-dimensional model test, the variations of jacking force and ground settlement inside a jacking pipe tunnel in silt stratum, under testing conditions which include non-injection and different synchronized injections of slurry, are simulated in order to study the effect of traditional thixotropic slurry (consisting of bentonite, CMC (Carboxymethyl Cellulose) and soda ash) and HL compound slurry to decrease frictional resistance and ground settlement. And then their mechanical properties are investigated according to the different slurry micro-structure features which are captured by an electron microscope. The tests and analysis demonstrate that: (1) injecting thixotropic slurry inside a jacking pipe tunnel has conspicuous effects in reducing frictional resistance, and (2) viscosity and condensation force of the slurry have a dominant effect on decreasing frictional resistance and ground settlement, respectively. To reach optimal jacking distance and efficiently control ground settlement, more attention should be given to slurry parameters in the actual engineering processes. The research results indicated excellent effects when they were applied to the jacking pipe of Shanghai Lingang New City Sewage Conduit.