Detection and analysis of slurry jacket for pipe jacking construction in soft ground

Grouting in pipe jacking can effectively decrease resistance and reduce disturbance to the ground, which is largely decided by the quality of slurry jacket around the pipe. Ground Penetrating Radar (GPR) enables visualization of the slurry outside the tube of pipe, and the actual thickness of the slurry jacket is obtained by utilizing the dielectric difference between the target and the surrounding medium. In this paper, an estimated formula for predicting the thickness of slurry jacket is proposed based on the principle of seepage flow. By comparing the monitoring values and calculated values in different environments, a validity of this estimated formula is achieved. Results show that dense and uniform slurry jacket can be formed outside the tube of pipe, which will vary in thickness with the stratigraphic environment for the pipe. The thickness is thinner when the pipe crosses a river, which should be paid more attention when encountering with grounds with a high-water level. Compared to shield tunnel, the detected thickness of the slurry jacket is smaller, which is due to the different properties of the slurry used in the shield tunnel and pipe jacking, while the water content and hydration speed of the slurry are two key factors to affect the speed of electromagnetic (EM) wave propagation in the medium.