Ground-penetrating radar measurement of the distribution of thixotropic slurry behind large-diameter segments in long-distance pipe-jacking construction

摘要

Pipe-jacking engineering requires monitoring of the spatial distribution of thixotropic slurry behind the pipe segments, but timely thickness measurements are difficult during construction. Ground-penetrating radar was used here during sewage pipe jacking, to evaluate the distribution of the slurry by considering its dielectric contrast with the surrounding soil. A series of circular ground-penetrating radar data was collected along the inner surfaces of the pipe segments using an antenna with a frequency of 900 MHz. To enable accurate interpretation of the ground-penetrating radar images, the dielectric parameters of the slurry were first measured by time-domain reflectometry. Statistical analyses revealed the slurry as a special medium with extremely high dielectric constant and conductivity. Numerical simulation indicated that the ground-penetrating radar images can be considerably improved by applying Karhunen Loeve transformation followed by f-k Stolt migration, which facilitates identification of the reflections from the slurry soil interface. Based on all the processed ground-penetrating radar field data, the thickness and the distribution of the slurry at different pipe segments were calculated using the two-way travel time and the radar signal propagation velocity in the slurry. The results show that ground penetrating radar is indeed effective for estimating the quality of slurry injected during pipe jacking.