Damaged old sewer pipes are known to often cause void/cavity or loosening in the surrounding soil, which may lead to a cave-in in the road. In this research, in order to understand the mechanism and governing factors of cavity formation/expansion in the ground, a series of model tests simulating flowout of soil through a crack/gap in a buried pipe was conducted.
   It was found that a cavity and surrounding loosening in the ground can extend rapidly upward when the ground consists of poorly graded sand, especially when it is fully saturated. Quantitative evaluation was also given to the loosening around a cavity. [This abstract is not included in the PDF]