Investigation of mechanism of ground sinking through 3-d GPR surveys and laboratory model tests

Abstract

In aging urban environments such as Seoul (South Korea), the ground cavities formed under roads are continuously increasing. 3-D GPR surveys using the Stream EM device equipped with a 38 channel multi-Antenna were performed to detect such cavities. Dozens of such cavities were found in Seoul, and excavations were performed to investigate their cause. It was demonstrated that the main cause of cavity formation is the damage and the detachment of the aging sewage pipelines. During a heavy rainfall, the water table quickly rises above the pipeline. When the water table drops, fine-grained soil particles are flushed into the sewage pipeline, causing a cavity to develop around the sewage pipeline. To investigate the mechanism of the cavity formation around sewage pipelines in detail, and assess the effects of soil type and other field conditions, a series of model tests was performed. Cyclic tests, in which the soil tank is saturated and then drained in multiple sequences, were performed, and the volume of the discharged soil was measured. It was shown that a number of properties including the density and the water content influence the discharge rate of soil, the rate of cavity size expansion, and the characteristics of the relaxed area around the cavity. ? 2017 19th ICSMGE Secretariat. All rights reserved.