Evaluation on the behavior and contributing factors of subsidence in the intersection area of Expwy 78 and Taiwan High Speed Rail based on in situ monitoring and numerical simulations

This paper discusses the behavior and contributing factors of land subsidence in the intersection area of Expressway (Expwy) 78 and Taiwan High Speed Rail (THSR), located on Choshui River alluvial fan-delta (CRAFD) to the midwest of Taiwan. Since the CRAFD has been suffering a long-time problem of land subsidence, the transportation safety of THSR and Expwy 78 thus has become a major concern. The subsidence of CRAFD can be attributed to several factors, including overexploitation of groundwaters for area development. However, additional loadings of Expwy 78 and THSR structures would appear to deteriorate the problem. It would be of interest to know the influence of various factors on subsidence of the study area where the subsidence has now become most serious along the entire THSR route. It would also be advisable to provide information on the potential effects of subsidence on the integrity of THSR structure. With these aims, we perform analyses on the subsidence of the area based on 8-year on-site monitoring and numerical simulations. Results indicate, in a period started approximately from Expwy 78 construction, the average subsiding rate would be 10.53 cm/year, with relative contributions of 14.1%, 55.2%, 11.8%, 11.6%, and 7.3%, respectively, by the factors of soil creeping, previous overpumping, groundwater fluctuations, and loadings of Expwy 78 and THSR. We also estimate 23% and 77% of total subsidence occurred as the compressions of soils within and beyond the installation depth of THSR piles, which might impair pile bearing capacity and vertical alignment, respectively, of THSR.