Geological Environmental Impact of Shallow Gas Release: A Case Study of Dayushan Island, East China Sea

Shallow gas widely exists in shallow sediments of coastal areas. Shallow gas leaks and accumulation influence the soil’s mechanical characteristics and jeopardize project construction, which is likely to result in casualties and financial losses. The eastern coast of China is a rapidly developing area for engineering construction as well as a shallow gas development area. The safety of the geological environment is gravely threatened by the presence of shallow gas in the sediments. In this study, we focus on the reclamation area of Hangzhou Bay Sea area. The study analyzed the data from the established shallow gas monitoring station to evaluate the characteristics of land engineering effects on shallow gas release. Meanwhile, numerical simulation methods are being combined to further study the spatial distribution characteristics of the impact of soil properties at various time scales after shallow gas release. The numerical simulation results are consistent with the monitoring data. The study indicates that maximum depth for shallow gas release impacts is between 32 and 65 m, and the radial impact range is within 8 m from gas release hole. The maximum soil lateral displacement is 40–50 mm, while the maximum ground settlement as a result of gas release is roughly 76.7 mm/year. By using numerical simulation and monitoring data, this work also exposes the geological environmental effects of shallow gas release in fine sediments, which can serve as a better foundation for site building and construction evaluation of gas-bearing soils in the area.