This paper provides a straightforward way to evaluate tunnel settlement caused by land subsidence in the soft deposits of Shanghai. By analyzing field measurements of tunnel settlement and land subsidence, it was found that the tunnel settlement was caused by ground subsidence under the tunnel, and was unrelated to the compression of the upper soil layers. Because significant compaction of the upper layers can occur due to urban construction, the measured land subsidence, which is the ground surface subsidence, cannot represent the sublayer subsidence. To solve this problem, this paper takes metro stations as the monitoring point at the depth of the tunnel, and uses a cubic spline function to fit the line of the station points. The derived fitting curve is then used to represent the ground subsidence under the tunnels. The rationality of taking the stations as monitoring points is verified based on a load transfer analysis. The proposed method is applied to investigate the settlement of metro tunnels in Shanghai. It was found that land subsidence–induced settlement accounts for 62.5% of the maximum cumulative settlement in some sections of Metro Lines No. 1 and No. 2 up until 2010.

It has been observed that in the urban center of Shanghai, land subsidence has accelerated, and the groundwater level has continued to drop even though the net withdrawn volume (NWV) of groundwater has remained unchanged since 1980. An analysis of monitoring data shows that drawdown of the groundwater level is one of the factors that have influenced land subsidence since 1980. The NWV of groundwater in urban areas, however, is not the critical factor controlling the drawdown of the groundwater level. Since the 1980s, there have been many underground works constructed in the unique strata of Shanghai, which has an interlayered structure known as a multi-aquifer-aquitard system (MAAS). Investigation into land subsidence caused by urban construction is now receiving much attention. Based on the principle of a strategic environmental assessment (SEA) for sustainable urban development, this paper presents a discussion and analysis of the factors which can influence the development of land subsidence during continued urbanization in Shanghai. The main factors include the additional loading caused by the construction of structures, the cut-off effect due to construction in aquifers, the drawdown of groundwater level caused by leakage into underground structures, and the decrease of groundwater recharge from neighboring zones. SEA is recommended for the future development of Shanghai.

An important component of modern landfills is the liner system for the prevention of leachate contamination of surrounding ground. Among landfill liner systems, geosynthetic clay liner (GCL) has gained widespread popularity across the world because of its lower hydraulic conductivity as well as its ability to self-heal local damage, which is almost unavoidable in the field. Over the past few decades, numerous studies have been conducted to examine the performance of GCLs, particularly in regard to hydraulic conductivity, chemical compatibility, water-swelling, self-healing capacity, diffusion characteristics, gas migration, and mechanical behavior. In this paper, a brief introduction on modern GCL products is firstly given. Subsequently, the main findings of previous publications on the critical properties influencing the long-term performance of GCLs are summarized in a comprehensive manner. Finally, further research perspectives on polymer-treated GCLs are presented. This paper provides general insights that help readers gain a state-of-the-art overview of GCLs and trends for future development.