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Soil in situ remediation, such as washing, always produces much sludge that has the characteristics of a high fine particle proportion, high moisture content, and high metal content. Problems such as high transportation costs, large land area, and the influence on landfill capacity often occur in the process of reclamation or landfill disposal. To solve the above problems, the vacuum preloading method was used to treat the sludge. The effect of this method on reducing the water content and volume of the sludge was investigated. Initial vacuum preloading (IVP) and step vacuum preloading (SVP) laboratory experiments were carried out on the sludge from the washing waste at a heavy metal soil remediation site in Shanghai. The drainage rate and settlement rate of the sludge during the experiment were recorded, and the moisture content and unconfined compressive strength (UCS) of the sludge samples after the experiment were tested and analyzed. Finally, the mechanism of uneven water content and shear strength of sludge treated by IVP and SVP were analyzed based on the grain size distribution. The results showed that the moisture content of the sludge near the prefabricated vertical drains (PVDs) decreased to 48.55%, and its volume decreased to 41.6% of the initial volume. The UCS of the sludge near the PVDs under SVP was 20.32% higher than that under IVP. The sludge treated by the vacuum preloading method can be disposed of in a landfill or other resource utilization. [ABSTRACT FROM AUTHOR]

In China, more and more underground structures are being built close to buildings of architectural merit. When installing deep foundations, three ways of controlling seepage are suggested. In Mode III, an installed curtain extends partly into the confined aquifer so that the hydraulic connection between the excavated section and the water in the host material is partly isolated. The combined effects of pumping, curtain efficiency and recharge are discussed. Based on the engineering geological conditions of the deep foundation pit of the Yishan Road Station of Metro Line 9, Shanghai, China, in situ pumping and recharge tests were carried out. The combined effects are similar to the results obtained using a three-dimensional finite difference method (FDM) numerical simulation. [ABSTRACT FROM AUTHOR]

• Dewatering-induced drawdown and settlement is analyzed statistically. • A hydro-mechanical coupling analysis of dewatering is carried out. • Coupling results are compared to those obtained by a non-coupling formula. • Effect of a micro-confined aquifer embedded in aquitard is discussed. Groundwater withdrawn in a multi-aquifer-aquitard system (MAAS) may cause vertical cross-flow supplement and result in groundwater drawdown and soil deformation in both aquifers and aquitards. This study investigates the responses of groundwater and deep soils to dewatering in the MAAS through statistical and numerical analyses. Field data of ten pumping tests conducted in the MAAS, in Shanghai urban area are collected, and a statistical analysis for groundwater drawdown and ground settlement is performed. Field measurements indicate that the drawdowns are distributed linearly along radial distance in logarithmic coordinates. However, the ground settlements are disproportional to the drawdowns and show a trilinear distribution along the radial direction. To examine the inconsistent distributions of the groundwater drawdown and the ground settlement, representative dewatering models are developed numerically and solved explicitly by the coupled Biot's three-dimensional consolidation theory. Numerical results of dewatering in MAAS are compared to those obtained by a non-coupling formula. Moreover, effect of a micro-confined aquifer on drawdown and soil deformation is discussed. It is found that soil compression in each stratum is closely related to the decline of the pore pressure, whilst small expansions are observed in early dewatering stages. Due to the hydro-mechanical coupling effect, the ground surface settlement near the pumping well obtained by the coupled numerical method is significantly smaller than that by the non-coupling formula. Owing to horizontal and vertical cross-flow supplement, an additional aquifer embedded in aquitard above the pumping aquifer can relief both the groundwater drawdown and ground surface settlement significantly. [ABSTRACT FROM AUTHOR]