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Mechanical thermal expression (MTE) was used for dewatering two lignites, Loy Yang (LY) from Australia and Shengli (SL) from China. The dewatering process was carried out with temperatures ranging from 24°C to 240°C. It was found that the moisture content of the MTE products decreased linearly with increasing temperature, and the residual moisture content was a function of compressibility. The MTE process was more effective for the low-rank LY lignite. The characterization of the lignite includes moisture content, C/H ratio, pore volume distribution from mercury intrusion porosimetry and, coal–water interaction from low-field nuclear magnetic resonance (LFNMR). Coal–water interaction only changed slightly with mechanical compression alone. Combined with heat mechanical effect found to compress the residual moisture into smaller pores. The coal–water interaction is stronger in the smaller pores, which makes dewatering progressively more difficult. The chemical characteristics were studied by solid-state 13C NMR, where no significant changes were apparent. Total organic carbon (TOC) analysis showed higher content of organics in the LY wastewater than in the SL wastewater. The chemical composition of the wastewater was analyzed by gas chromatography–mass spectrometry (GC-MS) and it was found that the majority of the compounds from LY and SL detected were acids, accounting for more than 50% of the organic compounds, followed by aromatic hydrocarbons, accounting for 27% in LY and 38% in SL wastewater. Lower levels of alkenes, alcohols, esters, and aliphatic hydrocarbons were also found in the wastewater. [ABSTRACT FROM AUTHOR]

Excessive water in a channel is an important factor that triggers channelized debris flows. In this study, we propose a new system for the separation of water and sediment and drainage in order to drain water away from channels and reduce the potential for debris flows. The main component of the system contains a siphon drainage pool covered with an inclined perforated plate and siphon drainage pipes. The inclined perforated plate can separate sediment from the water, and the siphon drainage pipe can drain flood water quickly. To test the effectiveness of the new structure, a field experiment was developed and tested in a small catchment in which debris flow was an issue. The experimental results showed that the drainage pool effectively decreased the maximum depth of the flow in the triggering area, thereby avoiding the occurrence of debris flow. To set the optimize design parameters of the pool, three main design parameters were evaluated, i.e., peak discharge during storms, separation ability of drainage pool, and the maximum depth of surface flow in the triggering areas. The peak discharge was obtained by using the NAM model and a rational formula, and the NAM model provided more accurate results. The results of the calculation of the separated ratio showed large runoff volumes and a lower separated ratio. The results of the NAM model were used to simulate the maximum depth of flow using the FLO-2D model. [ABSTRACT FROM AUTHOR]

Taking the deep excavation engineering of an office building for example, the key technology of design, construction and monitoring for the deep excavation project close to existing running tunnels of track traffic was discussed. The cautions in the construction process were also introduced. The results can provide the reference for other similar projects in Suzhou. [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]

Abstract: An account is given of the use of geotextile tubes to dewater dredged contaminated sediments at the Tianjin Eco-City site in China. Approximately 5 million m3 of contaminated sediments from the bed of a lake were dredged and dewatered in this way with the effluent water returned to the lake. The dewatered solids were utilized within the project site, or were disposed of in a landfill, depending on their degree of contamination. The paper details the tube dewatering evaluation process undertaken and presents the results on which the dewatering facility was designed. To enable an assessment of the full-scale dewatering performance various relationships were derived based on a conservation of mass of the dewatering process. The design, construction and operation of the dewatering tube facility for the treatment of the moderately contaminated sediment waste stream is also presented. [Copyright &y& Elsevier]

Coalfields in North China encompass more than ten Provinces. They contain six to seven coal seams in the Permo-Carboniferous strata. The lower three seams account for 37% of the total reserves and are threatened with intrusion of karst water from the underlying Ordovician limestone. Hundreds of water inrush incidences have occurred, in which a large amount of water suddenly flows into tunnels or working faces under high potentiometric pressure. Over 50 mines have been flooded over the last 30 years. Large-scale dewatering or depressurizing of the karst aquifer was considered essential to avoid water inrushes and keep the mines safely operational. This practice, however, has caused sinkholes, dry springs, water supply shortage, and groundwater contamination in the surrounding areas. One alternative water control measure is to make full use of the rock layer between the coal seam and the karst aquifer as a protective barrier to prevent or constrain water flow from the underlying aquifer into the mines. Grouting is effective when the hydrogeological conditions are favorable to this technique. Proper design of the grouting program and experience of the contractor are also important for a successful application. [ABSTRACT FROM AUTHOR]

This study comprehensively analyzes the environmental risk of heavy metals (HMs) in the dewatering process of dredged sediment. First, the toxicity leaching capacity, total content, and chemical speciation of the HMs (As, Cd, Co, Cr, Cu, Hg, Mo, Pb, Sb, Sr, Tl, Zn) in dewatered sediment were determined using toxicity characteristic leaching procedure and modified Community Bureau of Reference sequential extraction procedure. The ecotoxicity and environmental risk of the HMs were then evaluated based on sediment quality guidelines, geo-accumulation index, enrichment factor, potential ecological risk, and risk assessment code. The results showed that flocculants reduced the ecological risk of Hg and Mo in sediment, and promoted the transformation of Mo, Sb, and Tl from the biologically active fraction to the more stable fraction. The transformation percentages of Mo, Sb, and Ti were 45.15%, 50.59% and 76.44%, respectively, after chitosan (CTS) treatment, and 64.55%, 31.75% and 99.90%, respectively, after cationic polyacrylamide (CPAM) treatment. CTS reduced the potential risks of bioavailable As, Cr, Cu, Mo, Sb, and Hg by (at most) 46.28%, 45.92%, 43.01%, 100.00%, 44.45%, and 39.69%, respectively, whereas CPAM decreased the ecotoxicity of bioavailable Cd, Co, and Zn by (at most) 27.49%, 16.10%, and 20.89%, respectively. According to the result of principal component analysis, the main factors affecting the environmental risk of HMs in sediment dewatering were nitrogenous organic compounds (mainly protein substances), fulvic acid substances, and minerals. The most essential factor was nitrogenous organic compounds, which accounted for 89.52% of the total variance. Chemical speciation was apparently more suitable for environmental risk assessment of sediment dewatering than total content. This study provides an important basis for controlling the environmental risk of HMs caused by sediment dewatering., (Copyright © 2021 Elsevier Ltd. All rights reserved.)