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Zhang G.,Nanjing Southeast University | Zhang G.,Jiangsu Key Laboratory of Urban Underground Engineering and Environmental Safety | Xia C.,Tongji University | Zhao X.,Beijing University of Technology | Zhou S.,Tongji University
Applied Thermal Engineering | Year: 2016

A tunnel lining ground heat exchanger (GHE) uses surrounding rock as heat source and transfers heat through absorber pipes buried in the tunnel lining. In order to evaluate the effect of ventilation on the thermal performance of tunnel lining GHEs, thermal response field tests considering ventilation were performed in Linchang tunnel, and a 3D numerical model of tunnel lining GHEs was built and verified with the field monitoring data. The study results show that (i) the ventilation has a significant influence on the temperature field of surrounding rock; (ii) the heat exchange rate rises exponentially as convective heat transfer coefficient (CHTC) increases, and it increases significantly with the decreasing thickness of secondary lining; (iii) the heat exchange rate presents a linear variation as the inlet temperature increases, the growth gradient of the heat exchange rate rises exponentially as the CHTC increases and decreases gradually with the running time increase. © 2015 Elsevier Ltd. All rights reserved. Source


Liu S.-Y.,Jiangsu Key Laboratory of Urban Underground Engineering and Environmental Safety | Liu S.-Y.,Nanjing Southeast University | Li C.,Jiangsu Key Laboratory of Urban Underground Engineering and Environmental Safety | Li C.,Nanjing Southeast University
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2015

The carbonated deep mixing method is an innovative CO2 consuming method for ground improvement, in which the MgO binder is firstly mixed with the soft soils and then CO2 is injected for carbonating in few hours. Using the carbonated mixing method, higher soil-MgO stabilized strength can be obtained in very short time. The influence of MgO activity on the stabilization efficiency and its mechanism were studied in this paper. A typical clay from Wuhan was used as the target soil and three different activities of MgO were selected as binders for laboratory tests. The results show that the carbonated degree with different active MgO binders can be predominantly completed in 3~6 hours and reaches stability after 24 hours. There are almost the same volume expansion of about 16% during carbonating process at all MgO binders. While the MgO activity has significant influences on the efficiency of the carbonated mixing method. With the higher activity MgO binder, the higher carbonated degree and more carbonated products forming denser texture are observed. Its unconfined compressive strength after carbonating 6 hours with higher activity MgO gets to the similar strength of 28 day-cured cement-stabilized soils. The final strength with higher activity MgO carbonated mixing soils can reach 2.5 MPa, while that with much lower activity MgO is only 0.5 MPa. The carbonated MgO-stabilized soils have considerable lower pH value (9.0~9.6) than the pH value (12) of the cement-stabilized soils. ©, 2014, Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering. All right reserved. Source


Chen W.,Nanjing Southeast University | Chen W.,Jiangsu Key Laboratory of Urban Underground Engineering and Environmental Safety | Zhu Z.,Nanjing Southeast University | Zhu Z.,Jiangsu Key Laboratory of Urban Underground Engineering and Environmental Safety | Li L.,Hohai University
Shuili Xuebao/Journal of Hydraulic Engineering | Year: 2015

COD (Chemical Oxygen Demand) is one of the important indexes of landfill leachate. The shale is a kind of mineral with a high specific surface area, which potentially can retain the COD from leachate. Sorption experiments were conducted to compare the absorptive performance of the crushed shale with different grain size with that of, clay, ash and bentonite. The result showed that the crushed shale with the grain size of 0.075~2.0 mm displayed higher sorption rate for COD than the others. The hydraulic conductivity tests showed that the permeability of the mixes of crushed shale and clay was less than 1×10-7 cm/s, which meets the demand of the hydraulic conductivity of liner, when the ratio of the added shale was less than 10%. ©, 2015, Shuili Xuebao/Journal of Hydraulic Engineering. All right reserved. Source


Deng Y.,Nanjing Southeast University | Deng Y.,Jiangsu Key Laboratory of Urban Underground Engineering and Environmental Safety | Yue X.,Nanjing Southeast University | Yue X.,Jiangsu Key Laboratory of Urban Underground Engineering and Environmental Safety | And 5 more authors.
Engineering Geology | Year: 2015

Metakaolin (MK), widely used for high-performance concrete admixtures, is introduced into improving the percolation behaviors of cement-stabilized soft clays, which is a key performance when analyzing the permeability and consolidation in the grounds modified by deep mixing methods etc., the underground water seepage and the migration of pollutants in waterproof curtains by grouting methods etc. To investigate MK effect on the hydraulic conductivity of cement stabilized soils, the flexible wall permeameter was developed and mercury intrusion porosimetry (MIP) tests were performed. The results show that the addition can reduce the hydraulic conductivity 10-100 times when MK content arrives at 3% to 5%, which attributes to less total porosity and pore diameter. As the cement stabilized soils not only belong to a kind of special soils in geotechnical engineering, but also belong to cement-based reinforced materials, it is further discussed whether the unique expression of the hydraulic conductivity of these porous materials (clay, cement stabilized soils, cement pastes and concretes) existed. The results present that there is a good correlation between the hydraulic conductivity, the void ratio and median throat pore diameter for each kind of materials from clays to concretes respectively, and the hydraulic conductivity qualitatively increases with the void ratio and median throat pore diameter whatever clays, cemented soils and pastes or concretes. After several attempts, the combined variable nD502 was adopted to normalize the macro and micro characterization of porosity, and the relatively unique relation depicting the hydraulic conductivity of these materials was proposed. © 2015 Elsevier B.V. Source


Zhang D.-W.,Nanjing Southeast University | Zhang D.-W.,Jiangsu Key Laboratory of Urban Underground Engineering and Environmental Safety | Cao Z.-G.,Nanjing Southeast University | Cao Z.-G.,Jiangsu Key Laboratory of Urban Underground Engineering and Environmental Safety | And 3 more authors.
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2015

In order to explore the application potential of electrical resistivity method in the field of solidified heavy metal-contaminated soils, the artificial contaminated soils with five different lead contents are solidified using cement, and then their electrical resistivities and unconfined compressive strengths after various curing periods are tested. The relationship between the electrical resistivity and unconfined compressive strength is discussed. The test results show that the cement hydration reaction results in an increase of the electrical resistivity of solidified samples, but the electrical resistivity decreases with the increase of after-curing porosity, degree of saturation and lead content. A key parameter (nt·e100wPb)/ (aw·T0.5) (e is the Euler's number) is proposed to comprehensively reflect the effects of the lead content, cement hydration reaction and dense state of soils on the electrical resistivity of solidified soils. The Archie's electrical resistivity formula is extended to solidified heavy metal-contaminated soils by replacing the porosity by the key parameter. There is a power function relationship between the strength and the electrical resistivity while the lead content of solidified soils is certain. The electrical resistivity method can be used as a non-destructive, economical and continuous way to evaluate the quality of solidified heavy metal-contaminated soils. ©, 2015, Chinese Society of Civil Engineering. All right reserved. Source

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