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Impact of clay particle reattachment on suffusion of sand-clay mixtures

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第10期15卷 2720-2730页

作者： Jongmuk Won Yongjoon Choe Yerim Yang hangseok choi Department of Civil and Environmental Engineering University of UlsanDaehak-ro 93Nam-guUlsan680-749South Korea School of Civil Environmental and Architectural EngineeringAnam-dong 5-gaKorea UniversitySeoul136-713South Korea

The detached clay particles directly filtrated through the sand-clay mixture lead to suffusion;however,if the detached clay particles are subjected to reattachment,the degree of suffusion may be less *** study investigates the impact of clay particle reattachment on suffusion of sand-clay mixtures through laboratory soil-column *** observed breakthrough curves(BTCs)of kaolinite,illite,and montmorillonite for 5 different column lengths(3 in,6 in,9 in,12 in,and 18 in;1 in=2.54 cm)indicated that a higher breakthrough concentration was observed as the column length(L)decreased for kaolinite and illite,whereas a reverse trend was observed for *** addition,the increase in the fraction of filtrated clay particles(Me)with an increase in L(Me=10.42%for L=3 in and Me=3.59%for L=18 in)for the sand-illite mixture indicated that the reattachment effect became more significant as the travel length of detached clay particles *** observed BTCs,retention profiles after injection,and fraction of filtrated clay presented herein suggest the need to incorporate the reattachment effect when assessing the suffusion of clay-containing soils.

关键词： Suffusion Reattachment Sandeclay mixture Ionic concentration Column length

Applicability of cement-based grout for ground heat exchanger considering heating-cooling cycles

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Science China(Technological Sciences) 2011年第7期54卷 1661-1667页

作者： Moonseo PARK SunhongMIN Jeehee LIM Jong Min choi hangseok choi School of civil Environmental and Architectural Engineering Korea University Seoul Republic of Korea Department of Mechanical Engineering Hanbat National University Daejeon Republic of Korea

The applicability of cement grout （or cement-based grout） has been considered as an alternative to bentonite grout commonly used to backfill closed-loop vertical ground heat exchangers. In a geothermal heat pump system, repeated heating-cooling cycles may cause adverse effects on the integrity of cement grout in the ground heat exchanger. To account for the temperature cycling effect, the strength degradation of cement grout due to temperature cycling has been examined by measuring the unconfined compression strength of cured specimens in a humidity-temperature controlling chamber with applying temperature cycles between -5℃ and 50℃. There is a tendency that the unconfined compression strength decreases with an increase in the number of temperature cycles. On the other hand, an equivalent hydraulic conductivity of a pipe-embedded cement grout specimen was evaluated by carrying out a modified flexible wall permeameter test equipped with a water circulating system to control temperature inside the pipe section. The applied operating temperature range was from 5 to 35℃. After three cycles of heating-cooling circulation, the equivalent hydraulic conductivity becomes asymptotic to a constant value, which implies there is no severe detachment of the pipe from the cement grout.

关键词： cement grout bentonite grout thermal conductivity workability equivalent permeability coefficient

Numerical characterization of heat transfer in closed-loop vertical ground heat exchanger

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Science China(Technological Sciences) 2010年第1期53卷 111-116页

作者： Chulho LEE Hujeong GIL hangseok choi Shin-Hyung KANG School of Civil Environmental and Architectural EngineeringKorea University5-GaAnam-DongSeongbuk-GuSeoul 136-713Republic of Korea Pyungsan SI Co. Ltd.1337-31 Seocho-DongSeocho-GuSeoul 137-860Republic of Korea Department of Mechanical Engineering Konyang University119Deahak-RoNonsanChungnam 320-711Republic of Korea

A series of numerical analyses has been performed on the characteristics of heat transfer in a closed-loop vertical ground heat exchanger(U-loop).A 2-D finite element analysis was conducted to evaluate the temperature distribution over the cross section of the U-loop system involving high-density polyethylene(HDPE) pipe/grout/soil to compare the sectional efficiency between the conventional U-loop and a new latticed HDPE pipe system,which is equipped with a thermally insulating lattice in order to reduce thermal interference between the inlet and outlet *** addition,a 3-D finite volume analysis(FLUENT) was adopted to simulate the operation of the closed-loop vertical ground heat exchanger with the consideration of the effect of a distance between the inlet and outlet pipes,grout's thermal properties,the effectiveness of the latticed HDPE pipe system,and the rate of circulation *** was observed that the thermal interference between the two strands of U-loop is of importance in enhancing efficiency of the ground heat ***,it is recommended to modify the configuration of the conventional U-loop system by equipping the thermally insulating lattice between the two pipe strands.

关键词： ground heat exchanger HDPE pipe latticed pipe sectional efficiency

Numerical simulation for thermal response test performance in closed-loop vertical ground heat exchanger

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Science China(Technological Sciences) 2011年第7期54卷 1668-1673页

作者： choi Jong Min LEE Chulho PARK Moonseo KANG Shin-Hyung choi hangseok Department of Mechanical Engineering Hanbat National University School of Civil Environmental and Architectural Engineering Korea University Department of Mechanical Engineering Konyang University

In this study, a series of numerical analyses was performed in order to evaluate the performance of full-scale closed-loop vertical ground heat exchangers constructed in Wonju, South Korea. The circulating HDPE pipe, borehole and surrounding ground formation were modeled using FLUENT, a finite-volume method (FVM) program, for analyzing the heat transfer process of the ground heat exchanger system. Two user-defined functions (UDFs) accounting for the difference in the temperature of the circulating inflow and outflow fluid and the variation of ground temperature with depth were adopted in the FLUENT modeling. The thermal conductivities of grouts (cement vs. bentonite) measured in laboratory were used as input values in the numerical analyses to compare the thermal efficiency of the cement and bentonite grouts used for installing the closed-loop vertical ground heat exchanger. A series of numerical analyses was carried out to simulate in-situ thermal response tests performed in the construction site. From the comparison between the in-situ thermal response test results and numerical simulations, the average thermal conductivity of the ground formation in the construction site is back-calculated as approximately 4 W/mK. This value can be used in evaluating the long-term performance of the closed-loop vertical ground heat ex changer.

关键词： closed-loop vertical ground heat exchanger cement grout bentonite grout in-situ thermal response test finite-volumemethod thermal conductivity