• Title/Summary/Keyword: backfilling

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Experimental Study on Thermal Conductivity and Viscosity of Grouts for Backfilling Ground Heat Exchanger (수직 밀페형 지증 열교환기용 뒤채움재의 열전도 및 점도특성 연구)

  • Choi, Hang-Seok;Lee, Chul-Ho;Gil, Hu-Jeong;Choi, Hyo-Pum;Woo, Sang-Baik
    • 한국신재생에너지학회:학술대회논문집
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    • 2007.11a
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    • pp.529-532
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    • 2007
  • In order to characterize the thermal conductivity and viscosity of grout materials used for backfilling ground heat exchangers, nine bentonite grouts and cement grouts being adapted in the United State have been considered in this study. The bentonite grouts indicate that the thermal conductivity and viscosity increase with the content of bentonite or filler (silica sand). In addition, material segregation can be observed when the viscosity of grout is relatively low. The saturated cement grouts appear to possess much higher thermal conductivity than the saturated bentonite grouts, and the reduction of thermal conductivity in the cement grouts after drying specimens is less than in case of the bentonite grouts. Maintaining the moisture content of grouts is a crucial factor in enhancing the efficiency of ground heat exchangers.

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Predicting the Effective Thermal Conductivity of Sand-Water Mixtures Used for Grouting Materials (그라우팅 재료로 사용되는 모래-물 혼합물의 열전도도 예측)

  • Sohn, Byong-Hu;Lim, Hyo-Jae
    • Proceedings of the SAREK Conference
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    • 2008.06a
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    • pp.761-768
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    • 2008
  • This paper presents the results of a laboratory study on the thermal conductivity of sand(silica, quartzite, limestone, sandstone, granite and masonry sand)-water mixtures used in ground heat exchanger backfilling materials. Nearly 260 tests were performed in a thermal conductivity measuring system to characterize the relationships between the thermal conductivity of mixtures and the water content. The experimental results show that the thermal conductivity of mixtures increases with increasing dry density and with increasing water content. The most widely used empirical prediction models for thermal conductivity of soils were found inappropriate to estimate the thermal conductivity of unsaturated sand-water mixtures. An improved model using a exponential relationship to compute the thermal conductivity of dry sands and empirical relationship to assess the normalized thermal conductivity of unsaturated sand-water mixtures is presented.

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Development of inorganic thixotropic-grout for backfilling of shield TBM tail voids and its compatibility (쉴드 TBM 뒤채움용 무기계 가소성 그라우트의 개발 및 적합성 평가)

  • Kim, Dae-Hyun;Jung, Du-Hwoe;Jeong, Gyeong-Hwan
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.11 no.3
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    • pp.277-286
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    • 2009
  • A suitability of a thixotropic grout developed in this study has been examined through laboratory tests on strength, segregation, and viscosity. The thixotropic grout is a mixture of two types of liquid components. The A-liquid component consists of cement, water, and MG-A and the B-liquid component consists of scarlet, water, and MG-B. Unconfined compressive strength of specimens prepared with a prefer mix-proportion satisfied a design criteria for the backfilling of tail voids. A material segregation phenomenon under water condition was not observed in the thixotropic grout whereas it was observed in the existing silica-type grout. In addition, viscosity tests have been rallied out on the thixotropic grout to verify the capability of a long-distance delivery in the field. Both the A-liquid component and the B-liquid component maintained a viscosity of below 2,000 cP for 120 minutes. This experimental result confirms that two liquid components guarantees a long-distance delivery in tile field application.

Thermal Resistivity Measurement of Recycled Aggregates and Comparison with Conventional Prediction Model (송배전관로 되메움용 순환골재의 열저항 측정 및 기존 열저항 예측 모델과의 비교)

  • Wi, Jihae;Hong, Sungyun;Choi, Hangseok
    • 한국신재생에너지학회:학술대회논문집
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    • 2010.11a
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    • pp.199.1-199.1
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    • 2010
  • Use of recycled aggregates that are constituents of concrete or asphalt-based structures has become popular because the recycling is an eco-friendly way to overcome the depletion of natural aggregates. In order to adopt the recycled aggregates for backfilling a power transmission pipeline trench, their thermal resistivity should be low enough to prevent thermal runaway in the transmission system. In this study, a series of laboratory tests with QTM-500 and KD2 Pro was performed to measure the thermal resistivity of recycled aggregates prepared from various sources. Relationships between the thermal resistivity of recycled aggregates and the water content have been obtained with consideration of compaction effort. Similar to natural soils, the thermal resistivity of the recycled aggregates decreases with increasing the water content. In addition, this study compared the experimental data with conventional prediction models for the thermal resistivity in the literature, which suggests the availability of the recycled aggregates as backfill material substituting for natural aggregates when backfilling the power transmission pipeline trench.

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Laboratory Experiment to Characterize Thermal Properties of Recycled-Aggregate Backfill (실내시험을 통한 송배전관로 뒤채움재용 순환골재의 열적 특성 평가)

  • Wi, Ji-Hae;Hong, Sung-Yun;Lee, Dae-Soo;Han, Eun-Seon;Choi, Hang-Seok
    • Proceedings of the Korean Geotechical Society Conference
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    • 2010.09a
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    • pp.1231-1238
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    • 2010
  • Recently, the utilization of recycled aggregates for backfilling a power transmission pipeline trench has been increasing due to the issues of eco-friendly construction and shortage of natural aggregate resource. It is important to investigate the physical and thermal properties of the recycled aggregates that can be used as a backfill material. This study presents the thermal properties of two types of recycled aggregates with various particle size distributions. The thermal properties of the recycled aggregate were measured using the transient hot wire method and the probe method after performing the standard compaction test using an automatic compactor. Similar to silica sand, the thermal resistivity of the recycled aggregates decreased when the water content increased. This study shows that the recycled aggregate can be a promising backfill material substituting for natural aggregate when backfilling the power transmission pipeline trench.

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A study on development of the high-flowable filling material and application in the old tunnel (터널 배면공동 뒤채움재 개발과 노후터널의 적용에 관한 연구)

  • Ma, Sang-Joon;Seo, Kyoung-Won;Bae, Gyu-Jin;An, Sang-Chul;Im, Kyung-Ha
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.4 no.3
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    • pp.195-205
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    • 2002
  • Most tunnel damage such as cracks or leakage which exist in tunnel liner commonly, is caused by the cavities that exist behind the tunnel liner, through the tunnel safety inspections. These cavities were analysed to check if they affect the stability of tunnels. This study is on the development of the controlled low-strength and flowable filling material which an be applied to the cavity behind the tunnel lining. The backfilling material studied here is crushed sand and stone-dust which is in cake-state and is a by-product obtained in the producing process of aggregate. Varying the compound mixing ratio, laboratory tests of compression test and chemical analyses were carried out. In addition, the material was applied to an old tunnel for the performance assessment.

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Study on physical characteristics of grouts for backfilling ground heat exchanger (수직 밀폐형 지중 열교환기용 뒤채움재의 물리적 특성 연구)

  • Lee, Chul-Ho;Gil, Hu-Jeong;Choi, Hang-Seok;Choi, Hyo-Pum;Woo, Sang-Baik
    • Proceedings of the Korean Geotechical Society Conference
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    • 2008.03a
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    • pp.533-544
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    • 2008
  • To obtain the physical properties of grout materials, that is the thermal conductivity and viscosity, which are used for backfilling ground heat exchangers, nine bentonite grouts and cement grouts being adapted in the United State have been considered in this study. The bentonite grouts show that the thermal conductivity and viscosity increase with the content of bentonite or filler (silica sand). The saturated cement grouts appear to possess much higher thermal conductivity than the saturated bentonite grouts, and the reduction of thermal conductivity in the cement grouts after drying specimens is less than the case of the bentonite grouts. To investigate the performance of cement grouts, fifteen samples were prepared by varying the water/cement ratio and the amount of sand and bentonite added into the cement mortar. Maintaining the moisture content of grouts is a crucial factor in enhancing the efficiency of ground heat exchangers.

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An analytical solution for estimating the stresses in vertical backfilled stopes based on a circular arc distribution

  • Jaouhar, El-Mustapha;Li, Li;Aubertin, Michel
    • Geomechanics and Engineering
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    • v.15 no.3
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    • pp.889-898
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    • 2018
  • Backfilling of mine stopes with waste rocks or tailings is commonly done to enhance ground stability. It is also an alternative for mining wastes disposal. A successful application of underground backfilling requires an accurate evaluation of the stress distribution in stopes. Over the years, various analytical solutions have been proposed to assess these stresses. Most of them were based on the arching theory, considering uniform stresses across horizontal layer elements. The vertical and horizontal stresses in vertical stopes are principal stresses only along the vertical center line, but not close to the walls where there is rotation of the principal stresses. A few solutions use arc layer elements that follow the iso-contours of the minor principal stresses, based on numerical solutions. In this paper, a modified analytical solution is developed for the stresses in vertical backfilled stopes, considering a circular arc distribution. The proposed solution is calibrated with a few numerical modeling results and then validated by additional numerical simulations under different conditions.

Engineering Properties of Lightweight Foaming Grouting Materials for Underground Cavities (지반 공동의 충진을 위한 발포성 경량그라우트재의 공학적 특성)

  • Han, WooJin;Lee, Jong-Sub;Byun, Yong-Hoon
    • Journal of the Korean GEO-environmental Society
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    • v.19 no.2
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    • pp.5-12
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    • 2018
  • Underground cavities could induce road subsidence, which have been frequently observed in urban areas. Therefore, adequate backfilling materials and the restoring methods of the cavities are required to prevent the road subsidence. The objective of this paper is to evaluate the suitability of backfilling methods using foaming lightweight grouting materials considering the flow values, unit weights, and air contents at slurry and expanded states, and unconfined compressive strengths. The grouting materials consist of water, cement, and foaming agent whose proportions of water, cement, and foaming agent are 25: 25: 1.0 and 25: 25: 1.2. The flow values of the two materials are greater than 200 mm, and their unconfined compressive strengths at 28 days age are smaller than 1.3 MPa. From the results, the two proportions of materials are expected to be effectively used as a backfilling material. However, the material components should be carefully mixed because poor mix of these materials could induce non-homogeneous distribution of air bubbles. The unexpectedly non-homogeneous distribution of air bubbles may induce significant cracks or additional cavities.

Study on the Optimal Construction Method for the Compaction Method of Hydraulic Filling in Metropolitan Areas (도심지 물다짐 공법의 적정 시공방법에 관한 연구)

  • Jeong, Dal-Yeong;Jang, Jong-Hwan;Chung, Jin-Hyuck
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.21 no.2
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    • pp.175-181
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    • 2020
  • This paper suggests a proper hydraulic filling method in downtown areas. Road subsidence on roadways and sidewalks in downtown areas can result in vehicle damage and casualties. The representative cause of road subsidence is the fraudulent construction in nearby construction sites. A deficiency of excavation restoration causes approximately 25~49% of subsidence. This is performed by equipment or manpower. Hydraulic filling is used in backfilling narrow pipe conduits and spaces between structures. On the other hand, standard specifications and quality assurance standards regarding hydraulic filling principles and construction conditions are insufficient. Therefore, in-door model experiments on hydraulic filling principles, backfilling material, and compaction efficiency were performed. This paper suggests guidelines by investigating and analyzing construction status. In conclusion, thrown backfilling material has a particle size distribution and permeability coefficient as major factors, and detailed standards of the factors are suggested. To improve the compaction efficiency, 90% or more, compaction by the floor should be in units of 0.3m while ensuring a lower drainage layer. When an H-shape stabilizing pile is pulled out after filling, additional hydraulic filling should be in the disturbance range.