• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
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• pp.579-582
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• 2009

The thermal conductivity and viscosity(or workability) of graphite-added bentonite grouts and cementitious grouts have been evaluated and compared to determine the suitability of these materials for backfilling vertical boreholes of ground heat exchangers. Seven bentonite grouts from different product sources and a portland cement grout with various mixture ratios were considered in this paper. As a new additive for grout, we choose graphite which has high thermal conductivity. The bentonite grouts indicate that the thermal conductivity and viscosity increase with the content of bentonite or with an addition of Graphite compared with that of silica sand. In case of cementitious grout also increase the thermal conductivity and decrease the workability dramatically though an addition of Graphite. Therefore, we cautiously select the amount of graphite and mixture ratio of bentonite and cement considering not only thermal conductivity but also viscosity for the optimum condition of backfilling material.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회
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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.

• 신재생에너지
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• 제3권4호
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• pp.38-46
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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 the case of the bentonite grouts. Maintaining the moisture content of grouts is a crucial factor in enhancing the efficiency of ground heat exchangers.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 추계학술대회 논문집
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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.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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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.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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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.

• Journal of Advanced Research in Ocean Engineering
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• 제2권2호
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• pp.86-98
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• 2016

In this study, after the installation of a subsea pipeline, backfilling was performed in the trenched area. During these operations, a stability problem in the subsea pipeline occurred. The pipeline was directly impacted by environmental loading such as waves and currents that were caused by backfill material when scouring or sediment transport and siltation was carried out. Therefore, this study reviewed whether trenching was necessary, and conducted research into an indigenous seabed property that contains granular soil. A study of cohesive soil was also conducted in order to cross-correlate after calculating the values of the critical Shields parameter relevant to elements of the external environment such as waves and current, and the shear Shields parameter that depends on the actual shearing stress. In case of 1), sedimentation or erosion does not occur. In the case of 2), partial sedimentation or erosion occurs. If the case is 3), full sedimentation or erosion occurs. Therefore, in the cases of 1) or 2), problems in structural subsea pipeline stability will not occur even if partial sedimentation or erosion occurs. This should be reflected particularly in cases with granular and cohesive soil when a reduction in shear strength occurs by cyclic currents and waves. In addition, since backfilling material does not affect the original seabed shear strength, a set-up factor should be considered to use a reduced of the shear strength in the original seabed.

• 한국터널지하공간학회 논문집
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• 제11권3호
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• pp.277-286
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• 2009

본 연구는 쉴드 TBM 테일 보이드 동시주입용 가소성 그라우트의 적합성을 규명하기 위하여 강도특성, 수중 재료분리현상 및 점도특성 실험을 실시하였다. 무기계 가소성 그라우트는 쉴드 TBM 뒤채움 그라우트 주입 시 시멘트, 물, MG-A로 구성된 A액과 스칼렛, 물, MG-B로 구성된 B액을 주입하는 2액성 그라우트 주입공법이다. 적정 배합비로 제작된 무기계 가소성 그라우트의 일축압축강도는 초기강도 및 장기강도 기준을 만족하는 결과를 보였다. 지하수가 존재하는 현장에서 그라우트 주입 시 발생하는 재료분리현상을 관찰하기 위하여 기존 현장에서 적용된 규산계 그라우트와 무기계 가소성 그라우트를 비교하였으며, 그 결과 규산계 그라우트에서 발생하는 재료분리 현상이 무기계 가소성 그라우트에서는 관찰되지 않았다. 또한 무기계 가소성 그라우트의 장거리 이송에 대한 현장 적용성을 확인하기 위하여 A, B액의 점도를 측정한 결과 A, B액 모두 120분 이상 2000 cP 이하가 측정되었다. 이러한 결과는 추후 현장적용 시 A, B액의 원활한 이송이 가능한 점도를 확보하고 있음을 확인하였다.

• Geomechanics and Engineering
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• 제18권4호
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• pp.407-415
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• 2019

A controlled low strength material (CLSM) is a highly flowable cementitious material used for trench backfilling. However, when applying vertical loads to backfilled trenches, shear failure or differential settlement may occur at the interface between the CLSM and natural soil. Hence, this study aims to evaluate the characteristics of the interface friction between the CLSM and soils based on curing time, gradation, and normal stress. The CLSM is composed of fly ash, calcium sulfoaluminate cement, sand, silt, water, and an accelerator. To investigate the engineering properties of the CLSM, flow and unconfined compressive strength tests are carried out. Poorly graded and well-graded sands are selected as the in-situ soil adjacent to the CLSM. The direct shear tests of the CLSM and soils are carried out under three normal stresses for four different curing times. The test results show that the shear strengths obtained within 1 day are higher than those obtained after 1 day. As the curing time increases, the maximum dilation of the poorly graded sand-CLSM specimens under lower normal stresses also generally increases. The maximum contraction increases with increasing normal stress, but it decreases with increasing curing time. The shear strengths of the well-graded sand-CLSM interface are greater than those of the poorly graded sand-CLSM interface. Moreover, the friction angle for the CLSM-soil interface decreases with increasing curing time, and the friction angles of the well-graded sand-CLSM interface are greater than those of the poorly graded sand-CLSM interface. The results suggest that the CLSM may be effectively used for trench backfilling owing to a better understanding of the interface shear strength and behavior between the CLSM and soils.

• 한국지반환경공학회 논문집
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• 제19권2호
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• pp.5-12
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• 2018

최근 도심지 지역에서 도로함몰로 이어질 수 있는 지반 내 공동의 탐사를 수행하고 있으며, 도로함몰을 방지하기 위하여 지반 내 공동의 적절한 충진이 요구되고 있다. 본 논문에서는 발포성 경량그라우트재에 대하여 플로우 시험, 팽창 전후의 단위중량 및 공기량 측정, 그리고 일축압축강도 시험을 수행하여 공동 충진의 적합성과 공학적 특성을 평가하고자 하였다. 배합 재료는 물, 시멘트, 발포제를 사용하였으며, 발포제의 비율을 조절하여 두 가지 배합비로 조성된 시료에 대한 공학적 특성을 평가하였다. 각각의 시험 결과, 두 배합비 모두에서 플로우 값이 200mm 이상인 것으로 측정되고, 28일 일축압축강도가 1.3MPa 이하로 측정되어, 두 배합은 유동성 및 강도의 측면에서 공동 충진에 적합한 재료로 평가되었다. 단, 배합 시 물과 발포제가 충분히 혼합되지 않는 경우 재료 내부에 존재하는 기포가 불균질하게 분포될 수 있으므로 물과 발포제의 혼합 시 주의가 필요하다.