• Nuclear Engineering and Technology
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• v.27 no.4
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• pp.582-590
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• 1995

우리 나라에서 건설될 중저준위폐기물 처분장의 기본설계개념에 따르면, 중준위폐기물 동굴에는 점토질 뒷채움재가 설치될 예정이다. 이 뒷채움재의 후보물질로는 원료 입수의 용이성 및 경제성 측면에서 천연점토와 분쇄암석의 혼합물이 고려되고 있다. 그러나 이 혼합물이 폐기물처분장의 뒷채움재로 사용되기 위해서는 주요특성들이 뒷채움재의 요구사항을 만족시켜야한다. 이 보고서에서는 경상북도 연일지역에서 산출되는 천연점토와 분쇄암석 혼합물에 대해 핵종유출저지 관점에서 가장 중요한 특성인 수리특성과 방사성핵종 확산특성 및 역학적 특성을 측정하여 뒷채움재료로서의 사용 가능성을 평가하였다. 혼합물의 수리전도도는 동일 밀도에서 점토함량이 감소함에 따라 증가되었으나, 점토함량이 적은 경우에도 상당히 낮은 값을 유지하여 뒷채움재를 통한 핵종이동의 주요 메커니즘은 확산이 될 것이라는 것을 보여주었다. 압축점토에 대한 방사성핵종 복산계수 측정결과, 동일밀도의 나트륨벤토나이트에서 측정된 값의 범위 내에 있었으며, 점토-분쇄암석 혼합물의 액소성한계, 다짐특성, 압축강도및 압밀계수등의 역학적 특성도 나트륨벤토나이트-모래 혼합물에서 얻어진 값과 유사하였다. 이러한 결과들로부터 연일산 천연점토-분채암석 혼합물을 고가의 나트륨벤토나이트 대용으로 처분장 뒷채움재로 사용할 수 있다는 것을 알 수 있었다.

• Journal of the Korean GEO-environmental Society
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• v.10 no.7
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• pp.33-41
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• 2009

In the case of underground power utilities pipe such as circular pipe, the most difficult problem is low compaction efficiency of the bottom of pipe inducing the failure of utilities. To overcome this problem, various studies have been performed and one of these is CLSM (controlled low strength materials) accelerated flow ability. CLSM has already been stage of commercial use in the foreign countries led by power company. In this study, we estimated the behavior of flexible pipe with flowable backfill materials and sand to compare on the DB24 load. The results showed that the deformation of flexible pipe is affected by types of backfill materials. CLSM shows better behavior characteristics than compacting sand. But numerical and analytical results that peformed to compare to the field test results showed big gap with the field results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5C
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• pp.303-312
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• 2006

This study is to evaluate the mechanical characteristics of flowable backfill and offer a guide line of mixture proportion based on soil types for constructing underground power utilities. Flowable backfill is known as soil-cement slurry, void fill, and controlled low-strength material(CLSM). The benefits of CLSM are reduced equipment costs, faster construction, re-excavation in the future, and the ability to place materials in confined spaces, which are narrow parts or perimeters of underground power cables nearly impossible for compaction. The flowable slurry mixed with 17 soils and 6 accelerated mixtures in the laboratory were evaluated for flowability and unconfined compressive strength to meet the target values of this study.

• Tunnel and Underground Space
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• v.24 no.6
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• pp.405-417
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• 2014

In a high-level waste repository, the gap fill of the engineered barrier is an important component that influences the performance of the buffer and backfill. This paper reviewed the overseas status of R&D on the gap fill used engineered barriers, through which the concept of the gap fill, manufacturing techniques, pellet-molding characteristics, and emplacement techniques were summarized. The concept of a gap fill differs for each country depending on its disposal type and concept. Bentonite has been considered a major material of a gap fill, and clay as an inert filler. Gap fill was used in the form of pellets, granules, or a pellet-granule blend. Pellets are manufactured through one of the following techniques: static compaction, roller compression, or extrusion-cutting. Among these techniques, countries have focused on developing advanced technologies of roller compression and extrusion-cutting techniques for industrial pellet production. The dry density and integrity of the pellet are sensitive to water content, constituent material, manufacturing technique, and pellet size, and are less sensitive to the pressure applied during the manufacturing. For the emplacement of the gap fill, pouring, pouring and tamping, and pouring with vibration techniques were used in the buffer gap of the vertical deposition hole; blowing through the use of shotcrete technology and auger placement and compaction techniques have been used in the gap of horizontal deposition hole and tunnel. However, these emplacement techniques are still technically at the beginning stage, and thus additional research and development are expected to be needed.

• Journal of the Korean Geotechnical Society
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• v.17 no.6
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• pp.163-171
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• 2001

It is important to pay careful attention to the backfill construction for the structural integrity of concrete box culvert. To increase the structural integrity of culvert good compaction by the dynamic compaction roller with big capacity is as effective as good backfill materials. However structural distress of the culvert could be occurred due to the excessive earth pressure by great dynamic compaction load. In this study, two box culverts were constructed with change compaction materials and construction methods. Two type of on-site soils such as subbase and subgrade materials were used as backfill materials. In most case, dynamic compaction rollers with 11 to 12 ton weights were used and vibration frequency were applied from 2000 to 2500 rpm for the great compaction energy. Backfill compactions with good quality soils were carried out to examine the effect of cushions on dynamic lateral soil pressure. Expanded polystyrene (EPS) and rubber of tire were adapted as cushion materials and they are set on the culverts before backfill construction. This paper presents the main results on the characteristics of dynamic earth pressures. Test result indicates that the amounts of increased dynamic pressures are affected with backfill materials, depth of pressure cell, and compaction condition. The earth pressure during compaction can give harmful effect to box culvert because the value of dynamic earth pressure coefficient $(\DeltaK_{dyn}=\DeltaK\sigma_h\DeltaK\sigma_v)$ during compaction is greater than that of static condition. It was observed that cushion panels of EPS(t=10cm) and rubber(t=5cm) are effective to mitigate dynamic lateral pressure on the culverts.

• Clean Technology
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• v.24 no.4
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• pp.315-322
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• 2018

Industrial use of waste oyster shells is limited because of requiring excessive energy for converting natural oyster shells in the form of calcium carbonate ($CaCO_3$) into calcium oxide (CaO) for this purpose. This study aimed to develop energy-saving process for producing solidifying agent using waste oyster shells for backfill materials. It was suggested that oyster shells were converted to calcium sulfates which were mixed with sodium hydroxide solution and red clay, forming solid specimen. The optimal concentrations of sulfuric acid for sulfation of oyster shell and sodium hydroxide to generate calcium hydroxide ($Ca(OH)_2$), were determined. Unconfined compressive strength of solid specimen increased with increasing the content of solidifying agent while it increased also with increasing ratio of natural oyster shells to coal ash. The result clearly demonstrates that solidifying agent consisting of sulfuric acid-treated oyster shell, coal ash, and sodium hydroxide solution, can be effectively utilized for preparing backfill materials using natural oyster shell and coal ash. Sulfuric acid-treated oyster shell-based solidifying agent has not been previously developed and will contribute to broaden industrial application of waste oyster shells.

• Journal of the Korean GEO-environmental Society
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• v.7 no.6
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• pp.67-73
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• 2006

In this study, basic physical tests and mechanical tests of crushed rock were performed in order to investigate the field application of crushed rock as substitute materials of sand that is commonly being used as foundation and backfill materials of sewer conduit. Particle-size distribution curve of crushed rock is similar to sand and also it is well-graded soil than common sand. Maximum dry unit weight in proctor compaction test for crushed rock is higher than the values of common sand. So we can estimate that the crushed rock has advantages in workability than sand for the backfill compaction after construction of sewer conduit. When we investigate the results of direct shear test and triaxial compression test on the crushed rock, it has a similar value of shear strength parameters to sand at the same stress state and as time goes by, it tends to increase the unconfined compression strength. But, because the strength reaches at the constant value after 6~7 days, we expect that it can absorb the lateral strain of flexible conduit well. All the above experimental results just proves that crushed rock can substitute for sand as backfill materials and foundation of sewer conduit.

• Clean Technology
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• v.19 no.4
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• pp.423-429
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• 2013

This study aimed to develop flowable backfill material using oyster shell, coal ash, and surplus soil. The high temperature (> $800^{\circ}C$) reaction was required to convert $CaCO_3$ to CaO. The solid specimens formed by pozzlanic reaction between CaO and coal ash showed low unconfined compressive strength. The effect of kaolin and blast furnace slag was also examined. It was found that CaO and coal ash could not be utilized due to high cost and low performance. The use of oyster shell without calcination ($CaCO_3$) was evaluated. The specimens composing of oyster shell and cement showed the higher unconfined compressive strength than that composing of coal ash and cement. However, use of oyster shell is limited in mortar due to the presence of salt. Addition of soil into oyster shell-coal ash-cement mixture satisfied the specification of flowable backfill material by optimizing their ratio.

• Journal of the Korean Geotechnical Society
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• v.22 no.2
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• pp.29-39
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• 2006

In the companion paper (Paik 2006), a new formulation for calculating the nonlinearly distributed active earth pressure acting on a caisson backfilled with crushed rock and sand is proposed, and it takes into account arching effects as well as difference in internal friction angles and unit weights between sand and crushed rock. In this study, in order to partially check the accuracy of the proposed equation, the results of the proposed equation are compared with the equation proposed by Paik (2003a) for caissons with rough surface and homogeneous backfill, and are compared with results of Rankine's theory for caissons with smooth surface and homogeneous backfill. In addition, a parametric study is performed to investigate the effect of $phi_{r}$, $phi_{s}$, $\delta_{r}$, $\gamma_{r}$, $\gamma_{s}$ and $\beta$ on the magnitude of active earth pressure acting on the caisson, and construction methods for minimizing active earth pressure on the caisson are also provided based on the results of a parametric study.

• Tunnel and Underground Space
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• v.20 no.4
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• pp.284-291
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• 2010

In the present design concept of a high-level waste repository, the bentonite and bentonite-sand mixture are considered as the buffer and backfill material. For the Kyungju bentonite which is a candidate material, the thermal conductivities of compacted bentonite and bentonite-sand mixture were measured. A correlation has been proposed to predict the thermal conductivity of the Kyungju bentonite and the bentonite-sand mixture as a function of the dry density, the water content and the sand fraction. The proposed correlation can predict the thermal conductivity with a difference less than 10% under the experimental conditions.