• Title/Summary/Keyword: backfill

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Assessment of Equivalent Heights of Soil for the Lateral Earth Pressure Against Retaining Walls Due to Design Truck Load (표준트럭하중에 의해 옹벽에 작용하는 수평토압의 등가높이 산정)

  • Kim, Duhwan;Jin, Hyunsik;Seo, Seunghwan;Park, Jaehyun;Kim, Dongwook;Chung, Moonkyung
    • Journal of the Korean Geosynthetics Society
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    • v.17 no.4
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    • pp.119-128
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    • 2018
  • Limit state design has been implemented in Korea since 2015; however, there exists no specification of lateral load determination on retaining wall due to the Korean standard traffic load on retaining wall's backfill surface. The lateral load from traffic depends on lane number, standard truck's axle loads and locations, loading distance from the inner wall. The concept of equivalent height of soil accounting for traffic loadings is typically used for design of retaining walls to quantify the traffic loads transmitted to the inner wall faces. Due to the different characteristics of the standard design trucks between Korea and US (AASHTO), the direct use of the guidelines from AASHTO LRFD leads to incorrect estimation of traffic load effects on retaining walls. This paper presents the results of evaluation of equivalent height of soil to reflect the Korean standard truck, based on the findings from analytical solutions using Bounessq's theory and numerical assessment using 2D finite element method. Consequently, it was found that the equivalent heights of soil from the Korean standard truck load were lower for lower retaining wall height.

Properties Evaluation and flowability of Controlled Low Strength Materials Utilizing Industrial By-Products (산업부산물을 활용한 저강도 고유동 채움재의 유동성 및 물성평가)

  • Cho, Yong-Kwang;Kim, Chun-Sik;Nam, Seong-Young;Cho, Sung-Hyun;Lee, Hyoung-Woo;Ahn, Ji-Whan
    • Journal of Energy Engineering
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    • v.27 no.4
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    • pp.64-69
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    • 2018
  • The purpose of this study is to expand the use of coal ash and coal slag in thermal power plants. In addition, controlled low strength materials was developed to prevent mine settlement. Bottom ash and KR slag are mixed at ratio of 7:3 to expand the use of industrial by-products through carbonate reaction and inhibit the exudation of heavy metals. In order to efficiently fill the abandon mine, workability and physical properties were evaluated according to flow. As a result of elution of harmful substance experiment, it was confirmed that the carbonation reaction inhibited the elution of heavy metals. It was confirmed that the difference in water ratio was the difference in specific surface area of the controlled low strength materials. It was confirmed that the working efficiency is excellent when the flowability is 300mm compared to 260mm. compressive strength measurement result was relatively high at 260mm compared to 300mm because the number of pores due to decrease of water ratio was small.

Effects of Excavation Damaged Zone on Thermal Analysis of Multi-layer Geological Repository (다층 심지층처분장 열해석에 미치는 암반손상대의 영향)

  • Cho, Won-Jin;Kim, Jin-Seop;Kim, Geon Young
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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    • v.17 no.1
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    • pp.75-94
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    • 2019
  • As the present single-layer repository concept requires too large an area for the site of the repository, a multi-layer repository concept has been suggested to improve the disposal density. The effects of the excavation damaged zone around the multi-layer repository constructed in the deep host rock on the temperature distribution in the repository were analyzed. For the thermal analysis of the multi-layer repository, the hydrothermal model was used to consider the resaturation process occurring in the buffer, backfill and rock. The existence of an excavation damaged zone has a significant effect on the temperature distribution in the repository, and the maximum peak temperatures of double-layer and triple-layer repositories can rise to $7^{\circ}C$ and $12^{\circ}C$, respectively depending on the size of the excavation damaged zone and the degree of decrease of the thermal conductivity. The dominant factor affecting the peak temperature in the multi-layer repository is the decrease of thermal conductivity in the excavation damaged zone, and the excavation damaged zone formed around the deposition hole has more significant effects on the peak temperature than does the excavation damaged zone formed around the disposal tunnel.

An Influence Analysis on the Gap Space of an Engineered Barrier for an HLW Repository (고준위폐기물처분장 공학적방벽의 갭 공간이 미치는 영향 분석)

  • Yoon, Seok;Lee, Changsoo;Kim, Min-Jun
    • Journal of the Korean Geotechnical Society
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    • v.37 no.4
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    • pp.19-26
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    • 2021
  • The high-level radioactive waste (HLW) produced from nuclear power plants is disposed in a rock-mass at a depth of hundreds meters below the ground level. Since HLW is very dangerous to human being, it must be disposed of safely by the engineered barrier system (EBS). The EBS consists of a disposal canister, backfill material, buffer material, and so on. When the components of EBS are installed, gaps inevitably exist not only between the rock-mass and buffer material but also between the canister and buffer material. The gap can reduce water-retarding capacity and heat release efficiency of the buffer material, so it is necessary to investigate properties of gap-filling materials and to analyze gap spacing effect. Furthermore, there has been few researches considering domestic disposal system compared to overseas researches. In this reason, this research derived the peak temperature of the bentonite buffer material considering domestic disposal system based on the numerical analysis. The gap between the canister and buffer material had a minor effect on the peak temperature of the bentonite buffer material, but there was 40% difference of the peak temperature of the bentonite buffer material because of the gap existence between the buffer material and rock mass.

Geotechnical Characteristics of Reduced Slag-soil Mixtures in Electric Furnace (전기로 제강 환원 슬래그 혼합토의 지반공학적 특성)

  • Shin, Jaewon;Yoon, Yeowon;Yoon, Gillim
    • Journal of the Korean GEO-environmental Society
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    • v.12 no.7
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    • pp.31-37
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    • 2011
  • Only a few studies have been conducted using reduced slag as recycled material. The reduced slag in electric furnace is produced as a by-product in making a steel and a few applications of the reduced slag as expensive additives and bonding materials or as the stabilized soils was reported. The purpose of this study is to present the feasibility of the reduced slag as recycled material, especially, in a field of civil engineering. In order to achieve the purpose experiments such as SEM and XRF analysis was conducted for the reduced slag in electric furnace. Based on the results various geotechnical experiments were conducted to know engineering properties of slag-soil mixtures. Weathered soils and clay are mixed with reduced slag for various ratios. As the ratio of reduced slag to weathered soil increases, the maximum dry unit weight of the mixture decreased with increasing optimum moisture content. The results indicates that there is no effect on a reduced slag by compaction efforts. The shear strengths of the weathered soil-slag mixtures are slightly higher or similar to those of weathered soils. The permeability of the weathered soil-slag mixtures is similar to that of silty or sandy soils. Therefore, it is possible to use the mixtures as embankment or backfill materials in the fields. The unconfined strength of the mixtures of reduced slag and clay is higher than that of clay and it tends to increase with the curing time. Therefore it can be used to improve the soft ground.

Flow and Strength Characteristics of the Lightweight Foamed CLSM(Controlled Low-Strength Materials) with Coal Ash (석탄회를 활용한 경량기포유동화재의 플로우 및 강도 특성)

  • Lee, Seungjun;Lee, Jonghwi;Chae, Hwiyoung;Chun, Byungsik
    • Journal of the Korean GEO-environmental Society
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    • v.12 no.10
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    • pp.73-82
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    • 2011
  • Coal ash of industial by-products was not recycled about 30% in total emissions. Moreover, it caused environmental pollution as well as wasted unnecessary expenses and time. Currently, fly ash(FA) is recycled as construction material however ponded ash(PA) is mostly buried. Lightweight foamed Controlled Low-Strength Materials(CLSM) evaluated in this study reduces unit weight by mixing foam in the traditional Controlled Low-Strength Material and has lightweight and flowability to be available for backfill materials in construction. Flow test, unconfined compressive strength test, and foamed-slurry unit weight test were performed in this study and the applicability of lightweight foamed CLSM for construction materials was evaluated. The results indicate that the mixture ratio(PA:FA) ranging from 70:30 to 50:50, cement of 7%, foam of 2~3%, and water content of 26.5~29.5% were required to satisfy the following standards such as flow value(i.e., 20cm), unconfined compressive strength(i.e., 0.8~1.2MPa), and foamed-slurry unit weight(i.e., $12{\sim}15kN/m^3$).

A preliminary study for numerical and analytical evaluation of surface settlement due to EPB shield TBM excavation (토압식 쉴드 TBM 굴착에 따른 지반침하 거동 평가에 관한 해석적 기초연구)

  • An, Jun-Beom;Kang, Seok-Jun;Kim, Jung Joo;Kim, Kyoung Yul;Cho, Gye-Chun
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.23 no.3
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    • pp.183-198
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    • 2021
  • The EPB (Earth Pressure Balanced) shield TBM method restrains the ground deformation through continuous excavation and support. Still, the significant surface settlement occurs due to the ground conditions, tunnel dimensions, and construction conditions. Therefore, it is necessary to clarify the settlement behavior with its influence factors and evaluate the possible settlement during construction. In this study, the analytical model of surface settlement based on the influence factors and their mechanisms were proposed. Then, the parametric study for controllable factors during excavation was conducted by numerical method. Through the numerical analysis, the settlement behavior according to the construction conditions was quantitatively derived. Then, the qualitative trend according to the ground conditions was visualized by coupling the numerical results with the analytical model of settlement. Based on the results of this study, it is expected to contribute to the derivation of the settlement prediction algorithm for EPB shield TBM excavation.

A Fundamental Study on Shearing/Bonding Characteristics of Interface Between Rock Mass and Backfills in Mine Openings (폐광산 채움재와 암반 경계부의 전단 및 접합특성에 관한 기초 연구)

  • Kim, Byung-Ryeol;Lee, Hyeon-woo;Kim, Young-Jin;Cho, Kye-Hong;Choi, Sung-Oong
    • Tunnel and Underground Space
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    • v.31 no.6
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    • pp.623-646
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    • 2021
  • As the demand for electric power increases with acceleration of electrification at home and abroad, the needs for coal-fired electrical power plant are accordingly increased. However, these coal-fired electrical power plants induce also many environmental problems such as increase of air pollutants, increase of possibility of land contamination by reclamation of coal ash, even though these power plants have a good economical efficiency. In case of a by-product of coal-fired electrical power plants, only 70% of them are recycled and the remaining 30% of by-product are fully buried in surrounding ground. Consequently, this study deals with coal ash backfilling mechanism in abandoned mine openings for the purposes of increasing the coal ash recycling rate as well as securing the mine area stability. In order to analyze the backfill and ground reinforcement by interaction between rock mass and backfills, the copying samples of discontinuous surface with different roughnesses were produced for bond strength tests and direct shear tests. And statistical analysis was also conducted to decide the characteristics of bond and shear behavior with joint roughness and their curing day. Numerical simulations were also analyzed for examining the effect of interface behavior on ground stability.

A Study on Stress-Strain Behaviour of Geotube Structure Filled with Silty Sand Under Low Confining Pressure by Triaxial Compression Test (실트질 모래가 충진된 지오튜브 구조체의 저 등방조건에서 삼축압축시험에 의한 응력-변위 거동 연구)

  • Hyeong-Joo, Kim;Tae-Woong, Park;Ki-Hong, Kim
    • Journal of the Korean Geosynthetics Society
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    • v.21 no.4
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    • pp.69-78
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    • 2022
  • Geotextile tubes are widely used to prevent erosion in coastal areas and to replace the backfill for shore slopes in the reclamation of land using dredged soil. In this study, The triaxial confining pressures were chosen as 10kPa, 50kPa, or 100kPa for the specimens reinforced with geotextile considering the condition in the site. The strain behavior under various compressive stresses was then identified. At strains 0% to 7%, the stress-strain behavior was the same due to the effect of initial strain hardening, in which the force was exerted according to the relaxation of the geotextile regardless of the confining pressure (≤100kPa). At strains of 7% or more, the specimen with the small confining pressure had smaller deformation under load, which increases the tensile resistance provided by the reinforcing geotextile. Brittle fracture was then observed due to strain softening and the deviator stress abruptly decreased. This is different from the phenomenon in which the shear strength increases as the confining pressure increases in general triaxial compression tests. In the geoxtile-confined tests, geotextiles are primarily subjected to tensile displacement. Thereafter, the modulus of elasticity increases rapidly, which exhibits the elastic behavior of the geotextile.

Parametric Study for Seismic Design of Temporary Retaining Structure in a Deep Excavation by Dynamic Numerical Analysis (동적수치해석을 이용한 대심도 흙막이 가시설 내진설계 변수연구)

  • Yang, Eui-Kyu;Yu, Sang-Hwa;Kim, Dongchan;Kim, Jongkwan;Ha, Ik-Soo;Han, Jin-Tae
    • Journal of the Korean Geotechnical Society
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    • v.38 no.12
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    • pp.45-65
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    • 2022
  • In this paper, a diaphragm wall that supports soils and rock was modeled using FLAC, a finite difference analysis program, to evaluate the seismic behavior of temporary retaining structures in a deep excavation. The appropriateness of the numerical model was verified by comparing its results with those of the centrifuge test performed in a similar condition. The bending moment distribution along the diaphragm wall shows a very similar tendency, and the maximum acceleration obtained at the backfill and top of the wall shows a difference within 5%. Based on the developed model, a parametric study was conducted in various input earthquake, ground, and excavation conditions. The maximum structural forces and bending moment under earthquake loading were compared with the maximum values during excavation, from which the critical condition that requires a seismic design was roughly sorted out. The maximum bending moment of a wall that retains soil layers increased 17%. Particularly, the axial force of struts located in loose soils increased 32% under 100 years return period of an earthquake event, which strongly is estimated to require seismic design for structural safety.