• KCI Concrete Journal
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• 제12권1호
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• pp.47-56
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• 2000

Once a structure fabricated with mass concrete is in a form of wall such as retaining wall, side walls of a concrete caisson and so on, cracks induced by hydration heat have been known to be governed by exterior restraints which are mainly related to the boundary conditions of the structure. However, it is thought that the degree of restraints can be alleviated considerably only if a lift height of concrete placement or a panel size of the wall is selected properly before construction. As a way of minimizing thermal cracking commonly observed in massive wall-typed structure, this study aimed at evaluating effects of geometrical configuration on the temperature rise and thermal stress through parametric study. Evaluation of the effect was also performed for cement types using anti-sulphate cement, blast furnace slag cement and cement blended with two mineral admixture and one ordinary Portland Cement. so called ternary blended cement. As a result of analytical study, it was found that a lift height of concrete placement is the most important factor in controlling thermal cracking in massive wall, and the increase of a lift height is not always positive to the crack occurrence as not expected.

• Geomechanics and Engineering
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• 제5권1호
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• pp.37-55
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• 2013

An important issue in the design of soil-nailing systems, as long-term retaining walls, is to assess their stability during seismic events. As such, this study is aimed at simulating the dynamic behavior and failure pattern of nailed structures using two series of numerical analyses, namely dynamic time history and pseudo-static. These numerical simulations are performed using the Finite Difference Method (FDM). In order to consider the actual response of a soil-nailed structure, nonlinear soil behaviour, soil-structure interaction effects, bending resistance of structural elements and construction sequences have been considered in the analyses. The obtained results revealed the efficiency of both analysis methods in simulating the seismic failure mechanism. The predicted failure pattern consists of two sliding blocks enclosed by three slip surfaces, whereby the bottom nails act as anchors and the other nails hold a semi-rigid soil mass. Moreover, it was realized that an increase in the length of the lowest nails is the most effective method to improve seismic stability of soil-nailed structures. Therefore, it is recommended to first estimate the nails pattern for static condition with the minimum required static safety factor. Then, the required seismic stability can be obtained through an increase in the length of the lowest nails. Moreover, placement of additional long nails among lowest nails in existing nailed structures can be considered as a simple retrofitting technique in seismic prone areas.

• Earthquakes and Structures
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• 제9권2호
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• pp.281-303
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• 2015

The effects of infill panels on the response of r.c. frames subjected to seismic action are widely recognized. Numerous experimental investigations were effected and several analytical models were developed on this subject. This work, which is part of a larger project dealing with specific materials and structures commonly used in Italy, discusses experimental tests on masonry and samples of bare and infilled portals. The experimental activity includes tests on elemental materials, and 12 wall samples. Finally, three one-bay one-story reinforced concrete frames, designed according to the outdated Italian technical code D.M. 1996 without seismic details, were tested (bare and infilled) under constant vertical and cyclic lateral load. The first cracks observed on the framed walls occurred at a drift of about 0.3%, reaching its maximum capacity at a drift of 0.5% while retaining its capacity up to a drift of 0.6%. Infill contributed to both the stiffness and strength of the bare reinforced concrete frame at small drifts thus improving overall system behavior. In addition to the experimental activities, previously mentioned, the recalibration of a model proposed by Comberscue (1996) was evaluated. The accuracy of an OpenSees non linear fiber based model of the prototype tested, including a strut element was verified through a comparison with the final experimental results. This work has been partially supported by research grant DPC-ReLUIS 2014.

• Advances in concrete construction
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• 제5권6호
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• pp.659-669
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• 2017

Grouts compared to other material sources, could be highly sensitive to cold weather conditions, especially when the compressive strength is the matter of concern. Grout as one the substantial residential building material used in retaining walls, rebar fixation, sidewalks is in need of deeper investigation, especially in extreme weather condition. In this article, compressive strength development of four different commercial grouts at three temperatures and two humidity rates are evaluated. This experiment is aimed to assess the grout strength development over time and overall compressive strength when the material is cast at low temperatures. Results represent that reducing the curing temperature about 15 degrees could result in 20% reduction in ultimate strength; however, decreasing the humidity percentage by 50% could lead to 10% reduction in ultimate strength. The maturity test results represented the effect of various temperatures and humidity rates on maturity of the grouts. Additionally, the freeze-thaw cycle's effect on the grouts is conducted to investigate the durability factor. The results show that the lower temperatures could be significantly influential on the behavior of grouts compared to lower humidity rates. It is indicated that the maturity test could not be valid and precise in harsh temperature conditions.

• Geomechanics and Engineering
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• 제16권6호
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• pp.635-642
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• 2018

Braced excavation systems are commonly required to ensure stability in construction of basements for shopping malls, underground transportation and other habitation facilities. For excavations in deposits of soft clays or residual soils, stiff retaining wall systems such as diaphragm walls are commonly adopted to restrain the ground movements and wall deflections in order to prevent damage to surrounding buildings and utilities. The ground surface settlement behind the excavation is closely associated with the magnitude of basal heave and the wall deflections and is also greatly influenced by the possible groundwater drawdown caused by potential wall leakage, flow from beneath the wall, flow from perched water and along the wall interface or poor panel connections due to the less satisfactory quality. This paper numerically investigates the influences of excavation geometries, the system stiffness, the soil properties and the groundwater drawdown on ground surface settlement and develops a simplified maximum surface settlement Logarithm Regression model for the maximum ground surface settlement estimation. The settlements estimated by this model compare favorably with a number of published and instrumented records.

• Geomechanics and Engineering
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• 제25권4호
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• pp.275-282
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• 2021

Failure mechanism which can affect geotechnical infrastructures (shallow foundations, retaining walls, and piles) constitutes one of the most encountered problems during the design process. In this respect, the shear behavior of interfaces between grained soils and solid building materials, as well as those between cohesive soils should be investigated. Therefore, a range of ring shear tests with different cohesive soils and stainless-steel interfaces have been carried out through the Bromhead apparatus that allows simulating large displacements along a failure surface. The effects of steel rings roughness and soil type on the residual friction coefficient and the shear zone features (structure, thickness, and texture orientation angle) have been investigated using the Scanning Electron Microscopy. The obtained results indicate that the residual friction coefficient and the structural characteristics of the shear zone vary according to the surface roughness and the soil type. Scanning electron microscopy reveals that the particles inside the shear zone tend to be re-oriented. Also, the shear failure mechanism can be identified along with the interface, within the soil, or simultaneously at the interface and within the soil specimen.

• 한국지반공학회논문집
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• 제23권3호
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• pp.133-140
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• 2007

DCM공법(심층혼합처리 공법)은 흙막이 벽체 등 구조물 조성에 적용하였다. 이러한 DCM 벽체는 경질층에서 관입능력이 있어야 한다. DCM 장비에 부착된 교반날개에 의해 경질지반의 관입능력이 증가되는 알아보기 위해 특수교반날개가 고안되었다. 경질점토층에 관입되는 특수교반날개의 관입특성은 김해와 인천현장에서 조사하였다. 고안한 특수교반날개는 관입속도가 다소 느려도 N=30 이상 되는 지반까지 관입되었고 관입시 효율이 경질지반에서 낮아질 수 있으므로 경제적인 교반날개의 관입깊이를 분석하였다.

• Geomechanics and Engineering
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• 제38권6호
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• pp.611-620
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• 2024

The slope stabilization method is constructed on bedrock, but performance degradation occurs during an impact (earthquake, blasting, etc.) after construction, which may affect service life and factor of safety. In particular, the top-down method implies the possibility of damage caused by blasting vibration due to the construction procedure. However, the current blasting design only reflects damage to nearby facilities, so there is a limit in its ability to assess the damage of reinforcement methods caused by blasting vibration within the scope of influence. In this study, we aim to evaluate problems and damage levels caused by close blasting effects on rock-integrated structures, such as panel-type retaining walls, anchor-combined structures, and small nails, which are mainly constructed using the top-down method. We will also analyze factors affecting long-term performance according to changes in conditions after construction, such as tunnel excavation, to establish optimal design measures.

• Structural Engineering and Mechanics
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• 제57권1호
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• pp.1-20
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• 2016

On the basis of the geological conditions of high and steep mountainous slope on which an exit portal of an express railway tunnel with a bridge-tunnel combination is to be built, the composite structure of the exit portal with a bridge abutment of the bridge-tunnel combination is presented and the stability of the slope on which the express railway portal is to be built is analyzed using three dimensional (3D) numerical simulation in the paper. Comparison of the practicability for the reinforcement of slope with in-situ bored piles and diaphragm walls are performed so as to enhance the stability of the high and steep slope. The safety factor of the slope due to rockmass excavation both inside the exit portal and beneath the bridge abutment of the bridge-tunnel combination has been also derived using strength reduction technique. The obtained results show that post tunnel portal is a preferred structure to fit high and steep slope, and the surrounding rock around the exit portal of the tunnel on the high and steep mountainous slope remains stable when rockmass is excavated both from the inside of the exit portal and underneath the bridge abutment after the slope is reinforced with both bored piles and diaphragm walls. The stability of the high and steep slope is principally dominated by the shear stress state of the rockmass at the toe of the slope; the procedure of excavating rockmass in the foundation pit of the bridge abutment does not obviously affect the slope stability. In-situ bored piles are more effective in controlling the deformation of the abutment foundation pit in comparison with diaphragm walls and are used as a preferred retaining structure to uphold the stability of slope in respect of the lesser time, easier procedure and lower cost in the construction of the exit portal with bridge-tunnel combination on the high and steep mountainous slope. The results obtained from the numerical analysis in the paper can be used to guide the structural design and construction of express railway tunnel portal with bridge-tunnel combination on high and abrupt mountainous slope under similar situations.

• 한국조경학회지
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• 제44권3호
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• pp.1-12
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• 2016

본 연구는 설악산 국립공원 내 44번 국도를 대상으로 로지스틱 회귀분석을 실시하여 로드킬이 발생한 지역의 공간적 특성을 분석하고, 분석 결과의 적합도 및 예측도를 평가하여 로드킬 발생 근본 원인을 파악하고자 하였다. 2008년부터 2013년까지 구축된 81개의 로드킬 데이터를 종속변수로 설정하고, 선행연구 및 현장조사를 통해 도출한 경사, 향, 식생, 백두대간 등의 자연환경 요인과 펜스 옹벽 등의 인공시설물, 경작지, 주거지역 등의 토지이용 변수를 독립 변수로 설정하고, 로지스틱 회귀분석을 실시하여 회귀식을 추정하였다. 식생 영급, 하천으로부터의 거리, 펜스 옹벽 등의 설치구간, 주거지역 건물 등의 시설로부터의 거리가 로드킬에 영향을 미치는 변수로 선택되었다. 회귀모형에 포함된 모든 변수들은 유의수준(p<0.01)을 충족하였다. 회귀모형에서 로드킬 발생에 가장 큰 영향력을 보인 변수는 펜스 옹벽 등의 설치구간(회귀계수: -1.0135)으로 나타났으며, 가장 낮은 영향력을 보인 변수는 식생 영급(회귀계수: 0.0001)으로 나타났다. 즉, 펜스 옹벽 등의 설치 구간에서는 로드킬이 일어날 확률이 낮으며, 주거지역 건물 등의 시설로부터의 거리가 가까울수록, 하천으로부터의 거리가 가까울수록, 식생 영급이 커질수록 로드킬 발생이 높아질 수 있다. 추정된 로지스틱 회귀모형 결과로부터 로드킬이 일어날 것이라고 옳게 예측한 확률은 74.1%, 로드킬이 일어나지 않을 것이라고 옳게 예측한 확률은 70.4%로 나타났다. 전체적으로는 옳게 분류한 확률은 72.2%로 비교적 높은 비율을 보였다. 본 연구를 통해 로드킬 저감을 위한 계획 및 정책 수립, 방지시설 설치 계획 등의 공간의사 결정에 객관적 근거로 도움을 줄 수 있을 것으로 사료된다.