• 대한토목학회논문집
• /
• 제32권3C호
• /
• pp.85-94
• /
• 2012

본 논문은 액상화 지반에서의 지반-지하 중공구조물 상호작용에 따른 구조물의 rocking현상을 조사하기 위해서 수행한 원심모형실험에 관하여 서술하고 있다. 지진이 발생하였을 때 지반이 강한 진동에 노출되면 상대밀도가 낮은 느슨한 모래지반에서는 액상화가 발생하며, 액상화된 지반보다 작은 단위중량을 가진 지하 중공구조물은 부상한다. 지하 중공구조물이 부상하는 동안에 구조물의 동적 거동과 구조물의 부상량에 대한 원지반의 영향을 평가하기 위하여 원지반의 상대밀도를 다르게 모델지반을 제작하였고, 아크릴 박스를 이용하여 트랜치를 제작하여 모형실험을 수행하였다. 실험결과, 액상화된 원지반의 측방유동 및 주변지반의 전단변형에 의해 야기되는 지하 중공구조물의 rocking현상이 지하 중공구조물의 부상량의 규모에 크게 기여하는 것으로 나타났다.

• 한국토양비료학회지
• /
• 제49권5호
• /
• pp.548-554
• /
• 2016

Optimal range of soil physical quality to enhance crop productivity or to improve environmental health is still in dispute for the upland soil. We hypothesized that the optimal range might be established by comparing soil physical parameters and their interactions inhibiting crop growth. The parameter identifying optimal range covered favorable conditions of aeration, permeability and root extension. To establish soil physical standard two experiments were conducted as follows; 1) investigating interactions of bulk density and aeration porosity in the laboratory test and 2) determining effects of soil compaction and deep & conventional tillage on physical properties and crop growth in the field test. The crops were Perilla frutescens, Zea mays L., Solanum tuberosum L. and Secale cereael. The saturated hydraulic conductivity, bulk density from the root depth, root growth and stem length were obtained. Higher bulk density showed lower aeration porosity and hydraulic conductivity, and finer texture had lower threshold bulk density at 10% aeration bulk density. Reduced crop growth by subsoil compaction was higher in silt clay loam compared to other textures. Loam soil had better physical improvement in deep rotary tillage plot. Combined with results of the present studies, the soil physical quality was possibly assessed by bulk density index. Threshold subsoil bulk density as the upper value were $1.55Mg\;m^{-3}$ in sandy loam, $1.50Mg\;m^{-3}$ in loam and $1.45Mg\;m^{-3}$ in silty clay loam for optimal soil physical quality in upland.

• Geomechanics and Engineering
• /
• 제29권2호
• /
• pp.183-192
• /
• 2022

Piled raft foundations are widely used and effective in supporting high-rise buildings around the world. In this study, a piled raft system was numerically simulated using PLAXIS 3D. The settlement comparison results between the actual building measurements and the three-dimensional (3D) numerical analysis, were in good agreement, indicating the usefulness of this approach for the evaluation of the feasibility of using a piled raft foundation in Ho Chi Minh City subsoil. The effects were investigated of the number of piles based on pile spacing, pile length, raft embedment on the settlement, load sharing, bending moments, and the shear force of the piled raft foundation in Ho Chi Minh City subsoil. The results indicated that with an increased number of piles, increased pile length, and embedding raft depth, the total and differential settlement decreased. The optimal design consisted of pile numbers of 60-70, corresponding to pile spacings is 5.5-6 times the pile diameter (D_p), in conjunction with a pile length-to-pile diameter ratio of 30. Furthermore, load sharing by the raft, by locating it in the second layer of stiff clay, could achieve 66% of the building load. The proposed model of piled raft foundations could reduce the total foundation cost by 49.61% compared to the conventional design. This research can assist practicing engineers in selecting pile and raft parameters in the design of piled raft foundations to produce an economical design for high-rise buildings in Ho Chi Minh City, Viet Nam, and around the world.

• 한국토양비료학회지
• /
• 제27권2호
• /
• pp.65-71
• /
• 1994

석탄회(石炭灰)인 무연탄회(無煙炭灰)와 유연탄회(有煙炭灰)를 논토양(土壤)의 식양토(埴壤土)와 사양토(砂壤土)에 0, 4, 8, 12톤/10a 시용(施用)하였고 밭 토양(土壤)의 식양토(埴壤土)와 사양토(砂壤土)에 0, 3, 6, 9톤/10a를 시용(施用)하여 벼와 콩을 재배(栽培)한 후에 수확기(收穫期)에 표토(表土)와 심토(深土)에서 중금속(重金屬)인 Cd, Cu, Pb, Zn, Ni, Cr, Fe, Mn함량(含量)을 조사(調査)한 결과(結果)는 다음과 같다. 1. 무연탄회(無煙炭灰) 가. 논토양(土壤) 식양토(埴壤土)에서 Cu와 Zn은 표토(表土)에서, Cd와 Ni은 심토(深土)에서 석탄회(石炭灰) 시용량(施用量) 증가(增加)에 따라서 증가(增加)되었으나 그외 성분(成分)은 증가(增加)되는 경향이 없었고. 나. 사양토(砂壤土)에서는 Fe 만이 표토(表土), 심토(深土) 모두에서 증가(增加)되었다. 다. 밭토양(土壤) 식양토(埴壤土)에서는 Ni, Cr은 표토(表土)에서, Cd는 심토(深土)에서 증가(增加)되었고. 라. 사양토(砂壤土)에서는 표토(表土)에서 Cr, 심토(深土)에서는 Pb만이 증가(增加)되었다. 2. 유연탄회(有煙炭灰) 가. 논토양(土壤) 식양토(埴壤土)에서는 심토(深土)에서 Cu, Zn만이 석탄회(石炭灰) 시용량(施用量) 증가(增加)에 따라 증가(增加)되는 경향이었고. 나. 사양토(砂壤土)에서는 표토(表土)에서 Pb 및 Ni만이 증가(增加)되는 경향이 있었다. 다. 밭토양(土壤) 식양토(埴壤土)에서는 Ni, Fe는 표토(表土)에서, Pb는 심토(深土)에서 증가(增加)되는 경향이었고. 라. 사양토(砂壤土)에서는 Cr은 표토(表土)에서, Fe는 심토(深土)에서 Cu, Mn는 표토(表土), 심토(深土)에서 증가(增加)되는 경향이었다. 3. 논과 밭 토양(土壤)에서 대부분의 성분(成分)은 일정한 경향이 없었고 일부성분이 석탄회(石炭灰) 시용량(施用量) 증가(增加)에 따라서 증가(增加)되었으나 우리나라 토양(土壤)의 자연함량평균치(自然含量平均値) 또는 자연함량평균치(自然合量平均値)+(표준편차(標準偏差)와 유사(類似)하였다.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2005년도 춘계 학술발표회 논문집
• /
• pp.65-70
• /
• 2005

In this study, the large scale model tests were executed to estimate the Load Sharing Ratio(LSR) of raft in a piled footing under various conditions. The conditions such as the subsoil type, pile length, pile spacing, array type and pile installation method etc. were varied in the pile loading tests about the free-standing group piles and a piled footing. As the results of this study, it was found that there were no differences of the load-settlement curves, along with the pile installation method and subsoil type. The piles supported most of the external load until a yielding load of the piled footing, but the raft supported a considerable load after a yielding load. And it was also found that the LSR didn't be affected by the pile installation method and the subsoil type. As the relative density of sands increased, the LSR decreased. As the pile spacing was wider and the pile length increased, there was a tendancy for the LSR to increase.

• Structural Engineering and Mechanics
• /
• 제33권5호
• /
• pp.635-647
• /
• 2009

For the calculation of foundation settlement it is recommended to take into account so called influence zone inside the subsoil bellow the foundation structure. Influence zone inside the subsoil is the region where the load has a substantial influence on the deformation of the soil skeleton. The soil skeleton is pre-consolidated or over consolidated due to the original geostatic stress state. An excavation changes the original geostatic stress state and it creates the space for the load transferred from upper structure. The theory of elastic layer in Westergard manner is selected for the vertical stress calculation. The depth of influence zone is calculated from the equality of the original geostatic stress and the new geostatic stress due to excavation combined with the vertical stress from the upper structure. Two close formulas are presented for the influence zone calculation. Using ADINA code we carried out several numerical examples to verify the proposed analytical formulas and to enhance their use in civil engineering practice. Otherwise, the FEM code accuracy can be control.

• Geomechanics and Engineering
• /
• 제16권2호
• /
• pp.113-124
• /
• 2018

Under repeated loading, the residual stresses within the subgrade and subsoil can accelerate the deformation of the road structures. In this paper, a series of laboratory cyclic loading model tests and small-scale model tests were conducted to investigate the dynamic stress response within soils under different loading conditions. The experimental results showed that a dynamic stress accumulation effect occurred if the soil showed cumulative deformation: (1) the residual stress increased and accumulated with an increasing number of loading cycles, and (2) the residual stress was superimposed on the stress response of the subsequent loading cycles, inducing a greater peak stress response. There are two conditions that must be met for the dynamic stress accumulation effect to occur. A threshold state exists only if the external load exceeds the cyclic threshold stress. Then, the stress accumulation effect occurs. A higher loading frequency results in a higher rate of increase for the residual stress. In addition to the superposition of the increasing residual stress, soil densification might contribute to the increasing peak stress during cyclic loading. An increase in soil stiffness and a decrease in dissipative energy induce a greater stress transmission within the material.

• 한국토양비료학회지
• /
• 제48권6호
• /
• pp.628-633
• /
• 2015

It is necessary to assess soil physical properties and crop growth treated by compaction to establish the soil management standard. This study evaluated the bulk density, strength and crop growth after subsoil compaction for sandy loam and loam on the field in Suwon, Korea. The treatments were compaction and deep tillage. Sandy loam and loam were classified to coarse soil and fine soil, respectively, depending on clay contents. In coarse soil, bulk density of compacted plot was 8~17% greater than control and deep tilled plot. The root growth was worse in compacted plot compared with control. In fine soil, plow pan was not observed in deep tilled plot with 5~19% smaller bulk density than compacted plot and control. Deep tillage improved the crop growth. The soil physical properties by compaction were dependent on clay content and crop growth limit depended on the traffic driving.

• 환경생물
• /
• 제36권4호
• /
• pp.567-575
• /
• 2018

토지이용별로 토양 물리성 변화를 평가하기 위하여 2009년부터 2017년까지 전국의 밭, 과수원, 논을 대상으로 토양물리성 특성을 4년 주기로 분석하였다. 밭은 작토심, 심토 유기물 함량, 심토 산중식 경도가 증가하고 심토 용적밀도가 감소하며, 개량기준 초과비율도 지속적으로 감소하였다. 과수원은 경운심이 증가하였으나 심토 유기물 함량이 감소하고 적정기준을 초과하는 비율은 4년 전보다 증가하였다. 논은 작토심, 심토 유기물 함량이 감소하고 심토 용적밀도가 증가하며 개량기준 초과비율이 증가하는 등 물리성 불량이 심화되었다. 최근 10년간 밭, 과수원에 비해 논의 물리성이 악화되는 것을 확인할 수 있었으며, 공통적으로 심토 유기물 함량이 감소하고 심토 용적밀도가 증가하는 주요한 요인은 토양유기물로 평가되었다. 따라서 토양물리성 질 관리에 유기물은 중요한 요소이었으며, 특히 논에서 지속적인 유기물 관리와 경운방법 개선 등이 필요하다.

• 지질공학
• /
• 제33권1호
• /
• pp.15-25
• /
• 2023

화성암과 퇴적암으로 이루어진 국내 산림토양 중 표토와 심토에서 채취된 시료의 미생물군집 활성도에 미치는 산불의 영향을 알아보았다. 베타글루코시다아제의 분석결과, 화성암보다 퇴적암의 미생물군집에서 높게 나타났다. 산불 발생 초기에 효소 활성이 관찰되지 않았으나, 시간이 경과됨에 따라 활성이 회복되었다. 또한, 토양의 훼손여부와 상관없이 심토는 표토에 비해 활성이 33~46% 저해되었다. EcoPlate를 이용하여 산불이 미생물 기질이용성에 미친 영향을 알아보았다. 정상토와 훼손토의 평균반응구발색도 값 백분율은 표토에서 각각 52.7~56.8% 및 62.3~83.6%로 나타났다. 산불 발생은 토양 유기물의 분해를 촉진함으로 심토미생물군집의 다양성 및 기질이용성에 영향을 준 것으로 보여진다. 미생물군집의 종다양성지수인 샤논 인덱스(Shanon index, H)는 모든 시료의 표토에서 높게 나타났다. 샤논 풍부도는 퇴적암 토양미생물이 화성암에 비하여 높게 나타났으며, 표토가 심토보다 높게 나타났다.