• 지질공학
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• 제31권2호
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• pp.165-178
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• 2021

자연사면을 대상으로 강우에 따른 침투해석 및 사면안정해석을 통하여 사면토층의 흙-함수특성곡선(SWCC) 맞춤계수에 따른 안정성의 영향을 평가하였다. 연구 대상사면의 토질시료를 채취하여 토층의 물리적, 역학적 및 불포화 특성을 실험하였다. 현장조건의 흙-함수특성곡선(SWCC)의 맞춤계수 α 및 n을 변화시켜 침투해석을 통한 포화심도를 산정하였으며, 이를 고려하여 한계평형해석기법을 이용한 사면안정해석을 수행하였다. 강우에 의한 침투해석 결과에 따르면 맞춤계수 α가 감소함에 따라 토층 내 포화심도가 급격하게 증가하며, 전체 토층에 대한 포화시간도 짧아지는 것으로 나타났다. 그리고 포화심도를 고려한 사면안정해석결과에 의하면 맞춤계수 α가 감소함에 따라 사면안전율은 급격하게 감소하지만, 맞춤계수 n을 증가시키더라도 사면안전율의 변화는 매우 작은 것으로 나타났다. 따라서 강우침투로 인한 포화심도와 이를 고려한 사면안정성은 흙-함수특성곡선(SWCC)의 맞춤계수 α에 크게 영향을 받으며, 맞춤계수 n의 영향은 상대적으로 매우 작음을 알 수 있다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2007년 가을학술발표회
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• pp.502-513
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• 2007

This paper describes the rainfall-induced slope failures caused by infiltration due to prolonged rainfall. The emphasis was on quantifying the effect of fine-grained contents which are influencing on the infiltration rate in the wetting front of initially unsaturated slopes during rainfall. Suction tests by tensiometer were performed for five mixture specimens with varying fine-grained contents and then, numerical analyses for the stability of unsaturated slopes are carried out for different relative densities and mixture portions based on the soil water characteristic curves obtained by GCTS pressure plate. It is shown that the fines are highly influenced on wetting front suction of unsaturated soil slopes. Based on the results, it is found that until 15% fine content is the limit showing different wetting front suction, beyond which the wetting band depth do not affect considerably the stability of unsaturated slopes.

• Geomechanics and Engineering
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• 제5권4호
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• pp.363-377
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• 2013

Any structure constructed on the earth is supported by the underlying soil. Foundation is an interfacing element between superstructure and the underlying soil that transmits the loads supported by the foundation including its self weight. Foundation design requires evaluation of safe bearing capacity along with both immediate and long term settlements. Weak and compressible soils are subjected to problems related to bearing capacity and settlement. The conventional method of design of footing requires sufficient safety against failure and the settlement must be kept within the allowable limit. These requirements are dependent on the bearing capacity of soil. Thus, the estimation of load carrying capacity of footing is the most important step in the design of foundation. A number of theoretical approaches, in-situ tests and laboratory model tests are available to find out the bearing capacity of footings. The reliability of any theory can be demonstrated by comparing it with the experimental results. Results from laboratory model tests on square footings resting on sand are presented in this paper. The variation of bearing capacity of sand below a model plate footing of square shape with variation in size, depth and the effect of permissible settlement are evaluated. A steel tank of size $900mm{\times}1200mm{\times}1000mm$ is used for conducting model tests. Bearing capacity factor $N_{\gamma}$ is evaluated and is compared with Terzaghi, Meyerhof, Hansen and Vesic's $N_{\gamma}$ values. From the experimental investigations it is found that, as the depth of sand cushion below the footing ($D_{sc}$) increases, ultimate bearing capacity and settlement values show an increasing trend up to a certain depth of sand cushion.

• 한국농공학회지
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• 제30권2호
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• pp.55-66
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• 1988

This study was conducted to investigate the various engineering properties and correlationshops among the soil constants of alluvial clayey deposits distributed in the bay of Asan and their results are summarized as follows : 1. Grain size distribution of soil was consisted of 12 % of clay, 46-73 % of silt, 2-23 % of sand, and as for the consistency characteristics, 26-36 % of liquid limit, 18-21 % of plastic limit and 6-16 % of plastic index, and so the soil belonging to as a lower plastic nonorganic clay, it's specific gravity was 2,66-2.70, and the location on the plastic chart was approximately above the A-line. Z The natural moisture content and unit weight were 30-43 % and 1.76-1.87 g I cm$_3$, respectively, and according to increment of natural moisture content, the unit weight was decreased, and the initial void ratio and degree of saturation were shown of 0,87-1119 and 92- 100 %, most of saturated. 3. Cone resistance value which was shown 2.4 - 6.5 kg / $cm^2$ was a little lower and it was increased with the depth of layer and shown the formular $q_c=0.7_z+1.32$. 4. Unconfined compression strength was about 0.18-0.43kg /$cm^2$, cu, 0.1-0.22kg / $\psi$, $2-6^{\circ}$ under uu-test condition of triaxial, and CCU, 0.08-0.3 kg/cm , $\psi$, $12-18^{\circ}$ under the condition of cu-test. 5. Pre-consolidation load of characteristics of consolidation was 0.4-0.8 kg / $cm^2$, compression index, about 0.17-0.33. 6. Liquid limit and plastic index were incresased with the increment of clay content but most of alluvial clay was appeared as a normal through non-activity clay soil shown more natural moisture content than liquid limit, and their relationship as follows : LL=0.38( cy+54.8), PI=0.836(LL -17.8), PI =0.468(LL -0.48) 7. The initial void ratio presented correlationship of positive among clay content, natural moisture content and liquid limit, and that of reverse with unit weight, and their results as follws : $e_o=0.024(w_n+0.2)$, $e_o=e_o=0.0003c_y+0.0005 LL+0.0151 W_n+\frac{3.58}{r-t}-1.52$ 8. It was shown that the compression index has correlationship of postive among the clay content, liquid limit, plastic index, natural moisture content and initial void ratio, and their relationships as follows ; $c_c=0.44(e_o-0.47)$, $c_c=0.001$

• Geomechanics and Engineering
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• 제13권5호
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• pp.825-844
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• 2017

This study aimed to find out the pullout capacity of inclined strip anchor plate embedded in anisotropic and nonhomogeneous fully saturated cohesive soil in undrained condition. The ultimate pullout load has been found out by using numerical lower bound finite element analysis with linear programming. The undrained pullout capacity of anchor plate of width B is determined for different embedment ratios (H/B) varying from 3 to 7 and various inclination of anchor plates ranging from $0^{\circ}$ to $90^{\circ}$ with an interval of $15^{\circ}$. In case of anisotropic fully saturated clay the variation of cohesion with direction has been considered by varying the ratio of the cohesion along vertical direction ($c_v$) to the cohesion along horizontal direction ($c_h$). In case of nonhomogeneous clay the cohesion of the undrained clay has been considered to be increased with depth below ground surface keeping $c_v/c_h=1$. The results are presented in terms of pullout capacity factor ($F_{c0}=p_u/c_H$) where $p_u$ is the ultimate pullout stress along the anchor plate at failure and $c_H$ is the cohesion in horizontal direction at the level of the middle point of the anchor plate. It is observed that the pullout capacity factor increases with an increase in anisotropic cohesion ratio ($c_v/c_h$) whereas the pullout capacity factor decreases with an increase in undrained cohesion of the soil with depth.

• Structural Engineering and Mechanics
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• 제56권1호
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• pp.49-56
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• 2015

Dynamic compaction (DC) is a useful method for improvement of granular soils. The method is based on falling a tamper (weighting 5 to 40 ton) from the height of 15 to 30 meters on loose soil that results in stress distribution, vibration of soil particles and desirable compaction of the soil. Propagation of the waves during tamping affects adjacent structures and causes structural damage or loss of performance. Therefore, determination of the safe or critical distance from tamping point to prevent structural hazards is necessary. According to FHWA, the critical distance is defined as the limit of a particle velocity of 76 mm/s. In present study, the ABAQUS software was used for numerical modeling of DC process and determination of the safe distance based on particle velocity criterion. Different variables like alluvium depth, relative density, and impact energy were considered in finite element modeling. It was concluded that for alluvium depths less than 10 m, reflection of the body waves from lower boundaries back to the soil and resonance phenomenon increases the critical distance. However, the critical distance decreases for alluvium depths more than 10 m. Moreover, it was observed that relative density of the alluvium does not significantly influence the critical distance value.

• Geomechanics and Engineering
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• 제38권2호
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• pp.165-177
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• 2024

Liquefaction phenomenon refers to a phenomenon in which excess pore water pressure occurs when a dynamic load such as an earthquake is rapidly applied to a loose sandy soil ground where the ground is saturated, and the ground loses effective stress and becomes liquid. The laboratory repetition test for liquefaction evaluation can be performed through a repeated triaxial compression test and a repeated shear test. In this regard, this study attempted to evaluate the effects of the relative density of sand on the liquefaction resistance strength according to particle size distribution using repeated triaxial compression tests, and additional experimental verification using numerical analysis was conducted to overcome the limitations of experimental equipment. As a result of the experiment, it was confirmed that the liquefaction resistance strength increased as the relative density increased regardless of the classification of soil, and the liquefaction resistance strength of the SP sample close to SW was quite high. As a result of numerical analysis, it was confirmed that the liquefaction resistance strength increased as the confining pressure increased under the same relative density, and the liquefaction resistance strength did not decrease below a certain limit even though the confining pressure was significantly reduced at a relatively low relative density. This is judged to be due to a change in confining pressure according to the depth of the ground. As a result of analyzing the liquefaction resistance strength according to the frequency range, it was confirmed that there was no significant difference from the laboratory experiment results in the basic range of 0.1 to 1.0 Hz.

• 지질공학
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• 제27권2호
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• pp.153-164
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• 2017

지반 함몰 위험성에 대한 지질학적 인자는 매우 다양하다. 어떠한 지질학적 요인 또는 외부적인 영향에 의해 영향을 받을 수 있으며 동일한 지질학적 요인 내에서도 여러 가지 다른 물성값에 의해 지반함몰 영향인자가 결정될 수 있다. 다수의 논문 및 연구사례를 검토 한 결과 크게 7가지 범주의 지반함몰 요인이 있음을 알 수 있었다. 공동의 존재 여부에 따라 상재하중의 심도 및 두께가 지반침하에 영향을 줄 수 있고, 토사와 암반으로 구성된 지반에서는 그 경계면의 심도와 배향이 지배적 요소이다. 이 중 토사지반에서는 좀 더 다양한 영향인자로 구성이 되어있는데 토사의 종류, 전단강도, 상대밀도 및 다짐도, 건조단위중량, 함수비, 액성한계가 그것이다. 암반지반에서는 암석의 종류와 주 단열과의 거리 및 RQD가 영향인자로 구성될 수 있으며 수리지질학적 측면에서 접근했을 경우 강우 강도, 하천과의 거리와 심도, 투수계수 및 지하수위 변동이 영향을 줄 수 있다. 외부적인 요소도 지반함몰에 영향을 줄 수 있는데 굴착심도와 흙막이 벽과의 거리, 굴착공사 시 지하수 처리공법, 하수관로 등 인공시설물 존재 유무 등이 이에 해당된다. 최근 도심지의 지하구조물 건설에서 지반함몰 요소를 평가하는 것은 필수적일 것으로 예상된다. 본 연구에서 분석한 지반함몰 영향인자가 지반함몰위험 평가에 도움이 되기를 기대한다.

• 한국수자원학회논문집
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• 제52권1호
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• pp.51-60
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• 2019

본 연구에서는 Cosmic-ray 토양수분량 관측시스템 구축 시 필요한 검증 네트워크 설계 기법 개발에 목적을 두고 유전율식(dielectric constant) 장비인 Frequency Domain Reflectometry (FDR)와 연계하여 Cosmic-ray 검증시스템을 구축 운영하였다. Cosmic-ray 검증시스템 평가에 필요한 시범지역은 기존 계측 장비와의 연계성과 다양한 수문자료의 활용성을 고려하여 설마천 유역에 구축하였다. 시범지역은 Cosmic-ray 장비와 FDR 센서(10개소)로 구축하였으며 2018년 7월부터 현재까지 운영되고 있다. 본 연구에서는 검증시스템의 신뢰도를 높이기 위해 코어법(soil core sampling method)을 통해 산출한 용적수분함량(volumetric water content)을 유전율식 장비와 정기적으로 검증하였다. 연구기간 중 수행한 코어법과 FDR 센서를 검증한 결과, 두 자료의 통계량이 $bias=-0.03m^3/m^3$과 $RMSE=0.03m^3/m^3$의 유의한 값을 보였다. 또한 연구기간 동안 FDR 센서의 시계열 특성은 모든 강우에 정상적으로 반응하였다. 그러나 일부 지점에서는 낙엽 및 캐노피의 차단과 상부사면의 유출 등으로 인해 상이한 특성을 보였다. Cosmic-ray 영향원(influence line) 내 FDR 센서의 대표성 분석은 시간 안정성 해석법(temporal stability analysis, TSA)을 이용하여 토심별(10 cm, 20 cm, 30 cm, 40 cm)로 분석하였다. 10개소에 대한 토심별 토양수분량의 대표성을 TSA로 분석한 결과, 토심 10 cm에서는 FDR 5, 토심 20 cm에서는 FDR 8, 토심 30 cm에서는 FDR 2, 토심 40 cm에서는 FDR 1에서 가장 우수한 대표 특성을 보였다. 본 연구의 시범지역 운영 기간이 짧다는 한계는 있지만 지금까지의 분석 결과를 토대로 하여 볼 때, Cosmic-ray 관측시스템 구축 시에는 검증 장비로는 유전율식을 활용하고, Cosmic-ray 영향원 내 토양수분량의 대표성 분석은 TSA 방법으로 수행하는 것이 바람직할 것으로 판단된다.

• 한국토양비료학회지
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• 제43권1호
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• pp.68-74
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• 2010

담수상태의 토양이나 습지생태계에서 ${NO_3}^-$는 환원상태의 발달을 지연시키는 완충역할을 할 수 있다. 논토양에서 관개용수를 통하여 공급되는 ${NO_3}^-$가 Fe의 환원과 그에 따른 P의 가용화에 미치는 영향을 조사하였다. 관개용수중의 ${NO_3}^-$ 함량이 5 mg N $L^{-1}$ 수준일 경우 5 cm 깊이 토양에 도달하기 전에 대부분 탈질작용에 의해 제거되었으며, 5 cm 깊이 토양에서 일어나는 Fe의 환원과 P의 용출이 저해되었고 10 cm 깊이 토양의 환원현상에는 영향을 미치지 못하였다. ${NO_3}^-$ 함량이 10 mg N $L^{-1}$ 수준인 관개용수를 공급하였을 경우에는 10 cm 깊이 토양층까지 ${NO_3}^-$가 잔류 유입되었으며, Fe의 환원과 P의 용출을 현저히 억제하는 것으로 나타났다. 이상의 결과를 보면 관개용수를 통하여 ${NO_3}^-$를 포함한 질소가 과도하게 논토양으로 유입되면 질소과다현상을 유발할 뿐만 아니라 P의 가용화를 억제함으로써 인 결핍을 초래할 수도 있을 것이다.