• Title/Summary/Keyword: Elastic Soil

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Wave-Induced Response of Unsaturated and Multi-layered Seabed; A Semi-analytical Method (파랑으로 인한 불포화된 다층 해저지반의 거동;준해석적 방법)

  • ;Rahman, M. S.
    • Journal of the Korean Geotechnical Society
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    • v.15 no.6
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    • pp.45-55
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    • 1999
  • Wave-induced response, liquefaction and stability of unsaturated seabed are studied. The unsaturated seabed is modeled as a fluid-filled polo-elastic medium. The coupled process of fluid flow and the deformation of soil skeleton is formulated in the framework of Biot's theory. The resulting governing equations are solved using a semi-analytical method to evaluate the stresses and pore water pressure of unsaturated and multi-layered seabed. The semi-analytical method can be applied to calculate a pore pressure and the stresses of in anisotropic inhomogeneous seabed. The results indicate that the degree of saturation influences mostly on the magnitudes of a pore pressure and the stresses of unsaturated and multi-layed seabed. Based on the pore pressure and stresses in seabed, the analysis on the possibilities of liquefaction and shear failure was performed. The results show that the maximum depth of shear failure occurrence is deeper than the maximum liquefaction depth.

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Measurement of $G_{max}$ of Sands Using Bender Element in Resonant Column and Torsional Shear Equipment (공진주/비틂전단 시험 및 벤더엘리먼트 시험을 이용한 사질토 지반의 최대전단탄성계수 평가)

  • Kim Dong-Soo;Youn Jun-Ung;Lee Sei-Hyun;Choo Yun-Wook
    • Journal of the Korean Geotechnical Society
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    • v.21 no.10
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    • pp.17-25
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    • 2005
  • The bender element method is an experimental technique to determine very small strain ($<10^{-3}\%$), elastic shear modulus of a soil, $G_{max}$ by measuring the velocity of shear wave propagation through a sample. Bender elements have been applied as versatile transducers to measure small strain modulus of wet or dry soils in various laboratory apparatus. In this paper, bender element (BE), resonant column (RC) and torsional shear (TS) tests were performed on Toyoura sand at various testing conditions using the modified Stokoe type RC/TS testing equipment capable of performing BE test. Based on the results, applicabilities of the testing method using bender element were evaluated by comparing the values of $G_{max}$ obtained from RC/TS and BE testing methods. For more dependable evaluation, the loading frequency of each testing method was considered for the results obtained for samples in saturated condition by adapting Biot's theory.

A Study on the Liquefaction of Saturated Sand Layer under Oscillating Water Pressure (수압변동에 의한 포화 모래층의 액상화 연구)

  • Howoong Shon;Hyun-Chul Lim;Dae-Geun Lee
    • Journal of the Korean Society of Groundwater Environment
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    • v.7 no.2
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    • pp.59-65
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    • 2000
  • The vertical distribution of pore water pressure in the highly saturated sand layer under the oscillating water pressure is studied theoretically and experimentally. By the experiments it is shown that the water pressure acting on the sand surface propagates into the sand layer with the damping in amplitude and the lag in phase, and that the liquefaction, the state that the effective stress becomes zero, occurs under certain conditions. These experimental results are explained fairly well by the same theoretical treatment as for the ground water problems in the elastic aquifer. The main characteristics of liquefaction clarified by the analysis are as follows: 1) The depth of the liquified layer increases with the increase of the amplitude and the frequency of the oscillating water pressure. 2) The increase of the volume of the water and the air in the layer increases the liquified depth. Especially the very small amount of the air affects the liquefaction significantly. 3) The liquified depth decrease rapidly with the increase of the compressibility coefficient of the sand. 4) In the range beyond a certain value of the permeability coefficient the liquified depth decrease with the increase of the coefficient.

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A Study on the Prediction of Surface Settlement Applying Umbrella Arch Method to Tunnelling (Umbrella arch 공법의 적용에 따른 횡방향 지표침하량 예측에 관한 연구)

  • 김선홍;문현구
    • Tunnel and Underground Space
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    • v.12 no.4
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    • pp.259-267
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    • 2002
  • Recently, Umbrella Arch Method(UAM) is commonly used in order to enhance the stability of tunnel itself and stabilize the adjacent surface structure. But quantitative estimation of reinforcement effect is needed because UAM is designed and constructed only on the basis of empirical experience. By using 3-dimensional finite element method, parametric study is performed for elastic modulus of ground and overburden, and reinforcement effect is analyzed quantitatively. From the results, surface settlement decreases about 9%∼27% in soil tunnel, about 4%∼24% in weathered rock tunnel and 4%∼17% in soft rock tunnel when applied with UAM. The prediction equation for final surface settlement is suggested through regression analysis and the equation is expressed as exponential function which has variable Smax, unknown coefficient i and k.

Prediction of Driving Stresses in Piles (항타응력 추정)

  • 진병익;황정규
    • Geotechnical Engineering
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    • v.3 no.1
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    • pp.25-38
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    • 1987
  • The prediction of driving stresses in piles is necessary for optimum selection of driving hammers, better design of precast piles, enact assessment of drivabilities and complete description of piling specifications. However, the existing pile-driving formulas based on the theory of Newtonian impact have some defects and shortcomings; the numerical method by the wave equation analysis using electronic computer usually Involves various uncertainties and limitations which can yield erroneous outcomes because it employs soil constants of which the nature is unknown as essential parameters and ignores the effect of residual stresses set up in the pile .after each hammer blow; and the electronic measuring technique needs extra time and expense. The method developed herein is presented for the purpose of giving field engineers a reliable and convenient analytical procedure for the prediction of driving stresses along the full length of pile using the most effetive parameters without resort to electronic computer. This method is based on the fundamental mechanics of stress waves in elastic rods and takes into account the effect of residual stresses induced by reversed friction in piles.

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A Study on Creep Behavior of Geosynthetics Considering Effect of Temperature and Confining Stress (온도 및 구속응력을 고려한 토목섬유의 크리프거동에 관한 연구)

  • 방윤경;김홍택
    • Journal of the Korean Geotechnical Society
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    • v.19 no.5
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    • pp.291-299
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    • 2003
  • The effect of temperature and soil confining stress on geosyntheic creep behaviour was studied by performing the temperature dependent confined creep tests for HDPE geogrid and geomembrane specimen. The visco-elastic creep coefficients of the geosynthetics were evaluated by the test results and it was proposed that the simple expressions for the instantaneous and limit creep strain of geosynthetics was considered as a function of temperature and confining stress on geosynthetics. Based on the time-temperature superposition principle, a master curve has been drawn for extrapolating tensile creep strains to longer time intervals(1$\times$10 $^7$min.∼1$\times$10$^{10}$min.). By using this master curves, the shift factors which can be used in establishing master curve considering confining stress on geosynthetics were carried out. Each tests was performed during 8,000∼12,000 min., with temperature ranging between 5$^{\circ}C$ and 4$0^{\circ}C$ and with confining stress ranging between 0 t/$m^2$ and 9 t/$m^2$.

Evaluation of State of Concrete Pavement Sublayers Considering Direction of FWD (FWD 방향을 고려한 콘크리트 포장 하부 상태 평가)

  • Lee, Jae Hoon;Lee, Jae Hoon;Sohn, Dueck Su;Liu, Ju Ho;Jeong, Jin Hoon
    • International Journal of Highway Engineering
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    • v.16 no.6
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    • pp.69-78
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    • 2014
  • PURPOSES : The purpose of this paper is showing that the state of pavement sublayers can be evaluated differently according to direction of FWD. METHODS : The concrete pavement slabs above subgrade without anything, subgrade with cavity, and box culvert were modeled by finite element method(FEM). The modeled pavements were analyzed by changing the direction of falling weight deflectometer(FWD). The deflection results obtained from FEM were used to calculate radius of relative stiffness and composite modulus of subgrade reaction using AREA method. Then, the analyzed results were compared to the results of the test performed at the Korea Expressway Corporation(KEC) test road. RESULTS : The composite modulus of subgrade reaction increased with subgrade elastic modulus, while radius of relative stiffness decreased. The pavement sections of pure earth showed the consistent results regardless of FWD direction. In case there was cavity, the radius of relative stiffness was larger and composite modulus of subgrade reaction was smaller when FWD was leaving the cavity than when approaching the cavity. This pattern became clear when the cavity got larger. In case of the section with box culvert, the pattern was opposite to the case of cavity. When the soil cover depth increased, the effect of box culvert got smaller. When the load was applied far from the cavity and box culvert, the effect was also declined. The test performed at the KEC test road showed identical results to those of finite element analysis. CONCLUSIONS : The direction of FWD should be considered in evaluation of the state of pavement sublayers because it can be evaluated differently even under identical condition.

Characteristic evaluation of settlement and stiffness of cement-treated soils with the change of fines content under cyclic dynamic loading (세립분 함량 변화에 따른 반복 동하중을 받는 시멘트 혼합토의 침하 및 강성 특성평가)

  • Kim, Dae Sang
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.21 no.10
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    • pp.23-29
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    • 2020
  • The soil structures settle down continuously under cyclic dynamic loading after opening railway lines. This study examined the characteristics of the settlement and stiffness of cement-treated soils with the change in the content of fines under cyclic dynamic loading. Eighteen cases of the test were carried out with the changes in the fines content of soils, cement content, and curing days. Based on the test results, cement-treated soils containing more than 3% of cement could decrease settlement sufficiently even with a high portion of fines under cyclic dynamic loading. In addition, the elastic and plastic settlements could be reduced using 3 to 4% cement to the level of 1/4 and 1/6, respectively. In the viewpoint of stiffness, the resilient modulus of cement-treated soils increases with increasing cement content. Using more than 3% of cement, the 80MPa compaction stiffness standard for the upper subgrade of railways was satisfied, even with 40% of fines content of soils.

Cutting and Conveying Characteristics for Development of Chinese Leek Harvester (부추 수확기 개발을 위한 예취 및 이송특성 구명)

  • Jun H. J.;Kim S. H.;Hong J. T.;Choi Y.
    • Journal of Biosystems Engineering
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    • v.30 no.4 s.111
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    • pp.220-228
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    • 2005
  • This study was conducted to investigate the main factors that contain a rotating velocity ratio between wheel and conveyor belt, a tilt angle of conveyor belt and a rotating velocity of a dick cutter for mechanization of Chinese leek harvest. In the survey on the cultivation of Chinese leek, row spacing of 350 m and cutting height of 10 mm from the ground were set up for field tests. Test equipment was designed to cut, pick up and convey Chinese leek one row by one row. From the results of material tests, pick-up height of conveyor belt was set up at $60\~90m$ from the bottom, and the strain and stress at rupture of Chinese leek was 0.487 m/m and 0.01078 MPa. An elastic coefficient of the rubber (Neoprene) of conveyor belts was 1.1077 under the strain of 0.3 nym. from the results of field tests, the tilt angle of conveyor belt was the range of $25^{\circ}\~30^{\circ}$ under consideration far space of container, the velocity ratio between vehicle and conveying belt was 1 to 2.4~1.7 at 0.1~0.3 m/s of vehicle, and optimum rotating velocity of the disk cutter was 34.8 m/s or more under consideration for soil friction.

Evaluation of Drilled Shaft's End Condition by Impact-Echo Method (충격반향기법에 의한 현장타설 말뚝기초의 선단 조건 평가)

  • Kim, Dong-Soo;Kim, Hyung-Woo
    • Journal of the Korean Society for Nondestructive Testing
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    • v.23 no.2
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    • pp.89-97
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    • 2003
  • Experimental model studies were carried out to evaluate the end condition for drilled shafts by applying elastic impact on the top of the shaft, which is one of the various methods using stress waves. Typical impact responses corresponding to the various end conditions including free, fixed, rock-socketed, and soft-bottom with good and poor side contact conditions, were investigated. In order to simulate these renditions, mock-up shaft models made of cement mortar were used. Small-scale laboratory experiments were also performed, and field tests were carried out for the shafts that were socketed into weathered rock. It is found that the rock-socketed condition and depth of penetration into rock ran be identified from the reflection at the interface between the soil and rock in the waveform. The soft bottom rendition can be identified, only when the side contact between shaft and surrounding rock is poor, whereas it cannot be identified when the side contact is good because the waveform is similar to that of fixed end rendition.