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비선형 수치해석을 통한 단자유도 얕은기초 구조물의 지진 응답특성 검증
추연욱,이진선,김동수 한국지반공학회 2013 한국지반공학회논문집 Vol.29 No.3
Seismic response of single degree of freedom system supported by shallow foundation was analyzed by using nonlinear explicit finite difference element code. Numerical analysis results were verified with dynamic centrifuge test results of the same soil profile and structural dimensions with the numerical analysis model at a centrifugal acceleration of 20g. Differences between the analysis and the test results induced by the boundary conditions of control points can be reduced by adding additional local damping to the natural born cyclic hysteretic damping of the soil strata. The analysis results show good agreement with the test results in terms of both time histories and response spectra. Thus, it can be concluded that the nonlinear explicit finite difference element code will be a useful technique for estimating seismic residual displacement, earthpressure etc. which are difficult to measure during laboratory tests and real earthquake.
추연욱,신동훈,조성은,임은상,김동수 대한토목학회 2013 KSCE JOURNAL OF CIVIL ENGINEERING Vol.17 No.5
Sandy gravel materials have recently been utilized in place of crushed rock materials as the main rockfill materials in Concrete Faced Rockfill Dams (CRFD) to address geological and environmental problems. In this paper, an experimental scheme for centrifuge modeling was developed to simulate a Concrete Faced Gravel-fill Dam (CFGD). The dam considered in this study was designed to implement a drainage zone of high permeability in the main gravel-fill zone to enhance safety against accidental water infiltration into the dam. Two centrifuge tests were performed and compared to investigate the performance of the drainage zone. The first test was done with the drainage zone and the second without the drainage zone. In the centrifuge tests, water infiltration was simulated by raising the water table over pre-implemented cracks on the model face slab. The infiltration behaviors were monitored by pore water pressure transducers. The centrifuge tests showed that the drainage zone of the CFGD effectively drains infiltrating water out of the dam body in a short time. Numerical modeling was also performed to help understand the process of seepage through cracks.
추연욱,김동수,Choo Yun-Wook,Kim Dong-Soo 한국지반공학회 2005 한국지반공학회논문집 Vol.21 No.3
본 논문에서는 포화 및 배수 조건에 따른 사질토 지반의 변형특성을 개선된 Stokoe식 비틂전단시험기를 이용하여 비교$\cdot$관찰하였다. 기존의 Stokoe식 비틀 전단 시험기를 개선하여 시료의 완전 포화상태를 만들고, 포화 배수 및 비배수 조건에서 비틂 전단 시험이 가능하도록 하였고, 또한, 비배수 시험에서 간극수압을 동시에 측정할 수 있도록 하였다. 국내에서 채취된 금강모래와 일본의 토요라 모래를 사용하여, 건조, 포화 배수 및 포화 비배수 조건, 3가지 간극비, 4가지 구속응력 조건을 달리하여 비틂전단시험을 수행하였다. 시험결과를 바탕으로, 전단탄성계수와 재료 감쇠비를 각 조건에 대하여 반복하중 및 변형률 크기의 영향을 비교$\cdot$분석하고, 배수 조건에 따라 다르게 나타나는 사질토 지반의 저변형률 (c) 및 중간 변형률 (${10}^{-3}\%<\gamma_c<{10}^{-1}\%$)에서의 변형특성을 관찰하였다. In this study, dynamic deformation characteristics of sands under dry, saturated drained and undrained conditions were investigated at small to intermediate strains using the modified Stokoe-type torsional shear tests. The equipment was modified to saturate the specimen and to maintain the B-value above 0.99 during the test. On two types of sands, Geumgang sand from Korea and Toyoura sand from Japan, tests were carried out at various drainage conditions, void ratios, and effective confining pressures. Based on the test results, dynamic deformation characteristics, shear modulus (G) and damping ratio (D), and/or pore-water pressure were measured with strain amplitude and number of loading cycles. Variations of G and D at small ($\gamma_c<{10}^{-3}\%$) to medium (${10}^{-3}\%<\gamma_c<{10}^{-1}\%$) strains were measured under various drainage conditions, and test results were intensively compared considering drainage conditions.