When the foundation work of the underground part of the building structure or the excavation work of the civil engineering structure is carried out, there is the earthwork work by the inevitable process. As the economic situation continues to develop, construction in urban areas is becoming bigger and higher in scale due to the expansion of infrastructure and the rescue of urban dwellings in urban areas, and excavation of underground roads is inevitable. Excavation of the underground part may cause problems in the process difficulty and safety of the earthworks due to the complexity and various characteristics of the ground selected without consideration of the ground characteristics and site conditions. In order to complete the required facilities, it is necessary to secure the design and construction of the retaining walls. In order to complete the required construction, It is an important factor satisfying construction period and economical efficiency.

본 논문에서는 지반경계조건의 설정이 프리캐스트 아치구조물의 폭발저항성능 평가에 미치는 영향을 수치해석적 기법을 사용하여 파악하고자 하였다. 지반경계조건은 고정조건과 PML(perfectly matcher layer)을 이용한 경계조건의 두 가지로 적용하였으며, 폭발하중은 대상 구조물의 설계하중보다 큰 하중을 사용하여 경계조건의 영향을 명확히 비교할 수 있도록 하였다. 폭발압력의 분포 및 경로, 구조물에 발생하는 변위, 콘크리트의 파쇄여부, 콘크리트 및 철근의 응력을 비교․분석하였으며, PML을 적용하였을 때 지반 경계면에서 발생하는 반사파를 효과적으로 제거할 수 있음을 확인하였다. 또한, 이로 인해 구조물 기초부의 변위가 감소하는 것으로 나타났다. 하지만, 콘크리트의 파쇄여부, 콘크리트 및 철근에 발생하는 응력을 포함한 전반적인 구조물의 거동에는 뚜렷한 차이가 발생하지 않았다. 따라서 방호시설의 설계를 목적으로 폭발시뮬레이션을 수행하는 경우에는 지반경계조건에 고정조건을 적용하였을 때 안전측의 결과를 얻을 수 있으며, 해석시간이 단축되는 이점도 있으므로 이러한 면을 종합적으로 고려하여 지반경계조건을 고정조건으로 적용하는 것이 합리적이라고 판단된다.

In a seismic design, a structural demand by an earthquake load is determined by design response spectra. The ground motion is a three-dimensional movement; therefore, the design response spectra in each direction need to be assigned. However, in most design codes, an identical design response spectrum is used in two horizontal directions. Unlike these design criteria, a realistic seismic input motion should be applied for a seismic evaluation of structures. In this study, the definition of horizontal spectral acceleration representing the two-horizontal spectral acceleration is reviewed. Based on these methodologies, the horizontal responses of observed ground motions are calculated. The data used in the analysis are recorded accelerograms at the stations near the epicenters of recent earthquakes which are the 2007 Odeasan earthquake, 2016 Gyeongju earthquake, and 2017 Pohang earthquake. Geometric mean-based horizontal response spectra and maximum directional response spectrum are evaluated and their differences are compared over the period range. Statistical representation of the relations between geometric mean and maximum directional spectral acceleration for horizontal direction and spectral acceleration for vertical direction are also evaluated. Finally, discussions and suggestions to consider these different two horizontal directional spectral accelerations in the seismic performance evaluation are presented.

이 연구에서는 기초의 종류에 따라 지반-구조물 상호작용(SSI) 효과가 LNG 저장탱크의 지진응답해석에 미치는 효과를 분석하였다. 이를 위하여 직경 71m인 LNG 탱크와 기반암 위 점토지반의 깊이가 30m인 지반조건을 고려하였다. 그리고 기초형식으로 네 가지(얕은 기초, 말뚝지지 전면기초, 말뚝기초(지표면 접촉식, 부유식)를 고려하였다. 지반의 비선형성은 자유장 지반에 대하여 등가선형화기법으로 고려되었다. 또한, 말뚝기초의 시공과정에서 발생하는 동다짐 효과에 대해서도 분석하였다. SSI 해석을 위하여 진동수영역 해석프로그램인 KIESSI-3D를 이용하였다. 지반-구조물 상호작용 해석을 통해 LNG 저장탱크의 외조 벽체 쉘의 응력과 내조탱크의 밑면전단력 및 전도모멘트를 구하였다. 해석결과로부터 다음과 같은 결론을 얻을 수 있었다: (1) 고정 기초해석에 의한 외조와 내조탱크의 지진응답이 SSI 효과로 인한 지진응답보다 매우 컸다. (2) SSI의 효과가 내조탱크와 외조탱크의 동적응답에 미치는 영향은 기초의 형식에 따라 다르게 나타난다. (3) 말뚝지지 전면기초에서 동다짐 효과에 의한 구조물 응답의 변화는 약 10%로서 무시할 수 없을 정도로 큰 것으로 나타났다.

To calculate proper seismic design load and seismic design category, the exact site class for construction site is required. At present, the average shear-wave velocity for multi-layer soil deposits is calculated by the sum of shear-wave velocities without considering of vertical relationship of the strata. In this study, the transfer function for the multi-layered soil deposits was reviewed on the basis of the wave propagation theory. Also, the transfer function was accurately verified by the finite element model and the eigenvalue analysis. Three methods for site period estimation were evaluated. The sum of shear-wave velocities underestimated the average shear-wave velocities of 526 strata with large deviations. The equation of Mexican code overestimated the average shear-wave velocities. The equation of Japanese code well estimated the average shear-wave velocities with small deviation.

Among the soft ground improvement methods, PBD is the most common construction method because it is cheap and construction is fast. However, if the ground is rigid, additional work is required. In this study, the structural safety, natural vibration, and safety angle of the steel vertical tower structure were evaluated in the development of the PBD composite perforator which can be combined with drilling work and PBD construction. Structural safety was assessed when the wind load of 20 m/s was simultaneously applied to the PBD construction load of 20 tons, the perforating operation of 25 tons, and the wind speed of 50 m/s was applied only to the wind load. The natural frequencies were evaluated up to the sixth mode, and the safety angle was evaluated for static and dynamic safety angles.

PURPOSES: The purpose of this study is to verity the applicability of a portable small-loop electromagnetic survey method to underground cavity detection. METHODS: In order to evaluate applicability of the method, a test bed comprised of four sections was constructed. The two sizes of the four cavities artificially formed at two depths were contained in the test bed. Each cavity was positioned at center of each 6 m long section. Four types of pavement materials such as unpaved ground, bricks, asphalt, and concrete were used at every section. The portable small-loop electromagnetic device measured electrical conductivity as an exploration signal that varied according to the electrical properties underground. The electrical conductivity was converted into two-dimensional electrical resistivity distribution sections using an inverse analysis program. RESULTS : The results showed that the electrical resistivity of the non-cavity area was lower than that of the cavity area. The electrical resistivity increased as the measurement device moved closer to the cavity position. It was also found that the electrical resistivity values were not significantly affected by pavement type. The small cavity with diameter of 35 cm could be detected up to 1.2 m depth. CONCLUSIONS: Therefore, it was verified that the portable small-loop electromagnetic survey method is applicable to the detection of cavities in sections where ground subsidence is expected. This method can be effectively used for small-scale roads such as sidewalks, parkways, and side streets where large exploration equipment cannot enter.

The site coefficients in the common requirements for seismic design codes, which were promulgated in 2017, were reevaluated and the standard design spectrum for soil sites were newly proposed in order to ensure the consistency of the standard design spectra for rock and soil sites specified in the common requirements. Using the 55 ground motions from domestic and overseas intraplate earthquakes, which were used to derive the standard design spectrum for rock sites, as rock outcropping motions, site response analyses of Korean soil were performed and its ground-motion-amplification was characterized. Then, the site coefficients for soil sites were reevaluated. Compared with the existing site coefficients, the newly proposed short-period site coefficient Fa increased and the long-period site coefficient Fv decreased overall. A new standard design spectrum for soil sites was proposed using the reevaluated site coefficients. When compared with the existing design spectrum, it could be seen that the proposed site coefficients and the standard design spectrum for soil sites were reasonably derived. They reflected the short-period characteristics of earthquake and soil in Korea.

In this study, a numerical approach based on mid-point integrated finite elements and a viscous boundary is proposed for time-domain wave-propagation analyses in infinite poroelastic media. The proposed approach is accurate, efficient, and easy to implement in time-domain analyses. In the approach, an infinite domain is truncated at some distance. The truncated domain is represented by mid-point integrated finite elements with real element-lengths and a viscous boundary is attached to the end of the domain. Given that the dynamic behaviors of the proposed model can be expressed in terms of mass, damping, and stiffness matrices only, it can be implemented easily in the displacement-based finite-element formulation. No convolutional operations are required for time-domain calculations because the coefficient matrices are constant. The proposed numerical approach is applied to typical wave-propagation and soil-structure interaction problems. The model is verified to produce accurate and stable results. It is demonstrated that the numerical approach can be applied successfully to nonlinear soil-structure interaction problems.

In this paper, we study the existing results of the structure-soil-structure interaction (SSSI) effect on seismic responses of structures and summarize important parameters. The parameters considered in this study are a combination of buildings in the power block of a nuclear power plant, the characteristics of earthquake ground motions and its direction, and the characteristics embedded under the ground. Based on these parameters, the seismic analysis model of the structures in the power block of the nuclear power plant is developed and the structure-soil-structure interaction analyses are performed to analyze the influence of the parameters on the seismic response. For all analyses, the soil-structure interaction (SSI) analysis program CNU-KIESSI, which was developed to enable large-sized seismic analysis, is used. In addition, the SSI analyses is performed on individual structures and the results are compared with the SSSI analysis results. Finally, the influence of the parameters on the seismic response of the structure due to the SSSI effect is reviewed through comparison of the analysis results.

Underground cavities are frequently taking place in urban areas due to soil loss caused by structural defects of underground buried pipes. In this study, a field experimental program was conducted to detect ground condition using the electrical resistivity survey and the pneumatic cone penetration test. In addition, we proposed a method to estimate the weighted mean resistivity value by quantifying the electrical resistivity measurements through image analysis in order to compare the results of pneumatic cone penetration test. Consequently, it was found that as the weighted average resistivity value decreased, the smaller the N-value (penetration depth per blow number) from the pneumatic cone penetration test results. Based on the limited number of field experimental measurements, the correlation between weighted average resistivity value and the N-value of pneumatic cone penetration test is deemed promising in assessment of ground conditions associated with developing underground cavitation.

The Pohang earthquake with a magnitude of 5.4 occurred on November 15, 2018. The epicenter of this earthquake located in south-east region of the Korean peninsula. Since instrumental recording for earthquake ground motions started in Korea, this earthquake caused the largest economic and life losses among past earthquakes. Korea is located in low-to moderate seismic region, so that strong motion records are very limited. Therefore, ground motions recorded during the Pohang earthquake could have valuable geological and seismological information, which are important inputs for seismic design. In this study, ground motions associated by the 2018 Pohang earthquake are generated using the point source model considering domestic geological parameters (magnitude, hypocentral distance, distancefrequency dependent decay parameter, stress drop) and site amplification calculated from ground motion data at each stations. A contour map for peak ground acceleration is constructed for ground motions generated by the Pohang earthquake using the proposed model.

최근, 장기간의 집중호우 및 장마로 인하여, 상대적으로 구조가 불안정한 보도 하부에 공동이 발생하여, 상당수의 지반함몰이 발생되었다. 또한 내진·지질학 전문가들에 따르면 최근 잦아진 지진이 지반연화에 영향을 미쳐 지반함몰 현상이 더욱 늘어날 수 있다고 경고하고 있다. 이에 본 연구에서는 지반하부에 존재하는 공동을 EM방법을 활용하여 미연에 탐지함으로써, 인적·물적 피해를 최소화하고, 시민의 안전을 도모하고자 한다. 지반하부 공동 탐사에 이용되는 기존의 방법들은 탐사시간이 지나치게 길거나, 포장에 파손을 야기하고, 좁은 지역에서는 탐사가 불가능한 단점이 있다. 하지만 EM방법의 경우 탐사시간이 비교적 짧고, 비접지식이기 때문에 포장에 파손도 야기하지 않으며, 좁은 지역에서의 탐사도 가능하기 때문에, 본 연구에서는 보도, 공원도로, 이면도로 등 좁은 지역에 대해서 EM방법을 활용하여 지반함몰 위험지역 예측에 대한 기초연구를 진행하고자 한다. 기존에 사용되는 EM방법은 터널탐사 및 매립지 오염도 탐사에만 이용되고 있었기 때문에, 체코 GF Instrument사의 EM장비인 CMD Mini Explorer를 이용하여 기반하부 공동 탐사를 위한 실험을 진행하였다. 공동탐사 이외의 외부조건을 통일하기 위해서 나대지에서 실험을 진행하였으며, 기존 지반상태, 공동 모사상태, 공동 및 금속 모사상태에서 각각 탐사를 진행하였다. 탐사 결과, 금속의 존재유무와 관계없이 공동 위치에서 전기비저항 이상대가 나타났으며, 되메움 작업 시 다짐상태에 따라 일어난 지반의 교란이 층 형태의 전기비저항 분포로 나타났다. 따라서, EM방법은 공동 탐사에 있어 충분한 성능을 가지고 있으며, 금속에도 큰 영향을 받지 않는다는 것이 확인되었고, 연약지반에 대한 탐사에도 활용될 수 있을 것으로 판단되었다.

This study reviews concepts, theories and formulas included in standards on soil-structure interaction and also shows practical example of application for engineers. Real structures are 3 dimensional and multi degree of freedom but they are often idealized to single degree of freedom for convenience. In this study, detailed procedures to calculate soil spring constants and damping coefficients and method to model soil-structure system are explained. Additionally, case studies to judge fixed base condition and evaluation of applicability of simple analysis method based on response spectra are performed.

본 연구에서는 콘크리트 석션식 지지구조물을 사용한 해상풍력발전시스템의 지진응답 해석을 수행하여 그 거동 특성을 파악한다. 전체 시스템을 RNA, 타워, 지지구조물로 구성된 구조계와 이에 접하고 있는 유체 및 지반의 부분구조로 분리하여 운동방정식을 유도한다. 구조계에 작용하는 유체의 동수압과 지반의 상호작용력을 산정하고, 이를 구조계의 운동방정식과 결합하여 전체 시스템의 지배방정식을 도출한 후, 이 방정식의 해를 구하여 해상풍력발전시스템의 지진응답을 계산한다. 해 석 결과로부터 지반-구조물 상호작용은 콘크리트 석션식 지지구조물에 의해 지지된 해상풍력발전시스템의 지진응답을 크게 증가시킬 수 있음을 확인할 수 있다. 특히, 지반의 유연성으로 인해 시스템의 고차 고유모드 응답이 증가할 수 있으므로, 해 상풍력발전시스템의 동적거동 산정 시에는 반드시 지반-구조물 상호작용의 효과를 고려하여야 할 것이다.