• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.33 no.3
• /
• pp.1063-1075
• /
• 2013

The strength of frozen soils is one of the significant design parameters for the construction in frozen ground. The properties of frozen soils should be investigated to understand the strength of frozen soils. The objective of this study is to figure out the characteristics of elastic waves in frozen soils, which reflect the constituent and physical structure of frozen soils in order to provide fundamental information of those according to the degree of saturation. Freezing cell is manufactured to freeze specimens, which are prepared with the degree of saturation of 10%, 40%, and 100%. Piezo disk elements are used as the compressional wave transducers and Bender elements are used as the shear wave transducers. While the temperature of specimens changes from $20^{\circ}C$ to $-10^{\circ}C$, the velocities, resonant frequencies and amplitudes of the compressional and shear waves are investigated based on the elastic wave signatures. Experimental results reveal that the elastic wave velocities increase as the degree of saturation increases. The variation of resonant frequencies coincide with that of elastic wave velocities. A marked discrepancy in amplitudes of compressional and shear waves are observed at the temperature of $0^{\circ}C$. This study renders the basic information of elastic waves in frozen soils according the degree of saturation.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.21 no.10
• /
• pp.259-266
• /
• 2020

In this study, required drill bits and excavation methods were developed for an uneven drilling method that can solve the problem of performance degradation of rock bolts. The developed drill bit's excavation performance was verified using rock with a strength of 100 MPa or more. In addition, for the relative evaluation of the uneven excavation method, experimental specimens were prepared for models with and without irregularities, and tests were performed. As a result of the experiment, the model with unevenness exhibited an average critical draw resistance of 801.6 kN, which is about 1.7 times the value of 468.7 kN for the model without unevenness, thus confirming the effect sufficiently. Therefore, it is expected that the resistance performance will significantly increase despite an increase in the uneven hole diameter of 20 mm. In the future, the results of this study could be used as basic data when performing other studies using numerical analysis models and performance verification through experiments to obtain an optimized rock forming method.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.27 no.5
• /
• pp.315-323
• /
• 2015

Damage level of coastal structures has been scaled up according to increase of wave height and duration of the storm due to the abnormal global climate change. So, the design criteria for new breakwaters is being intensified and structural strengthening is also conducted for the existing breakwaters. Recently, interlocking concept has been much attention to enhance the structural stability of the conventional caisson structure designed individually to resist waves. The interlocking caisson breakwater may be survival even if unusual high wave occurs because the maximum wave force may be reduced by phase lags among the wave forces acting on each caisson. In this study, the dispersion characteristics of wave forces using interlocking system that connect the upper part of caisson with cable in the normal direction of breakwater was investigated. A simplified linear model was developed for computational efficiency, in which the foundation and connection cables were modelled as linear springs, and caisson structures were assumed to be rigid. From numerical experiments, it can be found that the higher wave forces are transmitted through the cable as the angle of incident wave is larger, and the larger the stiffness of the interlocking cable makes larger wave dispersion effect.

• Proceedings of the International Union of Geodesy And Geophysics Korea Journal of Geophysical Research Conference
• /
• 2003.05a
• /
• pp.17-17
• /
• 2003

한반도에 있어서의 지진의 영향을 분석하기 위해서는 강지진동 연구가 필수적이다. 강지진동 자료가 부족한 한반도의 특성상 모사를 통해 연구하고 있다. 강지진동 분석을 하기 위해서는 되도록 노이즈가 포함되어 있지 않은 지진파자료를 선택하여 그 지진자료의 스펙트럼 분석을 통해 감쇠상수 k, Q 등을 구한다. 이러한 감쇠상수 값을 통해 한반도의 진동 특성을 이해할 수 있다. 그러나 감쇠상수를 구하는 과정에서 감쇠상수 분석에 사용된 지진자료에 노이즈가 더해졌을 경우, 어떤 형태로 스펙트럼 영역에 영향을 미치고, 감쇠상수에는 어떤 영향을 미치는 지를 연구하여 노이즈효과를 제거할 수 있는 최적화된 분석에 관한 연구가 선행되어야 한다고 본다. 따라서 이번 연구에서는 강지진동 모사프로그램을 가지고 노이즈효과를 적용하면서 감쇠상수에 노이즈가 어떤 영향을 미치는 지에 대한 수치 해석적 연구를 실시하였다. 합성지진파에 이 합성지진파와 전혀 다른 주파수 형태를 보이는 노이즈를 강도를 달리하면서 합성해 본 결과, 노이즈효과를 고려할 수 있는 몇 가지 요소가 있음을 알 수 있었다. 감쇠상수 k값을 강지진동 모사프로그램으로부터 값을 달리하며 합성해 본 결과 노이즈효과를 보이는 것을 알 수 있었으며, 감쇠상수 k를 선형회귀를 통해 $k_{s}$ 와 $k_{q}$를 구할 때의 적용 주파수 범위를 변화시켰을 때도 일정한 양상의 노이즈 효과를 보였다. 또 지진자료와 노이즈를 중첩시킨 지진파 시계열 자료의 정부분만을 감쇠상수 k를 구하는 선형회귀에 이용했을 경우에도 노이즈 효과를 보였다. 또한 계산되어 나온 감쇠상수 값으로부터 특정지역의 지반운동의 특성을 이해할 수 있는 스펙트럼 가속도, 최대 가속도, 및 최대속도 값에 따른 감쇠식을 구하였다. 이것을 한반도와 같은 판 내부 환경인 ENA 값과 비교하였으며 기존의 연구와도 비교하였다.심으로부터 지오이드까지의 거리, 지오이드로부터 지표까지의 거리를 정의해주었으며, 각 격자점의 수직구조를 정의하기 위해 깊이에 따른 각 매질의 밀도, P파의 속도, S파의 속도, P파에 대한 Q값, S파에 대한 Q값을 정의 해주었다. S파의 속도를 구하기 위해서 지구 내부 물질을 포아송 매질이라는 가정 하에, 관계식을 $Vp{\;}={\;}SQRT(3){\;}{\times}{\;}Vs$ 이용하였다. 획득한 모델치들을 이용해 동해와 동해 인근 지역에 대한 초기모델을 구축하였다. 약 1 × 10/sup 6/ e/sup -//sec·n㎡ 의 전자선량에 해당되며 이를 기준으로 각각의 illumination angle에 대한 임계전자선량을 평가할 수 있었다. 실질적으로 Cibbsite와 같은 무기수화물의 직접가열실험 시 전자빔 조사에 의해 야기되는 상전이 영향을 배제하고 실험을 수행하려면 illumination angle 0.2mrad (Dose rate : 8000 e/sup -//sec·n㎡)이하로 관찰하고 기록되어야 함을 본 자료로부터 알 수 있었다.운동횟수에 의한 영향으로써 운동시간을 1일 6시간으로 설정하여, 운동횟수를 결정하기 위하여 오전, 오후에 각 3시간씩 운동시키는 방법과 오전부터 6시간동안 운동시키는 두 방법을 이용하여 품질을 비교하였다. 각 조건에 따라 운동시킨 참돔의 수분함량을 나타낸 것으로, 2회(오전 3시간, 오후 3시간)에 나누어서 운동시키기 위한 육의 수분함량은 73.37±2.02%를 나타냈으며, 1회(6시간 운동)운동시키기 위한 육은 71.74±1.66%을 나타내었다. 각각의 운동조건에서 양식된 참돔은 사육초기에는 큰 변화가 없었으나, 사육 5일 이후에는 수분함량이 증가하여 15일에는 76.40±0.14, 75.62±0.98%의 수분함량을 2회와 1회 운동시킨 참돔의 육에서 각각 나타났다. 운동횟수에 따른 지

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.4 no.2
• /
• pp.97-106
• /
• 2009

self-loading, various problems related to construction can be solved as well as the save of construction cost. Thus, this study has an aim of applying foam concrete to structural purpose by adding bottom ash as a reinforcing material like fine aggregate, in contrast to conventional non-structural usage such as soundproofing or insulating materials. In addition, it was evaluated in terms of unit volume weight, flow value, air void, water absorption and dosage of foam agent wether replacement of cement by granulated blast furnace slag or fly-ash has an effect on the material characteristics of foam concrete. As results of experiments, it can be found that the increase of fine aggregate ratio, that is to say, the increase of bottom ash results in the increase of unit volume weight, while decreasing air void and flow value. But, appropriate addition of bottom ash to foam concrete makes it easy to control a homogeneous and uniform quality in foam concrete due to less sensitive to bubbles. As the replacement ratio of mineral admixtures such as granulated blast furnace slag and fly-ash increases, as unit volume weight tends to decrease. In the meanwhile, serious effects were shown on fluidity of foam concrete when more than limit of replacement ratio was applied.

• Korean Journal of Construction Engineering and Management
• /
• v.16 no.6
• /
• pp.136-143
• /
• 2015

Snow-melting system has been applied not only to roads for car traffic but also to pavement for the pedestrians safety reason in some of the developed countries such as USA and Canada based on countermeasures against Natural Disasters Act revised in 2000. Even though this system was introduced in korea in 2006 and has been partly applied to car traffic roads, there is few places that the system has been applied. Therefore, in this research a snow-melting system with a block-type to cover a pavement that efficiently transfers heat form heat rays to the top of a pavement and protects the heat rays. A quality check showed that compression and bending strength was improved approximately 5 times stronger and 7 to 10 times more absorption rate than the KS(Korea Industrial Standard) requirement. Moreover, only 10 minute was required to increase temperature above zero with a block-type snow-melting system whereas approximately 180 minute was spent with the existing system. This research is expected to contribute to environmental issues and reduce accidents on a slippery road.

• The Journal of Engineering Geology
• /
• v.24 no.1
• /
• pp.23-38
• /
• 2014

The composition of carbonate sands from a sabkha at Ruwais in the UAE differs from that of silica sand, and these sands are crushed easily under low compression pressures. Accordingly, particle crushing of carbonate sand occurs under high pressure, which results in additional settlement and reduces the shear strength. In this study, consolidation and triaxial tests were conducted to analyze the characteristics of carbonate sands following particle crushing. The unusual shear strength graphs of the carbonate sands result from the degree of particle pre-crushing. For the range at p' > p in the p (p')-q diagram, negative (-) excess porewater pressures occur if the axial pressure causes particle crushing that induces exposure of the inner voids. In addition, the q value decreased after particle crushing. In conclusion, the unusual characteristics of the carbonate sands were induced by particle crushing. The triaxial tests revealed that the degree of particle pre-crushing influenced the excess porewater pressure.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.12 no.1
• /
• pp.79-87
• /
• 2008

Seismic performance evaluation of structure requires an estimation of the structural performance in terms of displacement demand imposed by earthquakes on the structure. Incremental Dynamic Analysis(IDA) is a analysis method that has recently emerged to estimate structural performance under earthquakes. This method can obtained the entire range of structural performance from the linear elastic stage to yielding and finally collapse by subjecting the structure to increasing levels of ground acceleration. Most structures are expected to deform beyond the limit of linearly elastic behavior when subjected to strong ground motion. The nonlinear response history analysis(NRHA) among various nonlinear analysis methods is the most accurate to compute seismic performance of structures, but it is time-consuming and necessitate more efforts. The nonlinear approximate methods, which is more practical and reliable tools for predicting seismic behavior of structures, are extensively studied. The uncoupled modal response history analysis(UMRHA) is a method which can find the nonlinear reponse of the structures for ESDF from the pushover curve using NRHA or response spectrum. The direct spectrum analysis(DSA) is approximate nonlinear method to evaluate nonlinear response of structures, without iterative computations, given by the structural linear vibration period and yield strength from the pushover analysis. In this study, the practicality and the reliability of seismic performance of approximate nonlinear methods for incremental dynamic analysis of mixed building structures are to be compared.

• The Journal of Engineering Geology
• /
• v.31 no.3
• /
• pp.357-366
• /
• 2021

Shear behavior dependent on the shape and roughness of rock joints can greatly influence the stability of the ground and rock structures. The efficient design of rock structures requires understanding of the shear behavior due to joints and accurate calculation of the shear strength. This work reports numerical shear tests using PFC2D on No. 1 (JCR-1), with smooth joints, and No. 7 (JRC-7) and No. 9 (JRC-9), with relatively rough joints, for the 10 shapes of standard joint profiles proposed by Barton and Choubey (1977). The aim was to investigate the shear behavior of rock joints with respect to their roughness. The results show the maximum shear stress to be about 3.2 to 5.0 times greater in the rougher JRC-7 and JRC-9 joints than in smoother JRC-1. The maximum shear displacement was approximately 4.1 to 5.8 times greater at the first normal stress than at the second. The rougher joints showed friction angles of the rock joints that were approximately 1.8 to 3.9 times greater than that in the smooth joint. Overall, increasing the rock joint roughness increased the maximum shear stress and friction angle.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.23 no.5
• /
• pp.84-95
• /
• 2019

This paper reports the process of seismic fragility analysis for the rahman-type continuous bridge system. The target structure was the five span highway bridge with maximum pier hight of 72m. OpenSees software was used for the nonlinear time history analysis. In this study, 50 ground motions are considered for nonlinear time history analysis. For each ground motion, PGA was scaled from 0.1g to 2.0g with intervals of 0.1g in order to consider a wide range of the seismic intensity measure. In addition, yield displacement and ultimate displacement of each pier were calculated through section analysis. Based on the result of non linear time history analysis and section analysis, damage condition of target bridge was classified according to the definition of damage condition proposed by Barbat et al. As a result, it was predicted that Extensive Damage occurred at P1 when 0.731 g earthquake occurred in the longitudinal direction. Based on the seismic fragility analysis results, it is found that the probability of occurrence of Extensive Damage in the 4,800 - year period earthquake was about 4.2%. Therefore the target bridge has enough safety for earthquake.