• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.494-504
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• 2008

Successful design, construction and maintenance of NATM tunnel demands prediction, control, stability estimation and monitoring of surface settlement, gradient and ground displacement with high accuracy. Back analysis using measured data and forward analysis have been and are indispensable tools to achieve this goal. Sakurai provided the hazard warning levels for assessing the stability of tunnels using the relation of critical strain and apparent Young's modulus. This paper performed the estimation of tunnel stability on construction. Firstly, the apparent Young's modulus concept and back analysis method is introduced for the assessment of tunnel safety during excavation a brief framework. Secondly, this paper deals with case study using "Apparent Young's modulus" and "Back analysis" for the purpose of estimating the stability of NATM tunnel in Korea. Finally, a general method that can be estimated the tunnel stability discussed by a flow chart.

• 한국재난정보학회 논문집
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• 제6권2호
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• pp.45-65
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• 2010

There has been tighten up the need of seismic retrofit about 31 public facilites since published "Korean Earthquake Damage Prevention Law". Therefore, seismic studies have been developed and enforced the studies. Measuring dynamic stiffness of subsurface materials influence on seismic performance evaluation to build up seismic retrofit. The soil dynamic properties for seismic performance evaluation are N-value from using SPT(standard penetration test), dynamic shear elastic modulus and dynamic deformation modulus using laboratory tests. The most unscientific element in ground dynamic properties involved uncertainties is obviously N-value using SPT. This study shows that effect of N-value included natural and artificial uncertainties to seismic performance evaluation of ground structures is not only approached probabilistic analysis using FOSM method and tornado diagram, but also review how to spread effect of seismic performance evaluation of ground structures.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2003년도 추계학술대회 논문집(III)
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• pp.333-338
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• 2003

Polymeric composite structures used in ground transportation applications such as the carbody of tilting train may be exposed to a ground environmental conditions during long-term missions. In this study, the degradation of mechanical and physical properties of graphite/epoxy composite and glass fabric/phenol composite under ground environmental conditions was investigated. Accelerated environmental conditions of ultraviolet radiation, temperature, and moisture were considered. Several types of specimens were used to investigate the effects of environmental conditions on mechanical properties of the composites. Also, storage shear modulus, loss shear modulus, and tan 8 were measured as a function of exposure times through a dynamic mechanical analyzer. Finally, composite surfaces exposed to environmental conditions were examined using a scanning electron microscope.

• Geomechanics and Engineering
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• 제12권5호
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• pp.739-752
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• 2017

This study was intended to evaluate the improved strength of the ground by applying the bio grouting method to a loose sandy ground. The injection material was prepared in the form of cement-like powder, with the bio injection material produced by microbial reactions. The grouting test was conducted under the conditions similar to the field where the bio injection material can be applied. In addition, the injection materials (cement and sodium silicate No. 3) used for Labile Waterglass (LW) method and the conventional grouting methodwere prepared through a two-solution one-step process. The injection into the specimens was done at a pressure of 150 kPa and then, with a bender element, their moduliof elasticity were measured on the 7th, 14th, 21st and 28th curingdays to analyze their strengths according to the duration of curing. It was confirmed that in all injection materials the moduli of elasticity increased over time. In particular, when 30% of the bio injection material was added to 100% cement, the modulus of elasticity tended to increase by about 15%. This confirmed that the applicability became higher when the bio injection material was used in place of the conventional sodium silicate.

• 접착 및 계면
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• 제13권3호
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• pp.121-130
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• 2012

본 연구에서는 대나무섬유의 분쇄 유 무에 따라 섬유함량이 각각 30, 40, 50 wt%인 대나무/PLA 펠렛을 압출공정으로 제조하고 사출공정을 통해 대나무/PLA 바이오복합재료를 성형하여 그들의 기계적, 열적, 충격 특성과 수분흡수성을 조사하였다. 대나무/PLA 바이오복합재료의 굴곡탄성률, 인장탄성률, 저장탄성률 및 충격강도는 neat PLA에 비하여 두드러지게 증가되었다. 특히 탄성률은 분쇄된 대나무섬유의 도입에 의하여 더욱 증가하였다. 또한 분쇄한 대나무섬유의 사용이 바이오복합재료의 장시간 동안 측정한 수분에 대한 저항성 증가에 효과적이었다. 대나무섬유의 사용이 neat PLA의 열변형온도를 약 16% 향상시키는 효과를 나타내었으나, 분쇄된 대나무섬유의 사용에 의한 증가는 미미하였다. 분쇄된 대나무섬유의 사용은 바이오복합재료의 인장강도와 충격강도에는 크게 영향을 주지 않았다.

• Geomechanics and Engineering
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• 제22권4호
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• pp.339-348
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• 2020

The uncertain geotechnical properties of frozen soil are important evidence for the design, operation and maintenance of the frozen ground. The complex geological, environmental and physical effects can lead to the spatial variations of the frozen soil, and the uncertain mechanical properties are the key factors for the uncertain analysis of frozen soil engineering. In this study, the elastic modulus, strength and Poisson ratio of warm frozen soil were measured, and the statistical characteristics under different temperature conditions are obtained. The autocorrelation distance (ACD) and autocorrelation function (ACF) of uncertain mechanical properties are estimated by random field (RF) method. The results show that the mean elastic modulus and mean strength decrease with the increase of temperature while the mean Poisson ratio increases with the increase of temperature. The average values of the ACD for the elastic modulus, strength and Poisson ratio are 0.64m, 0.53m and 0.48m, respectively. The standard deviation of the ACD for the elastic modulus, strength and Poisson ratio are 0.03m, 0.07m and 0.03m, respectively. The ACFs of elastic modulus, strength and Poisson ratio decrease with the increase of ratio of local average distance and scale of fluctuation. The ACF of uncertain mechanical properties is different when the temperature is different. This study can improve our understanding of the spatial autocorrelation variations of uncertain geotechnical properties and provide a basis and reference for the uncertain settlement analysis of frozen soil foundation.

• 한국지반환경공학회 논문집
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• 제22권12호
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• pp.15-24
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• 2021

대부분이 산악지역인 국내에서는 터널 및 지하공간개발의 비중이 점점 높아지고 있다. 지하공간개발 시 지반 개량공법을 적용하여 지반을 보강하지만 국내에서는 여전히 사건 사고가 빈번하게 발생하고 있다. 대표적인 지반 보강공법인 그라우팅 공법은 주입재의 총량과 실제 그라우팅 시공 시 사용한 주입재의 양을 비교하여 효과를 판정하였으며, 혹은 그라우팅 공법을 적용한 지반에 보링 후 시료의 일축압축강도 평가 혹은 현장 투수시험을 통하여 지반 보강여부를 판단하였다. 하지만, 시공 중 혹은 대상 지반 내에 지반 보강이 제대로 이루어졌는지는 판단하기는 어렵다. 이러한 문제를 해결하기 위해 전도성 재료인 탄소섬유와 그라우트 재료인 마이크로시멘트를 혼합하여 그라우팅을 수행한 후 전기비저항 측정을 통해 시공 중이나 시공 후에 품질관리가 가능한 새로운 방법에 대해 연구가 필요한 실정이다. 본 연구는 이에 대한 기초연구로 전도성 재료인 탄소섬유가 혼합된 그라우트 재의 성능을 평가하기 위해 탄소섬유 0%, 3%, 5%, 7%로 혼합된 시멘트 공시체를 제작하였으며, 제작한 공시체에 대하여 3일, 7일, 28일 습도 99%의 조건으로 습윤양생 시킨 후 압축파 속도 및 전단파 속도 측정을 수행하였다. 압축파 속도 및 전단파 속도 측정 결과 탄소섬유의 배합비 및 재령일수 증가에 따라 증가하는 경향을 보였으며, 재료의 강성인 탄성계수 및 전단탄성계수도 증가하는 것을 확인하였다.

• Geomechanics and Engineering
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• 제13권4호
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• pp.601-619
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• 2017

Cantilever retaining wall movements generally depend on the intensity and duration of ground motion, the response of the soil underlying the wall, the response of the backfill, the structural rigidity, and soil-structure interaction (SSI). This paper investigates the effect of material properties on seismic response of backfill-cantilever retaining wall-soil/foundation interaction system considering SSI. The material properties varied include the modulus of elasticity, Poisson's ratio, and mass density of the wall material. A series of nonlinear time history analyses with variation of material properties of the cantilever retaining wall are carried out by using the suggested finite element model (FEM). The backfill and foundation soil are modelled as an elastoplastic medium obeying the Drucker-Prager yield criterion, and the backfill-wall interface behavior is taken into consideration by using interface elements between the wall and soil to allow for de-bonding. The viscous boundary model is used in three dimensions to consider radiational effect of the seismic waves through the soil medium. In the seismic analyses, North-South component of the ground motion recorded during August 17, 1999 Kocaeli Earthquake in Yarimca station is used. Dynamic equations of motions are solved by using Newmark's direct step-by-step integration method. The response quantities incorporate the lateral displacements of the wall relative to the moving base and the stresses in the wall in all directions. The results show that while the modulus of elasticity has a considerable effect on seismic behavior of cantilever retaining wall, the Poisson's ratio and mass density of the wall material have negligible effects on seismic response.

• 한국도로학회논문집
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• 제16권2호
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• pp.43-52
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• 2014

PURPOSES : To solve problems in current compaction control DCPT(Dynamic Cone Penetrometer Test), highly correlated with various testing methods, simple, and economic is being applied. However, it、s hard to utilize DCPT results due to the few numerical analyses for DCPT have been performed and the lack of data accumulation. Therefore, this study tried to verify the validation of numerical modeling for DCPT by comparing and analyzing the results of numerical analyses with field tests. METHODS: The ground elastic modulus and PR(Penetration Rate) value were estimated by using PFC(Particle Flow Code) 3D program based on the discrete element method. Those values were compared and analyzed with the result of field tests. Also, back analysis was conducted to describe ground elastic modulus of field tests. RESULTS : Relative errors of PR value between the numerical analyses and field tests were calculated to be comparatively low. Also, the relationship between elastic modulus and PR value turned out to be similar. CONCLUSIONS : Numerical modeling of DCPT is considered to be suitable for describing field tests by carrying out numerical analysis using PFC 3D program.

• Geomechanics and Engineering
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• 제34권5호
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• pp.507-527
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• 2023

Accurately estimation of the geo-mechanical parameters in Artificial Ground Freezing (AGF) is a most important scientific topic in soil improvement and geotechnical engineering. In order for this, one way is using classical and conventional constitutive models based on different theories like critical state theory, Hooke's law, and so on, which are time-consuming, costly, and troublous. The others are the application of artificial intelligence (AI) techniques to predict considered parameters and behaviors accurately. This study presents a comprehensive data-mining-based model for predicting the Young's Modulus of frozen sand under the triaxial test. For this aim, several single and hybrid models were considered including additive regression, bagging, M5-Rules, M5P, random forests (RF), support vector regression (SVR), locally weighted linear (LWL), gaussian process regression (GPR), and multi-layered perceptron neural network (MLP). In the present study, cell pressure, strain rate, temperature, time, and strain were considered as the input variables, where the Young's Modulus was recognized as target. The results showed that all selected single and hybrid predicting models have acceptable agreement with measured experimental results. Especially, hybrid Additive Regression-Gaussian Process Regression and Bagging-Gaussian Process Regression have the best accuracy based on Model performance assessment criteria.