• 한국산학기술학회논문지
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• 제21권6호
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• pp.10-17
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• 2020

최근 경상북도 포항에서 일어난 강도 5.4 규모의 지진 영향으로 인하여 국내에서도 액상화 현상이 처음으로 발견되었다. 이와 같이 액상화 현상이 발생하면 물과 모래의 일부가 지면 위로 분출하여 공간이 생기게 되므로 지반의 침하, 건물 붕괴, 싱크홀 발생 등의 다양한 위험 상황으로 이어지게 된다. 최근 국내에서도 이와 같은 위험 요인인 액상화 가능지역을 사전에 파악하고자 액상화 위험지도 제작의 필요성이 커지고 있는 실정이다. 따라서, 본 연구에서는 액상화 위험지도 제작을 위해 국토교통부 국토지반정보 통합 DB센터에서 구축한 시추정보를 활용하였으며, 시추정보 데이터베이스 추출 기능과 시추정보를 바탕으로 한 기초데이터 모델링과 3차원 분석 기능을 구현하기 위한 모듈을 개발하였다. 본 연구를 통하여 국토지반정보 통합DB의 효과적인 연동기술을 확보하였으며, 지반 저항치, 액상화 위험지도 등 액상화 위험도 분석을 위한 단계별 3차원 정보 생성이 가능해졌다. 향후, 본 연구에서 개발한 기술을 통해 3차원 액상화 정보 구축을 위한 기반 마련과 액상화 대응체계 구축을 위한 종합적인 의사결정 지원기술로 유용하게 활용할 수 있을 것이다.

• 한국농공학회논문집
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• 제48권7호
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• pp.35-43
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• 2006

This study was carried out to investigate the liquefaction behaviour and predict deviator stress with matric suction, of unsaturated silty sand. The unsaturated soil tests were conducted using a modified triaxial cell and specimens were prepared using the moisture tamping method. The axis translation technique was used to create the desired matric suctions in the specimen. Undrained triaxial compression tests were carried out at matric suction of 0, 2, 5, 10 and 25 kPa. The specimens were sheared to axial strains of about 20% to obtain steady state conditions. The results showed that liquefaction of silty sand only occurs at matric suction of 0 kPa and 2 kPa. The results also show that at matric suctions of 5, 10 and 25 kPa, the resistance to liquefaction increases. As the suction increases, the undrained effective stress path approached the drained stress path. Also, the predicted and measured maximum deviator stress for unsaturated soils using the effective stress concept showed good agreement as matric suction increases. The deviator stress increase is nonlinear as matric suction increases.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2001년도 봄 학술발표회 논문집
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• pp.477-484
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• 2001

In this paper shows the evaluation of the liquefaction potential of soils using in situ test. There are different types of in situ test used in the evaluation the liquefaction potential. In the particular study the Standard penetration test(SPT), Cone penetration test(CPT), ad Seismic cone penetration test (SCPT) were used. The SPT N value has been used all over for a very long time. The evaluation of the liquefaction of soil was preformed using the worldwide renowned CPT and SCPT. Shake 91 program was used to evaluate the results obtained by different in situ test and were later analyzed.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2001년도 춘계학술대회 논문집
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• pp.443-450
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• 2001

This paper shows the reduction effect of tile earthquake-induced liquefaction potential of soils that improved by Vibro-Replacement Stone Columns. The Vibro-Replacement Stone Columns method transforms soft cohesive soils into a composite mass of compacted granular or crushed stone columns by using vibrating equipment and water jets. This study investigated and analyzed the behavior of the stone columns and composite ground using the results of in situ test and measurement at the job-site. This paper shows the evaluation of the earthquake-induced liquefaction potential of soils using in situ test. There are different types of in situ test used in the evaluation the liquefaction potential. In the particular study the Standard penetration test, and Cone penetration test were used. The N value of Standard Penetration test has been used all over for a very long time. The evaluation of the liquefaction of soil was performed using the worldwide renewed Cone penetration test

• Geomechanics and Engineering
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• 제4권2호
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• pp.91-103
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• 2012

Focusing on the effect of excess pore pressure dissipation on liquefaction-induced ground deformation, a series of 1-g shaking table tests were conducted in a rigid soil container by use of saturated Toyoura sand, the relative density of which was 20-60%. These tests were subjected to the sinusoidal base shaking with step increased accelerations: 100, 200, 300 and 400 Gals for 2-4 seconds. Shaking table tests were done using either water or polymer fluid with more viscous than water, thus varying the sand permeability of model tests. Excess pore pressures, accelerations, settlements and lateral deformations were measured in each test. Test results are presented in this paper and the effect of sand permeability on liquefaction and liquefaction-induced ground deformation was discussed in detail.

• Earthquakes and Structures
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• 제25권1호
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• pp.27-41
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• 2023

This study focused on nonlinear effective stress site response analysis using two coupled constitutive models, that is, the DM model (Dafalias and Manzari 2004), which incorporated a simple plasticity sand model accounting for fabric change effects, and the PMDY03 model (Khosravifar et al. 2018), that is, a 3D model for earthquake-induced liquefaction triggering and postliquefaction response. A detailed parametric study was conducted to validate the effectiveness of nonlinear site response analysis and porewater pressure (PWP) generation through a true coupled formulation for assessing the initiation of liquefaction at ground level. The coupled models demonstrated accurate prediction of liquefaction triggering, which was in line with established empirical liquefaction triggering relations in published databases. Several limitations were identified in the evaluation of liquefaction using the cyclic stress method, despite its widespread implementation for calculating liquefaction triggering. Variations in shear stiffness, represented by changes in shear wave velocity (Vs1), exerted the most significant influence on site response. The study further indicated that substantial differences in response spectra between nonlinear total stress and nonlinear effective stress analyses primarily occurred when liquefaction was triggered or on the verge of being triggered, as shown by excess PWP ratios approaching unity. These differences diminished when liquefaction occurred towards the later stages of intense shaking. The soil response was predominantly influenced by the higher stiffness values present prior to liquefaction. A key contribution of this study was to validate the criteria used to assess the triggering of level-ground liquefaction using true coupled effective-stress constitutive models, while also confirming the reliability of numerical approximations including the PDMY03 and DM models. These models effectively captured the principal characteristics of liquefaction observed in field tests and laboratory experiments.

• 한국지진공학회논문집
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• 제13권4호
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• pp.1-13
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• 2009

느슨한 포화 사질토 층에 위치한 구조물은 지진 시 액상화로 인해 막대한 인적 경제적 피해가 발생하기 때문에 액상화 발생 가능 지반으로 분류된 지역은 구조물의 설계 및 운영 시 액상화 발생 가능성에 주의를 기울어야 한다. 한반도의 경우 중진 지역에 해당되고 역사 문헌의 발생 기록을 제외한 어떤 액상화 피해도 보고되지 않음에 따라 오랫동안 액상화에 대해서는 안전지대로 여겨져 왔다. 하지만, 최근 해외 지진 사례에 의하면 국내 서해안 지역 지반과 유사한 비소성 실트질 흙에서의 액상화 발생과 이로 인한 피해 사례가 종종 보고되고 있다. 본 연구에서는 국내에서의 액상화 가능성 평가 기법 합리화의 일환으로 서해안 두 부지를 대상으로 피에조콘 관입시험(CPTu)과 표준관입시험(SPT) 결과를 이용하여 액상화가능지수(LPI)를 산정하였다. LPI는 심도 20m까지의 액상화 가능성을 통합 적분하여 액상화로 인한 지표면 피해 발생 정도를 지수로 제시한다. 먼저 대상 현장에 대해 시나리오별 액상화 발생 가능성을 평가한 후, CPTu와 SPT로부터 산정된 LPI 값을 비교하였다. 액상화 저항 강도를 의미하는 진동저항응력비(CRR) 값에 의하면, CPTu로부터 구한 보정 콘 선단저항력 (qc1N)CS가 40에서 120 사이인 경우 또는 CRR이 0.23 이하인 경우에 SPT로부터의 산정된 값보다 작게 평가되었다. 또한 CRR 차이는 세립질 함유량이 큰 흙에서 두 방법 간의 차이가 더 크게 나타났다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.320-327
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• 2005

Liquefaction characteristics of saturated sand under various dynamic loadings such as sinusoidal, wedge, increasing wedge and real earthquake loading are investigated focusing on the excess pore water pressure build up instead of liquefaction resistance strength in this paper. There are large differences between two types of earthquake loading - impact and vibration in liquefaction characteristics. The angle of phase change line of sinusoidal loading is very close to the vibration type, whereas the cumulative deviator stress and cumulative plastic strain are larger than two types of real earthquake loadings. On the other hand, the liquefaction characteristics of increasing wedge loadings are located in the range between vibration and impact earthquake loadings. It is concluded that the sinusoidal loading overestimates the resistance of soil under real earthquake loading. Based on results obtained, the increasing wedge loading can reflect the liquefaction behavior under real earthquake loadings more efficiently than sinusoidal loading based on equivalent uniform stress concept.

• Geomechanics and Engineering
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• 제36권3호
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• pp.247-258
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• 2024

Tailings are waste materials of mining operations, consisting of a mixture of clay, silt, sand with a high content of unrecoverable metals, process water, and chemical reagents. They are usually discharged as slurry into the storage area retained by dams or earth embankments. Poor knowledge of the hydro-mechanical behaviour of tailings has often resulted in a high rate of failures in which static liquefaction has been widely recognized as one of the major causes of dam collapse. Many studies have dealt with the static liquefaction of coarse soils in saturated conditions. This research provides an extension to the case of silty tailings in unsaturated conditions. The static liquefaction resistance was evaluated in terms of stress-strain behavior by means of monotonic triaxial tests. Its dependency on the preparation method, the volumetric water content, the void ratio, and the degree of saturation was studied and compared with literature data. The static liquefaction response was proved to be dependent mainly on the preparation technique and degree of saturation that, in turn, controls the excess of pore pressure whose leading role is investigated by means of the relationship between the -B Skempton parameter and the degree of saturation. A preliminary interpretation of the static liquefaction response of Stava tailings is also provided within the Critical State framework.

• Coupled systems mechanics
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• 제2권4호
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• pp.375-387
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• 2013

Soils consist of an assemblage of particles with different sizes and shapes which form a skeleton whose voids are filled with water and air. Hence, soil behaviour must be analyzed by incorporating the effects of the transient flow of the pore-fluid through the voids, and therefore requires a two-phase continuum formulation for saturated porous media. The present paper presents briefly the Biot's basic theory of dynamics of saturated porous media with u-P formulation to determine the responses of pore fluid and soil skeleton during cyclic loading. Kelvin elements are attached to transmitting boundary. The Pastor-Zienkiewicz-Chan model has been used to describe the inelastic behavior of soils under isotropic cyclic loadings. Newmark-Beta method is employed to discretize the time domain. The response of fluid-saturated porous media which are subjected to time dependent loads has been simulated numerically to predict the liquefaction potential of a semi-infinite saturated sandy layer using finite-infinite elements. A settlement of 17.1 cm is observed at top surface. It is also noticed that liquefaction occurs at shallow depth. The mathematical advantage of the coupled finite element analysis is that the excess pore pressure and displacement can be evaluated simultaneously without using any empirical relationship.