• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.1
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• pp.147-157
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• 2005

In this study, consolidation analysis methods reflecting various ground condition and changing coefficient of consolidation with consolidation process are presented. Research activities include development of numerical program consists of two parts considering vertical drainage only and both drainage condition with vertical and radial direction. Also, interface equation of adjacent two layers and function for changing coefficient of consolidation are added to developed program. This paper presents the results from a detailed consolidation analyses, which explores consolidation process with time in varying layered system and changing coefficient of consolidation

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.3
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• pp.21-28
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• 2009

The precise analysis of soil-pile-structure interaction requires a proper description of soil layer, pile, and structure. In commonly used finite element simulations, mesh boundaries should match the material discontinuity line. However, in practice, the geometry of soil profiles and piles may be so complex that mesh alignment becomes a wasteful and difficult task. To overcome these difficulties, a different integration method is adopted in this paper, which enables easy integration over a regular element with material discontinuity regardless of the location of the discontinuity line. By applying this integration method, the mesh can be generated rapidly and in a highly structured manner, leading to a very regular stiffness matrix. The influence of the shape of the soil profile and piles on the response is examined, and the validity of the proposed soil-pile structure interaction analysis method is demonstrated through several examples. It is seen that the proposed analysis method can be easily used on soil-pile-structure interaction problems with complex interfaces between materials to produce reliable results regardless of the material discontinuity line.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.24 no.1
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• pp.9-20
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• 1991

The characteristics of the unconsolidated sediment in Gwangyang bay was analyzed from the core samples. The porosity of the sediment showed irregular variation with respect to the sedimentation depth, which indicated that sediment weight-induced consolidation was not significant. Numerical analysis for the mechanical and hydraulic behavior of the unconsolidated sediment due to the tidal sea level change was processed. Because of the delayed excessive pore pressure change in the very low permeable mud medium, the magnitude of the excessive pore pressure for the duration of the minimum sea level exceeded the total stress from the sea water weight, which resulted in the negative (tensional) effective stress below the top surface. The in-situ effective stress, obtained by superposing the tensional effective stress on the solid weight-induced compressive stress, was remained to be tensile (quick-sand condition) near the top surface of the mud deposit. The occurrence of the quirk-sand condition provided a theoretical evidence for the insignificant consolidation and the irregular porosity variation of the sediment. When the sand is distributed on the top surface of the mud layer, the quick-sand condition occurred below the sandy mud layer and the downward movement of sand particles was facilitated.

• The Journal of Engineering Geology
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• v.15 no.1
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• pp.41-55
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• 2005

This research is aimed at investigating the ground characterization of the Cheongju granite area using the geophysical methods. Test site was chosen from the building site in Chungbuk University, Chongju, Chungbuk province. Furthermore, geophysical methods are employed on the outcrops in the east to map the distribution of fault and intrusion and reveal the degree of weathering. The subsurface structure mapped from seismic re-fraction survey mainly consists of two units of weathered soil and rock. Threshold of the units were determined on the basis of seismic velocity of 800 m/s, supported from the standard classification table. From the results of standard penetrating test(SPT), these units are found to show medium-high and high density, respectively. Weathering soil is subdivided in unsaturated layer and saturated layer with thresholds of seismic velocity (500 m/s) and resistivity (200 ohm-m). In particular, unsaturated layer is again classified into dry and wet portions using the GPR section. The boundary between unsaturated and saturated weathering soils corresponds to the groundwater table at depth of approximately 5～6.2 m, which is well correlated with the one from drill-core data. However, bedrock is not delineated by geophysical methods. In the GPR section, fault and intrusion observed on the outcrop are revealed not to extend to the building site. With respect to weathering degree, the outcrop characterized by low resistivity and velocity corresponds to the grade of 'completely weathered' from the geotechnical investigations.

• The Journal of Engineering Geology
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• v.21 no.1
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• pp.57-64
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• 2011

Three-dimensional slope stability analysis was applied to a failed dual-lithology slope containing both granite and an andesitic dyke, taking account of the differences in shear strength of the different lithologies. A direct shear test of the soil-rock boundary was performed to examine the shear strength of two different types of failure surfaces within different lithologies, and a laboratory test was performed on an upper, weathered soil layer. The test results indicate that shear strength was lower at the soil-rock boundary than within the weathered soil layer. A representative geological section was subjected to two-dimensional slope stability analysis using a limit equilibrium method to assess whether the distribution of lithologies upon the slope influences the results of stability analysis. The results were then compared with those of three-dimensional slope stability analysis, for which input parameters can be varied according to the distribution of lithologies upon the slope. The three-dimensional analysis yielded safety factors of 1.26 under dry conditions and 0.55 under wet conditions, whereas the two-dimensional analysis yielded unstable safety factors of 0.92 and 0.32, respectively. These findings show that the results of stability analysis are affected by the distribution of different lithologies upon the slope. Given that the studied slope collapsed immediately after rainfall, it is likely that the results of the three-dimensional analysis are more reliable.

• The Journal of Engineering Geology
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• v.7 no.3
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• pp.161-171
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• 1997

The exact information on geological structures and characteristics of the subsurface must be acquired to secure quality and safety of constructions. GPR technique, one of the most updated geophysical methods, is known for its applicability to shallow-depth underground surveys. The purpose of this study is to examine the usefulness of GPR method in constructions for detailed subsurface investigations, especially detecting the boundary between basement rock and its overburden. To find appropriate depths of the geological boundaries, it is necessary to obtain velocity of electromagnetic wave propagating into the ground. Wave velocity 0.096 m/ns estimated from velocity analysis using CMP gathers is used for depth conversion from time section. The depths of geological boundaries from GPR profiles are very well correlated with boring data. In addition, GPR survey has found some undulations of the geological boundaries due to weathering, which cannot be provided by conventional coring approaches.

• Journal of the Korean GEO-environmental Society
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• v.8 no.6
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• pp.37-43
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• 2007

The interface layer having different consolidation properties and nonlinear material function with permeability needs to be considered to predict consolidation behavior. In this study, interface equation between different layers has been derived and then applied to existing finite difference scheme for conducting consolidation analysis. These results have been compared with those by conventional method in which different layers are converted to single layer having conversion value of properties. Also, although the conventional consoilidation analysis is used to consider non-linearity of the permeability with effective stress, an approximated nonlinear method as a function of consoilidation coefficient with effective stress have been developed and applied to the consoilidation analysis for various cases.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.4 no.3
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• pp.49-54
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• 2001

It is common that the soil layer is a few meters below the earth's surface and the rock mass is below the soil layer in the view of geological characteristics in Korea. And the boundary between rock and soil is clearly divided. When dealing with the stability of rock masses, as in the case of rock slopes or dam foundations, the majority of the collapses is not within the soil layer, but within the soil-rock boundary. Therefore it is important to identify the shear strength characteristics between soil-rock boundary. And then in the method of reinforcement on landslide this chose a cut slope near Daemo elementary school in Seoul, surveyed shear strength between soil-rock contacts and considered a large scale collapse using a limit equilibrium method.

• Geotechnical Engineering
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• v.10 no.2
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• pp.121-140
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• 1994

This paper presents the probabilistic model to evaluate the three-dimensional stability of layered deposits and c-0 soil slopes. Rotational slides are assumed with a cylindroid control part terminated with plane ends. And the potential failure surfaces in this study are assumed with the logarithmic spiral curve refracted at boundary of layers. This model takes into consideration the spatial variabilities of soil properties and the uncertainties stemming from insufficient number of samples and the discrepancies between laboratory measured and in -situ values of shear strength parameters. From the probabilistic approxi mate method (FOSM and SOSM method), the mean and variance of safety factor are calculated, respectively. And the programs based on above models is developed and a case study is analysed in detail to study the sensitivity of results to variations in different parameters by using the programs developed in this study. On the basis of thin study the following conclusions could be stated : (1) The sensitivity analysis shown that the probability of failure is more sensitive to the uncertainty of the angle of internal friction than that of the cohesion, (2) The total 3-D proability of failure and the critical width of failure are significantly affected by total width of slope. It is found that the total 3-D probability of failure and the critical width of failure increase with increasing the slope width when seismic forces do not exist and the total 3-D probability of failure increases with increasing the slope width and the critical width of failure decreases when seismic intensity is relatively large, (3) A decrease in the safety factor (due to effect such as a rise in the mean ground water level, lower shear strength parameters, lower values for the correction factors, etc.) would result in reduction in the critical width of failure.

• Geotechnical Engineering
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• v.9 no.2
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• pp.41-54
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• 1993

This paper presents the two and three -dimensional stability analysis of nonhom- ogeneous, c-o soil slopes. Potential failure surface is assumed as a logspiral curve refracted in boundaries of layers. In 3-D analysis, rotational soil mass is assumed with a cylindroid central part terminated with plane ends. Seismic force is considered by sesmic intensity. The program developed in this study is compared with the program PCSTABLS. The ratio of three-dimensional minimum factor of safety to two-dimensional case is examined and factor of safety changes are showed for the ratio of cylindroid length to slope height and numbers of slice. On such bases the following conclusions may by made : (1) The program developed in this program is less conservative than the program PCSTABLS. (2) The value of F2 of this study shows the larger differences than that of PCSTABLS with increasing friction angle (3) Factors of safety computed for 3-D geometry differ considerablely from ordinary 2-D factors of safety. Since Fb/F2 exceeds unity, three -dimensional effects tend to increase the factor of safety. (4) As the ratio of three - dimensional failure width of slope height, b/H increase, the value of Fb/Ff decreases and approaches 1.0 when bye is 14. (5) In calculating the factor of safety using the developed program the number of slices is suitable with the ranges of 30-40