• Journal of the Korean GEO-environmental Society
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• v.4 no.4
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• pp.61-71
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• 2003

On the soft soil consisted of silty clay, the compulsion replacement method is useful for revetment and its safety is very much affected by compulsion replacement depth. Usual method calculating the compulsion replacement depth on silty clay is considered the bearing capacity of soft soil with undrained shear strength increase from ground surface and weight of revetment. But according to soil deposit, there are some cases of soft soil with inter sand layer or clayed silt, which affect the compulsion replacement depth. In this paper, the compulsion replacement depth on soft soil with inter sand layer is analyzed by layered weighted average bearing capacity considering influence effect of Perloff et al.(1967) and compared with numerical method(FLAC). In the result, the calculated depth from numerical method is nearest to layered weighted average bearing capacity in case that contact width under revetment is $0.2B_o$(soft soil with inter sand layer), $0.5B_o$(only soft soil) and the effect of contact width under revetment is less than undrained shear strength, thickness and location of inter sand layer. Also the compulsion replacement depth is as much as the inter sand thickness($d_2/B_o$) is thinner, the inter sand layer location($d_1/B_o$) is farther, and undrained shear strength is less.

• Geomechanics and Engineering
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• v.32 no.2
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• pp.145-157
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• 2023

This paper aims at investigating the face stability of large-diameter underwater shield tunnels considering seepage in soft-hard uneven strata. Using the kinematic approach of limit upper-bound analysis, the analytical solution of limit supporting pressure on the tunnel face considering seepage was obtained based on a logarithmic spiral collapsed body in uneven strata. The stability analysis method of the excavation face with different soft- and hard-stratum ratios was explored and validated. Moreover, the effects of water level and burial depth on tunnel face stability were discussed. The results show the effect of seepage on the excavation face stability can be accounted as the seepage force on the excavation face and the seepage force of pore water in instability body. When the thickness ratio of hard soil layer within the excavation face exceeds 1/6D, the interface of the soft and hard soil layer can be placed at tunnel axis during stability analysis. The reliability of the analytical solution of the limit supporting pressure is validated by numerical method and literature methods. The increase of water level causes the instability of upper soft soil layer firstly due to the higher seepage force. With the rise of burial depth, the horizontal displacement of the upper soft soil decreases and the limit supporting pressure changes little because of soil arching effect.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.11a
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• pp.142-143
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• 2021

The general ground conditions in Korea are distributed in order of fill, deposit soil, weathered soil, weathered rock, soft rock. The fill soil and deposit soil located at the top have relatively low strength compared to the lower layer, and they are sometimes classified as soft ground according to the standard penetration test results. In this study, the PF method, a ground improvement method, was applied to the soft layer, a large plate load test was conducted on the improved ground, and the results were reviewed.

• Geomechanics and Engineering
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• v.2 no.4
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• pp.281-302
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• 2010

An extended model for the response of a rigid footing on a reinforced foundation bed on super soft soil is proposed by incorporating the rough membrane element into the granular bed. The super soft soil, the granular bed and the reinforcement are modeled as non-linear Winkler springs, non-linear Pasternak layer and rough membrane respectively. The hyperbolic stress-displacement response of the super soft soil and the hyperbolic shear stress-shear strain response of the granular fill are considered. The finite deformation theory is used since large settlements are expected to develop due to deformation of the super-soft soil. Parametric studies quantify the effect of each parameter on the stress-settlement response of the reinforced foundation bed, the settlement and tension profiles.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2005.03a
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• pp.137-144
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• 2005

Seismic responses of a building are affected due to the site soil conditions. In this study, linear time history seismic analysis and nonlinear pushover static seismic analysis were performed to estimate the base shear forces of the 3, 5 and 7-story steel structure buildings considering the rigid and soft soil conditions. According to the study results, the steel structure buildings designed for the gravity loads and wind load showed the elastic responses with the moderate earthquake of 0.11g, and the soft soil layer increased the displacement and the base shear force of a building. Therefore it is more resonable to perform an elastic seismic analysis of a building structure with the moderate earthquakes considering the characteristics of the soft soil layer.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2005.10a
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• pp.423-428
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• 2005

If the load of constructing vehicles during the construction work acts on the road or the ground surface on the soft ground, due to the excess stresses in soils the trafficability of the vehicles influences the constructing efficiency, constructing period and so on. Stress distribution in soils is the very important element to design and to solve the problems of settlement, safety of foundations and trafficability of constructing vehicle in civil engineering. This research represents the comparative estimation of the actual and theoretical measurement on the underground stress of outer layer for each soil after the observation of each top soil layer for its vertical and horizontal stress in (1)homogeneous sand ground (2) weak stratum with the sand soil (3) weak stratum with gravel of the soil model, and it also investigates the effect of subsidence of ground by the repeated load. The underground stress turn out to be different in the value of theoretical and actual measurement after the trial examination of model.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.11c
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• pp.129-141
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• 1999

This paper presents the results of plate load test and dynamic load test performed to evaluate the performance of geocell where it is used to reinforce soft subgrade for high-speed railroad. Efficacy of geocell was observed in increase in bearing capacity of subgrade and reduction of thickness of reinforced sub-ballast. Plate load tests were carried out at four different places with varying foundation soil strength as a function of number of geocell layer, type of filler material, thickness of cover soil, and the presence of non-woven geotextile. Dynamic load tests were performed in a laboratory. The test soil chamber consists of, from the bottom, 50 cm thick clayey soil, one layer of geocell filled with crushed stone, 10 cm thick crushed stone cover, reinforced sub-ballast of varying thickness, 35 cm thick ballast. This configuration was determined based on the results of numerical analysis and plate load tests. For each set of the dynamic load tests, loads were applied more than 80,000 times. One layer of geocell underlying a 10 cm thick cover soil led to an increase in bearing capacity three to four times compared to a crushed stone layer of the same thickness substituted for the geocell and cover soil layer. Given the test conditions, the thickness of reinforced sub-ballast can be reduced by approximately 35 cm with the presence of geocell.

• Journal of the Korean Geotechnical Society
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• v.32 no.6
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• pp.5-16
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• 2016

In the geosynthetics-reinforced piled embankment the effects of soft soil stiffness, friction angle of the fill material, tensile stiffness of geosynthetics, and height of the embankment on the load transfer soil arch measured by the critical height were numerically investigated. Results from parametric studies show that the magnitude of the soft soil stiffness is the most influencing factor on the critical height. The contour charts of the critical height with respect to the combination of the soft soil stiffness and other parameters were presented. The charts show that the critical height sensitively varies with the combination of the soft soil stiffness and the height of embankment. Under the sufficiently low stiffness of soft soil, the critical height sensitively varies with the friction angle of the fill material. Once the geosynthetic layer is placed, however, the magnitude of the tensile stiffness of the geosynthetic layer hardly influences the critical height of the soil arch.

• Journal of the Earthquake Engineering Society of Korea
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• v.21 no.1
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• pp.69-76
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• 2017

Seismic analyses of a pile under a large rigid basement foundation embedded in the homogeneous soil layer were performed practically by a response displacement method assuming a sinusoidal wave form. However, it is hard to take into account the characteristics of a large mat foundation and a heterogeneous soil layer with the response displacement method. The response displacement method is relevant to the 2D problems for longitudinal structures such as tunnel, underground cave structure, etc., but might not be relevant with isolated foundations for building structures. In this study, seismic pile analysis by a pseudo 3D finite element method was carried out to compare numerical results with results of the response displacement method considering 3D characteristics of a foundation-soil system which is important for the building foundation analyses. Study results show that seismic analyses results of a response displacement method are similar to those of a pseudo 3D numerical method for stiff and dense soil layers, but they are too conservative for a soft soil layer inducing large soil pressures on the foundation wall and large pile displacements due to ignored foundation rigidity and resistance.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.1
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• pp.113-122
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• 1999

The importance of the vertical response of a structure was well recognized after the Hyogoken-Nanbu earthquake of Japan. However, most of the seismic design codes does not specified the site sail profiles, and the sail and foundations conditions were mostly neglected in the vertical seismic analyses of a structure. In this paper, the effects of foundation size, sail layer depth under the foundation, foundation embedment and pile foundation on the vertical seismic response spectra for both surface and embedded mat foundation were studied to investigate the effects of the soft soil layer on the vertical response of a structure excited with the vertical components of Taft and El Centro earthquakes, considering the sail profile types of $S_A,S_C,S_E$ in UBC-97, the medium and large size foundations, the soil layer depth under the foundation of 30 and 60m, the foundation embedment of 0 and 15m, and the precast reinforced concrete bearing piles installed in the soft soil deposit. According to the study results, the foundation size has a little effect on the vertical seismic response, However, the soil layer depth under the foundation of 60m has to be considered for the vertical seismic analysis of a structure as for the horizontal one. The embedded pile foundations as well as the surface ones built on the soft soil layer amplified the vertical seismic response of a structure very much.