• Geomechanics and Engineering
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• v.6 no.2
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• pp.173-194
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• 2014

Laboratory and field data showed that deep mixed (DM) columns accelerated the rate of consolidation of the soft foundations. Most analyses of consolidation of DM column-improved foundations so far have been based on the elastic theory. In reality, the DM columns may yield due to the stress concentration from the soft soil and its limited strength. The influence of column yielding on the degree of consolidation of the soft foundation improved by DM columns has not been well investigated. A three-dimensional mechanically and hydraulically-coupled numerical method was adopted in this study to investigate the degree of consolidation of the DM column foundation considering column yielding. A unit cell model was used, in which the soil was modeled as a linearly elastic material. For a comparison purpose, the DM column was modeled as an elastic or elastic-plastic material. This study examined the aspects of stress transfer, settlement, and degree of consolidation of the foundations without or with the consideration of the yielding of the DM column. A parametric study was conducted to investigate the influence of the column yielding on the stress concentration ratio, settlement, and average degree of consolidation of the DM column foundation. The stress concentration ratio increased and then decreased to reach a constant value with the increase of the column modulus and time. A simplified method was proposed to calculate the maximum stress concentration ratios under undrained and drained conditions considering the column yielding. The simplified method based on a composite foundation concept could conservatively estimate the consolidation settlement. An increase of the column modulus, area replacement ratio, and/or column permeability increased the rate of consolidation.

• Magazine of the Korean Society of Agricultural Engineers
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• v.37 no.5
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• pp.101-110
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• 1995

The use of geotextile as reinforced materials in Soil structures has become widespread throughout the world. Geotextile reinforcement has been used in retaining walls, slope of embankment and especially soft foundation, etc. In the past, however, its design and construction have been performed empirically. In this study, to investigate of the effect of geotextiles reinforced slope of the embankment on a very soft foundation, a limit equilibrium analysis program calculating the safety factor of embankment on very soft foundation was developed. The study was focussed on such factors as type of geotextile, tensile strength, amount of reinforcement, and inclination of embankment. And the 4imit equilibrium analysis program was written on the basis of Low's slope stability theory with some modification. The following conclusions were drawn from this study. (1) The orientation of reinforcement can be assumed either horizontal or tangential to the slip circle. The factor of safety with tangential reinforcement is larger than that with the horizontal reinforcement. (2) In general, the factor of safety increases, as the slope reduces. However, it is preferable to use geotextiles with higher tensile strength rather than to reduce the slope of the embankment, because it is difficult to adjust the slope as desired. (3) The factor of safety obtained by numerical computation is affected only by the tensile strength, but not by the type of the geotextile.

• Tunnel and Underground Space
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• v.20 no.2
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• pp.105-111
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• 2010

This study is to consider applicability of spiral bolt strain gauge as an instrument measuring behavior of soft ground foundation and rock slope. When the instrument was installed on the ground, it can be useful to identify the state of ground behavior because it has the characteristics of flexibility, as well as to apply the ground reinforcement because it has higher pull-out resistance to the ground. From the measurement of behavior to soft ground foundation, the strain shows a stable state in the beginning, then was observed significant change in the upper and the middle of spiral bolt strain gauge after 400 days. This is analyzed that ground loosening, which is due to occurred frequent earthquake of magnitude 1~2 with increased rainfall, lead to the instability of the ground. From the measurement of behavior to rock slope, the strain shows a stable state with very little change in a period of 0~50 days and the biggest strain at 4.2 m (P6) in a period of 50~100 days, then other places except P6 was maintained at a stable state in a period of 100~160 days. The reason is analyzed because that blasting for excavated limestone surrounding was affected to the largest at P6. However, based on the size of strain change by behavior of the soft ground foundation and rock slope, it is considered that the present condition are not effected on stability of retaining structure and rock slope. In conclusion, the proposed spiral bolt strain gauge can be useful to measure behavior of soft ground foundation and rock slope, and also to be measured behavior as well as reinforcement of the target ground.

• Journal of the Korean Geotechnical Society
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• v.23 no.5
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• pp.63-75
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• 2007

Piled raft is known to be an unfavorable foundation type in soft clay because foundation is associated with both excessive settlement and bearing capacity failure problems. Despite these reasons, in recent decades, an increasing number of structures have been constructed over soft clay area, piled raft concepts arouse interest as the foundation of structures on soft clay area becomes popular. This study described 3 dimensional behavior of piled raft on soft clay based on a numerical study using 3D finite element method. A series of numerical analyses were performed for a various pile lengths and the pile configurations on the raft were subjected to vertical uniform or point loading. Based on the results of the parametric study, comparisons were made among the effect of loading type, various pile length and configurations, and the load-settlement behavior and load sharing characteristics of piled raft were also evaluated. From the results, the characteristic of piled raft on soft clay was examined.

• Structural Engineering and Mechanics
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• v.21 no.1
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• pp.101-119
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• 2005

An efficient methodology is presented to evaluate the seismic behavior of a Fluid-Elevated Tank-Foundation/Soil system taking the embedment effects into accounts. The frequency-dependent cone model is used for considering the elevated tank-foundation/soil interaction and the equivalent spring-mass model given in the Eurocode-8 is used for fluid-elevated tank interaction. Both models are combined to obtain the seismic response of the systems considering the sloshing effects of the fluid and frequency-dependent properties of soil. The analysis is carried out in the frequency domain with a modal analysis procedure. The presented methodology with less computational efforts takes account of; the soil and fluid interactions, the material and radiation damping effects of the elastic half-space, and the embedment effects. Some conclusions may be summarized as follows; the sloshing response is not practically affected by the change of properties in stiff soil such as S1 and S2 and embedment but affected in soft soil. On the other hand, these responses are not affected by embedment in stiff soils but affected in soft soils.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.300-310
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• 2008

A series of numerical simulations on the several types of breakwaters on the foundation systems utilizing buoyancy were carried out in plane-strain conditions using the modified Cam-Clay model and the Biot's consolidation theory. Improved foundation system by the replacement of original ground with light weighted material, expandable poly-styrene (called below EPS) and several foundation systems with buoyant cells were used. From the results of numerical simulations we found that the foundation systems utilizing buoyancy are efficient to reduce the maximum consolidation settlements without reducing lateral safety.

• Structural Engineering and Mechanics
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• v.72 no.4
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• pp.525-540
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• 2019

The purpose of the present work was to study the dynamic instability of a three-layered, symmetric sandwich beam subjected to a periodic axial load resting on nonlinear elastic foundation. A higher-order theory was used for analysis of sandwich beams with soft core on elastic foundations. In the higher-order theory, the Reddy's third-order theory was used for the face sheets and quadratic and cubic functions were assumed for transverse and in-plane displacements of the core, respectively. The elastic foundation was modeled as nonlinear's type. The dynamic instability regions and free vibration were investigated for simply supported conditions by Bolotin's method. The results showed that the responses of the dynamic instability of the system were influenced by the excitation frequency, the coefficients of foundation, the core thickness, the dynamic and static load factor. Comparison of the present results with the published results in the literature for the special case confirmed the accuracy of the proposed theory.

• 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.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.157-171
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• 2009

A 151 storey super high-rise building located in an area of reclaimed land constructed over soft marine clay in Songdo, Korea is currently under design. This paper describes the design process of the foundation system of the supertall tower, which is required to support the large building vertical and lateral loads and to restrain the horizontal displacement due to wind and seismic forces. The behaviour of the foundation system due to these loads and foundation stiffness influence the design of the building super structure, displacement of the tower, as well as the raft foundation design. Therefore, the design takes in account the interactions between soil, foundation and super structure, so as to achieve a safe and efficient building performance. The site lies entirely within an area of reclamation underlain by up to 20m of soft to firm marine silty clay, which overlies residual soil and a profile of weathered rock. The nature of the foundation rock materials are highly complex and are interpreted as possible roof pendant metamorphic rocks, which within about 50m from the surface have been affected by weathering which has reduced their strength. The presence of closely spaced joints, sheared and crushed zones within the rock has resulted in deeper areas of weathering of over 80m present within the building footprint. The foundation design process described includes the initial stages of geotechnical site characterization using the results of investigation boreholes and geotechnical parameter selection, and a series of detailed two- and three-dimensional numerical analysis for the Tower foundation comprising over 172 bored piles of varying length. The effect of the overall foundation stiffness and rotation under wind and seismic load is also discussed since the foundation rotation has a direct impact on the overall displacement of the tower.

• Geomechanics and Engineering
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• v.32 no.2
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• pp.209-232
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• 2023

A comprehensive study was conducted to design economical foundations for a number of buildings on soft cohesive soil in the southern coastal regions of Iran. Both static and seismic loads were considered in the design process. Cyclic experiments indicated that the cohesive soil of the area has potential for softening. Consequently, the major challenge in the design stages was relatively high dimensions of settlement, under both static and seismic loadings. Routine soil-improvement methods were too costly for the vast area of the project. After detailed numerical modeling of different scenarios, we concluded that, in following a performance-based design approach and applying a special time schedule of construction, most of the settlement would dissipate during the construction of the buildings. Making the foundation as rigid as possible was another way to prevent any probable differential settlement. Stiff subgrade of stone and lime mortar under the grid foundation and a reinforced concrete slab on the foundation were considered as appropriate to this effect. In favor of an economical design, in case the design earthquake strikes the site, the estimations indicate no collapse of the buildings even if considerable uniform settlements may occur. This is a considerable alternative design to costly soil-improvement methods.