• Journal of the Korean Geotechnical Society
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• v.25 no.9
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• pp.19-27
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• 2009

In order to investigate anti-freeze process of precast concrete L-type retaining walls in cold regions, test walls were installed in the campus of Kitami Institute of Technology (KIT, Hokkaido, Japan). The wall consists of following three sections, i) back filled with frost susceptible clay soil, ii) using thermal insulation material, and back filled with frost susceptible soil, iii) back filled with frost-unsusceptible soil. The freezing front distribution and ground temperature within the backfill were observed and deflections of the walls were measured over three freeze-thaw seasons. Some understanding of the mechanisms of the build-up of frost heave pressure was gained, and the effectiveness of replacement method was observed. A simulation was performed to predict the shape of the freezing front in the backfill behind L-type walls with various cross sections. These findings were employed to propose a method for determining the appropriate zone to be replaced with frost unsusceptible backfill material in cold regions.

• Journal of the Korean Geotechnical Society
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• v.24 no.2
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• pp.59-65
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• 2008

Digital close-range photogrammetric technique can measure and describe 3D geometric farm from 2D image. This technique is increasingly applied in the field of sciences. In the fields of civil and mechanical engineering, which need precise measurements for design, expensive measuring equipments are widely used. In occasions where visual inspection is required in addition to other forms of measurements, appropriate measuring equipments have not been yet available. This study utilizes digital close-range photogrammetric technique to quantitatively analyze behavior patterns before and after destruction from test model of reinforced-soil wall. Then the results are compared with the measurements obtained using digital theodolite to verify the reliability of the proposed method.

• Journal of the Korean Geotechnical Society
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• v.23 no.2
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• pp.85-92
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• 2007

As the use of drilled shafts for foundation of a large size structure increases, the evaluation of the reliable bearing capacity of the pile has become important. The purpose of this study is to verify the reliability of bearing capacity equations for drilled shafts socketed in weathered rock by comparing the bearing capacity values from static load tests with values from bearing capacity equations. In this study, twelve data from static load test were selected from four field sites, and the data of load test and the properties of weathered rock were analyzed. Three methods widely used in practice were selected for analysis, namely the AASHTO method (1996), Carter & Kulhawy method (1988), and FHWA method (1999). The comparison of the bearing capacity values from the bearing capacity equations to those obtained from load tests showed that the Carter & Kulhawy method (1988) was the most reliable in giving conservative design values and smaller COV (Coefficient Of Variation).

• Journal of the Korean Geotechnical Society
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• v.23 no.4
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• pp.59-68
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• 2007

In this study, evaluation of load capacity and CPT-load capacity parameters were performed using calibration chamber tests for different types of piles including straight-side and tapered piles. Various soil conditions were considered in the investigation, aiming at establishing design procedure for foundation of electronic transmission tower structures. Test results show that no significant difference of total load capacity from straight-side and tapered piles, while individual components of base and shaft load capacities were quite different. Based on the test results, values of CPT-load capacity correlation parameters for different pile types were analyzed for the evaluation of both base and shaft load capacities.

• Journal of the Korean Geotechnical Society
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• v.23 no.9
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• pp.17-28
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• 2007

Urban tunnels are usually important in terms of prediction and control of surface settlement, gradient and ground displacement. This paper has studied the application of strain softening analysis to predict deformation behavior of an urban NATM tunnel. The applied strain softening model considered the reduction of shear stiffness and strength parameter after yielding with strain softening effects of a given material. Measurements of surface subsidence and ground displacement were adopted to monitor the ground behavior resulting from the tunneling and to modify tunnel design. The numerical analysis results produced a strain distribution, deformational mechanism and surface settlement profile, which are in good agreement with the results of case study. The approach of strain softening modeling is expected to be a good prediction method on the ground displacement associated with NATM tunneling at shallow depth and soft ground.

• Journal of the Korean Geotechnical Society
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• v.24 no.12
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• pp.41-52
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• 2008

This paper concerns the load carrying capacity of back-to-back reinforced soil wall for use in roadway and railway construction. Two test conditions, designed with due consideration of the FHW A design guideline, were first developed and a number of cases having different reinforcement lengths were tested under a surchage loading until failure. The results indicated that for cases in which two sides of reinforcements do not overlap, the wall behavior was similar to those of single wall. For cases in which the reinforcements overlap each other, on the other hand, the load carrying capacity of the wall significantly decreased when reinforced with reinforcement layers having lengths less than 50% of the wall height.

• Journal of the Korean Geotechnical Society
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• v.24 no.9
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• pp.33-40
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• 2008

This paper describes the performance of ground improvement project using prefabricated vertical drains of condition, in which approximately 10m dredged fill overlies original soft foundation layer in the coastal area composed of soft marine clay with high water content and high compressibility. From field monitoring results, excessive ground settlement compared with predicted settlement in design stage developed during the following one year. In order to predict the final consolidation behavior, recalculation of consolidation settlements and back analysis using observed settlements were conducted. Field monitoring results of surface settlements were evaluated, and then corrected because large shear deformation occurred by construction events in the early stages of consolidation. To predict the consolidation behavior, material functions and in-situ conditions from laboratory consolidation test were re-analyzed. Using these results, height of additional embankment is estimated to satisfy residual settlement limit and maintain an adequate ground elevation. The recalculated time-settlement curve has been compared with field monitoring results after additional surcharge was applied. It might be used for verification of recalculated results.

• Journal of the Korean Geotechnical Society
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• v.24 no.10
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• pp.5-15
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• 2008

The purpose of this study is to examine the validity of recycled aggregates (RAs) as a substitute for Sand-Mat material for soft ground improvement in the housing site development. To evaluate the possibility of RAs as a substitute for sand mat material, first of all, the criteria and regulations related with the quality of lateral drain layer were collected and checked. Secondly, both of the properties of RAs were compared with the properties of natural sand for the lateral drain layer. The material properties related to coefficient of permeability, pressure at-rest state and so on satisfied most standards. On the basis of the test results, RAs were used to the construction site as lateral drain layer. Accordingly, if the quality of RAs can be managed well, the application of these RAs as lateral drain layer to replace natural sand was highly effective. Also, based on cost analysis of two materials, RAs are proved to be very competitive.

• Journal of the Korean Geotechnical Society
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• v.24 no.10
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• pp.71-81
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• 2008

Wall displacements caused by earth pressure, rainfalls, rise in ground water level, inappropriate deep excavation and structural defects of the wall may produce differential settlements to existing buildings, which often result in damages and/or collapses of the building structures. In this case, measures to protect the walls and nearby structures would be required. One of the recent measures to reduce differential settlements and protecting walls is to reinforce the ground using micro-piles. In this study physical model tests were carried out to evaluate the performance of the micro-pile method. It is revealed that reduction of the settlement was maximized when the length of micro-pile is twice of the foundation width, distance between piles is twice of the pile diameter and the distance to wall is one tenth of the foundation width. Based on the test results some design recommendations were made.

• Journal of the Korean Geotechnical Society
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• v.24 no.8
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• pp.89-97
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• 2008

A series of field tests were performed to investigate the behavior of jacket anchor and to evaluate the ultimate bond stress of jacket anchor. From twelve sets of field tests on the jacket anchor and general type ground anchor, it was observed that the pullout resistance of jacket anchor is significantly larger than that of the ground anchor and that the plastic deformation of jacket anchor is significantly smaller than that of general ground anchor at the same loading cycle. Especially in gravel layers, the jacket anchor provides more than 250% increase in ultimate resistance and more than 600% reduction in plastic deformation, compared with the general ground anchor. Finally, the relationship between the injection pressure and overburden pressure is proposed to determine the optimum injection pressure, based on additional field test results.