• Journal of the Korean Geotechnical Society
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• v.36 no.7
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• pp.15-28
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• 2020

As the skin friction of an embedded pile is produced by the cement paste injected into the borehole, the skin friction cannot be evaluated by the end of initial driving test, which is conducted before the cement paste is cured. In addition, the total resistance of an embedded pile may not be properly evaluated during the restrike test if the base resistance is not fully mobilized because of the insufficient driven energy. The objective of this study is to suggest a new load-settlement curve of embedded piles by combining the results of the end of initial driving and restrike tests. Test piles are installed at fields by using the embedded pile method, and the results of the dynamic pile tests are analyzed using CAse Pile Wave Analysis Program (CAPWAP) after the end of initial driving and restrike tests are conducted. A new load transfer curve, which combines the behaviors of the pile base at the end of initial driving and of the pile shaft at the restrike, is suggested, and a new load-settlement curve is obtained. Subsequently, the resistances of the test piles are evaluated using the combined load-settlement curve, and compared with the results from the end of initial driving and restrike tests. The results showed that the resistances, which are evaluated using the combined load-settlement curve, may overcome the underestimation of the resistance because of the insufficient driven energy. In addition, the resistance resulted from the combined load-settlement curve may be more similar to that from the static load test because the suggested load transfer curve is closer to the behavior of the embedded pile compared to the results of end of initial driving and restrike tests. Therefore, this study demonstrates that the combined load-settlement curve may be effectively used for the evaluation of the bearing capacity of embedded piles.

• Journal of the Korean Geotechnical Society
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• v.18 no.1
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• pp.5-16
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• 2002

The pullout behavior of large-diameter steel pipe piles(diameter = 2,500mm, length = 38~40m), which were designed as compression piles but used as reaction piles during a static compression load test on a pile(diameter = 1,000m, length = 40m), was investigated. The steel pipe piles were driven by 20m into a marine deposit and weathered soil layer and then socketed by 10m into underlying weathered and soft rock layers. The sockets and pipe were filled with reinforced concrete. The steel pipe and concrete in the steel pipe zone and concrete and rebars in the socketed zone were fully instrumented to measure strains in each zone. The pullout deformations of the reaction pile heads were measured by LVDTs. Over the course of the study, a maximum uplift deformation of 7mm was measured in the heads of reaction piles when loaded to 10MN, and 1mm of residual uplift deflection was measured. In the reaction piles, about 83% and about 12% of the applied pullout loads were transferred in the weathered rock layer and in the soft rock layer, respectively. Also, at an uplift force of 10MN, shear stresses due to the uplift in the weathered rock layer md soft rock layer were developed as much as 125.3kPa and 61.8kPa, respectively. Thus, the weathered rock layer should be utilized as resisting layer in which frictional farce could be mobilized greatly.

• Journal of the Korean Geotechnical Society
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• v.30 no.12
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• pp.51-61
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• 2014

This paper presents an experimental study of the plugging effect on the capacity of open-ended piles installed in sandy soil. Full-scale tests, including dynamic and static axial-compression load tests, were carried out on three instrumented piles with different diameters (508.0, 711.2 and 914.4 mm). To measure the outer and inner shaft resistances acting on the piles, a double-walled system was utilized with instrumented strain gauges on the outside and inside walls of the pile. The results of field tests show that the inner shaft resistance was mostly mobilized at the location between the pile tip and 18-34% of the total plug length. It was found that the soil plugging in the lower portion has influence on the inner shaft resistance. In addition, it can be also demonstrated that the ratio of inner shaft resistance plus annulus load resistance to total resistance decreased with increasing pile diameters. The results of these tests show that the relationship between the degree of plugging and pile diameter is clearly established. Direct observations of the soil plugs were made and used to quantify both the plug length ratio (PLR) and the incremental filling ratio (IFR). Based on this result, it was found that the N value of the standard penetration test (SPT) is highly correlated with the IFR.

• Journal of the Korean Geosynthetics Society
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• v.16 no.4
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• pp.1-11
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• 2017

In this study, 1/6 small-scale model tests of helical piles were conducted to evaluate their installation time and ultimate capacities. Model sand layers were constructed using sand pluviating method to produce uniform soil relative density. For installation of different helical piles varying locations (vertical center-to-center spacings of 50 mm and 150 mm) of helix plates, two different rotation speeds of 15 rpm and 30 rpm were implemented. Cone penetration equipment was installed within the hallow section of the helical pile to increase ultimate capacity of helical pile and to evaluate soil properties of plugged soils and soils below pile tip after installation of the piles. Based on the test results, the most fasted installation was possible under the condition of "rotation speed of 30 rpm and center-to-center spacing of 50 mm", and the highest ultimate capacity was mobilized under the condition of "rotation speed of 30 rpm and center-to-center spacing of 150 mm with cone penetration implementation."

• The Korean Journal of Quaternary Research
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• v.20 no.2
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• pp.11-29
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• 2006

A bedrock river is a channel in which bedrock is exposed along the channel bed or walls for at least approximately half of its length. In some case, a continuous alluvial veneer may be present, but this is completely mobilized during floods. From the point of long term landscape evolution during the Quaternary, the bedrock channel determines local base level and the lowering rate of bedrock channels controls the rate of erosion and transport processes and forms on the adjacent hillslopes. In this review, various erosional processes in bedrock river channels are classified and discussed. Especially, theoretical and numerical models on channel bed abrasion with bed load sediment particles are introduced and discussed.

• Smart Structures and Systems
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• v.22 no.6
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• pp.675-687
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• 2018

In the previous studies on the porous rock strength the effect of pore number and its diameter is not explicitly defined. In this paper crack initiation, propagation and coalescence in Brazilian model disc containing a single cylindrical hole and or multiple holes have been studied numerically using PFC3D. In model with internal hole, the ratio of hole diameter to model diameter was varied between 0.03, 0.17, 0.25, 0.33, and 0.42. In model with multiple hole number of holes was different in various model, i.e., one hole, two holes, three holes, four holes, five holes, six holes, seven holes, eight holes and nine holes. Diameter of these holes was 5 mm, 10 mm and 12 mm. The pre-holed Brazilian discs are numerically tested under Brazilian test. The breakage load in the ring type disc specimens containing an internal hole with varying diameters is measured. The mechanism of cracks propagation in the wall of the ring type specimens is also studied. In the case of multi-hole Brazilian disc, the cracks propagation and b cracks coalescence are also investigated. The results shows that breaking of the pre-holed disc specimens is due to the propagation of radially induced tensile cracks initiated from the surface of the central hole and propagating toward the direction of diametrical loading. In the case of disc specimens with multiple holes, the cracks propagation and cracks coalescence may occur simultaneously in the breaking process of model under diametrical compressive loading. Finally the results shows that the failure stress and crack initiation stress decreases by increasing the hole diameter. Also, the failure stress decreases by increasing the number of hole which mobilized in failure. The results of these simulations were comprised with other experimental and numerical test results. It has been shown that the numerical and experimental results are in good agreement with each other.

• Journal of the Korean Geotechnical Society
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• v.35 no.11
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• pp.75-95
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• 2019

The numerical analysis on PHC piles socketed into weathered rocks through sandy soil layers was conducted to propose the table solution or the chart solution to obtain the mobilization capacity. The mobilization capacity was determined at the settlement of 5% pile diameter and applied a safety factor of 3.0. In order to utilize the excellent compressive strength of the PHC pile effectively, it is recommended that the allowable bearing capacity of ground would be designed to be more than the long-term allowable compressive pile load. A procedure for determining an allowable pile capacity for PHC piles socketed into weathered rocks through sandy soil layers is given by the sum of the allowable skin friction of the sandy soil layer and the weathered rock layer and the allowable end bearing capacity of the weathered rock layer. The design efficiency of the PHC pile is about 85% at the reasonable design stage in the verification of the newly proposed method. Thus, long-term allowable compressive load (P_all) level of PHC piles can be utilized in the optimal design stage.

• Journal of the Korean Geotechnical Society
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• v.35 no.12
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• pp.69-89
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• 2019

Design chart solution and table solution were proposed by Choi et al. (2019a), which conducted a parametric numerical study for the bored PHC piles socketed into weathered rocks through sandy soil layers. Based on the Choi et al. (2019a), the new prediction formulae for mobilized capacity components such as total capacity, total skin friction and skin friction of sand at the settlement of 5% pile diameter were proposed in this study. The proposed prediction formulae (EQ-G1) considers pile diameter, relative embedment length and ${\bar{N}}$ (i.e, corrected N) value and their verification results are as follows. The SRF calculated from the new proposed design method was 71~94%, which are greatly improved compared with results by the existing design method. The design efficiency of bearing capacity was in the range of reasonable design except 4 cases, and the design efficiency of the PHC pile was evaluated as 85%. Therefore, it is possible that allowable compressive load (P_all) of PHC pile can be utilized in the resonable design by means of the new proposed method using EQ-G1 equations. And the other new proposed equations of EQ-G2-3 can be utilized approximately in calculation of axial compressive bearing capacity components for prebored PHC pile.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.11
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• pp.5906-5914
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• 2013

Recently in Korea, the policy is being proceeded to build a intergenerational housing on artificial ground of railroad site for utilizing rental house. Due to narrow space of rail road site, suitable method have to be developed such as micropiles which is known as a method of a fast construction. However, If micropile is used as foundations for the super structure, construction cost is increases compared with other pile. Consequently, new concept micropile proposed to improve both bearing capacity and cost efficiency of general micropile. New concept micropile consists of waveform cement grout surrounding tread bar that formed by grouting the soil layer with jet grouting method as control the grout pressure and flow. The micropile with waveform is expected to decrease the construction cost by cut down pile length of general micropile. This paper examined the behavior of the new concept micropile with waveform subjected to axial load using two-dimensional axisymmetric numerical analyses method. According to the numerical result, there will cost effectiveness as the pile displacement decreased despite the length of waveform micropile is down about 5% from a general micropile under the same loading condition. Also, the effect of skin friction force which mobilized from the waveform of micropile appeared at relatively soft ground.

• Journal of the Korean GEO-environmental Society
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• v.7 no.6
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• pp.101-111
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• 2006

In case of drilled shafts installed by drilling through soft overburden onto a strong rock, the piles can be regarded as end-bearing elements and their working load is determined by the safe working stress on the pile shaft at the point of minimum cross-section or by code of practice requirements. Drilled shafts drilled down for some depth into weak or weathered rocks and terminated within these rocks act partly as friction and partly as end-bearing piles. The base resistance component can contribute significantly to the ultimate capacity of the pile. However, the shaft resistance is typically mobilized at considerably smaller pile movements than that of the base. In addition, the base response can be adversely affected by any debris that is left in the bottom of the socket. The reliability of base response therefore depends on the use of a construction and inspection technique which leaves the socket free of debris. This may be difficult and costly to achieve, particularly in deep sockets, which are often drilled under water or drilling slurry. As a consequence of these factors, shaft resistance generally dominates pile performance at working loads. The efforts to improve the prediction of drilled shaft pile performance are therefore primarily concerned with the complex mechanisms of shaft resistance development. In this study, the numerical analyses are carried out to investigate the behavior characteristics of side of rock socketed drilled shafts varying the loading condition at the pile head. The difference of behavior characteristics of side resistance is also evaluated with the effects of modelling of asperity.