• Journal of the Korean Geotechnical Society
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• v.29 no.12
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• pp.5-10
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• 2013

Bearing capacity of a drilled shaft can be separated into side resistance and base resistance. But in domestic design procedure side resistance is usually underestimated compared with base resistance. Results of bi-directional test showed that measured side resistances in each different layers are larger than those evaluated from several suggested methods. In this study, measured side resistances in each different layer of drilled shafts installed in domestic sites are analyzed and compared with evaluated side resistances from the method using revised SPT N value. For weathered rock and soft rock layer, from which rock core can hardly be obtained, we suggested new evaluated methods using revised SPT N value instead of the method using uniaxial compressive strength of rock. Resuts showed that the ranges of side resistance of cohesive and non-cohesive layer are $f_s{\leq}5tf/m^2$ and $f_s{\leq}15tf/m^2$ respectively. Range of side resistance in weathered rock is $15tf/m^2$ < $f_s{\leq}50tf/m^2$ and that in soft rock $f_s{\geq}35tf/m^2$.

• Journal of Korean Society of Steel Construction
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• v.16 no.3 s.70
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• pp.355-363
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• 2004

In order to obtain the effective length factor of beam-column members of plane frames, this paper extensively used an alignment chart approach, based on the nomograph given in LRFD-AISC specification commentaries. However, it should be noted that various simplifications and assumptions were introduced in constructing the alignment chart. To overcome the practical limitations of the alignment chart, this paper proposes a simple but accurate procedure that determined the effective buckling length for stability design of main members of cable-supported bridges. This method requires the full system buckling analysis. The numerical examples showing the suitability of the present scheme are discussed and some conclusions are drawn.

• Journal of the Korean Geotechnical Society
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• v.17 no.1
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• pp.99-107
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• 2001

일반적으로 샌드파일 설치로 인해 파일주변지반은 교란되어 스미어 영향과 배수저항에 의해 압밀지연 현상이 발생하는 것으로 알려져 있다. 특히 예민한 점성토 지반일 경우 교란정도가 크며, 틱소트로피현상이 지연될 경우 지지력 및 압축특성은 불리하게 된다. 본 연구에서는 원지반 특성이 파악된 채취시료를 이용하여 완전 교란조건에서의 실내모형시험과, 염분농도변화에 의한 실내역학시험을 실시하였다. 실내모형시험 결과 낮은 하중단계에서의 압밀계수는 비교란 시료의 특성과 유사하게 나타났으며, 염분농도 증가에 따라 일축압출강도가 증가하고 강도회복은 빠르며 압축지수는 작게 나타났다. 결과적으로 점성토지반 간극수중 염분농도는 강도증대와 압축특성 변화에 영향을 주며, 틱소트로피 증대의 영향요소가 적은 담수지반에서 샌드파일을 시공할 경우 발생하는 과다침하의 한 원인으로 여겨지는바, 이와 같은 요인은 측방유동에 의한 침하거동과 함께 고려하여야 할 영향요소로 파악되어야 할 것으로 판단된다.

• Journal of the Korean GEO-environmental Society
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• v.5 no.3
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• pp.31-39
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• 2004

The bored pile is widely used as a low noise and vibration piling method in Korea. However, there is design tendency to minimize the friction capacity of the bored pile because of uncertainty and the quality control specification is not set up. This research analysed the strength characteristics of cement paste after the uniaxial compression test with various condition. Test results show that the compressive strength of cement paste with w/c=0.83 was up to $156.0kgf/cm^2$, and the lower w/c ratio and the longer age, the strength of cement paste increased. Also the higher soil mixing ratio, the strength of soil cement decreased, and too high soil mixing ratio caused the malfuction of soil cement. Also this research analysed the 188 dynamic pile test results which were performed before and after hardening of cement paste. Analysis result showed that the average ultimate unit friction capacity was $9.1tf/m^2$ and this result surpassed the common design criteria of the bored pile.

• Journal of the Korean GEO-environmental Society
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• v.4 no.2
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• pp.5-13
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• 2003

The domestic design method for the shaft resistance of drilled shafts into a bedrock is based on the empirical method, where the uniaxial compressive strength of rock specimen is utilized for calculation of the shaft resistance. This method has uncertainties in prediction of capacity of drilled shafts and result in uneconomic engineering design. Recently a new improved design method was suggested, which reflects important factors that affect the strength of pile sockets. Socket roughness is one of the significant factors influencing the shaft resistance of drilled shaft socketed into rock. In this paper roughness information for the shaft resistance design of socket pile was suggested on the basis of statistical analysis of data measured from wall surface in the bore holes of drilled shafts.

• Journal of the Korean Geosynthetics Society
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• v.18 no.1
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• pp.39-53
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• 2019

Bi-directional pile load test (briefly called 'BDH PLT') cannot be performed at loading levels where ultimate bearing capacity could be assessed in field, it is not possible to precisely determine both ultimate load and yield load and under loading. Since the load is transmitted separately to the skin and the end unlike the static pile load test (briefly called 'SPLT') and the direction of loading on the skin is opposite, such methods could have a result different from actual movements of shafts. In this study, three-dimensional finite element method (briefly called '3D FEM') analysis was conducted from results of the BDH PLT, made with barret piles, which were large-diameter cast-in-place concrete piles, and the calculated design constants were applied to the 3D FEM analysis of the SPLT to interpret them numerically and then, actual behaviors of cast-in-place concrete piles were estimated. First, using the results of the BDH PLT with cast-in-place concrete piles, behaviors of the piles made by loading upwards and downwards were analyzed to calculate load-displacement. Second, the design constants, calculated by the 3D FEM analysis and the back analysis, were applied on the 3D FEM analysis for the SPLT, and from these results, behaviors of the SPLT through the BDH PLT was analyzed. Last, the results of the 3D FEM analysis of the SPLT through the BDH PLT was expressed in relationships as {A ratio of bearing capacity of the SPLT and of the BDH PLT (y)} ~ {A ratio of reference displacement and pile circumference (x)}, and they were all classified by reference displacement at 10.0 mm, 15.0 mm, and 25.4 mm.

• Journal of the Korean Geotechnical Society
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• v.15 no.6
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• pp.155-165
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• 1999

In completely weathered granite gneiss,8 of 40cm cast-in-situ concrete piles are constructed, and static pile load tests are executed on the piles to study the bearing behavior of rock-socketed piles. Subsurface explorations are carried out on the test site in three phases, in which 14 borehole investigations as well as the seismic investigation are performed. Rock socketd depths of the piles in the weathered rocks are varied as 3m, 6m and 9m to separate the shaft resistance from the end bearing resistance, and for a couple of piles, styrofoam of 10cm thickness is installed under the pile point to eliminate the effect of the end resistance. Strain gages are instrumented on re-bars to pick-up the transferred loads along the pile length. From the results of the pile load tests, the allowable shaft resistance and the allowable end bearing values of weathered rocks are proposed as $8.6t/m^2\;and\; 84t/m^2$, respectively. The empirical equation relating the elastic modulus of rock mass with the uniaxial compressive strength of the rock specimen is also proposed for the weathered rocks.

• Journal of the Korean Geotechnical Society
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• v.27 no.6
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• pp.5-16
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• 2011

Post-grouting for the drilled shaft is known to remarkably increase the end bearing capacity of pile by consolidating and reinforcing the disturbed ground containing slime around the pile tip. However, the general design guideline for post-grouting has not been established yet in Korea. Especially in the domestic application, the post-grouting is employed just for repairing the pile with unacceptable resistance rather than for increasing the design resistance of pile. Therefore, little is reported about the effect of post-grouting on the pile resistance itself. In this study, the effect of post-grouting on the resistance of drilled shafts installed in the weathered rock in Korea was estimated by performing the bi-directional load tests on the piles with and without the post-grouting. The test results presented that the initial slope of end bearing-base displacement curve in the pile with post-grouting was 4 times higher than that without post-grouting. At the acceptable settlement (1% of pile diameter), the end bearing capacities of piles with and without the post-grouting were estimated to be 12.0 MPa and 7.0 MPa, respectively, which indicate that the post-grouting could increase the end bearing resistance of pile in weathered rock more than 70%.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.1
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• pp.51-57
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• 2011

Irregular distributions of limestone cavity in Gang-Won province area may cause unexpected accidents from reduced serviceability or failure of structure. It is requested that an appropriate ground reinforcement method should be used to improve bearing capacity of structure, and the method should also be satisfied with environmental requirements. Among several methods used for foundation constructions in cavity area, Rod Jet Pile(RJP) method has been widely used. While the RJP method was used to improve bearing capacity for the railway bridge foundations, water pollutions of drinking water as well as fishery located adjacent to this project area were occurred. The main reason of the water pollution was cement runoff used in cement mortar during injecting material in RJP method. Laboratory tests were performed to prevent water pollution. The compaction mortar method using low movable material was selected for this project. The quality of water at a fishery adjacent to the site and the compressive strength of cores taken from the construction site were measured. Test results show that the water pollutions was minimized, and the average compressive strength of foundation material was over 5 MPa. As a result of this study, compaction mortar method can be used to ensure the bearing capacity of foundation and to prevent environment pollutions.

• Journal of the Korean Geotechnical Society
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• v.35 no.3
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• pp.5-16
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• 2019

With the recent concentration of urban populations, the constructions of large structures are increasing, along with the development of foundations for large structures. PHC Piles have been used in many structures ever since Japanese introduced the technology at the end of the 20th century. Recently, many studies on the use of the PHC Pile have been carried out as earth retaining using the merits of PHC piles. In this study, static axial compression tests were conducted on the PHC-W piles constructed as column-type in building underground additional wall using the PHC-W earth retaining wall. The end bearing capacity of pile was calculated using the axial load transfer measurement that was obtained from the static axial compression test result. Since end bearing capacity of the PHC-W pile embedded in weathered rock showed a different behaviour from the conventional PHC pile, the calculation method of end bearing capacity for column-type PHC-W piles would be proposed. The unit ultimate end bearing equation proposed for single and group PHC-W pile embedded in weathered rock is $q_b=13.3N_b$ and $q_b=6.8N_b$.