• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.489-498
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• 2005

In this study, the shaft resistance of drilled shafts socketed into weathered-and soft-rocks was examined by the constant normal stiffness(CNS) test. Large scale model tests were performed for different unconfined compressive strength, socket roughness, initial normal stress, and normal stiffness for identifying shear load transfer characteristics. Through comparisons with previous studies, it is found that the results by the present approach is good agreement with the general trend observed by existing empirical and analytical results.

• Proceedings of the KSR Conference
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• 2004.06a
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• pp.967-973
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• 2004

Rock socketed drilled shafts transfer significant portion of structural loads at the socketed part. Therefore, a proper design of side and base resistances of a shaft at the socket is a major concern for the geotechnical engineers. In this study, we modified the Hoek-Brown criterion to estimate side resistance of rock socketed drilled shafts. Earlier method to compute side resistance of a shaft is linear or power functions of intact rock masses. However, side resistance is mobilized like shearing which influenced by the mechanical properties of concrete and rock masses, adhesion of rock/concrete interface, roughness of rock socket. Therefore, a single coefficient or power of uniaxial compressive strength of intact rock cannot provide accurate values of side resistance in a wide range of the uniaxial compressive strength. A new approach proposed in this study can consider in situ rock mass condition (frequency or discontinuities, weathering condition), and rock types thus, it has a wider applicability than the earlier models.

• Proceedings of the Korean Geotechical Society Conference
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• 2007.09a
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• pp.440-449
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• 2007

Recently, researches for side resistances of drilled shafts considering socket roughness have been conducted actively. In order for these researches, roughness measurement devices using laser sensor were developed by two research groups. The devices were only applied in boreholes with dry conditions. In this research, a roughness measurement devices using the laser sensor (BKS-LRPS) was developed, which could apply in wet conditions and also measure vertical offsets of drilled shafts. In addition, the application of the laser sensor to the geotechnical engineering proposed in this paper.

• Proceedings of the Korean Geotechical Society Conference
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• 2007.09a
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• pp.105-114
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• 2007

Recently, construction of high-rise buildings have been increased all around the world, and their foundation are designed to carry heavy loads form superstructures. For this reason, the use of drilled shafts have been increased, and the proper understanding of drilled shafts have been issued, especially for socket roughness and vertical offsets. In this study, the BKS-LRPS using laser sensor was developed for the measurement of socket roughness and vertical offsets for the first time in Korea. The BKS-LRPS was applied for measuring of socket roughness and also vertical offsets at the specific field sites. Based on this study, BKS-LRPS was successfully applied for measurement of socket roughness and vertical offsets the in the fields, and more appropriate quality control for the vertical offsets have to be needed.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.518-525
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• 2009

The bi-directional high pressure pile load test(BDH PLT) which is a kind of pile load tests was conducted to find out a reasonable design procedure of large-diameter drilled shafts of large-size building structures. The behaviors of bearing capacity and settlement of the large-diameter drilled shafts were analyzed and the results obtained from BDH PLT were also compared with those obtained from the equations suggested in the specification. In case of the reasonable design procedure adopted, the construction cost could be saved at least 15 ~ 28%. It could be concluded that BDH PLT should be needed for the foundation construction cost reduction of the high-rise building structures.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.537-544
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• 2009

Several domestic and foreign design methods for rock socketed drilled shafts were introduced in this study. In order to verify these design methods, the results of field pile load tests were compared with predicted capacities using them. Based on this study, AASHTO(1996) and FHWA(1999) design methods tend to underestimate, and CFEM(2006) and NAVFAC(1982) tend to overestimate. The difference between the predicted and measured values was caused by reflecting different rock socket geometry and also different rock properties in each design method.

• Journal of the Korean Geotechnical Society
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• v.29 no.1
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• pp.161-170
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• 2013

In this paper, numerical pile segment analysis is conducted with an advanced soil elastoplastic model to investigate the diameter effects on skin friction behaviour of a drilled shaft in sand. Ultimate skin friction and 't-z' behavior from the pile segment analyses for drilled shafts show good agreement with those from design methods. Higher ultimate skin friction for the smaller diameter pile is related to the greater increase in the effective radial stress at the interface due to the localized dilation at and near the pile interface. Stiffer t-z curve for the smaller diameter pile is related to the early occurrence of three shear stages (early, dilation, constant volume shear stages). The diameter effects on ultimate skin friction of drilled shafts are more prominent for denser sand and lower confining pressure.

• Journal of the Korean Geosynthetics Society
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• v.19 no.3
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• pp.23-33
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• 2020

The lateral bearing characteristics are important factors in the case of large diameter drilled shafts and the measures to increase this are to improve the adjacent ground of the pile to increase the rigidity and to increase the rigidity of the pile itself. There are many suggestions for increasing rigidity by reinforcing casing on the pile, but few studies have been done related to this. Therefore, in this study, the lateral bearing characteristics according to casing reinforcement length were studied for each ground condition using non-linear analysis to evaluate the appropriate casing reinforcement length of the large diameter drilled shafts depending on the ground conditions. As a result, the lateral bearing characteristics of the large diameter drilled shafts are most effective if the casing reinforcement length ratio is 1.2, and depending on the ground conditions, the more loose the ground, the greater the reinforcement effect.

• Journal of the Korean Geotechnical Society
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• v.24 no.12
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• pp.33-40
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• 2008

The load distribution and deformation of rock-socketed drilled shafts subjected to axial loads are evaluated by a load-transfer method. The emphasis is on quantifying the effect of coupled soil resistance in rock-socketed drilled shafts using the 2D elasto-plastic finite element analysis. Slippage and shear load transfer behavior at the pile-soil interface are investigated by using a user-subroutine interface model (FRlC). It is shown that the coupled soil resistance provides the influence of pile toe settlement as the shaft resistance is increased to an ultimate limit state. The results show that the coupling effect is closely related to the value of pile diameter over rock mass modulus (D/$E_{mass}$) and the ratio of total shaft resistance against total applied load ($R_s$/Q). Through comparisons with field case studies, the 2D numerical analysis reseanably presented load transfer of pile and coupling effect due to the transfer of shaft shear loading, and thus represents a significant improvement in the prediction of load deflections of drilled shafts.

• Journal of the Korean Geotechnical Society
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• v.27 no.2
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• pp.35-42
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• 2011

The residual stress on drilled shafts is often neglected. Neglect of the existence of locked-in loads in the shaft is the main reason for conclusions of instrumented tests which suggest that shaft resistance is smaller when the shaft is loaded in tension than when it is loaded in compression. A few researchers studied the residual stress and mentioned that the residual stress is influenced by either the physical expansion/contraction of concrete during the curing or site stratigraphy. In this study, field measurements of residual stress on test shafts were conducted and the factors influencing the residual stress were figured out.