• Earthquakes and Structures
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• v.20 no.1
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• pp.87-96
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• 2021

Ground motions recorded in near-fault sites, where the rupture propagates toward the site, are significantly different from those observed in far-fault regions. In this research, finite element modeling is used to investigate the effect of pile cap stiffness on the seismic response of soil-pile-structure systems under near-fault ground motions. The Von Wolffersdorff hypoplastic model with the intergranular strain concept is applied for modeling of granular soil (sand) and the behavior of structure is considered to be non-linear. Eight fault-normal near-field ground motion records, recorded on rock, are applied to the model. The numerical method developed is verified by comparing the results with an experimental test (shaking table test) for a soil-pile-structure system. The results, obtained from finite element modeling under near-fault ground motions, show that when the value of cap stiffness increases, the drift ratio of the structure decreases, whereas the pile relative displacement increases. Also, the residual deformations in the piles are due to the non-linear behavior of soil around the piles.

• Journal of the Korean Geotechnical Society
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• v.22 no.4
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• pp.21-30
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• 2006

In this study, centrifuge model tests were performed to investigate the stress concentration ratio, bearing capacity and deformation modes of piles in clay ground improved by granular piles with two types of pile (CSCP, SCP) and various replacement ratios (0, 20, 40, 60%). According to the results of tests, the load ratio of ground improved by SCP and CSCP proportionally increased as replacement ratio increased. It shows that average normalized load of ground improved by CSCP is higher by about $8{\sim}21%$ than by SCP. As a result of rigid loading tests, it was evaluated that average stress concentration ratio of CSCP is higher than that of SCP. Only expansion failure occurred in CSCP, whereas SCP showed the expansion and shear failure simultaneously.

• Journal of the Korean Geotechnical Society
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• v.23 no.12
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• pp.5-11
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• 2007

Among soft ground improvement methods by using granular material, the sand compaction pile method has been widely utilized in Korea, but, as a result of shortage and increase of unit price of sand, a necessity of an alternative method has been required. In this study, a series of in-situ static load tests for crushed-stone compaction piles were performed. Pile diameter was fixed to 700mm and areas of loading plates were changed. The static load tests were performed for area replacement ratios of 20, 30 and 40% respectively. Based on the test results, bearing capacity of single crushed-stone compaction pile was estimated. It showed that the settlement decreases as the replacement ratio increases. Also, a yielding capacity equation of the crushed-stone compaction pile considering replacement ratio was suggested.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.6
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• pp.267-274
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• 2021

Among several methods for determining the allowable lateral resistances of piles, the subgrade reaction method and ultimate lateral resistance method are generally used. To determine the effects of the soil conditions, pile head restraint conditions, and pile lengths on determining the allowable lateral resistances of piles, computations of the allowable lateral resistances of piles using the two methods were executed, and the computation results were compared. For piles in soft cohesive soil, the pile design is governed by the allowable lateral resistance of a pile from subgrade soil reaction method regardless of the pile head restraints conditions and pile lengths. The allowable lateral resistance of a pile from the ultimate lateral resistance governs the design as the undrained shear strength increases. Except for the case of a short pile, which is installed in loose granular soil, the allowable lateral resistance of a pile from ultimate lateral resistance governs the design of laterally loaded piles. According to this study, computation of the ultimate lateral resistance of a pile is needed, even though some opinions suggest that the design of a laterally loaded pile is satisfied only by the subgrade reaction method. The pile width barely influences the coefficient of horizontal subgrade reaction. Realistically, the effect of the pile width can be disregarded in the condition of common pile widths of 20~90cm.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.1C
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• pp.27-35
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• 2010

Instrumented steel sheet piles being driven by vibratory pile driver were installed in granular soil deposit and behaviors of the sheet piles were investigated. One of the instrumented steel sheet pile was installed without clutch and the other was installed with clutch. Sheet pile with clutch means that of installed in connection with pre-installed sheet pile. Penetration rates of sheet piles measured from depth measuring drum has shown that interlock friction had great effect on penetration speed of sheet pile. Clutch friction shows irregular distribution along the depths of penetration and its magnitude was estimated as 19.1kN/m. According to the accelerations obtained from accelerometer, it was seen that steel sheet pile behaviored nearly as a rigid body. Efficiency factor of an isolated sheet pile was 0.42 and that of the connected sheet pile was 0.71. Shapes of dynamic load transfer curves obtained from analysis of measuring devices was similar to those suggested by Dierssen.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1415-1426
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• 2008

Stone columns, locally called "GCP (granular compaction pile)" can be used to improve strength and resistance against lateral movement of a foundation soil like rigid piles and piers. Also installation of such a discrete column facilitates drainage, and densifies and reinforces the soil in the sense of ground improvement. The integrity of the GCP has been indirectly controlled with the records of each batch including depth and the quantity of stone filled. An integrity testing was attempted using crosshole S-wave logging. The method is conceptionally same as the crosshole sonic logging (CSL) for drilled piers. The only and critical difference is that S-wave should be used in the logging, because P-wave velocity of the stone column is less than that of ground water. The crosshole sonic logger does not have the capability to measure S-wave propagating through the skeleton of crushed stone. An electro-mechanical source, which can generate either P- or SH-waves, and a 1-D geophone were used to measure SH-waves. Two 76mm diameter cased boreholes were installed 1 meter apart across the nominal 700mm diameter stone column. At every 10cm of depth, shear wave was measured across the stone column. One more borehole was also installed 1 meter outward from the one of the above boreholes to measure the shear wave profile of the surrounding soil. The diametric variation of the stone column with respect to depth was evaluated from the shear wave arrival times across the stone column, and shear wave velocities of crushed stone and surrounding soil. The volume calculated with these variational diameters is very close to the actual quantity of the stone filled.

• Journal of the Korean GEO-environmental Society
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• v.12 no.6
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• pp.5-15
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• 2011

In this study, centrifuge model tests were performed to investigate stress concentration ratio, stress characteristics of soft clay ground improved by granular compaction piles with changes of piles type, loading condition and area replacement ratio. From the results of rigid loading tests, while vertical stresses acting on clay ground is similar, vertical stresses acting on GCP is larger than those acting on SCP with same replacement ratio. Also, average stress concentration ratio is increased proportionally with increasing the area replacement ratio of GCP and SCP. It was evaluated that average stress concentration ratio of soft clay ground improved by GCP is larger than that of SCP. As a result of flexible loading tests, stress concentration ratio is the highest when replacement ratio of GCP and SCP is 40%. Average stress concentration ratio of soft clay ground improved by GCP is a little more higher than is improved by SCP.

• Geomechanics and Engineering
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• v.28 no.1
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• pp.11-23
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• 2022

The response of pile foundations under lateral loads are usually analyzed using beam-on-nonlinear-Winkler-foundation (BNWF) model framework employing various forms of empirically derived p-y curves and p-multipliers. In practice, the p-y curve presented by the American Petroleum Institute (API) is most often utilized for piles in granular soils, although its shortcomings are recognized. The objective of this study is to evaluate the performance of the BNWF model and to quantify the error in the estimated pile response compared to a rigorous numerical model. BNWF analyses are performed using three sets of p-y curves to evaluate reliability of the procedure. The BNWF model outputs are compared with results of 3D nonlinear finite element (FE) analysis, which are validated via field load test measurements. The BNWF model using API p-y curve produces higher load-displacement curve and peak bending moment compared with the results of the FE model, because empirical p-y curve overestimates the stiffness and underestimates ultimate resistance up to a depth equivalent to four times the pile diameter. The BNWF model overestimates the peak bending moment by approximately 20-30% using both the API and Reese curves. The p-multipliers are revealed to be sensitive on the p-y curve used as input. These results highlight a need to develop updated p-y curves and p-multipliers for improved prediction of the pile response under lateral loading.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4C
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• pp.137-145
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• 2011

The amount of material upheaved owing to the installation of a granular compaction pile (GCP) in the seabed was analyzed by a field execution. The amount of material upheaved was predicted by existing equations, proposed by the Korea Construction New-Technology Association (KCNET; 2003) and Shiomi and Kawamoto (1986), and compared with the amount measured by bathymetry in the field. As a result, the upheaval heights were found to show a clear increase with increasing replacement ratio. The measured amount was larger than the amount predicted by the equations, but the amount predicted from the equation proposed by KCNET (2003) was relatively close to the measured amount. The upheaval heights were found to be more sensitive to the replacement ratio than the installation depth. The increasing trends of the upheaval heights with the installation depth as predicted by the equation of KCNET (2003) were in agreement with the measured trends at a replacement ratio of 25%. As a result of comparing the coefficients of upheaval by the equations, the coefficients of upheaval determined by the equation of KCNET (2003) were larger than those determined by the equation proposed by Shiomi and Kawamoto (1986), which were relatively close to the measured trends. Specifically, the difference between results obtained by both these equations was large when the replacement ratio was relatively low.

• Journal of the Korean GEO-environmental Society
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• v.13 no.4
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• pp.71-76
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• 2012

Shear strength of soil is power that resists failure and sliding according to any face in soils and one of the most important factors during engineering properties of soil. Shear strength is used for engineering science problems as bearing capacity methods of foundation or piles, slope stability after dam or Cutting Embankment and stability problem analysis of soils as lateral earth pressure of soil structures, ets. This study has analyzed shear strength change of samples classified 2.00mm(10sieve)와 0.85mm(20sieve), 0.475mm(40sieve) using direct shear tester after removing and drying cohesive soil ingredient of Weathered granite soil Therefore, this study would help studies about shear strength properties by particle size.