• Geomechanics and Engineering
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• v.12 no.6
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• pp.899-917
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• 2017

Sixty four tests were performed in a steel tank to investigate the axial responses of piles driven into organic soil prepared at two different densities using a drop hammer. Four different pile materials were used: wood, steel, smooth concrete, and rough concrete, with different length to diameter ratios. The results of the load tests showed that the shaft load capacity of rough concrete piles continuously increased with pile settlement. In contrast, the others pile types reached the ultimate shaft resistance at a settlement equal to about 10% of the pile diameter. The ratios of base to shaft capacities of the piles were found to vary with the length to diameter ratio, surface roughness, and the density of the organic soil. The ultimate unit shaft resistance of the rough concrete pile was always greater than that of other piles irrespective of soil condition and pile length. However, the ultimate base resistance of all piles was approximately close to each other.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.365-372
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• 2002

Drilled and rock socketed piles are of increasing significance due to environmental(noise and vibration) and structural(increase of loads to carry) considerations. Drilled and rock socketed piles will therefore have much higher economic significance in the near future. The existing design of piles socketed into rock is traditionally based on empirical methods which are very unreliable. It is therefore necessary to use high factors of safety with these methods. It is appraised that this is inefficient and expensive and the potential savings from using more reliable design methods are very necessary. In this point of view, a new design approach(Seidel ＆ Collinwood, 2001) has recently been developed. This paper reviews and analyses state-of-the-art of rock socketed pile design methods for shaft resistance. On the basis of the analysis results, some recommendations for improvement of existing design method in Korea are given in this paper.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6C
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• pp.395-406
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• 2006

Drilled shafts are a common foundation solution for large concentrated loads. Such piles are generally constructed by drilling through softer soils into rock and the section of the shaft which is drilled through rock contributes most of the load bearing capacity. Drilled shafts derive their bearing capacity from both shaft and base resistance components. The length and diameter of the rock socket must be sufficient to carry the loads imposed on the pile safely without excessive settlements. 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 performance are therefore primarily concerned with the complex mechanisms of shaft resistance development. The shaft resistance only is concerned in this study. The nature of the interface between the concrete pile shaft and the surrounding rock is critically important to the performance of the pile, and is heavily influenced by the construction practices. In this study, the influences of asperity characteristics such as the heights and angles, the strength characteristics and elastic constants of surrounding rock masses and the depth and length of rock socket, et. al. on the shaft resistance of drilled shafts are investigated from elasto-plastic analyses( FLAC). Through the parametric studies, among the parameters, the vertical stress on the top layer of socket, the height of asperity and cohesion and poison's ratio of rock masses are major influence factors on the unit peak shaft resistance.

• Geomechanics and Engineering
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• v.21 no.5
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• pp.489-501
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• 2020

This paper conducts a complicated coupled effective stress analysis of X-section-in-place concrete (XCC) pile installation and consolidation processes using the dual-stage Eulerian-Lagrangian (DSEL) technique incorporating the modified Cam-clay model. The numerical model is verified by centrifuge data and field test results. The main objective of this study is to investigate the shape effect of XCC pile cross-section on radial total stress, excess pore pressure and time-dependent strength. The discrepancies of the penetration mechanism and set-up effects on pile shaft resistance between the XCC pile and circular pile are discussed. Particular attention is placed on the time-dependent strength around the XCC pile shaft. The results show that soil strength improved more significantly close to the flat side compared with the concave side. Additionally, the computed ultimate shaft resistance of XCC pile incorporating set-up effects is 1.45 times that of the circular pile. The present findings are likely helpful in facilitating the incorporation of set-up effects into XCC pile design practices.

• Tribology and Lubricants
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• v.11 no.5
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• pp.162-171
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• 1995

The application of reciprocating engine crankshaft bearings is of particular importance and interest among the plain bearing, not only because the sheer volume of intemal combustion engines now produced, but because the severe operating conditions they are subjected to. Demands for better performances of crankshaft bearings have provide an important impetus in the development of bearings and bearing materials. As engine design progresses toward higher outpt and higher efficiency, crankshaft bearings must perform under more seveve operating conditions. Higher load, temperature, and speed as well as lower viscosity oil are applied to the bearing sysem, resulting in a smaller minimum oil film thickness. This means more solid-solid contact between the shaft and bearing, and the bearing is exposed to more danger of seizure. Some engines may experience bearing seizure problems. However, understanding about the seizure behavior and mechanism is far from being enough. Seizure resistance of a bearing-shaft system will be affected by the properties of the shaft and bearing, especially their materials and surface texture. Commonly used engine bearing materials include Al-Pb-Si, Al-Sn-Si, Al-Sn, and Cu-Pb with Pb-Sn-Cu overlay. These materials have very different properties. They showed different behaviors dering seizure tests and seizure may occur with different mechanism for different bearing material. Shaft materials also affect the seizure resistance of the system. Surface texture of the bearing and shaft have apparent effects on the lubrication and solid-solid contact pattern, and therefore will affect the seizure behavior of the system. Bearings and shafts which are made of different materials and have different surface textures have been tested and analyzed. Their effects on seizure resistance are discussed and possible seizure mechanisms for different beatings are presented in this paper.

• Journal of the Korean GEO-environmental Society
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• v.9 no.4
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• pp.5-13
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• 2008

Just as infill material can reduce the shear strength of a rock joint, a layer of soft material between concrete and the surrounding rock socket can reduce pile shaft resistance of drilled shafts socketed in rocks. This can also result from construction methods that leave smeared or remoulded rock or drilling fluid residue on the sides of the rock sockets after concrete placement. The nature of the interface between the concrete pile shaft and the surrounding rock is critically important to the performance of the pile, and is heavily influenced by construction practice. Characteristics of the concrete-rock interface, such as roughness and the presence of the soft materials deposited during or after construction can significantly affect the shaft resistance response of the pile. In this study, we conducted the parametric study to examine the performance characteristics of drilled shafts socketed in smeared rock under the vertical load with the code of finite difference method of FLAC 2D. As the results of the current research, the parameters that affect the settlement of the pile head and the ultimate unit shaft resistance could be identified.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.11a
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• pp.209-236
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• 2002

Ultimate pile capacity - Point resistance - Frictional resistance - Determination of point and frictional resistances from field tests - Summary of recommendations from design Group effects Settlement analysis.

• Journal of the Korean GEO-environmental Society
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• v.6 no.1
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• pp.45-51
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• 2005

The distribution of shaft resistance is measured by the static load test with the strain gauge or stress gauge, so that the long-term load distribution must be considered for the pile design. However, the measurement by strain gauge generally assumes the 'zero reading', which is the reading taken at 'zero time' with 'zero' load and the residual stress, which is the negative skin friction(or the negative shaft resistance) caused by the pile construction, is neglected. Therefore, the measured value by strain gauge is different from the true load-distribution because residual stresses were neglected. In this study, the three drilled shafts were constructed, and the strain measurements were carried out just after shaft construction. As a result of this study, it is shown that the true load-distribution of drilled shaft is quite different with known load distribution and the true load-distribution of drilled shaft changed from the negative skin friction to the positive skin according to the load increment.

• 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.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.11a
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• pp.1-26
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• 2002

This study addresses preliminary design and construction specification for micropiles. Especially several design methods for micropiles in sands, clays or mixed soil layers are described. The bearing capacity of micropiles are mainly depended upon the shaft resistance. Therefore, the pressure of grouting is one of the most important design parameters for the bearing capacity evaluation of micropile. There is no theoretical way to evaluate the shaft resistance of micropile up to now because grouting method is another key parameter for micropile design approach. Because of above reasons, the present design approaches of the micropile are based on the collected field data The bearing capacities of designed micropiles should be verified by static load tests before and after construction at the planned site.