• Proceedings of the Korean Geotechical Society Conference
• /
• 2008.03a
• /
• pp.1106-1116
• /
• 2008

Single-pole transmission structures which are supported by drilled shaft foundations are usually subjected to large overturning moments with modest vertical and lateral loads. To analyze the behavior of the drilled shaft under such loading conditions, an analytical model was developed based on beam-column and subgrade reaction methods. Field model tests were performed to calibrate the developed analytical model in which additional subgrade spring models were adopted. The field test results estimated from the calibrated analytical model were compared with those calculated by one spring model and other commercial program. According to the comparison study, the developed analytical model was proven to be a useful tool to analyze the laterally loaded behavior of foundations for single-pole structures.

• Journal of the Korean GEO-environmental Society
• /
• v.6 no.1
• /
• pp.45-51
• /
• 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
• /
• v.16 no.1
• /
• pp.5-16
• /
• 2015

In the long span bridge construction, construction cost portion of large scale marine foundation is about 40% (KICTEP, 2007). In this study, designs for deep water depth large composite foundation of a super long span cable-stayed girder bridge of prototype were performed by three design methods (ASD, LRFD, Eurocode) and the behaviors of a large diameter drilled shaft were analyzed and the 3D numerical analysis was performed. As a result, the soft rock socket lengths in allowable stress design estimation method were the longest. The soft rock socket lengths estimated by the design approach 2 among Eurocode and the LRFD were similar. The longer the socket length socketed in the soft rock was, the smaller the axial force acting on a large-diameter drilled shaft head was and the smaller the settlement of drilled shaft was.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2009.09a
• /
• pp.545-553
• /
• 2009

A lot of long-span marine bridge, which connects land to island or island to island, are being designed and constructed lately in south-west coast in South Korea. In the past, caisson foundations in marine were mainly adopted in construction and stability aspect, however, nowadays with development of pile construction technology, drilled shaft foundations are mainly adopted. As the long span cable stayed bridge and suspension bridge applied with lots of loads are being designed, the scale of pile foundations are getting larger. As the construction cost of substructure including foundation in marine bridges is too high, the appropriate evaluation of the axial bearing capacity of pile becomes a core factor to decide the construction cost of foundation if the drilled shaft is adopted as foundation type of bridge. The evaluation values of skin friction and end bearing capacity of drilled shaft in weathered rock suggested in south Korea are only to introduce the foreign specifications, and most of them are designed in a kind of hard soil layer. Also the allowable load of pile section is less than the expected bearing capacity of pile in the soil condition since the allowable capacity of pile is undervalued. Recently in order to improve this factor the bi-axial hydraulic load test of pile was taken, the data of load transfer analysis of pile, unit of skin friction and end bearing capacity are accumulated. In our country, the design of piles are made with ASD, however, LRFD considering service, strength and extreme state was adopted in Incheon Grand Bridge implemented with BTL, and the research to systematize the resistance coefficient appropriate at home country are being progressed.

• Journal of the Korean Geotechnical Society
• /
• v.19 no.2
• /
• pp.237-246
• /
• 2003

The driven pile has environmental problems such as vibration and noise. Especially, if the site consists of gravel, cobble and weather rock, the driven pile can not be applied. Therefore, the application of the drilled shafts is increasing in Korea. However, the bearing capacity values by the suggested theoretical formulas are generally considered too conservative. In this paper, static load tests for the rock socketed drilled shaft at Gwangandaero and Suyeong3hogyo are performed and in order to estimate the side friction of the shaft, strain gauges are applied. The bearing capacities from the field test data and the bearing capacity values by the theoretical formula are compared. Even the static load tests didn't reach to the ultimate bearing capacity condition, and all the measured bearing capacity values were higher than those by the theoretical formulas. The field data also showed that the major bearing capacities were not due to end bearings but side friction resistances. Based on the above results, several suggestions are proposed for the drilled shaft design.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2002.11a
• /
• pp.140-167
• /
• 2002

A drilled shaft is a deep foundation that is constructed by placing fluid concrete in a drilled hole. Reinforcing steel can be installed in the excavation, if desired, prior to placing the concrete. Drilled shafts provide excellent foundation systems for civil structures. In order to utilize them effectively, it is essential that designers have a clear understanding for how drilled shafts are constructed and also understand the basis for design methods. This paper describes standard design methods for drilled shafts.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2006.03a
• /
• pp.494-505
• /
• 2006

In this study, using constant normal stiffness(CNS) direct shear tests, side shear load distribution were analyzed by the influencing parameters of unconfined compressive strength, surface roughness, confining stress, and material properties. Based on the CNS tests, side shear load transfer function of drilled shafts in rock is proposed using geological strength index(GSI), which indicates discontinuity and surface condition of rock mass in Hoek-Brown criterion. Though comparisons with results of nine drilled shafts's load tests, it is found that the load-transfer curve by this study is in good agreement with the general trend observed by in situ measurements, and thus represents a significant improvement in the prediction of bearing capacity of drilled shaft.

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

• Journal of the Korean GEO-environmental Society
• /
• v.5 no.2
• /
• pp.33-39
• /
• 2004

Most of pile foundations are a condition of fixed head on pile, but lateral loading test of pile have performed to free head on generally. This study performed field lateral loading test accompanying lateral displacement by depth of pile for two cases(fixed head and free head) and analyzed lateral behavior of large drilled shaft. Furthermore compared theoretical equation with result of lateral loading test.

• Proceedings of the Korean Geotechical Society Conference
• /
• 1999.10a
• /
• pp.431-438
• /
• 1999

Vertical congressive and horizontal pile load tests were performed to a instrumented large diameter (D : 1,000 mm) drilled shaft. A drilled shaft was penetrated into the weathered soil and weathered rock. PMT was done for evaluation of properties for these strata. It was expected to be difficult to get undisturbed samples of weathered soils and rocks. Thus. PMT was done at the several selected depths. In those strata, to prevent the test bore hole from collapsing, bentonite slurry was used for making the test bore hole. In this study. soil properties was evaluated by means of PMT results and estimating method (direct method, the Memard method) of vertical pile capacity and horizontal pile behaviors were summarized. Also, vertical and horizontal pile capacity were calculated using PMT and pile load test results.