• Journal of the Korean Geotechnical Society
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• v.20 no.5
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• pp.117-126
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• 2004

Recently, the top ＆ down method with drilled shafts as a foundation of high rise building is often adopted for the purpose of construction period reduction and construction cost effectiveness. It is common to omit the loading test as a quality assurance on account of the high capacity of drilled shafts for the top ＆ down method. It seems that the capacity of drilled shaft in recent top ＆ down method is beyond that of conventional loading test method. However, the quality assurance for the drilled shaft as foundation of high rise building becomes much more important since the drilled shaft should bear much higher working load. A small scale test pile can be an alternative as a quality assurance for the drilled shaft with hish capacities. Through a case study, this paper gives an idea for solving the limitation of the conventional loading test method for the quality assurance of drilled shaft with high capacities. In particular, this paper analyzed the scale effect for a small drilled shaft installed into bedrock, which could be used for an alternative.

• Journal of the Korean Geotechnical Society
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• v.23 no.1
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• pp.13-21
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• 2007

Rock socketed drilled shafts are used as foundations for bridges and other transportation structures because of their load carrying capabilities. However, only limited information is available in the literature on the effects of roughness on the unit side resistance of rock socketed drilled shafts. The objective of this study is to investigate the effect of drilling tools on the socket roughness in soft clay shale in Texas. Field study showed that the drilling tools, auger and core barrel, produced different roughness in the boreholes.

• Journal of the Korean GEO-environmental Society
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• v.2 no.4
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• pp.5-14
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• 2001

The NDT(Non-Destructive Testing) technique, detecting defects without damaging foundations, has, lately, been a matter of concern. In this study, the applicability of the borehole methods(CSL, CT, PS) and the surface reflection methods(SE, IR) to the evaluation of integrity of drilled shaft was investigated through field test. Ten drilled shafts, 0.4 m in diameter and 7.0 m long each, were constructed, one shaft with no defect and nine shafts intentionally with the combination of the common defects such as soft bottom, necking, bulging, cave-in, and/or weak concrete. Analysing each NDP test result on the constructed drilled shafts, an optimum combination of the NDP methods as well as the applicability of each NDP method to detecting defects of drilled shaft have been investigated.

• Journal of the Korean Geotechnical Society
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• v.31 no.2
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• pp.47-63
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• 2015

A fundamental study of drilled shafts subjected to lateral cyclic loading in weathered soil was carried out based on field tests and numerical analysis. The emphasis was given on quantifying the cyclic p-y curve function from lateral cyclic loading tests and three-dimensional finite element analysis. Lateral cyclic loading tests and three-dimensional finite element analysis were carried out to investigate the behavior of drilled shafts according to the direction of cyclic loading. Based on the field tests and numerical analysis, a modified lateral load transfer relationship and design chart with degradation factors were proposed by considering the characteristics of cyclic loading. It was found that the prediction by the proposed p-y curve function is in good agreement with the general trends observed by in-situ measurements, and it represents a practical improvement in the prediction of lateral displacement and bending moment distribution of drilled shafts subjected to cyclic loading.

• Journal of the Korean Geotechnical Society
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• v.20 no.5
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• pp.87-98
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• 2004

In this study reinforcing effect of soil nailed-drilled shafts subjected to axial and lateral loads was evaluated. Special attention was given to the reinforcing effects of soil nails placed from the drilled shafts to surrounding weathered- and soft-rocks based on model tests, numerical analyses and field tests. The model tests and numerical analyses are conducted to analyze the reinforcing effect of various conditions of number, inclination, position and length. The results of 1/40 scale model tests and numerical analyses show that as the number of reinforcing level increases, the incremental effect of reinforcement tends to increase, whereas the reinforcing effect on relative position is negligible. In addition there is a reinforcing effect as the inclination angle increase up to 30 degrees. Based on the results of tensile load tests, soil nailed-drilled shaft has a considerably smaller settlement to reach the ultimate level compared with the result of un-reinforced drilled shafts. For compression tests, there is a reinforcing effect of about 200% measured.

• Geomechanics and Engineering
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• v.31 no.1
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• pp.71-86
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• 2022

In Taiwan, an efficient approach for enhancing the stability of colluvium slopes is the drilled shaft method. For slopes with drilled shafts, the soil arching effect is one of the primary factors influencing slope stability and intertwines to the failure mechanism of the pile-soil system. In this study, the contribution of soil arching effect to slope stability is evaluated using the FEM software (Plaxis 3D) with the built-in strength reduction technique. The result indicates the depth of the failure surface is influenced by the S/D ratio (the distance to the diameter of piles), which can reflect the contribution of the soil arching effect to soil stability. When α (rock inclination angles)=β (slope angles) is considered and the S/D ratio=4, the failure surface of the slope is not significantly influenced by the piles. Overall, the soil arching effect is more significant on α=β, especially for the steep slopes. Additionally, the soil arching effect has been included in the proposed stability charts. The proposed charts were validated through two case studies, including that of the well-known Woo-Wan-Chai field in Taiwan. The differences in safety factor (FoS) values between the referenced literature and this study was approximately 4.9%.

• Journal of the Korean Geotechnical Society
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• v.20 no.1
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• pp.37-47
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• 2004

In this study the load distribution and settlement of soil nailed-drilled shafts subjected to axial loads were evaluated by a load-transfer approach. Special attention was given to the reinforcing effects of soil nails placed from the shafts to surrounding weathered- and soft-rocks based on an analytical study and a numerical analysis. An analytical method that takes into account the number, the positions on the shaft, the grade, and the inclination angle at which the soil nails are placed was developed using a load transfer curve methods. Through the comparative study, it is found that the prediction by present approach simulates well the general trends observed by the in-situ measurements and numerical results SHAFT 4.0. It is also found that the reinforcing effects of soil nails increases in the order of hard-, soft- and weathered-rock since the ultimate shaft resistance far large bored piles in weathered rocks is fully mobilized after small displacements of the shaft, compared to the soft- and hard-rocks and subsequently the side resistance is transferred down to the soil nails.

• Journal of the Korean Geotechnical Society
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• v.23 no.2
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• pp.85-92
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• 2007

As the use of drilled shafts for foundation of a large size structure increases, the evaluation of the reliable bearing capacity of the pile has become important. The purpose of this study is to verify the reliability of bearing capacity equations for drilled shafts socketed in weathered rock by comparing the bearing capacity values from static load tests with values from bearing capacity equations. In this study, twelve data from static load test were selected from four field sites, and the data of load test and the properties of weathered rock were analyzed. Three methods widely used in practice were selected for analysis, namely the AASHTO method (1996), Carter & Kulhawy method (1988), and FHWA method (1999). The comparison of the bearing capacity values from the bearing capacity equations to those obtained from load tests showed that the Carter & Kulhawy method (1988) was the most reliable in giving conservative design values and smaller COV (Coefficient Of Variation).

• Proceedings of the Korean Geotechical Society Conference
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• 1999.07a
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• pp.53-64
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• 1999

• Journal of the Korean GEO-environmental Society
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• v.13 no.10
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• pp.33-42
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• 2012

The efficiency of the current design methods for computing pile resistances is analyzed using field load-settlement tests results. Twelve load-settlement test data for drilled shafts and bored piles were obtained from the literature. These load-test data were fitted using the t-z method. Subsequently, the ultimate resistances were evaluated based upon the failure criteria from following methods: (1) the Davisson's approach and (2) settlement corresponding to 5% or 10% shaft diameter approach. The ultimate resistances for these drilled shafts and bored piles were also predicted using methods based on the design code from North America (United States, Canada), Europe, and Asia (Japan). The pile resistances determined from field load-settlement tests were compared with those calculated using the design codes. The comparisons show that most design codes predict a conservative resistance for drilled shafts and bored piles. However, in the case of drilled shafts, we find that some of the design codes can over-predict the resistance and, therefore, should be applied cautiously. This research also shows that the t-z method can be successfully used to predict the ultimate resistance and the load transfer mechanism for a single pile.