• Journal of the Korean Geotechnical Society
• /
• v.28 no.6
• /
• pp.19-29
• /
• 2012

Pack micropiles were recently developed to improve pile capacity of general micropiles. Pack micropiles were made by warping thread bar or steel pipe of general micropile by geotexlile pack and grouting inside the pack with pressure. According to the pressure, the boring hole could be enlarged. A series of pile uplift tests were performed on three micropiles. Two out of the three piles were the pack micropiles and the other was the general micropile, in which a thread bar was used in the boring hole. According to the pressure applied to the pack micropiles, the diameter of boring hole was enlarged from 152 mm to 220 mm. Unit skin friction mobilized on side surfaces of micropiles increased with displacement of pile head and reached on a constant value, which represents that the relative displacement between piles (or thread bar) and soils was reached on critical state. And the uplift resistance of pack micropile was higher than that of general micropile. Two reasons can be considered: One is that the frictional surface increases due to enlarging diameter of boring holes and the other is that the unit skin friction could increase due to compressing effect of surrounding soils by soil displacement as much as the enlarging volume of boring hole. The compression effect appeared at deeper layer rather than surface layer. The unit skin friction mobilized on micropiles with small diameter was higher than the ones on large bored piles.

• Journal of the Korean Geotechnical Society
• /
• v.34 no.1
• /
• pp.37-46
• /
• 2018

Hollow prestressed concrete filled steel tube (HCFT) piles, which compose hollow PHC piles inside thin wall steel tubes, are developed. In order to investigate the strength characteristics of HCFT piles, flexural and shear tests were conducted on HCFT piles as well as PHC and steel pipe piles with the same diameter. Results of the test program showed that the flexural strength of HCFT piles was 2.88 and 1.19 times those of ICP and steel pipe piles with thickness of 12 mm, respectively, and its shear strength was 2.40 times that of steel pipe piles. The shear key attached to the inside of thin wall steel tube did not affect the flexural behavior of HCFT piles. It was also observed that the flexural strengths of HCFT piles with diameters of 450 and 500 mm were 35 to 63% higher than the sum of the flexural strengths of its components, respectively, because the strength of concrete in compressive zone increased by confining effect of thin wall steel tube on concrete. HCFT piles used as upper piles in hybrid composite piles might decrease the lateral displacement and increase the structural safety of structures subjected to lateral loads.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.32 no.5C
• /
• pp.199-210
• /
• 2012

The effects of tunnelling in weak weathered rock on the behaviour of a pre-existing single pile and pile groups ($3{\times}3$ and $5{\times}5$ pile groups) above a tunnel have been studied by carrying out three-dimensional (3D) elasto-plastic numerical analyses. Numerical modelling of such effects considers the response of the single pile and pile groups in terms of tunnelling-induced ground and pile settlement as well as changes of the shear transfer mechanism at the pile-soil interface due to tunnelling. Due to changes in the relative shear displacement between the pile and the soil at the pile-soil interface with tunnel advancement, the shear stresses and axial pile force distributions along the pile change drastically. Based on the computed results, upward shear stresses are induced up to about Z/L=0.775 from the pile top, while downward shear stresses are mobilised below Z/L=0.775, resulting in a reduction in the axial pile force distribution with depth equivalent to a net increase in the tensile force on the pile. A maximum tensile force of about $0.36P_a$ developed on the single pile solely due to tunnelling, where $P_a$ is the service axial pile loading prior to tunnelling. The degree of interface shear strength mobilisation at the pile-soil interface was found to be a key factor governing pile-soil-tunnelling interaction. Overall it has been found that the larger the number of piles, the greater is the effect of tunnelling on the piles in terms of pile settlement, while changes of the axial pile forces for the piles in the groups are smaller than for a single pile due to the shielding effect. The reduction of apparent allowable pile capacity due to tunnelling-induced pile head settlement was significant, in particular for piles inside the groups.

• Journal of the Korean GEO-environmental Society
• /
• v.20 no.3
• /
• pp.21-30
• /
• 2019

Composite pile, which is composed of the steel pipe pile in which the large horizontal force acts and the PHC pile in which the small horizontal force acts by a special connecting devices, is being commercialized as a base material for civil engineering structures. The core of such a composite pile can be said to be a design criterion for estimating the joint position and stability of the connection device between steel pipe pile and PHC pile. In Korea, there is no precise specification for the location of composite pile joints. In the LH Design Department (Korea Land & Housing Corporation, 2009), "Application of composite pile design and review of design book marking" was made with reference to Road Design Practice Volume 3 (Korea Expressway Corporation, 2001). this is used as a basis of the design of the composite pile. It can not be regarded as a section change of the composite pile, so it has a limitation in application. Therefore, In this study, we propose a design criterion for the location of the section of the composite pile (joint of steel pipe pile and PHC pile) and evaluate the stability and economical efficiency of it by using experimental method and analytical method. Analysis of composite pile design data installed in 79 domestic bridges abutment showed that the stresses, bending moments, and displacements acting on the pile body and connection of the pile were analyzed. Through the redesign process, it was confirmed that the stresses generated in the connecting device occur within the allowable stress values of the connecting device and the PHC pile. In conclusion, the design proposal of composite pile joint location through empirical case study in this study is an improved design method considering both stability and economical efficiency in designing composite pile.

• Journal of the Korean GEO-environmental Society
• /
• v.14 no.1
• /
• pp.5-13
• /
• 2013

Soils around a pile are highly constrained when the vertical load is applied to the pile. However, the conventional direct shear test cannot evaluate the shear strength of the soils under the normal confinement condition. The goal of this study is to evaluate the shear behaviors according to the normal displacement confinement condition including free normal displacement (FND) and constrained normal displacement (CND) during direct shearing. Jumunjin sands were prepared at the different relative densities and loaded at the different normal stresses. The specimens were sheared according to the normal confinement conditions. Experimental results show that shear strengths obtained by the CND tests are higher than those obtained by the FND tests. In addition, for the constrained normal displacement condition, the increment of shear strength increases with the increase of relative density, while the increment of shear strength decreases with the initial normal stress. This study suggests that the effect of confinement condition on the shear strength should be considered when the stability of constrained soils is analyzed.

• Journal of the Korean Geotechnical Society
• /
• v.33 no.7
• /
• pp.17-28
• /
• 2017

This paper presents the investigation of dynamic behavior of a single pile in dry sand based on 1g shaking table tests. The natural frequency of soil-pile system was measured, and then a range of loading frequency was determined based on the natural frequency. Additionally, the studies were performed by controlling loading accelerations, pile head mass and connectivity conditions between pile and cap. Based on the results obtained, relatively larger pile head displacement and bending moment occur when the loading frequency is larger than the natural frequency of soil-pile system. However, the slope of the p-y curve is smaller in the similar loading frequency. Also, it was found that inertia force like input acceleration and pile head mass, and relation of the natural frequency of soil-pile system and input frequency have a great influence on the slope of dynamic p-y curve, while pile head conditions don't.

• Journal of the Korean Geotechnical Society
• /
• v.25 no.4
• /
• pp.77-90
• /
• 2009

In this study, experimental analysis was performed about lateral load capacity and behavior of laterally loaded-bored rigid piles in muti-layered soil conditions. Lateral pile load tests were performed for muti-layerd soils consisting of different relative density. Ultimated lateral load capacities were measured from lateral load-displacement curves and compared with estimated values using theoretical methods. Bending moments and unit lateral capacity distribution of surrounding piles were measured from attached strain gauges and earth pressure sensors on the pile. It was found that ultimated lateral load capacities were different from the muti-layered soil conditions, and measured values were lower than estimated values. The bending moment distributions of the pile were similar all the time. Unit lateral capacity distributions were a little different from muti-layered soil conditions, but basically similar to the distribution proposed by Prasad and Chari (1999).

• Journal of the Korean Geotechnical Society
• /
• v.24 no.4
• /
• pp.23-36
• /
• 2008

This study describes model tests on instrumented rectangular-shaped passive row piles embedded in horizontal sand-ground undergoing lateral soil movement. We tried to find the property of row piles dependent on the shape of pile, including the position of the pile in row, pile spacing, and soil movement. The results of test are as follows. The lateral earth pressure diagram variously appeared to be triangle, trapezoid and rectangular by shape and position of pile. The outer pile has a larger bending moment than the inner pile in the case of B-type, the inner piles has larger one than outer pile in case of H-type. $R_f$ (the ratio of resistance to lateral soil movement) was found to increase with increasing pile spacing irrespective of pile-shape. Y/L (location of action of lateral resistance force) for $d_s$ (displacement of soil) and $S_h$ (spacing of pile) appeared to be nearly regular position, and H-type is higher than B-type.

• Journal of the Korean Geotechnical Society
• /
• v.26 no.12
• /
• pp.31-40
• /
• 2010

This study describes the three-dimensional behavior of pile foundations based on a numerical study. A series of numerical analyses were performed for connectivity conditions between piles and cap under vertical and lateral loadings. It is shown that a fixed connection between pile and cap is able to transfer significant bending moment through the connection and increases the pile lateral stiffness and the bending moment. Based on the results obtained, it was found that the cross sectional shear force in the raft with fixed head condition was larger than that of pinned head condition. Thus, the reinforcement of pile head and thickness of the raft also increases in fixed pile head condition. From the results, it is found that the overall behavior and cross sectional forces of pile foundations is affected significantly by the pile head conditions. Furthermore, the design of pile foundations with pinned head condition was judged to be less costly and very useful for preliminary design stages.

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