• The KSFM Journal of Fluid Machinery
• /
• v.19 no.3
• /
• pp.43-47
• /
• 2016

Pile foundations constructed on extremely cold regions cause serviceability problems of superstructures from repeated actions of ground freezing and thawing. Oil sand module plants are mainly constructed on seasonal frozen ground. Due to the freezing and thawing actions of grounds, vertical movements of piles have been observed. To solve these erratic pile movement problems, thin vertical layer of PET aggregates is installed around the pile shaft to prevent potential unfavorable pile movements. There is no known method to calculate "thin PET aggregate layer" -surrounded pile shaft resistance (capacity) against vertical loads; therefore, this experimental research is conducted. Specifically, in this study, horizontal (normal) pressures on pile shaft were assessed varying PET aggregate layer thickness based on the experiment.

• Geomechanics and Engineering
• /
• v.20 no.2
• /
• pp.155-164
• /
• 2020

In recent years, the stability, safety and comfort of trains has received increased attention. The mechanical characteristics and differential settlement of the foundation are the main problems studied in high-speed railway research. The mechanical characteristics and differential settlement of the foundation are greatly affected by the ground treatment. Additionally, the effects of train load and earthquakes have a great impact. The dynamic action of the train will increase the vibration acceleration of the foundation and increase the cumulative deformation, and the earthquake action will affect the stability of the substructure. Earthquakes have an important practical significance for the dynamic analysis of the railway operation stage; therefore, considering the impact of earthquakes on the railway substructure stability has engineering significance. In this paper, finite element model of the CFG (Cement Fly-ash Gravel) pile + cement-soil compacted pile about composite foundation is established, and manual numerical incentive method is selected as the simulation principle. The mechanical characteristics and differential settlement of CFG pile + cement-soil compacted pile about composite foundation under train load are studied. The results show: under the train load, the neutral point of the side friction about CFG pile is located at nearly 7/8 of the pile length; the vertical dynamic stress-time history curves of the cement-soil compacted pile, CFG pile and soil between piles are all regular serrated shape, the vertical dynamic stress of CFG pile changes greatly, but the vertical dynamic stress of cement-soil compacted pile and soil between piles does not change much; the vertical displacement of CFG pile, cement-soil compacted pile and soil between piles change very little.

• Geomechanics and Engineering
• /
• v.15 no.2
• /
• pp.793-803
• /
• 2018

Based on the theory of porous media, an interaction system of a floating pile and a saturated soil in cylindrical coordinates subjected to vertical harmonic load is presented in this paper. The surrounding soil is separated into two distinct layers. The upper soil layer above the level of pile base is described as a saturated viscoelastic medium and the lower soil layer is idealized as equivalent spring-dashpot elements with complex stiffness. Considering the cylindrically symmetry and the pile-soil compatibility condition of the interaction system, a frequency-domain analytical solution for dynamic impedance of the floating pile embedded in saturated viscoelastic soil is also derived, and reduced to verify it with existing solutions. An extensive parametric analysis has been conducted to reveal the effects of the impedance of the lower soil base, the interaction coefficient and the damping coefficient of the saturated viscoelastic soil layer on the vertical vibration of the pile-soil interaction system. It is shown that the vertical dynamic impedance of the floating pile significantly depends on the real stiffness of the impedance of the lower soil base, but is less sensitive to its dynamic damping variation; the behavior of the pile in poro-visco-elastic soils is totally different with that in single-phase elastic soils due to the existence of pore liquid; the effect of the interaction coefficient of solid and liquid on the pile-soil system is limited.

• Geomechanics and Engineering
• /
• v.35 no.2
• /
• pp.165-179
• /
• 2023

This study investigates the uplift capacity of a single vertical belled pile buried at shallow depth in dry sand. The laboratory model experiments are conducted with different pile-tip angles and relative densities. In addition, image and FEM analyses are performed to observe the failure surface of the belled pile for different pile-tip angles and relative densities. Accordingly, the uplift capacity and failure angle in the failure surface of the belled pile were found to depend on the belled pile-tip angle and relative density. A predictive model for the uplift capacity of the belled pile was proposed considering the relative density and belled pile-tip angle based on a previous limit equilibrium equation. To validate the applicability of the proposed model, the values calculated using the proposed and previous models were compared to those obtained through a laboratory model experiment. The proposed model had the best agreement with the laboratory model experiment.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.29 no.1C
• /
• pp.33-39
• /
• 2009

Vertical soil stress near a pile subjected to negative skin friction (NSF) may be reduced due to shear transfer at the pile-soil interface. A three-dimensional finite difference analysis has been performed to clarify the influence of vertical and horizontal stress reductions on the pile behavour. In addition, a simple equation has been proposed to estimate vertical stress reduction of the soil near the pile. The vertical and horizontal stresses are reduced by substantial amount compared to corresponding stress components at the Greenfield condition. The horizontal extent of vertical stress reduction of the soil near the pile is rather limited to about up to 4-8 D, where D is the pile diameter. The findings from the current research indicate that widely used $\beta$-method may result in over-estimation of dragload (compressive force on piles due to NSF) and hence stress reduction needs to be incorporated in the original equation.

• Proceedings of the Korean Geotechical Society Conference
• /
• 1999.03a
• /
• pp.185-192
• /
• 1999

It had found that, as a result of cross-hole tonic logging test, concrete was not filled partially within the bottom 2.0 m of the large diameter (Ø= 2,500mm) rock socketed pile, MP20-P11(socket diameter (Ø= 2,200mm), which was a pile among piles group supporting a pier of Kwangan Grand Bridge. The pile was repaired by the combined cement grout injected through the pipes for the cross-hole sonic logging test and the bore holes for core samples. A month after the cement grouting, repairing was checked by coring and cross-hole sonic logging then 3 times of grouting and 2 times of coring were, in turns, peformed, then repairing was completed successfully. The vertical compressive capacity of the repaired large diameter socketed pile was evaluated by several formulas and software ROCKET, and was more conservative than design load (1,882 ton) of MP20-P11. It is expected that, in the case of the battered socketed piles, it could be more reasonable to analyze the behaviors of a battered pile using 3-D model. A 3-D analysis will be peformed in the future study.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.44 no.1
• /
• pp.142-154
• /
• 2002

This study was performed to investigate constraint effects of deformation (heaving, lateral displacement) of clayey foundation reinforced with sheet pile at the tip of banking on soft ground, under intact state (natural) and the state of vertical drain respectively. The following results are obtained. 1. In view of reduction in heaving or lateral displacement, sheet pile is not supposed to be of use. 2. Sheet pile is effective only when vertical drain is installed for acceleration of consolidation and gradual loading is applied.

• Journal of the Korean GEO-environmental Society
• /
• v.19 no.7
• /
• pp.5-11
• /
• 2018

Instead of a single pile, group piles are usually used for the pile foundation. If the earthquake occurs in the ground where group piles are installed, dynamic behavior of group piles are affected not only by interaction of piles and the ground movement but also by the pile cap. However, in Korea, the pile cap influence is not taken account into the design of group piles. Research on dynamic behavior of group piles has been performed only to verify interaction of piles and the ground and has not considered the pile cap as a factor. In this research, 1g shaking table model tests were performed to verify the thickness of the pile cap affects dynamic behavior of group piles that were installed in the ground where the earthquake would occur. The test results show that, as thickness of the pile cap increased, acceleration and horizontal displacement of the pile cap decreasd while vertical displacement of the pile cap increased. The results also showed that, among the group files tested, acceleration, horizontal displacement, and vertical displacement of the bearing pile are smaller than those of the friction pile.

• Korean Journal of Construction Engineering and Management
• /
• v.7 no.4 s.32
• /
• pp.78-90
• /
• 2006

There is no specific code and/or standard described in the specifications to check verticality for Pre-tensioned Spun High Strength Concrete pile installation process. The most commonly used method for the vertical PHC pile installation is a naked-eye measurement or water level measurement conducted by assistant crew in the construction sites. The main objective of the research is to develop the automated vertical controllable prototype equipment for PHC piles in order to achieve uniform construction qualify as well as improving safety and productivity. The paper explains the literature review on PHC pile and pile installation process, development of prototype, field test of the prototype and its performance evaluation in terms of quality and safety as well as productivity. The results of the research will lead the further researches on the automated pile installation system.

• Journal of the Korean Geotechnical Society
• /
• v.17 no.6
• /
• pp.193-205
• /
• 2001

In this study the behavior of pile groups is investigated experimentally. Special attention is given to the load transfer characteristics of pile groups and to the evaluation of the group effects under vertical and horizontal loadings. In the laboratory experiments, vertical and lateral loadings were imposed on model piles in sand. Model piles made of PVC embedded in Joomoonjin sand were used in this study. Pile arrangements($2\times2,\; 3\times3$) and pile spacings(2.5D, 5.OD, 7.5D) were considered. Load-transfer curves(t-z, q-z and p-y curves), load-deflection curves and group interaction factors were obtained from the experimental results. The group interaction factors under both vertical and horizontal loadings were proposed for the cases of $2\times2\; and\; 3\times3$ pile groups with varying ratios of pile spacings. p-multipliers in this study were found for the individual piles in $2\times2\; and\; 3\times3$ pile groups.