Sangseom Jeong

Effect of Lateral Rigidity of Offshore Piles Using Proposed p-y Curves in Marine Clay

The load distribution and deformation of offshore piles are investigated using experimental tests and a numerical analysis. Special attention is given to the soil-pile rigidity of laterally loaded piles. Rigid-and flexible-pile analyses were conducted for comparison. A framework for determining the lateral load transfer curve (p-y curve) is proposed from field and laboratory model tests. A numerical analysis that takes into account the proposed p-y curves was performed for major parameters on pile flexibility such as the pile diameter, the pile length, pile bending stiffness, and the modulus of subgrade reaction. Based on the analysis, it is shown that there are significant differences in bending moment and lateral displacement in flexible piles rather than rigid piles. Through the comparative studies, it is found that the p-y curves influence the behavior of a flexible pile more than of a rigid pile and, thus, the magnitude and distribution of the p-y curves highly influence the pile behavior when it is designed as a flexible pile.

Wedge Failure Analysis of Soil Resistance on Laterally Loaded Piles in Clay

A fundamental study of pile-soil systems subjected to lateral loads in clay soil was conducted by using experimental tests and a lateral load-transfer approach. The emphasis was on an improved wedge failure model developed by considering three-dimensional combination forces and a new hyperbolic p-y criterion. A framework for determining the p-y curve on the basis of both theoretical analysis and experimental load test results is proposed. The proposed p-y method is shown to be capable of predicting the behavior of a large-diameter pile under lateral loading. The proposed p-y curves with an improved wedge model are more appropriate and realistic for representing a pile-soil interaction for laterally loaded piles in clay than the existing p-y method.

Estimation of in situ dynamic modulus by using MEPDG dynamic modulus and FWD data at different temperatures

A fundamental study of a dynamic modulus for asphalt pavements was conducted using experimental tests and numerical simulations. The emphasis was on the loading frequency–vehicle speed relationships directly caused by the test results of vertical compressive stress pulse durations along the depth. A framework for determining the dynamic modulus is proposed based on the dynamic effects. It is shown that the proposed dynamic modulus is capable of predicting the asphalt pavement behaviour with varying vehicle speeds. The converting factor that can estimate the in situ dynamic modulus from the undamaged dynamic modulus is also proposed using a falling weight deflectometer modulus. Through comparisons with case histories, the maximum relative error of longitudinal strain is 50.4% with an undamaged dynamic modulus and 10.5% with an in situ dynamic modulus. The proposed methods with a converting factor are in agreement with the general trend observed by in situ measurements along the vehicle speeds.

Analysis of downdrag on pile groups by the finite element method

Abstract The downdrag on friction and endbearing pile groups was investigated, based on a numerical analysis. The emphasis was on quantifying the reduction of downdrag on pile groups, with a flexible pile cap, due to group effect. The case of a single pile and, subsequently, the response of groups were analyzed by developing interaction factors obtained from a three-dimensional nonlinear finite element study. Based on a limited parametric study, it is shown that the downdrag on piles in a group is much less than the downdrag on a single pile and is highly influenced by the group spacing, total number of piles, and the relative position of the piles in a group. In light of all these influencing parameters, a simple method is recommended for square groups of 9–25 piles with spacing-to-diameter ratios of 2.5 and 5.0 for downdrag loads.

Thermo-mechanical properties and microfabric of fly ash-stabilized gold tailings

This paper studies the changes in thermal conductivity, temperature, and unconfined compressive strength of gold tailings and fly ash mixtures during the curing period of 5 days. The microfabric of the cured mixtures was investigated with mercury intrusion porosimetry (MIP). The mixture samples were prepared at their maximum dry unit weight and optimum moisture content. Effect of adding fly ash to gold tailings (i.e., 0, 20, and 40% of the dry weight of tailings) was examined, and a comparison was made on samples prepared at the same fly ash content by replacing gold tailings with humic acid (i.e., gold tailings and humic acid ratios of 100:0, 90:10, and 80:20 by weight) or by varying pore fluid chemistry (i.e., water and salt solutions of 1M NaCl and CaCl2). The results show that the initial thermal conductivity of the samples is sensitive to the mixture proportion and a declination in the thermal conductivity is observed due to hydration of fly ash and evaporation. Inclusion of fly ash and salts into gold tailings improves the unconfined compressive strength but the presence of humic acid in samples leads to the decrease of the strength. MIP results reveal the pore structure changes associated with the packing states of the samples that reflect the influential factors considered.

Failure Case Study of Tieback Wall in Urban Area, Korea

In this study, numerical analysis was performed to reproduce the sequential behavior of an anchored retaining structure in an urban area. The numerical analysis was verified through comparisons between the prediction and a field failure case. Emphasis was placed on the wall behavior and the location of the sliding surface based on elasto-plastic method and shear strength reduction FEM method. Through the comparison study, it was found that coupled analysis using shear strength reduction method can be effectively used to perform back calculation analysis to find a critical surface in the anchored wall structures, whereas uncoupled analysis by elasto-plastic method can be applicable to the preliminary design of a retaining wall with a suitable safety factor.

Response of Single Piles in Marine Deposits to Negative Skin Friction from Long-term Field Monitoring

The behavior of single piles subjected to negative skin friction in soft soil was conducted by analyzing the results from full-scale long-term field measurements and three-dimensional (3D) numerical analyses. A skin friction coefficient (α and β coefficients) of the instrumented piles is back-calculated at different degrees of consolidation (U) of soft marine clay. Back-calculated β-values ranged from 0.15 to 0.35 for clay, and from 0.30 to 0.55 for sand, respectively. In addition, back-calculated α-values ranged from 0.1 to 0.3 for coated pile, and from 0.2 to 0.8 for uncoated pile when undrained shear strength of the soft clay was about 30–60 kPa, respectively. Moreover, this study describes behavior of a pile based on full-coupled 3D finite element (FE) analysis. The appropriate parametric studies needed for verifying the pile-soil interaction with consolidation are presented in this paper. Compared to the results from the measurements, it is shown that the computed results are capable of predicting the pile-soil behavior under consolidation. The major parameters that influence the pile behavior are discussed for different soil-pile conditions.

Analysis of Steel Reinforcement Ratio for Bent Pile Structures Considering Column-Pile Interaction

In this study, an interactive analysis considering column-pile interaction is performed on the basis of an equivalent base spring model for supplementing virtual fixed point design of bent pile structures. Through this analytical method, the application of the minimum steel reinforcement ratio of the pile (0.4%) is analyzed by taking into account the major influencing parameters. Furthermore, the limit depth for steel reinforcement ratio is proposed through the relationships between column and pile conditions. To obtain the detailed information, it is found that an interactive analysis is intermediate in theoretical accuracy between the virtual fixed point model analysis and full-modeling analysis. Base on this study, it is also found that the maximum bending moment is located within cracking moment of the pile when material nonlinearity is considered. Therefore, the minimum steel reinforcement ratio is appropriately applicable for the optimal design of bent pile structures. Finally, the limit depth for steel reinforcement ratio (LAs=x%) is proposed by considering the field measured results. It is shown that the normalized limit depth ratio for steel reinforcement ratio (LAs=x%/LP) decreases linearly as the length-diameter ratio of pile (LP/DP) increases, and then converges at a constant value.

The Effect of Stabilizing Piles on a Self-Supported Earth-Retaining Wall

The behavior of a self-supported earth-retaining wall with stabilizing piles was investigated using a numerical study and field tests in urban excavations. Special attention is given to the reduction of lateral earth pressures acting on a retaining wall with stabilizing piles. Field tests at two sites were performed to verify the performance of the instrumented retaining wall with stabilizing piles. A number of 3D numerical analyses were carried out on the self-supported earth-retaining wall with stabilizing piles to assess the results stemming from wide variations of influencing parameters such as the soil condition, the pile spacing, the distance between the front pile and the rear pile, and the embedded depth. Based on the results of the parametric study, the maximum horizontal displacement and the maximum bending moment are significantly decreased when the retaining wall with stabilizing piles is used. In engineering practice, reducing the pile spacing and increasing the distance between the front pile and the rear pile can effectively improve the stability of the self-supported earth-retaining wall with stabilizing piles.

Theoretical and Experimental Analysis of Rock-Socked Drilled Shafts

The load distribution and deformation of rock-socketed drilled shafts subjected to axial loads were evaluated by a load-transfer approach The emphasis was on quantifying the shear load transfer characteristics of rock-socketed drilled shafts based on constant normal stiffness (CNS) direct shear tests performed by varying major influencing factors. Based on the CNS tests and the Hoek-Brown failure criterion, a nonlinear triple curve was proposed for a shear load transfer function of rock-socketed drilled shafts. An analytical method that takes into account the soil coupling effect was developed. Through comparisons with results of load tests, it was found that the proposed function and analytical method in the present study are in good agreement with the general trend observed by in situ measurements.