Kyung Jun Kim

Reliability-based calibration of resistance factors for static bearing capacity of driven steel pipe piles

As part of a study to develop load and resistance factor design (LRFD) codes for foundation structures in South Korea, resistance factors for the static bearing capacity of driven steel pipe piles were calibrated in the framework of the reliability theory. A database of 52 static load test results was compiled, and the data from these load test piles were sorted into two cases: a standard penetration test (SPT) N-value at pile tip (i) less than 50 and (ii) equal to or more than 50. Reliability analyses and resistance factor calibration for the two static bearing capacity analysis methods adopted in the Korean Design standards for foundation structures were performed using the first-order reliability method (FORM) and the Monte Carlo simulation (MCS). Reliability indices and resistance factors computed by the MCS are statistically identical to those computed by FORM. Target reliability indices were selected as 2.0 and 2.33 for the group pile case and 2.5 for the single pile case. The resistance factors rec...

North Carolina Department of Transportation’s Practice and Experience with Design–Build Contracts: Geotechnical Perspective

The North Carolina Department of Transportation (NCDOT) began using design–build contracting for highway construction projects in 2001 and now is authorized to award up to 25 design–build contracts annually. Because subsurface investigation is an expensive and time-consuming task usually requiring environmental permits from various federal and state agencies, NCDOT performs the subsurface investigations and provides the information to the design–build teams. The cost of subsurface investigations for nine design–build projects was compared with the historical data for subsurface investigations on conventional contract projects. Case studies of bridge foundation design and construction for two of the nine projects are presented along with comparison with conventional contract projects.

Reliability Based Calibration of Resistance Factors for Axial Capacity of Driven Piles

Resistance factors were calibrated using the framework of reliability theory for the Load and Resistance Factor Design (LRFD) of driven pile’s axial capacity in North Carolina utilizing pile load test data available from the North Carolina Department of Transportation (NCDOT). A total of 140 Pile Driving Analyzer (PDA) data and 35 static load test data were compiled and grouped into different design categories based on four pile types and two geologic regions. Resistance statistics were evaluated for each design category in terms of bias factors. Reliability analysis of the current NCDOT practice of pile foundation design was performed to evaluate the level o f safety and to select the target reliability indices. Resistance factor calibration was performed for the three methods of static pile capacity analysis commonly used in the NCDOT: the Vesic (1977), the Nordlund (1963), and the Meyerhof (1976) methods. Two types of First Order Reliability Methods (Mean Value First Order Second Moment method and Advanced First Order Second Moment method) were used for the reliability analysis and the calibration of the resistance factors. The calibrated resistance factor s varied significantly for the different pile types and geologic regions. The advanced first order second moment method resulted in larger resistance factors than the mean value first order second moment method. Recommended resistance factors are presented for the three methods of static pile capacity analysis and for seven different design categories of pile types and geologic regions.

A Case Study of LRFD Implementation for Static Bearing Capacity of Driven Steel Pipe Piles in Korea

Resistance factors for static bearing capacity of driven steel pipe piles were calibrated in the framework of reliability theory. In order for the verification of resistance factors and the implementation of the LRFD, a case study on an actual bridge foundation designs using both the ASD and the LRFD methods is comprehensively accomplished. Detailed analysis showed that both of the design concepts gave the design bearing capacities equal to or more than the design loads. The LRFD method, however, could provide the quantitative provability of failure of the pile foundation, whereas the ASD method showed nominal level of safety. ABSTRACT: Resistance factors for static bearing capacity of driven steel pipe piles were calibrated in the framework of reliability theory. In order for the verification of resistance factors and the implementation of the LRFD, a case study on an actual bridge foundation designs using both the ASD and the LRFD methods is comprehensively accomplished. Detailed analysis showed that both of the design concepts gave the design bearing capacities equal to or more than the design loads. The LRFD method, however, could provide the quantitative provability of failure of the pile foundation, whereas the ASD method showed nominal level of safety.

Measured Soil Setup of Steel HP Piles from Windsor Bypass Project in North Carolina

Restrikes were performed on piles driven for a North Carolina Department of Transportation highway construction project to verify the required bearing capacity, which was not achieved at the end of initial drive (EOID). Driving records of 98 piles with both initial driving and restrike blow counts and hammer stroke were collected. Six of these piles were driven with a pile-driving analyzer, and Case Pile Wave Analysis Program analysis was performed on the collected pile-driving analyzer data. All piles were steel H-pile piles, and the restrikes were done within 144 h after the EOID. The pile bearing capacities of both EOID and restrike were estimated from the blow counts and hammer stroke using the GRL Engineers Inc. Wave Equation Analysis Program, Version 2005. Soil setup ratios of these piles were computed and statistically analyzed to find a reliable setup ratio that can be applied to the bearing capacity obtained at the EOID of the remaining piles in this project to ensure the required bearing without a restrike. The mean soil setup ratio of all piles in this project was estimated at 1.41. However, no setup ratio can be applied to the EOID bearing capacity of an individual pile with a 98% confidence level. Restrike of every pile is required to ensure this level of confidence. A setup ratio of 1.10 can be applied with a 90% confidence level. The setup ratios vary greatly from pile to pile. Soil setup occurs rapidly after EOID in this project. Soil setup is more significant in loose or soft soils than in dense or stiff soils.

EVALUATION OF RESISTANCE BIAS FACTORS FOR LOAD AND RESISTANCE FACTOR DESIGN OF DRIVEN STEEL PIPE PILES

Resistance bias factors for the two static bearing capacity analysis methods of driven steel pipe piles adopted in the Korean Design Standards for Structure Foundations were evaluated as part of study to develop LRFD codes for foundation structures in South Korea. Of the 2,227 static load test data on driven steel pipe piles collected from all around the country, only 43 were found to be useful for this study. These load test piles were sorted into two cases: pile tip in soil case and pile tip in rock case. Pile bearing capacities were measured from the load-displacement curves by six different failure criteria, and Davissons criterion was found to be most reliable. Statistical analysis of the resistance bias factors was performed, and the results show a significantly high degree of variation in the resistance bias factors.

Performance assessment of geosynthetics and cement as subgrade stabilization measures

Work in this paper presents the results of field testing on four instrumented roadway sections constructed on poor subgrade soils and stabilized with select fill, geosynthetics, or cement. Loading was applied using 1000 consecutive truck passes and profile surveying was performed to provide permanent deformation (rutting) data. Peak vertical stresses at the subgrade as well as moisture conditions were also monitored during testing. Results indicated that the deep undercut (31 in./790 mm) with select material backfill section produced the largest cumulative rut depths due to shallow incremental plastic strains induced during each axle pass. The use of a thin Aggregate Base Course (ABC) surface layer (3 in./75 mm) over the select material reduced the rate of rutting. The biaxial geogrid and the high strength geotextile showed a relatively equal performance in all aspects of the study. The cement stabilized section produced a slightly larger average rut depth than the geosynthetically-reinforced sections due to localized areas of pronounced cumulative rutting. However, there were several areas of the soil-cement test section that performed as well as the geosynthetically-reinforced sections.

RELIABILITY ANALYSIS OF STATIC BEARING CAPACITY EVALUATION OF DRIVEN STEEL PIPE PILES USING MCS

As part of Load and Resistance Factor Design implementation effort in South Korea, reliability of the two static bearing capacity analysis methods for driven steel pipe piles adopted in the Korean Standards for Structure Foundations was evaluated. Over 2,000 static load test data on driven steel pipe piles were collected from all around the country. After review of the load-displacement curves, subsurface investigation reports, and other related documents, only 43 load test data were found to be useful for the reliability analysis. These load test piles were sorted into two cases: pile tip on soil case and pile tip on rock case. Resistance bias factor statistics of each pile tip case were evaluated for the two static design methods. Reliability analysis was performed by two types of First Order Reliability Methods, Mean Value First Order Second (MVFOSM) method and Advanced First Order Second (AFOSM) method, and Monte Carlo Simulation (MCS) method. Reliability of the static bearing capacity analysis methods for pile tip on soil case appears to be unacceptably low for safety factors in the range of 3 to 5. Reliability of the static bearing capacity analysis methods for pile tip on rock case is not conclusive. AFOSM method resulted in a little larger reliability indices than MVFOSM method, but the difference was not significant. Reliability indices computed by the MCS method were almost identical to those by the AFOSM method.

Limit Equilibrium and Deformation Analyses of a Geogrid-Reinforced Embankment

Limit equilibrium analyses and 2-dimensional numerical simulations are performed to estimate the performance of a geosynthetic-reinforced embankment supporting a bridge abutment. Geogrid reinforcement was evaluated as a means of improving the stability of the embankment slope and reducing deformation under design loads. Results indicated a reduction in total and differential deformation due to the inclusion of reinforcement. The deformation of the embankment slope was correlated to the global factor of safety. Vertical and lateral movements for the reinforced case were computed to be 65% and 78%, respectively, of those of the unreinforced embankment case. The load carrying capacity of the reinforced embankment was estimated to be 5 times larger than the unreinforced case while providing the same limit equilibrium factor of safety.