Kyuho Paik

Effect of Pile Installation Method on Pipe Pile Behavior in Sands

Open-ended pipe piles are often used for the foundations of both land and offshore structures because of their relatively low driving resistance. In this study, calibration chamber tests were conducted on model pipe piles installed in sands with different soil conditions in order to investigate the effects of the pile installation method on penetration parameters and bearing capacity. Results of the test program showed that both the hammer blow count necessary to install the piles and the incremental filling ratio (IFR), which is used to indicate the degree of soil plugging in open-ended piles, decreased (1) with increasing hammer weight for the same driving energy, and (2) with increasing hammer weight at the same fall height. The base and shaft load capacities of the piles were observed to increase (1) with increasing hammer weight for the same driving energy, and (2) with increasing hammer weight for the same fall height. It was also observed that the noise level observed during pile driving decreases (1) as the driving energy decreases and (2) as the hammer weight increases for the same driving energy. Model jacked piles were also installed and tested. The jacked piles were found to have higher bearing capacities than identical driven piles under similar conditions, mostly due to the more effective development of soil plugging in jacking than in driving.

Axial Response and Bearing Capacity of Tapered Piles in Sandy Soil

14 calibration chamber tests were performed to investigate the axial responses of tapered piles in sandy soil. Three instrumented model piles with different taper angles, designed to have the same volume, were used in the tests. Results of the model pile load tests showed that the shaft load of tapered piles continuously increased with pile settlement, whereas that of cylindrical piles reached the ultimate values at a settlement equal to about 2 % of the pile diameter. The ratio of the load capacity of tapered piles to that of cylindrical piles was found to vary with both the taper angle of the piles and the soil condition of the sands. The ultimate unit shaft resistance of tapered piles was always greater than that of cylindrical piles irrespective of soil condition, whereas the ultimate unit base resistance of tapered piles was greater than that of cylindrical piles for dense sand with lateral earth pressure coefficients higher than 0.42. It was also observed that the ultimate unit shaft resistance of piles increases with increasing taper angle regardless of the relative density and stress state of the sand. However, the ultimate unit base resistance of piles increases with increasing taper angle for medium sand, but decreases for dense sand. In addition, based on the results of the model pile tests, taper factors for the ultimate unit base and shaft resistances, which can be used to estimate the base and shaft load capacities of tapered piles, were proposed.

Estimation of Axial Load Capacity for Bored Tapered Piles Using CPT Results in Sand

Tapered piles in comparison to cylindrical piles can be beneficial in terms of the load capacity. In this paper, estimation of the load capacity for tapered piles using cone penetration test (CPT) resistance was investigated. Fourteen calibration chamber load tests using different pile types and six CPTs were conducted under various soil conditions. From the calibration chamber test results, the total, base, and shaft load capacities were analyzed in terms of soil conditions and taper angle. To evaluate CPT-based load capacity of tapered piles, normalized base and shaft resistances were obtained from normalized unit load-settlement curves. Based on the normalized base and shaft resistances, design equations that can be used to evaluate the base and shaft resistances of tapered piles were proposed. The proposed method is valid for sands of medium to dense conditions, while it may result in unconservative predictions for loose sands. To check the accuracy of the proposed method, field load tests using both cylindrical and tapered piles were conducted and compared with the predictions using the proposed method. A simplified approach using an equivalent cylindrical pile was also investigated and compared.

LOAD TESTS ON PIPE PILES FOR DEVELOPMENT OF CPT-BASED DESIGN METHOD

This research focused on the drivability and load-carrying capacity of both open and closed-ended steel pipe piles. Two pipe piles (one open-ended, the other closed-ended) were installed in a sandy soil to the same depth. The site was extensively characterized. Standard penetration tests (SPTs) and cone penetration tests (CPTs) were performed both before and after pile installation. A variety of soil indices and shear strength parameters (such as the constant-volume friction angle) were measured in the laboratory. The piles were fully instrumented, permitting separate measurement of shaft and base capacity for the closed-ended pile and shaft, annulus and soil plug capacities for the open-ended pile. The results are presented in a variety of ways. In particular, values of pile resistance are presented normalized with respect to CPT cone resistance values both along the shaft and base of the piles for quick reference. The test results for the open-ended piles are quite unique. Two design methods are proposed for open-ended piles based on the field load test as well as on results found in the literature. In one method, pile resistances are referred to either the soil plug length or incremental filling ratio. In the other method, pile resistances are correlated to the CPT cone resistance. Comparisons of the proposed methods with the load test results and with methods currently in use are quite favorable. The present research suggests current pile design methods may be excessively conservative. It seems that cost savings from similar research, where complete measurement of all variables of interest both for the piles and for the soil deposit where the piles are installed are done, can be very substantial if the methods proposed here are validated further. It appears that such savings would be in the interest of state departments of transportation and the Federal Highway Administration.

Estimation of Ultimate Lateral Load Capacity of Piles in Sands Using Calibration Chamber Tests

Current practice for the estimation of the ultimate lateral load capacity of piles is typically based on the vertical effective stress σ′v, while the effect of the lateral effective stress σ′h is not specifically considered. In the present study, calibration chamber lateral pile load tests are conducted to investigate the load response and ultimate lateral load capacity Hu of laterally loaded piles under various soil and stress conditions. In order to determine Hu from load-deflection curves, different criteria are explored and analyzed. From the test results, it is shown that Hu increases significantly with increasing σ′h for a given σ′v. It is also found that lateral deflection of pile at ultimate state tends to increase as the relative density and lateral stress increase. On the basis of the test results, the lateral stress correction factor reflecting the effect of the lateral effective stress σ′h on Hu is proposed. From the test results, it is seen that the proposed procedure using the lateral stress correction factor produces more realistic estimation of Hu. Case examples are selected from the literature and used to compare results measured and predicted using the proposed approach.

Analysis of active earth pressure against rigid caissons backfilled with crushed rock and sand

Arching effects in backfill materials generate a nonlinear active earth-pressure distribution behind a rough, rigid retaining wall. There are several analyses for estimating the nonlinear active earth pressures on a retaining wall exerted by a homogeneous backfill in the presence of arching. However, it is not possible to use these analyses for a caisson backfilled with crushed rock and sand, which is common in marine structures. In this study, a new formulation is proposed for calculating the nonlinear active earth pressure acting on a caisson backfilled with crushed rock and sand. The new formulation allows important insights, including the dependence of the slope angle of the crushed rock – sand interface that minimizes the active force and overturning moment on the caisson on the shear strengths of the crushed rock and sand and the geometry of the problem.