Junhwan Lee

Estimation of Lateral Load Capacity of Rigid Short Piles in Sands Using CPT Results

Conventional methods for the estimation of the ultimate lateral pile load capacity are typically based on certain expressions of the lateral soil resistance pu and assumed distributions of the lateral soil pressure mobilized along the pile embedded depth. When soils are nonhomogenous, however, the application of conventional methods represents significant difficulties due to the nonlinear and irregular variation of pu with depth. In this study, a cone penetration test (CPT)-based methodology for the estimation of the ultimate lateral pile load capacity Hu was proposed, which can take full account of entire soil profile through the CPT cone resistance qc . A normalized correlation between qc and pu was proposed with correlation parameters corresponding to different existing methods. In order to validate the proposed CPT-based methodology, case examples of laterally loaded piles in various soil conditions were prepared and used to compare values of Hu from original and proposed methods. Calibration chamber ...

Penetrometer-Based Assessment of Spudcan Penetration Resistance

Estimation of spudcan penetration resistance is an important design step to guarantee the stability and functionality of offshore mobile jack-up units. Dependence on in situ penetrometer test data to evaluate the stratigraphy and resulting spudcan capacity profile has been increased. However, this becomes difficult in intermediate soil types in which the degree of consolidation during penetration falls between the extremes of fully drained or fully undrained. In this study, a penetrometer-based methodology utilizing results from cone and T-bar penetration tests is developed. Three main steps are involved, comprising estimation of the relative penetration resistance of spudcan and cone or T-bar penetrometer under fully drained and fully undrained conditions, and then quantifying the effect of the different normalized penetration rates for spudcan and penetrometer. Values of the various correlation parameters for the proposed model are evaluated. The validity and accuracy of the proposed methodology are evaluated through case studies from centrifuge tests in clay and a field example of spudcan installation in interbedded carbonate silts and sands. The comparisons confirm the potential of the proposed methodology for interpretation of penetrometer tests and application to the prediction of foundation performance.

Comparative Analysis of Various Interaction Effects for Piled Rafts in Sands Using Centrifuge Tests

AbstractIn the current study, the load responses and interaction effects of piled rafts embedded in sands were investigated. A series of centrifuge load tests were conducted using different types of model foundations. Single piles, group piles, piled rafts, and unpiled rafts were adopted in the tests to analyze various interaction effects of piled rafts. The load-settlement curves of piled rafts were similar to those of group piles for the initial settlement range and became similar to those of rafts as settlement increased. The pile-group, pile-to-raft, and raft-to-pile interaction factors showed state-dependent and nonlinear variations with settlement. Both pile-to-raft and raft-to-pile interaction factors decreased within the initial settlement range and increased with increasing settlement. The range of pile-to-raft interaction factor values was much larger than the range of values for the raft-to-pile interaction factor. The load response and load transfer relationship of piles for piled rafts were d...

Normalized Resilient Modulus Model for Subbase and Subgrade Based on Stress-Dependent Modulus Degradation

The flexible pavement system consists of layered structures. Each layer is composed of different materials and represents different response to loading. Successful pavement design, therefore, requires proper evaluation of mechanical properties for the sublayers, which can realistically describe the behavior of pavement substructures. The resilient modulus is an important mechanical property widely used for the analysis and design of flexible pavements. In this study, a normalized resilient modulus model applicable to both subbase and subgrade materials is proposed. A series of laboratory test results for subbase and subgrade materials are collected and analyzed to investigate effects of the confining and deviatoric stresses on the resilient modulus. Based on test results, a normalized degradation relationship of the resilient modulus as a function of normalized stresses is developed. Values of model parameters for the proposed model are also evaluated and presented. To check validity of the model, a finite element analysis is performed and compared with measured responses of pavement structures.

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.

Experimental Investigation on the Coefficient of Lateral Earth Pressure at Rest of Silty Sands: Effect of Fines

The coefficient of lateral earth pressure at rest (K0) is an important state variable of soils and is often estimated using Jakys K0 equation, which is based on the internal friction angle (φ′). When fines are contained in sand, the effect of the fines content needs to be properly taken into account for the φ′-based estimation of K0, as the strength characteristics change because of changes in particle interlocking and contact conditions. In this study, an experimental testing program was established to measure and analyze K0 and its correlation to shear strength characteristics of sand–silt mixtures focusing on the effect of silt content. Thin-wall oedometer tests, triaxial tests, and other property tests were conducted to obtain K0 values and characterize the test materials. The values of K0 became higher as the relative density and silt content decreased, which was found because of decreasing particle interlocking and friction angle. Jakys K0 equation using the peak strength tended to underestimate K0 at lower relative densities, whereas the K0 matched closely to measured values for higher relative densities. The K0 correlation based on the mobilized inter-particle strength was proposed and was applicable to various sand conditions. The calculated results using the proposed K0 correlation matched the measured results well, confirming the effectiveness of the proposed method.

Pile design based on cone penetration test results

The bearing capacity of piles consists of both base resistance and side resistance. The side resistance of piles is in most bases fully mobilized well before the maximum base resistance is reached. As the side resistance is mobilized early in the loading process, the determination of pile base resistance is a key element of pile design. Static cone penetration is well related to the pile loading process, since it is performed quasi-statically and resembles a scaled-down pile load test. In order to take advantage of the cone penetration test for pile design, load-settlement curves of axially loaded piles bearing in sand were developed in terms of normalized base resistance versus relative settlement. Although the limit state design concept for pile design has been used mostly with respect to either 5% or 10% relative settlement, the normalized load-settlement curves obtained in this study allow determination of pile base resistance at any relative settlement level within the 0-20% range. The normalized base resistance for both non-displacement and displacement piles were addressed. In order to obtain the pile base load-settlement relationship, a 3-D nonlinear elastic-plastic constitutive model was used in finite element analyses. The 3-D nonlinear elastic-plastic constitutive model takes advantage of the intrinsic and state soil variables that can be uniquely determined for a given soil type and condition. A series of calibration chamber tests were modeled and analyzed using the finite element approach with the 3-D nonlinear elastic-plastic stress-strain model. The predicted load-settlement curves showed good agreement with measured load-settlement curves. Calibration chamber size effects were also investigated for different relative densities and boundary conditions using the finite element analysis. The value of the normalized base resistance was not a constant, varying as a function of the relative density, the confining stress, and the coefficient of lateral earth pressure at rest. The effect of relative density on the normalized base resistance was most significant, while that of the confining stress at the pile base level was small. At higher relative densities, the normalized base resistance was smaller (0.12-0.13 for 90% relative density) than at lower relative densities (0.19-0.2 for 30% relative density). The values of the normalized base resistance for displacement piles are higher than those for non-displacement piles, being typically in the 0.15-0.25 range for 5% relative settlement and in the 0.22-0.35 range for 10% relative settlement. The values of the normalized base resistance for silty sands are in the 0.12-0.17 range, depending on the relative density and the confining stress at the pile base level. The confining stress is another important factor that influences the value of the normalized base resistance for silty sands. For lower relative density, the value of the normalized base resistance decreases as the pile length increases while that for higher relative density increases.

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.