Individual Piles Research Articles

Evaluation of Harbor Tranquility with Bouyancy-Driven Vertical Piling Breakwater

Recently, the Bouyancy-driven vertical piling breakwater, which is proposed as a barrier for tsunami in original, is expected to apply as a drastic measure for harbor tranquility. In this case it is very important to consider its permeability for wind waves because it has a narrow gap between individual piles. In this paper, a sponge layer model and a porous layer model, those are often applied to partial wave reflection boundaries, are used as a permeable boundary in a Boussinesq wave model, and harbor tranquility is evaluated in an actual harbor. The porous layer model can reproduce both transmission and reflection rate with a standard gap but not with more wide or narrow gap. A numerically installed such breakwater can increase harbor tranquility in a whole year, but it is not enough in more severe seasons because its transmissivity is not so small.

Nonlinear Analysis of Torsionally Loaded Pile Groups

An empirical approach is developed to analyze the nonlinear torsional behavior of free-standing pile groups with rigid pile caps. In this approach, the lateral and torsional responses of individual piles in a pile group are modeled by p-y and τ-θ curves; the interaction among lateral resistances of the individual piles is predicted through Mindlin's elastic solutions; the interactions between the torsional and lateral resistances of the individual piles are described through Randolph's solution; and the coupling effect of lateral resistance on torsional resistance of the individual piles is quantified using an empirical factor β. The proposed approach is capable of capturing the most significant aspects of pile-soil-pile interactions and coupling effect in pile groups subjected to torsion. The proposed approach is verified using results of centrifuge model tests. In general, the applied torque-twist angle response and the transfer of applied torque in pile groups can be reasonably well predicted and are sensitive to the pile group configuration.

Shaking Table Model Tests on Pile Groups behind Quay Walls Subjected to Lateral Spreading

This paper presents experimental results of 1-g shaking table model tests on a 3×3 pile group behind a sheet-pile quay wall. The main purpose was to understand the mechanisms of liquefaction-induced large ground deformation and the behavior of the pile group subjected to the lateral soil displacement. The sheet-pile quay wall was employed to trigger the liquefaction-induced large deformation in the backfill, and a study was made of the effect of several parameters such as soil density, amplitude and frequency of input motion, pile head fixity, and superstructure on the magnitude of soil lateral displacement and the maximum lateral force of liquefied soil. Furthermore, distribution of the maximum lateral force within the group pile was thoroughly studied. It was found that the force varies depending on the position of individual piles in the group. To evaluate the contribution of each pile in the total lateral force, a new two-dimensional parameter that is called contribution index was introduced and recom...

Behavior of Pile Groups Subject to Excavation-Induced Soil Movement in Very Soft Clay

A series of centrifuge model tests was conducted to investigate the behavior of pile groups of various sizes and configurations behind a retaining wall in very soft clay. With a 1.2-m excavation in front of the wall, which may simulate the initial stage of an excavation prior to strutting, the test results reveal that the induced bending moment on an individual pile in a free-head pile group is always smaller than that on a corresponding single pile located at the same distance behind the wall. This is attributed to the shadowing and reinforcing effects of other piles within the group. The degree of shadowing experienced by a pile depends on its relative position in the pile group. With a capped-head pile group, the individual piles are forced to interact in unison though subjected to different magnitudes of soil movement. Thus, despite being subjected to a larger soil movement, the induced bending moment on the front piles is moderated by the rear piles through the pile cap. A finite element program developed at the National University of Singapore is employed to back-analyze the centrifuge test data. The program gives a reasonably good prediction of the induced pile bending moments provided an appropriate modification factor is applied for the free-field soil movement and the amount of restraint provided by the pile cap is properly accounted for. The modification factor applied to the free-field soil movement accounts the reinforcing effect of the piles on the soil movement.

Ground improvement techniques for railway embankments

A high-speed railway project for trains of speeds of up to 160 km/h is currently being constructed between Rawang and Bidor (110 km long) in Peninsular Malaysia. The ground improvement methods adopted in the project are vibro-replacement with stone columns, dry deep soil mixing (cement columns), geogrid-reinforced piled embankments with individual pile caps and removal/replacement works. This paper provides a detailed insight into the design and implementation of vibro-replacement and the deep soil mixing treatment methods used in the project. The use of plate bearing tests and field instrumentation to monitor the performance of the stone columns and soil mixing ground treatment methods is also discussed. This paper also provides a brief overview of other treatment methods implemented in this high-speed railway project such as a pile embankment with geogrids and removal/replacement works.

Experimental study of interaction and coupling effects in pile groups subjected to torsion

Piles in a pile group subjected to torsion simultaneously mobilize lateral and torsional resistances. Hence, complicated pile–soil–pile interaction effects and load deformation coupling effects occur in the pile group. In this study, a series of centrifuge model tests were carried out to investigate these effects in three-diameter spaced 1 × 2, 2 × 2, and 3 × 3 pile groups subjected to torsion in both loose and dense sands. The test results showed that the effect of horizontal movement of a pile on lateral behaviors of its adjacent piles is significant in 3 × 3 pile groups and such effect varies with group configuration and pile position. The p-multiplier concept can be used to quantify the effect and values for the p-multiplier are suggested. The effect of lateral movement of a pile on the torsional resistances of its adjacent piles and the effect of torsional movement of a pile on the lateral resistances of its adjacent piles were found to be minor in these tests. For an individual pile in a pile group subjected to torsion, the mobilized lateral resistance was found to substantially increase the torsional resistance of the pile. Such a coupling effect is quantified by a coupling coefficient, β, which describes the contribution of subgrade reaction to the increase of torsional shear resistance.

Small Mammal Responses to Fine Woody Debris and Forest Fuel Reduction in Southwest Oregon

Abstract:Despite its importance for wildlife, most forests in the Pacific Northwest contain low volumes of large downed wood compared to fine woody debris (FWD). We used a replicated experiment to compare short‐term responses of deer mice (Peromyscus maniculatus) and western red‐backed voles (Clethrionomys californicus) among 3 arrangements of FWD: piled, lopped and scattered, and pile burning, a commonly used method of fuel reduction in commercial Douglas fir (Pseudotsuga menziesii) forests in southwest Oregon, USA. We assessed habitat use, density, and survival of mice and voles during 2 consecutive summers (Jun—Aug 1999 and 2000). Both mice and voles used FWD cover disproportionately from its availability, and they differed in their responses to specific FWD arrangements. Mice used piled FWD (proportional use = 37.0%, 90% CI = 33.0–44.0) 43% more than expected (26.0). Number of mice captured (x̄ = 1.9 mice, 90% CI = 1.5–2.5) and index of home range size (x̄ = 4.8 m, 90% CI = 0.7–8.9) at individual FWD piles decreased up to 16% and increased up to 50%, respectively, for each 1‐m increase in distance from piles. Voles used all FWD cover classes in proportion to availability, but number of voles captured increased slightly (x̄ = 0.016 voles/m, 90% CI = 0.001–0.031) for each 1‐m increase in distance from piles. Piled FWD had no discernable effect on population density and apparent survival of mice, but analyses had low power (0.25, 0.67). Our results suggest that piling FWD would benefit deer mice, whereas lopped and scattered FWD might benefit voles. Thus, a combination of methods to reduce fire risk should be considered to accommodate multiple small mammal species. (JOURNAL OF WILDLIFE MANAGEMENT 72(3):625–632; 2008)

Effect of pile-cap connection on behavior of torsionally loaded pile groups

To evaluate the responses of fixed and pinned pile groups under torsion, a method is presented to analyze the nonlinear behavior of free-standing pile groups with rigid pile caps. The method is capable of simulating the nonlinear soil response in the near field using p-y and τ-θ curves, the far-field interactions through Mindlin’s and Randolph’s elastic solutions, and the coupling effect of lateral resistance on torsional resistance of the individual piles using an empirical factor. Based on comparisons of the solutions for fixed- and pinned-head, 1×2, 2×2, and 3×3 pile groups subjected to torsion, it was found that pile-cap connection significantly influences the torsional capacity of pile groups and the assignment of applied torques in the pile groups. In this study, the applied torques for the pinned-head pile groups are only 44%∼64% of those for the corresponding fixed-head pile groups at a twist angle of 2°. Such a difference is mainly due to the change of the lateral resistances of individual piles in the groups.

Centrifuge Modeling of Torsionally Loaded Pile Groups

This paper reports a series of centrifuge model tests on torsionally loaded 1×2, 2×2, and 3×3 pile groups in sand. The objectives of the paper are to investigate: (1) the response of the pile groups subjected to torsion; (2) the way in which the applied torque is transferred in the pile groups; (3) the internal forces mobilized in these torsionally loaded pile groups and their contributions to resist the applied torque; and (4) the influence factors that affect the load transfer, such as soil density and pile-cap connection. In these model tests, the group torsional resistances of the pile groups increased monotonically in the test range of twist angles up to 8°. Both torsional and lateral resistances of the individual piles were simultaneously mobilized to resist the applied torque. The torsional resistances were substantially mobilized at small twist angles, while the lateral resistances kept increasing in the whole range of twist angles. Thus, the contribution of the torsional resistances to the applied torque decreased at large twist angles. The piles at different locations in a pile group could develop not only different horizontal displacements, but also different pile–soil–pile interactions and load–deformation coupling effect, hence, the torsional and lateral resistances of the piles are a function of pile location. The soil density had a more significant effect on the torsional resistances than on the lateral resistances of the group piles.

Centrifuge Modeling of Large-Diameter Bored Pile Groups with Defects

In this research, centrifuge model pile-load tests were carried out to failure to investigate the behavior of large-diameter bored pile groups with defects. The model piles represented cast-in-place concrete piles 2.0 m in diameter and 15 m in length. Two series of static loading tests were performed. The first series of tests simulated the performance of a pile founded on rock and a pile with a soft toe. The second series of tests simulated the performance of three 2X2 pile groups: One reference group without defects, one group containing soft toes, and one group with two shorter piles not founded on rock. The presence of soft toes and shorter piles in the defective pile groups considerably reduced the pile group stiffness and capacity. As the defective piles were less stiff than the piles without defects, the settlements of the individual piles in the two defective pile groups were different. As a result, the applied load was largely shared by the piles without defects, and the defective pile groups tilted significantly. The rotation of the defective pile groups caused large bending moments to develop in the group piles and the pile caps. When the applied load was large, bending failure mechanisms were induced even though the applied load was vertical and concentric. The test results confirm findings from numerical analyses in the literature.

Time-settlement behaviour of piled raft foundations using infinite elements

Although there has been a great deal of attention paid to the settlement of pile groups and piled raft foundations, little attention has been paid to the time-dependent behaviour. In this paper, a full three-dimensional finite element analysis (making use of infinite elements) is carried out to estimate the rate of consolidation of piled rafts, and to calculate the magnitude of differential deflections and the associated moments that develop in the raft with time. It is shown that the settlement of a full scale structure can be reasonably predicted by use of the method and that the moment build up with time can be predicted. Comparison is also made with approximate methods that treat the piles, soil and raft as a single block of material with equivalent properties to the individual piles and the soil contained between them.

A modulus‐multiplier approach for non‐linear analysis of laterally loaded pile groups

AbstractA modulus‐multiplier approach, which applies a reduction factor to the modulus of single pile p–y curves to account for the group effect, is presented for analysing the response of each individual pile in a laterally loaded pile group with any geometric arrangement based on non‐linear pile–soil–pile interaction. The pile–soil–pile interaction is conducted using a 3D non‐linear finite element approach. The interaction effect between piles under various loading directions is investigated in this paper. Group effects can be neglected at a pile spacing of 9 times the pile diameter for piles along the direction of the lateral load and at a pile spacing of 6 times the pile diameter for piles normal to the direction of loading. The modulus multipliers for a pair of piles are developed as a function of pile spacing for departure angle of 0, 90, and 180sup>/sup> with respect to the loading direction. The procedure proposed for computing the response of any individual pile within a pile group is verified using two well‐documented full‐scale pile load tests. Copyright © 2006 John Wiley & Sons, Ltd.

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.

Nonlinear three-dimensional analysis of pile group supported columns considering pile cap flexibility

A numerical method that takes into account the coupling between the rigidities of the piles, the cap, and the column has been developed for analyzing the response of pile group supported columns. Special attention is given to consideration of pile cap flexibility. A load transfer approach using t– z/ q– z and p– y curves is used for the analysis of single piles. The finite element technique is used to combine the pile stiffness with the stiffness of the cap and column. The numerical method developed has been verified by comparing the results with other numerical methods for pile groups. Through comparative studies, it has been found that the maximum load on the individual piles in a group is highly influenced by pile cap flexibility. The prediction of the lateral loads and bending moments in the pile cap is much more conservative in the present analysis than in FBPier 3.0 and shows a definitely larger lateral load and bending moment for various cap thicknesses.

Discussion of “Lateral Resistance of a Full-Scale Pile Group in Liquefied Sand” by Kyle M. Rollins, Travis M. Gerber, J. Dusty Lane, and Scott A. Ashford

The discussers have used the Strain Wedge Model (SWM) developed by Ashour and Norris (2003) to compare the test program results based on field test data the authors compiled (but without the authors' adjustment factors) for laterally loaded pile and pile group response in liquefied soil. The discussers observed that the SWM predicts limited group effect of the p-y curves for CISS single and individual pile (in a 3 X 3 group at 0.3 m, 1.3 m, and 2.3 m depths) under fully liquefaction conditions. In partial liquefaction conditions, though, the SWM predicts a greater group effect at the same depths.

Use of stiffness inserts in pile groups and piled rafts

In all but small symmetrical pile group configurations, the load distribution will be non-uniform, with a tendency for larger loads to be carried by piles near the perimeter of the pile group, while the inner piles may carry a significantly smaller load. If the design requires that a certain minimum factor of safety be applied to individual piles, the load that can be applied to a pile group may be limited by the most heavily loaded pile in that group. This may lead to an over-conservative design in many cases. This paper describes the use of stiffness inserts at the head of the more heavily loaded piles in a group. These inserts consist of a compressible material incorporated in the head of a pile, below the pile cap. By selecting appropriate stiffnesses for these inserts, it is possible to obtain an almost uniform distribution of axial load within the group, together with a specified settlement. In this way, the allowable load on a group can be increased, usually at the cost of a modest increase in the settlement. The paper sets out a relatively simple method for assessing the required stiffness of the inserts, which involves firstly an analysis of the pile group without inserts in order to compute the stiffness of each pile within the group environment. On the basis of this analysis, the required insert stiffness for each pile can be computed. The paper gives two examples of the difference in the load–settlement characteristics of a pile group with and without stiffness inserts where non-uniform load and/or settlement behaviour would occur without the inserts. A third case involves a piled raft, and demonstrates that improved settlement performance may be achieved without compromising the requirements for ultimate vertical capacity.

Analysis of piles and pile grillages on heaving soils

The concept of interaction between a heaving soil and individual and group piles and pile grillages, which makes it possible to determine both the magnitude of layer-by-layer uplift of soil around an individual pile and within a group of piles, and the piles themselves, is discussed. Specific examples of solutions are cited with comparison of predicted and actual values.

Rust never sleeps: Keeping the Golden Gate Bridge covered with paint is a major challenge for crews, management, and coatings systems

A large scale model test of a 1 × 2 pile group was conducted in silts to investigate its behavior under eccentric lateral loading. The model pile group consisted of two well instrumented steel piles and was installed in a large soil tank with a close spacing of three-pile diameters on centers. The test results revealed that the eccentricity of lateral loads had limited effect on the overall performances of the 1 × 2 pile group, but significantly contributed to the unevenness of internal forces of the individual piles. The coupling effect between the lateral deflection and torque gave rise to the substantial increase in the torsional resistance of individual piles within the group, comparing to that of a torsionally loaded single pile. The contribution provided by the torsional resistances of individual piles in resisting the external torque continually decreased when the applied lateral load increased. In addition, a three-dimensional finite-element analysis for the pile group was performed and the simulated response was found to be in good agreement with the measured test results. Based on the same model, more cases with different loading conditions were further analyzed. It could be concluded from the analyses that the layout of individual piles within the group obviously affected the behavior of the 1 × 2 pile group under eccentric lateral loads.

Automated Mapping of Stream Features with High-Resolution Multispectral Imagery

The capabilities of high-resolution, multispectral remote sensing imagery to map important stream features is investigated. Eighty centimeter spatial resolution CASI imagery was acquired in eight spectral bands over Tofino Creek on the west coast of Vancouver Island, British Columbia. A spectral angle mapping algorithm was used to classify stream habitat including hydraulic habitat, substrate material, and woody debris. Subclasses were attempted in terms of streambed material and water depth, but results were not reliable. A classification of deep water, moderate depth water, shallow water, sand, gravel and cobble, and woody debris in sunlit conditions, however, proved accurate (80 percent on average). Individual logs and piles of woody debris were consistently detected. Silty substrate in a tidal flats zone was also classified, but results indicated that different substrate material beneath the water may require separate classes and can result in problematic water depth classification. Patterns of general classes were reasonably represented within shadowed areas cast by isolated trees or groups of trees. However, problems do arise within lengthy shadowed stretches. Some boundaries of stream features with surrounding forest and between some zones of sand, gravel, and cobble were also misclassified. High-resolution, multispectral imagery in four or more bands combined with good geometric correction, image mosaicking, and appropriate automatic classification techniques offer a viable tool for stream mapping to meet a variety of issues and applications. In the future, a powerful suite of stream information may be compiled from multispectral classification combined with high-resolution thermal and lidar data.

Design and Construction of Three Instrumented Test Piles to Examine Time Dependent Pile Capacity Gain

Abstract Three heavily instrumented test piles were designed, constructed, and installed at a bridge reconstruction site in Newbury, Massachusetts as part of a research initiative into time dependent pile capacity gain. Pile instrumentation consisted primarily of an alternating pattern of piezometers and strain gages, allowing for correlation between pile capacity gain and excess pore pressure dissipation along discrete pile segments. Additional instrumentation within the piles included accelerometers, telltales, and radial pressure cells, allowing monitoring of total pressure at the pile wall. Standard dynamic gages (strain gages and accelerometers) were also attached to the piles during dynamic testing. A total of 86 vibrating wire, 17 electrical resistance, 17 telltales, and 4 piezo-resistive gages were installed within the test piles to record strain, displacement, pressure, and acceleration. This paper describes (i) the initial installation location of the test piles, (ii) the design and layout of the individual test piles, (iii) the selection and installation design of the individual instrumentation within the test piles, and (iv) assembly of the test piles. Sample measurements of the various instruments and a summary of the instrumentation performance are also presented.