Design and Performance Verification of Ultra-High Performance Concrete Piles for Deep Foundations
Author: Vande Voort, Thomas L Suleiman, Muhannad T | Size: 9.02 MB | Format:PDF | Quality:Original preprint | Publisher: Iowa State University, Ames | Year: 2008 | pages: 224
The strategic plan for bridge engineering issued by AASHTO in 2005 identified extending the service life and optimizing structural systems of bridges in the United States as two grand challenges in bridge engineering, with the objective of producing safer bridges that have a minimum service life of 75 years and reduced maintenance cost. Material deterioration was identified as one of the primary challenges to achieving the objective of extended life. In substructural applications (e.g., deep foundations), construction materials such as timber, steel, and concrete are subjected to deterioration due to environmental impacts. Using innovative and new materials for foundation applications makes the AASHTO objective of 75 years service life achievable. Ultra High Performance Concrete (UHPC) with compressive strength of 180 MPa (26,000 psi) and excellent durability has been used in superstructure applications but not in geotechnical and foundation applications. This study explores the use of precast, prestressed UHPC piles in future foundations of bridges and other structures. An H-shaped UHPC section, which is 10-in. (250-mm) deep with weight similar to that of an HP10×57 steel pile, was designed to improve constructability and reduce cost. In this project, instrumented UHPC piles were cast and laboratory and field tests were conducted. Laboratory tests were used to verify the moment-curvature response of UHPC pile section. In the field, two UHPC piles have been successfully driven in glacial till clay soil and load tested under vertical and lateral loads. This report provides a complete set of results for the field investigation conducted on UHPC H-shaped piles. Test results, durability, drivability, and other material advantages over normal concrete and steel indicate that UHPC piles are a viable alternative to achieve the goals of AASHTO strategic plan.
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Use of Reinforced Soil Foundation (RSF) to Support Shallow Foundation
Author: Abu-Farsakh, Murad Y | Size: 3.99 MB | Format:PDF | Quality:Original preprint | Publisher: Louisiana Transportation Research Center | Year: 2008 | pages: 218
This research study aims at investigating the potential benefits of using reinforced soil foundations to improve the bearing capacity and reduce the settlement of shallow foundations on soils. To implement this objective, a total of 117 tests, including 38 laboratory model tests on silty clay embankment soil, 51 laboratory model tests on sand, 22 laboratory model tests on Kentucky crushed limestone, and 6 large scale field tests on silty clay embankment soil, were performed at the Louisiana Transportation Research Center to study the behavior of reinforced soil foundations. The influences of different variables and parameters contributing to the improved performance of reinforced soil foundation were examined in these tests. In addition, an instrumentation program with pressure cells and strain gauges was designed to investigate the stress distribution in soil mass with and without reinforcement and the strain distribution along the reinforcement. The test results showed that the inclusion of reinforcement can significantly improve the soil’s bearing capacity and reduce the footing settlement. The geogrids with higher tensile modulus performed better than geogrids with lower tensile modulus. The strain developed along the reinforcement is directly related to the settlement, and therefore higher tension would be developed for geogrid with higher modulus under the same footing settlement. The test results also showed that the inclusion of reinforcement will redistribute the applied load to a wider area, thus minimizing stress concentration and achieving a more uniform stress distribution. The redistribution of stresses below the reinforced zone will result in reducing the consolidation settlement of the underlying weak clayey soil, which is directly related to the induced stress. Insignificant strain measured in the geogrid beyond its effective length of 4.0~6.0B indicated that the geogrid beyond this length provides a negligible extra reinforcement effect. Additionally, finite element analyses were conducted to assess the benefits of reinforcing embankment soil of low to medium plasticity and crushed limestone with geogrids beneath a strip footing from the perspective of the ultimate bearing capacity and footing settlement. Based on the numerical study, several geogrid-reinforcement design parameters were investigated.
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Comparison of Five Different Methods for Determining Pile Bearing Capacities
Author: Long, James H | Size: 3.96 MB | Format:PDF | Quality:Original preprint | Publisher: University of Illinois, Urbana-Champaign | Year: 2009 | pages: 176
The purpose of this study is to assess the accuracy and precision with which five methods can predict axial pile capacity. The methods are the Engineering News formula currently used by Wisconsin Department of Transportation (WisDOT), the FHWA-Gates formula, the Pile Driving Analyzer, the method developed by the Washington State DOT (WSDOT), and further analysis conducted on the FHWA-Gates method to improve its ability to predict axial capacity. Improvements were made by restricting the application of the formula to piles with axial capacity less than 750 kips, and by applying adjustment factors based on the pile being driven, the hammer being used, and the soil into which the pile is being driven. Two databases of pile driving information and static or dynamic load tests were used to evaluate these methods. Analysis is conducted to compare the impact of changing to a more accurate predictive method, and incorporating load and resistance factor design (LRFD). The results of this study indicate that a “corrected” FHWA-Gates and the WSDOT formulas provide the greatest precision. Using either of these two methods and changing to LRFD should increase the need for foundation (geotechnical) capacity by less than 10 percent.
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Modification of LRFD Resistance Factors Based on Site Variability
Author: McVay, Michael | Size: 2.76 MB | Format:PDF | Quality:Original preprint | Publisher: University of Florida, Gainesville | Year: 2009 | pages: 146
Current practice by the Florida Department of Transportation (FDOT), Federal Highway Administration (FHWA), and American Association of State Highway Transportation Officials (AASHTO) for deep foundation design is to use a constant load and resistance factored design (LRFD) Φ depending on redundancy, but independent of pile/shaft dimension. Unfortunately, soil/rock properties vary from point-to-point (CVq: coefficient of variation) and are typically spatially correlated. Since both the skin friction and end bearing involve spatial averaging of soil/rock properties over the shaft surface, the resulting total shaft resistance variability (CVR) will not share the same point variability (CVq). Moreover, the total shaft variability (CVR) will also vary with different degrees of spatial correlation, typically represented with a covariance function and a correlation length a. This work employs well established geostatistical principles to establish both the covariance function (e.g., variogram) and expected total pile/shaft variability (CVR) using borehole data. Consideration is given to the number of borings, the location of borings relative to each other, and to the design foundation (e.g., if the borings are within the footprint of the design pile/shaft). Since the resulting pile/shaft variability CVR is a function of pile/shaft dimensions, soil/rock variability CVq, and its spatial correlation, the resulting LRFD Φ is not constant for any site. To help the designer, four quadrant iterative design charts are developed for single and group pile/shaft layouts, which consider side and tip resistances, as well as layered systems. To better define the total pile/shaft variability CVR, the practice of load testing is also incorporated into the proposed approach. The work includes multiple design examples and data from existing FDOT bridge sites (e.g., 17th Street, Fuller Warren, and Jewfish Creek bridges).
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Foundation Design for High Tension Cable Guardrails
Author: Zhu, Ling | Size: 3.53 MB | Format:PDF | Quality:Original preprint | Publisher: University of Nebraska, Lincoln | Year: 2010 | pages: 49
High tension cable guardrail is becoming increasing popular in median and roadside applications due to the promise of reduced deflections upon impact and reduced maintenance. As the performance of these systems is observed in service, there is a growing concern over the end anchorage foundation performance of current systems. Foundations for high tension systems must not only be capable of restraining the impact load of a vehicle but must also restrain the initial pretension on the cable system as well as temperature induced loads. While it may be acceptable for many roadside safety devices to require foundation repair after impact, foundation failure due to environmentally induced loads would be a serious maintenance problem. As initial tension and temperature induced loads can be greater than those loads applied during impact, this type of loading must be considered in foundation design. Foundation deflection can reduce cable tension, increasing deflection of the system during impact and letting the cables sag after impact. The soil conditions in which these foundations are placed vary significantly. This report considers the potential impact, tension, and temperature loads and develops a set of suggested foundation designs to accommodate a range of in situ soil conditions. These designs will vary significantly in different areas around the nation due to variations in both weather and in situ soil conditions. Deflection during full-scale crash tests may not accurately represent the foundation deflection that will be experienced in the field.
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This report and the accompanying software are part of efforts to improve the characterization and analysis of pile-stabilized slopes using one or two rows of driven piles. A combination of the limit equilibrium analysis and strain wedge (SW) model technique is employed to assess the stability of vulnerable slopes before and after using driven piles to improve the slope stability. This report focuses on the entry of input data, interpretation of the output results, and description of the employed technique. In addition to a comparison study with a full-scale load test, the finite element (FE) analysis using a general-purpose FE package, “PLAXIS,” is performed to verify the results. The characterization of lateral load induced by slipping mass of soils can be accomplished using the modified SW model technique. The SW model for laterally loaded pile behavior is a new predictive method (recommended as an alternative method by AASHTO [2007]) that relates the stress-strain behavior of soil in the developing three-dimensional passive wedge in front of the pile (denoted as the strain wedge) under lateral load to the one-dimensional beam-on-elastic foundation parameters. Two failure scenarios are employed in the developed computer program to include pile stabilization for 1) existing slip surface of failed slope and 2) potential failure surface. The two scenarios evaluate the distribution of the soil driving forces with the consideration of the soil flow-around failure, soil strength, and pile spacing. The developed procedure can also account for the external pile head lateral load and moment along with the driving force induced by the sliding mass of soil. The developed computer program is a design tool in which the designer can select an economic pile size to stabilize slopes. In addition to the external lateral loads applied at the pile head, the presented research work determines the mobilized driving force caused by sliding mass of soil that needs to be transferred via installed piles to stable soil layers below the slip surface. The side and front interaction between piles and sliding mass of soil is one of the main features of this project. The work presented also evaluates the appropriate pile spacing between the piles in the same pile row (wall) and the spacing between the pile rows. The computer program provides a flexible graphical user interface that facilitates entering data and analyzing/plotting the results. The finite element analysis (using PLAXIS) was used to investigate the results. A field test for pile-stabilized slope is used to validate the results obtained from the finite element analysis and the developed technique.
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Group Efficiencies of Grout-Tipped Drilled Shafts and Jet-Grouted Piles
Author: McVay, Michael | Size: 11.03 MB | Format:PDF | Quality:Original preprint | Publisher: University of Florida, Gainesville | Year: 2011 | pages: 206
In current practice, driven piles/drilled shafts are constructed in a group at 3D center to center (c/c) spacing to minimize group interference (i.e., group efficiency factor ~ 1) as well as reduce the cost of the reinforced concrete cap. Presently, group efficiency factors for a number of new foundation types, e.g., post-grouted drilled shafts and jet-grouted piles, are unknown. This research looked into the group interaction of post-grouted drilled shafts and jet-grouted piles at typical 3D spacing. Two sets of group tests for grout-tipped drilled shafts and jet-grouted piles were performed in the Florida Department of Transportation (FDOT) test chamber in medium dense sands. The experimental top down group testing revealed that the jet-grouted piles behaved as a block at 3D spacing, whereas postgrouted drilled shafts acted independently of one another, i.e., no group interaction. A group interaction factor, as well as an analytical approach for predicting load versus displacement for single or group of jet-grouted piles, is suggested. In the case of the grout-tipped drilled shafts, the grout pressure always resulted in an upward flow of grout alongside the shaft which increased both the side and tip areas. The increased areas and grout tip preload were the three factors identified with the increased shaft and group resistance. Due to uncertainty in estimating areas, a conservative design approach for assessing single and group capacities of post-grouted drilled shafts at 5% displacement is proposed. Finally, the use of stage grouting to assess the increase in shaft capacity (skin and tip) is suggested.
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Author: Helwany, Sam Panda, Ritu Titi, Hani | Size: 5.67 MB | Format:PDF | Quality:Original preprint | Publisher: University of Wisconsin, Milwaukee | Year: 2011 | pages: 127
The alternate post system offers benefits such as ease of construction, reduced construction time, and lower wall costs. While this system seems feasible, there are concerns regarding its performance, in particular the amount of bending in the post and the defection of the wall due to active earth pressures exerted by the retained soil. Other concerns include the potential damage to the plate during driving, control and accuracy of post alignment, and long term issues such as corrosion and soil creep. The objective of this research project is to assess the feasibility of the alternate post system. If the system is deemed feasible, the research team will develop design criteria for the alternate post system based on exposed wall heights, applied soil loads, post dimensions, and parameters of the retained soil and the foundation soil.
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Author: Pierson, Matthew | Size: 4.49 MB | Format:PDF | Quality:Original preprint | Publisher: University of Kansas, Lawrence | Year: 2011 | pages: 164
Mechanically stabilized earth (MSE) walls are recognized as a cost effective earth retention technology. In some cases structural foundations must pass through the reinforced fill due to the required footprint of the reinforced zone behind the facing. Limited information about the interaction between the structure and the MSE mass has been published, making efficient design difficult. It would be prohibitively expensive to construct and test all possible geometries or applications; therefore numerical modeling must be used to supplement physical data. This report contains a discussion of the analysis of physical test data and numerical modeling of an MSE test wall containing foundation elements. The test wall consists of an MSE wall with cast-in-place shafts contained within and solely supported by the reinforced fill. The finite difference numerical modeling program FLAC3D was used for analysis. A parametric study was conducted to determine how the various constituents of the physical wall as well as wall height affect wall-shaft behavior. Geogrid properties, particularly stiffness, were found to have the greatest influence on behavior. Wall height has a large influence on capacity at shaft movement of more than 2 inches. Analyses of the modeling results were used to create design recommendations for MSE walls with foundation elements.
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Drilled Shaft Bridge Foundation Design Parameters and Procedures for Bearing in SGC Soils
Author: Houston, William N Arizona State University, Tempe Harraz, Abdalla M Walsh, Kenneth D Houston, Sandra L Arizona State University, Tempe Perry, Courtland | Size: 2.11 MB | Format:PDF | Quality:Original preprint | Publisher: Arizona State University, Tempe | Year: 2011 | pages: 126
This report provides a simplified method to be used for evaluating the skin friction and tip resistance of axially loaded drilled shafts. A summary of literature and current practice was completed and then a comprehensive set of field and laboratory tests was performed. Several soil samples were collected from different sites from Arizona and surrounding states. Large scale direct shear apparatus was developed and used to determine the friction between soil and concrete. Finite element analyses were conducted on several prototype cases to determine effect of soil parameters such as dilation on the skin friction values. A step-by-step simplified approach was introduced to determine the skin and tip resistance of drilled shaft foundations in gravelly soils. An example application was presented to guide users in utilizing the simplified approach.
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