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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Drilled shaft foundations are principally used to support many structures such as bridge piers, towers, buildings, transmission towers, and roadway cable barriers. This research focuses on the use of drilled shafts in the cable median barrier systems which play an important role in protecting people’s lives due to cross-over collisions on highways. During December 2006 to February 2007, several failures of 3-cable median barrier (TL-3) were observed in Kaufman County near Dallas without any traffic-related vehicular impacts. Preliminary investigation of failures showed that failed drilled shafts were located in high plasticity clay. Causes of failures are attributed to cold temperature induced shrinkage in the cables that increased in the tension in them, soil saturation due to long periods of rainfall and small sizes of drilled shafts used. Various sizes of drilled shafts were established and constructed in an environment similar to the one in which foundation distress was observed. Geotechnical sampling and laboratory testing were performed, and a new test setup for the application of an inclined tensile loading on drilled shafts was designed to simulate the loading under real field conditions. The capacities of different sizes of drilled shafts from field test were tested and measured under this setup. Once good simulation was obtained, the models are used for various foundation dimensions and various undrained shear strengths of soils which, in turn, provided results that are used in the development of foundation design charts. Additionally, construction guidelines and recommendation for periodic maintenance are provided in this report.
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Geosynthetic Reinforced Soil for Low-Volume Bridge Abutments
Author: Vennapusa, Pavana Iowa State University, Ames White, David Klaiber, Wayne Iowa State University, Ames Wang, Shiyun | Size: 15.32 MB | Format:PDF | Quality:Original preprint | Publisher: Iowa State University, Ames | Year: 2012 | pages: 132
This report presents a review of literature on geosynthetic reinforced soil (GRS) bridge abutments, and test results and analysis from two field demonstration projects (Bridge 1 and Bridge 2) conducted in Buchanan County, Iowa, to evaluate the feasibility and cost effectiveness of the use of GRS bridge abutments on low-volume roads (LVRs). The two projects included GRS abutment substructures and railroad flat car (RRFC) bridge superstructures. The construction costs varied from $43k to $49k, which was about 50 to 60% lower than the expected costs for building a conventional bridge. Settlement monitoring at both bridges indicated maximum settlements ≤1 in. and differential settlements ≤ 0.2 in transversely at each abutment, during the monitoring phase. Laboratory testing on GRS fill material, field testing, and in ground instrumentation, abutment settlement monitoring, and bridge live load (LL) testing were conducted on Bridge 2. Laboratory test results indicated that shear strength parameters and permanent deformation behavior of granular fill material improved when reinforced with geosynthetic, due to lateral restraint effect at the soil-geosynthetic interface. Bridge LL testing under static loads indicated maximum deflections close to 0.9 in and non-uniform deflections transversely across the bridge due to poor load transfer between RRFCs. The ratio of horizontal to vertical stresses in the GRS fill was low (< 0.25), indicating low lateral stress on the soil surrounding GRS fill material. Bearing capacity analysis at Bridge 2 indicated lower than recommended factor of safety (FS) values due to low ultimate reinforcement strength of the geosynthetic material used in this study and a relatively weak underlying foundation layer. Global stability analysis of the GRS abutment structure revealed a lower FS than recommended against sliding failure along the interface of the GRS fill material and the underlying weak foundation layer. Design and construction recommendations to help improve the stability and performance of the GRS abutment structures on future projects, and recommendations for future research are provided in this report.
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Unknown foundations affect about 9,000 bridges in Texas. For bridges over rivers, this creates a problem regarding scour decisions as the calculated scour depth cannot be compared to the foundation depth, and a very conservative costly approach must be taken. The objective was to develop a global approach, which will reduce significantly the level of uncertainty associated with unknown foundations. This approach was developed in two parts: a data mining and inference approach where no testing at the site was necessary, and a testing approach where new tests for unknown foundations were used. The data mining and inference task made use of existing data such as soil type, known foundations on neighboring bridges, design practice, and the age of the bridge to infer the type and length of unknown foundation elements. The testing task consisted of developing two geophysical techniques, resistivity and induced polarization imaging, to obtain a picture of the soil and foundation below the surface level or river bottom. The outcome was a global framework in which one of the approaches or any combination thereof, as well as the most useful current techniques (nondestructive testing methods if necessary), can be used to decrease dramatically the uncertainty associated with the unknown foundation. The inference process was trained by using bridges where the foundation was known and verified by comparison against case histories. The two testing techniques mentioned above were tested at the National Geotechnical Testing Site on Texas A&M’s Riverside campus and then against full-scale bridges selected in cooperation with TxDOT.
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Development of Variable LRFD Φ Factors for Deep Foundation Design Due to Site Variabi
Author: McVay, Michael C Klammler, Harald Faraone, Michael A Dase, Krishnarao Jenneisch, Chris | Size: 3.68 MB | Format:PDF | Quality:Original preprint | Publisher: University of Florida, Gainesville | Year: 2012 | pages: 134
The current design guidelines of Load and Resistance Factor Design (LRFD) specifies constant resistance factors (Φ) values for deep foundation design, based on analytical method selected and degree of redundancy of the pier. However, investigation of multiple sites in Florida reveals significant variability of soil/rock properties from site to site (coastal conditions) suggesting the introduction of variable Φ values based on reliability-based design approach. Building on previous work (BD545-76) a geostatistical (variograms) approach was developed to quantify the spatial uncertainty for site specific conditions. As a result, Φ values are evaluated due to both a site’s measured spatial uncertainty and error associated with a particular analytical method. This report summarizes subsequent efforts to further expand the applicability of the reliability design to the analytical models currently available in the FB-DEEP software program. For the geostatistical analysis, a simple yet robust graphical user interface (GUI) was developed, which considers two design scenarios: 1) conditioning to nearby boring data, and 2) unconditional mean site data. For either scenario the GUI generates thousands of potential data sets, which are evaluated by FB-DEEP to assess mean pile/shaft resistance and spatial uncertainty at a pier location. Spatial uncertainty is then combined with the design method error associated with the selected FB-DEEP model to assess Φ. For demonstration of the application of the GUI, standard penetration test (SPT) and laboratory strength data were collected from seven FDOT projects and subsequent Φ values were evaluated. The Φ values ranged from 0.3 to 0.7 depending upon amount of subsurface data, measure summary statistics, and degree of spatial correlation. The report concludes with recommendations (in situ measurements, load testing, etc.) on improving the computed Φ on a site-by-site basis.
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This report documents two studies that were conducted to review, assess, and provide recommendations regarding the seismic design of bridge foundations. Specifically, the report addresses modeling approaches and parameters that affect the seismic design and response of pile groups and drilled shafts. The report attempts to bridge the interface between the structural and geotechnical design process by describing a two-step design and analysis procedure for these bridge foundation components. Recent research results on pile group effects and the design of pile foundations to resist lateral spreading of liquefiable soils are also reviewed. Recommendations are provided concerning: modifications to p-y curves to account for cyclic loading conditions, pile group effects and soil-pile interaction behavior, and development of p-y curves for the design of drilled shafts.
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GEOTECHNICAL ENGINEERING CIRCULAR NO. 4: GROUND ANCHORS AND ANCHORED SYSTEMS
Author: Sabatini, P J Pass, D G Bachus, R C | Size: 4.51 MB | Format:PDF | Quality:Original preprint | Publisher: GeoSyntec Consultants | Year: 1999 | pages: 312
This document presents state-of-the-practice information on the design and installation of cement-grouted ground anchors and anchored systems for highway applications. The anchored systems discussed include flexible anchored walls, slopes supported using ground anchors, landslide stabilization systems, and structures that incorporate tiedown anchors. This document draws extensively from the FHWA-DP-68-IR (1988) design manual in describing issues such as subsurface investigation and laboratory testing, basic anchoring principles, ground anchor load testing, and inspection of construction materials and methods used for anchored systems. This document provides detailed information on design analyses for ground anchored systems. Topics discussed include selection of design earth pressures, ground anchor design, design of corrosion protection system for ground anchors, design of wall components to resist lateral and vertical loads, evaluation of overall anchored system stability, and seismic design of anchored systems. Also included in the document are two detailed design examples and technical specifications for ground anchors and for anchored walls.
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USING GEOLOGIC MAPS AND SEISMIC REFRACTION IN PAVEMENT-DEFLECTION ANALYSIS
Author: Paine, J G | Size: 6.95 MB | Format:PDF | Quality:Original preprint | Publisher: University of Texas, Austin | Year: 1999 | pages: 128
The researchers examined the relationship between three data types - geologic maps, pavement deflection, and seismic refraction data - from diverse geologic settings to determine whether geologic maps and seismic data might be used to interpret deflections and assess pavement condition. Deflections measured with the Falling-Weight Deflectometer (FWD) are correlated to bedrock type as depicted on geologic maps, particularly at distant sensors. Comparisons of FWD data with mapped geologic units along six roadway segments revealed differences in FWD response that are likely to be related to differences in either bedrock type or depth. From FWD data alone, it is difficult to determine whether the relationship between rock type and deflections is caused by differences in bedrock type or depth. To resolve this ambiguity, the researchers employed the FWD and a soil-probe hammer as impulsive sources for seismic-refraction experiments at three test sites. The refraction experiments suggest that combined FWD-refraction systems could be used on pavement to aid deflection analysis by estimating bedrock depth and assist in rock-type identification by measuring compressional velocities for bedrock and overburden. The success of the refraction experiments led to the design and construction of a refraction system optimized for on-pavement use.
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