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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UNDRAINED LATERAL PILE AND PILE GROUP RESPONSE IN SATURATED SAND
Author: Ashour, Mohamed Norris, G M | Size: 5.16 MB | Format:PDF | Quality:Original preprint | Publisher: University of Nevada, Reno | Year: 2000 | pages: 160
This report examines the use of strain wedge (SW) model formulation to evaluate the response of single piles or groups of piles in layered soils under lateral static loading. Application of the model provides behavior prediction under a wide range of strain or deflection. In this study, the capability of the SW model is extended to predict the response of a single pile or pile group under lateral loading in liquefied soil. The results from the tests suggest that the behavior of laterally loaded piles is both a function of soil and pile properties and is influenced by the level of porewater pressure that is built up in the soil surrounding the pile. Under these conditions the capacity of a loaded pile or pile group might drop significantly under such conditions.
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Author: Patty, Jill Seible, F University of California, San Diego Uang, Chia-Ming University of California, San Diego | Size: 18.66 MB | Format:PDF | Quality:Original preprint | Publisher: University of California, San Diego | Year: 2001 | pages: 146
This report describes a research program that involved experimental testing and force transfer modeling in order to characterize the behavior of a bridge design detail that integrates a steel superstructure with a concrete substructure using a concrete bent cap. During a seismic event, it is essential that the bent cap remain elastic. Focus of the research was therefore to establish a behavior profile of the bent cap connection to define limit states. The effect of two design parameters on the bent cap torsional behavior and moment capacity was examined through a series of four component tests. The two parameters examined included: bent cap reinforcement, and girder web configuration inside the bent cap. Results from the tests indicate a recommended design of stiffened steel girders integrated with a post-tensioned bent cap. Design guidelines for an integral bridge were developed, based on the experimental finds and force transfer models. The methodology for determining the bent cap torsional strength for a given earthquake, as well as recommended limits, is indicated in a design example.
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METALLIC DAMPERS FOR SEISMIC DESIGN AND RETROFIT OF BRIDGES
Author: Chen, G Mu, H Bothe, E R | Size: 6.34 MB | Format:PDF | Quality:Original preprint | Publisher: University of Missouri, Rolla | Year: 2001 | pages: 146
A practical bearing scheme is proposed in this study, consisting of expansion rocker bearings and steel rods (metallic dampers). It can accommodate seismic effects while it allows for free thermal expansion. Tests of metallic dampers have shown that dampers of straight rods can contribute over 10% damping at the small-to-medium displacement range. Extensive tests on a 1/10-scale bridge model indicated that metallic dampers can also significantly reduce the dynamic responses of the bridge by isolating vibration propagating from the substructure to the superstructure. High rocker bearings provided considerable damping to the bridge-damper system by dissipating energy along the friction surface between pin and web of the bearings. They remain stable even at the peak ground acceleration of 0.54g at resonance. To account for pounding effect at the expansion joints of bridges, design equations for determining the equivalent viscous damping corresponding to various sizes of bridge joints were developed. Integrating the equivalent damping into the response spectrum analysis procedure allows engineers to analyze the bridges with pounding effect in a linear fashion.
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