Naser Abu-Hejleh

PERFORMANCE OF GEOSYNTHETIC-REINFORCED WALLS SUPPORTING BRIDGE AND APPROACHING ROADWAY STRUCTURES

This paper describes a unique field application in which a geosynthetic-reinforced soil system was designed and constructed to support both the foundation of a two-span bridge and the approaching roadway structure. The reinforced soil system not only provides bridge support, but it was also designed to alleviate the common bridge bump problem. This structure was considered experimental and comprehensive material testing and instrumentation programs were conducted. These programs would allow assessment of the overall structure performance and evaluation of Colorado Department of Transportation and AASHTO design assumptions and procedures for reinforced soil structures supporting both bridge foundations and approaching roadway structures. Large-size direct shear and triaxial tests were conducted to determine representative shear strength properties and constitutive relations of the gravelly backfill used for construction. Three sections were instrumented to provide information on external movements, internal soil stresses, geogrid strains, and moisture content during various construction stages and after the structure opening to traffic. Results from a pilot (Phase I) instrumentation program and some preliminary results from a more comprehensive (Phase II) instrumentation program are presented in the paper. The results suggest that current design procedures lead to a conservative estimation of both the backfill material strength and horizontal earth pressures, and that the overall performance of this structure, before its opening to traffic, has been satisfactory.

IMPROVEMENT OF THE GEOTECHNICAL AXIAL DESIGN METHODOLOGY FOR COLORADO'S DRILLED SHAFTS SOCKETED IN WEAK ROCKS

Drilled shaft foundations embedded in weak rock formations support a large percentage of bridges in Colorado. Since the 1960s, empirical methods that entirely deviate from the AASHTO design methods have been used for the axial geotechnical design of these shafts. The margin of safety and expected shaft settlement are unknown in these empirical methods. Load tests on drilled shafts provide the most accurate design and research data for improvement of the design methods. Four Osterberg axial load tests were performed in Denver on drilled shafts embedded in soil-like claystone, very hard sandy claystone, and extremely hard clayey sandstone. An extensive program of simple geotechnical tests was performed at the load test sites, including standard penetration tests (SPT), unconfined compressive strength tests (UCT), and pressuremeter tests (PMT). Information on the construction and materials of the test shafts was documented, followed by thorough analysis of all test results. Conservative equations were sugges...

Development and Use of High-Quality Databases of Deep Foundation Load Tests

Foundation load test databases are needed by researchers in reliability calibration to develop accurate and economical foundation geotechnical design methods (for implementation of load and resistance factor design) and by designers to evaluate and improve the geotechnical design for production foundations in their projects. These databases should include a complete and adequate number of high-quality records of data at load test sites. FHWA developed the Deep Foundation Load Test Database (DFLTD), which was used by researchers and state departments of transportation (DOTs) to develop their databases. Only a few reliability-based resistance factors for foundations have been developed by AASHTO and state DOTs because of a lack of high-quality databases of foundation load tests. Therefore, transportation agencies (e.g., state DOTs) and universities should work together to develop local, regional, and national databases of foundation load tests that cover all common foundation design and construction conditions encountered in the United States. The goal of this paper is to help transportation engineering agencies develop and use consistent and high-quality deep foundation load test databases. Initially, the paper describes the contents and applications of foundation load test databases and then the contents, limitations, and distribution of the DFLTD. Contents and use of other deep foundation load test databases are also described. Finally, recommendations for the development and sharing of high-quality databases of foundation load tests are presented, followed by a roadmap to implement the recommendations.

MSE WALLS WITH INDEPENDENT FULL-HEIGHT FACING PANELS

In 1996, the Colorado Department of Transportation (CDOT) completed the construction of a unique mechanically stabilized earth (MSE) wall with an independent full-height facing (IFF) for the ramp connecting northbound Interstate-25 to Interstate -70 in Denver, Colorado. The new MSE/IFF wall has four major components: 1) a self-stable welded wire fabric (WWF) reinforced soil mass, 2) full-height concrete facing panels not attacked to the soil reinforcements (i.e., independent) that are allowed to tilt around their base, 3) flexible face anchors to provide for attachment of facing panels to the reinforced soil mass and accommodate movements of the wall system, and 4) a trench with flowfill to brace the panels during construction only (before the face anchors are placed). Since this MSE wall system is the first of its kind, it was considered experimental and a comprehensive instrumentation and monitoring program was performed. The main objective of this study was to upgrade the I-25/I-70 MSE/IFF wall for future standard use of this wall system by identifying modifications and additions to the design and construction of the I-25/I-70 MSE/IFF wall that would improve performance and save money and time. This report provides insight into material, construction, construction problems and corrective actions, monitoring, performance and design assessment of the I-25/I-70 MSE/IFF wall. The wall system performed as intended in the design. The flexibility of the MSE wall system smoothly accommodated the movements of the wall system, especially those induced by heavy compaction close to the facing, and allowed for the mobilization of tensile resistance in the WWF reinforcements, thus taking most of the lateral load off the facing panels. The average lateral earth pressure measured on the facing was a low value of 32 psf. After five years in service, the structure performance has been excellent with no signs of distress and the facing remained properly aligned.

Inventory System for Retaining Walls and Sound Barriers

An inventory system for retaining walls and sound barriers includes information about location, age, service, type, dimensions, and appraisals of a structure together with element-level models and element-level condition reports. Many of the inventory items and appraisals are adapted from the U.S. National Bridge Inventory record. Elements for walls and barriers indicate structural form and material, much like Commonly Recognized (CoRe) bridge elements. Potential uses of the inventory system in maintenance management and asset preservation are noted.

Evaluation and Recommendations for Flowfill and Mechanically Stabilized Earth Bridge Approaches

To alleviate the common bridge bump problem, the Colorado Department of Transportation (CDOT) has employed three new alternatives for bridge abutment backfill since 1992: flowfill, mechanically stabilized earth (MSE) using well-graded granular Class 1 backfill (reinforced soil mass as in MSE walls), and MSE using free-draining Class B filter material. However, the occurrence of bridge bump problems is still reported. A study evaluated CDOT current practice for design and construction of bridge approaches and then developed recommendations to improve this practice (improve performance and reduce costs) on the basis of the results of the following: (a) best practices for bridge approaches collected from CDOT staff and reported in the literature, (b) evaluation of the performance and cost-effectiveness of Colorados MSE and flowfill bridge approaches, and (c) identification of the causes of significant bridge approach settlement problems observed in some of Colorados MSE and flowfill bridge approaches. Evaluation procedures and forensic investigations were developed and applied to obtain the information needed for the first two items. Flowfill should remain a viable alternative for certain field and construction scenarios that justify its higher costs. MSE approaches with both Class B and Class 1 backfill materials should be routinely used in future CDOT projects with documentation of their performance and cost (construction and repair costs) for a future evaluation. Comprehensive recommendations are presented to mitigate the observed bridge approach settlement problem; the most important recommendations are for improved support and drainage systems for the sleeper slab where the settlement problem occurs.

Design of Drilled Shafts Supporting Sound Walls

Abstract Drilled shafts are widely adopted as the foundation for sound walls. However, there has been a lack of uniformity in design and analysis methods and design criteria, in terms of factor of safety against ultimate capacity failure as well as the allowable deflection. In order to establish a uniform design methodology for the drilled shafts supporting sound walls in cohesive and cohesionless soils, respectively, a database of fullscale lateral load tests on fully instrumented drilled shafts was collected. Based on the compiled database, existing design methods and design criteria of laterally loaded drilled shafts were evaluated. Broms method and COM624P (or LPILE) are suggested as the design methods for drilled shafts supporting sound walls in both cohesive and cohesionless soils. Additionally, the corresponding design criteria, including factor of safety and permissible deflection, for both design methods are recommended. Two full-scale lateral load tests on fully instrumented drilled shafts were subsequently conducted in Colorado to further verify the design recommendation. A comprehensive geotechnical investigation program was also carried out at the two new lateral load test sites that included pressuremeter test, SPT, as well as laboratory triaxial consolidated undrained tests and direct shear tests on the soil samples taken from the lateral load test sites. The test results obtained at these two load test sites were employed to validate the recommended geotechnical design and geotechnical testing methods for the drilled shafts supporting sound walls.

COLORADO TYPE 7 AND 10 RAILS UNDER HIGH TEST LEVEL LOADS

Colorado impact rail designs follow the AASHTO Standard Specification for bridge deck overhangs, whereas it uses a 44.5 kN equivalent service load. In the AASHTO LRFD 2000 Code, the impact load was changed to an ultimate static load of TLI (60 kN) to TL6 (780 kN) without providing design details and the Colorado Department of Transportation (CDOT) began its research to establish design details. Colorado railings in bridge approach usually sit on mechanically stabilized earth (MSE) walls and the impact load transfer from rails to walls becomes critical to rail stability and MSE wall design. Nonlinear quasi-static and impact load finite element analysis were performed to evaluate the stability and impact transfer efficiency of Colorado Type 7 and Type 10 rails with concrete and steel barriers, respectively under TL4 (240 kN) and TL5a (516 kN) impact loads. The finite element modeling demonstrated that the current design was effective at resisting impact loads if the rails were long and continuous. However, the modeling indicated that the system might not perform adequately if the impact occurred close to the end of the rail. Further research is needed to simulate true dynamic loading and to validate the results with actual crash tests.