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238 Accomplishment of the objectives will require at least the following tasks: Phase I Evaluate and Validate the "Guide Speci- fications" Task 1. Review the literature for information on the multiple performance-level concept, barrier warrants, bar- rier design, vehicle crash testing, car and truck accident studies involving vehicle contact with bridge railings and other longitudinal barrier systems, and any other related subjects deemed appropriate by the researchers. In ad- dition, identify accident data bases that can be used to validate the criteria used to develop the performance levels identified in the "Guide Specifications." Task 2. Evaluate the information assembled in Task 1 and develop a working plan for evaluating and validating the performance levels and performance-level selection procedures contained in the "Guide Specifications." Pre- pare and distribute to the NCHRP Project Panel a letter report describing the results of Tasks 1 and 2. Task 3. Implement the working plan developed in Task 2. Also identify potential modifications to the "Guide Specifications" along with the advantages and disadvan- tages of implementing each modification. Prepare and distribute to the NCHRP Project Panel an interim report describing the results of this task. . Phase II Assess Implementation of the "Guide Specifications" Task 4 Develop a detailed working plan for applying the performance-level selection procedures to a represen- tative sample of state, county, and city roadways In a minimum of 5 states, to be selected by NCHRP, for the purposes of: (a) estimating the impact of implementing the "Guide Specifications"; (b) assessing the effects of implementing the potential modifications to the "Guide Specifications" identified in Task 3; and (c) evaluating the sensitivity of the performance-level selection procedures to variations in actual roadway and traffic characteristics. Submit the working plan developed in this task to the NCHRP Project Panel for review and approval. Approval of the working plan is required before initiation of Task 5. Task 5. Implement the working plan developed in Task 4. Also develop recommended modifications to the "Guide Specifications." Prepare and distribute to the NCHRP Project Panel an interim report documenting the findings of this task. Phase III- Extend The Multiple Performance-Level Concept Task 6. Evaluate the feasibility of extending the mul- tiple performance-level concept to all longitudinal bar- riers. Based on this evaluation, draft a detailed working plan for development of a roadside-appurtenance design guide. This plan shall include, but not be limited to, the identification of variables involved, the methodologies for accommodating these variables, and a strategy for vali- dating the approach. Phase IV Prepare the Final Report Task 7. Prepare a final report documenting the results of Tasks 1 through 6. AREA 23: SOILS PROPERTIES No projects AREA 24: SOIL MECHANICS AND FOUNDATIONS Project 24-1 FY '79 Manual on Subsurface Investigations Research Agency: Principal Invest.: Effective Date: Completion Date: Funds: Haley and Aldrich, Inc. Dr. A. W. Hatheway April 2, 1979 December 31, 1980 $75,000 The over-all objective of this project was preparation of a manual on subsurface investigations applicable to the general transportation field that could be considered for publication by AASHTO. Research has been completed, and the final report has been published by AASHTO. Copies of the new manual, AASHTO Manual on Subsurface Investigations, are avail- able from AASHTO, 441 North Capitol Street, N.W., Suite 225, Washington, D.C. 20001. Project 24-2 FY 983 Reinforcement of Earth Slopes and Embank- ments Research Agency: Principal Invest.: Effective Date: Completion Date: Funds: Dames & Moore Dr. Willem C. B. Villet August 22, 1983 May 21, 1987 $150,000 The problem of economically constructing and main- taining stable slopes within limited right-of-way is a con- tinuing concern. Where increasing traffic requires the addition of lanes within the same right-of-way, earth re- taining structures are often necessary. Such structures are required also where existing or proposed slopes are unst- able and flattening of the slope is not feasible. In recent years, some of the most noteworthy advances in geotechnology have been in the area of earth reinforce

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239 meet. Earth reinforcement systems are comprised of re- inforcement material, backfill or in-place soil, and facing elements. Innovative techniques have been initiated and are being developed here and abroad that have the po- tential for improving stability at reasonable cost. Some techniques are proprietary, and information on many of the innovative methodologies has not been widely dis- tributed. Therefore, a need existed to collect, evaluate and disseminate the current state of the art to realize the full potential of their use and determine their applicability. Research is complete. The final report for the project provides a comprehensive compilation of information on various earth reinforcement systems used to construct embankments and stabilize existing slopes. The report includes an all-inclusive overview of earth reinforcement and details on specific earth reinforcement systems cov- ering their mechanisms, behavior, applications, designs, and durability. The guiding objective in the preparation of this document was to make it sufficiently complete to be a valuable handbook-type reference source for the re- searcher and the practicing engineer in considering ap- plications of earth reinforcement. The final report has been published as NCHRP Report 290, "Reinforcement of Earth Slopes and Embankments." Project 24-3 FY '86 Laboratory Evaluation of Piles Installed with Vibratory Drivers Research Agency. Principal Invest.: Effective Date: Completion Date: Funds: University of Houston University Park Drs. Michael W. O'Neill and Cumaraswamy Vipulanandan January 6, 1986 August 31, 1988 $200,000 State Departments of Transportation often are re- quested by contractors to use vibratory drivers rather than the more conventional impact hammers to install piles. Vibratory pile drivers can provide substantial savings by reducing the amount of driving time to final penetration under certain soil conditions. However, the lack of a reliable dynamic method of estimating bearing capacity limits their usefulness. Presently, the most common method to determine capacity is to restrike the pile with an impact hammer, but the validity of this method is unproven and the extra operation reduces the potential savings. Developing a reliable method for dynamically deter- mining bearing capacity of piles installed with vibratory drivers is a complex problem. To supplement current activity, laboratory studies are needed to provide insight into the basic behavior of piles installed with vibratory drivers compared to impact hammers and the influence of various soil parameters on the behavior of piles. Lab oratory studies will also assist in the design of future field tests and the analysis of results. The overall objective of this study is to evaluate the load-deformation behavior of piles installed in the labo- ratory with vibratory drivers. Specific objectives include: (1) a comparison of load deformation behavior of piles installed with vibratory drivers and impact hammers; (2) the identification of soil parameters that significantly af- fect load-deformation behavior of piles installed with vi- bratory drivers; (3) a comparison of load-deformation behavior of piles installed by vibratory drivers with and without restriking using an impact hammer to evaluate the effect of restriking; and (4) the development of a recommended predictive method of determining bearing capacity for further field verification. The research will include the following tasks: The agency preliminary draft report has been submitted and revised. The agency will now respond to that review and furnish the revised final report in early 1989. Project 24-4 FY '87 Load Factor Design Criteria for Highway Structure Foundations Research Agency: Principal Invest.: Elective Date: Completion Date: Funds: Virginia Polytechnic Institute and State University Richard M. Barker, James M. Dun- can, Kamal B. Rojiani September 1, 1987 May 31, 1990 $375,000 Until the early 1970's all transportation structure de- sign was performed using the working stress design method. Then, in the mid-1970's, AASHTO adopted load factor design into the AASHTO Standard Specifications for Highway Bridges as an approved design method for those portions of the bridge structure above the foun- dation. Many states have adopted AASHTO's load factor design criteria for bridge superstructures. As a result, engineers have been faced with the inconsistency of de- signing those portions of the structure above the foun- dation by the load factor method while still designing the foundations by working stress. This inconsistency in design format requires the de- signer to perform considerable duplication in compiling design forces for the highway structure and its foundation. The development of suitable load factor design criteria for highway structure foundations would eliminate this inconsistency, saving time and money. Additionally, this would lead to a more uniform margin of safety for all the structural components in a highway structure and should result in a more consistent and efficient use of materials. Research is needed so that designers of highway struc- tures may take advantage of the load factor design concept for the design of highway structure foundations. The re

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240 search needs to consider both the loading and the resist- ance sides of the strength design equation. The objective of this research is to develop load factor design criteria for highway structure foundations. The design criteria shall be developed for, but not necessarily limited to, drilled piles and shafts, driven friction piles, driven end-bearing piles, spread footings on rock, spread footings on soil, and rigid retaining walls. The loadings to be considered shall include vertical loads, horizontal loads, moments, and combinations thereof. The research will include the following tasks: Task 1 Review relevant current domestic and foreign practice, performance data, and research findings. This information shall be assembled from both technical lit- erature and the unpublished experiences of bridge and geotechnical engineers, consultants, and owners of high- way structures. Task 2 Analyze and evaluate the information gen- erated in Task 1 to establish a framework for the devel- opment of the load factor design concept as it should be applied to the design of highway structure foundations. This shall include a description of the proposed meth- odology for the development of the load factor design criteria. Task 3 Develop a comprehensive outline of the an- ticipated load factor design criteria for highway structure foundations. Discuss the significance of each topic in the proposed outline. Task 4 Present the findings of Tasks 1 through 3 in an interim report to be submitted not later than 12 months after initiation of the research. The interim report shall include a detailed research plan for Tasks 5 through 9. NCHRP approval of the interim report will be required before commencing Tasks 5 through 9. Task 5 Develop values for appropriate load and re- sistance factors and loading combinations for all foun- dation types from the information obtained in the preceding tasks. These factors should be based on the reliability of load prediction, probability of load occur- rence, soil or rock parameter characterization, bearing capacity, and deformation criteria. Serviceability criteria considering the total structure shall be addressed. Specific consideration should be given to soil-structure interaction and time-dependent soil behavior. Task 6 Develop detailed load factor design criteria for highway structure foundations in a format suitable for consideration by the AASHTO Subcommittee on Bridges and Structures. The recommended criteria shall be accompanied by a detailed commentary and examples of specific applications intended to facilitate understand- ing and use of the criteria. Task 7-Perform appropriate calibrations of the cri- teria developed in Task 6 against existing working stress design procedures. The calibration will be performed to establish the accuracy of the proposed criteria, to provide a comparison of the results obtained by the load factor and working stress designs, and to rationalize the differ- ences between these results. This shall be done for as many of the load and resistance criteria that were devel- oped as is necessary to validate the criteria. Task 8 Identify and comment on other sections of the AASHTO Bridge Specifications that may be affected by the proposed changes in the foundation design criteria. Task 9 Prepare and submit a final report containing the research findings and proposed load factor design criteria. Define the limits of applicability of the criteria. Identify additional research that may be needed for future development and refinement of the proposed criteria. Through December 31, 1988, research on the project is proceeding on schedule. The interim report was re- viewed and approved near the end of 1988. The scope of work was modified towards the development of a load and resistance factor design (LRFD) based specification. This will provide compatibility with the comprehensive bridge specification being developed under NCHRP Proj- ect 12-33. Project 24-5 FY '88 Downdrag on Bitumen-Coatecl Piles Research Agency: Texas A&M Research Foundation Principal Invest.: Dr. Jean-Louis Briaud Elective Date: June 15, 1988 Completion Date: June 14, 1991 Funds: $200,000 Foundation piles are subject to downdrag forces when- ever the soil surrounding them settles. The settlement of thick compressible soils under embankments can cause downdrag forces significantly larger than the structural load the pile must carry. This additional load may result in unacceptable settlements of the piles or even failure of part of the pile group. Downdrag forces have been reduced by coating the piles with bitumen. Several approaches for predicting and reducing downdrag forces have been published but little verification of design methods and material properties is available. Research is needed to verify and improve the present state of the art in both design and construction techniques for using bitumen-coated piles. This research is expected to improve design and testing procedures for practical use and to provide a basis for design confidence. The overall objective of this research is to develop practical guidelines for use of bitumen-coated piles in- cluding: (1) coating material specifications and tests, (2) design techniques, and (3) construction practices. It is