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Section 9: Pavement Design Reports

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Projects Requiring Pavement Design and Pavement Design Reports

A pavement design and a pavement design report are required for the following projects that are over 500 ft long:

Tie-ins, such as bridge approaches, do not require pavement designs when following department or district proven standards. A new design is not necessary. Previously approved design can be used if through an analysis, considering traffic, environmental and subgrade conditions, the pavement design analysis yields the same thickness. However, adjustments to designs thicknesses and specific conditions, even within a project, should be considered in the design process for economic purposes.

HMA overlays, approximately 2-in. thick and less, are considered a preventative maintenance treatment; therefore, a pavement design report is not required where adequate structural capacity is documented. Considering the significant investment thin overlays represent; these treatments should be taken into account in an overall pavement preservation program. An analysis should be performed that substantiates the appropriateness of this maintenance strategy.

The pavement design for special cases will typically be based on engineering judgment, historical performance, district policy, and other guidelines (e.g., this guide, industry guidelines, and research findings). A design report may be required for documentation purposes.

The following list provides examples of special cases that require documentation of the criteria and rationale for the strategy selected for projects greater than 500 ft long:

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  • approaches on a bridge replacement
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  • detours
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  • pavement widening including shoulders
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  • HMA overlays of rigid pavements. The only “rational” approach generally available to department engineers for designing a HMA overlay to an existing rigid pavement is the AASHTO Overlay procedure (automated in DARWin™). However, this process is highly subjective.
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  • bonded rigid overlays on rigid pavements
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  • thin whitetopping of flexible pavements.

For design categories not covered above, contact the district pavement engineer for guidance about recommended design procedures and documentation requirements.

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Pavement Design Report and Other Documentation

A pavement design report is a formal engineering document that presents all analyses, data, policies, and other considerations used to design the structural aspects of a pavement. The pavement design report should include the following:

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  • Cover sheet showing highway designation, district, county, project CSJ, geographical limits, and signatures of persons involved in the preparation and approval.
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  • Narrative discussing the overall objective, site particulars (location, facility type, soil conditions and subgrade Texas Triaxial Classification [TTC], drainage considerations), PMIS data analysis/pavement condition surveys for 3-R projects, conclusions, and recommended pavement structure. The narrative should include a discussion of the factors that significantly affect pavement performance, and a summary of laboratory tests conducted on any materials extracted from the existing structure.
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  • If the pavement structure selected is different from the structure recommended by the design procedure, a discussion of the selection process must be included in the report.
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  • Location map. Maps should be detailed enough to distinguish urban or rural project locations, and the presence of water features such as lakes, streams, etc.
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  • Soils map of the project area with a brief description of each type of soil located within the project area. Provide information pertaining to shrink/swell potential and plasticity.
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  • The study of the presence of sulfate bearing compounds, organic content, and any mitigation technique selected.
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  • Determination of PVR mitigation requirements, if any. Obtain and provide approval to use PVR mitigation techniques when roadway characteristics do not meet policy criteria (see Chapter 3, Geotechnical Investigation for Pavement Structures)
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  • Existing and proposed typical sections. For the proposed structure, clearly define the various pavement layers, thickness, and materials with specification item. For the existing structure, sections should be as detailed as possible. Proposed or existing positive drainage systems should be indicated on the typical sections.
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  • The project specific factors used for selecting the pavement type.
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  • TPP Traffic Data and any adjustments to the traffic data.
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  • Identification of the base grade chosen, whether shown on the typical section or in the report text. Provide approvals for use of Grade 1 base, if required (see Chapter 3, Flexible (Unbound) Base Selection, for criteria and requirements).
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  • Results of NDT to characterize the existing structural condition (including the MODULUS backcalculation summary).
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  • Design input values and output.
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    • FSP-19W summary, modified Texas Triaxial check, mechanistic checks, stress analysis, etc. for flexible pavement.
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    • AASHTO (DARWin or TSLAB86) design summary for rigid pavements.
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    • Alternate pavement design, if appropriate, using past successful practices.
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  • Conclusion. The pavement design report will conclude with a recommended pavement design based on the data, analyses, and procedures included in the report. The information included in the report should be a synthesis of all work performed to arrive at the recommended pavement structure.
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  • Appendices.
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    • Surface Aggregate Selection Form 2088 (Wet Weather Accident Reduction program, flexible pavements only)
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    • Additional appendices (results of borings, material lab tests, raw PMIS data, life-cycle cost analysis, drainage analysis, design exceptional approvals, etc.), as needed.

For other reporting requirements, contact the DPE for guidance.

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Completing the Pavement Design Report

The pavement design report may be prepared by anyone with knowledge of the specific project under development and familiar with the analysis tools used. The first licensed engineer in the chain of responsibility will review and sign the report. After completion of the pavement design report development phase, please complete the report by using the following procedure:

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Anchor: #i1007738Table 2-5: Completing Pavement Design Report

Step

Action

1
  • The District Engineer (DE) provides approval of final pavement design. In metropolitan districts, the DE may delegate final pavement design approval to the District Director of Construction or the District Director of Transportation Planning and Development for projects less than $20 million.
  • The district pavement engineer (DPE) reviews the technical content of the report and appropriateness of the design for conditions cited within the report.
2
  • Upon DPE approval of the report, the DPE signs and provides their respective profesional engineer (PE) license number on the report cover.

    NOTE: If the district does not have an assigned DPE, the report must be forwarded to the director of CST-M&P for review and endorsement.

  • Forward to the DE for approval. If the report is approved, the approval is indicated by the DE signature and date on the report cover sheet.
3

Add the statement “This document is released for the purpose of interim review and is not intended for bidding, construction, or permitting purposes.” after the engineer’s license number on the approved pavement design report, in accordance with paragraph 137.33[e] of the Texas Engineering Practice Act.


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Pavement Design Report Review and Archive

CST-M&P archives pavement designs for the state for the purposes of forensics and knowledge-based pavement performance. Districts are asked to transmit a scanned copy of completed pavement design reports to CST-M&P (Flexible Pavement and Rigid Pavements Branches).

Archived reports can be viewed on the TxDOT intranet (site not available to internet users) at the “Plans Online” page located at http://iplans/ under the heading, “Pavement Design.”


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