Manual Notice: 2011-1

From: Russel W. Lenz, P.E., Director, Construction Division

Manual: Pavement Design Guide

Effective Date: January 01, 2011

Purpose

This manual notice is intended to transmit changes to the content of the Pavement Design Guide.

Changes

Chapter 1, Section 1, Guide Overview

Under subsection, “Purpose,” added wording to the end of the first sentence to identify the projects described in this manual as “traditionally-let.”

Chapter 2, Section 1, Introduction

  • Added information on preliminary pavement design, pavement design concept conference, and pavement design standard operationg procedure.

Chapter 2, Section 2, Pavement Design Standard Operating Procedure (SOP)

  • Added new section on pavement design standard operating procedure.

Chapter 2, Section 3, District Pavement Engineer’s Role

  • Information was moved from Chapter 2, Section 2.

Chapter 2, Section 4, Pavement Types

  • Information was moved from Chapter 2, Section 3.
  • Figure 2-2. Generalized perpetual pavement design was updated. The “Construction Considerations” document was updated.

Chapter 2, Section 5, Pavement Type Selection

  • Information was moved from Chapter 2, Section 4.
  • Under subsection, “Principal Factors,” added information to the first paragraph describing alternate bidding for higher volume highways and recommended screening criteria for an alternate bid contract.
  • The new policy for alternate pavement design was added.
  • Under subsection Life-cycle Cost Analysis (LCCA) the term tool is replaced with an analysis in the third paragraph. In the last paragraph is modified to mention LCCA is only one of many processes.

Chapter 2, Section 6, Approved Pavement Design Methods

  • Information was moved from Chapter 2, Section 5.
  • Under subsection, “Introduction,” modified the bulleted list: combined the AASHTO design methods from two items into one and removed the experience bullet.
  • Under subsection, “Flexible Pavement System - Window version (FPS-19W)”:
    • in the first paragraph, added information about the preferred method for designing flexible pavements on higher volume highways (>10,000 ADT, 5 M ESALs) and added information about the availability of design procedure training
    • in the third bullet, added recommended data value to enter into the program for Central Texas climate
    • in the seventh bullet, added reference to graphs contained in the archived version of “Tex 117-F, Triaxial Compression for Disturbed Soils and Base Materials”
    • added bullet about the use of a mechanistic design check
  • Added new subsection, “Other Acceptable Design Procedures”:
    • Moved three paragraphs about the FPS-11 and 1993 AASHTO design procedure from “Flexible Pavement System - Window version (FPS-19W)” and created a new section. Added information on Pavement Design staff availability to consult on AASHTO design procedures.
  • Under subsection, “Basic Design Types,” added information on Type 4 design.
  • Under subsection, “AASHTO Design Procedure”:
    • title changed to “AASHTO Design Procedure (for flexible and rigid pavement designs)”
    • under second level subsection, “Rigid Design,” added projected retirement and scheduled replacement of DARWinTM 3.10
  • Added new subsection and corresponding content for, “Experience-Based Design..”

Chapter 2, Section 7, Pavement Design Categories

  • Information was moved from Chapter 2, Section 6.
  • Updated Figure 2-8. Design process for a new pavement or full reconstruction of pavement
  • Updated Figure 2-9. Design process for flexible pavement rehabilitation.
  • Updated Figure 2-10. Design process for rigid pavement rehabilitation.

Chapter 2, Section 8, Pavement Design Reports

  • Informaton was moved from Chapter 2, Section 7.
  • Under subsection, “Traffic Loads”:
    • Under second level subsection, “Tire Loads,” deleted the equation and equation definitions
    • Under second level subsection, “Traffic Projections”:

      added note about 20 yr. traffic projections and rigid structures

      added instructions to use Form 2124, Request for Traffic Data, for design purposes

      added “caution” note to complete Form 2124 for quick turnaround and other data options

      added paragraphs labels, “Units of Measurement” and “Loading Estimates” to existing content

    • added new information labeled, “Projections and Special Factors.” This section highlights Form 2124, Request for Traffic Data, and includes instructions to complete the form. Also included, other tools recommended to verify or determine traiffic data.

  • Under subsection, “Serviceability Index,” updated Figure 2-12. Pavement Performance Relationships
    • Changed the status of “Reliability (confidence level)” from second level subsection to first level subsection.
  • Under subsection, “Reliability (confidence level)”:
    • added the types of pavements the department reliability of 90 to 95 % is usually applied
    • added information about the type of pavements lower reliability may be applied
  • Under subsection, “Drainage Characteristics”:
    • in the second level subsection, “Internal (Positive) Pavement Drainage,” added a paragraph label, “Department Policy,” to the sentence beginning, “Aspects of the department’s policy are evident. . .”

Chapter 2, Section 9, Pavement Design Reports

  • Information was moved from Chapter 2, Section 8
  • Under subsection, “Pavement Design Report and Other Documentation”:
    • added new bullet item on PVR mitigation
    • added new bullet item on identification of the base grade chosen
    • added new second level bullet about alternate pavement design to the bullet item, “Design input values and output.”
  • Under subsection, “Completing the Pavement Design Report”:
    • In the table, “Completing the Pavement Design Report,” added bullet to step 1 to provide information on District Engineer’s responsibility. In step 2 of this table, actions were added and defined for district staff, district pavement engineer (DPE), and District Engineer (DE).

Chapter 3, Section 2, Geotechnical Investigation for Pavement Structures

  • Under subsection, “Preliminary Investigation”:
    • In the second paragraph starting, “Site inspections are frequently conducted. . .” changed text to encourage frequent site inspections in this stage.
    • In Table 3-1: Existing Data Sources, under column “External Data Sources,” changed the bullet order from second level to first level for items: Commercial Internet and Topographic. Change the bullet item, “university library files,” to “engineering library files” and changed the bullet order for this item from second level to first level.
    • Under Table 3-2: Reconnaissance Areas of Interest:, in the bullet named, “Surface Soil Exploration,” after the last second level bullet in the list, added reference to the test procedure required if sulfur-bearing compounds are detected in the soil.
    • In the second level subsection, “Preliminary Evaluation,” under bullet, “Structural Support,” added information on the condtions to use triaxial classification
  • Under subsection, “Subsurface Exploration”:
    • in the second level subsection, “Material Evaluation,” under bullet, “Swell potential”:

      added guidance and reference information on the use of potential vertical rise (PVR)

      added the recommended test procedure for determining PVR

      added recommendations for best conditions to determine PVR

      added specific criteria that determine whether a pavement structure design proposing to include PVR reduction strategies will require Construction Division review and approval or review only

      added a list of items pavement designers should address in their submission for review and approval in conjunction with the pavement design.

      added criteria that would allow designs incorporating PVR mitigation.

Chapter 3, Section 3, Flexible (Unbound) Base Selection

  • Added new reference, “Flexible Base Selection Guide,” along with corresponding description of the guide and its contents. Added reference to memo, “Use of Grade 1 Flex Base,” along with the memo’s effective date. Describes conditions when use of Grade 1 flexible base will require justification.
  • Added new subsection, “Flexible Base Description.”
  • Under subsection, “Flexible Base Description”:
    • moved information referencing Item 247 from “Flexible (Unbound) Base Selection.” The number of different grades changed from four to five. Added Grade 5 to the sentence, “Grade 1 and Grade 2 base materials are the primary base material grades for base course performing as a structural layer in a pavement structure.” Added guidance on use of Grade 4.
    • reorganized and formatted information of each grade of flexible base, from 1 through 5, into a bullet list. Added new information describing the characteristics and best use of each grade.
  • Added new subsection, “Base Selection.”

Chapter 3, Section 5, Hot Mix Asphalt Concrete Pavement Mixtures

  • Under subsection, “General”:
    • added temperature parameters for creating warm mix asphalt (WMA)
    • added information on benefits of using warm mix asphalt (WMA)
  • Under subsection, “Use of Perpetual Pavements”:
    • reformatted the information about stone matrix asphalt. Added conditions when RBL should be considered.

Chapter 3, Section 8, Hydraulic Cement Concrete

  • Reformatted the information in this section and created four subsections:
    • Primary Ingredients
    • Determining Ingredient Proportions
    • Creating Workability, Durability, and Adequate Strength - Changed wording for the sentence, “For the concrete to have good workability, durability, and adquate strength, two conditions are to be met:” to “. . . two condtions must be met:”
    • Three Concrete Classes - reformatted the information for concrete classes P, K, and HES into a table.

Chapter 3, Section 9, Geosynthetics in Pavement Structures

  • Under subsection, “Geosynthetics for Geotechnical Reinforcement,” in the third paragraph, removed “and will concluded in late 2006.” from the sentence beginning “Addtional research on the contribution of geogrid. . . “

Chapter 5, Section 1, Overview

  • Reorganized the information

Chapter 5, Section 2, Types of Flexible Pavements

  • Under subsection, “Types of Hot Mix Asphalt-Surfaced Pavements,” in the last sentence of the last paragraph, added “cement” to the list of typical stabilizers.
  • Under subsection, “Perpetual (HMA) Pavement”:
    • removed reference to “heavy duty” mixes and its uses
    • added conditions for the use of stone matrix asphalt and the approval required for this substitution.

Chapter 5, Section 3, FPS-19W Design Parameters

  • Reorganized the information and created two subections, Program Tools and Data Input Components.
  • Under subsection, “Program Tools,” added information to indicate the manual information supersedes the guidance provide on the program “Help” screen.
  • Under subsection, “Data Input Components,” added new table, Table 5-1: FPS-19W Design Input Requirements.
  • Under subsection, “General Inputs”:
    • in the second level subsection, “Program Main Menu,” the information was reformatted to numbered list. A caution note to prevent program crashing was added
    • in the second level subsection, “Basic Design Criteria (Card #3),” and in the paragraph named, “Analysis Period,” corrected format of the caution note.
    • In the paragraph named “Minimum Serviceability Indes,” changed the value of ESALs for highways of higher importance from “exceeds 1,000,000” to “5 M.” For the highways with moderate traffic, changed the ESAL value from “500,000 to 1,000,000” to “1 M to 5 M ESALs.” Changed the definition of low volume highways from “less than 1,000 vehicles per day (vpd)” to “less than 3,000 vehicles per day.” Changed the value of cumulative ESALs from “less than 500,000” to “less than 1,000,000.” Changed the terminal serviceability of low volume highways from “2.5” to “2.0 to 2.5”

      Updated Figure 5-1. Added an interpretation of Figure 5-1. Pavement Performance Relationships. Added information on factors that shorten the serviceability over time and how it can be restored.

      In the paragraph named, “Design Confidence Level,” added confidence level recommendations by ESAL values.

    • Table 5-2. Output Variations was originally Table 5-1. This table’s contents were completely updated. Under column header, “Traffic Volume,” a “High” designation was added and each traffic volume level was defined by an ESAL value. Column headers, “Initial SI” and “Termin SI” were added. Column headers, “Initial Performance Period” and “Overlay” were modified with “T1” in the units of measurement.
    • in the second level subsection, “Program Controls (Card #4),” defined output pages further
    • in the second level subsection, “Construction and Maintenance Data (Card #7),” in the paragraph named, “Initial Serviceability Index,” added recommended index values based on pavement condtions.

      In the paragraph named, “Serviceability Index after Overlay,” changed the index value of 2-3 in. overlays from “4.0” to “4.0 - 4.2.” For thick overlays, changed the index value from “a higher value” to “up to 4.5.”

    • in the second level subsection, “Detour Design for Overlays (Card #8),” added caution note to prevent program crashing. Added Pavement Design Task Force’s recommendation for removing possible cost bias in accounting for user costs on low- to medium-volume highways.
  • Under subsection, “Traffic Inputs”:
    • added reference to internal Form 2124, Request for Traffic Data, for design traffic requests. Added guidance noted by the Pavement Design Task Force (PDTF, 2009) to districts to review traffic analysis for highway design report to verify data reasonableness.
    • in the second level subsection, “20-Yr. 18-kip ESALs (One Direction), added information that describes when lane distribution factors are appropriate
    • in the second level subsections, “Average Speed in the Overlay Direction” and “Average Speed, Non-overlay Direction,” added recommended value to enter to avoid computation of associated user costs in the overall estimate of project costs.
  • Under subsection, “Environment and Subgrade”:
    • updated the information on this feature’s effectiveness and added best use of this feature. Added recommendation of the use of Tex 124-E, Determining Potential Vertical Rise, for evaluation of mitigation of soil movement. Added reference to Chapter 3, “Materials Investigation and Selection Information,” for more information on approval requirements for soil movement mitigation.
    • in second level subsection, “District Temperature Constant,” added default value which corresponds to a Central Texas value. Added specific guidance for use of the default value in program FPS-19.
    • in second level subsection, “Swelling Probability,” added default value and provided conditions when the default value should not be used
    • in second level subsection, “Potential Vertical Rise,” explained the consequence of using zero in “Swelling Probability” and added reference to Chapter 3, Section 2, Geotechnical Investigation for Pavement Structures, for designs to mitigate potential rise and provides conditions on how and when it should be used.
    • in the second level subsection, “Swelling Rate Constant,” added the effect of this field when zero is entered for Potential Vertical Rise or for Swelling Probability.
  • Under subsection, “Material Parameters”:
    • in the second level subsection, “Modulus, E (ksi),” in Table 5-3: Recommended Material Design Modulus Values, the following changes were made:

      Table 5-3 was moved from Table 5-2.

      Material Type name, Dense-graded Hot (Warm) Mix Asphalt, was updated by adding “(Warm).” For the Dense-graded Hot (Warm) Mix Asphalt, the Design Modulus content and values were modified.

      Material Type name, Permeable Friction Course, the Comment field was updated.

      Material Type, Performance Design Mixtures, the Design Modulus values were modified. The Comment field was modified, included changing the ksi value from 350 ksi to 500 ksi.

      Material Type, Stone-Matrix Asphalt, the Design Modulus content was modified.

      Material Type, Flexible Base, modified Comment field.

      Material Type, Cement Stabilized Base, modified Comment field.

      Material Type, Lime or Cement Stabilized Subgrade, modified Comment field.

      Material Type, Subgrade, modified Poisson’s Ratio and Comment fields.

    • in the second level subsections, “Minimum Depth” and “Maximum Depth,” modified the last bullet starting, “For subgrade, use the average depth to bedrock. . .”
    • in the second level subsection, “Poisson’s Ratio,” added more guidance for selecting a value to enter
    • in the second level subsection, “Check (CHK) Column,” changed the designated job title from “responsible engineer” to “project engineer” for the last sentence starting, “Leeway is granted to. . . “
  • Under subsection, “Modified Texas Triaxial Check”:
    • part of the information was reformatted into step-action Table 5-4: Texas Triaxial Design Check. Steps 6 and 7 are new content.
    • the other part of the information was reformatted into second level subsection, “Subgrade Triaxial Class Number.” Added details about specific archived versions of the Tex-117-E reference. A table was created to display information on the design check routine.

Chapter 5, Section 4, Pavement Detours and Pavement Widening

  • Under subsection, “Pavement Detours”:
    • content was reformatted, included the addtion of a bullet list for some content. Added information on estimating traffic loading when a detour is in effect and provides guidelines to request traffic data for detours.
    • in second level subsection, “Structural Design of Detours,” added suggestion to use the falling weight deflectometer (FWD). Added proven design strategies the districts may employ. Added an alternative option of the modified TTC check. Added suggested routine, TRAFFIC6, or similar routine to estimate cumulative ESALs over the detour design life. Parts of this section were used to create “Material and Construction Considerations for Detour Structures.”
    • in second level subsection, “ Material and Construction Considerations for Detour Structures,” added details about preparing subgrade and the resulting pavement structure. Added a new construction consideration for detour structures that involve placing 4 in. of flexible base and provides the resulting condition. Added instructions to recycle detour structures when no longer needed.

Chapter 5, Section 5, Perpetual Pavement Design and Mechanistic Design Guidelines

  • Under subsection, “Designing a Perpetual Pavement using FPS-19W”:
    • reformatted content into Table 5-6: Designing Perpetual Pavement Using FPS-19W and created a list of corresponding guidance for each step

      At step 6, added new information about a minimum “time to first overlay.”

      At step 7, added new information about renewing the surface at periodic intervals and added new note “Analysis period is not pertinent to perpetual design.”

  • Under subsection, “Checking the Proposed Design for Compliance with Limiting Strain Criteria”:
    • changed the value for “the maximum tensile strain at the bottom of all HMA layers” from “52 µ-strain (< 70)” to “46 µ-strain (< 70)”
    • changed the value for “the maximum compressive strain at the top of the subgrade” from “124 µ-strain (<200)” to “115 µ-strain (<200)”
    • added recommendation to check strain levels from ATHWLD with computuations outside the current FPS-19W program

Chapter 8, Section 4, Recommended Input Design Values

  • Under subsection, “Input Values,” removed “subbase” from the third bullet. The item originally read “Effective Modulus of Subbase/Subgrade Reaction, pci”
  • Under subsection, “Effective Modulus of Subgrade Reaction: k-value”:
    • reformatted the information and created two second level subsections, “TxDOT-Required Base Layer Combination” and “Selecting Appropriate Strength”

      In “TxDOT-Required Base Layer Combination,” added an option for designers to use a higher k-value. Added instructions to determine and respond to k-value.

  • Under subsection, “Load Transfer Coefficient,” in Table 8-1: Load Transfer Coefficients, modified the coefficient value when the answer is “yes” to both criteria.
  • Under subsection, “Reliability, %”:
    • added design ESALs value after the phrase, “a reliability of 95% should be used for rigid pavement. . .”
    • added information for “a reliability of 90%”

Chapter 8, Section 5, Determining Concrete Pavement Thickness

The first sentence in the first paragraph, changed the phrase from “round the thickness up to the next higher whole inch” to “round the thickness up to the nearest full or half inch.” Changed the values in the example.

In the bulleted items, values were changed. These changes are explained in the two paragraphs following the bulleted list.

Chapter 8, Section 6, Concrete Pavement Design Standards

In the first bullet, the beginning value changed from “8” to “6.”

Chapter 8, Section 7, Bonded and Unbonded Concrete Overlays

Under the main section, a large part of the content was rewritten and updated.

  • The new subsection, “Overlay Thickness Design,” was added.
    • The new second level subsection, “Determination of Effective Slab Thickness by Condition Survey Method,” was added.
  • The new subsection, “Joints and Cracks Adjustment Factor, Fjc,” was added.
  • The new subsection, “Durability Adjustment Factor, Fdur,” was added.
  • The new subsection, “Fatigue Damage Adjustment Factor, Ffat,” was added.
    • The second level subsection, “Steel Design,” was added.
  • The new subsection, “Unbonded Concrete Overlays,” was added.
    • The second level subsection, “Overlay Thickness Design,” was added.
    • The second level subsection, “Determination of Effective Slab Thickness by Condition Survey Method,” was added.
    • The second level subsection, “Steel Design,” was added.

Chapter 12, Section 6, Super Heavy Load Evaluaton Process

In the first sentence in this section, the value for the “trailer tire load” changed from “exceeding 5,000 lb.” to “exceeding 6,000 lb.”

Contact

Contact the Construction Division, Materials & Pavements Section (CST-M&P) at (512) 465-3686 for further information regarding the methods in this manual.

Archives

Past manual notices are available in a pdf archive.


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