Bridges & Structures

Geotechnical Aspects of Pavements Reference Manual

Chapter 2.0 State Agencies

2.1 Host Agency And Other Identified Guests

Various state agencies take different approaches to pavement design. Local practices often vary in terms of 1) the methods for obtaining subsurface information and laboratory testing in relation to pavement design; 2) design guides followed by the agency (usually a variation of current or previous AASHTO guidelines); and 3) field construction monitoring for subgrade approval and pavement component approval, as well as contractors' quality control requirements for pavement component construction. This chapter presents issues related to each of these items, discussed by a representative of the agency conducting this course. A questionnaire for an agency to document and evaluate their own practice in relation to geotechnical aspects of pavement design is provided.

Issues that should be specifically addressed by each agency include:

• Current subsurface investigation practices and procedures for new construction, reconstruction, and rehabilitation pavement projects, including in-house facilities (field and laboratory) and outsourced capabilities, noting prequalification and QC/QA requirements for outsourced programs.
• Special or complex subsurface conditions (e.g., soft soils, frost susceptible soils, swelling soils, collapsible soils, caliche, karst topography, etc.) encountered in this state.
• The standard pavement systems (including pavement type, base and subbase layers, drainage requirements, and subgrade treatments) currently used by the agency.
• Current design approach (i.e., AASHTO referenced to year of provision, state agency procedure, or other) and implementation status of empirical-mechanistic design approach.
• Current pavement projects requiring special or complex procedures.
• Construction and design verification procedures, including determination of subgrade stabilization requirements during construction (e.g., undercut, use of geosynthetics, lime, etc.).
• Agency organizational structure, as it relates to personnel involved with pavement material evaluation, design, construction, and maintenance.

There are also many impediments such as time, money, and personnel to performing an adequate subsurface investigation program for pavement design. Agencies should always be aware of these issues and the continual work to remove such impediments. The cost benefit of performing an adequate subsurface program will be discussed in Chapter 4. However, a cost-benefit analysis as evaluated in Pavement Management Programs could substantially assist individual states in assessing their own priorities.

2.2. Questionnaire On Geotechnical Practices In Pavement Design

1. Which of the following pavement design methods (or modification thereof) is currently used by your agency? (Please circle appropriate method and provide details of any modifications.)
   • AASHTO 1972
   • AASHTO 1986
   • AASHTO 1993 with 1998 Supplement
   • Mechanistic-Empirical design (please identify reference method) ____________________
   • Other (please identify or describe) ____________________

    
    
    

2. What are the design performance periods (a.k.a. design life) assigned to each of the following type of roads in your state?

   Type	Performance Period (# or years)
   	Asphalt	PCC
   I Secondary
   II Primary
   III Interstate and Freeway

   Comments:
    
    

3. Does your current design achieve the performance period? (If no, what is the typical actual performance period, or range?)

    
    
    

4. What method(s) or test(s) do(es) your state use to evaluate subgrades for inputs values (e.g., CBR, R-value, resilient modulus, etc.) to pavement design?

    
    
    

5. Which group within your agency (i.e., pavement design, geotechnical, hydrology, or other) is responsible for design of pavement drainage?

    
    
    

6. Of the following, which method(s) do(es) your state perform for evaluating subgrade conditions in the field?

   Method	Frequently	Sometimes	Never
   Remote sensing* (e.g., air photo, landsat photos, etc.)
   Geophysical Non-destructive Tests*
   Falling Weight Deflectometer, FWD
   Ground Penetrating Radar, GPR
   Surface Resistivity, SR
   Seismic Refraction
   In-situ Investigation*
   (Cone Penetration Test, CPT)
   (Dynamic Cone Penetration Test, DCP)
   (Standard Penetration Test, SPT)
   Disturbed sampling (usually with borings)
   Undisturbed sampling (usually with borings)

   * Please list the equipment that you have available and identify it as 1) in-house or 2) outsourced.

    
    
    

7. How is the frequency and spacing determined for borings along the alignment (e.g., standard spacing - provide, available info, site recognizance, etc.) and where are the borings located (e.g., centerline, wheel path, shoulder, other)?

    
    
    

8. What method(s) or test(s) do(es) your state use to evaluate/control subgrade construction?

    
    
    

9. Which of the following stabilization methods are used in your state?

   Stabilization Method	Yes	No
   Undercut and Backfill
   Thicker Aggregate
   Geotextiles and Aggregate
   Geogrids and Aggregate
   Cement
   Lime
   Lime-Flyash
   Lime-Cement
   Lime-Cement-Flyash
   Bitumen Modification
   Other - Please provide details