4.4.6 Geotechnical Surveys

Preliminary geotechnical surveys can vary from simple, visual inspections to various forms of subsurface exploration, depending on information needed. Once preliminary bridge, retaining wall and sound wall locations are determined, preliminary geotechnical surveys can be performed. Preliminary geotechnical surveys are performed to guide early project layout and design and determine feasibility of the preliminary design and limitations on construction staging. Preliminary geotechnical survey can help determine if certain design options are viable. (i.e., below grade/tunnel options). Preliminary geotechnical testing also serves to determine if additional, more in-depth geotechnical testing is needed.
For large structures, preliminary geotechnical surveys form the basis for more rigorous testing. On major projects, a small number of preliminary borings must be obtained to aid in the preliminary project layout.
Geotechnical surveys for pavement design may also be needed and may include roadway pavement testing such as Falling Weight Deflectometer (FWD) testing.
Considerations for performing preliminary geotechnical surveys include:
  • Consult existing as-built construction plans and District laboratory staff to obtain existing test information if available – this can assist in determining the extent of additional testing that might be needed;
  • Obtain ROE prior to entering private property for geotechnical testing;
  • Locate utilities prior to testing – geotechnical firms will typically do this prior to testing, however, additional coordination with the geotechnical firm and utility companies to ensure this happens should be performed; and
  • Coordinate with District environmental staff for any type of hazardous soil materials in the testing areas.
4.4.6.1 Preliminary Pavement Design and Report
A preliminary pavement design is performed early in project development to ensure a viable design is generated. The pavement structure represents one of the costliest items in a typical highway project budget. The objective for completing a preliminary pavement design early is to select a pavement structure capable of carrying traffic loads safely, comfortably and with minimum physical deterioration and to ensure the project is adequately funded for the desired pavement section. Waiting to develop the pavement design often results in reduction of the pavement structure due to restricted project funding.
The cost of different pavement options should be evaluated prior to pavement section selection.
A pavement design and pavement design report are required for the following project types that are over 500 ft. long:
  • New location (flexible and rigid);
  • Reconstruction (flexible and rigid);
  • Rehabilitation (3R) (flexible and rigid); and
  • Unbonded concrete overlays of existing rigid pavements.
Each District maintains and updates a pavement design standard operating procedure (SOP). The SOP will also establish the final authority for pavement design within the District.