General Report Requirements
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Geotechnical reports should contain an interpretation of the type and layering of soil and rock, and groundwater levels that are representative of the site. Estimates of soil and rock strength parameters with supporting testing or documentation will be presented. The report should have an assessment of foundation type(s) (e.g., piling, spread footings, drilled caissons, micropiles, etc.). In addition, cut slope design, fill placement, lift thickness recommendations, stability analysis, and settlement considerations should be provided when these items are germane to the project. The report should discuss past and potential coal mining, gas wells, quarriable stone, and other background information when pertinent. Provide a brief discussion of the subsurface investigative sampling and testing procedures used and any deviation from our standards. Include a brief discussion of the laboratory testing methods used. The report should contain a discussion of the relevant geologic structure including strike/dip of strata as it relates to cut/fill slopes and foundations. Foundation bearing elevations, including pile tips, and shaft/micropile socket tops/tips, should be recommended. The report should provide recommendations and conclusions, including critical assumptions that the recommendations are based on. It should point out any geotechnical hazards and precautions needed for the project. Other failure modes (e.g., instability, excessive settlement, lateral squeeze, mine subsidence, scour, etc.) should be addressed, and remedial measures be recommended when applicable. Controlled fill placement (vert.-ft./week) and quarantine times in Lieu of monitoring are preferred. Potential problems that require further investigation before finalizing the design should be pointed out. The report should have a list of recommendations to be noted on the plans. The report appendix should have as a minimum the following: boring plan, boring logs, color core photos, laboratory test sheets, calculations, and analysis screenshots (screenshots of input and output results are preferred over lengthy printouts or raw data).
Bearing resistance for spread footings, drilled shafts, and concreted in piles should be calculated using either the general bearing resistance equation or the lower bound equation presented in the 2012 LRFD Bridge Specifications. The selection of the equation should be based on the Rock Mass Rating (RMR) presented in the 2012 edition of LRFD. The GSI system presented in later editions of LRFD is not to be used. A resistance factor of 0.45 should be used for both equations. Side resistance, when applicable, should be also calculated by the method presented in the 2012 edition of LRFD. A resistance factor of 0.55 should be used for side resistance (0.40 for uplift). Both these resistance factors should be reduced based on non-redundancy and sloping strata or may be increased based on field testing per LRFD and as recommended in the report.
For driven pile foundations, an end of driving analysis using a wave equation (such as the GRLWEAP program) should be performed showing that the selected pile/hammer combination can set the pile to the factored resistance of two times (2X) the maximum factored load without damaging the piles.
Lateral earth pressure coefficients should be included and their application to fixed and flexible abutments, and walls should be discussed. Lateral analysis parameters for software such as Lpile should be recommended as needed. Soil-structure interaction factor(s) for buried structures should be provided, when applicable.
Stability analysis should be performed on slopes greater than 10 feet in height and soil/rock parameters should be based on laboratory testing results or the WVDOH standard presumptive values. Stability analysis should considered normal and high groundwater levels in each of the critical sections.
Settlement analyses should consider preconsolidation pressure for cohesive soils and the report should discuss whether the soil is considered overly or normally consolidated and why.
Where cut and/or fill slopes are associated with the project, the geotechnical reports should provide slope and benching, and/or fill benching recommendations and the need for SE (and potential source of SE) on a section, or station-to-station, basis. Cut and fill slope designs should be in accordance with the WVDOH 400 series Design Directives (DD’s). Any deviation from our DD’s should be demonstrated using the CRSP program using the WVDOH presumptive parameters (see “Cut Slope Guidelines” on the web site) or field observations/back analysis.
For small bridges with a single foundation type, the WVDOH prefers an 8.5”x11” letter report with a body of 5 pages or less and the attachments mentioned in the first paragraph above. For larger bridges, roadway reports, or projects with more complexity, a full report in 11”x17” format is preferred. For box culverts, large pipe culverts, and simple pile wall designs, a single, 8.5”x 11” data sheet with boring logs and supporting information attached, is preferred.
All geotechnical reports and datasheets, except for geotechnical data reports, are to be sealed by a registered engineer practicing geotechnical engineering in the state of West Virginia.