MDOT SHA Access Manual - Geotechnical Guidance

Pavement and Geotechnical Design Requirements

The recommendations contained in the final pavement and geotechnical report must appear in the plans and specifications developed for the project. A copy of the final pavement and geotechnical report must be provided to the contractor.

Highway cut and fill slopes shall be 2:1 or flatter. The factor of safety shall be 1.3 or greater for all slopes that impact Maryland Department of Transportation State Highway Administration (MDOT SHA) roadways. Foundation soils and groundwater shall be considered when determining the Factor of Safety. When surface water features, including storm water management facilities, are adjacent to cut or fill slopes, the presence of the surface water feature shall be considered in the stability analysis for the slope.

All material used in highway embankment construction or as backfill in areas that impact MDOT SHA roadways must meet the minimum requirements consistent with its intended use.

When coarse, open-graded material is used to bridge unstable highway embankment foundation soils in conformance with 204.03.02, a geotextile shall be used as a separator between the coarse, open-graded material and the native and embankment soils.

All highway embankment foundation and highway subgrade shall be test rolled. Where highway embankment is being placed over existing pavement, the bound materials in the pavement shall be removed prior to placing embankment material.

All pavements shall be designed in accordance with the 1993 AASHTO Guide for Design of Pavement Structures and MDOT SHA Pavement and Geotechnical Design Guide. All pavement materials selected for placement in the pavement section shall be in accordance with the latest MDOT SHA Standard and Supplemental Specifications and Provisions for Construction and Materials.

Pavement edge drain (longitudinal underdrain) shall be constructed along the entire base widening/reconstruction along the entire project limits. The longitudinal underdrain shall be placed behind the curb in closed sections and at the outside edge of the shoulder in open sections. The longitudinal underdrain shall be let out at low points and into other drainage structures wherever possible at intervals not to exceed 250 ft. The minimum diameter of the longitudinal underdrain shall be 6 in. The location of underdrains, pavement edge drains (longitudinal underdrain), outlets and other subsurface drainage, and any detail modifications shall be shown on the Developer’s construction drawings.

Geotextiles used in subsurface drainage, separation, and permanent erosion control applications for MDOT SHA roadways shall be in conformance with AASHTO M288. When used in pavement edge drain (longitudinal underdrain), the apparent opening size and permittivity of the geotextile must conform to the filtration and flow requirements for both the subgrade soils and graded aggregate base.

Do not place ponds or infiltration trenches within 15 ft. of an MODT SHA roadway or shoulder.

Grading that impacts MDOT SHA roadways must be in accordance with Section 200 of the latest MDOT SHA Standard and Supplemental Specifications and Provisions for Construction and Materials unless otherwise specified in the final pavement and geotechnical report provided by the developer.

For additional information visit the MDOT SHA Access Manual.