Geotechnical Report Guidelines
The Developer shall develop and submit a Final Geotechnical Report for the project to the Office of Materials and Technology Geotechnical Explorations and Pavement Divisions. The report shall contain the Developer's plans for addressing all soils, rock, groundwater, existing pavement, and new pavement issues on the project impacting Administration hihgway property. A geotechnical engineer, who is a registered professional engineer, and who shall also seal the Final Geotechnical Report, shall supervise the work. The Developer shall obtain all soils and pavement information necessary to properly complete the Final Geotechnical Report, and the design and construction of the project. The Developer shall perform borings, sampling, in-situ and laboratory testing, analysis, and design required for this purpose. All subsurface investigations, including sampling and laboratory testing, shall be performed in accordance with Maryland State Highway Administration Standard Specifications for Subsurface Explorations. If a specialized test is not covered by these specifications then testing shall be performed in accordance with the 1988 AASHTO Manual on Subsurface Investigations, AASHTO Standards and ASTM Standards. The existing structural capacity of all impacted shall be determined through in field non-destructive testing either a formal visual condition survey or deflection testing and/or pavement borings. Laboratory testing shall be performed in an AMRL or Maryland SHA certified laboratory. The recommendations contained in the Final Geotechnical Report shall be incoporated into the plans and specifications developed for the project. The Developer Shall be responsible for utility clearance and any traffic control required for his investigation. The appropriate District Office shall approve the Developer's Maintenance of Traffic Plan for the subsurface and pavement investigation. Any investigative methods that pose a hazard to the general traveling public shall not be used. Any borings taken in roadway or shoulder areas shall be backfilled in kind with material before the area is re-opened to traffic.
The following shall be included and addressed in the Final Geotechnical Report. Additionally, other items deemed important by the Developer shall also be included.
- Soil, rock, soil moisture and groundwater conditions;
- Existing functional and structural condition of all impacted roadway surfaces within project limits;
- Traffic data used for pavement design. Including, but not limited to the following: Average daily traffic (ADT), percent FHWA Class 5 trucks or greater, directional Distribution, truck weight information (truck factor), and lane distribution;
- Subgrade strength used for design of pavements expressed in terms of resilient modules, CBR values are acceptable;
- Topsoil, pH adjustment and nutrient requirements that will allow vegetative growth to be established on slopes;
- The existing pavement structure of all materials above subgrade and the subgrade soil classification and moisture conditions of all roadways and shoulders within the project limits. Existing roadways and shoulders considered to be impacted include the following: pavement resurfacing areas, pavement areas adjacent to widening locations, pavement reconstruction areas, pavement areas adjacent to widening locations, pavement reconstruction areas, and any and every pavement location subjected to traffic during construction under the maintenance of traffic plan;
- Specifications for all materials to be used in embankment or as backfill;
- The suitability of excavated material for re-use as embankment or trench backfill on the project;
- Analysis and design of all cut slopes including methods proposed for use in controlling groundwater seepage, erosion and surficial instability;
- Analysis and design of all embankments, including internal drainage design of side hill fills and methods proposed for use in controlling erosion and surficial instability;
- Slope stability analyses shall be performed for all slopes in excess of 12 ft in height. Foundation soils and proposed storm water management practices shall be considered when determining the Factor of Safety of less than 1.3, the report shall identify modifications to the slope to provide a minimum Factor of Safety of 1.3;
- The methods proposed for dealing with unstable embankment foundations;
- Methods of subgrade preparation including the methods proposed for dealing with areas of unstable subgrade;
- Ability of native soils to provide vertical drainage;
- Proposed methods for dealing with groundwater and existing subsurface drainage systems including existing pavement edge drain (longitudinal underdrain) systems;
- Geotextiles to be used in subsurface drainage, separation, and permanent erosion control applications;
- If rock is encountered, proposed methods of rock excavation (ie. blasting or non-blasting) and any necessary safety requirements;
- Proposed methods for dealing with unusual geologic or man-made conditions particular to the area (ie. sinkholes, contaminated soils, underground storage tanks, etc.);
- Pre-rehabilitation repairs to existing roadway prior to final resurfacing, i.e. full-depth and partial-depth patching, grinding, milling, etc.;
- Pavement design recommendations for existing and new roadways. Recommendations shall include material selection and thickness.
- Structural capacity of shoulders to support maintenance of traffic (MOT) and/or MOT pavement sections;
- Proposed method for dealing with any significant change in the existing pavement cross slope or elevation;
- Comments regarding pavement drainage;
The Final Geotechnical Report for any portion of the project shall be submitted with or before construction for earthwork grading for that portion of the project.
Geotechnical Design Requirements
The recommendations contained in the Final Geotechnical Report shall be incorporated into the plans and specifications developed for the project. A copy of the Final Geotechnical Report shall 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 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 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 pavement shall be done in accordance with the "1993 AASHTO Guide for Design of Pavement Structures" and MDSHA Pavement Design Guide. All pavement materials selected for placement in the pavement section shall be in accordance with the latest MDSHA Standard Specifications for Construction and Materials and subsequent Special Provision Inserts. The MDSHA, Office of Materials and Technology, Pavement Division, has established numerous pavement design input parameters based on the functional class of roadway, existing site conditions, and standard pavement materials as specified in the MDSHA Pavement Design Guide.
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 outletted 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 Administration roadways shall be in conformance with AASHTO M288. When used in pavement edge drain (longitudinal underdrain), the Apparent Opening Size for Permittivity of the geotextile shall conform to the filtration and flow requirements for both the subgrade soils and graded aggregate base.
Ponds and infiltration trenches shall not be placed within 15 ft. of a SHA roadway or shoulder area.
Grading that impacts SHA roadways shall be in accordance with Section 200 of the latest MD SHA Standard Specifications for Construction and Materials and subsequent Special Provision Inserts unless otherwise specified in the Final Geotechnical Report provided by the Developer.
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