Geotechnical Review Unit
The DPIE Site/Road Plan Review Division (SRPRD) Geotechnical Unit administers County geotechnical permitting requirements. These requirements are meant to ensure code compliance, achieve durable construction of public and private site and roadway development, and ensure slope stability. County requirements are listed herein, but not meant to replace the judgement of the Geotechnical Engineer of Record (GER) nor the Geotechnical Inspector of Record (GIR). The published County requirements do not cover 100% of what needs to be presented in the permit-related reports nor what needs to be completed in the field. The published County requirements touch on some critical issues. For instance, some of the requirements of normally consolidated and over consolidated highly plastic soils may need to be applied for other soil types as well, if so determined by the GER or by DPIE.
The DPIE SRPRD Geotechnical Unit provides the following services:
- Reviews and approves Geotechnical studies for Site/Road Concept Permits if the site contains problematic soils.
- Reviews and approves Geotechnical studies and requirements for Site/Road Grading and Street Construction Permits.
- Reviews and approves soil–cement requests for roadway subgrade soils.
- Reviews and comments on recycled concrete aggregate (RCA) for Site/Road permits.
- Provides Geotechnical review of certain retaining walls.
Geotechnical Requirements: Codes, Specifications, Standards, Guidelines, Policies and Techno-grams
The geotechnical requirements in Prince George’s County are defined by County Codes, Specifications, Standards, Guidelines, Policies and Techno-grams. Refer to the following:
- Prince George's County Code Part II, Title 17, Subtitle 32 — Water Resources Protection and Grading Code
- Prince George's County Code Part II, Title 17, Subtitle 23 — Roads and Sidewalks
- Prince George's County Code Part II, Title 17, Subtitle 24 — Subdivisions
- Prince George’s County, Maryland, Department of Public Works and Transportation (DPW&T) Specifications and Standards for Roadways and Bridges — Latest Edition
- Prince Georges County Stormwater Management Design Manual —Latest Edition
- Techno-gram 005-2016 Setting Basement Elevation above the Groundwater Table
- Techno-gram 004-2018 Geotechnical Requirements for Stormwater Management Devices
- Techno-gram 005-2018 Geotechnical Guidelines for Soil Investigations and Reports (Over Consolidated Clays)
- Techno-gram 001-2021 Topsoil Certification
- Techno-gram 002-2021 Retaining Walls
- Techno-gram 003-2022 Roadway Underdrains
- Techno-gram 002-2023 Polypropylene Pipe
- Techno-gram 003-2023 Recycled Concrete Aggregate
Geotechnical Reports — General Requirements
- Submit geotechnical studies for the correct project phase or area to be permitted.
- If geotechnical studies are older than eight years, verification borings will be required for approximately 30% of the original borings. Verification borings shall be located no farther than 15 ft from the original borings.
- “Preliminary” geotechnical studies are acceptable for Site Development Concept submittals, in most cases.
- “Final” geotechnical studies are required for Site Development Grading Permits and Street Construction Permits.
- If the permit site contains over-consolidated soils, such as Marlboro Clay, Christiana Clay, Potomac Group or Howell Group, a more extensive geotechnical study is required at the Site Development Concept stage and again at the Site Development Grading Permit and Street Construction permit stage. Slope stability analyses shall be submitted during the conceptual and final permit stage of the project. See Techno-gram 005-2018 for further guidance.
- If areas of the permit site contain contaminated soils, debris, trash, uncontrolled fill or other unsuitable soils or materials, a more extensive geotechnical study is required at the Site Development Concept stage and again at the Site Development Grading Permit and Street Construction permit stage.
- If contamination is known or suspected, Geotechnical studies shall delineate such areas, estimate the percentage of unsuitable materials, and reflect the limits on the boring location plan and the permit plan. Test pits with colored photos shall be provided to substantiate the delineation.
- If contamination is suspected, environmental site assessments are required to identify contaminants that possibly exist in the soils and water of known or suspected areas. For such areas, Geotechnical reports shall recommend completion of the environmental cleanup operations prior to resuming invasive Geotechnical investigation or conducting site grading/clearing. The environmental cleanup operations shall be included in a Rough Grading Permit, scoped only to address the proper removal of contaminants and/or site remediation.
- Geotechnical studies shall cover all proposed stormwater management (SWM) ponds/devices, per Techno-gram 004-2018, the last page of Techno-gram 005-2018, and the Prince George’s County Stormwater Design Manual, particularly Tables 9-1 and 10-1, which are amended by Techno-gram 004-2018, and the Prince George’s County Soil Conservation District guidelines. For stormwater management “small ponds,” the Geotechnical borings and analysis shall comply with MD 378.
- Geotechnical studies shall include sufficient 3D investigation and analysis to comply with the general practice of the Geotechnical industry as well as all County requirements.
- Geotechnical studies shall include engineering recommendations and mitigation for all areas of the site development. Recommendations for removal and/or mitigation of unsuitable soils are required; deferring such engineering recommendations and mitigations to the construction phase is not acceptable.
- Geotechnical reports shall comply with the “General Requirements for Geotechnical Reports” listed in the Department of Public Works & Transportation (DPW&T) Specifications & Standards for Roadways and Bridges, Section I, Chapter 3, A.2 through A.4 and relevant Tables & Appendices (pages 19 to 27).
- Geotechnical reports shall cite all applicable Techno-grams, comply with them, and address applicable geotechnical issues.
Geotechnical Reports — Street Construction Permits (SCP) and Site Development Grading Permits
Geotechnical reports for these permits shall comply with DPW&T Specifications & Standards for Roadways and Bridges. In particular, refer to Section I, Chapter 3, A.4, pages 29 to 45, and relevant Tables & Appendices.
- One geotechnical boring is required for every 300 linear feet of proposed roadway (or full depth widening pavement) or fraction thereof. This is required for public and private roadways.
- Geotechnical borings for general site grading shall be provided to cover the site area to be graded and developed. The borings shall be approximately spaced to cover as many soil types & conditions as possible, particularly problematic soil types, as recommended by the GER. At a minimum, the geotechnical evaluation outside the public right-of-way shall identify the location and removal of unsuitable material, uncontrolled fills, debris, trash and contamination that may otherwise impact the right-of-way.
- Where steep slopes are present or planned on either side of the proposed roadway, slope stability analyses are required for highly plastic soils. The need for further slope stability analysis in other soil types shall also be considered by the GER in order to achieve acceptable slopes that result in a minimum factor of safety of 1.5. Lower factors of safety are not acceptable.
- Geotechnical borings for major box culverts shall be at least one boring within the footprint of each wingwall and at least one boring in the middle of the box culvert footprint. For arch culverts or bridges, at least one boring is required at the location of each pier.
- The pavement sections for public roadways and private roadways in residential single family and townhouse projects shall comply with the standard pavement sections included in the DPW&T Specifications & Standards for Roadways and Bridges, SECTION III — Standard Roadway Sections and Details and the DPW&T Urban Street Design Standards, latest editions.
- The pavement sections for other private roadways and parking lots shall be as recommended by the GER.
- If cement is needed for roadway subgrades, low rates of cement (≤ 3%) may be applied in coordination with DPIE Inspector but without preapproval of the DPIE Geotechnical Engineer. This technique is sometimes utilized to dry out on-site soils with high moisture contents or to improve their engineering properties.
- If soils in the roadway subgrade need to be amended with cement at a rate higher than 3%, preapproval from the DPIE Geotechnical Engineer is required in writing. Refer to the Soil–Cement General Requirements, and to the DPW&T Specifications and Standards for Roadways and Bridges, pages 23 through 25 of Section I, Chapter 3, A.4.
- The use of soil–cement based on trial lab tests is further explained in the Soil–Cement General Requirements. Pre-approval from the DPIE Geotechnical Engineer is required in writing. Use the Soil–Cement Request Template format for requesting soil-cement application based on trial lab tests.
- For roadways with approval to use soil–cement, a waiver of subbase stone can be approved only for Secondary Residential Roadways (26 ft wide curb-to-curb for urban and suburban roads or 30 ft wide shoulder-to-shoulder for rural roads) if included in the soil–cement request. This waiver must be preapproved in writing by the DPIE Geotechnical Engineer.
- Underdrains are required for all public roadways. Underdrains are required for all private roadways constructed in residential single family and townhouse projects. For closed section roadways, underdrains are required continuously on both sides of the road. For rural section roadways, underdrains are required in certain areas. Refer to Techno-gram 003-2022 for more information.
Geotechnical Reports — Single Family Residential Structures
- Single Family Residential Building Permits require at least one soil and groundwater test boring per lot extending at least 6 ft below the lowest slab-on-grade. The borings shall identify the elevation of the groundwater table. The borings can be performed prior to grading permit issuance if the houses will be built in a year or two after grading; otherwise, the boring shall be performed prior to applying for building permits for the houses.
- If basements are proposed, the house shall be elevated as required to comply with Techno-gram 005-2016. In general, the groundwater or perched water elevation shall be at least 2.5 feet or more below the basement floor elevation.
Geotechnical Reports — Retaining Walls
- Retaining Walls taller than 2 feet shall comply with Techno-gram 002-2021. The geotechnical studies shall cover the footprints of all retaining walls at a rate of one soil test boring for every 100 linear feet of the proposed wall length.
- Building Permits are required for retaining walls taller than 2 feet. Retaining Wall Building Permits shall be applied for prior to issuance of the Site Grading Permit.
- Refer to Techno-gram 002-2021 for detailed requirements pertaining to slope stability analysis, swales and drainage, backfill, restriction of other construction within the wall reinforced earth zone, and other critical requirements.
- Sonotube®, Sleeve-it®, or equivalent product shall be used under the ground for posts of planned fences, handrails and guardrails adjacent to retaining walls. Fences, handrails and guardrails shall be placed less than 3 feet from concrete walls or retaining wall segmental units.
Geotechnical Reports — All Other Building Construction
Consult with the DPIE Building Plan Review Division.
Geotechnical Reports — Sites with Over-Consolidated Highly Plastic Clay (Such as Marlboro/Christiana Clay)
- A detailed geotechnical investigation and delineation of over-consolidated, highly plastic clay is required at the early concept site development stage. This analysis shall be updated at the time of Site Development Grading Permits and Street Construction Permits, to re-evaluate slopes and conditions based on the final site grading.
- Marlboro clays’ approximate locations are shown on the County website PGAtlas.com for the purpose of site investigation planning, not for the purpose of construction.
- The geotechnical investigation, delineation and analysis for these sites shall comply with Techno-gram 005-2018.
- For sites with over-consolidated, highly plastic clays, the location and type of stormwater management (SWM) and storm drain systems shall comply with the Prince George’s County Stormwater Management Design Manual and Techno-gram 005-2018. Generally, the preferred site layout is to locate SWM devices below the outcropping of the over-consolidated, highly plastic clays. If that is not possible, placing them at a distance above the highly plastic soils with outfalls possibly running through such soils may get approved by DPIE provided that their pipes and connections are watertight.
- Global stability or slope stability analyses are required where over-consolidated, highly plastic clays are located on or adjacent to 5H:1V or steeper slopes. The existing slopes shall be analyzed to achieve a 1.5 factor of safety. Factors of safety (F.S.) are acceptable only if their values are 1.5 or higher. Factors of safety less than 1.6 shall be used to form a 1.5 F.S. line.
- The location of the 1.5 F.S. shall be shown on the Site Development Concept plan, Site Development Grading Permit plan, Street Construction Permit plans, and the Maryland–National Capital Park and Planning Commission (M–NCPPC) plat. Areas of the site below the 1.5 FS line shall remain undeveloped unless mitigation is approved by DPIE and M–NCPPC.
- The area of the site below the 1.5 F.S. line and within 25’ above the 1.5 F.S. line is typically restricted from development. This area shall be defined on the permit plans as not buildable and outside the building restriction lines. Refer to the County Code, Section 24-131 — Unsafe Land. Contact the M–NCPPC Environmental Planning Section for more information.
- Global stability or slope stability analyses are also required for other soil types when deemed necessary by the GER or by the DPIE Geotechnical Engineer.
Recycled Concrete Aggregates
- Use of Recycled Concrete Aggregates (RCA) in site construction has required approval of a waiver, with limitations on where the RCA material may or may not be used onsite.
- Techno-gram 003-2023 now permits the use of RCA, on a limited basis, without a waiver. The use of RCA material must be approved on the permit. The permit plans shall expressly indicate the locations where RCA material is to be installed onsite, in conformance with this Techno-gram. This RCA plan shall be reviewed and approved by the DPIE Geotechnical Engineer as part of the Site Development Grading Permit process.
- Use of RCA is acceptable if processed in an acceptable aggregate processing plant, in accordance with Techno-gram 003-2023.
- Use of onsite generated construction debris is not permitted. For example, demolition of buildings and onsite processing of the demolition debris for incorporation into onsite fills is not permitted.
Geotechnical — Forms and Checklists
The DPIE website includes many helpful forms and checklists. Go to:
- Soil–Cement — General Requirements
- Soil–Cement — Trial Tests (General Requirements, paragraph C)
- Soil–Cement Request Template
- Approved Asphalt Plants
Geotechnical Review — Fees
The DPIE geotechnical engineering review is included in the review fees established for Site Development Concepts, Site Development Grading Permits and Street Construction Permits.
Geotechnical — Inspection Requirements
- During construction, the permittee is required to hire a third-party Geotechnical Inspector of Record (GIR) to conduct onsite inspections and testing to confirm the acceptable removal and installation of soils, fills, site improvements, stormwater management, storm drains, drainage, concrete, asphalt and all other site construction. The Geotechnical Engineer of Record (GER) is not permitted to serve as GIR.
- The permittee’s Geotechnical Inspector or Record shall keep daily inspection reports and photographs that are available to the County upon demand. The GIR shall coordinate all fieldwork with the County Inspector, inform the Inspector by texts or emails of any fieldwork (compaction, proof-rolling, paving, etc.) at least one business day in advance, and inform the Inspector and the Permittee when construction is not code compliant and correction is required.
- The permittee’s GIR shall provide the following certifications to demonstrate code-compliant construction prior to permit closure:
- Geotechnical Certification
- Topsoil Certification
- Stormwater Management Certification(s)
- Asphalt Certification(s)
- Concrete Certification(s)
- Retaining Wall Certification(s)
- Other certifications required by the DPIE Geotechnical Engineer and stated in the Geotechnical Requirements that are incorporated on the first sheet of the grading plans