308 Geotextiles for Base

308 – Geosynthetics for Base

<![if !supportLists]>1 <![endif]>General Description

<![if !supportLists]>1.1 <![endif]>Definitions and Terms<o:p></o:p>

Geogrid: Geogrid is a type of geosynthetic material employed to enhance the strength and stability of soil or aggregate layers.

Geotextile: Geotextile is a specialized fabric with the capacity to filter, separate, reinforce, and facilitate drainage in roadway applications.

Geotextile Separator: Geotextile separator is a fabric designed to prevent intermixing between different layers, effectively serving to separate and maintain distinct layers. The fabric may be woven or non-woven depending on desired application.

Geotextile Stabilization: Geotextile stabilization involves the use of fabrics placed over inadequate soils to provide support while allowing water drainage. The fabric may be woven or non-woven depending on desired application.

<![if !supportLists]>1.2 <![endif]>General Overview

Geosynthetic materials are used as a base to enhance stability and strength in areas where unsuitable soils are encountered. They also prevent intermixing of materials between different layers of the roadway foundation due to repeated loading over time.

During design and development, a geotechnical engineer performs an investigation to assess the suitability of the existing soils. This evaluation aims to identify any unsuitable soils that could lead to expensive deep excavation or necessitate modifications to the intended design. Based on these findings, the geotechnical engineer makes a recommendation to use geosynthetic materials during construction.

During construction, geotextiles are used for remediation of unstable soils under the direction of the construction Engineer based on the recommendation from a geotechnical engineer.

<![if !supportLists]>2 <![endif]>Materials

All materials must meet acceptance requirements in the <a href="https://www.michigan.gov/mdot/Business/Construction/Materials-Source-Guide">Materials Source Guide</a> and be listed on the Contractor-provided Material Source Lists in the project files.

Materials associated with installation of geosynthetics are to meet <a href="https://mdotwiki.state.mi.us/images_construction/9/95/2020-Standard-Specifications-Construction.pdf#page=902">Section 910 of the Standard Specifications for Construction</a>.

Geosynthetic materials are delivered by the supplier in rolls of different widths and lengths and are generally wrapped in a black plastic film. It is essential to store these rolls elevated above the ground and away from chemical exposure. Additionally, ensure protection from moisture, extreme temperatures (above 140 degrees F or below -20 degrees F), and ultraviolet light. To prevent ultraviolet degradation, avoid exposing geotextile fabric and geogrid to sunlight for more than 7 days. Geosynthetics must conform to <a href="https://mdotwiki.state.mi.us/images_construction/9/95/2020-Standard-Specifications-Construction.pdf#page=905">Table 910-1</a> and <a href="https://mdotwiki.state.mi.us/images_construction/9/95/2020-Standard-Specifications-Construction.pdf#page=906">Table 910-2</a> of the Standard Specifications for Construction.

<![if !supportLists]>2.1 <![endif]>Description of Materials

<![if !supportLists]>2.1.1 <![endif]>Woven Geotextile Fabric

Woven geotextile fabric can be made of polyester or polypropylene slit films, fibrillated yarns, or monofilaments. Individual threads are woven to create strong geotextile fabric used for separation and reinforcement. <a name="_Hlk178071774">The texture is an easily seen coarse weave. </a>Woven geotextiles are semi-impermeable. Due to their poor permeability, woven geotextiles should not be used in areas where vertical drainage is critical.

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<a name="_Hlk157174028">Woven Geotextile Fabric</a> Close-Up Woven Geotextile Fabric Roll

<![if !supportLists]>2.1.2 <![endif]>Non-Woven

Non-woven geotextile fabric is made of synthetic materials such as polyester or polypropylene fibers. Short and long fibers are bound together through needle punching or other methods, and heat treatment is usually applied to improve strength. <a name="_Hlk178071883">The texture is </a>similar to felt material. Non-woven fabric is more permeable than woven fabric and is used for filtration and separation.

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Non-Woven Geotextile Fabric Close-Up Non-Woven Geotextile Fabric Roll

<![if !supportLists]>2.1.3 <![endif]>Geogrid

<a name="_Hlk188949088">Geogrid is comprised of extruded polypropylene and can have varying strength axes depending on the application. It comes in uniaxial, biaxial, or multiaxial forms. The openings in the geogrid allow aggregates to interlock with the geogrid. This provides confinement and restrains aggregate from lateral movement. The geogrid is sized for the aggregate that will be placed over it. The main difference between each form is the strength axis. </a>

<![if !supportLists]>· <![endif]>Uniaxial geogrid has strength in one direction and the placement orientation is dependent on this direction. Care must be taken to ensure the strength axis is placed appropriately in the field.

<![if !supportLists]>· <![endif]>Biaxial geogrid has strength in both axes. Biaxial geogrid provides more stabilization than uniaxial geogrid. This is the most commonly used type of geogrid on roadway projects.

<![if !supportLists]>· <![endif]>Multiaxial geogrid has strength in multiple directions and provides the most stability. The grid pattern and amount of strength axes can vary depending on the application.

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Biaxial Geogrid Close-Up Biaxial Geogrid Rolls

<![if !supportLists]>3 <![endif]>Equipment

The Contractor may use a front-end loader or other appropriate equipment to deliver the material to a specific location. The placement of geosynthetic material is done by hand.

<![if !supportLists]>4 <![endif]>Preconstruction

General certifications from an independent testing laboratory must be furnished to the Engineer prior to material use. The Inspector should perform the following activities prior to the start of geosynthetic construction:

<![if !supportLists]>1. <![endif]>Review the plans to verify the locations for the geosynthetic material.

<![if !supportLists]>2. <![endif]>Verify the base material elevation and cross slope have been confirmed by a survey.

<![if !supportLists]>3. <![endif]>Review the plans and the Special Provision for Maintenance of Traffic. There may be restrictions or staging requirements impacting installation of the material. <a name="_Hlk161814906">Installation restrictions are </a>typically associated with staging requirements and access to side streets and driveways.

<![if !supportLists]>4. <![endif]>Verify all materials are approved for use and meet specifications, and verify that stockpiled materials are protected from weather and sunlight as required by the specifications and manufacturer recommendations.

<![if !supportLists]>5. <![endif]>Obtain photographs of material labels, storage method, and location.

<![if !supportLists]>6. <![endif]>Discuss with the Contractor the methods that will be used to install the geosynthetic material, include protection after placement, overlap requirements, and sequencing of placement.

<![if !supportLists]>a. <![endif]>Verify the installation procedure is in accordance with the manufacturer’s recommended installation procedure.

<![if !supportLists]>7. <![endif]>Contact residents and businesses if there will be temporary access restrictions.

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Sample General Certification of Test Results

<![if !supportLists]>5 <![endif]>Construction

Geosynthetic materials come in rolls and are ready for installation. The surface should be properly prepared as shown on the plans, noted in the specifications, or as directed by the Engineer, before placing the geosynthetic layer. To prevent undue exposure or damage to the materials, the Contractor should place only the amount required for immediately pending work.

Construction equipment is prohibited from running directly on the material. The Contractor should stage their work such that aggregate placement will allow construction equipment the ability to spread the aggregate over the material as the work progresses.

The Contractor should regularly inspect the geosynthetic layer after placement to ensure no visible damage has been done to it during unwrapping and placement procedures.

<![if !supportLists]>5.1 <![endif]>Geotextile Fabric

The Contractor should place geotextile fabric in direct contact with the soil below in accordance with the manufacturer’s installation guidelines. Placement should commence from the downstream location and continue upstream. Refer to the profile sheets of the plans to determine flow direction for the roadway. All wrinkles or waves developed during placement should be eliminated. The Inspector should verify all seams are shingle-lapped a minimum of 2 feet for both longitudinal and transverse seams. At the stage line, additional material may need to be placed to allow for the required overlap once the subsequent stage has begun. If the Contractor elects to stitch the seam together, they should follow the manufacturer’s recommendations and the seam should face upwards for inspection purposes. The Inspector should verify stitching of seams is not completed with nylon thread. Ensure the field or factory seams meet the minimum grab tensile strength for the application in accordance with ASTM D4632/D4632M. Any damage or tears to the geotextile fabric during placement must be repaired by the Contractor in accordance with the manufacturer’s recommendations at no expense to the contract. Typically, the repair patch will extend a minimum of 3 feet beyond the damaged area.

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Geotextile Fabric, Installation

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Typical Repair Detail

<![if !supportLists]>5.2 <![endif]>Geogrid

The Contractor will unroll the geogrid parallel to the roadway centerline, and in accordance with the manufacturer’s installation guidelines. Verification the strength axis of the geogrid is placed in accordance with the manufacturer’s guidelines is key to the functionality of the geogrid. Failure to do so could cause the geogrid not to perform its intended purpose. They should anchor the geosynthetic material in place, eliminate wrinkles or waves, and overlap adjacent rolls a minimum of 2 feet, or according to manufacturer guidelines. <a name="_Hlk156553987">The Inspector should verify the geogrid is taut prior to placement of the subsequent aggregate layer. To assist in tensioning the geogrid, placement of the subsequent aggregate layer must proceed from the centerline of the geogrid and be placed outward whenever possible. The Contractor should verify any wrinkles that developed during aggregate placement are flattened prior to being covered. A minimum of 6 inches of the subsequent aggregate layer should be placed over the geogrid before allowing construction vehicles on the geogrid. </a>

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Biaxial Geogrid, Installed

<![if !supportLists]>5.3 <![endif]>Aggregate or Granular Material Placement<o:p></o:p>

After the Contractor places the geosynthetic material, they are to spread and shape the subsequent layer of aggregate or granular material to create a stable work platform before compaction. Additional aggregate or granular material may be placed, as required by applicable sections, and compacted. All ruts should be filled with additional aggregate or granular material and compacted before placing each subsequent layer. Some deformation of the geosynthetic material will occur during aggregate installation as the materials interlock together. Minor waviness is acceptable as long as it is not bunched or pinched as aggregate is placed. Bunching or pinching will lead to damage or reduced performance of the geosynthetic material. To reduce waviness and prevent bunching and pinching, the Contractor should ensure the geosynthetic is placed taut prior to placing aggregate on it.

<![if !supportLists]>6 <![endif]>Inspection & Testing

<![if !supportLists]>6.1 <![endif]>Inspection Procedures<o:p></o:p>

The Inspector should utilize, at a minimum, the following tools to perform the required inspection:<o:p></o:p>

<![if !supportLists]>· <![endif]>100-foot tape measure or longer

<![if !supportLists]>· <![endif]>25-foot tape measure

<![if !supportLists]>· <![endif]>Measuring wheel

<![if !supportLists]>· <![endif]>6-foot stick ruler

<![if !supportLists]>· <![endif]>4-foot level

<![if !supportLists]>· <![endif]>Working plans

<![if !supportLists]>· <![endif]>Camera

Verify the product is the correct type as shown on the plans and noted in the specifications. Check the material for damage and defects prior to installation. During installation watch for proper overlap at edges and ends. Ensure the geotextile is flat and wrinkles and/or waves have been removed except as noted above. During aggregate or granular material placement, confirm the material does not move and that the overlap is not impacted by the operation.

<![if !supportLists]>6.2 <![endif]>Testing<o:p></o:p>

Geosynthetic materials must be tested according to the <a href="https://www.michigan.gov/mdot/-/media/Project/Websites/MDOT/Business/Construction/Materials-Quality-Assurance-Procedures/2023-MQAP-Final-Links.pdf?rev=67f395ebd7dd49eeaf8061226ef47efd&hash=A1CA9FFDE08C78A232A52DACA633D1BE">Materials Quality Assurance Procedures (MQAP) Manual</a> prior to installation on the project. The Inspector should work with the testing agency to obtain a sample prior to installation of the material. Geotextiles must be unwrapped one full roll circumference prior to sampling. All samples must be rolled and not folded during shipment to prevent creases in the fabric.

<![if !supportLists]>6.2.1 <![endif]>Geotextile Fabric<o:p></o:p>

Geotextile fabric testing is required for the first 500 to 1,500 syd, then one test for every additional 4,000 to 25,000 syd, depending on the work item. Geotextile fabric may be accepted by visual inspection (VI) for a maximum of 500 syd per material per project. It is recommended to anticipate 28 calendar days for testing of geosynthetic material. Appropriate sampling time must be considered to prevent delay during construction. The Contractor should be encouraged to get their geosynthetic materials delivered to the site as soon as possible to allow for sampling and testing to be performed.

<![if !supportLists]>6.2.2 <![endif]>Geogrid<o:p></o:p>

One test per lot per shipment is required for biaxial geogrid. <o:p></o:p>

<![if !supportLists]>7 <![endif]>Measurement, Documentation & Payment

<![if !supportLists]>7.1 <![endif]>Measurement and Payment<o:p></o:p>

Measure the geotextile fabric and geogrid in place to the limits shown on the plans. The unit of payment is square yard.

<![if !supportLists]>7.2 <![endif]>Documentation Requirements <o:p></o:p>

The Daily Work Report (DWR) should show the Inspector’s measurements, computations, and supporting documentation verifying the quantity submitted for payment. All materials used must be VI by the Inspector and noted on the DWR.

The Inspector should note in the remarks section of the DWR the condition of the base material, material verification, and equipment used for the delivery, placement of the geosynthetic material, and placement of aggregate.

The <a href="https://mdotwiki.state.mi.us/images_construction/5/56/Documentation_Guide_2022_Final_04062022.pdf">MDOT Documentation Guide</a> provides additional information.

<![if !supportLists]>8 <![endif]>Local Agency Projects

Reserved

<![if !supportLists]>9 <![endif]>Rail Projects