307 - Aggregate Shoulders and Approaches

307 Aggregate Shoulders and Approaches

GENERAL DESCRIPTION

Definitions of Terms

Aggregate: Aggregate refers to the material used as the foundation of infrastructure. It typically consists of sand, gravel, crushed stone, or recycled materials like crushed concrete.

Approach: An approach is the section of roadway leading up to a bridge, culvert, or a main roadway. It is designed to provide a smooth transition.

Automated Machine Guidance (AMG): Automated machine guidance is the process of automatically adjusting the motion of a machine with an onboard computer that obtains its position from global positioning systems, robotic total stations, lasers, or combinations of similar methods while referencing the Contractor’s model developed for the project.

Booking Grade: Booking grade is the process of documenting verification checks of the grade to ensure elevation and slope are within the project specifications.

Concrete Crushing Plant: A concrete crushing plant is a facility where concrete rubble is crushed and processed into aggregate for reuse in construction projects.

Dense-Graded Aggregate: Dense-graded aggregate is a mixture of aggregates with an even distribution of different size aggregates.

Salvaged Aggregate: Salvaged aggregate refers to granular material salvaged from the project site. The material is tested to meet specific gradation requirements prior to re-use on the project.

Segregation: Segregation in construction refers to the separation of different sizes or types of aggregate particles within a mixture. It can occur during handling, transport, or placement of materials and can lead to inconsistencies in the composition and performance of the final product.

Shoulder: The shoulder is the portion of the roadway adjacent to the main driving lanes. It provides additional space for emergency stopping, vehicle breakdowns, and pedestrian use, and also helps to support the road edge.

Subbase: Subbase is a layer of material placed beneath the road surface or pavement layers and roadway base course. It provides additional support, drainage, and stability to the pavement structure, helping to distribute loads and prevent uneven settlement.

Subgrade: Subgrade is the existing ground or soil surface upon which the road or pavement section is constructed. It serves as the foundation for the road layers above and must be properly prepared and compacted to ensure stability and durability.

General Overview

An aggregate shoulder is the smooth layer of aggregate adjacent to the paved roadway surface. The aggregate shoulder is intended to provide additional stability to the roadway surface for vehicles that may need to use the shoulder.

Aggregate approaches are utilized for low volume streets or driveways where a hard paved surface may not be warranted.

Trenching is a method of removing existing roadway shoulder to a defined width and depth in preparation for the installation of a new shoulder.

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MATERIALS

All materials must meet acceptance requirements in the Materials Source Guide and be listed on the Contractor-provided Material Source Lists in the project files.

Description of Materials

Michigan Class 21AA, 21A, 22A, 23AA, and 23A dense-graded aggregate, salvaged aggregate, and existing material should be used in accordance with Section 902 of the Standard Specifications for Construction.

Material requirements are dependent on the class of the shoulder or approach as detailed in the project documents.

1. Class I:
   • WILL Receive a Paved Surface: 21A, 21AA, or 22A aggregates.
   • Will NOT Receive a Paved Surface: 22A aggregates.
2. Class II: 23A or 23AA aggregates.
3. Class III: 23A, 23AA, or salvaged aggregates.
   • Salvaged aggregates must have approved test results before use.
4. Class IV: Existing material.

When crushed concrete is used in the aggregate base course, it cannot be within 100 feet of a waterbody. Project documents typically include details in the Notice to Bidders for areas where the use of crushed concrete is restricted.

Pictures of Materials

21AA Material

23A Aggregate Surface Course for a Roadway

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EQUIPMENT

The following equipment can be used for aggregate shoulder and approach work:

• Excavator
• Cold mill machine
• Road widener
• Backhoe
• Grader
• Skid Steer
• Dump truck
• Bulldozer
• Front end loader
• Vibratory roller
• Plate compactor
• Transit or laser level
• Leveling/grade poles

Description of Equipment

Aggregate Shoulders

There are several equipment types typically used in aggregate shoulder installation. Three common types are:

1. An excavator obtains material directly out of a truck and places in on the grade. With assistance from a skid steer or grader, the aggregate shoulder is shaped to the desired dimensions. A vibratory roller compacts the aggregate after it is placed. If the area is narrow or has a shallow depth, a plate compactor may be used to compact the material.
2. A shoulder widener is used to place the aggregate on the grade. The shoulder widener is set up to ensure the finished product meets the plan dimensions. A truck dumps aggregate into a shoulder widener, which places the aggregate off the edge of the pavement. Final grading may require touch-up by a grader prior to compaction. A vibratory roller compacts the material behind the shoulder widener.
3. A truck, such as a flowboy or spreader, is used to place the aggregate on the shoulder. Following behind the trucks is a grader, which shapes the aggregate shoulder to the desired dimensions. A vibratory roller compacts the aggregate once it is graded out.

Excavator Placing Aggregate Material along Shoulder Edge

Aggregate Approaches

Aggregate approaches tend to have limited equipment access during installation. This could be due to lane closure restrictions or ditching adjacent to the proposed approach. Following are two common equipment scenarios used to install aggregate approaches:

1. An excavator obtains material directly out of a truck and places in on the grade. With assistance from a skid steer or grader, the excavator grades the aggregate approach to the desired dimensions. A vibratory roller compacts the aggregate after it is placed. If the area is narrow or has a shallow depth, a plate compactor may be used to compact the material.
2. For larger areas, a truck dumps aggregate directly on the grade. Either an excavator or bulldozer grades the aggregate approach. Typically, a grade checker assists the equipment operator to ensure the aggregate approach is being built to the plan dimensions. In some cases, equipment utilizes AMG to effectively shape the approach. Final grading may require touch-up by a grader prior to compaction. A vibratory roller compacts the aggregate after it is graded. In swamps or peat marsh areas, the use of vibratory compaction may be prohibited due to settlement or liquefaction concerns.

Trenching

A cold mill machine can be used to remove the existing surface to the plan dimensions. The milling is loaded directly into a truck and removed from the site. If required, an excavator with a ditching bucket or grader with a shoe follows the mill to clean up the trench. At times, a grader with a shoe fully trenches the shoulder. Depending on the width of the trench, either a vibratory roller or plate compactor compacts the existing grade.

Pictures of Equipment

• 

  Grader

• 

  Backhoe

• 

  Skid Steer

• 

  Laser Transit

• 

  Road Widener

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PRECONSTRUCTION

Prior to the start of construction, the Inspector should perform the following:

1. Review the plans to verify the location of the work.
   • Take note of areas where vibratory compaction use is excluded, if applicable.
2. Verify the existing subgrade and/or sand subbase are in sound condition and have been accepted. A proof roll or geotechnical analysis may be conducted to determine condition of existing subgrade. If poor soils are encountered, coordinate with the Engineer for testing and/or removal of the soils.
3. Verify project control points are established and matching between the Contractor and the inspection staff.
4. Verify the AMG plan is in place and review the work with the Contractor.
   • If AMG is not used, verify a surveyor has provided grade stakes for the work.
5. Verify the subgrade and subbase are at the required elevation and the cross-slope is in accordance with the project specifications.
6. Review the plans and the Special Provision for Maintenance of Traffic. There may be restrictions or staging requirements for the installation of the aggregate. Installation restrictions are typically associated with staging requirements on a project and access to side streets and driveways.
7. Verify all materials are approved for use and meet specifications, and verify stockpiled materials are protected from weather and sunlight as required by the specifications and manufacturer recommendations.
8. Obtain photographs of material tickets, storage method, and location.
9. Review the Stockpile Management Plan if crushed concrete produced from an onsite crushing facility is used.
10. Hold an onsite meeting with the Contractor to discuss:
    • The construction methods that will be used to complete the work.
    • Required traffic control measures, proximity of traffic to the work area, and maintaining driveways during construction.
    • Communication required if impacting residents or businesses during installation.
      • Residents and businesses should be contacted if there will be disruptions to services. Coordination by the Contractor with impacted users may be required if disruption is necessary.
    • Review of local ordinances.
    • Disposal of excavated material and material stockpile locations. The Contractor should provide authorization letters to the Engineer noting material stockpile and disposal locations.
    • Soil erosion and sedimentation control measures that will be utilized to minimize soil erosion and subsequent sedimentation.
    • Methods for securing the site during work operations and at the end of each workday.

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CONSTRUCTION

Due to potential drop-offs associated with shoulder and approach work, traffic control must be carefully planned during trenching operations on existing shoulders and when placing aggregate for shoulders or approaches. The project documents will specify the minimum required distance from a traveled lane to a drop-off within the work zone. This distance will determine whether the placement of traffic control devices is sufficient to delineate the work zone or if additional measures, such as temporary aggregate placement to reduce the drop-off, are necessary. It is essential to review traffic control plans related to potential drop-offs before construction begins to identify the measures the Contractor must take to meet the project document requirements. The Contractor must place and maintain traffic control devices in accordance with Section 812 of the Standard Specifications for Construction. Additionally, if offset distances are not met, the shoulder or approach area must be brought flush with the existing pavement at the end of the workday or as directed by the Engineer.

Aggregate Shoulders

The subbase or existing grade should be accepted prior to aggregate shoulder placement. The grade must not be frozen, soft, rutted, or generally unstable. Aggregate being used should be verified to ensure it meets the class requirements.

Aggregate shoulders should be placed in a way which does not damage the adjacent pavement. The cross slope of the aggregate shoulder should be verified after compaction to ensure plan requirements are met and proper drainage is achieved. The width and depth should meet the plan requirements with the finished layer thickness after compaction within ±1/2-inch of the plan. The final grade must have positive drainage or meet the cross slope on the plans and must not create ponded areas.

For a hot mix asphalt (HMA) overlay project, aggregate shoulders should be installed flush with the new HMA pavement. If less than 3 inches of material is being placed, the existing aggregate shoulder must be scarified to a minimum depth of 2 inches prior to placement of new material. The compacted aggregate should be maintained flush with the existing pavement surface.

Shoulder Widener Placing Aggregate Material along Shoulder Edge

Aggregate Approaches

Similar to aggregate shoulders, aggregate approaches require the subbase or existing grade to be accepted prior to placement. The grade must not be frozen, soft, rutted, or generally unstable. Aggregate being used should be verified to ensure it meets the class requirements.

If being placed adjacent to pavement, the aggregate approach should be placed in a way which does not damage the pavement. As aggregate approaches can have multiple slopes, radii, or varying geometry, it is important to verify the Contractor follows the plans during installation. Adjacent approach areas can vary significantly; therefore, it is important to reference the appropriate location on the plans for each aggregate approach. The finished layer thickness should be within ±1/2-inch of the plan thickness, meet density requirements, and meet the minimum requirements for the class of aggregate approach.

Trenching

Proper setup of traffic control devices is imperative as the work operations can move quickly along a roadway for shallow trenching operations. The Contractor will excavate, shape, and compact the trench in accordance with the plan requirements. If there is an existing paved surface, the Contractor typically mills off the paved surface. Multiple passes may be required if trenching the full depth of the pavement. The material removed should be removed from site that day.

The trench should have squared-off sides and not have windrows of material against the banks. The Contractor must remove all loose material within the trench before compaction is completed.

The trench bottom must meet the requirements in Subsection 307.03.A of the Standard Specifications for Construction before the trench is filled. All trenches should be backfilled and compacted the same day. Since trenching operations tend to move more quickly than backfilling operations, the Contractor should be reminded they are required to have all trenches backfilled by the end of the day. If trench backfilling is not completed in the same day, the Contractor should plan accordingly to protect exposed subgrade, especially if poor weather is forecasted. To alleviate potential saturated subgrade issues, additional drainage measures may be required, and additional subgrade evaluation may be necessary.

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INSPECTION & TESTING

Inspection

The Inspector should utilize, at a minimum, the following tools to perform the required inspection:

• 100-foot tape measure or longer
• 25-foot tape measure
• Measuring wheel
• Chaining pin
• 6-foot stick ruler
• 4-foot level
• Working plans
• Survey rod
• Camera
• Nuclear density gauge
• Shovel
• Hand auger
• Sample containers

The Inspector should take the following steps during construction:

1. Observe that the existing subbase and/or subgrade is in sound condition.
   • If unsound subgrade is found, contact the Engineer to have the soils evaluated for a subgrade undercut.
2. If material is paid by weight, obtain moisture checks on the new aggregate material.
3. During placement, verify and document that the Contractor is placing the aggregate in a manner that is not damaging the roadway or any feature near the work.
4. Verify the installation procedure is not causing the aggregate to become segregated.
5. Verify the required density is achieved (see Section 6.2, Testing, below).
6. Perform depth checks on the aggregate to verify thicknesses have been achieved.

Testing

For evaluation of aggregate materials, use only certified aggregate sampling and testing technicians. Refer to the Procedures for Aggregate Inspection manual and project specifications for testing requirements and frequencies. The Engineer should track the approved testing of installed aggregate and coordinate with the respective testing lab to ensure the required number of aggregate tests for the project are being completed.

For every new source, new day, or suspected change in material, a moisture check needs to be completed. Obtaining moisture readings from a nuclear density gauge is only an approximation and is often used as a guide in the field. Official determination of moisture content will be made from a field sample stored in a plastic bag with the moisture content checked for payment using the oven dry method only if it’s paid for by weight.

Density requirements are determined by the class of shoulder or approach. If less than 3 inches of material is being placed, 2 inches of the existing material must be scarified before placing and compacting the new material. The Inspector should ensure the minimum number of required density tests are being performed per the Density Testing and Inspection Manual.

1. Class I Shoulders and Approaches: Minimum 98% compaction of the maximum unit weight at no greater than optimum moisture content.
2. Class II Shoulders and Approaches: Minimum 95% compaction of the maximum unit weight at no greater than optimum moisture content, except layers 3 inches thick or less.
3. Class III Shoulders and Approaches: Minimum 95% compaction of the maximum unit weight at no greater than optimum moisture content, except layers 3 inches thick or less.
4. Class IV Shoulders: Minimum 95% compaction of the maximum unit weight at no greater than optimum moisture content, except layers 3 inches thick or less.
5. Trenching: The bottom of the trench should be compacted to a minimum of 98% compaction of the maximum unit weight at no greater than optimum moisture content if the trench will be under HMA. For all other cases, the trench should be compacted to 95%.

MEASUREMENT, DOCUMENTATION & PAYMENT

Measurement and Payment

Aggregate Shoulders and Approaches

Aggregate shoulders and approaches can be paid by weight, area, or volume for any class. Each load ticket must include the required information. Refer to Subsection 307.03.B of the Standard Specifications for Construction for the information required on each ticket.

• By weight: The scale weight of the material will be paid for. If the moisture content exceeds 8%, reductions to the load ticket to remove the excess moisture will need to be made. Final measurement will be in tons.
• By area: The area will be measured by the length and width shown on the plans for the given thickness in square yards.
• By volume: The volume will be measured based on plan dimensions for the aggregate shoulder or approach in cubic yards. If loose measure (LM) is noted in the pay item, the hauling units need to be counted, measured, and inspected.

Weighing Materials

Materials paid for by weight are required to be weighed on an approved scale system. There are permanent and portable scale systems.

Permanent Scale System

A permanent scale system is defined as a weighing device that has not been moved from a given location within the last six months. Scale inspections will be conducted by a private scale agency or the Michigan Department of Agriculture. These inspections are valid for one year. The scale owner will provide the Engineer and the regional materials personnel written verification that the scale system has been inspected according to specifications.

Portable Scale System

For portable scales, the Contractor will obtain scale approval from a local official sealer of weights and measures, or the Engineer may give approval based on verifying the results of the portable scales by passing the loads over another scale that has an official seal.

Platform Scales

If platform scales (permanent or portable) are observed in operation, the following are important:

• The scales are operating freely.
• The scales are reasonably clean.
• The approaches are in relatively good condition.

Platform scales need to be balanced at zero and should be periodically checked throughout the day. The Engineer will require a coupled vehicle to be reweighed with each unit being uncoupled at least monthly during its use on the project. The total weight of the uncoupled units must agree with the total weight of the coupled units within ±0.2%.

Tare Weights

Tare weights should be recorded at least twice a day: once in the morning and once in the afternoon. It is good practice to ensure the hauling units are reasonably clean when performing this operation. Aggregates are weighed to the nearest 100 pounds.

Trenching

Trenching is paid by station along the pavement edge referencing the centerline stationing. If trenching will be performed on both sides of a roadway, each side will be paid for separately. It is important to note which side of the roadway the work is being performed on to prevent doubled or missed postings. Referring to the item history is important to ensure the start station matches the previously completed end station and no gaps are created.

Documentation

The Daily Work Report (DWR) should show all computations, measurements, and supporting documentation needed to verify the quantity submitted for payment.

Depth checks must be included with the DWR when the pay item is noted by the inch.

Form 1900, Aggregate Inspection Daily Report, will need to be completed for every sublot of aggregate to track gradation acceptance.

Form 0582B, Moisture and Density Determination – Nuclear Method, is used to record density testing results.

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LOCAL AGENCY PROJECTS

Some local agencies have stricter gradation requirements than MDOT. Refer to the project specifications for aggregate shoulders and approaches to ensure the proper material gradation is being followed.

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RAIL PROJECTS

-Reserved-

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