Difference between revisions of "301 - Subbase"

From MediaWiki
Jump to navigation Jump to search
 
(13 intermediate revisions by 3 users not shown)
Line 1: Line 1:
 +
  
 
<center><span STYLE="font: 60pt arial;">'''301'''</span></center>
 
<center><span STYLE="font: 60pt arial;">'''301'''</span></center>
Line 4: Line 5:
 
<center><span STYLE="font: 40pt arial;">'''Subbase'''</span></center>
 
<center><span STYLE="font: 40pt arial;">'''Subbase'''</span></center>
  
−
<center>[http://mdotcf.state.mi.us/public/specbook/files/2012/301%20Subbase.pdf 2012 STANDARD SPECIFICATIONS FOR CONSTRUCTION - SECTION 301]</center>
 
  
  
−
==[[#GENERAL|GENERAL]]==
 
  
−
<span style="color: red"> -Reserved- </span>
+
==[[#GENERAL|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.
 +
 
 +
'''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.
 +
 
 +
'''Fine-Graded Aggregate:''' Fine-graded aggregate is a mixture of aggregates with a uniform distribution of small size aggregate particles passing through a #4 sieve.
 +
 
 +
'''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.
 +
 
 +
'''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 ===
 +
Subbase is the dense-graded aggregate material that uniformly disperses the load placed upon it to the subgrade. Subbase course work consists of placing a granular base course on a grade that is approved by the Engineer.
  
 
{{top}}
 
{{top}}
Line 15: Line 32:
 
==[[#MATERIALS|MATERIALS]]==
 
==[[#MATERIALS|MATERIALS]]==
  
−
Granular Material Class II will be used for constructing subbase.
+
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 ===
 +
Subbase is constructed of granular Class II material. Refer to Section 902 of the Standard Specifications for Construction for granular Class II material requirements.
 +
 
 +
=== Photos of Materials ===
 +
{| class="wikitable"
 +
|+
 +
|-
 +
| [[File:301-001.jpg|300px|thumb|center|'''Class II Sand Placed for Road Subbase''']] || [[File:301-004.jpg|300px|thumb|center|'''Class II Sand Being Placed for Road Subbase''']]
 +
|-
 +
|}
 +
 
 +
 
 +
 
 +
{{top}}
 +
 
 +
==[[#EQUIPMENT|EQUIPMENT]]==
 +
The following equipment can be used for installation of subbase:
 +
* Excavator
 +
* Backhoe
 +
* Front end loader
 +
* Bulldozer
 +
* Roller for aggregate compaction
 +
* Plate compactor
 +
* Ho-Pac attachment
 +
* Gravel train
 +
 
 +
=== Description of Equipment ===
 +
Subbase granular material is typically delivered to the project by a truck, placed with an excavator or truck, and rough graded into place using a bulldozer. Fine grading is performed with a bulldozer, which typically utilizes automated machine guidance (AMG) to achieve the correct cross-section. The granular material is then compacted with a roller to achieve the required density.
 +
 
 +
=== Photos of Equipment ===
 +
{| class="wikitable"
 +
|+
 +
|-
 +
| [[File:301-006.jpg|300px|thumb|center|'''Gravel Train Truck Delivering Subbase Material''']] || [[File:301-008.jpg|300px|thumb|center|'''AMG-Equipped Bulldozer Placing Sand Subbase Over Underdrain''']]
 +
|-
 +
| [[File:Excavator-3.jpg|300px|thumb|center|'''Excavator''']] || [[File:Smooth drum roller.jpg|300px|thumb|center|'''Smooth Drum Roller''']]
 +
|-
 +
|}
 +
 
 +
 
 +
{{top}}
 +
 
 +
==[[#PRECONSTRUCTION|PRECONSTRUCTION]]==
 +
Preconstruction meetings are held for the Engineer and Contractor to discuss and understand installation requirements, stockpile management, placement of the subbase course, and acceptance/payment.
 +
Prior to the start of construction, the Inspector should perform the following:
 +
# Review the plans to verify the location of the work.
 +
# Verify the existing subgrade is in sound condition and has 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 and Region Soils Engineer for testing and/or removal of the soils.
 +
# Verify project control points are established and matching between the Contractor and the inspection staff.
 +
# 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.
 +
# Verify the subgrade is at the required elevation and the cross-slope is in accordance with the project specifications.
 +
# Review the plans and the Special Provision for Maintenance of Traffic. There may be restrictions or staging requirements for installation of the aggregate. Installation restrictions are typically associated with staging requirements on a project and access to side streets and driveways.
 +
# 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.
 +
# Obtain photographs of material tickets, storage method, and location.
 +
# Hold an onsite meeting with the Contractor to discuss:
 +
#* The Class II material the Contractor will use from a pre-qualified pit. If the material is not being sourced from a qualified pit, additional testing requirements are required. Subbase material should not be incorporated into the project without passing material tests supporting the quantity to be placed.
 +
#** Salvaged material may be used upon request, or by direction of the Engineer, once material testing has been completed to verify the Class II material requirements are met.
 +
#** If salvaged material is coming from a borrow pit, an earth change plan must be approved prior to any material being removed form the borrow pit.
 +
#* 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 local ordinances.
 +
#* Disposal of trimmed 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.  
  
 
{{top}}
 
{{top}}
  
 
==[[#CONSTRUCTION|CONSTRUCTION]]==
 
==[[#CONSTRUCTION|CONSTRUCTION]]==
 +
It is extremely important that the construction method used does not distort the existing subgrade. The Contractor should take care not to place any subbase material on unstable, saturated, or rutted subgrade. Placement methods and/or equipment must not distort (rut) the existing subgrade. A rutted subgrade will hold water and lead to future issues with the pavement. If unsuitable material cannot be stabilized, an undercut will be required.
 +
Subbase is not to be placed on a frozen subgrade. If freezing weather is anticipated, cold weather protection should be used. Frozen material shall be removed and replaced with suitable material.
 +
Subbase should be placed, compacted, and trimmed to the proposed cross-section in lifts no greater than 18 inches.
 +
The subbase transition to an existing subgrade or subbase should be a minimum of 12 inches deep per 50 feet of horizontal length. Existing subbase left in place will be transitioned with new sand subbase material to avoid differential frost heave.
 +
Difficulty obtaining density may be attributed to a lack of sufficient moisture content. The Contractor may have to rewater the grade to maintain and achieve density.
 +
 +
{| class="wikitable"
 +
|+
 +
|-
 +
| [[File:301-014.jpg|300px|thumb|left|'''Additional Water being Applied to Aid in Densification''']]
 +
|-
 +
|}
 +
 +
 +
 +
 +
The subbase must be free from defects and contamination. Distorted areas in the subbase should be investigated for rutting or saturated subgrade. The Contractor must remove, repair, or replace damaged areas at no expense to the contract.
  
 +
{{top}}
  
−
===[[#Procedure|Procedure]]===
+
==[[#INSPECTION & TESTING|INSPECTION & TESTING]]==
 +
=== Inspection ===
 +
Grade checks are required every 50 feet across the section to ensure all layers are within ±1 inch. Checking via a string line or survey methods is acceptable. Depth checks should also be performed periodically to ensure the subbase conforms to the plan thickness.
 +
The Inspector should utilize, at a minimum, the following tools to perform the required inspection:
 +
* Measuring wheel
 +
* 100-foot tape measure or longer
 +
* 25-foot tape measure
 +
* Chaining pin
 +
* 6-foot stick ruler
 +
* 4-foot level
 +
* Working plans
 +
* Total Station and/or GPS for documenting grade checks if AMG is used by the Contractor
 +
* String line or laser level if traditional survey stakes are used
 +
* Camera
 +
* Hand auger
  
−
The subbase will be placed on an approved subgrade surface that meets density and cross section requirements.
+
The Inspector should take the following steps during construction:
 +
# Observe delivery, placement, and compaction of the material for conformance to the project documents.
 +
# Perform a moisture test on the aggregate material if payment is based on weight.
 +
# Complete the required daily verification of compaction efforts of either a proof roll or density testing, whichever was agreed to by the Engineer. If density testing is the agreed upon method, 95% of the maximum unit weight with a moisture content not greater than optimum is required as established with a Michigan Cone if natural or slag aggregates are used.
 +
# All salvaged material should be either removed from the site or stockpiled for testing to be approved for re-use onsite.
 +
# Complete quality assurance verification of the trimmed grade and document results of these checks. Possible checks include:
 +
#* Cross-section checks.
 +
#* Top surface elevation checks.
 +
#** If AMG is used by the Contractor, a surveyor with a Total Station and/or GPS should be utilized to check surface elevations of the subbase.
  
−
Verify that subgrade has been examined for possible undercut areas prior to placing subbase material.
+
{| class="wikitable"
 +
|+
 +
|-
 +
| [[File:301-016.jpg|300px|thumb|left|'''Booking Grades''']]
 +
|-
 +
|}
  
−
Care should be taken not to place any subbase material on unstable, saturated or rutted subgrade and that placement methods or equipment do not distort (rut) the existing subgrade.
 
  
−
Subbase should be placed, compacted and trimmed to the proposed cross section.
+
=== Testing ===
 +
For evaluation of aggregate materials, use only certified aggregate sampling and testing technicians. Refer to the [https://www.michigan.gov/mdot/-/media/Project/Websites/MDOT/Business/Construction/Standard-Specifications-Construction/CFS-Manuals/Procedures-Aggregate-Inspection.pdf?rev=e2f19aadca344460afca48b7b9ddb31e&hash=5D3CB25E2CD084FACCFD616004CCEB82 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.
  
−
Difficulty in obtaining density may be attributed to the lack of sufficient moisture content.
+
Density for each lift needs to be achieved before subsequent layers are built up. The maximum lift thickness permitted is 18 inches after compaction. The entire depth of material should be checked for density. Varying the depths for each density check should be based on the maximum depth the nuclear gauge can check. Density needs to achieve a minimum of 95% compaction. The Inspector should ensure the minimum number of required density tests are being performed per the [https://www.michigan.gov/mdot/-/media/Project/Websites/MDOT/Business/Construction/Standard-Specifications-Construction/CFS-Manuals/Density-Testing-Inspection-Manual.pdf?rev=6ea61069b3b649e5bbd9362f000a4e0b&hash=44138356CA520616DF23E2E1D8E49AE0 Density Testing and Inspection Manual].
  
−
The Contractor may have to rewater the grade to maintain density.
+
All salvaged granular material should be tested for adherence to Class II requirements before placement.
  
−
The completed work should be checked by string line or other methods to ensure that the proper slope and elevation have been obtained.  This information needs to be recorded in a field book or other documentation.
+
{{top}}
  
−
The subbase must be free from ruts and contamination.
+
==[[#MEASUREMENT, DOCUMENTATION & PAYMENT|MEASUREMENT, DOCUMENTATION & PAYMENT]]==
 +
=== Measurement and Payment ===
 +
Subbase that is measured compacted-in-place will be documented and paid for by the “staked section” method, which is described in [https://mdotwiki.state.mi.us/images_construction/9/95/2020-Standard-Specifications-Construction.pdf#page=158 Section 205.04 of the Standard Specifications for Construction]. When the pay unit is loose measure, the volume of the hauling units will need to be determined. The Contractor must provide load tickets for each load for payment to be processed.
 +
If grading and compacting existing material is included in the contract, it will be paid by the square yard and determined by the actual dimensions of the work done. It includes any additional water needed to achieve compaction.
  
−
Distorted areas in the subbase should be investigated for rutted or saturated subgrade.
+
=== Documentation ===
 +
The Daily Work Report (DWR) should show all computations, measurements, and supporting documentation needed to verify the quantity submitted for payment. Primary supporting documentation includes moisture, grade, and depth checks.
  
−
Distorted areas from rutted or saturated subgrade will be removed, repaired and replaced at the Contractor’s expense.  A work order may have to be used to get this accomplished.
+
[https://mdotjboss.state.mi.us/webforms/GetDocument.htm?fileName=1900.pdf Form 1900, Aggregate Inspection Daily Report], will need to be completed for every sublot of aggregate to track gradation acceptance.
  
−
Subbase transition to an existing subgrade or subbase will be a minimum of 12 inches (300 mm) of depth per 50 feet (16 m) of horizontal length. Existing subbase left in place will be transitioned with new sand subbase material to avoid differential frost heave.
+
[https://mdotjboss.state.mi.us/webforms/GetDocument.htm?fileName=0582B.pdf Form 0582B, Moisture & Density Determination - Nuclear Method], is used to record density testing results.
  
−
Subbase is not to be placed on a frozen subgrade without a written work order from the Engineer. If it is, it will be tested for density in the spring and recompacted if necessary.
+
Delivery tickets must be verified for the source of material against the approved Material Source List. Each ticket must include the required information. Refer to [https://mdotwiki.state.mi.us/images_construction/9/95/2020-Standard-Specifications-Construction.pdf#page=110 Subsection 109.01.B.6 of the Standard Specifications for Construction] for the information required on each ticket.
  
 
{{top}}
 
{{top}}
  
−
==[[#MEASUREMENT AND PAYMENT|MEASUREMENT AND PAYMENT]]==
+
==[[#LOCAL AGENCY PROJECTS|LOCAL AGENCY PROJECTS]]==
 +
Some local agencies have stricter gradation requirements than MDOT. Refer to the project specifications for subbase to ensure the proper material gradation is being followed.
 +
{{top}}
  
−
Plan quantity plus or minus any known changes, if agreed to by the Engineer and Contractor, as a basis for final quantity for subbase, is encouraged whenever possible.  Subbase measured by the cubic yard (cubic meter) (CIP) will be documented and paid for by the “staked section” method which is explained in [[104 - Construction Surveying|Section 104]] of this manual.  Sometimes actual measurements will be used for small volumes.  When the pay unit is cubic yards (cubic meters) - loose measure, then the volume of the hauling units will need to be determined. The Contractor will need to provide load tickets for each load.
+
==[[#RAIL PROJECTS|RAIL PROJECTS]]==
  
−
If the pay item '''Grading and Compacting Existing Material''' is included in the contract, it will be paid by the square yard (square meter) which will be determined by the actual dimensions of the work done.  It will include any additional water needed to achieve compaction.
+
<span style="color: red"> -Reserved- </span>
  
 
{{top}}
 
{{top}}
  
 
[[Category:Construction Manual]]
 
[[Category:Construction Manual]]
 +
[[Category:Division 3]]
 +
[[Category:Section 301]]
 +
[[Category:New CM Format]]

Latest revision as of 13:21, 8 September 2025


301
Subbase



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.

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.

Fine-Graded Aggregate: Fine-graded aggregate is a mixture of aggregates with a uniform distribution of small size aggregate particles passing through a #4 sieve.

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.

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

Subbase is the dense-graded aggregate material that uniformly disperses the load placed upon it to the subgrade. Subbase course work consists of placing a granular base course on a grade that is approved by the Engineer.

[top of page]

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

Subbase is constructed of granular Class II material. Refer to Section 902 of the Standard Specifications for Construction for granular Class II material requirements.

Photos of Materials

Class II Sand Placed for Road Subbase
Class II Sand Being Placed for Road Subbase


[top of page]

EQUIPMENT

The following equipment can be used for installation of subbase:

  • Excavator
  • Backhoe
  • Front end loader
  • Bulldozer
  • Roller for aggregate compaction
  • Plate compactor
  • Ho-Pac attachment
  • Gravel train

Description of Equipment

Subbase granular material is typically delivered to the project by a truck, placed with an excavator or truck, and rough graded into place using a bulldozer. Fine grading is performed with a bulldozer, which typically utilizes automated machine guidance (AMG) to achieve the correct cross-section. The granular material is then compacted with a roller to achieve the required density.

Photos of Equipment

Gravel Train Truck Delivering Subbase Material
AMG-Equipped Bulldozer Placing Sand Subbase Over Underdrain
Excavator
Smooth Drum Roller


[top of page]

PRECONSTRUCTION

Preconstruction meetings are held for the Engineer and Contractor to discuss and understand installation requirements, stockpile management, placement of the subbase course, and acceptance/payment. Prior to the start of construction, the Inspector should perform the following:

  1. Review the plans to verify the location of the work.
  2. Verify the existing subgrade is in sound condition and has 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 and Region Soils 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 is 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 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. Hold an onsite meeting with the Contractor to discuss:
    • The Class II material the Contractor will use from a pre-qualified pit. If the material is not being sourced from a qualified pit, additional testing requirements are required. Subbase material should not be incorporated into the project without passing material tests supporting the quantity to be placed.
      • Salvaged material may be used upon request, or by direction of the Engineer, once material testing has been completed to verify the Class II material requirements are met.
      • If salvaged material is coming from a borrow pit, an earth change plan must be approved prior to any material being removed form the borrow pit.
    • 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 local ordinances.
    • Disposal of trimmed 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.

[top of page]

CONSTRUCTION

It is extremely important that the construction method used does not distort the existing subgrade. The Contractor should take care not to place any subbase material on unstable, saturated, or rutted subgrade. Placement methods and/or equipment must not distort (rut) the existing subgrade. A rutted subgrade will hold water and lead to future issues with the pavement. If unsuitable material cannot be stabilized, an undercut will be required. Subbase is not to be placed on a frozen subgrade. If freezing weather is anticipated, cold weather protection should be used. Frozen material shall be removed and replaced with suitable material. Subbase should be placed, compacted, and trimmed to the proposed cross-section in lifts no greater than 18 inches. The subbase transition to an existing subgrade or subbase should be a minimum of 12 inches deep per 50 feet of horizontal length. Existing subbase left in place will be transitioned with new sand subbase material to avoid differential frost heave. Difficulty obtaining density may be attributed to a lack of sufficient moisture content. The Contractor may have to rewater the grade to maintain and achieve density.

Additional Water being Applied to Aid in Densification



The subbase must be free from defects and contamination. Distorted areas in the subbase should be investigated for rutting or saturated subgrade. The Contractor must remove, repair, or replace damaged areas at no expense to the contract.

[top of page]

INSPECTION & TESTING

Inspection

Grade checks are required every 50 feet across the section to ensure all layers are within ±1 inch. Checking via a string line or survey methods is acceptable. Depth checks should also be performed periodically to ensure the subbase conforms to the plan thickness. The Inspector should utilize, at a minimum, the following tools to perform the required inspection:

  • Measuring wheel
  • 100-foot tape measure or longer
  • 25-foot tape measure
  • Chaining pin
  • 6-foot stick ruler
  • 4-foot level
  • Working plans
  • Total Station and/or GPS for documenting grade checks if AMG is used by the Contractor
  • String line or laser level if traditional survey stakes are used
  • Camera
  • Hand auger

The Inspector should take the following steps during construction:

  1. Observe delivery, placement, and compaction of the material for conformance to the project documents.
  2. Perform a moisture test on the aggregate material if payment is based on weight.
  3. Complete the required daily verification of compaction efforts of either a proof roll or density testing, whichever was agreed to by the Engineer. If density testing is the agreed upon method, 95% of the maximum unit weight with a moisture content not greater than optimum is required as established with a Michigan Cone if natural or slag aggregates are used.
  4. All salvaged material should be either removed from the site or stockpiled for testing to be approved for re-use onsite.
  5. Complete quality assurance verification of the trimmed grade and document results of these checks. Possible checks include:
    • Cross-section checks.
    • Top surface elevation checks.
      • If AMG is used by the Contractor, a surveyor with a Total Station and/or GPS should be utilized to check surface elevations of the subbase.
Booking Grades


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.

Density for each lift needs to be achieved before subsequent layers are built up. The maximum lift thickness permitted is 18 inches after compaction. The entire depth of material should be checked for density. Varying the depths for each density check should be based on the maximum depth the nuclear gauge can check. Density needs to achieve a minimum of 95% compaction. The Inspector should ensure the minimum number of required density tests are being performed per the Density Testing and Inspection Manual.

All salvaged granular material should be tested for adherence to Class II requirements before placement.

[top of page]

MEASUREMENT, DOCUMENTATION & PAYMENT

Measurement and Payment

Subbase that is measured compacted-in-place will be documented and paid for by the “staked section” method, which is described in Section 205.04 of the Standard Specifications for Construction. When the pay unit is loose measure, the volume of the hauling units will need to be determined. The Contractor must provide load tickets for each load for payment to be processed. If grading and compacting existing material is included in the contract, it will be paid by the square yard and determined by the actual dimensions of the work done. It includes any additional water needed to achieve compaction.

Documentation

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

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

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

Delivery tickets must be verified for the source of material against the approved Material Source List. Each ticket must include the required information. Refer to Subsection 109.01.B.6 of the Standard Specifications for Construction for the information required on each ticket.

[top of page]

LOCAL AGENCY PROJECTS

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

[top of page]

RAIL PROJECTS

-Reserved-

[top of page]

Retrieved from "https://mdotwiki.state.mi.us/construction/index.php?title=301_-_Subbase&oldid=9437"