205 - Roadway Earthwork
GENERAL
Definitions of Terms
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.
Borrow: Borrow refers to suitable material outside the excavation limits of the project, which may be used within the project upon approval by the Engineer.
Compacted-In-Place (CIP): Compacted-in-place refers to a material (like soil, gravel, or asphalt) that has been compressed and densified in its final location. This compression process typically involves using specialized machinery, like tampers or rollers, to press down on the material and force out air voids.
Frost Heave Textured Material: Frost heave is a phenomenon where soil expands due to freezing water content, potentially causing foundations and pavements to lift or crack. Typically, material with more than 50% silt materials by weight and a plasticity index of less than 10 are frost susceptible.
Loose Measure (LM): Loose measure refers to measuring material dumped out of dump truck and not compacted. When this type of measurement is used, the Inspector will need to know the size of the haul unit bringing in the material. Measuring the haul unit may be required.
Peat: Peat is a type of organic soil material that forms in wetlands, bogs, fens, and marshes through the partial decomposition of plant matter under anaerobic conditions.
Silt: Silt is material with a particle size of from 0.002 mm to 0.075 mm which has a floury feel when dry and a slippery texture when wet. Silt does not hold its shape.
General Overview
Roadway earthwork is a crucial component of road construction projects, involving the preparation and modification of the natural landscape to create a stable foundation for the road. It encompasses a series of tasks aimed at reshaping the terrain to meet the roadway design specifications. During the design phase, surveys are used to determine the topography of the land, soil composition, and other existing features. Onsite work begins with site preparation, which involves the removal of vegetation, debris, and structures to make way for the road alignment and grades as specified in the plans.
Excavation is then undertaken to achieve the necessary depth and width for the transportation infrastructure; this could involve anything from cutting through hillsides to removing existing pavement. Safety measures such as shoring and sloping are implemented to prevent collapses or cave-ins during excavation. The excavated materials are disposed of in compliance with environmental regulations. Disposal must not take place within floodplains or wetlands.
Embankments are constructed using suitable earth materials to build up the roadbed to the required elevation. Compaction is achieved through layering using compaction equipment to meet density and stability standards. Drainage considerations are integrated into the design, ensuring proper water flow to prevent erosion and maintain roadway integrity.
MATERIALS
All materials must meet acceptance requirements in the Material Source Guide and be listed on the Contractor-provided Material Source Lists in the project files.
Description of Materials
Aggregate
Aggregate is a collective term for a variety of inert granular materials, such as sand, gravel, crushed stone, or recycled materials like crushed concrete or slag, that are used in construction applications. Aggregates are typically sourced from natural deposits, quarries, or recycled from demolition waste, and they are commonly classified by size, shape, and gradation.
Granular Material (Class II or Class III)
Granular backfill, often comprised of sand, is used for roadway subbase, embankment, and to fill the space around the drainage system components or voids from excavation. This material provides support and stability, as well as aids in the drainage system while facilitating water movement. Refer to Section 902 of the Standard Specifications for Construction for material requirements.
Geosynthetics
Geosynthetics are synthetic fabrics made from materials like polypropylene or polyester, primarily used for separating materials, such as a sand subbase and an aggregate base. Geosynthetics, such as biaxial geogrids, can provide stabilization to a road base by interlocking with aggregate materials to improve overall stability. In some cases, geosynthetic fabrics are used to facilitate the drainage of storm water that infiltrates the road base by directing the water to an underdrain system or to ditches. These materials are important because they enhance the structural integrity of infrastructure, reduce the need for additional material layers, improve drainage, and extend the lifespan of roadways by reducing soil movement and providing necessary reinforcement.
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. The texture is an easily seen coarse weave. Woven geotextiles are semi-impermeable. Due to their poor permeability, woven geotextiles should not be used in areas where vertical drainage is critical.
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. The texture is similar to felt material. Non-woven fabric is more permeable than woven fabric and is used for filtration and separation.
Geogrid
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.
- 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.
- 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.
- 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
Sound Earth
Sound earth typically refers to soil that is stable and suitable for supporting the weight and traffic loads of the road surface. Sound earth is free from excessive moisture, organic matter, and other contaminants that could compromise its stability or load-bearing capacity. Refer to Section 205 of the Standard Specifications for Construction for material requirements.
Borrow/Use of Excess Property
Unless called for on the plans or in the proposal, the Contractor will be required to furnish all borrow material. The Contractor will not be paid for excavation of borrow material. The Contractor will not remove borrow from the highway right-of-way (ROW) or from MDOT-owned excess property unless authorized by the Engineer. Prior to authorization of the use of MDOT-owned excess property, the Region real estate agent must be contacted by the Engineer for concurrence in the proposed use of the excess property. Their concurrence and the date should be noted on the authorization.
MDOT no longer provides state-furnished borrow pits due to claims related to the quality and/or usefulness of the borrow material. If the Contractor requests to remove borrow material from outside the grading limits (and either inside or outside the ROW), a statement disclaiming the quality and usefulness of the material must be included within the authorization.
If the Contractor wishes to use borrow material, there are several factors which must be considered:
- The Contractor must ensure the property is not enrolled in Public Act 116 agreements or the Farmland and Open Space Preservation Act by contacting the appropriate Michigan Department of Natural Resources authorities. Certain uses of properties enrolled in Public Act are prohibited. The Contractor is to familiarize themself with all rules, laws, and/or regulations governing properties involved in Public Act 116 agreements and operate accordingly.
- Local agencies may require a Special Use Permit prior to the Contractor using any property outside the ROW line. It is the Contractor's responsibility to secure any such Special Use Permits. The Contractor must consider the amount of time required to obtain a Special Use Permit. Any delays caused in obtaining a Special Use Permit will not be considered for a delay to the project.
- The Contractor must submit a plan to the Engineer detailing exactly where they intend to dispose of any excess materials or remove any materials from the site(s) within MDOT ROW, including proposed grading limits and elevations. This plan should be attached to the authorization. All conditions of Subsection 205.03.P of the Standard Specifications for Construction also apply.
- All costs associated with topsoil stripping and storage at the site(s); hauling of materials to the site(s); grading, embankment and/or excavation of materials at the sites(s); respreading of topsoil at the site(s); restoration of the site(s) in accordance with MDOT specifications; construction and restoration of the haul route(s) from the project location(s) to the site(s) in accordance with MDOT specifications; any required soil erosion and/or sedimentation control devices associated with the haul road(s) and/or site(s); etc., will be at no cost to the contract. The Engineer reserves the right to include other costs for the use of MDOT properties, as may be required, at the time of authorization.
- For private properties, the property owner reserves the right to detail requirements pertaining to their property. Details of these requirements should be included in the authorization provided to the Engineer.
- If the Contractor is requesting to borrow material from outside of the grading limits, either within or outside of the ROW, and the contract documents at the time of letting did not indicate that MDOT would consider the allowance of borrow, a charge should be placed on the borrow material (if the allowance of borrow is indicated in the contract documents, all bidders will have taken the allowance into consideration at the time of making their original bids and a charge is not necessary). Generally, earth such as clay has a lesser charge assessed than granular material. Regions may contact the Construction and Technology Grading/Drainage Engineer for a current charge based on project-specific information.
- The authorization should clearly state the final condition, as provided by the property owner, in which the Contractor is to leave the site(s), such as “property was drainable farmland prior to excavation and should be returned to that state,” or “open water to a maximum depth of 12 inches is allowed.” Refer to Subsection 205.03 of the Standard Specifications for Construction for other final condition requirements.
- If the Contractor requests to use a site for storage (e.g., temporary concrete barrier wall) or as a Contractor's yard, the authorization should include an end date for which this use is allowed so it does not become a "permanent" storage location for the Contractor. The end date should generally not exceed the end date of the construction project.
- If the Contractor elects to remove borrow from an underwater source by dewatering, the Contractor will be responsible for any damages, such as flooding or drying up of water wells, resulting from the operation.
- It is sometimes possible to allow borrow material to be safely removed from infields of ramps and to have the site restored as a wetland for possible credit as a "Moment-of-Opportunity" wetland. It may then be possible to receive credit for the wetland for mitigation purposes on a future construction project (this is especially true if there are proposed future projects near the Moment-of-Opportunity wetland site). The Construction and Technology Grading/Drainage Engineer should be contacted for further details.
Pictures of Materials
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EQUIPMENT
The following equipment is typically used for construction of roadway earthwork:
- Bulldozer
- Excavator
- Grader
- Front end loader
- Backhoe
- Single or dual drum roller
- Sheep’s foot roller
- Compactors
- Water truck
- Aggregate trimming machine
- Shoulder spreader
- Crane
- Survey equipment
Description of Equipment
The roadway earthwork process can be completed using various equipment types to add and remove material. Excavators and bulldozers of various sizes are the primary types of equipment used. Most equipment is equipped with AMG to obtain the correct roadway cross-section. Once aggregate or granular material is placed, it is then compacted with a roller to achieve the required density. A water truck is sometimes used to increase the moisture content of the embankment material during compaction or to minimize dust during work operations.
Pictures of Equipment
PRECONSTRUCTION
Prior to the start of construction, the Inspector should perform the following:
- Review the plans to verify the location of the work.
- Verify items called out be removed or placed.
- Verify MISS DIG has flagged existing private and MDOT utilities.
- Verify a surveyor has provided stakes for the work.
- If AMG is used, verify the AMG plan is in place and review the work with the Contractor.
- Review all pertinent environmental restrictions. This will be included within the project plans, special provisions, and/or permits. This can include restrictions due to bats or other protected and invasive species and to reduce the spread of disease between trees. Special provisions might include specialty removal instructions the Contractor should follow.
- Review all soil erosion and sedimentation control measures.
- Review the plans and the Special Provision for Maintenance of Traffic. There may be restrictions or staging requirements. Restrictions are typically associated with staging requirements on a project and access to side streets and driveways.
- Review the plans and proposal for the following special provisions:
- Vibratory exclusion areas.
- Vibration monitoring.
- Crushed concrete exclusion areas.
- 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 construction methods that will be used to complete the work.
- Required soil erosion and sedimentation control measures.
- Methods or operations that will be used if existing facilities must be maintained during 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.
- Environmental restrictions associated with the project site.
- Methods for securing the site during work operations and at the end of each workday.
CONSTRUCTION
Roadway Foundation Preparation
Preparing the roadway foundation is a critical step in road construction that ensures a stable and durable base for the subsequent layers of the roadway. The process begins with clearing and grubbing the construction site, which involves removing topsoil, vegetation, brush, rocks, and other unsuitable materials that could compromise the integrity of the foundation. This initial phase requires the use of heavy machinery such as bulldozers, excavators, and brush cutters to efficiently clear the area. Topsoil, which is rich in organic matter and not suitable for a roadway foundation, is typically stripped off and temporarily stockpiled within the right-of-way (ROW). The Contractor must fill out Form 1568, Project Staging or Excess Material Location on MDOT ROW, to request a staging yard or location for stockpiled material to be stored within the ROW, and submit it for approval by MDOT. This stockpiled topsoil can later be used for landscaping and rehabilitation purposes after construction is complete. Topsoil within peat and muck areas is not to be removed. Refer to the Peat Excavation/Swamp Backfill section below for more details.
After clearing and grubbing, the site is prepared for excavation and embankment construction. Any remaining rocks or large debris are removed, and the subgrade is inspected for stability. If the natural soil is found to be weak or unstable, it may require stabilization or replacement with more suitable fill material. Throughout this process, it is essential to maintain proper drainage to prevent water accumulation, which can weaken the foundation. Temporary drainage measures, such as ditches or culverts, may be installed to manage surface water.
Salvaged material from the site may be incorporated into the construction process at the Contractor's request, provided all testing confirms the material meets the contract requirements. This practice can be cost-effective and environmentally friendly. However, the Contractor must properly dispose of any material deemed unsuitable or non-compliant.
Rock Excavation
Rock excavation involves the removal and management of solid rock formations and large boulders encountered during the creation of a roadbed. This process begins with a thorough survey to identify the location, extent, and type of rock formations within the construction site. Engineers and geologists then perform geotechnical studies to assess the characteristics of the rock, including its hardness, fracturing, and weathering properties, which help determine the appropriate excavation methods and equipment.
For very hard rock that cannot be easily broken, drilling holes and using controlled explosives (blasting) is a common method. This process breaks the rock into manageable pieces that can be removed with heavy machinery. In areas where blasting is not feasible or the rock is moderately hard, mechanical excavation methods are employed. Hydraulic breakers, rock saws, and other specialized equipment are used to break and remove the rock. These methods are selected based on the rock’s properties and the proximity to structures or sensitive areas.
When questionable material appears in a cut section, it should be brought to the Engineer's attention, who may consult with the MDOT Region Soils Engineer and if necessary MDOT Construction Field Services (CFS) Division personnel for a field determination. This careful attention to detail ensures a stable and durable foundation, crucial for the longevity and safety of the roadway.
Field Cross-Sections for Determining Volume
Due to the high cost of rock excavation, field cross-sections for determining volume should be taken at a maximum spacing of 25 to 30 feet. Enough additional sections should be taken to show a true representation of the rock surface. The quantities of rock excavation are to be computed by the average end area method determined from original field cross-sections and the neat line of the typical cross-section shown on the plans. Final cross-sections are taken to determine that projections do not exceed the tolerances allowed by specification.
Boulders
Boulders are to be measured by the Inspector as they appear in the excavation. The volume is computed from average dimensions taken in three directions. These measurements are to be recorded along with a sketch showing the location where excavation occurred. The location of disposal should also be documented. The Contractor's foreman or superintendent should be provided with a duplicate copy of measured boulders at the end of the day's activities. The Inspector should enter all measurements and other pertinent details on the Daily Work Report (DWR). The item should not be reported for pay until it is properly disposed of. This procedure will provide an accurate record and properly document quantities for final measurement.
In sections of the state where frost penetration extends below the rock excavation elevation in solid rock cuts, it is extremely important that no pockets are left where water can be trapped and cause detrimental frost action. Where water pockets occur, they should be sealed off by filling in with sand-cement mixture or other suitable means as directed by the Engineer.
Blasting
The Contractor must obtain written approval from the Engineer before using explosives on a project. This written approval does not relieve the Contractor of liability nor responsibility for damages resulting from the use of explosives. It is the Contractor’s responsibility to comply with all laws, regulations, and ordinances and exercise the utmost care not to endanger life or property, including new work. Typically, the Contractor is required to submit a demolition plan to the Engineer for review prior to written approval for use of explosives onsite.
Before using explosives on a project, the Contractor is to furnish the Engineer with a copy of the rider or clause in the insurance policy as evidence that there is adequate insurance coverage for using explosives. Some sureties require inspection by their safety engineer before selling such coverage. To avoid delays, the Contractor should make insurance arrangements well in advance of starting work. All blasting operations must be supervised by a competent and experienced blaster. When these requirements have been met, the Engineer will initiate a work order or a no-pay recommendation authorizing the Contractor to perform demolition blasting. This work order/recommendation will list the requirements to be met and prescribe any limitations imposed on the work.
The Inspector should check all blasting operations for strict conformance with safety precautions and regulations, especially in residential or built-up areas. All blasts must be properly covered with mats, sufficient thickness of sand, or other acceptable cover to ensure flying rocks will not cause harm to people or damage to property.
The DWR should indicate the following information:
- Method of breaking rock (ripper, blasting, etc.).
- Location and number of holes, type and quantity of explosives placed, and time of detonation of each charge.
- Type of blast protection.
- Type of detonation (electric, time fuse, etc.).
- Location of warning signs (to warn people and prohibit use of 2-way radios).
Peat Excavation/Swamp Backfill
Complete peat excavation and swamp backfill in accordance with the Standard Plan R-103 series. Remove peat, muck, marl, and very soft, underlying clay as shown on the plans. Coordinate removal with swamp backfill operations.
Peat excavation and swamp backfill are specialized processes in roadway construction that address the challenges of building on soft, unstable ground. These processes should be performed in accordance with the Standard Plan R-103 series and Section 205 of the Standard Specifications for Construction.
Peat is typically found in swampy or marshy areas. It is generally highly compressible and retains a significant amount of water, making it unsuitable for supporting the weight of a roadway. Therefore, peat is excavated from the site with heavy machinery, such as excavators and backhoes, and transported away from the construction site. Decomposed peat and muck may be approved as topsoil for turf establishment after testing has been completed. In this case, the excavated peat is stockpiled onsite.
Once the peat has been excavated, the next step is to backfill the excavated area with suitable material that can provide a stable foundation for the roadway. Typically, for all methods of swamp treatment, peat excavation and swamp backfill operations are conducted simultaneously as the excavation is wet. The backfill material will consist of granular material Class III. The swamp backfill is placed in the wet area and pushed into place until the peat excavation is complete, and it is approximately 2 feet above the water surface. At this time, geosynthetics can be placed above the swamp backfill for reinforcement and additional material is placed in layers with density obtained prior to subsequent layers being placed. Proper drainage must also be incorporated into the design to prevent water from accumulating in the backfilled area, which could compromise the stability of the road foundation due to the amount of water removed during the peat excavation and swamp backfilling operations.
Treatment of Peat Marshes
Method A
Method A is used for deposits up to 15 feet deep and is referred to as “total excavation.” This is sufficiently shallow for the excavating equipment to reach the bottom and remove all the peat for the full width of the roadway. Side squeezing is usually slight enough to maintain an open excavation long enough to determine that all peat has been removed and to obtain cross-sections for pay quantities. The backfill must be placed progressively behind the excavation except where a dry trench results. Even in this case, the backfill should be placed as soon as possible because seepage and surface drainage water often fill the excavation and cause side sloughing. Specifications require the excavation to be backfilled to 2 feet above original ground with granular material Class III (unless otherwise specified). All embankment material placed above this elevation must be compacted according to the controlled density method.
When excavating swamps using Method A, the trench is partially or completely filled with water. Systematic probing must be performed as the excavation progresses to confirm complete peat removal. Cross-sections must also be taken as the work progresses. Checking to determine if all unstable material has been removed before backfilling is the most important inspection function for Method A treatment.
When Method A is used for swamps exceeding 10 feet in depth, or when the excavation results in a wet trench, a 10-foot moving surcharge must be maintained as the backfill progresses. The purpose of the surcharge is to push the peat forward in the trench and squeeze out any small pockets of peat not detected by probing or cross-section readings.
Method B
Method B is used for swamps greater than 15 feet in depth (muck depth could be less than 15 feet) and is generally referred to as "partial excavation and displacement." Total excavation (Method A) cannot be accomplished in deep swamps because the great fluid pressure of the peat closes the excavation before the backfill can be placed. Method B displaces the soft peat with heavier stable granular material. The displacement is accomplished by means of a moving surcharge of granular material. The height of the surcharge, measured from the original ground, must be at least equal to the depth of the swamp. The lead end of the surcharge is placed by the end dump method to that elevation. All surcharge material above subgrade elevation is continually moved forward as peat excavation progresses. This surcharge is sometimes referred to as a rolling surcharge.
Upheaved peat must be continually excavated from the trench ahead of the surcharge. To create a condition of maximum unbalance, the trench is required to be maintained at a minimum depth of 15 feet below the original ground (or depth of the peat, if less than 15 feet) ahead of the surcharge for a distance in length equal to the depth of the swamp.
Good displacement action is generally evidenced by continual transverse cracking and settlement of the lead end of the surcharge. This surcharge settlement often appears as a series of steps that are caused by shear planes within the surcharge. The distance that this surcharge cracking occurs back from the lead end is proportionate to the depth of the swamp. If observed closely, the settlement cracking and movement can be seen. The sinking surcharge displaces the deep peat that is continually upheaving into the trench ahead of the surcharge. It is important for the front of the surcharge to be maintained at the proper height to ensure enough weight to displace the unsuitable material beneath. If satisfactory displacement action is not obtained, the Contractor may be required to loosen the peat below the 15-foot trench by pulling the dragline bucket through it. Occasionally, for stiff peat, additional surcharge height may be required to affect proper displacement.
The rate the surcharge is advanced must be kept in balance with the rate of excavation of the peat. A problem often occurs when the rate of placement of fill material exceeds the capacity of the peat excavating equipment. In this event, the displaced peat builds up ahead of the surcharge and can cause sufficient resistance to trap peat beneath the fill. To correct the problem, the Contractor must either use additional draglines to excavate the peat or reduce the number of units hauling backfill. The timing of surcharge advancement to peat excavation is extremely important.
Draglines
For a dual roadway where temporary storage has been provided on the plans, experience indicates two draglines are a desirable minimum because of the width the peat must be cast and the greater volume of peat that must be handled. For swamps deeper than approximately 25 feet, additional draglines are often necessary because the large volume of waste peat requires recasting further back from the excavation to prevent it from flowing back into the excavation. In no case during the mucking operations may any material be disposed of, either temporarily or permanently, beyond the normal plan fill slope across any wetland or floodplain. The plans should indicate protective measures to prevent the flow of materials into a wetland outside of the slope stake lines (e.g., geotextile silt fence). The requirement to dispose of excess material in upland disposal areas may necessitate the use of extra draglines to handle and load excess material into the hauling equipment. On dual roadways, innovative planning is often required to handle a full-width mucking operation. No additional payment is made for these types of rehandling.
The draglines that excavate the upheaving peat ahead of the backfill may operate either from the surcharge or from the original swamp surface ahead of the excavation. When working from the swamp surface ahead of the excavation, the dragline is at a lower elevation and can more effectively and efficiently maintain the trench ahead of the backfill. When the dragline works from the top of the surcharge, its effective reach is reduced. To compensate for this, the Contractor may tend to keep the surcharge height lower than required. Often, the dragline being used is too small for the job. In some cases, draglines are positioned on lower benches, which are notched into the sides of the surcharge. When this is done, the benches should extend beyond the lateral limits of the fill and not be formed by reducing the effective width of the surcharge.
The location of the peat excavation stakes for Method B treatment does not depend on the depth of the swamp and, therefore, swamp sounding is not required for staking purposes. The stakes are set in accordance with the current Standard Plan R-103 series.
As soon as the Method B swamp treatment completion date can be reasonably estimated, a request for check borings should be directed to the Construction and Technology Support Area, Geotechnical Services Unit. Both the Engineer and Region soils personnel should be in agreement with the submittal of the request for borings. Borings are taken to determine that the peat has been satisfactorily displaced and to verify the quantity of peat excavation for which the Contractor is paid. The normal pattern of borings is one cross-section every 50 feet. Additional borings may be requested if required by unusual conditions.
Where borings reveal that peat remains beneath the embankment, the Geotechnical Services Unit soils personnel may recommend additional treatment. The additional treatment is often the placement of a time surcharge as further described below.
Method C
Typically Method C is used for swamp backfill, as detailed in the Standard Plan R-103 series. Method C is specified when the swamp treatment is conducted parallel to an existing roadway, usually to facilitate widening. This involves a rolling surcharge and an excavated area not exceeding the reach of equipment. The speed at which this operation is completed is important to ensure full peat displacement and removal is completed and to prevent the trapping of peat below the new material. Check borings may be completed to verify the peat has been removed and contamination with the backfilled material did not occur, or to determine quantities removed.
Peat Disposal Area
Peat must be disposed of on upland sites, not in wetlands or floodplains. In most cases, this will prevent casting the peat excavation off to the side beyond the slope stake line for storage. Standard Plan R-103 series do allow peat to be placed within the normal slope limits called for on the plans. The project proposal and plans should be reviewed thoroughly so the peat disposal methods are thoroughly understood.
Time Surcharge
Frequently, a surcharge of granular fill material is recommended to be placed over the swamp backfill to facilitate displacement or to compress the unstable foundation material. The surcharge is to remain in place until the swamp backfill has stabilized or the required settlement has taken place, as determined by the Engineer (generally a period not exceeding 90 days).
Material from the surcharge becomes the property of the Contractor. The Contractor is paid half the cost of the swamp backfill material quantity to place the surcharge. The remaining half of the cost of the swamp backfill material quantity is paid once peat excavation is completed.
Surcharge Undercutting
There are four types of subgrade undercutting, all of which include backfilling and compaction:
- Type I will be backfilled with selected clay or other similar approved material.
- Type II will be backfilled with granular material Class II.
- Type III will be backfilled with the excavated material after it has been effectively mixed to break up any undesirable pockets or strata of soils or by disposing of the undercut material and replacing it with approved backfill material.
- Type IV will be backfilled with 21AA dense-graded aggregate or 4G open graded aggregate. When 4G is used, it must be encapsulated with geotextile separator.
Accurate records are necessary to ensure the proper type of subgrade undercutting is reported.
Subgrade undercutting will be excavated within the limits established by the MDOT Region Soils Engineer and the excavated material will become the property of the Contractor. When approved by the Engineer, such material may be placed in embankments if the moisture, density, and sound earth specifications are met.
When excavation has been completed to within 6 inches of the subgrade, or the topsoil has been stripped in preparation for placing embankment, MDOT Region Soils Engineer will be notified by the Inspector. Timely notice is important so an investigation can be made while the cut is fresh and soil textures and conditions are more readily identifiable.
MDOT Region Soils Engineer will determine if any material or drainage condition would result in differential frost heave and recommend the necessary treatment. A written recommendation is required to document the item of subgrade undercutting and describe the limits. The depth of excavation below plan grade varies from 3-1/2 to 4 feet in the southern and central parts of the state and to 5 feet in the northern part of the state, depending on conditions.
The excavation width varies with the extent of the deposit of undesirable material and the width of pavement, shoulders, or structures. At each end, the excavation should be extended so there is a gradual transition from full depth cut to no cut. The transition at each end is generally 25 to 50 feet long.
The excavated area may be backfilled with material having the same physical characteristics as the adjacent soil, as directed by MDOT Region Soils Engineer. Where high moisture or water table is encountered, it will be necessary to backfill with granular material to obtain proper compaction and stability. Where granular backfill is used in areas of heavy soils, it is necessary to provide drainage. To accomplish this, it is necessary to undercut and backfill with granular material out to the side ditch or provide an underdrain.
In all cases where the surrounding soil is an impervious material, a granular backfill must be drained and the bottom of the excavation must be sloped at not less than 2% grade to the outlet.
Earth Excavation
Earth excavation in roadway construction involves the systematic removal and management of soil to establish a stable and uniform foundation for the road. Using heavy machinery such as excavators and bulldozers, the excavation progresses by cutting into high areas and filling low areas to achieve the desired road grade and alignment.
During excavation, it is crucial to adhere to engineering specifications and environmental regulations. Excavated soil is categorized based on its suitability for reuse. Materials meeting specified criteria for compaction, typically a minimum of 95% of maximum density, are reused as fill elsewhere on the site. This reuse reduces disposal costs and environmental impact.
Unsuitable materials, such as organic-rich soil or contaminated earth, must be carefully disposed of according to environmental guidelines and in accordance with Subsection 205.03.P of the Standard Specifications for Construction. The disposal process often involves transporting these materials to designated disposal sites or recycling facilities.
Any salvaged and stockpiled material should be located in such a manner to not impede drainage or damage trees and other vegetation.
When excavating to finish grade, any stone or rock exceeding 3 inches in diameter is to be removed. All slopes are to be finished to Class B tolerance unless Class A is called for in the plans. Tolerances for excavation are as follows:
- Subgrade:
- With subbase installation, within 1 inch of the required plan grade.
- Without subbase installation, within 3/4 inch of the required plan grade.
- Slopes:
- Class A: Within 1 inch of the average slope shown on the plans measured at a right angle to the slope.
- Class B Backslopes: Within 6 inches of the average slope shown on the plans measured at a right angle to the slope.
- Class B Fill Slopes: Within 2-1/2 inches of the required grade and cross section to a distance 3 feet from the edge of the outside shoulder and measured at a right angle to the slope.
Ditch Cleanout
The purpose of a ditch is to provide drainage of the surface water from the roadway, to relieve seepage from the subbase and to convey drainage to a natural watercourse. Ditches constructed on the project must be maintained and kept reasonably free from debris until final acceptance.
The ability of the pavement structure to provide trouble-free performance depends more on the adequacy of drainage than on any other factor.
The Engineer and Inspector should check the drainage system, particularly during and after severe storms, and inform the Contractor to make any modifications necessary.
The Standard Specifications for Construction requires the roadbed and ditches to be maintained in such condition that the site will always be well-drained without causing accelerated erosion. The Contractor must maintain positive drainage at all times, providing temporary measures when and where necessary. The Inspector should ensure ditches are cut to the required dimensions, not only during the rough grading stages but also during final trim and cleanup. Ditch depth can easily be checked with a folding ruler and hand level, using the pavement for a reference grade. Be sure to allow for any sodding or other restoration item(s) that would be placed at a later time. Check to see that ditches are slightly lower than culvert outlets and that excessive water will not stand in the ditch at any time.
Removal of material from ditches is generally classed as earth excavation since ditches are normally excavated along with general road cut using typical earth moving equipment. Material no greater than 2 feet deep is removed based on the profiles detailed in the plans. Ditch cleanout includes:
- Removal of cattails, brush, and miscellaneous debris.
- Removal of trees 6 inches or less in diameter.
- Blending of ditch profiles to match existing ditch.
- Removal of soils/spoils from the project site.
The Contractor must ensure heavy soils do not block the free drainage of the subbase into roadside ditches. Clay, loam, muck, or other heavy soils deposited on the slopes outside of the sand subbase during final trimming operations is detrimental to lateral drainage of the subbase. The project specifications should be referenced for details on disposal of the excavated material due to invasive species, such as phragmites, which may be contained within the excavated material. Disposal requirements must be followed for material containing invasive species or other contaminated material.
Subsection 208.03.B of the Standard Specifications for Construction stipulates that all grading sections be brought to final grade immediately as the grading progresses, and that permanent soil erosion controls be completed within 5 calendar days after final grading. Where it is not possible to permanently stabilize a disturbed area, temporary erosion controls must be implemented within 5 calendar days after cessation of grading activity, whether or not the area has been brought to final grade. Strict adherence to this specification will help prevent problems. Limit the grading activity and discontinue submission of biweekly estimates, if necessary, to ensure completion of these controls. See Section 208 of this manual for other means of bringing the Contractor into compliance with these stabilization issues.
If it is found necessary to make any drainage change during construction, there must be a design check of the situation before the Contractor is advised to make the change. Any request to deepen ditches or change drainage, in any way, made by the Drain Commission, U.S. Department of Agriculture, County Agricultural Agent, or others, must be cleared through the MDOT Region office, as MDOT may require a formal agreement. A phone call to the appropriate MDOT Construction/Design Engineer for authorization to make immediate changes is suggested.
Channel Excavation
Channel excavation includes any trimming, straightening, widening, deepening, or relocation of a stream or watercourse. Channel excavation includes:
- Removal and disposal of excavated material.
- Removal of masonry and concrete structures.
- Maintaining flow in existing channel until new channel is built.
Channel excavation should be completed in compliance with the contract documents. There may be various special provisions detailing different environmental restrictions. These could limit the period when work operations can take place due to fish spawning or specify disposal requirements for excavated material due to invasive species.
Disposal of Surplus and Unsuitable Material
The Contractor is responsible for disposal of all surplus and unsuitable material. If it is disposed of in a storage area, special consideration should be given by the Engineer and Inspector to drainage from the roadway and adjacent property. A toe of slope ditch may be required or the spoil bank may require a ditch constructed through it to allow water to flow from the roadway ditch or from the adjacent property.
When material is wasted outside the ROW, the Contractor is required to file with the Engineer a written agreement from the property owner for permission to waste material on the property. Disposal of material in a wetland or floodplain is strictly prohibited by law. This applies to both public and private property as required in the specifications or special provisions. All public and private sites used for disposal of material removed from a project must be reviewed by the Region resource specialist prior to disposal to ensure the proposed disposal site(s) do not contain floodplains or wetlands. Restoration and erosion control measures are required in accordance with Section 105, Section 205.03, and Section 208 of the Standard Specifications for Construction for disposal of material on MDOT property. A private property owner has the right to state their required restoration requirements after disposal of material is finished. The Contractor must provide authorization letters from the property owner of any disposal areas, including restoration requirements, to the Engineer.
Cost Overruns from Offsite Soil Disposal
In projects where clean soil will need disposal, it is important to find out the requirements of the disposal location as early as practical. Cost overruns due to unanticipated soil disposal costs are possible. Projects with large quantities of soil that must be disposed of offsite are of particular concern, even if contamination is not suspected, because soil disposal facilities are increasingly requesting laboratory analysis of the apparently clean soil to confirm that material they are accepting is truly “clean fill.”
If laboratory testing is required, the Engineer should arrange for proper sample collection. This material is not covered by the Special Provision for Non-Hazardous Contaminated Materials Handling and Disposal; therefore, the Contractor should not collect the samples. Soil samples collected for this laboratory analysis will potentially determine how the project soils will be disposed. Several things can cause misleading laboratory results:
- Improper sampling and handling may result in sample contamination during collection or transport to a laboratory.
- Construction activity, such as diesel equipment movement onsite, may cause incidental contamination that gets picked up in the sample.
- Naturally occurring heavy metals, such as arsenic and lead, may exceed documented regulatory background concentrations, creating the appearance of contaminated soil.
If soil is determined to be non-hazardous contaminated, it may still be possible to avoid landfilling. Depending on the type and concentration of the contaminant, the soil may be returned to an excavation as suitable fill material or used as embankment in areas of similar contamination.
Disposal facilities may reject soil if the sample analysis of the material exceeds a background concentration, even if it does not exceed Michigan Department of Environment, Great Lakes, and Energy cleanup criteria.
If the soil is rejected by the Contractor’s disposal location, other disposal options may be available. Contact the Environmental Services Section for assistance with these situations. Local agencies may also contact this office for assistance with projects with State of Michigan or federal funding.
Roadway Embankment
Compaction is critical during fill placement to ensure the stability and load-bearing capacity of the subgrade. Fill material is placed in controlled layers, or lifts, and compacted using heavy rollers or vibratory compactors in accordance with the specifications. Each lift is compacted to achieve maximum density, minimizing future settlement and ensuring a strong foundation for the roadway structure.
Structure Embarkments
Structural embankments must be constructed by the controlled density method:
- When placed under structure footings supported by piling, the structure embankment material will be Granular Material Class III, except that if placed between April 1 and November 15, sound earth is allowed for structure embankment.
- When placed under structure footings for which piling is not specified, the structure embankment material will be granular material Class III.
- Density will be 100% of the maximum unit weight when piling is not required and 95% when piling is required.
- Structure embankment will be protected from freezing until the overlying footings are cast.
Stepping Side Slope Embarkments
Stepping side slope embankments are constructed on existing slopes of 1:6 or steeper, forming steps with a horizontal dimension of at least 3 feet as in accordance with the Standard Plan R-105 series. This technique is important because it helps to stabilize the embankment, preventing slippage and erosion by providing horizontal surfaces that resist downhill movement. By creating steps, the overall stability of the slope is enhanced, reducing the risk of landslides and ensuring the longevity and safety of the roadway.
Borrow
Contractors are required to complete Form 1568, Project Staging or Excess Material Location on MDOT ROW, for borrow activities, defined in Subsection 105.03 of the Standard Specifications for Construction. After removing borrow material, side slopes are shaped as flat as practical but not steeper than 1:4. Tops and bottoms of slopes are rounded with vertical curves to blend into adjacent terrain. Borrow areas are shaped to facilitate drainage. In granular soils, leave at least 12 inches above the high groundwater level; in cohesive soils, leave at least 12 inches above the high-water elevation of the drainage outlet. If drainage is impractical, create a pond or wetland and fence ponded borrow areas. Borrow areas are restored in accordance with plans and specifications to ensure the land remains usable. Restoration outside the ROW must comply with permit and land use requirements.
Winter Grading
Winter grading is difficult, and it is up to the Engineer and grade Inspector to ensure the embankment is free of frost and constructed under density control. If frost or snow is buried, settlement will take place when thawed. Attempting to work with cohesive soil that has moisture more than 2% above optimum is generally unsuccessful during freezing weather because it is impossible to dry the soil. The lowest temperature cohesive soils, at optimum moisture, have been successfully placed is approximately 20°F. Little success in compaction, even with clean granular material, has resulted with the temperature below 15°F.
During the winter months, topsoil removal may necessarily be in excess of the actual topsoil depth due to the frost penetration. Topsoil and frozen material removed to facilitate the Contractor's operation will be at no cost to the contract. If adherence to the progress schedule, as set up in the proposal, specifically requires the Contractor to construct embankments during the winter, payment will be made for excavation to the actual frost depth and for the embankment required to replace the material removed.
Embankments may be started on original ground (after removal of topsoil) that has a maximum of 4 inches of frost except in those areas that will support a structure. More than 4 inches of frost will require stripping. Frost will be stripped prior to embankment construction regardless of the height of fills. Once embankment is started, no frozen material will be placed; and if work is stopped, frost will be removed before restarting. It will be removed in the areas between the 1 on 1 slope lines from the outer clay grade shoulder point and stockpiled outside the grading limit until thawed.
Placing and Compacting Embankment
Embankments are constructed with sound earth and stones, broken rock, or concrete, except in the top 3 feet. Inspector confirmation is required for stones, rock, and concrete in embankments. Frost heave materials are not placed in the top 3 feet below subgrade. The top 3 feet of embankment must consist of a uniform textured material. Materials are deposited and compacted using the controlled density method. Refer to the special provisions within the contract documents for additional details about compaction of material.
- Controlled Density Method
- Cohesive materials must be placed and compacted in lifts not exceeding 9 inches deep of loose material for the full width of the embankment area.
- Within top 3 feet of embankment: Moisture content must not exceed optimum moisture content.
- Deeper than 3 feet from top of embankment: Moisture content must not be more than 3% over optimum moisture.
- Granular materials must be placed and compacted in lifts not exceeding 15 inches deep.
- Cohesive materials must be placed and compacted in lifts not exceeding 9 inches deep of loose material for the full width of the embankment area.
Each layer, regardless of material or method, must meet moisture and compaction requirements. Drainage of granular material (sand) cannot be blocked by a pervious material (clay).
Rock Embankments
Rock embankments consist of shattered rock placed in layers not exceeding 3 feet thick, sourced from roadway cuts or borrow areas of waste mine rock. Rock size must not exceed 12 inches in greatest dimension. Rocks are to be deposited and pushed over the fill by bulldozers, not dumped directly over the end. The surface of the rock embankment is to be filled with small rock fragments, rock fines, or granular material Class III to prevent infiltration of other fill materials. Rock embankments are not used in fills less than 4 feet deep, and no stone or broken rock layers are placed within 3 feet of the subgrade surface. If a structure is to be buried by rock embankment, place a 2-foot boundary of granular material Class III along the sides and top of the structure prior to placement of the rock embankment.
During winter, rock fills in subfreezing temperatures are limited to fill slopes outside the 1-on-1 clay shoulder point to avoid irregular settlement due to frozen particles. In guardrail fill sections, rock fills are kept below the depth of guardrail posts.
Granular Blanket
In cases where poor or unstable ditch or sloped sections are found, granular blankets are installed to provide a more stable material and aid in improved drainage. Once the unsuitable material is excavated, one of two types of granular blankets are installed:
- Type 1: Backfilled with granular material Class II.
- Type 2: Backfilled with a 3-inch nominal granular material Class II layer before placing a drainage layer and a subsequent 12-inch layer of granular material Class II on top of the drainage layer. The drainage layer can consist of:
- A 2-inch layer of open-graded aggregate with geotextile blankets above and below the layer.
- A three-dimensional mesh with geotextile blankets above and below it.
- Other geocomposite section approved by the Engineer.
INSPECTION & TESTING
Inspection Procedures
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
- 6-foot stick ruler
- Working plans
- Camera
- Survey equipment
- 4-foot smart level
The Inspector should take the following steps during construction:
- Observe delivery, placement, excavation, and compaction of the material for conformance to the contract documents.
- Excavation Activities:
- Verify excavation is conducted to the depth and dimensions required by the design specifications.
- Ensure removal of unsuitable materials such as organic-rich soil, peat, or rock that do not meet project requirements.
- Monitor excavation methods to prevent damage to adjacent structures or environmental resources.
- Check for proper disposal or reuse of excavated materials according to environmental guidelines and project plans.
- Embankment Activities:
- Complete the required daily verification of compaction efforts: either a proof roll or density testing, whichever was agreed to by the Engineer.
- Inspect embankment materials for compliance with specified quality and size requirements.
- Verify placement of materials in controlled lifts or layers in accordance with compaction requirements.
- Monitor compaction operations using controlled density or specified layer methods.
- Ensure embankment slopes are shaped and graded according to design plans to prevent erosion and ensure stability.
- Confirm proper drainage features are incorporated into embankments to manage surface water runoff effectively.
- Rock Excavation and Embankment Activities:
- Verify the Contractor is following the approved demolition plan.
- Inspect rock excavation to ensure compliance with specified depth and dimensions.
- During blasting, ensure the Contractor does not damage other property or endanger other workers.
- Verify shattered rock sizes and placement methods in embankments, ensuring adherence to design plans.
- Monitor choking of rock surfaces with fines or sand to prevent infiltration of other materials.
- Check for compliance with restrictions on placing stone or broken rock layers near subgrade surfaces.
- Check compliance of vibration monitoring system.
- Peat Excavation and Swamp Backfill Activities:
- Verify peat excavation depth and removal of organic-rich soil to stabilize the foundation.
- Ensure proper disposal according to environmental regulations.
- Monitor excavation methods to minimize disturbance to surrounding ecosystems and waterways.
- Check for restoration of excavated areas with suitable backfill materials, such as granular soil, to provide a stable base and facilitate proper drainage.
- Confirm shaping of backfilled areas to ensure effective drainage and prevention of water accumulation.
- Winter Grading Activities:
- Confirm winter grading limits are established and followed to manage frozen ground conditions.
- Monitor removal of ice, snow, or frozen materials before embankment placement to prevent future settlement issues.
- Ensure stockpiling of frozen materials outside earth disturbance limits to maintain construction efficiency and safety.
- Verify thawed materials used meet moisture requirements to achieve proper compaction and stability.
- General Inspection Practices:
- Conduct regular inspections throughout construction activities to ensure compliance with project plans, specifications, and environmental regulations.
- Document observations, deviations, and corrective actions taken.
- Communicate findings promptly with the Engineer and project team.
- Coordinate with contractors, subcontractors, and stakeholders to address issues and ensure timely resolution.
- Maintain thorough records of inspections, testing results, and approvals to ensure quality assurance and project documentation.
Testing
The Inspector should perform a proof roll or density testing on compacted backfill in accordance with the specifications.
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.
The Inspector should ensure the minimum number of required density tests are being performed per the Density Testing and Inspection Manual. Density for backfill needs to be achieved for each lift before subsequent layers are built up:
- Load Bearing Backfill: The maximum lift thickness permitted is 6 inches after compaction. Density needs to achieve a minimum of 100% compaction.
- Non-Load Bearing Backfill: The maximum lift thickness varies per density method used. Density needs to achieve a minimum of 95% compaction.
Geosynthetic materials must be tested according to the Materials Quality Assurance Procedures (MQAP) Manual prior to installation on the project. The Inspector should work with the testing agency to obtain a sample prior to installation of the material.
MEASUREMENT, DOCUMENTATION AND PAYMENT
Measurement and Payment
In situ material from the job site may be used for backfilling after the Contractor completes gradation testing of samples taken from an onsite stockpile. The respective MDOT material lab will confirm the gradation of the onsite material meets the requirements for the desired backfill material.
All excavation, embankment, and undercutting pay items are paid for by the cubic yard, and ditch cleanout and grading is paid by the station.
If no changes occur during construction and there are no known design errors, final quantities for earth excavation, embankment CIP, and the top 3 feet of embankment CIP (if provided), may be based on plan quantities (plan quantity plus or minus known changes is encouraged if Contractor staking, where the Contractor is responsible for determining final earthwork quantities, is not included in the contract documents). Verification with design must be completed prior to agreeing with the Contractor to pay plan quantity.
When it is determined not feasible to develop quantities based on plan quantities, earthwork volumes will be computed by average end areas. The cross-sections will be generated using the staked-section method. This method uses the original cross-sections taken prior to construction, and final cross-sections developed from the slope stake and grade stake data in the field notes.
The staked-section method eliminates the necessity for taking final cross-sections in the field. However, a sufficient number of field checks must be taken to assure compliance with the staked grades and tolerances. The recommended frequency is one check section per 5-station interval.
Peat excavation is measured using original and final cross-sections. Final cross-sections for deep peat excavations may require the use of borings to determine the depth of displacement.
Progress Payment for Earthwork
Progress documentation of excavation and embankment pay items may be based on a recorded estimate of work done. Excavation and embankment estimates using daily load counts and motor scraper and hauling unit capacities listed under the current Associated Equipment Distributors' Rate Book (or other equipment manufacturer book indicating capacities of equipment) may be used for this purpose. The Inspector should perform the following and document it in the DWR:
- Obtain the daily load count. Make independent spot checks of the load number at frequencies determined by the Engineer. These spot checks will be recorded on the DWR noting time interval of observation and load number. Variances between the project check and load count received should be evaluated.
- Select the struck capacity from the tables in the Associated Equipment Distributors' Rate Book, or equivalent, for the model(s) being used. When equipment of differing capacities is used in the same spread, assign each kind loads in proportion to the number hauling. Identify types of hauling equipment as it is brought to or leaves the project.
- Multiply the product of the load count and struck capacity by 80% for regular excavation and by 65% for compacted-in-place material.
- Generally, 80% partial payment is used for granular material and 65% partial payment is used for clay material.
- If necessary, revise the excavating and hauling unit capacities once sufficient earth has been moved and measured by engineering methods.
When load count quantities are limited by plan balances or by plan sheets and design quantities are not exceeded in any balance or plan sheet, other spot checks will not be required. Earthwork may be paid up to plan quantity on progress estimates based on load counts. Where subbase sections are uniform, template section computations may be used. Peat swamp excavation may be estimated from design volume sheets related to the portions completed.
Final Earthwork Quantities
Several methods are available to calculate final construction earthwork pay quantities:
- Planimeter Method/Digitizer
- Double Coordinate Method
- Computer Processing
On smaller projects, earthwork is more conveniently accomplished in the conventional manner of plotting and planimetering sections, or computing by the double coordinate method. However, earthwork on larger projects could be determined by conventional plotting and conversely, a computer could be used for smaller projects. This determination must be made by the Engineer based on conditions. On most projects, earthwork quantities are determined using a computer.
Plotting Cross-Sections
The original cross-section and slope stake notes are reduced and checked. The points are then accurately plotted on cross-section paper using a scale of 1-inch equals 5 feet both horizontally and vertically. The plotting of points are checked. Label the points for distance and elevation if one person is reading off the points while another plots. The plotter may then read back the points plotted. The persons most familiar with the terrain should make a cursory check for unusual variations in the cross-section. The slope stake points should be plotted and designated so they can be distinguished from other points. Slope stake data (distance, cut, ditch cut, and slope) should also be copied on the cross-section above the slope stake point. This will be used for checking later. The original section may be inked to distinguish it from other plots. Line quality is important not only for accuracy but for ease in tracing with the planimeter/digitizer. The progression of plotting should be from the bottom to the top of the sheet. Each section shall be identified with the proper stationing, lane, or ramp, directly below the section at the centerline. Datum elevation should be shown on the left edge on the heavy line that most nearly crosses the section at the centerline.
The final cross-section topsoil stripping, clay grade, undercuts, and boring notes are plotted over the original sections using the same coordinates and the same degree of care in plotting and checking. Colored pencil lines are often used to distinguish sections. Be sure to identify the significance of the color when color coding lines. Cross-sections showing the amount of topsoil removed should be plotted over the original section in both cut and fill sections, as this will be entered in the loss column on the volume sheet. The area occupied by the pavement, shoulders, subbase, sodding, and topsoil surface is also considered in determining the final end areas. The original and final cross-sections should close reasonably near the slope stake points, taking slope rounding into consideration.
To standardize field records and procedures and ensure legibility, a rubber stamp should be used to mark cross-section rolls. This information should be stamped at the beginning and ending of each roll and intermittently as needed. Following is a sample of the stamp to be used:
| Date | Initials | |
|---|---|---|
| Originals Plotted | ||
| Originals Checked | ||
| Finals Plotted | ||
| Finals Checked | ||
| Planimeter or Computed | ||
| Planimeter Checked |
A computer is now often used to plot cross-sections.
Planimeter/Digitizer
The planimeter/digitizer is used in determining the areas of cut and fill defined by the cross-sections by moving the tracing point of the instrument clockwise around the perimeter of the plotted area. Before planimetering/digitizing cross-sections, the horizontal and vertical scale of the planimeter/digitizer needs to be set. It is also necessary to check the setting of the planimeter/digitizer by circumscribing a known area. It is important that the sides of the trial square are laid out according to the scale of the cross-section paper, as swelling or shrinking of the paper due to weather conditions affects the accuracy of the work.
To ensure accuracy, each area should be circumscribed twice. The reading at the end of the second circuit should be twice the reading at the end of the first circuit. Furthermore, it is important to check the area roughly by observation or by scaling and rough calculation. Overall, the planimeter/digitizer will give results with less than 1% error, except for very small areas. The areas of cut and fill are determined in units of square feet for each section and entered on the standard volume sheets (Form 1198, Volume Record).
Computer programs are more readily used now in place of a planimeter and digitizer.
Measurements with Survey Equipment
Any survey equipment used to make digital measurements must follow the standards for equipment and use as specified in the MDOT Design Survey Standards of Practice. The type of equipment used (total station, GPS, etc.) must be appropriate for the pay item and the applicable tolerance. The measurement method used for each pay item must follow Subsection 109.01.B.1 of the Standard Specifications for Construction. Refer to the Digital Calculations for Payment of this manual for more information on survey equipment tolerances and required information to be included with each measurement.
Area Take-off
An end area measured in increments should be totaled and checked to ensure cuts and fills are entered in their appropriate columns.
Fill Section
If topsoil was stripped, the area stripped is entered on the cut sheet. The area of fill includes the stripped area plus the areas from natural ground to the bottom of the subbase. This is entered on the fill sheet. If final sections were taken after pavement was placed, the area of pavement, shoulders, selected subbase, and subbase are deducted from the total area. Subbase is ordinarily figured on a separate volume sheet, as it often originates from special or select locations. Topsoil surface and sodding are also subtracted from the fill area if these items were placed before final sections were taken. It is important that only topsoil stripped be considered as cut (except muck or peat as described later), since cutting below this is classified as subgrade undercutting and is paid for as such.
Cut Section
Cut area includes everything from subgrade (clay grade) to original ground, including area of topsoil stripped. If final sections were taken after pavement, etc., was placed, the area of pavement, shoulders, base, subbase, topsoil surface, and sodding must be added to the cross-sectioned area and entered on the cut sheet.
Peat Section
The peat that is excavated or displaced is entered as cut on the peat excavation volume sheet. Excavation and displacement of peat should be allowed only per limits of the peat excavation stakes, as set prior to the operation. A slide-out beyond the peat excavation stakes is not considered peat excavation. The full amount of material required to stabilize the swamp will be paid for as Backfill, Swamp, regardless of the limits set on stakeout. Swamp backfill, when practicable, will be measured in its original position. If it is not considered practicable to measure in its original position, the volume will be computed within the limits shown on the Standard Plan R-103 series and will then be increased by a 15% shrinkage factor.
Volume Calculation
The following formula should be used to determine volumes by the average end areas method: [(A1 + A2) / 2] * D = V Where A1 and A2 are the cross-section end areas in square feet D is distance between sections in feet V is volume in cubic feet
Double Coordinate Method
An alternate method of computing earth excavation, embankment, etc., is by latitudes and departures by the double coordinate method using a printout calculator.
The printout calculator also readily adapts itself to other operations such as computing clearing, seeding, etc.
Theoretically it may be possible to compute areas without plotting the cross-sections. However, in most cases, cross-sections should be plotted. At every point plotted, it is important to label the distance from centerline and elevation. A consistent system should be maintained throughout. An error in plotting will ordinarily not affect the area as long as the point is labeled correctly.
To compute an area, follow these steps in conjunction with the following figure.
- Divide the area at centerline or 0 distance out.
- Starting at a convenient point, proceed to set up a table of distances and elevations as Tables 1 and 2, making sure to close by repeating the starting point. For the area left of centerline, proceed in a clockwise direction; to right of centerline proceed in a counterclockwise direction. In the tables, distances are always on the left and elevations on the right. Proofread the tables against points.
- Proceed to cross-multiply down the table, multiplying the number on the left with the number on the right the next line down.
- When the bottom of the table is reached, total cross-multiplications. If used correctly, most calculators will accumulate this total as they go along.
- Cross-multiply up the table starting at bottom left and multiplying by the next line up to the right. These multiplications are all negative.
- When the top of the table is reached, cumulate negative totals and subtract from positive total. On most machines this total will have been carried continuously.
- Divide total by two, which will give the area computed.
- Add left and right areas together for total section.
- Proofread tapes against tables.
- Sign and date tapes. Label tapes.
For volume computations of earth excavation, embankment and swamp excavation, proceed in the same manner as used in the planimeter method/digitizer.
Documentation
The DWR should show the Inspector’s measurements, computations, and supporting documentation verifying the quantity submitted for payment and work performed. All materials used must be visually inspected by the Inspector and noted on the DWR.
The Inspector should note in the remarks section of the DWR the condition the excavated material, material verification being placed, and equipment used for the delivery, and placement of the geosynthetic material.
Additional documentation once the work is completed should include:
- Length, width, and height being paid on each date.
- Survey or other approved methods for verification the roadway earthwork was constructed in conformance with the contract documents.
- Volume and tonnage of bedding and backfill material placed.
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.
LOCAL AGENCY PROJECTS
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RAIL PROJECTS
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