205 - Roadway Earthwork
GENERAL
-Reserved-
MATERIALS
Borrow/Use of Excess Property
Earth material found outside the grading limits is considered borrow material. This can include material either inside or outside the ROW. 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 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 needs to be included within the authorization.
Occasionally, parcels of excess property may be available to the Contractor for use as a source of borrow, for permanent and/or temporary storage of disposed materials, and for Contractor's yards and the like. The availability of excess property may be indicated in the contract documents and often a real estate vicinity map further detailing the excess properties is included (this is especially true in the construction of relocated freeway projects where several properties adjacent to the project are considered excess properties). MDOT makes no commitments or guarantees as to the Contractor's ability to use these excess property parcels outside of the project ROW at the time of the bid letting and without the prior authorization of the Engineer after the bid letting. However, for the Contractor to be able to use these properties, several factors need to be taken into consideration and, if applicable, included in the authorization language. These include:
- The Contractor will be responsible for ascertaining whether any of the excess properties and/or surrounding parcels indicated in the contract documents, or proposed for use, are enrolled in Public Act 116 agreements, 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 himself 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 (SUP) 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 amount of time required to obtain a SUP may be a minimum of three months.
- 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), including proposed grading limits and elevations. This plan should be attached to the authorization. All conditions of subsection 205.03 of the Standard Specifications for Construction (Disposing of Surplus and Unsuitable Material) 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 those of the Contractor. The Engineer reserves the right to include other costs for the use of these properties, as may be required, at the time of authorization.
- 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 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 (300 mm) is allowed. Refer to subsection 205.03 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 that 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. See Section 210, Environmental, of this manual for Contractor yard requirements relating to this issue.
- 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.
CONSTRUCTION
Earth Excavation
Section 205 of the Standard Specifications for Construction details construction operations necessary to complete the earth grade. Excavated materials should always be free of debris from other operations. Material susceptible to frost heave, such as silt, will not be placed within the top 3 feet (1 m) of subgrade when constructing embankments.
Soil type, quality and compaction are vitally important to any engineering structure. Although preliminary soil investigations will have been made on any grading job before construction, they may fail to disclose various contrasting localized soil conditions. Only excavation during construction will reveal them. When these variant soils are encountered, they must not be ignored, as additional treatment may be necessary. Project personnel should contact Region soils personnel to make an inspection.
Each office should have a copy of the Field Manual of Soil Engineering available as an aid to project personnel in soil identification and treatment. Unless otherwise designated, all excavated material will become the Contractor’s property except as provided under Salvaging Materials in subsection 205.03 of the Standard Specifications for Construction.
The roadbed and ditches should be maintained so the work will be well drained at all times while still controlling erosion and sedimentation. The ditch sections and roadway slopes will be checked during construction to ensure that the cross section is according to plan and slope stakes. Check drainage outlets before constructing ditches to determine the direction of flow. Outlet ditches and channels should be excavated before starting other items of roadway excavation or drainage structures. This prevents flooding other operations and work can proceed more efficiently. The standard specifications permit disposal of undesirable or surplus material in the ROW. However, this material shall not be deposited in any wetland or flood plain on either public or private property.
Staked Section Method
The staked-section method for computing final earthwork quantities precludes the necessity of taking final cross sections. Slopes should be checked and adequately documented to make sure they are not "hollow" or "bellied out." Back slopes will be finished to either Class A or Class B slopes, as shown on the plans. Should cut or embankment slopes exceed these tolerances, the slopes will either be corrected or a deduction will be made from the final volume quantities.
The end and top sections of all cuts will be rounded or turned out for better appearance. Turning out the ends of cuts and rounding the top of the slope greatly improves the appearance of the finished highway section and is a requirement of the standard specifications.
Intercepting Ditches
Intercepting ditches will be placed back of the top of the slope where necessary for erosion control. These intercepting ditches should be placed, even though not shown on plans, as recommended by Region soils personnel. Intercepting ditches are measured by length along the ditch centerline in meters and reported on the IDR.
The grade inspector should become familiar with the typical cross section and staking procedures used on the project and should work closely with the survey crew so that all necessary field measurements of undercuts, etc., may be made with a minimum of inconvenience. Earthwork is final measured by average end area and not load count or other means. The grade inspector should be familiar with the planned drainage and all material sources and should know the limits of the ROW and borrow sites, as well as any conditions imposed by deeds or agreements. Disposal sites will be restored according to subsections 105.03 and 205.03 of the Standard Specifications for Construction.
Reporting earthwork quantities requires accurate observation and documentation. Design quantities can be inadequate, particularly if building demolition work has been done. Design cross sections do not always include basement excavations. Document any known plan omissions or revisions.
Preparing Roadway Foundation
The roadway foundation must be properly prepared to provide uniform support and a stable structure. During embankment construction, the following operations should be performed as required.
Removing and Salvaging Topsoil
Reduce vegetation to a height of approximately 6 inches (150 mm) and remove all litter or foreign material. Topsoil should be removed within the grading limits from roadway embankment and cut areas unless otherwise specified. The topsoil will be completely removed to the required depth prior to the beginning of regular excavation or embankment. The inspector should be careful that the Contractor does not strip too deep in embankment areas. It is not necessary to remove "B" horizon material in the stripping operation; however, scraper operators are inclined to continue stripping as long as they see dark material. If the inspector has any problem differentiating between "A" and "B" soil horizons, the Engineer or Region soils personnel should be consulted.
Structure Embankment
Strip topsoil from areas within the grading limits of the structure embankment and compact the stripped natural ground area to a minimum of 95 percent of maximum unit weight to a depth of 9 inches (250 mm).
Winter Grading
Remove all snow and ice from the embankment area. If the original ground contains more than 0.3 foot (90 mm) of frost within the limits of 1 on 1 slopes spreading outward from the finished shoulders, the frozen material will be completely removed.
All ground containing frost within limits of 1 on 1 slopes, spreading outward in all directions from the bottom of structure footings, will be removed.
Waste or stockpile the frozen material outside the grading limits.
Unless the progress schedule requires a winter operation, removal of frozen material and embankment to replace such excavated material will not be paid for.
Stepping Steep Side Slopes
Where embankments are to be placed on existing side slopes steeper than 1 on 6, cut horizontal 3 foot (1 m) benches into the slope.
Salvaging Material
When material is salvaged and stockpiled, it should be located so as not to impede drainage or damage trees.
Cross Sectioning
All stripped areas under embankments should be cross-sectioned prior to placement of fill material. Location and dimensions of each area should be recorded by the inspector and/or survey crew.
Grading Cut Sections
As all excavated material becomes the Contractor=s property, unless otherwise designated, it may be used for any other item of work provided specification requirements are met for that item.
The subgrade is to be compacted to 95 percent of the maximum unit weight to a depth of 9 inches (250 mm). If the natural material is to be left in place for subbase, the compacted depth will be increased to 12 inches (300 mm), except when other requirements are specified.
Care must be taken to avoid removing or loosening material outside the required slopes. Any such material so removed or loosened will be replaced and thoroughly compacted. Material placed in this manner has a greater tendency to slide than undisturbed earth.
Rock surface encountered within the grading limits will be sufficiently exposed to permit adequate measurement prior to removal of the rock.
Rock Excavation
This work consists of the removal of solid rock or cemented soils that do not soften when wet or cannot be excavated without continuous drilling, blasting or continuous use of a ripper or other special equipment. It also includes excavation of all boulders 0.5 yd3 (0.5 m3) or more in volume. Rock in the excavation will be removed to the required cross section. No rock will project more than 6 inches (150 mm) above the lines of the required cross section. The back slopes are to be excavated to the neat lines shown on the plans with no rock projecting more than 12 inches (300 mm) from the true slope. The inspector should not make a determination of what constitutes indurated or firmly cemented material that should be classified as rock.
When questionable material appears in a cut section, it should be called to the Engineer’s attention who may contact the Region soils personnel to make a field determination.
Field Cross Sections for Determining Volume
Because of the high cost of rock excavation, field cross sections for determining volume should be taken at a maximum spacing of 25 to 30 feet (8 to 10 m). 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 IDR. 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
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.
The Engineer should also ensure that explosives will be used only in the manner provided by law, including local ordinances, and the work will 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 that no flying rocks will cause harm to people or damage to property.
The IDR should indicate the following information:
- Show method of breaking rock (ripper, blasting, etc.).
- Location and number of holes, type and quantity of explosives placed and the 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).
Subgrade Undercutting
There are three 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.
Accurate records are necessary to ensure that the proper type of subgrade undercutting is reported.
Subgrade undercutting will be excavated within the limits established by the 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 specification are met.
When excavation has been completed to within 6 inches (150 mm) of the subgrade, or the topsoil has been stripped in preparation for placing embankment, Region soils personnel will be notified. Timely notice is important so an investigation can be made while the cut is fresh and soil textures and conditions are more readily identifiable.
Region soils personnel 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 (1 to 1.2 m) in the southern and central parts of the state and to 5 feet (1.5 m) in the northern, depending on conditions.
The width of excavation 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 (8 to 15 m) long.
The excavated area may be backfilled with material having the same physical characteristics as the adjacent soil, as directed by Region soils personnel. 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 will be 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 percent grade to the outlet.
Frost heave also occurs where there is an abrupt change in soil texture. The condition is corrected by selective excavation or by thoroughly mixing the two soils. The mixing operation is generally accomplished with scrapers by excavating half width of the area and stockpiling. Material from the remaining half is then excavated and placed in the half already removed. The stockpiled material is then used to complete the backfill. Handling of the excavated material is limited to one and one-half times by this method.
Transition areas occur where the grade changes from cut to fill. The grade should generally be undercut to eliminate topsoil and the less stable "B" horizon material while providing a longer transition and mix from one type of soil to another.
Constructing Ditches
Removal of material from ditches is generally classed as earth excavation as ditches are normally excavated along with general road cut using typical earth moving equipment. 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 will 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 make any modifications necessary.
The Standard Specifications for Construction requires the roadbed and ditches to be maintained in such condition that the work will always be well drained without causing accelerated erosion. Be positive with drainage at all times, providing temporary measures when and where necessary. The inspector should ensure that ditches are cut to the required dimensions, not only during the rough grading stages but also during final trim and cleanup. Too often ditches become filled with excess material trimmed or eroded from slopes. 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.
Be sure that 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.
Subsection 208.03 of the Standard Specifications for Construction stipulates that all grading sections will be brought to final grade immediately as the grading progresses, and that permanent soil erosion controls will be completed within 5 calendar days after final grading. Where it is not possible to permanently stabilize a disturbed area, temporary erosion controls will 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 the completion of these controls. See Section 208, Soil Erosion and Sedimentation Control/NPDES, of this manual for other means of bringing the Contractor into compliance with these stabilization issues. If the Contractor violates the law, then so does MDOT.
If it is found necessary to make any drainage change on 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, Soil Conservation Service USDA, County Agricultural Agent or others, must be cleared through the Region office, as MDOT may require a formal agreement. A phone call to the appropriate Region Engineer for authorization to make immediate changes is suggested.
Disposing of Surplus and Unsuitable Material
The Contractor will be 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. The 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 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 use for disposal to ensure that the proposed disposal site(s) do not contain wetlands. Restoration and erosion control measures as per Sections 105, 205.03 and 208 of the Standard Specifications for Construction are required.
Cost Over Runs From Off Site Disposal of Soil
This section serves to inform construction project engineers of the potential for cost over runs due to unanticipated soil disposal costs, along with options available to avoid or reduce those costs. Projects with large quantities of soil that must be disposed of off-site are of particular concern, even if contamination is not suspected. This is because soil disposal locations are increasingly requesting laboratory analysis of the apparently clean soil to confirm that material they are accepting is truly “clean fill”. The soil samples collected for this laboratory analysis will potentially determine how the project soils will be disposed. Several things can cause misleading laboratory results. These include:
- Improper sampling and handling may result in sample contamination during collection or transport to a laboratory.
- Construction activity, such as diesel equipment movement on site, 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.
In projects where large volumes of clean soil will need disposal, it is important to find out the requirements of the disposal location as early as practical. If laboratory testing is required, make arrangements for proper sample collection. This material is not covered by the Special Provision for Non Hazardous Contaminated Materials Handling and Disposal; therefore, the construction contractor should not collect the samples.
Disposal locations may reject soil if the sample analysis of the material exceeds a background concentration, even if it does not exceed Michigan Department of Environmental Quality cleanup criteria.
If the soil is rejected by the contractor’s disposal location, other disposal options may be available. Contact Environmental Services for assistance with these situations. Local agencies may also contact this office for assistance with projects with State of Michigan funding.
Constructing Embankment
Embankments are generally constructed by three methods. (The last method will be discussed under Swamp Treatment.
- Controlled density method.
- 12 inch (300 mm) layer method.
- Embankment construction through swamps.
Highway construction methods and needs often result in the construction of the roadway embankment and pavement during the same construction season. This rapid rate of construction necessitates rigid control of embankment compaction. It is important for the grade inspector to maintain continual visual inspection of embankment operations to ensure density testing is adequate.
Embankments should be constructed and maintained so that the work will be well drained. If rain appears imminent, the embankment can be rolled with rubber-tired equipment to seal the surface and slow water absorption. Water should be drained away by gutters or other temporary drainage facilities. In loam and clay soils, the problems of obtaining stability and density become worse as the moisture content rises above optimum.
Heavy earth moving equipment generally causes some "kneading" or movement of a compact clay fill under passing wheel loads, even though the soil meets density requirements. In all but dry, clayey soils, a moderate amount of such movement is to be expected and is not detrimental. Overall, the surface should rebound after the wheel passes and should not leave ruts more than 1 to 3 inches (25 to 75 mm) deep.
Occasionally, some sensitive clays are observed to rut deeply, even though the density and moisture requirements are within specifications. When this occurs, density test computation procedures and equipment should be reviewed to confirm that specification requirements are being met. If the condition continues, it is suggested that the Engineer consult with Region soils personnel to determine whether disking and drying should be performed to assure a more stable embankment and firm subgrade.
Although the type of compactive equipment used is entirely the Contractor=s option, experience has shown that certain equipment is more efficient in compacting one type of soil than another:
- Sheepsfoot Roller - More effective in compacting clay than sand.
- Vibratory - Very effective on granular soils and relatively inefficient for compacting clay.
- Heavy, Multi-wheeled, Pneumatic Rollers - Effective for all types of soils.
- Small Plate Vibrators - More efficient than tampers in compacting granular trench backfill.
For many soil types, the top 2 inches (50 mm) or so of the layer being compacted remains loose until it has been confined by placement of the succeeding layer. For that reason, it is important that the loose surface be scraped away before the density test is taken.
Winter Grading
Winter grading is difficult and it is up to the Engineer and grade inspector to see that 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 percent above optimum is generally unsuccessful during freezing weather because it is impossible to dry the soil. 20°F (-6°C) is about as low a temperature as cohesive soils, at about optimum moisture, have been successfully placed. Little success in compaction, even with clean granular material, has resulted with the temperature below 15°F (-9°C).
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 not be paid for. 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 0.3 foot (90 mm) of frost except in those areas that will support a structure. More than 0.3 foot (90 mm) 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.
Controlled Density Method
The controlled density method applies to the placement of all embankment and backfill material unless otherwise specified on the plans or in the proposal. Methods for performing density tests are detailed in the Density Control Handbook available in each density kit. The material must be placed in layers not more than 9 inches (250 mm) thick and compacted to the minimum specified density before the succeeding layer is started, except that granular material may be placed in layers up to 15 inches (350 mm) in thickness if the specified density is obtained. It should be noted that under this method, the means of compacting the material or the type of equipment used by the Contractor is not specified.
Obtaining Density
Where tests indicate inadequate density, it is generally due to one of two reasons:
- improper moisture content
- insufficient compactive effort
Improper moisture content of the soil being compacted is the greatest single cause of difficultly in attaining the specified minimum density, especially for cohesive soil. For cohesive soils, the specification requires that moisture content be no greater than 3 percent above optimum, except that the moisture content of the top 3 feet (1 m) of embankment will not exceed optimum. If the moisture is significantly above this, the required density cannot be attained regardless of the amount of compactive equipment or effort applied. In that event, the material must be disked, aerated and dried.
Where large areas of embankment are to be constructed, a layer of wet material may be left to dry while placing or compacting operations are alternately being performed at another embankment area. Because the natural moisture content of clay soil is often near optimum or above, the addition of water is generally not required except for the upper 3 feet (1 m) that may be found to be excessively dry during the summer months. Where the cut material is composed of both wet and dry material, loads including both materials or alternate layers of each may result in an average moisture that will permit proper compaction. Such operations may require some mixing after the material is deposited on the grade before compacting.
Although it is generally not economically practical, the Contractor may elect to waste the wet material and replace it with an equal volume of drier material. When weather conditions permit little or no evaporation, wet material cannot be manipulated, aerated and dried. During such periods, which generally include late fall, winter and early spring, the Contractor often chooses to wait for more favorable construction weather.
Compacting Granular Soils
The compactive characteristics of sand soils are much less sensitive to moisture variation, and sand can be satisfactorily compacted over a wide range of moisture. Inasmuch as the natural moisture of sand deposits is often in a bulking range of 3 percent to 5 percent, compaction can often be attained quicker and with less effort by adding water. Excessive moisture is generally not a problem with sands except for saturated fine sand that has been excavated from below the water table. The usual solution is to stockpile or to place a layer of the material and allow it time to drain before compaction is attempted. This procedure should not be used in a mixed clay-sand fill or over clay. The compaction of granular material can generally be done in wet weather and sometimes in freezing weather.
Sometimes the soil comprising the original ground contains excessive moisture so that the first layer of a clay embankment cannot be satisfactorily compacted. It is common for the spongy condition to progress upward into each succeeding layer that is placed. It may be possible to overcome the problem by disking and aerating the original ground. If the original ground contains so much excess moisture that manipulation is not practical, it may be necessary to construct the first layer using granular material to attain stability. The specifications allow a layer of granular material over poorly drained soil.
When the moisture content of the embankment material is at or near the optimum, the Contractor should have little difficulty in obtaining satisfactory density, if adequate compactive effort is being applied. With modern earth moving equipment, compaction is often attained by the hauling units alone if the spread covers a large area, the material is placed in thin layers and the units break track for maximum compactive coverage. A compaction problem may occur when many units are hauling a short distance to a small embankment area. Either supplemental compactive equipment must be added, or the number of hauling units reduced, to attain a balanced operation.
Whenever the density tests indicate the Contractor has not obtained specified density, he must be advised that the succeeding layer may not be placed until the specification requirement is met. The decision as to what corrective work is to be done is left up to the Contractor. From the test results and from observation, however, the inspector will recognize the reason for low density and should suggest appropriate action such as disking to dry wet soil, adding water to a dry soil, or simply doing more rolling, if moisture is not a problem.
While the specifications permit the placing of a layer not to exceed 9 inches (250 mm) [15 inches (350 mm) for granular soils], it will be found that from the Contractor's standpoint, under most conditions, the most efficient layer thickness is 3 to 6 inches (80 to 160 mm). This layer thickness requires less compactive effort to obtain specified density and promotes better hauling conditions.
Frozen Material
No frozen material will be allowed in the embankment area being constructed under density control. The embankment will be completed to grade with no frozen material in it. Any frozen material on partially completed fill will be removed and stockpiled before placing any more fill on the embankment. The thawed material from the stockpile may be used in embankment slopes outside the 1 on 1 slope lines from clay shoulder points. The embankment outside the 1 on 1 slope may be completed by the 12 inch (300 mm) layer method. Fills should be built by the "ramp" method during freezing weather to help minimize the frost problem.
Embankments should be constructed in a manner to provide stable slopes. Internal granular drainage should not be blocked by placing impervious material on the outside. If this situation occurs, the operation must be changed or other corrective measures taken. An unstable condition can also be created by pockets of pervious and impervious material in the embankment.
Topsoil as Embankment
If the stripping operation produces more topsoil than necessary for topsoil surface on the project, the excess material may be placed in the embankment outside the 1 on 1 slope from the earth grade shoulder when the finished slope is to be 1 on 4 or flatter, if shown on the plans or directed by the Engineer. This topsoil will be compacted according to the 12 inch (300 mm) layer method.
Structure Embankments
Structure embankments will be constructed by the controlled density method as follows:
- 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 percent of the maximum unit weight when piling is not required and 95 percent when piling is required.
- Structure embankment will be protected from freezing until the overlying footings are cast.
Top 3 Feet (1 m)
The top 3 feet (1 m) of embankment will be constructed to a stable, nonrutting condition by using a uniformly textured material. This material will not contain more than 50 percent silt or have a plasticity index less than 10 percent. A 50 foot (15 m) long longitudinal transition will be used between two different uniformly textured materials.
Constructing Rock Embankments
Rock embankment will be constructed of shattered rock in layers not to exceed 3 feet (1 m) in thickness. This rock can come from cut sections in the roadway or from borrow areas of waste mine rock. Shattered rock will not exceed a maximum size of 12 inches (300 mm) in greatest dimension and will be deposited on the fill and pushed over the end of the fill by means of bulldozers. Dumping the rock directly over the end of the fill will not be permitted. The surface of the rock embankment will be choked with small rock fragments, rockfines or sand to prevent infiltration of other fill materials placed on the rock. This method will not be used in fills less than 4 feet (1.5 m) in depth. In no case will stones and broken rock layers be placed within 2 feet (1 m) of the subgrade surface.
During winter operations, fills made of rock in subfreezing temperatures should be avoided or should be limited to fill slopes outside the 1 on 1 clay shoulder point. Too often frozen particles of ice and snow are on the surfaces of the rock and a completely compacted fill cannot be constructed. The snow or ice upon thawing will cause irregular settlement with accompanying maintenance problems. In guardrail fill sections, rock fills should be kept to a grade line below the depth of the bottom of guardrail posts. In no case will the rock embankment be placed within 2 feet (600 mm) of the earth grade.
Where structures are located under rock embankment, they will be covered with not less than 2 feet (600 mm) of Granular Material Class III before the rock embankment is placed over structures.
Swamp Treatment
All swamp areas should be shown on plans with a specific method of treatment indicated. All low, poorly drained areas not shown as peat or muck should nevertheless be checked to confirm that organic material is not present. Peat that has been covered by a layer of nonorganic soil is generally shown as Wallkill soils series and should be treated the same as deposits identified as peat or muck. Region soils personnel should be called if a Wallkill condition is suspected and not shown on the plans.
Swamp backfill material is designated as Granular Material Class III that allows a maximum of 15 percent loss by wash unless otherwise specified on the plans. Swamp treatment is to be performed according to the current standard plans unless modified on the plans or by special provision. Unsuitable material that is covered by this standard includes peat, muck, marl and very soft clay.
Methods of swamp treatment are identified as Method A, B or C. Refer to Standard Plan R-103 Series. The number 1 or 2 following the letter refers to single or dual roadway.
Method A
This method is referred to as total excavation and is designated for deposits up to 15 feet (4500 mm) deep. 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 (600 mm) 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.
In excavating Method A swamps, usually the trench is partially or completely filled with water. Systematic probing must be done 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 in relation to Method A treatment.
Where Method A is used for swamps exceeding 10 feet (3000 mm) in depth, or where the excavation results in a wet trench, a 10 foot (3000 mm) moving surcharge will 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 probings or cross section readings.
Method B
This method is used for swamps often greater than 15 feet (4500 mm) in depth [muck depth could be less than 15 feet (4500 mm) also] 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 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. In order to create a condition of maximum unbalance, it is required that the trench be maintained at a minimum depth of 15 feet (4500 mm) below original ground [or depth of the peat, if less than 15 feet (4500 mm)] 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 that the front of the surcharge be maintained at the proper height to ensure enough weight to displace the unsuitable material beneath. If satisfactory displacement action is not being obtained, the Contractor may be required to loosen the peat below the 15 foot (4500 mm) trench by pulling the dragline bucket through it. Occasionally, for stiff peat, additional surcharge height may be required to effect proper displacement.
The rate the surcharge is advanced must be kept in balance with the rate of excavation of the peat. A common problem 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 cause trapping of peat beneath the fill. To correct the problem, the Contractor must either use additional draglines to excavate peat or reduce the number of units hauling backfill. This 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 has shown that two draglines are a desirable minimum because of the width that the peat must be cast and the greater volume of peat that must be handled. For swamps deeper than approximately 25 feet (7.5 m), additional draglines are often necessary because the large volume of waste peat requires recasting further back from 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. 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.
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 (20 m). 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
Method C is used where an existing road is to be widened and there is little soft peat left under the existing fill or if it is so consolidated that it does not require removal. The treatment consists of excavating the peat along the sides of the existing embankment. This method generally applies only to shallow swamps where total excavation can be successfully accomplished. Therefore, the requirements of Method A also apply to Method C. Trench widths are usually more restricted.
Peat Disposal Areas
Peat disposal will be on upland sites and not in wetlands or floodplains. This will, in most cases, prevent casting the peat excavation off to the side beyond the slope stake line for storage. The proposal and plans for the project should be reviewed thoroughly so that the peat disposal methods are thoroughly understood. The standard plans do, however, allow peat to be placed within the normal slope limits called for on the plans.
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 and paid half the cost of the swamp backfill material removed as earth excavation.
Test-Rolling
Test-rolling the grade is a very important procedure for determining uniform stability of the subgrade. Perhaps the most important subgrade quality to attain is stability. Test-rolling is to be done in addition to the density control testing where it is set up on the job or recommended by soils personnel.
Note: This procedure is detailed by special provision only and is no longer described in the Standard Specifications.
The testing operation with the heavy pneumatic-tired test roller consists of one complete coverage of the test roller over both embankment and cut sections. Because of wheel spacing, two passes are required to provide complete coverage. The Engineer may request a second coverage if it is necessary. Any cut or fill area showing signs of instability, but not showing complete failure after one coverage, should be test-rolled a second time for possible weakness. Generally in urban areas, where underdrainage or utility lines might be damaged, test-rolling will not be conducted.
Ordinarily, the test roller is operated with a load of 40 tons (36 metric tons) at normal operating tire pressure. However, specifications provide for varying both gross weight and tire pressure by the Engineer. Sensitive clays that show a kneading and rebound movement under heavy wheel loads may have to be tested under reduced load. Failure is defined as a shear or rutting and is considered unacceptable. Failures should be checked for density as soon as possible after detection. If failure is caused by low density in the embankment material, the Contractor will be required to correct the failure areas at his own expense. Unstable soil shall be removed by the Contractor and the grade completed with suitable material.
Test-rolling of the grade during the winter operations will be required as specified, except for sand embankments. Sand embankments may be completed to grade without test-rolling during winter construction with prior approval. Test-rolling with two coverages must be done after the frost has gone. Under no conditions will test-rolling of a frozen grade be permitted. Test-rolling of sand subbase will not be required.
Note: This procedure is detailed by special provision only and is no longer described in the Standard Specifications.
The testing operation with the heavy pneumatic-tired test roller consists of one complete coverage of the test roller over both embankment and cut sections. Because of wheel spacing, two passes are required to provide complete coverage. The Engineer may request a second coverage if it is necessary. Any cut or fill area showing signs of instability, but not showing complete failure after one coverage, should be test-rolled a second time for possible weakness. Generally in urban areas, where underdrainage or utility lines might be damaged, test-rolling will not be conducted.
Ordinarily, the test roller is operated with a load of 40 tons (36 metric tons) at normal operating tire pressure. However, specifications provide for varying both gross weight and tire pressure by the Engineer. Sensitive clays that show a kneading and rebound movement under heavy wheel loads may have to be tested under reduced load. Failure is defined as a shear or rutting and is considered unacceptable. Failures should be checked for density as soon as possible after detection. If failure is caused by low density in the embankment material, the Contractor will be required to correct the failure areas at his own expense. Unstable soil shall be removed by the Contractor and the grade completed with suitable material.
Test-rolling of the grade during the winter operations will be required as specified, except for sand embankments. Sand embankments may be completed to grade without test-rolling during winter construction with prior approval. Test-rolling with two coverages must be done after the frost has gone. Under no conditions will test-rolling of a frozen grade be permitted. Test-rolling of sand subbase will not be required.
Trimming and Finishing Earth Grade
After the earth grade has been constructed to the required grade, all stones and rocks more than 3 inches (80 mm) in diameter appearing on the surface will be removed. The subgrade shall be trimmed to the grade called for on the plans and within the tolerance stipulated in the specifications. All irregularities on the earth grade outside the subgrade will be trimmed to the required lines and grades.
Class A slopes will be finished to the slopes shown on the plans with no variations at any point more than 0.1 foot (30 mm) above or below the established grade measured at right angles to the slope.
Class B back slopes will be finished to the slopes shown on the plans with no variations at any point more than 0.5 foot (150 mm) above or below the established grade measured at right angles to the slope. Abrupt variations will not be permitted.
Class B fill slopes will be finished to within 0.2 foot (60 mm) of the required grade and cross section from the outside shoulder line for a distance of 3 feet (1 meter) down the slope. The remainder of the fill slope will conform to the requirements of Class B back slopes.
Wetland Construction
If a wetland is to be constructed in association with a project for mitigation purposes, there will generally be plan sheets detailing the construction requirements as well as a special provision for Wetland Replacement that should be followed. It is extremely important that all wetland construction work be done in close conformance with the plans and cross sections for fulfillment of the mitigation requirements.
If the plans do not specifically address these issues, the following should be taken into consideration:
- Permanent fencing is generally installed prior to the beginning of any excavation of the wetland site. There may be other specific requirements of the SUP issued to MDOT for construction of the wetland that will need to be followed by the Contractor.
- All excavated material will become the property of the Contractor. The Contractor may elect to use excavated material, where suitable, for construction requirements elsewhere on the project. Payment for the wetland is now made to the Contractor for excavation to the original plan contours and elevations to ensure that all excavation takes place as planned, regardless of suitability of material (the pay item is generally Excavation, Earth-Wetland or Excavation, Earth).
- No over-excavation of the wetland should be allowed unless the Engineer can be guaranteed that the Contractor has suitable material to return the wetland to the planned contours and elevations. Over-excavation, if allowed, needs to be authorized by the Engineer. The authorization should clearly state that the Contractor will not be paid to overexcavate the wetland site (as either Excavation, Earth-Wetland or Excavation, Earth), will not be paid to place the replacement material at the site to return it to planned contours/elevations and an appropriate charge should be made for the over-excavated material (unless over-excavation was allowed as a part of the original contract documents). If a forested wetland is to be constructed and over-excavation is requested by the Contractor, the replacement material is critical and needs to be able to support the tree plantings that will be made at the wetland.
- Dewatering, if allowed for the construction of the wetland, will not be paid for separately. In sensitive locations, such as several houses surrounding the wetland construction site, the plans may indicate that if dewatering is used, the Engineer may require the Contractor to stop dewatering at any time due to groundwater fluctuations as indicated in the monitoring wells. The Contractor will not be allowed claims on the basis of dewatering.
- The placement of monitoring wells (either by contract or in advance of the contract) is not to be construed to relieve the Contractor of any responsibility for damage to adjacent property as outlined in subsection 107.07 of the Standard Specifications for Construction
MEASUREMENT AND PAYMENT
Machine Grading
Machine grading is used only when light grading, such as may be accomplished with a blade grader, is required to develop the desired section. This item includes the shoulders, slopes and ditches and does not involve any loading and hauling of earth, unless modified by a special provision.
Measurment of Earthwork
If no changes occur during construction and there are no known design errors, final quantities for earth excavation, embankment CIP and top 3 feet (1 m) 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).
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 utilizing 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 should be taken to assure compliance with the staked grades and tolerances. The recommended frequency is one check section per 5 station (200 m) interval.
Peat excavation will be 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 of Earthwork
Progress documentation of excavation and embankment pay items may be based on a recorded estimate of work done. Excavation and embankment estimates utilizing 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 procedure to be used is as follows:
- Obtain the daily load count. Independent spot checks of the load number will be made periodically by the inspector at frequencies determined by the Engineer. These spot checks will be recorded on the IDR 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, each kind will be assigned loads in proportion to the number hauling. Types of hauling equipment will be identified in the IDR when the hauling equipment is brought to or leaves the project.
- Multiply the product of the load count and struck capacity by 80 percent for regular excavation and by 65 percent for compacted-in-place material.
- The above information and calculations will be recorded in the IDR.
- When sufficient earth has been moved and measured by engineering methods, capacities of the excavating and hauling units may be revised.
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. They are:
- Planimeter Method/Digitizer
- Double Coordinate Method
- Computer Processing
On small projects, the earthwork is more conveniently accomplished in the conventional manner of plotting and planimetering sections, or computing by the double coordinate method. However, earthwork on longer projects could be determined by conventional plotting and conversely, the computer could be used for shorter projects. This determination must be made by the Engineer based on conditions. On most projects, earthwork quantities are determined using the 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 (25 mm equals 1.5 m) both horizontally and vertically. The plotting of points is 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:
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Originals Plotted |
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Originals Checked |
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Finals Plotted |
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Finals Checked |
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Planimeter or Computed |
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Planimeter Checked |
The 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 percent error, except for very small areas. The areas of cut and fill are determined in units of square feet (square meters) for each section and entered on the standard volume sheets (Form 1198).
Area Take-Off
An end area measured in increments should be totaled and checked to be sure that cuts and fills are entered in their appropriate columns. Following are examples of area take-off for typical sections.
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 Sections
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 Sections
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 percent shrinkage factor.
Volume Calculations
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 (square meters)
D is distance between sections in feet (meters)
V is volume in cubic feet (cubic meters)
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. These machines may be readily available for use at the project offices.
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, work these instructions in conjunction with Figure 205-1.
- 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.
Computer Processing of Earthwork
For plotting of cross sections and determination of earthwork quantities, the computer is often used. Two computer programs are generally used for the plotting/computations. These are IGRDS (Design Files) and CAICE. Eventually, all TSCs will be equipped with these computer capabilities. In the interim, the Construction and Technology Support Area, Construction Section may be contacted for assistance in determination of earthwork quantities using the computer.