Greenroads™ Manual v1.5 Materials & Resources
EARTHWORK BALANCE GOAL MR-3 Reduce need for transport of earthen materials by balancing cut and fill quantities.
CREDIT REQUIREMENTS Minimize earthwork cut (excavation) and fill (embankment) volumes such that the 1 POINT percent difference between cut and fill is less than or equal to 10% of the average total volume of material moved. For purposes of this credit, use the method and definitions detailed in Chapter 8 (Earthwork) of the Road Design Manual from the South Dakota Department of Transportation (SDDOT), or equivalent, to compute cut and fill volumes. RELATED CREDITS Include miscellaneous additional cut and fill such as outlet ditches and muck PR‐8 Low Impact excavations (see definitions in Chapter 8 of the Manual) and account for moisture and Development density as well as shrink and swell. MR‐2 Pavement Reuse tBalance cu and fill material volumes: MR‐4 Recycled Materials A = Volume of Cross Section Cut MR‐5 Regional B = Volume of Cross Section Fill Materials C = Volume of Miscellaneous Cut D = Volume of Miscellaneous Fill SUSTAINABILITY
For points, show that design volumes AND actual construction volumes meet: COMPONENTS Ecology Economy
Extent Experience
Note that for purposes of this credit, all volumes are positive quantities. SDDOT’s BENEFITS Chapter 8 is available here: http://www.sddot.com/pe/roaddesign/plans_rdmanual.asp Reduces Fossil Fuel Use Details Reduces Air Emissions Projects with minimal earthwork or with no earthwork do not qualify for this Reduces Greenhouse credit. “Minimal earthwork” means that the total excavated cut or imported fill Gases volume is less than one full dump truck volume, based on the smallest dump Reduces Solid Waste truck used on the project. Reduces Manmade Where soil stabilizer materials or other soil additives are used, include the Footprint volume of those materials in the total imports. Mechanical stabilizers such as Reduces First Costs rock bolts and geotextile fabric materials do not need to be included in volume Reduces Lifecycle calculations. Costs Removed topsoil materials must be included in calculations. Unused cut or imported fill materials placed in stockpiles that serve no purpose on the project must be treated as exported materials and may not be used to count toward the final “balanced” section for purposes of calculating this credit. Sometimes this practice is called “soil banking” since these materials are often placed in embankments that may be used at some later time, often on different nearby sites. This practice often helps successfully avoid import of new materials, so it still may qualify for 1 point. Structural aggregate for base courses in pavements, foundations, or
MR-3 Earthwork Balance Materials & Resources Greenroads™ Manual v1.5
superstructures such as bridges need not be included in the total volume calculations. Structural backfill and drain rock specifically intended for utility trenches and stormwater infrastructure need not be included in the total volume calculations. Rock (Stable Rock, defined by the Occupational Health and Safety Administration) cuts sourced within the project boundary that are intended for use as structural aggregate within the project boundary do not count toward the total cut volume of materials.
DOCUMENTATION Copy of the grading plan. The grading plan must report total cut and fill quantities, total miscellaneous cut/fill, and show that they are within 10% of one another. Calculate and report actual construction earthwork volume for the project. This calculation shall show the following:
Actual cut and fill volumes during construction. Actual volume of unused embankment materials (include excess import and excess cut materials) Actual volume of earthwork material imported to the project site. Actual volume of earthwork material exported from the site. Show that:
100% 10% 1 2
APPROACHES & STRATEGIES Use a project design that balances cut and fill volumes. This assumes that cut material from one area of the project site is suitable for use as fill material in another. This may not always be possible. Use soil improvement or stabilization techniques in an effort to avoid removing existing soil.
Apply binding agents, additives and other processes to unsuitable soils such that they become suitable for use. This often involves improving their bearing capacity so they can accept overburden or structures. Use in‐situ mitigation techniques to solve problems with unsuitable soils through ground improvement solutions such. Usually this involves forms of compacting, preloading, installed drains (to lower moisture levels) or other similar methods. Improve load bearing capacity of soils by placing geosynthetics over them. This can force the potential bearing capacity failure surface to develop along alternate, higher strength surfaces.
Use recycled material from other structures (e.g., crushed recycled concrete material – RCM or reclaimed asphalt pavement – RAP). Use design software and computer aided drawings (CAD) to calculate the design volumes of earthwork to be reported in relation to this credit. Note that these drawings and calculations will be superseded by final volume calculations in the field in the event that they differ.
Example: Sample Calculation The South Dakota Department of Transportation Road Design Manual, Chapter 8, contains a detailed example of balancing cut and fill volumes using computer software, titled “Example of Earthwork Quantities with Moisture & Density Control (Undercut)” (p. 8‐6). The example below shows how the calculation can be done by hand for this credit. There are a number of additional sample calculations in the referenced chapter.
Variable Description Volume (cy) A Normal cross‐section excavation 54,889
Earthwork Balance MR-3 Greenroads™ Manual v1.5 Materials & Resources
A Adjustment for moisture and density 9,233 C Miscellaneous extra excavation (unstable 805 material below undercut) B Normal cross‐section embankment 49426 B Adjustment for moisture and density 11079 D Miscellaneous additional embankment 1490 (unstable material below undercut) D Adjustment for moisture and density 298 A+C Total volume of excavated materials 64927 B+D Total volume of embankment materials 62993 ½ (A+B+C+D) Average total volume of materials 63557
64927 62993 100% . % 10% Project qualifies for 1 point 63557
Example: O’Hare Airport Modernization Program – Phase 1 The Chicago O’Hare Airport Modernization Program (OMP), which was ongoing as of early 2010, made a substantial effort to be more sustainable in their approach to airport design and construction. One of the features of their sustainability efforts is balanced earthwork. Phase 1 moved 15 million cubic yards of soil under a “balanced earthwork plan” that reportedly saved over $100 million by reducing truck trips and fees for dumping at landfills.
Figure MR‐3.1: Runway 10C‐28C Paving and Electrical (West): Excavation in Area G5 (Photo Courtesy Chicago O’Hare Moderization Program)
MR-3 Earthwork Balance Materials & Resources Greenroads™ Manual v1.5
Figure MR‐1.2: June 2010 Runway 10C‐28C Paving and Electrical (West): Placing and compacting Bit concrete base course on taxiway (Photo Courtesy Chicago O’Hare Moderization Program)
Example: Wattstown Business Park Road Extension The Wattstown Business Park Road Extension Project in Coleraine, Ireland implemented a balanced cut and fill strategy that allowed all of the excavated materials to be re‐used on site including excavated topsoils in order to minimize waste and hauling. The vertical alignment of the road was also kept to a minimum in order to minimize earthwork.
Figure MR‐3.3: Wattstown Business Park (CEEQUAL,n.d.)
Example: Kicking Horse Canyon – British Columbia Ministry of Transportation The Kicking Horse Canyon project near Golden, British Columbia, is a 26 km corridor upgrade that began construction in 2002. One of the project goals was to minimize the need for earthwork along the entire corridor in order to reduce greenhouse gas emissions from hauling trips (and to save money) in accordance with
Earthwork Balance MR-3 Greenroads™ Manual v1.5 Materials & Resources
objectives of the British Columbia Ministry of Transportation (BCMoT) Climate Action Program. This balanced earthwork program also included addressing safety concerns on the project, which called for improvements to slope stability on roadway excavations as well as avalanche control and rockfall protection in several locations along the corridor’s new alignments.
Slope stabilization on Phase 2 of the project was accomplished in some steep areas using 11,000 m3 of high tensile strength steel mesh that also allowed for seeding to grow, which can add stability to upper soil layers (BCMOT, n.d.). The mesh is tied to rock layers below the slope to stabilize the hillside (see Figure 4). Rockfall areas are protected by approximately 20,000 m3 of drapery mesh (BCMOT, n.d.). Excess fill soils were also stockpiled within the corridor for future lanes of highway (BCMOT, 2006). Construction of Phase 3 East ‐ Brake Check to Yoho National Park (underway) is also following a balanced earthwork design program (see Figures MR‐3.6 and MR‐3.7).
Figure MR‐3.2: Tecco® high‐strength steel mesh used for slope reinforcement. (BCMOT, 2010)
Figure MR‐3.3: West Alignment of Phase 2, Kickinghorse Canyon, showing approximate cut and fill boundary for corridor segment (BCMOT, 2006)
MR-3 Earthwork Balance Materials & Resources Greenroads™ Manual v1.5
Figure MR‐3.4: Phase 3 of The Kicking Horse Project: Excavation on north side of the highway (BCMOT, 2010)
Figure MR‐3.5: Phase 3 earthwork on east side of highway (BCMOT, 2010)
Example: Software Tools for Designers The most straightforward means of balancing earthwork is to design and construct the project such that the volume of cut within the project is equal to the volume of fill. For designers and contractors there are numerous software packages that can provide exact and/or estimated earthwork quantities. The following are examples of software packaging that can be used to achieve balanced cut and fill.
Earthwork Balance MR-3 Greenroads™ Manual v1.5 Materials & Resources
Trakware Inc. Earthworks Software Pizer Inc. EARTH Software Trimble Inc. Paydirt Software Vertigraph Inc. SiteWorx/OS Roctek Inc. WinEx Master Software
POTENTIAL ISSUES 1. When using stabilization material it is possible that the life cycle inputs for such material (e.g., energy use and emissions associated with their manufacture, transport and use) may be greater than that associated with moving soil associated with unbalanced earthwork. 2. Subsurface conditions may not be well known for the project site. Therefore, a balanced earthwork design that assumes a certain soil type and characteristics may not be feasible if, during earthwork, different soil types, moisture conditions or other characteristics are found. 3. Geosynthetics and stabilization additives may add significant cost over conventional methods. 4. Contractor familiarity and experience with alternative methods and materials can be highly variable. 5. Some roadwork does not lend itself to a balanced earthwork plan. For instance, work in an urban area may not work because the primary concern is typically maintaining existing elevation. Therefore, if a thicker pavement section is placed, some earth must be removed. 6. In a waterway corridor (area near a river or other waterway) balanced earthwork may not be sufficient. It is more important to ensure that earthwork does not reduce either the flood storage or flood carrying capacity of the waterway area (City of Brisbane, n.d.). 7. Rain events or prolonged wet periods can render on‐site material unsuitable for fill until it is sufficiently dried. There may not be enough time in the construction schedule to allow adequate drying time. 8. Designers may neglect to consider or poorly estimate shrink or swell of soil material. 9. Earthwork on a phased project may not be completed by the same contractor. 10. Efforts across phases may be difficult to coordinate without clear documentation of intent of stockpiled materials.
RESEARCH Most roadway construction involves some earthwork (moving of soil mass from one location to another). Earthwork can represent a significant project expense, especially in roadway projects. Because of the cost of landfill and truck transport most roadway designs seek to minimize earthwork as much as possible. When other ecological costs are added (i.e., landfilled waste, fuel use, truck emissions) the incentive to minimize earthwork grows. Thus, the goal is to minimize the earth moved and to minimize the distance it is moved. Ideally, a balanced earthwork project is one that matches cut and fill volumes and therefore does not required cut export or fill import. This section reviews typical methods used to achieve balanced earthwork.
Balancing Earthwork The most straightforward means of balancing earthwork is to design and construct the project such that the volume of cut within the project is equal to the volume of fill. In rural projects this can often be accomplished by choosing the appropriate gradeline (roadway profile) so that cut volumes are roughly equal to fill volumes. For urban environments, this may be more difficult as urban projects are often severely constrained by right‐of‐way or required to match existing abutting elevations (e.g., other streets, parks, drainage conveyances, etc.). For designers and contractors there are numerous software packages that can provide exact and/or estimated earthwork quantities.
Once in construction, a balanced earthwork design may not be achievable for several reasons. First, earthwork often involves unknown quantities. Although geotechnical engineers can attempt to characterize existing soil with test pits, soil borings and laboratory tests, these characterizations are usually only done on a few locations within the project site and cannot guarantee the condition of untested locations. Therefore, it is possible that unexpected soil is encountered that when excavated is unsuitable for use as fill elsewhere. Second, environmental conditions
MR-3 Earthwork Balance Materials & Resources Greenroads™ Manual v1.5 can change causing previously acceptable soil to become unacceptable. For instance precipitation can substantially alter the moisture content of in‐situ material making it unsuitable for use as fill elsewhere. Finally, design estimation may be inaccurate or, more likely, changes to the design during construction may add cut or fill quantities such that the overall effect is unbalanced earthwork.
Unsuitable Material One of the most common impediments to balanced earthwork is in‐situ material that is either (1) unsuitable to be used as fill elsewhere, or (2) unsuitable to be used as a foundation for other items such as structures (bridges, walls, etc.) and pavements. The most straightforward option in these cases is often to remove the unsuitable material and replace it with suitable fill. While this is feasible, it may result in unbalanced earthwork. It may be advantageous to treat the in‐situ soil rather than remove and replace it. This section discusses several treatment options.
Traditional Soil Stabilization Soil stabilization is the process of improving the engineering properties of soils through the use of additives that are mixed into the soil (Army, Navy, Air Force, 1994). These improved engineering properties can include:
Reduced plasticity Drying Reduced swelling Improved stability
Stabilization can be done by mixing soils of two different gradations to achieve desirable qualities (mechanical stabilization) or by adding binding materials (additive stabilization). This section briefly reviews three common soil stabilization additives. The Army, Navy and Air Force Soil Stabilization for Pavements (1994) offers a means to choose between portland cement, lime and asphalt as soil stabilization additives.
Portland cement. When added with water, portland cement hydrates and binds adjacent soil particles together resulting in a stiffer and perhaps stronger stabilized material. Portland cement can generally be used with well‐graded granular materials with sufficient fines to mix with the portland cement (Army, Navy, Air Force, 1994).
Lime. Added in the form of quicklime (CaO), hydrated lime (Ca[OH]2) or lime slurry. Lime does three basic things: drying (through hydration with existing water in the soil), modification (Ca ions migrate to clay particle surfaces and displace water making the soil more granular), stabilization (increases the pH of the soil causing clay particles to break down). The National Lime Association (2004) states, “When added with In general, fine‐grained clay soils (with a minimum of 25 percent passing the #200 sieve (74mm) and a Plasticity Index greater than 10) are considered to be good candidates for stabilization.” Asphalt emulsions. Most suitable for silty sand and granular materials since these are more likely to have all particles fully coated by the emulsion.
Ecological Impacts of Soil Stabilization Mroueh et al. (2001) reviewed several different combinations of industrial byproducts for use in earthwork. Results generally show that soil stabilization (as Mroueh et al. describe it this involves cement stabilization) generally has a higher environmental loading than simple soil replacement in most all areas (e.g., fuel use, energy, CO, particulate, SO2, CO2, VOC) except the amount of natural materials used.
GLOSSARY Additives Manufactured commercial products that, when added to the soil in the proper quantities, improve some engineering characteristics of the soil such as strength, texture, workability, and plasticity (Army, Navy, Air Force 1994).
Earthwork Balance MR-3 Greenroads™ Manual v1.5 Materials & Resources
Stabilization Process of blending and mixing materials with a soil to improve certain properties of the soil. Can be done mechanically (blending gradations of soils) or by using additives (Army, Navy, Air Force 1994).
REFERENCES British Columbia Ministry of Transportation and Infrastructure. (2010). Kicking Horse Canyon Project Fact Sheet. Accessed 14 August 2010. Available at http://www.th.gov.bc.ca/kickinghorse/updates/KHCP_Fact_Sheet.pdf.
British Columbia Ministry of Transportation and Infrastructure. (2010). Kicking Horse Canyon Project: Photo Gallery‐Phase 3 East Construction. Accessed 14 August 2010. Available at http://www.th.gov.bc.ca/kickinghorse/khc_gallery‐01‐Phase3_east.htm
British Columbia Ministry of Transportation and Infrastructure. (2010). Kicking Horse Canyon Project. Accessed 14 August 2010. Available at http://www.th.gov.bc.ca/kickinghorse/index.htm
British Columbia Ministry of Transportation and Infrastructure and Partnerships British Columbia. (2006, June). Project Report: Achieving Value for Money ‐ Kicking Horse Canyon – Phase 2 Project. Available at http://www.th.gov.bc.ca/kickinghorse/reports/0606_PBCKickingHorse.pdf
British Columbia Ministry of Transportation. (n.d.). Did You Know? Accessed August 15, 2010. Available at http://www.th.gov.bc.ca/kickinghorse/documents/KHCP_Did_You_Know_080304.pdf
CEEQUAL. (2010). Wattstown Business Park Road Extension: Interim Client and Outline Design Award. Accessed 13 August 2010. Available at http://www.ceequal.co.uk/awards_063.htm
City of Brisbane. (n.d.). Compensatory Earthwork Planning Scheme Policy. Accessed 12 January 2010. Available at http://www.brisbane.qld.gov.au/bccwr/lib181/appendix2_compensatoryearthworks_psp.pdf.
City of Chicago, Aviation. (2010). City of Chicago: Construction Progress. Accessed August 16, 2010. Available at http://www.cityofchicago.org/city/en/depts/doa/provdrs/omp/svcs/blank.html
Department of the Army, the Navy and the Air Force. (1994). Soil Stabilization for Pavements. ARMY TM 5‐822‐14, AIR FORCE AFJMAN 32‐1019.
Mroueh, U‐M., Eskola, P. & Laine‐Ylijoki, J. (2001). Life‐cycle impacts of the use of industrial by‐products in road and earth construction. Waste Management, 21, 271‐277.
National Lime Association. (2004). Lime Treated Soil Construction Manual: Lime Stabilization and Lime Modification. National Lime Association.
Pizer Inc. EARTH: Earthwork Quantity Software. Accessed 14 August 2010. Available at http://www.earthworksoftware.com/
Roctek Inc. Excavation/ Cut and Fill: WinEx Master. Available at http://www.roctek.com/
Trakware Inc. Earthworks Excavation Software. Accessed 14 August 2010. Available at http://www.trakware1.com/
Trimble Inc. Trimble Paydirt. Accessed 14 August 2010. Available at http://www.trimble.com/paydirt.shtml
Vertigraph Inc. SiteWorx/OS. Accessed 14 August 2010. Available at http://www.interworldna.com/vertigraph/siteworx_os.php
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