6.30 EXCAVATION
The importance of being able to identify soil types cannot be overemphasized. Some soil types have to be placed in the proper location. For example, Standard Road Plan EW-102 illustrates where unsuitable soils are allowed to be placed in the roadway. The inspector must be sure that the work is performed according to the plans.
The inspector should be familiar with all the "Standard Road Plans" listed, in particular SW standards for sewer construction, MI standards for incidental construction, EC standards for erosion control, SI or BA standards for guardrail, DR standards for drainage, and EW standards for excavation and embankment.
Grading plans show cut equals fill plus/or minus shrink or swell respectively. Shrink is the change in quantity from cut to fill and includes subsidence, change from in situ density to compacted density, incidental loss, and all other factors changing density. Swell is the increase in class 12 excavation from ledge rock to broken rock in the fills. The swell factor will include other losses or increases.
SOILS CLASSIFICATION CRITERIA
Roadway and Borrow Excavation is divided into the following classifications:
Class 10
Includes all normal earth materials, such as loam, silt, gumbo, peat, clay, soft shale, sand, and gravel. Class 10 is subdivided into Unsuitable Soil and Suitable Soil.
UNSUITABLE SOIL ‑ Use Standard Road Plan EW-102
Topsoil Applications
n Peat or muck
To be wasted off-site, unless shown otherwise in the contract documents
n Soils with Plasticity Index (P.I.) 35 or greater
n A‑7‑5 or A‑5 having less than 85 PCF AASHTO T‑99 or Materials IM 309 proctor density
Type C Disposal ‑ Placed 3 feet below top of subgrade in Fills
n All soils other than A‑7‑5 or A‑5 having a AASHTO T‑99 or Materials IM 309 proctor density of 95 PCF or less
n All soils other than A‑7‑5 or A‑5 containing 3.0% or more carbon
Type B Disposal ‑ 5 ft below top of subgrade in fills
n A‑7‑6 (30 or greater)
n Residual clays (overlaying bedrock), Paleosols, claypan, gumbo, and gumbotils regardless of classification
Type A Disposal in Fills –5 ft below top of subgrade in fills but placed in alternate layers with Type C Unsuitable or Suitable Soil
n Shale
n A‑7‑5 or A‑5 soils having a AASHTO T‑99 or Materials IM 309 proctor density greater than 86 PCF but less than 95 PCF.
SUITABLE SOIL
n AASHTO T-99 or Materials IM 309 Proctor Density of 95 PCF or greater, and
n AASHTO M 145 Group index less than 30
n Liquid Limit (LL) less than 50.
Class 12
Includes granite, quartzite, chert, limestone, sandstone, hard shale, and slate. Includes estimated or measured volumes of boulders.
Class 13
Commonly referred as "Unclassified Excavation." The contract documents will specify the limits for Class 13.
Select Soils
Must meet all criteria.
Cohesive Soil
n Must have 45% or less silt content. Silt size particles are 2.91 to 0.79 mils (0.074 to 0.002 mm).
n Must have a proctor AASHTO (T‑99) or Materials IM 309 density of 110 pcf or greater
n A‑6 or A‑7‑6 soils of glacial origin
n Must have a plasticity index (PI) of 10 or greater
Granular Soil
n Must have a proctor density of 110 PCF or greater
n Must have a combined silt and clay content of 15% or less (finer than 0.074 mm or #200 sieve)
n PI = 3 or less
n A‑1, A‑2, or A‑3(0)
Class 10, Waste material may be incorporated into the project if the material’s soil classification is acceptable for use as select treatment material. The contractor is required to follow the submittal requirements of Specifications Section 2102 and Materials IM 545. Payment will still be made for Class 10, Waste, even if the contractor uses the material as contractor furnished select treatment material.
6.31 PEAT EXCAVATION
Design Bureau uses two methods for peat removal. In both methods, it is required to de-water the excavated area during the placement of the granular blanket and the embankment.
Total Removal of Peat
In this method, the peat is removed entirely down to an identifiable soil layer. Soil sheets in the plans will identify the soil type found below the peat. If problems in identifying this soil class are encountered, the Design Bureau (Soils Section) or the Construction and Materials Bureau should be contacted for assistance.
Partial Removal of Peat
In areas where the peat is very deep, partial removal is designed with an overload specified to remove most of the settlement which will occur due to the remaining peat. The Design Bureau (Soils Section) has calculated the stability of the area under the plan requirements; therefore, the plan should be explicitly followed to prevent possible failure.
To fill the excavated area below water, material with 85% or more sand may be placed without de-watering. Placement of material with less than 85% sand requires de-watering and Type A compaction.
6.32 ROCK EXCAVATION
Rock excavation is defined as excavation which cannot be made with equipment normally used for Class 10. Any excavation requiring ripping or blasting is considered rock excavation (Class 12). The soil sheets of the road plans are useful in determining the depth at which Class 12 excavation begins.
Because Class 12 excavation requires field judgment, overburden removal should begin near the centerline so the backslope can be adjusted to meet the design template in case the rock elevation is not uniform.
The backslope on rock excavation is usually 1/2:1 except where presplitting is indicated on the plans.
Presplitting is a multiphase blasting operation:
Phase 1: Drill holes into rock ledge
Phase 2: Detonate a "light" explosive charge to pre-fracture the ledge
Phase 3: Production blasting to remove material and develop a uniform rock face
Presplitting is a part of the Class 12 excavation quantity with the locations shown on the soil cross sections by the 1/4:1 slope. This work may also be tabulated on the "C" plan sheets.
Since Class 12 excavation is a measured item, elevations are required before and after rock excavation.
The “Blasters' Handbook”, a good source of information about explosives, is available from:
International Society of Explosive Engineers
29100 Aurora Road
Cleveland, OH 44139
(Telephone 440‑349‑4400)
During design, shale might be classified as Class 12 excavation. However, in many cases it can be moved in a manner normal to Class 10. Where shale can be handled in a manner normal to Class 10, the shale should be measured and paid for as Class 10 (unless specified otherwise in the contract documents). Shale cuts are usually benched and covered with topsoil in accordance with the plans. If unexpected shale is found, the shale should be covered with topsoil if possible.
Payment for "rock pick‑up" should be measured and paid for as Class 12. If Class 12 is not included as an item in the contract documents, the quantity should be paid for at 10 times the contract price of Class 10 excavation or embankment‑in‑place item.
6.33 USE OF AND PAYMENT FOR WATER USED FOR EXCAVATION AND EMBANKMENT
The placement of select backfill and special backfill both have moisture limit requirements. When either type of backfill is moisture deficient, water should be added
and mixed into the backfill material prior to compaction. If water is added, and there is no contract item for water, then it should be paid for as extra work if in accordance with Specification 2102.05, A, 5.
Furnishing and applying water will not be paid for separately when compaction with moisture or moisture and density control is specified.
For fugitive dust control, see Construction Manual 2.12.
6.34 ALTERNATE BORROW AREAS AND CONTRACTOR FURNISHED BORROW
The contractor may submit to use an alternate borrow area in lieu of the designated borrow area(s). Also on some projects, the contract documents will require contractor furnished borrow. In both cases, the contractor is responsible for:
n Providing approved fill material by selecting a site (or sites) for each plan required soil type
n Obtaining all necessary environmental clearances and permits.
n Reviewing for impacts to, but not limited to the following:
A) Culturally sensitive sites or graves. (Refer to Construction Manual 6.35. Contact information: Office of the State Archaeologist, 319-384-0735, to request an Iowa Site File Search)
B) Wetlands or “Waters of the U.S.”, including streams or stream banks below the “ordinary high water mark”, without an approved U.S. Army Corps of Engineers Section 404 Permit. (Refer to Construction Manual Chapter 10. Contact information: US Army Corps of Engineers, 309-794-5057)
C) Threatened or endangered species. (Contact information: US Fish and Wildlife Service, 309-757-5800, or Iowa DNR, 515-725-8464)
D) Floodplains. (Contact information: Iowa DNR, 866-849-0321)
E) Sovereign lands. (Contact information: Iowa DNR, 515-330-6432)
F) Storm water discharge. (Refer to Construction Manual Chapter 10. Contact information: Iowa DNR, 515-217-0875)
G) Regulated materials
Below are some helpful links:
n State Listed Threatened and Endangered Species
https://programs.iowadnr.gov/naturalareasinventory/pages/Query.aspx
n Federally Listed Threatened and Endangered Species
http://www.fws.gov/midwest/endangered/lists/iowa_cty.html
n Step by Step Section 7 Guidance
http://www.fws.gov/midwest/Endangered/section7/s7process/index.html
n I-Sites Public Website – historic properties
https://archaeology.uiowa.edu/services/i-sites
n National Wetland Inventory
http://www.fws.gov/wetlands/Data/Mapper.html
n U.S. Army Corps of Engineers Regulatory Guidance Letter 05-05: Ordinary High Water Mark Identification
https://www.nap.usace.army.mil/Portals/39/docs/regulatory/rgls/rgl05-05.pdf
n Iowa Department of Natural Resources – Facility Explorer
https://facilityexplorer.iowadnr.gov/facilityexplorer/Default.aspx
n U.S. Environmental Protection Agency – Envirofacts
The above links are provided for reference only. A contractor should consider consulting a qualified professional with expertise in wetland delineations, cultural resource surveys, and/or species/habitat surveys to determine the presence of protected resources within a potential borrow area.
Some contracts may contain a requirement for the contractor to submit an Environmental Review Certification Form (Form 536003) to Doc Express for review by the Location and Environment Bureau and the Army Corps of Engineers. The form is required for any contractor furnished areas/sites, including borrow or waste sites, off-site stockpiling, or staging areas, or created access/haul roads. The form is also required for contractor furnished borrow material that is provided from inside DOT ROW. Form 536003 would be a separate submittal than the Proposed Borrow Report per Materials I.M. 545 that is referenced in the “Contractor Furnished Borrow” section below.
The Environmental Review Certification Form User Guide (Form 536004) provides additional guidance and suggested resources that can be used to complete Form 536003. A flowchart showing the process for review and approval of Form 536003 is provided in Appendix 6-1.
For other projects, submittal of Form 536003 is not required but encouraged, and it will be reviewed by Location and Environment Bureau if submitted.
Alternate Borrow
Specification Section 2102.03, F. 2. requires the contractor to submit a plan to the Engineer for use of all alternate borrow areas or designated borrow areas intended to be used in a manner different from that shown in the contract documents. The plan should include subsurface and testing information plotted similarly to borrow plan sheets used for design borrows and include surface elevation, thickness of layers, soil sample locations and soil classifications. The contractor shall also obtain and provide soil samples to the project engineer for verification testing by the Contracting Authority (verification testing to be completed at the discretion of the District Materials Engineer).
Assuming that the proposed alternate borrow site meets the design criteria for the intended soil type, that all clearances have been obtained and that the plan site is not a mandatory borrow, an alternate borrow site may be approved as follows:
n If use of the alternate Borrow site results in no change in quantities, the change may be executed as a mutual benefit change and plan quantity agreement.
n If the alternate Borrow site results in significant savings, this is to be executed as a Value Engineering Incentive Proposal.
On projects where the Contracting Authority has not provided borrow areas, this section on Alternate Borrow will not apply.
Contractor Furnished Borrow
Section 2102.03, F, 3 provides information on required submittals for contractor furnished borrow. Materials I.M. 545 provides detailed information on submittal requirements and the DOT processing procedure where project quantity of contractor furnished borrow is greater than 10,000 cubic yards. The Contractor should upload the Proposed Borrow Report to Doc Express (Contractor Borrow in the Shop Drawings drawer) for review by the Construction & Materials Bureau and the Soils Design Section.
Soil samples should also be provided by the Contractor for contractor furnished borrow material. This material shall be verified by the Contracting Authority for compliance with the soil type requirements. However, if the material is not placed under the proposed road, the District Materials Engineer, Soils Design, or Construction and Materials Bureau may waive testing.
If a Contractor is proposing to mine (i.e. excavate below template cut) for Select soil material within the project limits to then provide it as Contractor Furnished Select Treatment, this is typically handled through a Value Engineering proposal.
6.35 PRESERVATION OF CULTURAL RESOURCES
Cultural resources include archaeological sites, as well as historic objects, structures, and districts. Archaeological sites may consist of stone tools, pottery, animal bone, burned earth, as well as other items like historic privies, cartridges, buttons, and ceramic containers. Archaeological sites may also contain human remains. Historic objects, structures and districts may include stone foundations and cellars, cisterns, and other resources like steam systems.
The Code of Iowa, Chapters 263B and 314.24, and FHWA require that action be taken to ensure that cultural resources are not damaged nor destroyed.
If a cultural resource is discovered during construction, the contractor is required to temporarily discontinue work at the site. This is according to the Code of Iowa and to Specification 2102.03, J. Upon discovering such a site, the project engineer shall immediately notify the Location and Environment Bureau (515-239-1225) and the Construction and Materials Bureau (515-239-1352) of the finding. Iowa Department of Transportation Policy and Procedure 500.17 outlines the procedures to follow.
Alternate Borrow Areas and Contractor Furnished Borrow
The contractor is required to comply with Specification 1106.07, which includes reviewing for impacts to culturally sensitive sites or graves. For most contractors to comply with this, they will need to contact the Office of the State Archaeologist (OSA), who will review the database of cultural resources. There is a nominal fee for OSA’s review. This expense is the contractor’s responsibility.
6.36 WASTE AREAS
Similar to contractor furnished borrow areas, the contractor is required to obtain necessary environmental clearances and permits for waste sites. Refer to Section 6.34 for a list of potential impacts and helpful links. Additional FAQ’s are provided at: https://iowadot.gov/construction_materials/FAQs/Environmental