****THIS IS A NEW IM. – PLEASE READ CAREFULLY.****
CONTRACTOR FURNISHED BORROW
This procedure describes requirements on sampling, testing, submittal, and approval of Contractor furnished borrow sites/sources where project quantity of Contractor furnished borrow is greater than 10,000 cubic yards (7650 m3).
Types of borrows covered in this IM are:
1. Excavated, which includes:
Drainable Borrow: A drainable borrow is one that has the intention of returning the site, as close as possible, to the previous activity/use, and
Pond Borrow: A pond borrow is one that has the intention of excavation below the natural ground and leaving a body of water for a designated purpose.
2. Non-excavated, such as stockpiled material, which includes:
Closed/Existing: A stockpile that will not have material added during the course of the project, and
Open/Active: A stockpile that will have material added during the course of the project.
PROPOSED BORROW REPORT SUBMITTAL REQUIREMENTS
A complete investigation of each proposed borrow shall include an adequate boring layout, a field log of each boring, appropriate sampling, and complete test results. Test pits instead of borings are allowed; however, this applies only for soil layer descriptions and sampling above the water table.
Only those sites that the Contractor intends to utilize for project construction shall be submitted as proposed borrows. The proposed borrows shall collectively satisfy the borrow need for project construction.
The Engineer will inform the Contractor of the acceptance or non-acceptance of the Proposed Borrow Reports.
If the volume of available suitable soil is insufficient due to the disapproval of a borrow or borrows, the Contractor shall make a new submittal. Any new submittal shall follow the same procedure as previous submittals.
An open/active stockpile submittal will require information on the stockpile material currently in place (see submittal requirements for non-excavated borrows) and information on material that will be excavated and added to the stockpile during the course of the project (see submittal requirements for excavated borrows).
The purpose of the proposed borrow submittal is only for the evaluation of the site. There will be no spatial requirements, restrictions, or limitations placed on the borrow design (conceptual or final).
A complete Proposed Borrow Report for each proposed borrow shall include:
For excavated borrows: in addition to the location of the borrow site, the aerial photo shall show the conceptual design and the location of the borings along with their identification numbers. A conceptual design is a general outline of the proposed borrow excavation limits.
For non-excavated borrows: in addition to the location of the stockpile, the aerial photo shall show the sampling locations along with their identification numbers.
a. Sample/Boring Layouts:
i. For excavated borrows, a boring layout pattern shall spatially cover a potential borrow site to adequately identify the soil layers encountered throughout the site, and provide for sufficient profile representation. Borings shall be spaced to maximize the coverage and at intervals no greater than 400 feet (120 m) (subject to borrow shape and general outline). An example of a boring layout is provided in Appendix B.
As an example: a 40 acre (16.2 ha) (square) borrow site will typically require a minimum of nine borings.
Boring depths shall extend to a reasonable depth below the anticipated maximum excavation for both drainable and pond borrows (such as 10 feet (3 m)) to help accommodate potential material shortfalls. If additional excavation during construction is required to meet the borrow need, additional borings (with sampling and testing) are required.
ii. For non-excavated borrows, a sampling layout pattern shall spatially cover a potential borrow site to adequately represent the site and define the composition of soil material to be encountered. Sampling shall be spaced to maximize coverage and represent the entire site. Spacing shall be no greater than 400 feet (120 m) (subject to borrow shape and general outline).
i. Loose/bulk samples of sufficient size (30 - 40 pounds (14 - 18 kg)) shall be taken, multiple times throughout the borrow site, for each soil layer encountered for excavated borrows or for each soil type for non-excavated borrows. For excavated borrows, a sample may only represent a similar layer in an adjacent boring no more than 400 feet (120 m) distant. Each sample shall be labeled with the boring ID and depth of sample, and shall be tested for mechanical analysis, determination of Atterberg limits, Munsell color comparison, percent of grain sizes, USDA textural and AASHTO classification, etc. (see Section “Laboratory test results” below). At least two samples for each predominant soil layer encountered shall be tested for Proctor density and optimum moisture.
ii. Samples obtained prior to execution of contract shall be preserved by the Contractor. For samples obtained after execution of contract, the Engineer shall collect verification samples (split samples) from boring or test pits sampled by the Contractor. At the discretion of the Engineer, random verification samples (split samples) shall be submitted to the Central Materials Lab for verification testing.
a. For excavated borrows, a descriptive field log of each borrow boring shall be submitted. An example is provided in Appendix B. The following is the expected information for each boring in a borrow boring field log.
· Boring ID number and GPS location (either State Plane or Lat/Long Coordinates).
· A field description of each soil layer (color, soil type, consistency, and geologic origin if possible).
· Depth to bottom of each soil layer.
· A notation indicating if a layer was sampled.
· In-place moisture conditions of the soil layers.
· Measured water table depth and amount of time between drilling and reading.
b. For non-excavated borrows, a descriptive log of each sampling site shall be submitted. An example is provided in Appendix B. The following is the expected information for a sampling log.
· Sample ID number and GPS location (either State Plane or Latitude and Longitude Coordinates).
· A field description of each sample (color, soil type, and consistency) and depth.
The testing of the borrow samples shall be performed by an accredited lab in accordance with Materials IM 208.
The test results shall be submitted in report or tabulated form. An example of a tabulated form is provided in Appendix B.
Each test report shall contain:
· Boring/Sample ID number, and GPS Location (either State Plane or Latitude and Longitude Coordinates).
· For excavated borrows only, depth of sample (from – to) and in units of feet (meters).
· Atterberg Limits (AASHTO T 89 and T 90, or ASTM D 4318).
· Percent Gravel, Sand, Silt, and Clay (AASHTO T 88 or ASTM D 422).
· Textural classification (USDA).
· AASHTO classification (AASHTO M 145).
· Proctor density and optimum moisture, when tested (see Section “Samples” above) (AASHTO T 99, ASTM D 698, or Materials I.M. 309)
· Percent Carbon Content, where applicable (Office of Materials Test Method No. Iowa 111).
· Sieve analysis (Percent Passing) (AASHTO T 88 or ASTM D 422).
· Munsell Color comparison.
PROCESSING CONTRACTOR BORROW SUBMITTALS, APPROVAL, AND ACTIVITY
This section outlines the procedures on projects where the Iowa DOT is the Contracting Authority that the Resident Construction Engineer, Office of Construction and Materials, and Soils Design Section of the Office of Design will follow for excavated and non-excavated contractor furnished borrow.
A. Verification Sampling.
B. Proposed Borrow Report.
C. Borrow Excavation/Use.
The Resident Construction Engineer will monitor the use of the borrow material. If there are questions concerning quality of borrow material, the Resident Construction Engineer will request verification samples to determine material suitability and acceptable use.