This IM describes the Quality Control Program (Embankment Construction) and quality assurance procedures for soils used in embankment construction that require moisture control or moisture and density control. 




A.    Sampling.


The Contractor shall sample the soil per Materials IM 312.


B.    Required Testing.


The Contractor shall use test procedures per Materials IM 204, Appendix A.


1.     Proctor.


The Contractor shall determine optimum moisture content and maximum density by Proctor testing for each type of excavated or mixed soil which varies as to change the expected AASHTO classification, or if directed by the Engineer.


With Engineer’s approval, and for soils that can be identified during excavation, the Contractor may use the optimum moisture content and maximum density as shown on the soils 'Q' sheets in the contract documents. In lieu of using values from the 'Q' sheets, the Contractor may choose to determine optimum moisture and maximum density from a field sample.


If the Engineer deems the optimum moisture and maximum density of material being excavated and/or mixed is not represented by that shown on the 'Q' sheets, the Contractor shall determine optimum moisture and maximum density from a field sample.


When determined from a field sample at the option of the Contractor or at the Engineer’s request, the optimum moisture and maximum density values from the field sample prevail over that shown on the 'Q' sheets.


2.     Moisture Content and Density.


The Contractor shall test and verify that moisture content of material placed is within optimum moisture content range and if required, greater than or equal to required minimum density. Upper and lower control limits for field moisture content of embankment material will be shown in the contract documents.


3.     Frequency.


The Contractor shall test for proctor optimum moisture content and embankment moisture content and density at minimum frequencies in Materials IM 204, Appendix A.


If source of excavation and moisture have been consistent and within moisture control limits and density has been greater than or equal to minimum density (if required), testing of each lift will be waived for areas less than 1300 cubic yards, or for embankment placed as median dikes or safety dikes. Where testing per lift is waived, the contractor shall test randomly selected samples at a minimum frequency of one test per compacted volume of 1300 cubic yards.


C.    Documentation.


The Contractor shall document changes in soil type, fill placement procedures/locations, and test results and submit to the Engineer weekly by uploading to DocExpress.




A.    Required Testing.


The Contractor shall retain split samples of Proctor testing when requested by the Engineer. The Engineer may select any or all Contractor-retained split samples for verification or independent assurance testing at the minimum frequencies in Materials IM 204, Appendix A.


The Engineer will determine the random location of moisture and (if required) density verification tests and will test at the minimum frequencies in Materials IM 204, Appendix A. The Contractor shall obtain a sample at the same location as directed by the Engineer and provide results to the Engineer. Verification test results will be provided to the Contractor immediately after the Contractor's quality control test results have been reported.


The Engineer will periodically witness field testing being performed by the Contractor. If the Engineer observes quality control field tests are not being performed according to the applicable test procedures, the Engineer may stop production until corrective action is taken. The Engineer will notify the Contractor of observed deficiencies, promptly, both verbally and in writing. The Engineer will document witnessed testing.


B.    Acceptability of Test Results.


The Contractor’s quality control test results will be validated by the Engineer’s verification test results using the criteria in Materials IM 216. If Engineer’s verification test results validate the Contractor’s test results, the Contractor’s results will be used for material acceptance.


In the event that the Contractor’s results cannot be validated, Engineer will investigate the reason immediately. Engineer's investigation may include:


·        Comparison of Contractor’s past and current test results with those of the Engineer,

·        Reviewing data and calculations,

·        Checking equipment operation, calibrations, and tolerances,

·        Observations of Contractor's sampling and testing procedures and

·        Testing of other locations or samples.


C.    Referee Testing.


If a difference in procedures for sampling and testing and/or test results exists between the Contractor and the Engineer which they cannot resolve, the Iowa DOT’s Central Materials Laboratory will provide referee testing. The Engineer and Contractor will abide by results of referee testing.



The Engineer will base final acceptance of tests and materials on results of the Contractor's quality control testing as validated by Engineer's quality assurance.


Personnel and laboratories performing tests used in acceptance of material shall participate in the Quality Assurance Program covered in Materials IM 205.