Permeability of Base Aggregate and Sand
Project Start Date: Sept. 1, 2019
Project End Date: Aug. 31, 2020
Lack of proper pore water drainage is one of the main causes of the failure of geosystems. Many geosystems such as roadway base course and retaining wall backfills are designed to quickly drain pore water to minimize elevated pore pressure, minimize freeze-thaw damage, and prevent failure of the geosystem. The requirements for drainability vary depending on the specific requirements of the structure. A simple and reliable tool capable of estimating drainability values for common aggregate types will aid in material selection and design. Additionally, when a failing material is used on a project, knowing the material's permeability will aid the engineer in deciding whether the material should stay in place with a monetary price adjustment assessed, or be removed.
Most existing formulations assess permeability of coarse aggregates from D10 (sieve opening size that passes 10% by weight of the material) and fines content (percent passing sieve #200). However, coarse materials of different gradations but of the same D10 and fines content may have very different permeability. There is a need to assess the permeability from more information about the particles such as grain size distribution, crushing percentage, fines content, angularity, and material type.
The objective of this project is to quantitatively assess permeability of a wide range of course materials from base course (2" minus) to sand size (less than 20% finer than sieve #200) for design. Laboratory permeability tests will be conducted on aggregates of different types, gradations, angularity, fine contents, and crushing percentages. The test results will be analyzed using statistical methods to develop a simple predictive tool that may be used to assess permeability from gradation, crushing percentage, fines content, aggregate angularity, and material type.
- Task Descriptions:
Task 1: Initial Memorandum on Expected Research Benefits and Potential Implementation Steps
During the proposal phase and the development of the work plan, key benefits were selected to clearly define the benefits the state(s) will receive from the results and conclusions of this research. Provide an initial assessment of research benefits, a proposed methodology, and potential implementation steps.
Deliverable: A memorandum providing initial estimates of expected research benefits, documentation of the methodology, and potential implementation steps.
Task 2: Literature Review
-Conduct a thorough literature review to gather available information on permeability of coarse aggregates and sands used in geosystems and existing methods for estimating permeability from other properties (e.g., gradation, unit weight, porosity, etc.).
-Collect and critically analyze the available research results on permeability of aggregates as a function of affecting factors such as gradation, void ratio, level of compaction effort, fines content, angularity, material type, and other factors.
-Collect and synthesize available case studies on performance evaluation of geosystems such as pavement base course, sub base, and retaining wall backfills at various drainage capacity.
-Place emphasis on performance of systems at different drainage conditions and permeability levels of base course or sub base layers.
-Also include in the literature review available analytical relationships between aggregate permeability and other index properties, including a critical summary of pros and cons, applicability, and limitations for each relationship.
Deliverable: A summary document containing all the available information on the relationship between the hydraulic conductivity of aggregates and relevant affecting factors as well as pavement performance will be submitted as deliverable to this task.
Task 3: Laboratory Tests and Data Analysis
-Plan and conduct laboratory tests on various coarse materials ranging from base course aggregates to sands that are used as subbase layer.
Include the aggregate types that are more susceptible to crushing such as limestone, dolostone, and recycled concrete aggregates.
-Select the materials to cover the upper and lower boundaries of gradation ranges covered by the National Road Research Alliance (NRRA) member states for base course and subbase materials. The experimental plan contains two parts: Part 1 includes index tests to evaluate gradation, fines content, compaction characteristics, crushing percentage, angularity, and other relevant properties (identified in Task 2) that will affect permeability. Part 2 includes permeability tests on each material.
-Conduct rigid wall permeability tests per ASTM D5856 or ASTM D2434.
-Utilize small-scale and large-scale permeameters (ranging from 2 to 12-in diameter) in the Soil Mechanics Lab of the University to conduct permeability tests on samples of different particle sizes from base aggregates to sands.
-Compact and measure the aggregates according to specifications and gradations, crushing percentage, particle angularity, and permeability.
-Further Compact replicate compacted specimens under dynamic cyclic loads (representing traffic loads) to simulate aggregate crushing under traffic loads (with corresponding fines generation measured).
-Measure permeability, gradation, crushing percentage, and particle angularity (the latter by optical measurements). The crushing of particles under larger loads will continue until these parameters cover representative ranges commonly occurring in field construction applications.
-Evaluate the particle angularity using Aggregate Imaging System available at the University.
-Establish relationships between the measured permeability and other properties in Part 1 as required to develop a simple tool to predict permeability of the aggregates.
-Analyze laboratory test data, and utilize suitable statistical methods (such as multi-regression analysis) to establish relationships between permeability of aggregates and affecting parameters such as crushing percentage, fines content, gradation, void ratio, material type, and particle angularity. This predictive tool will aid in evaluating the pavement drainage performance, service life, and life cycle costs.
-Utilize the permeability values for each material for design and material acceptance.
-Compare (and supplement) results from the relationship developed here with the suite of existing relationships identified during the literature review (Task 2) to clarify the pros, cons, and limitations of each and to develop more robust (larger dataset) relationships.
Deliverable: Based on the laboratory test results and multi-regression analysis, analytical relationships, and design graphs will be generated to predict aggregate permeability from gradation, fines content, crushing percentage, and angularity. Recommendations on material acceptance based on specification criteria will be provided.
Task 4: Final Report
-Prepare a draft final report, following MnDOT publication guidelines, to document project activities, findings, and recommendations. This report will be reviewed by the Technical Advisory Panel (TAP), updated by the University to incorporate technical comments, and then approved by the Technical Liaison (TL) before this task is considered complete.
-Schedule a TAP meeting to facilitate the discussion of the draft report.
Deliverable: A draft final report for TAP review, and a revised report that is technically complete and approved by the TL for publication.
Task 5: Editorial Review and Publication of Final Report
-Work directly with MnDOT's contract editors to address editorial comments and finalize the document in a timely manner. The contract editors will publish the report and ensure it meets publication standards.
Deliverable: Final Report that meets MnDOT's editorial guidelines and standards.
Principal Investigator: William Likos
Co-Principal Investigators: Tuncer Edil, Ali Soleimanbeigi
Technical Liaison: Terry Beaudry, Minnesota Department of Transportation
Project Technical Advisory Committee (TAP) –
Raul Velasquez (MN)