Effective Depth of Soil Compaction in Relation to Applied Contactive Energy

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 Project Brief Final Report

Primary Investigator

Dante Fratta, Ph.D.
University of Wisconsin-Madison
1415 Engineering Drive
Madison, WI 53706
Ph: 608-263-3175
fratta@wisc.edu

Abstract

The WisDOT uses up to 10% of its annual improvement project budget on embankment construction. During the construction of embankments, compaction operations are designed to create stable structures that should be able to transmit traffic loads to the foundation soil while undergoing acceptable deformation levels and contributing to the overall health of pavement or embankment structures.

To achieve stable embankment structures, WisDOT has developed specifications for compaction density and water contents. It has also established specifications for the thickness of embankment lifts during construction. These construction specifications limit the lift thickness to 8 inches for most soil conditions and up to 12-inch lift thickness for granular soils. These lift thickness limits were established based on field experience and the typical WI contractors’ methods and equipment. This practice also has practical implications as it contributes to adequate embankment compaction without the need of a demanding inspection operations by the DOT.

However, the systematic use of 8-inch lifts during embankment construction may have created unnecessary construction costs. Furthermore, modern earth moving equipment has increased in size and weight and new compactors are capable of delivering greater energy levels. Some studies have claim that modern dynamic compaction equipment are capable of properly compacting lift layers as thick as 6 ft (and even greater thicknesses – see Zou et al. 2005). For these reasons, the WisDOT would like to re-evaluate the 8-in lift embankment construction requirement and carefully develop energy and compaction efficiency data. These data and analyses will determine if the limitations in lift thickness can be increased while maintaining construction quality, embankment’s performance, and, at the same time, reducing construction costs.

Objectives

  • Collect data and develop analyses needed to determine optimum lift thickness for WisDOT embankment construction projects.
  • Establish a relationship between the applied compaction energy and the level of compaction achieved at increasing depths for a number of different soils and moisture contents.
  • The data, analyses, and correlations will help WisDOT officials in proposing possible revisions to current constructions specifications including the need to change the established 8-inch lift thickness in the construction of compacted embankments.
  • The successful completion of this research will also help WisDOT officials in improving construction operations by creating more stable and economical subgrade structures.

Tasks

  1. Overall literature review.
  2. Theoretical/numerical analyses to relate degree of soil compaction at various depths below as a function of energy applied to the surface, compactor weight, and footprint.
  3. Development of a monitoring system to evaluate received energy and degree of compaction at various depths both in the laboratory and under actual field conditions for different compactor geometries.
  4. Determination of the influence of soil parameters (e.g., texture, plasticity, and moisture content) on energy dissipation and compaction achieved.
  5. Draft recommendations to optimize lift thickness as function of Wisconsin construction experience and typical compaction equipment and delivered energy.

Project Information

  • Duration: 18 months
  • Dates: January 31, 2008 – July 31, 2008
  • Budget: $54,916
  • Modal Orientation: Highway
  • Project ID: CFIRE 01-08
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