Preferred Design Procedure

The high energy Impact Roller (IR) technology is a construction method used for in-situ soil densification and concrete pavement rubblization applications. The design procedure should determine:

• Required number of roller passes.
• Optimal rolling pattern.
• Optimal roller travel speed for a specific shape and size of the drum to achieve the desired soil engineering properties.

Currently, there is no FHWA document that addresses the design procedure. However, some references (Pinrad 1999, 2001; Kelly 2000; and Landpac 2008a) present direct measurement of compaction improvement depth from field compaction trials, which can be used as guidance to determine the parameters defined above. The concept of this procedure is relatively simple, but the process is subjective to the type of conditions encountered, variability in the subsurface stratigraphy, and spatial variability in the material properties. Although IR technology is currently being used on many projects in the US for pavement rubblization application (www.impactor2000.com), very limited literature (e.g., Avalle and Grounds 2004) is available on this topic.

The current design procedure does not address how the compaction process and the obtained measurements relate to pavement design. In-situ test measurements (such as stiffness/modulus, CBR, etc.) obtained as part of the compaction process can potentially be linked to mechanistic‑empirical pavement design process. New developments in integrating IR technology with continuous monitoring systems, such as Continuous Impact Response (CIR), have potential to contribute to the mechanistic-empirical pavement design process. Improvements in soil properties may contribute to improvement in the service life of pavements and also reduction in the thickness of pavement sections. Improvements to the design procedure and well-documented case histories in the US are essential to promote implementation of IR technology.

Table 1 provides the typical inputs and outputs for the design and analysis procedures.

Table 1. Typical inputs and outputs for design and analysis procedures.

Performance Criteria/Indicators

Minimum change in elevation
CPT tip resistance (to a specified depth)
DCP tip resistance
Stiffness/modulus
Unit weight/relative Density

Subsurface Conditions

Groundwater elevations
Delineation of Stratigraphy
Gradation
Atterberg Limits
Unit weight
Organic Content
Relative Density

Loading Conditions

Traffic loads
Embankment loads
Structure loads
Earthquake acceleration and duration

Material Characteristics

Unit weight/relative density
Water content
Particle size distribution
Plasticity
Shear strength
California bearing ratio
Compressibility
Stiffness/modulus
Permeability

Construction Techniques

Number of passes
Number of impacts per minute (travel speed)

Geometry

Type of the roller drum (solid or wheel type)
Shape of the drum (three-, four-, or five-sided)
Rolling pattern
Improvement depth