ABSTRACT:
A field study comprised of experimental testing and statistical analyses was conducted to evaluate the Caterpillar machine drive power (MDP) and Geodynamik compaction meter value (CMV) compaction monitoring technologies applied to Caterpillar rollers. The study was comprised of three projects, all of which were conducted at the Caterpillar Edwards Demonstration facility near Peoria, IL.
The first project investigated the feasibility of using MDP applied to a Caterpillar self-propelled non-vibratory 825G roller. A test strip was constructed, compacted using the prototype 825G roller, and tested with in situ test devices. The second project also consisted of experimental testing on one-dimensional test strips.
This project, however, used five cohesionless base materials, which were compacted using a CS-533E vibratory smooth drum roller with both MDP and CMV measurement capabilities. The independent roller measurements were compared and described in terms of soil engineering properties. The final project was conducted with only one cohesionless material.
Four test strips (three uniform strips at different moisture contents and one with variable lift thickness) were constructed and tested to develop relationships between roller measurements and soil engineering properties. Using the material of the test strips, two-dimensional test areas with variable lift thickness and moisture content were then tested.
Spatial analyses of the insitu measurements were performed to identify the spatial distribution of soil properties. The interpretation of the ground condition was then compared to machine output for evaluating the roller measurement systems and the proposed roller calibration procedure.
RESEARCH METHODOLOGY
Description of Compaction Monitoring Technologies:
Machine Drive Power
The use of MDP as a measure of soil compaction is a concept originating from study of vehicle-terrain interaction. MDP, which relates to the soil properties controlling drum sinkage, uses the concepts of rolling resistance and sinkage to determine the stresses acting on the drum and the energy necessary to overcome the resistance to motion.
Using MDP to describe soil compaction, where higher power indicates soft or weak material and lower power indicates compact or stiff material, is documented by White et al. (2004) and White et al. (2006).
Compaction Meter Value
Intelligent vibratory compaction is an equipment-based technology that uses instrumentation to track roller drum accelerations in response to soil behavior during compaction operations. The dynamic response measurements of a vibrating roller drum on soil has been likened to dynamic plate load tests.
In Situ Test Measurements:
Moisture and Density
The nuclear moisture-density gauge was incorporated into the testing program to provide a rapid measurement of density and moisture. These tests provided an average measurement over the compaction layer, generally about 200 mm.
Soil Strength and Stiffness
Soil strength and modulus were determined using the Clegg impact hammer, DCP (compaction layer), soil stiffness gauge (SSG), portable falling weight deflectometer (PFWD), and plate load tests (PLT). CIVs have been empirically related to California bearing ratio (CBR).
DCP tests were performed to develop strength profiles with depth. For test strips, DCP index values for the compaction layer were used in regressions with MDP and CMV. Determining DCP index values for spatial areas is discussed in the respective report sections.
Design of Experimental Testing:
An earlier research project (White et al. 2006) evaluated MDP applied to static and vibratory padfoot rollers for indicating compaction of cohesive soils. Experimental testing for the project described in this report addresses MDP applied to alternative roller configurations for cohesive and cohesionless soils. As before, the experimental designs consider (1) state of soil compaction (i.e., roller pass or percent compaction), (2) soil type, (3) lift thickness, and (4) moisture content.
PROJECT 1. EDWARDS FACILITY, SELF-PROPELLED NON-VIBRATORY 825G ROLLER
Project Description and Objectives:
Establishing the feasibility of applying MDP technology to various roller configurations in order to indicate soil compaction has significant implications for earthwork construction practice.
First, validating MDP as an indicator of soil properties broadens the current scope of intelligent compaction and compaction monitoring technology to include non-vibratory systems. Further, MDP applied to alternative roller configurations expands the number of applications for which the technology may be used (e.g., compaction of municipal waste).
Construction and Testing Operations:
At the test site, loose Edwards till material was placed over existing, relatively stiff Edwards till subgrade. The material was moisture conditioned to optimum moisture content (12%) using a water truck . The soil was then mixed in situ using a reclaimer, set to give a nominal loose lift thickness of about 200 mm . Immediately following construction, the test strip was compacted using the 825G roller.
Moisture Conditioning Test Strip.
Material Properties:
Testing was conducted using Edwards glacial till material. This moderately plastic soil is fine grained and classifies as CL Sandy lean clay. Moisture-density tests were performed following the Standard and Modified Proctor test methods (ASTM D 698-00 and ASTM D 1557-98, respectively). The moisture-density curves are provided.
Compaction Monitor and In Situ Measurements:
Compaction monitoring technology output is summarized in using screen captures from the Caterpillar Viewer program. Compaction history at ten 3 m spaced locations along the test strip, also obtained from the Caterpillar Viewer program.
Screen Captures at Two Viewing Scales for Coverage and MDP With the Test Strip Outlined.
Linear Regression Analyses:
To further support MDP as a quantifiable indicator of soil compaction and change in soil condition, the relationships between roller and in situ spot measurements were investigated. The averages of data along the test strip were used to develop scatter plots relating MDP and in situ measurements, with each point representing the average measurement following a given roller pass.
PROJECT 2. EDWARDS FACILITY, CS-533 VIBRATORY SMOOTH DRUM
Project Description and Objectives:
Project 2 was conducted from August 1 to August 4, 2005, to evaluate both MDP and CMV for vibratory compaction of five cohesionless soil types. The experimental testing plan of this study, comprised of five test strips for the respective soils, is provided . The specific objective of experimental testing and subsequent analyses was to investigate relationships between MDP, CMV, and soil properties, including soil density, moisture content, strength, and deformation characteristics.
Construction and Testing Operations:
Five 30 m long test strips were constructed using five different cohesionless subbase materials. The test strips were constructed with widths of approximately 3.0 m, slightly wider than the roller drum.
The soils were placed on well-compacted subgrade at approximately natural moisture content, varying by soil type, with loose lift thicknesses ranging from 280 mm to 360 mm between test strips. Additional material was placed at the ends of the test strips to transition from the existing ground surface to the test strip elevations.
Test Strips 1-5 (left to right) Comprised of Base Materials.
Material Properties:
Evaluating the applicability of intelligent compaction technology to various cohesionless soil types was an important aspect of the current field study. As a result, experimental testing involved compaction and field testing of five soils. Recycled asphalt pavement (RAP), CA6-C, CA5-C, FA6, and CA6-G (Illinois DOT classifications) were obtained from local sources. Each soil was coarse-grained with low plasticity.
Compaction Monitoring and In Situ Measurements:
The nuclear moisture-density gauge was incorporated into the testing program to provide a rapid measurement of density and moisture. For each test, density was determined for the full depth of the compacted soil layer (i.e., variable depth depending on state of compaction). Soil strength was determined using the Clegg impact hammer and DCP. Soil modulus was determined using the SSG, PFWD, and PLT.
Regression Analyses:
The relationships between soil engineering properties, MDP, and CMV.These scatterplots are comprised of only five data points, with each data point representing the average measurement (from 10 tests) for the roller pass that was followed by field measurements (1, 2,4,8,and 12). Dry unit weight, CIV, DCP index, SSG modulus, PFWD modulus, and PLT modulus are all predicted from a logarithmic relationship with MDP. The soil properties show a linear relationship with CMV.
PROJECT 3. EDWARDS FACILITY, CS-533 VIBRATORY SMOOTH DRUM
Project Description and Objectives:
This section describes a project conducted from June 12 to June 15, 2006. Experimental testing and results are described to establish the applicability of using averaged roller data from one-dimensional calibration test strips to assess the compaction of a two-dimensional (i.e., spatial) area. Such an evaluation is necessary for verifying the reliability of using one-dimensional test strip calibrations as a specification component (see ISSMGE [2005]) for using compaction monitoring technologies.
Material Properties:
Compaction curve and spatial testing were conducted using CA6-G (Illinois DOT classification) from a local source. This non-plastic soil is coarse-grained (Cu = 30, Cc = 2.7) and classifies as SW-SM well-graded sand with silt and gravel according to USCE, and A-1-b according to AASHTO soil classification.
Machine Calibration Using Regression Analysis:
Calibration of CMV and MDP was accomplished using Strips 1 and 2 by correlating the collected roller data to the measured in situ soil properties. Considering the variability associated with the two compaction monitoring technology measurements, as well as the measurement variability of each in situ spot measurement, data were averaged along the length of the test strips to produce a single data point for each roller pass.
Source: Iowa State University
Authors: David J. White | Mark J. Thompson | Pavana Vennapusa