DYNAMIC ON-ROAD MEASUREMENTS OF DRY UNIT WEIGHT AND MOISTURE CONTENT VIA SOIL RESISTIVITY

Abstract

The current study examines the potential of electrical resistivity, specifically the Wenner four-electrode method, as a non-destructive, efficient, and dependable technique for predicting the in-situ moisture content and dry unit weight of soil during compaction. Although conventional measurement methods are precise, they are frequently time-consuming and labor-intensive, rendering them less effective for real-time field applications. This research establishes a rapid alternative for on-site assessments by establishing an association between critical soil properties, including moisture content, dried unit weight, resistivity values, and the number of compactor passes (compactive effort).Extensive laboratory testing was conducted on a diverse array of soil types, such as sand, and fat clay, using the standard and modified proctor compaction methodologies. To optimize the number of compactor passes and simulate field conditions, a soil strip container and electrical resistivity meter was designed to accommodate electrode placement and facilitate resistivity measurements. Molds were modified to include vertical apertures. The experiments demonstrated an inverse correlation between soil density and moisture content and electrical resistivity. The rate of electrical resistivity change varied considerably depending on whether the soil was on the dry or saturated side of the optimum moisture content (OMC). The complex interaction between these soil properties was underscored by the observation of a steeper decline in resistivity on the dry side as both density and moisture content increased. A walk-behind resistivity meter, custom-built, was utilized to measure electrical resistivity. This meter was engineered for dynamic on-road resistivity measurements and is equipped with four cylindrical electrodes that are equally spaced. Field testing confirmed the laboratory results, indicating an important connection between resistivity readings and in-situ moisture content, as well as dry unit weight.Upon the establishment of a laboratory compaction curve, the study introduces a soil strip method technique for predicting dry unit weight and moisture content in the field using electrical resistivity measurements with the increase of the compactive effort. This method has the potential to be applied to a diverse range of soil types and provides a cost-effective, reliable, and expedited solution for soil compaction monitoring. In order to accomplish these results, the compaction parameters of sandy soil were assessed using geotechnical-electrical relationships. Two soil types, which were collected and evaluated, were prepared and compacted under conditions that are frequently encountered in geotechnical practice. In order to classify the soil in accordance with the Unified Soil Classification System (USCS), laboratory experiments were implemented, including sieve analysis, liquid limit, and plastic limit. Electrical resistivity measurements were conducted using the Instek GDM-8341 instrument in accordance with ASTM standards, in which the specimens were compacted under varying moisture content, dry density, and compaction efforts. The poorly graded sand was found to have an OMC of 8.5% and an MDD of 120.5 lb/ft³ under Standard Proctor conditions, and an OMC of 8.0% with an MDD of 132.5 lb/ft³ under Modified Proctor conditions. Furthermore, this investigation introduces a soil strip technique that utilizes the relationship between electrical resistivity and the number of passes (compaction effort) of the walk-behind electrical compactor to forecast moisture content and dry unit weight in the field. The findings indicated that soil resistivity is significantly influenced by critical compaction parameters, including moisture content, dry density, and compaction energy, particularly at low moisture content. These results serve to underscore the significance of geotechnical-electrical relationships in the enhancement of the precision and efficacy of soil compaction monitoring.