Soil Characterization Utilizing GPR Technique
Al Kej, Fateh Tamam
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Engineering properties of soil, such as shear strength parameters, water content, degree of saturation, and permeability are essential for safe and economic design of any structure involving soil structure interactions. The invasive conventional testing methods for determining soil properties usually commence by extracting soil samples from different depths, testing them in the geotechnical lab, and comparing lab results with field test results for verification. These steps and procedures are time consuming and highly expensive, which is expected to affect the construction time and cost of any project. Noninvasive, nondestructive techniques represent a suitable alternative to the time consuming and expensive conventional site investigation procedures. However, to practically implement nondestructive techniques with acceptable confidence, a database of correlation equations need to be acquiredand well established. The work conducted in this research is a major step on a long term research project to build such database to correlate Ground Penetrating Radar (GPR) output to different soil engineering properties. GPR is an attractive tool for subsurface inspection and quality control on construction projects due to its time saving, economy, and noninvasiveness. In the current research, a group of index tests has been conducted in order to relate soil resistivity to water contents for different sandy soils. In addition, laboratory direct shear tests were conducted to measure the soil shear strength parameters at different water contents and different particle distributions. The soil dielectric constant at different water contents and different gradations is measured using the GPR technique. Index test results indicate that soil electrical resistivity is inversely proportional with the water content and compaction effort. In addition, electrical resistivity of sandy soil increases as both particle size and void ratio increase. Finally, soil resistivity increases with clay content up to certain limit and decreases thereafter. GPR test results show that, the soil dielectric constant is directly proportional to water content and inversely proportional to compaction effort. Results of index tests, lab tests, and GPR scanning test output are analyzed and correlated using regression analyses, and a 3-dimensional yet practical graph is produced for the soil types considered in this study. The proposed graph can be used to extract the soil friction angle from a rapid GPR in site scanning of any soil with similar properties.