Author(s)

Ehsan Kianirad,

Advisor(s)

Akram N. Alshawabkeh

Contributor(s)

Mishac K.Yegian, Thomas C. Sheahan, Luca Caracoglia

Date of Award

2011

Date Accepted

4-2011

Degree Grantor

Northeastern University

Degree Level

Ph.D.

Degree Name

Doctor of Philosophy

Department or Academic Unit

College of Engineering. Department of Civil and Environmental Engineering.

Keywords

California Bearing Ratio, Cone Penetration Test, Dynamic Cone Penetrometer, In-Situ, Soil Characterization System

Subject Categories

Soils - Analysis, Detectors

Disciplines

Geotechnical Engineering

Abstract

Rapid and accurate in-situ measurement of shallow soil properties is still a challenge and there is a need for new and advanced devices and methods. The RapSochs (Rapid Soil Characterization System) is newly developed as a man-portable instrument for rapid comprehensive field characterization of near surface soil properties. Potential applications include construction quality control, contingency site selection, and quick determination of load carrying capacity of unfamiliar unpaved airfields and terrains. Sensing technologies similar to Electronic Cone Penetrometer and a moisture sensor are combined in a small impact driven system similar to DCP (Dynamic Cone Penetrometer) configuration. The main objective of this research is to develop and assess methods to interpret geotechnical properties from the RapSochs measurements.

Several real-size tests are conducted in different soil samples prepared in large soil cells. The DCP is used as a benchmark for soil strength profiles and RapSochs performance is compared with that of the DCP. An analytical physics-based energy model to predict soil-instrument interaction in dynamic penetration is developed. The model is calibrated for RapSochs and DCP and is used to explain the penetration process. It is shown that this model is more accurate than the widely-used Dutch formula. The model is used to correlate the RapSochs penetration rate to DCP and CBR (California Bearing Ratio). The RapSochs-CBR correlation is proved to predict CBR with acceptable accuracy, higher resolution, and near-to-ground surface measurements.

The Maximum Likelihood Estimation method is adopted for the average dynamic cone and friction forces estimation. Cone and friction strength, and friction ratio profiles similar to those measured by the CPT are developed based on estimated forces. The effect of variable applied energy on the soil strength estimation is found to be insignificant. This method is proven to provide acceptable estimation of the soil resistance in different soil types. Soil classification to cohesive and cohesion-less materials is accomplished using a chart developed based on cone and friction resistance. Effects of overburden, sample size, boundary conditions, variable hammer drop height, and penetration rate on RapSochs measurements are also assessed.

It is concluded that the RapSochs instrument provides consistent, repeatable and reliable results in laboratory prepared homogenous soil samples. The algorithms and methods to obtain strength profiles of in-place soil or compacted layers are developed. The estimation of soil strength and friction resistance, soil classification, and correlation to CBR is achieved. While the approach is developed specifically for RapSochs, it is applicable to a wide class of dynamic penetrometers.

Document Type

Dissertation

Rights Information

Copyright 2011

Rights Holder

Ehsan Kianirad


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