University of Twente Student Theses


Integrated Geophysical Approach to Determine Engineering Parameters of Expansive Soils

Libarge, Tesfaye Kassaye (2009) Integrated Geophysical Approach to Determine Engineering Parameters of Expansive Soils.

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Abstract:It is vital for geotechnical engineers to understand the in-situ behaviour of soil particularly the expansive soils which have profound effect on the damage of engineering works. Current practice of study of expansive soil is based on laboratory testing. These tests are expensive, time consuming and labour intensive; these tests use disturbed soil samples may not represent real ground conditions. Implementation of geophysical techniques such as EM and ER would be adopted in this paper to evaluate the capability of identifying expansive soils. These methods provide better understanding of the overall soil electrical properties in a manner that benefits engineering projects such as highway and construction. EM and ER methods are a fast, efficient, and cost effective geophysical tool for mapping spatial variations in soil conductivity beneath roadways. EM and ER measurements were performed in Ethiopia, along the newly designed road from Addis Ababa to Nazareth on 22 transects / data points and soil samplings were grabbed from the center of each transect for determining soil moisture content. The geophysical survey has been performed in the location where soil samplings were already taken for engineering parameters determination. Inversion of soil ground conductivity and inversion of soil apparent resistivity were made using Tikhonov Regularization model and master curve matching with RESIT model respectively for characterizing the soil in different layer depth to associate the result with soil physical and chemical properties. Strong correlations have been found between geophysical measurements (EM & ER) and soil moisture content. The soil moisture content could be estimated from soil ground conductivity with the relation expressed in equation Y=0.092 *X + 12.72, and correlation coefficient of R2 =0.709. ER method was also established good correlation with soil moisture content and it could estimate soil moisture as explained in equation Y= -2.83 *X + 33.34, and correlation coefficient of R2 =0.729. However the in-situ geophysical measurements, EM & ER were established weak correlation with engineering parameters. The geophysical method could differentiate the electrical properties of the two types of soil, the Andosols and Vertisols. It was distinctively differentiate the soil conductivity of Vertisols with conductivity higher than 89 mS/m and Andosols with conductivity of lower than 60 mS/m. The EM method also mapped the soil conductivity variation in laterally and vertically which would provide a qualitative characterization of the soil of the study areas. Key words: Expansive soils, Electromagnetic (EM), Electrical resistivity (ER), engineering parameters, Tikhonov Regularization, Master curve, RESIST model etc.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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