Soil collapse monitoring with EM measurements

Abstract

Collapsible soils, widely regarded as problematic soils, undergo large volume changes when subjected to saturation by water, which in turn causes damage on the structures unwittingly built on such deposits. In this work, a new approach for the monitoring of water caused deterioration process in collapsible soils based on experimental high frequency electromagnetic (HF-EM) investigations with an open ended coaxial line technique is presented. The tests are performed in a one dimensional controlled loading cell under simultaneous measurements of complex dielectric permittivity or conductivity, vertical stress, deformation and other soil hydro-mechanical conditions. A strong increase in the values of complex dielectric permittivity of the collapsible soil was observed at a critical water content, which triggered the collapse by means of chemical reactions of water with clay and/or silt bridges, which hold and bind the relatively coarser grained particles in the soil structure. These reactions produce, changes in the soil structure, and a rise in the concentration of Na+, Ca++, OH- and other alkali ions in the pore water solution, thus increasing the complex dielectric permittivity of the soil. Furthermore, the variations of the complex dielectric permittivity of the collapsible soil with water content, porosity, matric suction and vertical stress were studied independently and in different joint combinations, as the collapse mechanism is highly influenced by soil hydro-mechanical conditions. In this regard, the physical relationship between HF-EM soil properties in terms of the frequency dependent complex dielectric permittivity and soil hydro-mechanical conditions is theoretically analyzed with an advanced theoretical HF-EM mixture model.