S. Stamataki

Correlation of Thermal Conductivity and Electrical Resistivity of Soil - For Near Surface Geothermal Applications

SUMMARY Soil thermal conductivity (k) is a critical parameter in various engineering applications, where heat transfer takes place and depends on numerous factors such as mineralogical composition, grain size of soil and physical properties (moisture, dry density, saturation). Same factors have also an influence on the electrical resistivity of soil (ρ). This work presents an experimental determination of soil thermal conductivity and electrical resistivity, in various soil types with different grain size and mineral composition, in terms of variable moisture content and dry density. The change of thermal (k) and electrical (inverse of resistivity, ρ) conductivity values in terms of the increasing saturation is interpreted with the increasing presence of water over the air in the pore space that facilitates heat and current transportation. The study of thermal conductivity and electrical resistivity variation according to the fluctuation of physical properties of soils, can lead to the qualitatively and quantitatively correlation between kand ρ. Such an empirical correlation can be used to estimate the thermal conductivity of subsurface, by applying electrical resistivity tomography in combination with geotechnical data. At the present time, it is a subject of further research exploiting various models of k and ρ.

Marine Resistivity Tomography Prior Excavation Works in Port Construction

SUMMARY The detection of bedrock relief under the sea bottom is of great importance for the excavation works in port construction as well as for the foundation of various installations. Marine resistivity tomography profiles, properly positioned to cover the area under investigation and to avoid various obstacles, can provide this information. Precise knowledge of bathymetry is required in order to give reliable results. Well data for reference are valuable in defining and verifying the sudden changes of resistivity values in the sections. The Schlumberger electrode configuration is preferred with its more efficient signal-to-noise ratio. Pole-Pole can give information which is less accurate in horizontal layering but offers deeper detection. The RMS error in interpretation takes higher values when the sea bottom is deeper. Marine cable with 3m electrode distance and 32 lead takeouts is easily elaborated and effective to detect bedrock relief for depths of sea bottom: 5-15m and depth of investigation for Schlumberger array 20m and polepole 40m.

Marine Resistivity Measurements for the Foundation of Lavrion Old (1888) French Bridge

Marine resistivity measurements can give valuable information for the sedimentation under the sea bottom if the latter is not too deep. The Schlumberger configuration is preferred with its more efficient signal-to-noise ratio. Pole-Pole can give information which is less accurate in horizontal layering but offers deeper detection and possible positioning of lateral inhomogeneities in the event of great resistivity contrasts. The old (1888) iron “French Bridge” in Lavrion Port suffers from corrosion by seawater and displacements and needs protection with the plan all to be mounted in a new substructure with the less visible changes. The marine resistivity survey gives valuable information to the engineer like where the old foundation lays, where to position the geotechnical drillings for additional information and outlines the environment of the structure to be built for the protection of the bridge.