Airfield suitability assessment from geophysical methods

The construction of new airfields on semi-prepared terrain and the repair of existing airfield requires a quick and accurate suitability assessment of the subgrade soil strength and stability. The suitability of an airfield for regular operations is a function of the stiffness of the subgrade soil under small deflections. Stiffness is characterized by the elastic modulus of the soil. In-situ soil modulus values are commonly estimated from California Bearing Ratio (CBR) values via an empirical relationship. Currently, the dynamic cone penetration (DCP) testing method is the most widely used technique for determining the in-situ CBR. For airfield design, a DCP value is used to estimate a CBR value, which in turn, is used to estimate a modulus value. When these individual empirical equations are combined, the errors inherent to each empirical equation are compounded. Geophysical measurements such as seismic wave velocity and electrical resistivity can directly quantify modulus and eliminate a need for a multistep empirical process. This paper presents the results of an effort to use seismic wave velocity and electrical resistivity data to determine airfield design parameters. For the reported study, CBR values estimated from DCP penetration resistance were compared to equivalent CBR values estimated from shear wave velocity and electrical resistivity values. Relationships linking the geophysical measurements to CBR estimates were established using laboratory data. These relationships were then applied to field in-situ measurements. The field in-situ measurements were further used to calculate airfield design parameters such as allowable aircraft load and the number of aircraft passes. The results of this study show that CBR values estimated from shear wave velocity measurements well matched DCP-derived CBR values. Thus, establishing the viability of utilizing geophysical methods to assess airfield suitability.