Philip M. Reppert

Dielectric constant determination using ground-penetrating radar reflection coefficients

A method to determine ground-penetrating radar (GPR) velocities, which utilize Brewster angles, is presented. The method determines the relative dielectric constant ratio at interface boundaries where the radar wave is traveling from a low-velocity to a high-velocity medium. Using Brewster angle analysis is currently the only means to determine the velocity of the medium below the deepest detectable reflector. Data are presented for water-saturated clean sand with a known velocity of 0.52 m/ns, which overlays a sandy silt with a known velocity of 0.13 m/ns. Brewster angle analysis of a common midpoint (CMP) survey gives a relative dielectric constant ratio of 33/4.77. The Brewster angle relative dielectric constant ratio is in good agreement with the relative dielectric constant ratio calculated from the known velocities.

Electromagnetic cave-to-surface mapping system

This paper presents the principle, design, construction, and methodology for an electromagnetic (EM) system to be used in the detection/location and mapping of underground cavities using surface measurements. The EM instrument consists of a loop-loop transmitter/receiver system with the transmitter placed inside the cavity. The transmitters position and depth are determined by analyzing the shape and distribution of the transmitted field on the surface. From the perspective of a cylindrical coordinate system, the vertical component of the through rock transmitted magnetic field peaks at the point where the transmitter and receiver are vertically collinear. On the other hand, the horizontal component reaches a minimum at this point. Based on these observations, a procedure is presented and tested that efficiently locates the position as well as the depth of the transmitter. A physical model for the system was developed and compared to the results of calibration experiments, with very good agreement. The model allows the study of different responses for EM waves/fields propagating through a homogenous Earth of different electrical characteristics and therefore enables several type-curves to be generated that aid in the development of an optimal system.

Investigations of andesitic volcanic debris terrains: Part 2 — Geotechnical

Here, results of geotechnical investigations for the proposed Dominica international airport are presented. The main geotechnical investigative method is comprised of boreholes to 30 m depth with standard penetrating testing (SPT) and undisturbed Shelby tube and disturbed split-spoon soil sampling. The geotechnical investigation confirms the findings of a companion geophysical investigation, which concludes that bedrock is not likely to be encountered within the proposed depths of excavation for the airport. Geophysical and geotechnical data correlations are developed. Seismic velocity and the number N of blow counts with SPT (SPT N) appear to be well correlated by a linear model. A model relationship between SPT and seismic dynamic elastic modulus is developed using seismic velocity. SPT N is better correlated with the dynamic elastic modulus than with seismic velocity. The study shows that the seismic velocity and the derived dynamic elastic moduli can accurately predict soil strength as measured by SPT...