Fractures and rock properties estimated by 3D directional borehole radar
Borehole radar is widely used in civil engineering work such as fault and fracture exploration, salt dome investigation, tunnel detection, UXO detection, exploring locations of foundation piles and sheet metal piling walls, and so on. Borehole radar surveys in resistive rock field have been applied successfully due to the lower attenuation of the rock media. Through those studies, many researchers have become interested in the detectability of thin open fractures and their locations. Though there are some numerical computing studies [1] on its detectability related to the open widths of fractures, there are very few experimental field studies. Thus studies using directional borehole radar system are essentially required at borehole sites where geometrical features and open widths of the fractures are well investigated. We are conducting experimental evaluation surveys for our 3D directional borehole radar system, “ReflexTracker®”. In soft ground in an alluvial plain, a single-hole measurement was carried out to evaluate the detection ability of a conductive cylinder buried 2m from the survey hole and found that the system could detect 3D reflectors representing the target and provided information on the direction of arrival wave and distance to the target [2]. We conducted another experimental measurement to evaluate fracture detectability of the system in rock field. The experimental borehole (BOA-200), a vertical borehole with diameter of 86-115 mm reaching 200 m depth in andesite rock, is located in a rock quarry in Ishikoshi Town, Miyagi Prefecture, Japan. Fractures in the borehole and their geometrical features such as strikes, dips and open widths were investigated in detail by borehole scanner [3], and the electrical characteristics were also obtained by a logging survey for all depths. The radargrams obtained by the non-directional antenna indicate that the arrival times and amplitudes were clearly related to rock mass classification and fracture densities, i.e., the higher the density, the larger the amplitude and the earlier the arrival time. Moreover, interpreted relative permittivities were negatively correlated with resistivities. On the other hand, the interpreted 3D reflectors derived from the directional antenna resulted in significantly good fitting with some of the known fractures' extended planes. Through the experimental study in the rock field, the ReflexTracker shows high potential for applications in fracture extractions and rock property investigations.
$\hbox{HE}_{11}$ Mode Effect on Direct Wave in Single-Hole Borehole Radar
In this paper, we investigate the influence of radar sonde eccentricity on a direct wave between a transmitting and a receiving antenna in a single-hole borehole radar measurement. We analyze the direct wave using an analytical method with the approximated solution of branch cut integrals and that of residues of poles. According to our calculation, at high frequencies above 200 MHz, guided waves, which are caused by the poles, play a vital role in the direct wave. We found that the most important pole is the HE11 mode one, which is excited only when the antenna is eccentered in the borehole. We show that this causes artificial noise in the moving average subtraction, which is a common signal processing method used to remove the direct wave. In a laboratory experiment with a ground plane, we confirmed the excitation of the guided waves when the antenna was eccentered. In field experiments in granite, we conducted a special experiment, in which the location and rotation of the radar sonde were controlled mechanically. We found the excitation of the HE11 mode at high frequencies when the sonde was noncentered by 1.7 cm in a borehole. These effects are also predicted in a theoretical analysis.
Lupin alkaloids from teratogenic and nonteratogenic lupins. II. Identification of the major alkaloids by tandem gas chromatography-mass spectrometry in plants producing crooked calf disease.
The major alkaloids of lupin plants producing crooked calf disease were identified by tandem gas chromatography-mass spectrometry and infrared analysis. The gas chromatography peak invariably present in teratogenic plants proved to be anagyrine. A minor but irregular contaminant of the peak was α-isolupanine. Other alkaloids present but apparently not associated with crooked calf disease were lupanine and two others that were probably epimethoxylupanine and 5,6-dehydrolupanine.