Ground penetrating radar technique to locate coal mining related features: case studies in Texas

摘要

The goal of this research project is to identify the efficacy of the groundpenetrating radar (GPR) technique in locating underground coal mine related subsidencefeatures at Malakoff and Bastrop, Texas. The work at Malakoff has been done incollaboration with the Railroad Commission of Texas (RRC). RRC has been carryingout reclamation of abandoned underground coal mines at Malakoff since the early1990??s. The history of the specific mining operations (at Malakoff and Bastrop) thattook place in the early 1900??s has been difficult to ascertain; therefore, the use of ageophysical techniques like ground penetrating radar to identify hidden voids andpotential subsidence features is vital for future reclamation process. Some of theunderground mine workings at the field site have collapsed over time affecting thetopography by creating sinkholes. GPR data, employing 25 MHz, 50 MHz and 100MHz frequency antennae, have been collected in common offset patterns and azimuthalpattern. GPR data indicate the mine tunnels possibly connecting existing sinkholes byradargram hyperbolae that correspond with mine openings observed visually or duringreclamation. This study also denotes the importance of understanding the variablephysical properties of the stratigraphy, which could lead to false alarms bymisinterpretation of the radar signals. Natural and man-made above-ground structurescause obstructions in data collection, and hence an optimal design is required for eachsurvey. RRC successfully ground-truthed the data during its reclamation process. Inturn, the acquired geophysical data helped to guide the reclamation. At Bastrop, GPRdata along with historical documentation led to the conclusion that coal mining did existin this region but is not a major concern to the immediate stability and safety of the fieldsite. It can be concluded from both the studies that the GPR technique identifiesanomalous shafts/tunnels possibly connecting potential failure.