1887

Abstract

This study used several seismic techniques to aid different phases of a subsidence investigation at an<br>abandoned coal mine subsidence site in a community located in the anthracite fields of eastern<br>Pennsylvania. Two surface collapse features, each about 3-5 m (lo-l.5 ft) in diameter, developed on<br>an athletic field underlain by an abandoned room-and-pillar mine 20 m (60 ft) deep. In a multiphase<br>investigation, surface seismic techniques were utilized to characterize mine level and overburden<br>conditions, and to design an effective drilling pattern for the remediation phase. Subsequently,<br>borehole pressure grouting techniques were used as an abatement procedure to stabilize the ground.<br>During this phase, borehole seismic techniques were used to further characterize subsurface<br>conditions as more than 680 stere (890 cubic yards) of grout was injected. The surface seismic study<br>included walkaway tests followed by a series of common offset lines that traversed the athletic field.<br>A signal enhancement seismograph, lOO-Hz geophones, and a sledge hammer were used for data<br>acquisition. The seismic data combined with information from a mine map and several borehole logs<br>suggested that the athletic field was divided into two zones: the western portion of the field<br>characterized by open mine voids, and the eastern portion of the field characterized by mine voids<br>more likely to be ftied with collapsed rubble. Using these results, a drilling pattern was<br>recommended and more than 20 boreholes were drilled in preparation for the remediation phase.<br>Borehole logs corroborated the predicted trends. All boreholes that would allow placement of grout<br>were selected for the grouting operations and the borehole seismic study was conducted concurrently<br>with grouting. One shot hole and three receiver holes were selected. An air gun served as an energy<br>source and downhole receivers consisted of 4O-Hz geophones arranged in a triaxial configuration.<br>Shot-receiver crosshole traveltimes were acquired for selected depths and these were used to<br>determine crosshole velocity distributions prior to and during injection. Preliminary analyses of the<br>crosshole data indicated a correlation between high velocities and competent mine overburden. In<br>contrast, velocities tended to decrease as the mine level was reached. Both the surface seismic and<br>the crosshole seismic studies provided valuable data and additional subsurface constraints for the<br>characterization and remediation of this abandoned coal mine site.

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/content/papers/10.3997/2214-4609-pdb.206.1995_019
1995-04-23
2024-03-28
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http://instance.metastore.ingenta.com/content/papers/10.3997/2214-4609-pdb.206.1995_019
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