Microgravity Mapping of an Inception Doline Shaft System

摘要

Reactivation of an inception doline shaft system through anthropogenic actions, precipitation, and possibly seismic activity induced subsidence in a hospital emergency room that was under construction in State College, PA. The convergence of Tropical Storm Lee and Hurricane Irene is interpreted to have caused the building's brick edifice to fall and induce vertical shifts in the reinforced concrete entrance floor slab. Microgravity mapping of the existing hospital emergency room entrance; the emergency room building under construction; and the parking lot in front of the emergency room entrance documented the presence of a doline shaft system (i.e., inter-connected sinkhole). Groundwork for the construction of the new emergency room included grading and leveling of the property. Surface water runoff entered the construction site from a parking lot that sloped toward the addition and to a non-functioning stormwater inlet. The grading for the new construction exposed an open fracture for surface runoff. Subsequent channeling of surface water to the conduit provided drainage for surface runoff, but it also initiated subsidence throughout the existing structure and the addition that was under construction. Engineering rehabilitation included a limited mobility (LM) grout program to plug subsoil fracture karren drainage systems and stabilize the surface. Drilling progressed in four stages, initially focusing on areas of greatest subsidence. In total, 60 injection points were completed to a mean depth of 24 m below grade in an area measuring approximately 370 m(2). During LM grouting, 867 m(3) of a sand-and-cement grout mixture were injected to stabilize the area.