Case Studies of Massive Flow Conduits in Karst Limestone

摘要

During the crisis of a flooding limestone or dolomite mine, a thorough site investigation of the karst flow conduit must be performed before any remedial work is attempted. A plan for remediation which is based on an accurate understanding of the flow conditions, rather than a concept, obviously has a much greater chance of success. The considerable risk of attempting to seal a flow conduit is reduced with an accurate site model. Three different models of flooding flow conduits have emerged. Site 1 is a Pennsylvania dolomite quarry which intersected a flooding flow conduit at 130 feet ((40 m) depth, allowing 10,000 gpm (38,000 L/min) of river water to flood the quarry. A conduit of 1,500 feet (460 m) connects the river and quarry. The local geology is Ontelaunee dolomite. River water enters a bedding-controlled conduit aligned with a master joint structure. The floodwater flows from here into a solutioned high-calcium limestone bed which follows the limb of an anticline structure to the quarry pit. Site 2 is a Pennsylvania limestone quarry with inflows of river water at 60 feet (18 m) and 120 feet (37 m) depth. The local geology is Myerstown-Annville-Ontelaunee-Epler. Water flows into epikarstic caverns beneath the river and to a conduit near the Annville-Ontelaunee contact. A zone of densely-spaced high angle faults pass east to west through the floor of the quarry, are solutioned, and channel the flow to several artesian outflows. Site 3 is a West Virginia Dolomite quarry with in excess of 10,000 gpm (38,000 L/min) of river inflow at 120 feet (37 m). This is the site of North America's largest bitumen grout curtain in karst limestone. A new conduit developed adjacent to the remediated feature. The local geology is Tomstown dolomite-Antietam sandstone. Water enters sinkholes in the riverbed over a zone of karstified limestone that is intercalated within dolomite. The conduit follows the strike of limestone bedding which has been intensively deformed within a plunging syncline structure. Recent mining has deepened the quarry into the projected pathway of the flow conduit. More models will be offered as guidance as projects are completed. These case studies are offered as templates to apply to other sites for expediting the conceptual site modeling, and characterization work, thus improving on the chances of a successful remediation.