Geology of Indianapolis, Indiana, United States of America

Abstract

The engineering geology of Indianapolis, Indiana, is strongly influenced by glacial drift, which covers Marion County with a thickness varying from 10 to 350 ft (3.1 to 106.7 m), averaging 140 ft (42.7 m). Nearly all major structures are supported on spread footings bearing either on overconsolidated Wisconsin till or on dense sand and gravel outwash deposits along White River or Fall Creek. Spread footings supporting high rise buildings (up to 38 stories) in downtown Indianapolis are typically designed for bearing pressures of 8 to 12 kips/ft 2 (3.9 to 5.9 kg/cm 2 ). For the relatively small number of structures supported on deep foundations, pressure-injected footings, auger cast piles and drilled piers are the most common types. The main geologic resources of commercial importance in Marion County are sand and gravel, which are obtained from outwash deposits along major streams, and, to a lesser degree, mined limestone. Ninety-five percent of the water withdrawn by the Indianapolis Water Company is from surface sources, as three water supply reservoirs have been formed by constructing dams across major streams. Recent studies have shown that significant quantities of ground water are available within outwash aquifers along White River and Fall Creek.