PERMFILE57051 - Laserfiche WebLink

Home Browse Search

,- >J Brinefield Subsidence at Windsor, Ontario III IIIIIIIIIIIIIIII Ruth D. Terzaghi Research Fellow in Engineering Geology Harvard University Cambridge, Massachusetts ABSTRACT !n 19-18, settlement cracks were rzoticed in btttldings u•ithi/t the Sartdwiclt brine field area of It'irtdsor, Ontario. Thereupon about 85 reference points were established on structures in the area. Changes in elcaation of These points were measured at yearly irtten~als. The results of the second annual survey indicate that a shallow bowl of subsidence with a radius of about 1000 feet had developed at tke time of the survey. !ts dept!: l:ad ittrreased by about 2.5 indees sieve the initial surrey. The re- sults of subsequent surveys show that the bowl continued to deepen at an accelerating rate. During the fifth year its depth increased by 10.5 incites to a total value in excess of 16 incites. In 195d, about four months after the fifth an- nual survey, a rapid subsidence took place in the central part of the bowl. {t'itltin a few hours, a [cater-filled depression, about 500 feet in diameter and [store lira![ twent~~ flue feet in maximum depth, teas formed. Structures located within rite area of rapid subsidence were damaged beyond repair. Subsequent irtoestigations indicated that sudden important subsidence was rite culminating event in a progressive failure of strata ouerlyireg a solution cavity produced by brine extraction from salt de- posits located at depths :it excess of 1000 feet be- low the surface of the grooved INTRODUCTION In February, 1954, the sudden subsidence of the central portion of a brine field itt rite Sandt+ich district of 11'indsor, Ontario, produced a botvl- shaped, water-filled depression t+ith a maximum depth of about ttvcnty-five for[ and width of -100 29S to 500 feet. Uelike many of the surface depres- sions associated t+•ith brine extraction, the \1'indsor depression, locally called the sinkhole, teas cen- tered neither about a single hell nor about a group of wells. It appears rather to be the result of sub- sidence of rock strata into extensive cavities in underl}'ing salt deposits. The roof of the upper- most cavity t+•as located at a depth of about 1000 feet below the ground surface. At the time of the subsidence, the brine field ryas ot+ned in part by Canadian Industries Ltd., and in part by the Canadian Salt Co. I am indebted to both organizations for permission to publish an account of the interesting and relatively t+•ell- documented series of events connected with the subsidence. The account is based almost entirely on information contained in unpublished reports by Carl A. Bays, Ralph B. Peck, and fCarl Terzaghi, tvho were retained under a co-operative agreement between the owners to investigate the subsidence. b1r. J.D. i\9air, Vice President of Canadian Salt Co., has kindly made additional data available to me. GEOLOGICAL CONDITIONS' The Sandwich brine field is underlain by uncon- solidated Pleistocene deposits consisting chieiiy of stiff silt and clay, known in the area as "Lake Erie Blue Clay" (T.B. Piper, personal communication, 1969). Local!}', the clay rests on lenses of sand or gravel t+ith a maximum thickness of a fet+• feet. 1Ve11 logs indicate that the total thickness of the 1. Unlen other+'ise noted, the sectiotn on geological conditions and brine production are based on Dr. Ba}~s' report (19i~), and on the s.cll recta: ds included therein.