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grinelield Subsidence ar Windsor, Onrar~ <br />W <br />I <br />W <br />W <br />0 <br />rn <br />m <br />v, <br />A B <br />O 1949 <br />1950 <br />5 1951 <br />1952 <br />to <br />15 <br />1953 <br />20 HORIZONTAL SC4LE -FT. <br />0 100 270 300 I[0 <br />MARCH ' <br />25 1954 <br />Figure 5. Successive profiles through sv<sterly portion of subsiding <br />area, along line A-B, shown in Figure 2. <br />0.0 <br />I.0 <br />0 <br />6.0 <br />7.0\ <br />Origins/edge <br />o/sinkha/e ~` <br />.'~ ~. <br />r <br />r t <br />I I <br />I I <br />I I <br />t <br />t <br />\ I. <br />I <br />~ 1 <br />i <br />Figure 7. View o[ sinAh ole, 1954. <br />the plan[ at this time. There was awater-filled de- <br />Q pression, "the sinkhole," roughly elliptical in <br />shape, vvith a maximum diameter of nearly 500 <br />Ecet and a maximum depth in excess of ?5 feet. <br />The pond occupied the center of a larger bovvl- <br />\ shaped depression with a radius of about 1000 <br />1 feet. Many of the plant buildings \vere damaged <br />beyond repair. <br />Brine production at the Sandwich field was per- <br />manently discontinued after the sinkhole had <br />formed. <br />In the months following [he formation of the <br />sinkhole, the pond was pumped out and the de- <br />pression was Filled with sand and gravel. <br />-- <br />PLANT NORTH <br />SCALE - FT. <br />100 50 0 100 200 300 400 500 <br />Figure 6. Differtnee in rates of subsidence of 1953 and 1949, inches <br />per year. <br />taken place. In the early afternoon, additional jets <br />or "fountains" developed at points which eventu- <br />all}' became submerged. One of the largest of these <br />formed a wall oC water four feet in hei¢ht and 75 <br />~ 1 <br />J <br />303 <br />feet long. In general, individual jets remained active <br />for periods of two to five minutes. The water <br />\vhich thus spurted from the ground appeared <br />black and had a sulphurous odor. <br />B}' midafternoon, movement had virtually <br />ceased. Figure 7 shows the conditionof a part of <br />POST-SUBSIDENCE INVESTIGATION <br />Following the formation of the sinkhole, the <br />Canadian Salt Co. and Canadian Industries Ltd. re- <br />tained a panel of consultartts of which Carl A. <br />Bays, Ralph B. Peck, and Karl Terzaghi were mem- <br />bers. <br />The prograrrl recommended by tltr panel in- <br />cluded the determination of the depth to bedrock <br />in the sinkhole area b}' means of a large number of <br />washborings. Before any borin¢s had been made, a <br />seismic sune}' was carried ou[~a[ the suggestion of <br />r <br />