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Mining Subsidence • • 471 <br />r <br />z <br />v <br />~f <br />n <br />e <br />y <br />to <br />td <br />b- <br />r- <br />m <br />i- <br />:i- <br />n- <br />re <br />In <br />8a <br />ed <br />v <br />nn <br />ttil <br />vmm. <br />- _-_ ~. <br />i <br />200 <br />t, <br />~~`SGb <br />'. ~ `S'a <br />~ .P <br />,~~Pe 400 <br />. e~~h <br />. ,`h <br />.d~~ <br />` yY` `~ 600 <br />~ P <br />~// 4 <br />~ ~,4qF <br />2 ~ `~ ~ A,2 <br />_ w~3 .S`6S _- -- 800 <br />- aW16 ..~co~ - -- ___-----1000 <br />Farm ~P?c,~ <br />~~d^ <br />- ~ yy 17 N ~ 'h 1200 <br />X93 <br />k~P// ' <br />~: <br />- Bm1183 ~ W24 ,8 ?4- =AREA ~ 1400 <br />w1e~~ - <br />- _ <br />_o tqo zoo aoom - - ' 1600 <br />1963 1964 ~ 1965 ~ 1966 1967 <br />Figure 7. Comparisons of the rate of subsidence of bench marks in the two su bsiding areas. Akzo <br />Hengelo, Netherlands. <br />1978. Of course, there was no prediction for only one point TABLE I <br />in the subsiding area. Figure 9 elves the predicted subsi- Prognos is of the Subsidence of Bench Mark H (Area 2) <br />dente for a lint from the center o(the bowl towards the east Over t he Period 1973-1983 in Comparison with the <br />compared with the subsidence profiles actually measured Subsidence Actually Measured of Bench Mark IB' (Area 1) <br /> m the Period 196 3-1973 <br />over the same line. The subsidence in this area started in <br />May 1973, so the September 1977 line is already nearly half Bench Mark 18' Bench mark H <br />the prediction. However, by this time the volume of the Actually Act°aliy <br /> Year measured Year Prediction Measured <br />subsidence bowl is only 1790 of the volume of [he original (la) (1) (2a) (2) (3) <br />cavity. 1962 21 mm 1972 21 mm 21 mm <br />Figure 10 is a eery simplified layout of the purification 1963 653 mm 1973 31 I mm 31I mm <br />and the vacuum plant. In this plan the predicted figures are 191x1 533 mm ~ 1974 300 mm 299 mm <br />given for the angle of tilt in minutes and for the shortening 1965 207 mm 1975 200 mm I I3 mm <br />and lengthening in millimeters per five meters of length at 1966 99 mm 1976 125 mm 94 mm <br />the surface. The figures are given for circular areas around 1967 82 mm 1977 75 mm <br /> 1968 82 mm 1978 bl mm <br />the cen[er of subsidence. It is an idealized situation, because 1969 81 mm 1979 60 mm <br />in reality the subsidence bowl has more or less the shape of 1970 61 mm 1980 60 mm <br />an ellipse with its longest axis in [he northeast-southwest 1971 80 mm 1981 60 mm <br />direction. This direction coincides with the direction of dip 1972 80 mm 1982 60 mm <br />of the salt layer. 1963 thru 1,976 mm 1973 thru 1,315 mm <br /> 1972 1962 <br />