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Mining Subsidence <br />West East <br />m. <br />Figure 9. Actual measured and predicted subsidence in area 2 during the period 1973- 1983. <br />473 <br />were then given a tilt in the opposite direction. It is expected TABLE 2 <br />that the tanks will move downwards again and tilt back to Tilt of t he Purificatio n Tanks in <br />horizontal position, or even more without maintenance to be \linutes and Centimete rs Till 1983 <br />done within the next flee years. The same has been done Distance <br />with a small building with a stiff reinforced concrete founds- Diameter To Cenur Titt Tilt <br />tion and brick walls. Tank (deters) (Veters) (Minutes) (Centimeters) <br />Finally, Figure I I shows a Casing-Collar-Log and a tt) (Z) (3) (s) (51 <br />Gamma-Loe of a suspect well. On the surface no subsi- V 100 11.00 10-20 15.5' <br />' a.9 <br /> V 101 ?2.40 5-30 19.3 12.5 <br />dente has been measured up till now. Yet the txpectation is V 105 19.07 ?5-95 aR.l' 26.7 <br />that somethin, will happen in the near future. This well is VII? 14.25 30-a0 41.3' 17.1 <br />still accessible for logging and it is planned to make these V 205 19.07 50-70 61.0' 33.8 <br />logs every year. From this example it can be seen the origi- V 219 10.90 50-60 61.9' 19.6 <br />nal casing list set against aCasing-Collar-Log taken in 1976 Cond. 10.90 30-a0 41.3' 13.1 <br />and a 1973 Gamma-Log compared with the Gamma-Log of R 100 8.00 30-35 37.8' 8.8 <br />1976. In both logs a vertical displacement increasing with R 103 3.00 a0-50 55.0' 12.8 <br />depth can distinctly be noticed. At a depth of 250 meters a R 202 10.00 35-a0 4-t.7' 13.C <br />vertical displacement of about 2 meters can be read from the R ?O,i I0.00 60-70 60.2' <br />' I7.5 <br /> R _OS 10.00 65-75 58.4 17.C <br />logs, whereas at a depth of 80 meters displacement is only a <br />half a meter. These movements have already reached the S 100 18.30 3S-SS Sa. l' <br />' ZS.E <br /> S 101 .00 50-70 61.0 30... <br />unconsolidated clay and will probably soon be measurable S 200 ;; <br />.00 35-60 55.7' 35.6 <br />at the surface. This kind of information is considered to be a S 201 20.00 75-95 48.1' 28.0 <br />first warning fur possible movemens at the surface. 5 301 20.00 70-90 53.3' ?1.0 <br /> <br />,~---SU85IOING -AREA i6O meter - <br />~~COMPRESSION AREA--~~ EXTENSION AREA- <br />, , <br />CENTRE ; <br />