The Alaska daily empire., 1917-04-23

from going into the portion of the mine which caved.
 Weakening Evidence
 The first evidence of any weaken ing to the hanging wall was noticed about four years ago, when sub sidence occurred at the Mexican mine and which was in all respects simi- lar to the slight subsistence occur ring in the vicinity of the Natator- ium last Saturday and Friday. Along about this same time there were a number of shocks experienced on Douglas Island and these were of sufficient extent to have the effect of an earthquake; one shock in par ticular was noticed even in Douglas. That movement was no doubt the be- ginning of a long protracted subsi- dence which eliminated in the large cave of Saturday night This grad ual breaking, due to the constant strain, is called by engineers "fa- tigue of materials other words, the hanging wall of a mine has been exposed to a strain for a number of years past and this constant strain has finally found release in the form of cave.
 Any mine, whose operation are continued under the sea, is con stantly menaced by similar possibili- ties and the surest way to avoid dis aster is not to mine at all. Per sistent mining operations conducted under the sea, will eventually let the sea in unless a sufficient amount of ore is left behind to provide ample support for overlaying rock. In such a case however, the profits would be reduced to a minimum, and this would have practically the same ef- feet as not having any mine at all. Ready Bullion Safeguard In anticipation of such a subsi- dence, there was placed, several years ago, in the drift which con- meets the Mexican and Ready Bull lion mines, two concrete bulkheads, each IA feet long. At more recent date, it was decided that in order to doubly secure to extend one of these 14-foot bulkheads by the addition of 20 feet more of solid concrete. This block was placed against one of the 14-foot blocks previously installed, so there is a solid plug 34 feet long to hold the water back. This plug is wedge shaped and it would be physically impossible to move. How ever, to make assurance dOubly se- cure, and to remove all doubts as to the security of the Ready Bullion mine, the company is now adding 30 feet more so that the plug itself will eventually be sS4 solid feet of concrete The buikhead now install ed received the severest test possible early Sunday morning when the air pressure in the mine was sufficient to raise the water through the Mex ican shaft several hundred feet in the air. There is no doubt at this particular instant there was an addi- tional head over the maximum that now exists, of 300 feet. Because the bulkhead has sustained an impact due to a sudden addition head of 800 feet, there is no doubt whatever, in any ones mind as to it's ability to With stand the pressure now against 1t, even without an additional 50 feet of concrete bulkhead.
 Great Loss to Property.
 Few people realize the great loss that has been caused by the cave-in. On the surface, with the exception of the big water hole, where it is known that two build- ings were engulfed and sucked down, there are only few cracks to indicate that anything unusual has occurred. There is, however, the stiffness on the air that denotes strange thing has happened. Be- low it is far different and the levels are filled with several thou sans of dollars of hoisting machin- cry, drills, cars and many other mine accessories.
 Five million tons of ore were al- ready blocked out for mining in the lower levels of the mines. most of which work has been done within the past two years. at an expend- iture running into millions of dol lars, all of which is a dead loss unless the mine is re-opened.
 The Mexican shaft had been deepened from the 1900 foot level to the, 2,2000 foot level. new steel head frame constructed and much other development work accomplish ed looking towards the extraction of vast quantities of this reserve ore