THE PANAMA CANAL 



173 



Though at first confined to a length of 

 800 feet, measured along the line of ex- 

 cavation, the slide has extended to in- 

 clude the entire basin south of Gold Hill 

 or for a length of about 3,000 feet. The 

 original slide covered an area of about 

 six acres, but the latest surveys show 

 that is has extended to cover 47 acres. 



no danger from slides after canal is 

 completed 



There are all told nine "slides" and 

 "breaks" to be reckoned with, and there 

 is nothing to do but to remove all the 

 material embraced within their limits. 

 As the cut is deepened these may be ag- 

 gravated or others may develop. There 

 is no method known to stop or to pre- 

 vent them. Usually the first indication 

 received, if there be a forewarning, is the 

 lifting or moving of a shovel and tracks. 



The cut has therefore developed into 

 the uncertain and experimental feature 

 of the work and its completion will mark 

 the date of finishing the canal. No ap- 

 prehension is felt because of the slides 

 after the completion of the work. They 

 develop as the depth of the cut increases, 

 and the banks slide or break because of 

 the condition of unstable equilibrium 

 that results from the cutting ; when 

 grade is reached equilibrium will be es- 

 tablished, and the back pressure of the 

 water will result in greater stability. 

 Whatever slides occur subsequently will 

 be relatively small, and the material can 

 be easily handled by steam shovels on 

 the berms that will be left and by 

 dredges that will be available. 



Some idea of the magnitude of the 

 slides can be obtained from the fact that 

 during the fiscal year 1909, of 14,325,876 

 cubic yards removed, 884,530 cubic 

 yards, or 6 per cent, were from slides. 

 For the fiscal year 1910, of 14,921,750 

 cubic yards that were removed, 2,649,- 

 000, or 18 per cent, were from slides or 

 breaks that had previously existed or 

 that had developed during the year. 



THE MATERIAL IS ALL ROCK 



Except for the slides, which are of 

 earth, the material to be removed is 

 rock, and requires blasting to enable the 

 shovels to handle it expeditiously. The 



largest part of the drilling is done by 

 churn or well drills, though tripod drills 

 replace them where the others cannot be 

 used to advantage. The drills are oper- 

 ated by compressed air, supplied by three 

 compressor plants, which are connected 

 together by a 10-inch pipe line about 

 five miles long, with 6-inch and 4-inch 

 leads running into the cut. The drills 

 operate in batteries of from 4 to 12; the 

 holes, from 15 to 27 feet in depth, are 

 spaced from 6 to 16 feet apart. 



The explosive used is dynamite, 45 

 per cent to 60 per cent nitro-glycerine. 

 Excessive moisture and water in the 

 holes prevent the use of blasting powder. 

 When the holes in any section are ready 

 for blasting, they are "sprung" — that is, 

 four to six sticks of dynamite are low- 

 ered to the bottom and exploded — 

 thereby forming a chamber for the re- 

 ception of the charge. The charges vary 

 from 25 to 200 pounds, depending upon 

 the local conditions ; the tamping fol- 

 lows, and the explosion is effected by an 

 electric current from one of the lighting 

 plants. 



THE EARTH AND ROCK FROM THE CULEBRA 

 CUT ARE USED FOR THE BREAK- 

 WATERS AND EMBANKMENTS 



Through the blasted area the steam 

 shovel cuts its way, averaging 34 feet 

 wide at the bottom and 50 feet at the 

 top for the "pilot cuts," which are 8 to 

 12 feet deep. The widening cuts are 

 about 26 feet wide and from 15 to 24 

 feet deep. 



The best results are secured with the 

 95-ton shovels, though the 45-ton and 

 70-ton shovels are also used. The 95- 

 ton shovels have dippers of four and 

 five yard capacities, the former remov- 

 ing rocks containing as much as six 

 cubic yards. 



When the rocks are too large to be 

 lifted by the shovel, they are "dobie" 

 blasted, and thus broken to sizes con- 

 venient for the dipper. This is done by 

 placing three or more sticks of dynamite 

 on the rock, covering them with mud 

 and igniting by means of a slow match. 



The shovels load the material on dirt 

 trains, consisting of 20 flat cars and 



