THE PANAMA CANAL 



167 



same method, the only difference being 

 in the character of machinery used. The 

 width of the channel adopted by the 

 French was 74 feet; the present plan is 

 for a channel 300 feet at the bottom, so 

 that the first work undertaken by the 

 Americans was directed to securing the 

 necessary widths for the upper reaches 

 before attempting any increase in depth. 



Whatever water entered from rains 

 and seepage was drained from the sum- 

 mit of the cutting by gravity to the Rio 

 Grande on the south and to the Chagres 

 River on the north. As shovels in ex- 

 cess of those required for widening be- 

 came available, they were put to work to 

 secure increased depth, care being taken 

 to maintain, as far as possible, free, 

 easy, and rapid drainage. Shovels are 

 started at either end and carried towards 

 each other, cutting out at a new summit. 

 These pioneer shovels on the next lower 

 grade make the "pilot cuts," which con- 

 stitute the new drains and to which 

 water is led by laterals from various 

 parts of the excavated area adjacent. 

 The average grade or slope is about 36 

 feet per mile. The loading tracks for 

 these shovels are on the level above. 



When the "pilct cut" has progressed 

 sufficiently far, its cut or trench becomes 

 the loading track for a second shovel, 

 which is started to widen out the cut al- 

 ready made by the pioneer, and so the 

 work moves forward, the shovels ap- 

 proaching the summit from either direc- 

 tion in echelon. 



In 1904 the summit of the excavation 

 was at Gold Hill and at reference 193 

 above sea level. The summit at present 

 is between Empire and Culebra and is at 

 reference 106 above sea level. The 

 drainage to the south is still by gravity, 

 through the old bed of the Rio Grande 

 to the west of the Pedro Miguel locks. 

 It is expected that before the next wet 

 season the center culvert of the locks 

 will be utilized. 



On the north side conditions are now 

 different. The reference of the low- 

 water surface of the Chagres is 43 at 

 the point of its intersection with the 

 center line of the canal. The bottom of 



the completed canal is at reference 40. 

 A dike separates the cut from the Cha- 

 gres, but this is overtopped during the 

 high floods. To get rid of the accumu- 

 lated flood water, 24-inch pipes are laid 

 through the dike, each with a suitable 

 valve, and so arranged that all water 

 above the pipes is carried into the Cha- 

 gres by gravity after the subsidence of 

 any flood. 



Recourse must be had to pumping 

 whatever water remains from the floods 

 below this level, and such as may be col- 

 lected by drainage from the south ; for 

 this purpose a sump has been dug to ele- 

 vation 32 and pumps installed. It is not 

 possible to estimate the quantity of water 

 that will have to be handled, but three 

 pumps are in place, each capable of dis- 

 charging 12,000 gallons of water per 

 minute. 



VERY TROUBLESOME SLIDES 



The greatest difficulty encountered in 

 the excavation is due to slides and 

 breaks, which cause large masses of ma- 

 terial to slide or move into the excavated 

 area, closing off the drainage, upsetting 

 steam shovels, and tearing up the tracks. 

 The term "slide" is applied to the move- 

 ment of the overlying clay upon smooth, 

 sloping surfaces of rock or other ma- 

 terial harder than the clay. 



"Breaks" occur at points where the 

 underlying rock is of poor quality, inter- 

 sected by vertical seams or seams slop- 

 ing toward the canal, and which is un- 

 able to bear up the superimposed mass. 

 Generally, the upper surface of the 

 broken portion of the bank remains ap- 

 proximately horizontal, settling nearly 

 vertically. The weight of the broken por- 

 tion forces up and displaces laterally the 

 material lying directly below it in the 

 bottom or on the berms of the canal. As 

 the material thus forced up is taken 

 away the upper part gradually settles 

 and moves toward the axis of the canal 

 until the entire broken portion is re- 

 moved. 



The greatest slide is at Cucaracha, and 

 gave trouble when the French first be- 

 gan cutting, in 1884, and still continues. 



