THE PANAMA CANAL 



193 



of steel and, for the straight portion of 

 the walls, so designed as to permit con- 

 struction of monoliths 36 feet in length 

 extending from the floor to the top of 

 the walls. The forms for the main and 

 the lateral culverts are of steel and are 

 collapsible. 



FROM GATUN TO THE OCEAN 



The channel from the locks to deep 

 water in Limon Bay, approximately 

 seven miles in length, is being excavated 

 in part by steam shovels and the remain- 

 der by dredges. 



South of the French Canal the Mindi 

 Hills cross the line of our canal between 

 Gatun and Limon Bay, rising to the ele- 

 vations 50 and 60. As the bulk of the 

 excavation is rock, steam shovels were 

 put to work to secure the requisite width 

 and depth. It was thought that when 

 sea-level was reached the shovels would 

 have to be replaced by dredges, as the 

 Mindi River is within a few hundred 

 yards of the area, and the French Canal 

 borders it. As the work progressed, 

 however, notwithstanding the seamy na- 

 ture of the rock, it was found that a 

 relatively narrow levee would keep out 

 water from the French Canal, and the 

 seepage was so small as to be easily han- 

 dled by pumps. One shovel-cut to grade 

 was made, when the high water in. De- 

 cember, 1909, flooded the pit and work 

 was suspended until recently, when the 

 soft material was removed by a suction 

 dredge. The water is being pumped from 

 the pit so as to permit completion of the 

 work by steam shovels. 



Over the area to be dredged, a sea- 

 going suction dredge removes the softer 

 material, while ladder and dipper dredges 

 handle the rock and stiff clays. The 

 underlying rock is drilled and blasted 

 prior to dredging. A total of over 35,- 

 000,000 cubic yards was the estimated 

 amount to be excavated, of which 60.3 

 per cent is completed. 



THE LOCKS AT PEDRO MIGUEL 



In the Pacific Division the work con- 

 sists of the construction of duplicate 

 locks at Pedro Miguel overcoming a 30- 



foot difference of level, with the neces- 

 sary dams ; two locks in flight, also in 

 duplicate, at Miraflores, connected with 

 the adjacent hills by one earth and one 

 concrete dam ; excavating the channels 

 between the locks to the required depths, 

 and the excavation of the channel to 

 proper width and depth to deep water in 

 the Pacific. 



The Pedro Miguel locks connect the 

 summit or 85-foot level with the 55-foot 

 level. The excavation for the locks, 

 amounting to 770,000 cubic yards, is 

 completed, and of the 837,400 cubic yards 

 of concrete required for their construc- 

 tion, 57 per cent is completed. 



The west dam connects the head of 

 the locks with the hills to the northwest 

 and performs the same function at the 

 south end of the lake that the Gatun 

 dam does at the north. It is to be of 

 earth, about 1,400 feet long, 40 feet wide 

 at the top, which will be at reference 107 

 above mean tide, and have side slopes of 

 8:1. It will be subjected to a maximum 

 head of 40 feet, though the average head 

 is from 25 to 30 feet. 



In its construction two rock piles are 

 formed ; between these two masses of 

 material (from which an existing stratum 

 of gravel was removed), selected mate- 

 rial will be placed properly puddled and 

 rolled. This central portion will have a 

 thickness of 140 feet at the bottom. 

 Concrete core walls will connect the dam 

 with the hill and lock. The dam, which 

 contains about 1,000,000 cubic yards, is 

 26 per cent completed. The natural sur- 

 face of the ground from the east wall 

 to an adjacent hill is above the upper 

 level, but it is to some extent pervious 

 to water. To cut off any possible flow, 

 the lock wall is returned toward the hill, 

 with which it will be connected by a con- 

 crete core wall. 



THE LOCKS AT MIRAELORES 



The Miraflores locks are two in flight, 

 overcoming the difference in level be- 

 tween Miraflores Lake, whose surface is 

 at reference 55, and the sea-level section. 

 As the fluctuations in tide are about 20 

 feet and mean tide is the datum, it will 



