• The dense vegetation in the water, the bulhado, existed in all the access and construction areas, making it impos- sible to use self-propelling vessels to move the barges. • The environmental regulations only allowed a 5 m (16 ft) wide opening inside the axis of the line. They did not allow deforestation of the access regions. Solutions 1. Using very light driving equipment and splitting the auxiliary equipment between several barges: The solution adopted assumed that the driving equipment should be as light as possible, and distributed between more barges, with lighter weight on each. This lowered the draft of the barges, and resulted in lower penetration in the bulhado vegetation. The lightest possible driving equipment would be a gravity hammer, with the lightest ram that would still allow driving piles to the required depth. These devices weighed about 90 KN (20 kips), with 10 KN (2.2 kips) of auxiliary equipment. The total weight of this configuration was 100 KN (22 kips), compared to about 3,000 KN (670 kips) of the solution used in the “Chinese Tower.” Gravity hammers, however, have a much lower productivity than vibratory or diesel hammers. Driving a pile with vibratory or diesel hammers of equivalent energy can be up to 10 times faster, due to their much higher blow rate. Further- more, the crane used by the first contractor had a tall boom, which allowed lifting up to 48 m (160 ft) long pieces. They could weld the pile segments all at once on the ground, greatly speeding up the installation process. The solution adopted precluded the use of such tall booms, making it necessary to weld each segment during driving, which slowed down the process even more. Due to the much lower productivity of the system now used, a larger number of piling rigs had to be used in order to comply with the time constraints. Fifteen rigs were used, each one with its own barge. Additional barges were also required for navigation, for temporary living and resting quarters for the crew, and for transporting the piles to the driving site. Forty small barges were used in total, in place of the two large ones used in the crossing of the Amazon River. A crew of 150 people was required for the gravity hammers, instead of the 10 people required by the heavy equipment. A solution that at first seemed more expensive and slower proved, however, to be up to the challenge. The more sophisticated original solution failed. Figure 4 shows the driving system used to drive the steel pipe piles. the loader. This piece, moving close to the water surface by the loader shell, worked as a paddle. The idea of the loggers was the basis of the solution adopted for propelling the barges, except that a 25 tonne (55 kips) hydraulic excavator now replaced the loader, for added maneuverability. The shell of the excavator worked as a paddle, and since it can move in several directions, so could the barge. The hydraulic excavator on a barge was the sole means of propulsion used. It acted the same way as an outboard motor tug, with the advantage of not having the motor underwater, thus eliminating the risk of the propeller Figure 4. Light gravity driving system, on a small barge 2. Use of excavators over barges to propel the driving systems and auxiliary equipment: Before 2003, when the Alagados area was declared an environ- mental reserve, there was a period of intense exploration of hardwood from large trees. The lumbermen transported logs weighing several tons, and they did that by means of a loader on a barge: they placed a reinforced wooden structure, 1.5 m (5 ft) wide and 4 m (13 ft) long, on the shell of tangling in the dense vegetation, as shown in Figure 5. Navigating Traditional Paths & Trails The riparian paths. The Aiquiqui and Uiuy Rivers were used to access the axis of the transmission line. Descendants of the native Indians have lived by the margins of those rivers for hundreds of years. They know the deepest spots in the Alagados region, so the contractor hired them as DEEP FOUNDATIONS • JAN/FEB 2014 • 55
