Brasfond suggested an alternative solution using three lines of Chemical Churning Pile (CCP) columns instead, a technology already widely used in reinforcement soil works. These had the same purpose as the root piles: to preserve the foundations of existing neighboring buildings and serve as an emergency containment structure in case of excavation collapse during execution. The second challenge was that the tunnel would pass beneath a canal with very little cover and close proximity to the station. The canal connected the Atlantic Ocean to Rodrigo de Freitas Lagoon. The client was concerned with possible flooding of the station and of the tunnel, causing an unrecoverable delay and missing the Olympic Games. Two solutions were discussed to mitigate the effects of possible flooding. First, a JG mass was designed to start from the diaphragm wall of the station and extend below the canal and 20 m (66 ft) beyond it. This would ensure that there was enough contact between the tunnel segment lining and the JG mass so there would be no possibility of water entering the tunnel. The 1.2 m (4 ft) diameter JG columns were designed to go from the bottom of the canal down to the top of rock. Since it was not possible to block the flow of the canal in order to JG beneath it, the work was divided in two phases. In phase 1, sand bags were placed into half of the canal to form a platform for the rig. Then the sand bags were removed and placed on the other half so that JG could be accomplished on the other side. The columns in the middle were drilled again in phase 2 to guarantee overlap of the columns. Internal view of CCP wall For each JG column, the main parameters measured and controlled while drilling were rotational speed of drill string, depth and penetration tension. For the injection, the time, depth, injection pressure and flow, air pressure and flow, volume of grout slurry, rotation and lift speed were measured. The second flooding protection employed was an arched CCP wall built inside the station from top to bottom to function as a barrier in case a flood did happen. Conclusions The successful interaction between the owner, the Rio de Janeiro Metro authority; the general contractor, Linha 4 Sul JV; the designer, Promon Engineering; and Brasfond, the foundation contractor, made this project a success. This project marked the first time that a hydromill was used to build a station in Rio de Janeiro. Overall, 12,000 columns of JG and CCP were constructed, with an overall drilled length of 250,000 m (820,000 ft) in soil and 2,000 m (6,600 ft) into rock, of which 110,000 linear m (361,000 ft) were injected. The consumption of cement for the Jardim de Alah station was an impressive 65,000 tonnes (71,650 tons). The hydro- mill and clamshell diaphragm wall were composed of 233 panels, and a total of 22,700 cu m (29,700 cu yd), 3,200 tonnes (3,527 tons) of steel and 24,500 cu m (32,000 cu yd) of concrete were used. We would like to thank everyone involved in the project, especially Linha 4 Sul JV for providing photos and information for this article. We wish them success in completing the line and hope for a great Rio 2016 Olympic Games.
