El Milagro, Villanueva
Bridge, Road, Drainage
The village of El Milagro is a community of approximately 6,000. It is located northeast of the municipal center of Villanueva on the flood plain of the Chamelecon River. The neighborhood is subject to periodic flooding.
A dirt track leads north from El Milagro into vast agricultural lands of sugar cane plantations. The path crosses the Chasnigua Stream on what was a single lane timber structure. Little now remains since Hurricane Felix of September 2007. During Hurricane Felix, the water level reached approximately one and a half meters, approximately five feet, above the level of the old bridge deck.
Global Community Development was asked by the municipality and the community to construct a new structure with sufficient clearance to stay above that flood level. The project will consist of three components: road improvements, a new bridge structure, and drainage improvements in the Brisas de Milagro neighborhood.
The proposed structure for the stream crossing will consist of a corrugated aluminum arch founded on sloped reinforced concrete walls with bagged concrete headwalls. The dirt road leading to the stream crossing will be raised to above flood levels equal to the level of the proposed bridge deck.
Culverts will be installed to improve the drainage in the Brisas de Milagro neighborhood. The neighborhood is located southeast of the proposed stream crossing. The culverts installed at several locations will allow flood waters to cross the proposed dirt road that will be elevated. Improved drainage ditches are proposed on each side of the alley passageways, running through the Brisas de Milagro neighborhood, perpendicular to the road to be raised.
The existing bridge at Gran Bretaña, also known as the Swayback Bridge, is a two-span, 11m and 18m, steel girder, reinforced concrete structure. It was constructed between 2006 and 2007. During the floods of Hurricane Felix in September 2007, the center pier was undermined and settled approximately half a meter with a slight cant downstream.
According to municipality engineers, the pier is founded on a spread footing whose base is approximately two and a half, 2 m, meters below the stream bed. The basic structure of each span is a pair of I-beams salvaged from a dismantled bridge elsewhere in the municipality. There was no foundation investigation as the municipality has no equipment for conducting sub-soil investigations. The bridge could not be skewed to more closely conform with the stream alignment so the center pier is skewed to the stream flow creating eddies during high flows.
Global Community Development proposes to inject a mix of Portland Cement with fine to medium sand under air pressure under and around the pier footing to create a bubble of non-erodable material. A grout curtain, similarly created, should also be built in front of each abutment to prevent further scour.