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Olmos Dam Modifications, 1982 OCEA
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Considering a rapid increase in development in the Olmos Basin Area and vulnerability of the region to heavy rainfall, concern grew that the basin could overtop the dam. In fact, a study was conducted in 1973 which indicated that flood routings produced by severe storms would in fact overtop the dam, that the structure would be overstressed, and that it could fail. The modifications that followed included: post-tension cables that extended  down through the dam and anchored into the solid limestone strata below, modification and/or replacement of the control gates, construction of a new control house, and  relocation of the two-lane roadway from its original location across the top of the dam to a new location below the dam. Prestressing of the east and west non-overflow segments used a hard limestone layer (7-10 ft thick) 50 feet below the base of the dam as anchorage. Reconstruction of the roadway also included two bridges – one over the outlet channel and one to connect the new roadway to the remaining existing street, and replacement of the roadway on the west end with an ogee spillway.

 

One innovative method utilized during construction included the use of explosives to remove the upper portions of the dam, clearing the way for construction of the spillway crest. This type of demolition – partial removal of increments of an existing dam using explosives - had never been attempted before its use on the Olmos Dam Modifications. Engineers got the idea from pre-splitting techniques used in quarrying. This method saved considerable time and money and produced less shock to the structure than would have been inflicted by a hydraulic ram. The completion of the project in 1982 marked a great moment of relief for the community from the growing anxiety of an impending dam failure. Construction management and coordination of engineering was handled by the San Antonio River Authority (SARA), which recorded total cost of the project at $8,661,483.90.  


Owner:
City of San Antonio
Project Manager: 
San Antonio River Authority (SARA)
Engineer:
JV of W. E. Simpson Co. and Hensley-Schmidt Inc.
Contractor:
Clearwater Constructors Inc.
 Photo:  ©2014 ASCE, Texas Section

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