Olmos Dam Rehabilitation using Permanent Strand Anchors

Olmos Dam was built in 1928 on Olmos Creek after the city of San Antonio, Texas, USA experienced a major flood disaster during which much of the city was flooded and many people lost their lives.

The dam accumulates and controls water diversion from the entire San Antonio River basin. The straight, concrete gravity dam is about 610m (2,000ft) long, and its crest reaches 17m (58ft) high in some places including 6m (20ft) foundation depth.

A major dam rehabilitation program had to be implemented in order to prevent damage during maximum overflow. This included the installation of 68 Permanent DYWIDAG Tie Down Anchors with six or twenty Ø 15.2mm high strength strands with double corrosion protection (DCP) into the bedrock. The dam’s spillway was also increased to better handle future inundations.

DSI Long Beach, CA, plant fabricated the anchors with attached grout tubes and wedge plates and supplied them separately from the 1.5mm thick corrugated HDPE anchor sheathing.

A very skilled and experienced contractor built a special mobile platform placed on the dam that was able to support and carry the drilling, grouting and stressing equipment along the narrow dam crest. Thus, the contractor was able to drill efficiently, passing strict water pressure tests of the drilled hole and corrugated sheathing. Partly, drilling and anchor installation had to be carried out in very tight spaces.

Strand anchors were inserted inside the corrugated sheathing and lowered into the drilled hole using an uncoiler provided by DSI. Some of the anchorages incorporated load cells for permanent load monitoring. The wedge plates placed over the strands had an external heavy duty thread allowing for anchor re-stressability and load adjustment if necessary. Performance and proof testing operations were carried out successfully with DYWIDAG jacks supported by special stressing chairs.

Supplyrental of equipment

Bexar County, USA

The Judy Company Inc., USA

Freese and Nichols, Inc, USA

Archer Western Contractors Ltd, USA

Freese and Nichols, Inc, USA