Record Jacking Project In San Antonio

By Jeff Griffin, Senior Editor | July 2012, Vol. 67, No. 7

Culverts are essential components of highway drainage systems, carrying water beneath roadway surfaces to prevent flooding and erosion from washing away supporting soils.

In many situations, various methods of trenchless construction can rehabilitate failing culverts and installing new culvert pipes prevents making a deep excavation across a roadway, an option usually considered unacceptable because of the disruption of traffic it would cause.

However, rehabilitation methods won’t work in all situations and conventional trenchless replacement methods have limits to the size of culverts that can be installed.

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The city of San Antonio faced such a situation when two, nine-foot-square concrete box culverts under Interstate 37 southeast of downtown were determined to be undersized and high velocities coming from them were causing erosion. The two existing culverts would be unable to accommodate a 100-year rain event.

The solution was to install a new 294-foot-long, 11-by-9-foot box culvert by jacking 49, 6-foot-long, 11-by-9-foot reinforced concrete boxes, one at a time, through a 12 by 24-foot shaft, 19-feet deep at flow line beneath the highway.

Making a deep excavation across a busy interstate highway obviously was not an option for installing the new culvert, and the jacking method selected was used because it minimized impact on traffic during construction. The new culvert is adjacent to the existing culverts.

The project owner was the city of San Antonio with funding provided by a city bond program administered by the Capital Improvements Management Services Department (CIMS). Anibal Gutierrez, P.E., was CIMS project manager. The firm Fernandez Frazer White & Associates was project engineer. The contractor was Boring & Tunneling Company of America (BorTunCo).

Shaft construction

The project began with constructing the shaft. During planning, both the city of San Antonio and BorTunCo conducted geotech coring to determine the soil conditions on the site, said Dennis Ritchards, BorTunCo tunneling division manager.

“Unfortunately,” he added, “the results did not represent the actual subsurface content which was 90 percent rock and sandstone.