Value Engineering County Bridge Replacement-Paper

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The paper describes a value-engineering alternative for foundations on a county bridge replacement spanning a 200-foot-wide river. The new, wider, two-span bridge was originally designed with 173 steel-cased micropiles supporting its abutments and center pier. However, installing micropiles at the center pier would be difficult and time-consuming because of restricted access within a cofferdam and the need for dewatering and excavation.<br /><br />Subsurface conditions consisted primarily of sand over shallow sandstone bedrock. Because the foundations lie in the riverbed, designs also had to account for substantial scour during 100- and 500-year storm events, which could remove soil needed to brace deep foundation elements.<br /><br />The revised design replaced the west abutment’s micropiles with 93 driven steel H-piles. Analysis showed sufficient dense sand would remain there after the design scour event to provide pile fixity. The east abutment retained its original micropile design because scour would leave inadequate embedment for driven piles.<br /><br />At the center pier, four large-diameter, steel-cased drilled shafts with 10-foot rock sockets replaced 39 micropiles. The rock sockets provide support and lateral restraint where scour could remove much of the overlying soil. The drilled shafts were designed for substantial compression and shear loads.<br /><br />The case demonstrates how engineers, contractors, owners, and officials can collaborate to develop practical alternatives suited to site conditions. The authors report that the changes reduced construction time and material costs while preserving the required foundation performance.

Keywords

value engineering

bridge foundation

micropiles

driven steel H-piles

drilled shafts

scour analysis

river bridge replacement

rock sockets

deep foundations

construction cost reduction