October 2, 2019 ITS Money: Matthew Glisson, P.E., M. ASCE

Matthew Glisson, P.E. | Braun Intertec

Using Load Testing to Save Money and Time on the I-35W Bridge Project

The cost and time of performing design-phase load testing or altering the design based on the load tests at the start of construction often inhibits the use of load tests. A case history of a transportation project in the Minneapolis-St. Paul area demonstrates significant monetary and time savings that can come from load testing before, or at the start of construction. The I-35 Bridge project utilized a bi-directional load test to reduce shaft lengths, which not only saved material costs but also dramatically reduced construction time.

Findings

• The cost of the initial design: $15.2 million; the cost of the additional testing: $ 0.6 million; the cost of the final design (incl. additional testing): $ 8.3 million.
  Net savings from testing: $6,853,364 or 11 times the cost of the additional testing.
• The initial design called for 3,114 ft of rock sockets, which was reduced to 836 ft in the final design.  Based on the observed drilling rate, this 2,278 feet of less drilling translated in a time savings of between 23 to 95 days.