The North Texas Municipal Water District‘s Sabine Creek WWTP expansion will double the plant’s capacity from 3.0 million gallons per day (mgd) to 7.0 mgd to better serve a rapidly growing population along the Dallas Metroplex’s northeastern sector. Eagle Contracting, the project’s General Contractor, partnered with Geotex to provide construction materials testing and inspection services.
As construction began, the contractor engaged Geotex to design, implement and analyze axial and lateral load testing to verify the headworks structure’s drilled shaft foundation design. Geotex geotechnical engineers suggested implementing bi-directional load testing using Osterberg cell techniques for the axial load testing instead of traditional top-down testing to expedite results and reduce cost.
With the top-down test, shafts are typically loaded 2 to 3 times the design load with little or no shaft displacement. The true Factor of Safety is unknow and likely excessive. The bi-directional test offers superior results, measuring actual ultimate bearing capacities and resulting in a 2X Factor of Safety. This test method allows geotechnical engineers to more accurately estimate pier capacity and provide more cost-effective foundation design recommendations.
Through close coordination with Eagle and Geotex sub-consultants, the recommended tests were expeditiously conducted and results delivered less than 40 days after the procedures were approved, allowing drilled shaft installations to proceed without significant delay.
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