OVERVIEW:
The Clean Rivers Project is DC Water’s ongoing program to reduce combined sewer overflows into the District’s waterways. The Project is a massive infrastructure and support program designed to capture and clean wastewater during rainfalls before it ever reaches the rivers. The project is comprised of a system of deep tunnels, sewers and diversion facilities to capture combined sewer overflows and deliver them to a wastewater treatment plant.
CHALLENGE:
This particular section of tunnel runs down the center of a busy road, so scheduling was restrictive and keeping install time to a minimum was a priority. There was also limited access for installation equipment and staging materials. In addition, the installation of piles was weather dependent, and therefore subject to change without notice.
SOLUTION:
Creative Concepts Group, Inc. presented STELCOR Drilled-In Displacement Micropiles (DDM) to the D.C. Water & Sewer Department as an alternate. Engineers believed that a helical pulldown pile was substandard and would have failed in torsion at less than 20,000 ft⋅lbf. A STELCOR pile was tested and exceeded the requirements. STELCOR had a resistance of 30,000 to 40,000 ft⋅lbf in the top 10 feet and had a torque capacity of over 50,000 ft⋅lbf. With limited access and a tight schedule, a total of 46 STELCOR piles were installed for this thrust block reinforcement foundation. The STELCOR piles were able to bear higher loads at lesser depths, saving time and money.
INSTALLER:
Creative Concepts Group, Inc.
GEOTECHNICAL ENGINEER:
D.C. Clean Rivers Project
STRUCTURAL ENGINEER:
Bryant Blake P.E.
ARCHITECT:
Reitan Architects LLC
LOADS:
Anticipated – 200 kips factored (compression and tension)
Actual – 102 Kips (Compression) 114 Kips Tension
Piles met refusal at less than half of the anticipated depth
PILE DETAIL:
STELCOR 1600
18” tip or drive plate
16” corrugated grout column
13” solid grout column
8” reverse auger
5.5” O.D. X 0.361″ W.T. – 80 ksi central shaft
SOILS + EMBEDMENT DEPTH:
Soils consisted of clayey sands, silty sand, and silty gravel with sand. (SEE SOILS REPORT)
Piles were intended to go 62’ but all piles met refusal at approximately 30’.
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