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.

DC Water and Sewer Dept Stelcor Drilled-In Displacement MicropilesCHALLENGE: 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.

DC Water and Sewer Dept Stelcor Drilled-In Displacement Micropiles 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’.

DC WATER & SEWER – CLEAN RIVERS – FULL CASE STUDY