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.
Creative Concepts Group, Inc.
D.C. Clean Rivers Project
Bryant Blake P.E.
Reitan Architects LLC
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
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’.