SOLVED

SAK, in joint venture partnership with Oscar Renda Contracting, Inc.
and Southland Contracting, Inc. was awarded this project on
03/24/09. The project, being completed for the Washington
Suburban Sanitary Commission (WSSC) consists of 5.3 miles of tunnel
excavated through competent bedrock 90 to 280 feet below ground
surface.
The deep water tunnel in the Washington, DC area will help meet the
growing demand in Montgomery and Prince George's Counties and
provide a dependable, high‐pressure clean water source during highuse
periods, droughts and emergencies.
The project requires three 150 foot deep shafts excavated through
overburden and rock. The Connecticut Avenue Shaft is the main
working shaft. The Stoneybrook Shaft and the Tuckman Shaft are
hole‐thru shafts excavated at the end of each tunnel segment.
Excavation by TBM will occur in two separate drives. The first drive
extends 4,124 lf from the Connecticut Avenue Shaft to the
Stoneybrook Shaft; this leg was completed on 11/23/10. The second
drive will extend 23,760 lf, without an intermediate access shaft,
from the Connecticut Shaft to the Tuckman Shaft. This leg of the
tunnel is expected to be completed sometime in October, 2012.
After completion of tunnel excavation, mortar lined steel pipe with a
diameter of 84 inches will be installed within the tunnel. Specially
designed pipe carriers will transport each 50 foot long section of pipe
into the tunnel. Sections of pipe are then blocked, and welded
together. Once installed, backfill grout will be placed within the
annulus between the pipe and tunnel wall.