Employing the Micro-Tunnelling
method and provide access through 10' and 15'
diameter deep drilled shafts in the street Shirley
forces and subcontractors began construction and
in less than 12 months had completed over 9600
feet of micro-tunnel and over 20' deep large diameter
access shafts that ultimately became the manhole
access to the sewer. The sub soils were typically
running sands with a significant head of water
due to depth and the tidal influences in Old Town
Alexandria and required the MCT (Micro-Tunnel)
equipment to be capable of earth pressure balance
to allow the vitrified clay pipe to be pulled
/ jacked along behind the MCT Unit. Laser guided
for direction and elevation the tolerances required
to provide adequate fall for the sewer were significant
and required close attention to detail and engineering
expertise. The project required a labor force
of great diversity from including divers, tunnel
specialists, highway and utility workers, maintenance
of traffic personnel, operators of all types,
and numerous engineers and management staff to
coordinate the effort.
