Underground Construction - September 2022 - 15

only required five shafts to complete,
BRH-Garver's proposal also included
installing manholes needed for future
connections after microtunneling was
complete.
" VMT input the path of the tunnel
into the guidance system, which displayed
a virtual laser at the control console, "
Ellett explained. " The operator
guides the path towards that virtual laser
exactly the same as if it was with a standard
laser targeting system. "
As the tunnel was excavated, CCFnel
segments all shorter than 700 feet, "
said Ellett. " With our recent purchase of
a Herrenknecht AVN 1200 microtunnel
system, we were in a good position to propose
changes to the project alignment. "
BRH-Garver worked from 24-footdiameter
jacking shafts and 15-footdiameter
receiving shafts.
inch sanitary main feeding the Upper
Brays Wastewater Treatment Plant.
Microtunneling choice
The decision to use slurry microtunneling,
a precise method of excavating a tunnel
while simultaneously jacking pipe, was
the right choice by the city and designer,
according to David Ellett, vice president
of BRH-Garver. It provided the accuracy
needed for tight line and grade work at
the 60-foot-plus installation depths, the
varying soil conditions well below the water
table, and the high volume of surface
traffic above the tunnel alignments.
" The project's initial design of Segment
1A included 60-inch microtunnel
from tunnel shafts located at nine
planned manhole locations, making tunThe
Herrenknecht AVN 1200 system
includes a 600-ton jacking frame,
controls for multiple intermediate jacking
stations (IJS), and an automatic
bentonite lubrication injection system.
BRH-Garver added to their purchase a
traditional laser-based guidance system,
and the gyroscope-based guidance system,
GSN-P, develop by VMT.
Before
construction
began, BRHGarver
proposed an alternate alignment
that combined shorter tunnels, eliminated
shafts and utilized a curved microtunnel
alignment.
" Our proposal eliminated three mansaid.
holes
and corresponding tunnel shafts, "
Ellett
It changed the nine-drive
alignment to three long microtunnel
drives, leaving the short downstream
drive as designed.
Although the alternate alignment
PRMP gravity-flow sewer pipe was simultaneously
installed.
The first microtunnel drive was a traditional
straight tunnel of 1,436 feet. However,
the second drive of 1,609 feet included
a 5,130-foot radius curve at a length
of 738.9 feet. Herrenknecht and VMT
worked with the construction crew to accomplish
this initial curved microtunnel.
Next up was tunnel drive number
three consisting of 1,502 linear feet with
a 4,016-foot radius curve and a curve
length of 586.4 feet. The curved microtunnel
segments were completed three
months ahead of the original design
schedule. Overall, the project was completed
85 days ahead of deadline.
Ellett credits successful completion
of the revised plan, to hard work by the
Garver crew members, support from
Herrenknecht and VMT, and the partnership
between the contractor, city
of Houston and design that led to the
curved alignment. UC
FOR MORE INFORMATION:
BRH Garver, (713) 921-2929, brhgarver.com
Herrenknecht, herrenknecht.com/en
Hobas, (800) 856-7473, hobaspipe.com
VMT, vmt-gmbh.de/en
Hazen, (212) 539-7000, hazenandsawyer.com
UCONonline.com | SEPTEMBER 2022 15
http://www.brhgarver.com http://www.herrenknecht.com/en http://www.hobaspipe.com http://www.vmt-gmbh.de/en http://www.hazenandsawyer.com http://www.UCONonline.com
Underground Construction - September 2022

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