DJ Wisor and Sons, Inc. used a Grundoram
pneumatic pipe ramming tool to install 16-in. casings
on a sanitary sewer installation project for the Decatur
Township, Pennsylvania. |
An increasing number of sewer, water
and gas projects bid today are designed with trenchless technology
in mind. Advances in trenchless methods such as directional drilling,
horizontal boring, pipe bursting and pipe ramming has allowed
project engineers to think in ways they were unable to just a
few years ago. Many jobs specifically require the use of trenchless
technology to some degree. Contractors that are able to utilize
a range of trenchless equipment are benefiting from this new way
of thinking.
The Decatur Township, Pennsylvania
recently awarded a large-scale sanitary sewer installation project.
While a good portion of the project was designated as open-cut,
several key areas required the use of trenchless technology. Local
water and sewer contractor Dale Wisor of DJ Wisor and Sons, Inc.
accepted the challenge.
The job called for the installation
of 55,000 lf of new 8-inch SDR 35 PVC sewer main and 4-inch laterals.
Eight sections of sewer main traveled under state roadways. The
Pennsylvania DOT required that the new sections be placed within
16-inch steel casings. The Wisor crew decided to use a pipe ramming
tool for placement of the steel casings and a piercing tool for
installation of the 4-inch laterals. They turned to TT Technologies
Product Specialist Mike Schultz for technical support.
Trenchless Technology
The Wisor crew chose a 5 3/4-inch diameter
Grundoram for the lateral lines and an 8.5-inch diameter Grundoram Hercules pneumatic pipe ramming tool for the 16-inch casings.
Because of the large number of bores, conventional augering was
not economical. According to Schultz, the accuracy of both tools
was essential to success of the job. Schultz said, "Because
this was a gravity fed sewer system, all of the bores and rams
were grade critical. The system needed to have a specific amount
of ‘fall’ in order to ensure proper flow."
Grade critical bores and rams were
not the only things that made this project difficult. The soil
conditions in Decatur Township can be extremely challenging. Schultz
said, "The Wisor crew encountered a little bit of everything
on this job including wet areas, layered shale, coal and clay.
Some of the bores began in clay and ended in coal. Some areas
even had abandoned mine shafts to avoid."
A 5 3/4-in.-diameter Grundomat piercing
tool was used to install 4-in. lateral lines. |
Horizontal Boring
In all, 35 lateral installations, ranging
in length from 35 to 60 feet, were completed using the piercing
tool. Depending on length, bores took a half-hour to 45 minutes
to complete. Proper grade was maintained by using a Grundoscope
aiming frame and surveyor stake, a smart level and a launching
cradle. But even with these set- up tools, the piercing tool itself
needed to maintain a its path in difficult soil conditions.
According to Schultz, the Grundomat was the perfect choice for this project. Schultz said, "The
Grundomat piercing tool has a reciprocating head. The chisel head
assembly moves independently of the main casing, creating a pilot
bore for the rest of the tool body to follow. This ultimately
leads to greater bore accuracy."
Pipe Ramming
The Wisor crew performed eight separate
pipe rams. Installations averaged one hour and ranged in length
from 40 feet to 60 feet. Pipe ramming accessories including a
segmented ram cone, two tapered ram cones and a soil port adapter
were used to make the connection between the 16-inch casing and
the 8.5-inch diameter tool.
The crew paid special attention to
the grade of the rams by using a transit and smart level to calculate
the correct angle needed to obtain the proper fall for the system,
similar to horizontal boring.
In most installations spoil from the
casings was blown out using compressed air, other times, the crew
used other methods of spoil removal. Schultz said, "Because
the length of rams were relatively short, the crew would often
remove the entire casing before removing the spoil and replace
it with a new one. It was just faster that way."
Once the spoil was removed, the PVC
main line was inserted into the casing. Adjustable "spider-type"
spacers were used to secure the 8- inch main line inside the 16-inch
casing. This also gave the Wisor crew the ability to make minor
adjustments to the grade of the line within the casing.
The Reaction
The trenchless pipe installation methods
chosen for this job were ideal. Wisor said, "On a cost per
foot basis, these tools saved us money. The piercing tool is very
efficient. We would not have been able to complete as many bores
from 25 to 60 ft, in as many locations, as quickly, with a directional
drilling unit or conventional augering. The same is true with
pipe ramming. When you take into account the number and the length
of installations, as well as the different locations, conventional
augering wouldn’t have been as economical as pipe ramming."
Decatur Township was extremely pleased
with the results of the project. The utilization of trenchless
technology in key areas of the project allowed roadways to remain
open and kept disruption to a minimum. It also allowed work to
be done in difficult access areas where conventional equipment
was not the best option.
Equipment Today,
January 2000, Page 22
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