Insituform Technologies, Inc., Jacksonville, Florida
As communities grow with residential, business and other public works amenities, new methods of construction using the latest available technologies
are being considered as alternatives to current methods of construction.
Such was the case in Jacksonville, Florida, when the Jacksonville Electric Authority (JEA) required five sets of gravity sewers to be installed along S.R. 13. When installed, the sewers would connect two sets of manholes located along of S.R. 13, a heavily-traveled roadway, with one manhole feeding into the other. Unlike a pump station which uses a force main to apply pressure to the sewage to move it through the sewer lines, a gravity sewer relies on the force of gravity and the sewer pipe’s slope to move the sewage from one point to another without any assistance from additional apparatus.
The project would affect an operating nursery business, as the majority of the input manholes were located on nursery right of way. The rest of the manholes were located outside the property. Another consideration was the aesthetic appearance of the ‘scenic corridor’ of S. R. 13 – trees, bus stop benches, street lights, stop lights, and the like. Ideally, the road was to remain intact and unaffected.
Due to the location of the project and the desire to keep excavating to a minimum, many options of how to begin this construction project were discussed. Originally, the area was to be open cut, excavating the entire area of the project to install the gravity sewers. This was not a viable option. Excavating the entire area of the project would yield an excavation of 1,300’ x 40’, which would result in harm to the ‘scenic corridor’, would cause the nursery to either relocate its inventory or shut down, while construction commenced, and would possibly cause a lane closure of S.R.13 in that section of town.
Another option to launch the project was conventional microtunneling. Conventional microtunneling is a process that uses a remotely controlled boring machine combined in a pipe jacking technique to directly install pipelines under the ground in a single pass. This eliminates the need to open cut the entire area.
Conventional microtunnelling could have been used for this application, but previous experience showed this would be a costly option. However, Insituform Technologies, Inc., offered a better, more cost-effective alternative.
Insituform proposed using another method of microtunnelling, called the hybrid method – a new technology introduced to the Jacksonville area for
the first time with this proposal. This process is perfect for smaller diameter (8-15”) sewer lines.
The operation comprises installing a large diameter metal shaft, inserted vertically into a small excavation, to be used as protective sheeting and allow installation crews and equipment to be placed inside the pipe (see illustration above). Once the large diameter shaft was installed, a small “window” would be cut directly, for the microtunneling, into the shaft in the direction that the sewer pipe would eventually be installed.
First, a pilot tube with a jacking machine is installed into the window online in grade - at the correct percentage of slope – using a computerized guidance system called a theatellite. The pilot tube acts as a guide for the drilling crews to bore the hole for the sewer pipe to be inserted. As the drill pushes out the pilot tube, it leaves behind the drill stem to hook up to the pipe to pull back the final sewer pipe. After the drilling is completed, the gravity sewer line is then pulled into the hole and is connected to the manholes at the desired slope. The hybrid method would be used in all five excavation sites on the project.
Kendall Welsh, Project Manager for Insituform, led the operations for this pilot project. Welsh visited the jobsite and took borings of the soil where the shaft was to be installed and contacted Thompson Pump’s Jacksonville, FL Branch for their assistance. The installation of the shaft was an important part of the operation and dewatering of the area had to be performed expertly.
Pressure from any underground water that comes into contact with the shaft could cause it to rise out of the excavation or lean at an angle Thompson Pump
representatives analyzed the soil borings and, after visiting the jobsite as well, provided Welsh with their equipment recommendations.
According to Welsh, “the first phase is how we’re going to design the microtunnel shafts. And that’s purely based on the soil conditions, i.e.: sand, clay and then water – which in Jacksonville, or in any part of Florida, are going to be the biggest factor. And that’s where we utilized Thompson coming in to help us determine how were going to dewater these areas.”
Thompson Pump proposed to install small wellpoint systems, consisting of approximately 20 wellpoints and covering approximately 400 square feet in a horseshoe shape around each excavation area. The soil boring results showed that loose sand was prevalent in the soil conditions. This meant that jetting would be
required to install the wellpoints.
Thompson Pump provided a 6-inch High Pressure Jet Pump to assist with jetting the wellpoints into the ground. With the wellpoints installed, Thompson Pump provided four of their Vacuum-Assisted Trash Pumps and connected them to each wellpoint system to remove the groundwater.
The last part of the dewatering operation was the most critical. The last excavation site was where the gravity sewers were to connect into an existing manhole. Excavation depths were much deeper than the excavations of the other four locations. For this excavation site, Thompson Pump provided an 8-inch Rotary Wellpoint Pump to handle the wellpoint system due to its larger volume capacity and its ability to displace more air. With the wellpoint systems in place removing the groundwater, the excavations could commence and the shafts could be installed for the microtunneling of the gravity sewer lines.
Insituform utilized Molehead Construction & Boring, Inc., to do the actual microtunnel drilling. With the ‘hybrid’ technology so new, both companies are trying to perfect using this new technology.
According to Welsh, working with Thompson Pump on this project was an easy decision to make. “Mainly because we’ve had a relationship with Thompson Pump for three years now, and we used [Thompson] on all of our pipe bursting work,” said Welsh. “Pricing that has been provided on our pump rentals was competitive. Service hasn’t really been an issue, but when we need them, they’re out there. The thing with this being a pilot-type project, we weren’t sure exactly how this equipment was going to react to these grounds, so the dewatering factor was a major role.”
Special thanks to Kendal Welsh, Project Manager for Insituform and Ashton Milam, Thompson Pump Jacksonville Branch Sales Representative for their help on this project.