Many traditional utility projects still rely on trenching and excavating to get the job done, but as the hole gets bigger and deeper, the dangers increase for construction crew members down in the pit. To ensure that each trenching and excavating project is done as safely and efficiently as possible, it is necessary to use the right trench shoring and shielding equipment.
On one recent project, a contractor had to install a concrete utility vault in dry, sandy soil. The excavation was planned to be approximately 39 feet long, 36 feet wide and 21 feet deep.
The challenge on the job site was the sandy soil, which was extremely poor. These poor soil conditions, combined with the sheer size of the excavation, required a careful analysis of the situation in order to use the correct shoring system for maximum productivity and safety. The contractor was also operating with a tight budget and needed to provide a shoring system that would be affordable.
Brett Sondergard, a shoring specialist with Coble Trench Safety, met with the contractor to review several shoring systems. It was decided that a beam and plate system would be the most viable option because of its affordability and ease and speed of installation.
Sondergard engineered the system to be site-specific. The system used beams driven 30 feet into the ground with a vibratory hammer. A steel plate was then inserted into the flanges to provide support for the soil between the beams. The final component to the design was the use of a beam as a waler approximately 8 feet from the top of the excavation.
This job was extremely demanding in both planning and installation. However, because of Brett Sondergard's experience in site-specific applications with Coble Trench Safety's inventory of shoring equipment, the contractor was able to focus on the safe completion of the project — not the shoring system.
On another project, shoring specialist Teddy Phillips assisted a contractor in developing a shoring system for a wet well installation. The excavation was planned at 16 feet by 16 feet by 24 feet deep. The contractor had stepped the excavation back, so the shoring system only needed to be 20 feet deep since the wet well would be installed at a depth of 24 feet. Since the contractor had no practical experience with a slide rail system, the job became a teaching opportunity for Phillips.
The job site was not very spacious, and the land developers required that trees on two sides of the well remain undisturbed, decreasing the working area even further. The contractor was only able to dig from one point on the site throughout the entire excavation due to the lack of room adjacent to the slide rail. The soil was also very wet, with a wetlands area at the back of the excavation contributing to the condition. These factors presented major obstacles that had to be addressed during the project.
Phillips, however, brought with him a wealth of knowledge and experience working with slide rail systems along the coastal Carolinas. He was able to incorporate active instruction, teaching the contractor about the slide rail system while installing it.
After the slide rail system was installed, the contractor was able to advance the panels down into the ground, providing continuous soil support as cuts were made to the excavation. This support prevented the poor soil from seeping back into the excavation, as well as providing a very sound protective system for the workers.
Grade depth for the slide rail was reached at 5:00 p.m. on the first day of the installation. The next day the contractor placed the wet well and removed the slide rail. He then dug an adjacent hole to get good soil to backfill the wet well. This hole was approximately 7 feet deep, yet it had 3 or more feet of water in it, necessitating well-pointing of the site. In these cases, the slide rail is a very common and practical application for C-60 soil after it has been dried out from well-pointing.
Teddy Phillips' experience allowed him to assist and teach the contractor using the optimal protective equipment for the job site. Without any previous experience, the contractor was able to easily install a slide rail system in poor soil conditions, perform the necessary work, and remove the system in two days.