Trench sloping or shoring? One is surprisingly less expensive

It is difficult to argue with the numbers. And the numbers are in showing that trench shielding during excavation is superior to sloping or benching in just about any circumstance.

By Joyce Everhart
Editor, Public Works Online

For centuries, the best way to dig a deep hole without having the sides cave in on the workers was to either slope or bench (terrace) the sides. Today, however, there is a better choice.

The more modern method is known as trench shoring or shielding. Upon first glance, construction managers will often opt for sloping. There is no additional equipment required and it is a safe, tried and true procedure, as long as proper slope degrees are maintained and the weather doesn't interfere.

Safe, neat, efficient and time-saving. Those
are the words used to describe trench shielding
shown above. Efficiency Productions, Inc. photo

Trenching, however, done properly can actually cost much less and is less time consuming. In case after case, this has been proven.

133% increase in productivity with shields
Efficiency Production, Inc. recently reported on a cost analysis done on one job site using its shields while laying a concrete pipe. The example given was a crew laying two 8-foot long pipes per cut, using two trench shields 20 feet long (stacked) installing 224 lineal feet of pipe in an 8-hour day. In comparison, the same crew using bank sloping or benching would only install 96 lineal feet of pipe in the same time. Since the time it take to lay a pipe is constant, the main factor in determining productivity is the amount of excavation per cut. Using trench shields, the trench excavation can be reduced from 255 cubic years to 79 cubic yards per cut. This can result in a 133% increase in daily pipe productivity.

Additionally, Efficiency Productions points out, since less excavation is needed, trench shields can save trees, mature shrubs and lawns along the job site as well as protect curb and gutters along the road. This is a particularly desirable when doing urban construction.

Pipeline & Utilities Construction magazine quoted a job superintendent saying, "Using the trench shield on this job saved in trench excavation, trucking and backfill to the amount of approximately $48.60 per lineal foot, a savings based on type B soil of one to one slope (not taking into consideration street and lawn restoration)."

David Dow, president of Trench Safety and Supply, Inc. (Memphis, TE) drew up a chart for Underground Focus magazine that also clearly illustrated the cost comparisons of sloping versus trenching.

Amount of landscape restoration less
He detailed the amount and cost of tasks related to a trench needed for a sewer line under a street. Costs include saw-cutting the asphalt, removing it and the gravel base, excavating the soil, backfilling with sand, and replacing the gravel and asphalt. The amount of landscape restoration needed with sloping versus trenching was not even considered.

The total cost comparison Dow illustrated was $71,190 to complete the job using sloping and an astounding $15,962 using a trench shield. The cost of renting the trench shield? $750.

And then there is the safety factor. Trenching has proven to be safer when installed properly, particularly in uncertain weather.

More information about trenching can be found by contacting the following companies:

3M Corrosion Protection Products
3M Corrosion Protection Products
3M Corrosion Protection Products

Edited by Joyce Everhart
Editor, Public Works Online