This is the final installment in a four-part series on trenching and excavation. “Trenching by the Numbers” (http://incident-prevention.com/ip-articles/trenching-by-the-numbers), the first article in the series, presented a simple method for recalling OSHA’s trenching and excavation requirements. The second article focused on soil mechanics (http://incident-prevention.com/ip-articles/soil-mechanics-in-the-excavation-environment), taking an in-depth look at the behavior and characteristics of different soil types and their relationships with water and air. In the June 2016 issue of Incident Prevention, I covered “Protective Systems for Trenching and Excavations” (http://incident-prevention.com/ip-articles/protective-systems-for-trenching-and-excavations). To close out the series, I will present techniques for creating a safer, more productive trenching environment, and then provide some food for thought about how to sell these techniques to management.
Dewatering Using Well Points
It’s no secret that water can greatly contribute to the success or failure of any trenching and excavation activity. OSHA requires that employers take steps to keep workers from being exposed to standing water conditions. One of the more proactive approaches to dewatering a site is to install well points. A hole is augured into the ground, and a perforated pipe is inserted into it. Then, a submersible pump is placed inside the pipe. This technique can be especially effective in sandy soils.
However, there are two caveats to keep in mind with this technique. First, it works best when performed three to five days before excavating begins. This is because water is self-leveling; thus, when a void is created by the pump, the water in nearby soil leeches into the work area. If excavation activity takes place too soon after the well point is installed, one could misguidedly conclude that well points make conditions worse when, in reality, poor planning and a misunderstanding of the process are to blame.