Whatever process or technology is used, experienced contractors agree that trenching is one of the most challenging applications. The reason for this is that a trench is normally deeper than it is wide, it is therefore very confined and the rock on surface is usually weathered and fractured, is often porous like sandstone can be, and leaks gas.

The basic formula applicable is as follows:

• break out a trench row by row towards a free face, which if necessary must be created by vee-ing it out.
• Use an excavator, under your control, to dig it out row by row continuously
• drilling pattern triangular, two holes on each edge’ one in the middle further back, same spacing, like an isosceles triangle .
• therefore 5/6 holes per linear metre are required; (work it out on graph paper)
• there must be a foolproof sign off criterion for final level, preferably the client’s responsible person’s signature, otherwise you will be called back to remove ‘bumps’ and similar imperfections at your cost!
• Do not try to drill the trench upfront, then initiate; it seldom works
• Don’t make any other philanthropic assumptions; trenching is a tough challenge, the reason it is often sub-contracted.
• Doing it this recommended way, it is possible to change burdens and charge rates as circumstances relating to rock condition in nature varies
• This method statement is failsafe effective; all other methodologies are lotteries of imperfection and hope!

Variations on the Trenching Theme

Large trenches for big pipelines usually go deeper, like six metres, and change the ground rules, such as decking more than one cartridge per hole, with intermediate stemming. Consult with us about major pipelines.