Before we begin probing into the art of trenching and using trench shields, let’s look at this question.
How willing are you to jump from a cliff with a blindfold without checking the landing area first, not knowing if you’ll land safely in water or on land?
If the answer is ‘not willing at all’, you have just shown me you believe in safety first.
Ponder this: If a trench collapses onto you, you have more chance of surviving a jump off a cliff into water than you do being buried under several tonnes of dirt – slowly suffocating and being crushed to death simultaneously. Your co-workers are frantically digging with shovels and hands, not knowing precisely where you are buried. The 20T digger is turned off and moved away, because it’s too dangerous to use for fear the bucket might cut you in half in its mission to dig you out quickly.
Now, let us explore the basics. An excavation is classified as any cut or hole in the ground. A trench is a cut in which the depth is greater, or deeper than the trench is wide. We will be looking at trenches specifically today.
New Zealand’s laws specify you must use trenching protection when working in a trench 1.5m or deeper. This is all very well if you’re standing up in the trench and the good conditions are perfect. However, if you’re bending or kneeling down whilst working on a pipe or cables, or the soils is wet, sandy, or loose you’re at risk. As a rule of thumb – If your head is below ground level when you are working, or there is any doubt at all about the ground conditions, you need a shield! Each cubic of soil can weigh between 1200kg to 1600kg. To find out the regulations you must meet, check out New Zealand’s safety regulations on NZTA https://worksafe.govt.nz/topic-and-industry/excavation/excavation-safety-gpg/
The good news is we are here to help! We have many options ranging from the humble but efficient soldier trench shield to the large drag shield. Each option has many benefits, of which the first is to protect you and your workers from unforeseeable trench collapses. In fact, several of our trench shields are able to be widened whilst in the trench, creating positive ground pressure. This decreases the chances of collapses dramatically and prevents the ground from cracking and crumbling. Some are able to be stacked, giving you greater working depth. Some can even be configured in several ways with the same components, giving you more flexibility in any job.