Trenches are quite common in many engineering and construction sites. They’re used for laying telephone lines, pipes as well as many other constructions. While some are quite deep, others may be extremely shallow. Based on the soil’s quality, trench walls will not support themselves for long. A steel or aluminum trench box supports the trench walls to ensure it’s safe to work there without the danger of walls collapsing on equipment and people. Other names for trench boxes are manhole boxes, sewer boxes, tap boxes, or trench shields.
Before excavation starts, the location must go through a comprehensive risk assessment to identify any potential risks, the equipment needed as well as the employees needed. The need for additional access is also looked at.
Then the trench will have to be looked at. How deep should it be? How large should it be? Trenches that over 5 ft need support from one of these: trench box, sloping, or shopping. But if it’s more than 20 feet deep, a registered engineer is required to design the trench’s support. How will people enter the trench? Is it through a ramp, steps or ladders? The trench needs to always be safe for access by workers within 25 feet, in emergency cases. The atmosphere inside the trench may also need to be tested for toxic gases or low oxygen levels. Trench boxes are made to be simple to install but it’s unsafe to stack boxes over each other so check it out!
Taking care of the trench
The trench box or trench support should be inspected daily for any signs of movement or damage.
All workers on the site need to wear their own protective gear, hard hat, steel-toed boots, high visibility clothing and so on.
Ensure that all heavy tools as well as equipment are kept far from the trench’s edge.
It is probably more difficult to extract a trench box than install it because of the earth’s movement around the trench. It’s best to extract using a chain sling, through any of these 3 ways.
Straight pull–a sling is just attached to the two lifting or extraction points and lifted out.
Half pull–this involves attaching a sling to the side of a manhole box, lifting it as high as possible, switching the sling to the other side and repeating the action until the manhole box is removed.
Single pull–one chain sling leg is attached to a lifting/extraction point and the corners of the panel are raised in turns; when the trench support moves freely, the manhole box is removed with the straight pull.
To summarize, trenches save lives. It’s a legal requirement to use them and they need to be planned for. So long as they’re used and maintained properly, they make work so much easier and safer.
For further reading/watching, please visit https://www.youtube.com/watch?v=O3bjzxULlG0 .