Trench boxes are simple, robust, two sided mechanical excavation support systems with integrated return/end panels designed to be installed by an excavator utilizing the dig and push technique. Lightweight box are suitable for 20kN capacity (2 tons per m2) for Trench shores and 40kN capacity (4 tons per m2). They are ideal for handling by small sized excavators. They have a clearance under the lower strut which is 900mm. Trench box is a fast, safe and economical method of providing trench safety using trench safety equipment.
Here are some instruction’s which should be adhered to when using trench safety equipment:
- Only qualified authorized personnel should be allowed to operate trenches and accessories.
- The operative should be trained and assessed competent.
- The competent person must supervise the installation, alteration or removal of excavation support.
- A risk assessment must be completed prior to the use of this trench safety equipment.
- Correct manual handling techniques must always be used and PPE such as hard hat, safety gloves, and goggles must be used.
- It is also recommended to use a gas detector and breathing equipment which is available for hire.
- A land and ground survey must also be carried out to check also for any utilities (electrical, telephone cable and gas or water supply) below the trench.
- Continually monitor groundwater, soil and air by sight, smell and use gas detection equipment when working in an excavation.
- The operating instructions should be always available.
- Trench Box should only be used in the configurations shown in section 1.0.
- Trench Box should not be used in very weak ground (especially very soft clays and peats) or where significant groundwater is present.
- Boxes are not suitable for usage in trenches with multiple service crossings.
- Boxes are not normally suitable for use where ground movement is an issue and are therefore not recommended for use in live carriageway situations or adjacent to existing buildings/structures.
- The lifting of the box above the base of the excavation is strictly prohibited.
- Boxes should not be left in-situ for extended periods within cohesive soil as adhesion on the panel surfaces may prevent safe removal.
- Ladders must be present around the excavation to provide easy access to an exit in the trenches. (Usually about 8 meters or less)
When Installing a Trench Box | Trench Safety Equipment
When installing trench safety equipment, lay one section face down on the ground with the spigots pointing upwards, Locate the struts in the spigots, Secure with pins and R-clips, Install the second with the face upwards and locate facing spigots onto the free ends of the struts and Secure with pins and R-clips. Note that the handling of trench safety equipment has an increased risk of it. Care must take to avoid the equipment slipping causing injuries or trapping.
The following should be taken note of when installing a trench box:
- Excavate approximately 1.0m below the existing ground level to the overall plan size as required.
- Place the assembled Trench Box in the excavation using the 4-Leg Chain. Ensure that the panels of the Trench Box are vertical at rest.
- Progressively install the Trench Box by a ‘cut and lower’ technique, using the excavator to apply downward pressure to each corner of the unit.
- If the required excavation depth is greater than the height of a single Trench Box, Top extension units should be used. When the top of the Trench Box Base is at or just above existing ground level, position the assembled Trench Box Top on the installed base unit, connecting each corner of the assembly using the corner connectors supplied.
- Continue to install the Trench Boxes until formation level is achieved. If required, a second Top unit can be used to increase the height of the box further. It is not recommended that more than 2 Top units be used with any one Base unit.
- When the pipes have been installed, the Trench Box is removed by applying a sudden upward force to break the friction/adhesion between the panels and the soil. The Trench Box should be progressively withdrawn, as the excavation is backfilled.
A visual inspection is required to be carried by a competent person before and after a Trench safety equipment is used. A competent person must inspect excavations at the start of each shift before work begins, after an event likely to have affected the strength or stability of the excavation and after an accidental fall of rock, earth or other material. Any distortion, damage or security concern about the boxes or its accessories must be reported to the competent person and the trench box must not be used until it is deemed safe. Make sure that the connector pins and R-clips are in good condition. A written report should be made after most inspections. Stop work if the inspections show the excavation or equipment is unsafe. Before leaving a site or depot, the site or depot supervisor must make sure the dismantled trench box is properly laid flat and securely strapped to the lorry. The strapped panels must not create any hazard while in transit.