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How to size a trench shield/trench box?

Below are the essential questions to be answered to properly determine the model, size, and spreaders/struts needed for a trench shield.  The answers to these questions will allow the user of the trench shield to not only have the correct trench shield for the project, but also enable them to minimize site restoration costs.

How to determine what Trench Shield requirement is for your project?

1. What material ESC Trench Shields are made of? Is it economical?

ESC shields are manufactured from high grade steel. Steel shields, unlike aluminum, can serve all kinds and magnitude of excavation and trenching projects even in the most adverse conditions. Looking into overall value, they are way more than worthy of their cost due to long life span and extreme durability while providing maximum protection to workers.

2. What is the use of a “knife-edged bottom” emphasized in OSHA Requirements?

As stipulated in OSHA 1926.652(g)(1)(ii), shields shall be installed in a manner to restrict lateral or other hazardous movement of the shield in the event of the application of sudden lateral loads. The knife-edge part at bottom of the panel holds the shield from being displaced dragging your bedding or maybe installation out of setting.

3. What type of project is it?

Sewer, Repair, Water main, Manhole, Bore pit, etc... The type of project may dictate the style of trench shield that will need to be used. If the project is a bore pit, smaller shields may be used, but they may require a height adapter to provide the vertical clearance needed for the bore machine.

4. When would you use a trench box?

Under OSHA 1926.652(a)(1)(ii), a protective system is not necessary if excavations are less than 5 feet (1.52m) in depth, and examination of the ground by a competent person provides no indication of a potential cave-in. At one point, this can be interpreted that boxes are required in excavations 5 feet deep and above. However, it is also clear that a protective system should be utilized in all excavations, even those less than 5 feet deep if it poses indications of a potential cave-in.

5. Depth of cut

Knowing the required depth of the project will allow ESC to determine how tall the shield(s) need to be, whether stacking gear required and how thick the sidewalls will need to be. Also consider additional surcharge loads from battered slopes, construction loads etc.

6. Soil Conditions or type?

What is the soil like? Dry, wet, standing water, rocky...? Soil types should follow the OSHA definitions or be taken from soil investigation reports. Soil information should be determined by a Competent Person or a qualified engineer.

7. Outside diameter of pipe/structure (at largest point)?

To minimize the amount of soil to remove, and to provide adequate working room, it is recommended that a trench shield be 12" wider than pipe/structure.

8. Overall bucket width (including side cutters)?

ln cases that the pipe or structure is small, the overall width of the excavator bucket can be used to gauge what the internal width of the system should be. It is recommended that inside width of trench shield be 12" wider than bucket width.

9. Pipe/Structure length?

It is recommended that a trench shield be 4' longer. This allows for the pipe or structure to be lowered directly into the shield instead of trying to snake the pipe or structure between smaller shields. This will protect the workers when they are working on the end of the pipe in case of a cave-in.

10. Lift capacity of machine?

1.5 times the overall weight of the trench shield plus spreaders, at 20' (6m), at grade level. This assures that not only will the machine be able to set the trench shield system, but it also should be able to remove the system as well.

11. Minimum vertical pipe clearance needed?

Allow for pipe diameter plus any bedding requirements. It is a good idea to allow additional free space of at least 4” between the top of the pipe and the bottom of the spreader.

12. Do you provide customized design for specific use?

ESC offers custom box sizes and can manufacture units as per client’s drawings and specifications.

In ESC, customer service matters. We hope our responses to those frequently asked questions have been informative. For further information, you may drop us your questions below. We look forward hearing from you soon!

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