You are smart! You have concluded that a shield is the best option for your project. Time, money and safety are big priorities.
Renting and installing a trench shield is very easy, but there are a few things to figure out before you rent:
Size of Trench: Width, Length, Depth?
Equipment on site: What can you handle? Weight? Max Reach? Bucket Size?
This will determine what type of shield or box you can handle. Aluminum shields are light and customizable, and can be moved around with just about anything. They are stackable if weight is still an issue. We can give you 2 shorter shields instead of 1 tall shield.
Steel trench shields are heavier just by the fact that they are made of steel. If you need a shield that can take a hit, go with steel. You will need equipment that can handle the extra weight, but just like the aluminum shields we can send out 2 or 3 smaller shields that can be stacked instead of 1 tall, long heavy shield.
Soil Type: There are many questions regarding soil, but the main question is can it stand on it's own? Can the trench stand up long enough to set the shield? More than likely you are comparing Type B and Type C soil. Type A soil is very rare in California due to the constant threat of vibrations. According to OSHA soil can also not be type A if the soil is fissured, the soil has been previously disturbed, is part of a sloped, layered system where the layers dip into the excavation on a slope of four horizontal to one vertical or greater, or the material is subject to other factors that would require it to be classified as a less stable material. There are also 2 classes of Type C soil. C-60 and C-80 soil. C-60 will hold its form or shape long enough to install a shield. C-80 soil will usually cave in as soon as you dig it. A steel shield would work best for C-80 soil. You can dig and push the shield in to your desired depth. You can technically do the same with an aluminum shield but it will not hold up like a steel shield.
What are you installing? Do you need a certain amount of clearance? Are you installing down the trench line or are there cross utilities? How much coverage do you need or do you need a shield that is 2, 3 or 4 sided? What kind of ID(inside dimension) do you need?
Steel trench shield ID width is determined by the OD(outside diameter) of the pipe or backfill requirements for the project. Each shield wall is 4-6in thick so take that into consideration what digging your trench. Inside length clearance of pipe is approximately 2ft less than the overall length of the shield. Shield must be 2 to 4ft longer than pipe.
A taller trench shield will give you greater pipe clearance. High clearance arch spreaders are also an option for those projects that require extra clearance. Steel trench shields are 2 sided(see attached picture). Depending on the project, steel plates and/or sheet piles can get installed to close in the open sides. Water tapping boxes or manhole boxes can be used for certain 4 sided needs. The boxes are only 8ft ID square and come it heights of 4, 6, 8 and 10ft tall. There are bolted in "dog doors" on all 4 sides that can be removed if needed.
Aluminum shields or build-a-boxes are more customizable. They can come 2, 3 or 4 sided, with bottom panels missing, with legs kits for extra clearance or even with wheels so someone can stay in the trench and push the box down the trench as he/she works. Aluminum shields don't however come in sizes as long or wide as a steel shields. So if you want, as an example, a clear span 24ft long x 16ft wide shield, you will have to go with a steel shield system.
Knowing what you need and the correct sizes will make the installation process go smoothly. It will also help those working inside the shield that everything is where it is suppose to be. Depending on the sizes, Shore-Tek will build the shields at our location so everything is tested, inspected, and ready to drop in the ground. We want to make sure you get the right shield the first time and every time. We will also provide different accompanying accessories, if needed, such as rigging, ladder platforms, railing systems, and confined space equipment. Whatever shield you end up going with either option is safer, and more cost effective than the alternative.