The meaning of trench shielding, and trench shoring can be very simple to the public – reinforcing or supporting a trench to avoid collapse. To many, these two may be used interchangeably and still refer to a common thing. It makes sense basically, but they are two different construction support systems.
Shielding and shoring are both important techniques used in construction and excavation projects to protect workers and prevent accidents. Although they share the same purpose, the two are significantly different from each other as follows.
1. Function
Shielding refers to the use of a barrier to protect workers from soil, rock, and other surrounding materials that can collapse and bury them while working inside a trench or excavation. Trench shields act as a cage to give breathing room for workers inside the trench while waiting for retrieval rescue when soil collapse happens. Trench shields or trench boxes serve their ultimate purpose as an untoward incident happens.
Shoring on the other hand, pertains to the use of support systems to prevent surrounding soil, rock, or adjacent structures from collapsing due to excavation works. They are used to reinforce underground excavations during construction, and to provide temporary support for above-ground structures while waiting for completion of construction or repairs. Shoring therefore prevents incidents from occurring.
2. Components
Shield is a modular equipment with two major components – two sidewalls which are placed opposite to each other, against the trench walls, and spreaders which are horizontal supports that hold the sidewalls apart. Shields are usually made of steel and aluminum. They come in a variety of sizes, from simple trench boxes with fixed spreaders to trench shields that involve hydraulics to fit specific trench widths and geometry.
Shoring is a more complex support system. Shoring systems can be made of timber, concrete, steel, or combinations. It includes many components which are strategically put together to perform effectively as a defense mechanism against collapse. There are many types of shoring: Raking shores, Flying shores, and Dead shores. Each type involves several components such as beams, metal plates, planks, braces, struts, props, piles, cleats, screws, hydraulic sets, spreaders, and many more.
3. Application
Both trench shield and trench shore are applicable to suffice the requirements set by Occupational Safety and Health Administration (OSHA) in Trench Excavation Safety. Generally, all excavations deeper than 1.5 meters or 5 feet, unless on stable rock, should have protective system against cave-in or erosion. The decision on what protection system to employ depends entirely on factors such as magnitude of the excavation, budget at hand, required level of safety, and ease of handling.
Trench Boxes are typically used for shallow excavations. Although some of them are designed to be stackable, they are generally used for excavations that are less than 6 meters deep. They are advantageous for smaller trenching works due to easy installation and retrieval, lower cost, and maximum space for the activities inside the trench. Trench boxes are ideal for maintenance works and laying underground utilities such as pipes and cables.
Trench Shoring is ideal for heavy duty applications such as large excavations, 20 feet deep or more. Unlike shields, it requires more time, resources, and technicality to integrate and dismantle. This makes them suitable for applications requiring long exposure, extra safety, and enormous coverage. Applications and purpose of trench shoring are:
Protection of the nearby buildings or structures during foundation works.
Provide reinforcement to weak walls or structures to facilitate repairs or re-construction.
Provide vertical support to upper structural parts while modifying or fortifying below sections of a structure.
Provide lateral support for piling walls against enormous hydrostatic and backfill pressures.
Provide support for formworks against buckling during concrete placing or backfilling works.
4. Types
There are hydraulic and static or mechanical type trench boxes. Hydraulic shields are equipped with hydraulic-operated struts or spreaders which adjust automatically according to trench wall configuration. They are favorably used in trenches with irregular shapes. Static or mechanical types have telescopic spreaders that are adjusted manually. Every spreader has a line of holes with close increments to create the best distance of sidewalls that fits the trench walls best. The stretch of the spreader is then locked by inserting a hard steel pin through the hole.
In contrary, there is a wide variety of trench shoring system. These are the following:
Sheet piles. A very simple but effective type of shoring, used in areas where there is intrusion of liquids.
Pneumatic shoring. It is operated by compressed air and is expensive.
Hydraulic shoring. It incorporates heavy-duty struts and is operated by hydraulic mechanism. It is also more expensive than the other types.
Screw jack struts. Combined with timber planks as vertical pads, this type needs manual adjusting of screws inside the trench which is considered a risk.
Timber shoring. It requires a lot of lumber to be utilized. It is recommended in remote areas with abundant timber.
Lagging. Steel beams are fully driven to the ground. As excavation progresses, timber or wooden planks are inserted at the steel pile until excavation is complete or the first timber insert has reached the bottom plane.
Engineered Systems. These are utilized when excavation exceeds 20 feet in depth. They are also used when additional exposures exist, such as an adjacent structure. Learn more about engineered systems at www.esctrenchshoring.com and www.escpiling.com/construction.
The meaning of trench shielding, and trench shoring can be very simple to the public – reinforcing or supporting a trench to avoid collapse. To many, these two may be used interchangeably and still refer to a common thing. It makes sense basically, but they are two different construction support systems.
Tips To Remember
While shielding and shoring share similarities, they suit different areas of application. In some situations, they complement each other. Some experts claim that shoring is safer and more effective. Safer – probably yes, but not necessarily more effective in all cases. Simple shields or trench boxes are cost-effective for smaller jobs but cannot sustain the needs of major excavation or foundation work which can only be delivered through sophisticated shoring systems. This works vice versa.
No job is going to be a scenario of one-size-fits-all, and this is why choosing the right system, inch by inch, with caution, is very important. On top of everything, finding someone who has a vast amount of experience and proven footprints of expertise in the industry is imperative to keeping your people at site unharmed.
When dealing with any excavation or trenching job – you must Bench It, Slope It, Shield It, or Shore It! Not only because violation penalties are painful but because we care for human lives. What exactly to do and how to do it? – hear from our trenching specialists at: https://www.esctrenchshoring.com/contact