What is Shoring In Construction?

It's easy to see how fully finished buildings stand on their own without fail. However, buildings in the interim stage that have suffered damage, or require upgrades, often can't support their weight without a bit of help. This is where shores, construction's temporary structural supports, come in handy.

What is shoring?

Shoring is the process of providing temporary structural support to a building. This can be necessary when buildings could collapse due to compromised foundations, when it's undergoing repairs, or a section of an attached structure is being demolished. With shores, an opening is being built into existing walls and reinforcing trenches so that people can work inside them and fix the situation.

Essentially, shores prop up and support a structure while it's in a weakened state. Once work is complete and the structure can bear its weight, contractors slowly remove shores from the bottom to the top. This process ensures that workers are always protected during construction.

What's the difference between shoring and scaffolding?

Shoring and scaffolding perform similar functionality but provide varying degrees of support.

Shores bear the weight of walls or roofs within structurally compromised buildings by transferring the load's weight into the earth. They also protect people working on or near unstable structures while preventing building collapse.

In contrast, scaffolding is a series of platforms set at different working elevations. Scaffolding provides people with access to formerly inaccessible work areas, such as the front of a building 10 feet off the ground. It's commonly used when inaccessible work areas require materials storage, such as painting and plaster work.

Both shoring and scaffolding are temporary structural supports. However, the former adds stability while the latter creates access. Due to the functionality difference, shores support much more weight than scaffolding does.

Factors to Consider When Installing Shores

Before going into the different shoring methods, there are a few considerations to keep in mind when it comes to installation. Soil bearing capacity, proximity to neighboring structures, excavation depth, and the water table all influence the best approach for your job site.

Soil bearing capacity refers to the amount of weight the soil beneath a structure can safely support. It's always important to inspect the surrounding soil before excavation, as different kinds of soil can support different amounts of weight. For shallow trenches dug in high-bearing capacity soil, contractors use a technique called sloping to reduce the risk of collapse. This is when the upper portion of the trench walls are cut at an angle, which prevents soil from sliding into the trench while people are working inside. Soils with medium to lower bearing capacities require shoring so people can safely work in trenches.

How close the unstable structure is to other buildings is another main determinant of the type of shore used. Some techniques require more excavation space and materials to build. Excessive construction can also disrupt neighboring buildings' foundations and their structural integrity, which will rule out some methods over others.

Required shore depth will help you decide which technique you'll use. Some techniques cover a range of depths, including 4 to 16 feet and 16 feet or more. Be sure to check the shore requirements at various depths before construction, as they vary by jurisdiction.

An area's water table indicates the amount of moisture found within the soil. Areas with higher water tables have saturated soil that contains higher levels of water. Many types, including tangent pile and soldier pile walls, will compromise structural integrity if used in areas with higher water tables.

Types of Shoring

There are multiple shoring approaches used in construction. Depending on the structure, they each have different applications that work best in certain conditions. Listed below is an overview of eleven different techniques:

Dead Shoring

As indicated by its name, dead shoring supports dead loads or the structure's entire weight. Commonly known as vertical shores, they're made with two vertical beams connected by a horizontal beam called a needle. The entire structure resembles the top three sides of a square.

This technique is used when the lower portion of a wall is cut out to make space for an opening, when load-bearing walls require repairs at their base, and when the building itself is structurally damaged. A hole is cut through the wall for the horizontal needle to pass through, while one vertical beam stands on either side of that wall. The needle transfers the unstable structure's load into the vertical beams, which transfer it to the ground below. Steel plates reinforce dead shores to provide additional stability.

Raking Shoring

Contractors build raking shores by attaching sloped pieces of wood called rakers to the unstable walls they're supporting. For the rakers to fully transfer the load's weight, you must place them in the center of the wall or floor bearing. If multiple floors intersect the wall requiring support, then one raker per floor is placed at a 60-70 degree angle.

To provide additional support, unstable walls are reinforced with steel wall plates. Rakers attach to the steel wall plate, forming the raking shore design.

Flying Shoring

Flying or horizontal shoring is placed between parallel walls when one or both of them require additional support. This process connects the two walls with a horizontal shore, uses diagonal shores to form load-bearing triangles, and attaches each one to a wall plate for reinforcement.

Diagonal shores should be placed at no more than 45 degrees to the horizontal shore. In addition to supporting weak walls, this technique is used when tearing down a portion of an adjacent building.

The following methods use piles or deep foundation supports to temporarily support unstable structures:

H and I-beam Shoring

Some of the oldest methods that are still practiced today are H and I-beam shoring, commonly known as soldier pile walls. This technique helps repair foundations, improve structural integrity in homes, and hold up trenches on construction and archeological sites.

To construct soldier pile walls, H or I-shaped steel piles, known as soldier piles, are vertically placed into the ground at equal intervals. Caissons, concrete, or timber piles can be used in place of H and I-beams. After that, poured concrete or wooden boards are placed in between the piles. This creates a lagging wall: a type of shore that transfers the load found between piles to the piles themselves, who then transfer that load into the ground.

Soldier pile walls are best suited to excavation sites ranging from 4 to 16 feet deep. The excavation area must have a low water table, as lagging walls are less stable in soils with higher moisture content. The higher the lagging wall is, the closer together soldier piles should be built to increase stability.

Contiguous Pile Shoring

Contiguous or tangent pile shoring forms a similar structure to soldier pile walls. The main difference is where the piles are placed.

In contiguous shores, the piles lie tangent to one another, which is another way of saying they're placed close together to the point of touching. From afar, this appears to be the case. However, piles are actually placed 2 to 6 inches apart. This method is popular for basement construction and bridge abutments, which are the supporting walls found beneath a bridge's end post.

This is another technique that shouldn't be used in areas with high water tables since water can seep through the piles and wet the structure the shores are supporting. To prevent water damage, you can fill the spaces between piles with grout to make the space slightly more water resistant.

Secant Pile Shoring

There are no gaps between piles in secant pile shoring. Instead, they're created by two interlocking walls which overlap together. The interlocking walls are formed by connecting a row of un-reinforced piles, also known as the primary wall, to a row of reinforced piles, known as the secondary wall.

To construct a secant wall, you cast the primary wall with poured concrete. Before the concrete dries, you cut crescents into the concrete to form a mold for the secondary piles. This creates the scalloped pattern found between interlocking pile walls. Once the mold is cast, the secondary piles are formed with reinforced concrete, leaving an interlocked wall between the primary and secondary piles.

Whenever you don't have enough space for proper excavation or the structure requiring support is too close to other structures, secant pile walls are the best option.

Sheet Pile Shoring

Sheet pile shoring uses interlocking sheet piles to form a supporting wall. Sheet piles are made from steel sheets that have been bent into a "U" shape. Little feet attached to the "U" connect the sheet piles in a zig-zag pattern. This style is often used when structures need to be separated from a body of water, such as constructing harbors.

In addition to water, sheet pile walls can also hold soil in place. They're an ideal choice in areas with higher water tables, since water won't seep through steel the same way it can through other materials.

The following methods use structural supports that differ from piles:

Hydraulic Shoring

Hydraulic shoring uses hydraulic pistons, hollow chambers filled with fast-moving water, to exert force onto the side of a wall and hold it in place. Hydraulic shores are often paired with steel plates, which lie on the wall and take the brunt of the water pressure. This prevents the walls from taking any damage.

The above-mentioned methods are commonly used for long-term projects. Whereas hydraulics are a great short-term option used on excavation sites that take less time to complete. This technique is often used to repair sewers or complete work near bodies of water.

Pneumatic shoring works the same way as the hydraulics method but instead uses air pressure to do so.

Soil Nails

Soil nail shoring adds stability to cliff sides and soil beds with steel nails. This technique is generally permanent but can be used as a temporary effort. Steel nails are inserted into the soil angled downwards, which improves soil density.

Diaphragm Walls

For excavation sites deeper than 16.4 feet, diaphragm walls are a durable technique fit for the job. Made from reinforced concrete, diaphragm walls are capable of supporting weight in deep excavation sites like tunnel construction. However, these walls are difficult to remove when they aren't needed anymore, so they're commonly used for more permanent supports.

In Summary

To conclude, shores support unstable structures until work has been completed which makes them self-sufficient. They're a temporary solution that ensures the safety of people and neighboring structures on site. There are multiple shoring types that work best in different building environments. Considering soil bearing capacity, proximity, available space for excavation, and the area's water table will narrow down your choice between techniques.

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Frequently Asked Questions:

What's the purpose of shoring?

The goal is to temporarily support a structure while it's unstable. This usually occurs when structures are being repaired, are at risk of collapse, and when openings are being built into supporting walls. Shores prop up the structure and transfer its load into the foundation.

What are the types of shoring?

There are eleven main types of shoring, which are listed above. The most common methods are H and I-beam, raking, dead, and flying shoring.

At what depths do you need shoring?

OSHA guidelines require shoring in trenches 4 feet or deeper. However, it may be required at shallower depths when soil-bearing capacity is lower. It's also required to support structurally compromised buildings.