Construction projects are complex and require extreme care. However, sometimes an adjacent structure needs to be dismantled, cracks need to be repaired, or openings enlarged on a wall. That’s where shoring comes in.
Shoring refers to the process of supporting a structure or building temporarily with props. The technique is used during alterations, repairs, or when there’s a risk of collapse. The phrase shoring means a shore, a metal prop, or timber.
Individuals in construction may use shoring for different reasons. We’ll discuss some situations that justify the use of shoring and cover a few types of shoring used in construction.
What Exactly Is Shoring?
Shoring refers to the process of supporting a structure to prevent collapse. The phrase shoring is from the word shore, which means a metal or timber prop.
There are various methods of shoring that one can use, but this depends on the circumstances. Shoring is common during the early construction stages. During the excavation process, shoring is used to reinforce below-ground such as trenches. Trenches tend to collapse, which necessitates trench shoring to add to the stability.
Shoring is used to offer support:
- During excavations
- When walls are undergoing reinforcement or repair
- When there are enlarged openings or when the creation of spaces is required in a wall
- To ensure walls don’t fall out.
- When a nearby structure needs to be pulled down
What Is the Difference Between Shoring and Scaffolding?
Scaffolding refers to temporary structures used to provide support for workers. Masons can use these scaffolds to stand and do their work like painting, plastering, or bricklaying. Scaffolding is also present where maintenance or demolition work needs to be done.
Shoring, on the other hand, is only used to support an unsafe structure. It is used when a building wall exhibits signs of leaning outward. It’s also used when reconstructing or dismantling a defective building wall. Shoring is meant to provide support to the roof or floors that are connected to the wall.
What Is the Role of Shoring in Excavations?
Shoring provides a temporary structure for construction projects to prevent the collapse of systems on the site. Nonetheless, shoring does more than prevent the destruction of structures. Below are some reasons why shoring is crucial to the success of most construction projects.
- Enhanced safety: Excavation is a common practice during the construction of foundations and basements. Shoring helps to protect the workers in temporary holes and trenches. Shoring works to hold the earthen walls up and prevent collapse. The technique is used as a preventive measure to hold the unstable structure in place before construction resumes.
- Ensures time is not lost during construction: Having to excavate a site twice could lead to delays that can put the contractor off schedule. Shoring leads to expedited scheduling as workers are less likely to make errors that could lead to lost time.
- Reduced costs: Collapsed excavations can lead to more work and losses. However, shoring simplifies the process by ensuring the builders remain on a budget as they don’t have to deal with collapsed structures. Shoring promotes efficiency by ensuring the excavations are completed safely and on time. There’s no need for remedial work that can lead to wasted resources and delays in case of a collapse.
- Peace of mind: When construction workers have to worry about the structure collapsing, they can’t work effectively. That could lead to them making mistakes. However, shoring gives the workers peace of mind as they are assured they have the right support around their work area.
Types of Shoring in Construction
Shoring is one of the best methods to support a structure to prevent it from collapsing. Various methods of shoring are used to stabilize a system during construction. The type of shoring will depend on the severity of the situation and the project being done.
Here are some common types of shoring:
Dead or Vertical Shoring
Dead or vertical shoring involves positioning what is considered a dead shore in a vertical form. Once the vertical structure is set up, it’s used to support the horizontal needles. The needles then help with the transfer of load off the floors, walls, and roof.This type of shoring is also used when rebuilding a defective load-bearing wall. Dead shores have beams and posts arranged to support the weight of the whole structure and transfer the weight to the ground underneath the foundation.
How Are Dead Shores Installed? The process of installing dead shores is simple once the technique is mastered. There are a few steps that need to be followed to set up dead shores to support unstable structures and walls before the excavation and construction work continues. The requirements are:
- Making holes in the wall at a calculated height.
- Using thick woods or steel sections to make needles inserted into the holes made in the wall.
- The needles are made as vertical posts or dead shores on both sides.
- The props are tightened by folding wedges at their bases while the junction between the needle and prop is secured.
One thing to note is that the process of installing dead shores may lead to shocks and vibrations. Sometimes raking shores are erected before the operation for safety reasons. The raking system needs to be removed after the dead shore system has been removed.
When Are Dead Shores or Vertical Shores Installed? Dead or vertical shores can be used in different circumstances. A good example is when an existing foundation or structure needs to be rebuilt or made deeper. Dead shores can also be installed before rebuilding a defective lower part of the wall. Vertical shores may also be installed when using underpinning to make large openings at the lower level of an existing wall.
Flying shoring is also referred to as horizontal shoring. This type of shoring provides horizontal support to two parallel party walls when collapse or removal of the intermediate building. Flying shores are all types of shoring systems that support the unsafe structure in which the shores do not touch the ground.
A flying shore consists of needles, well plates, struts, cleats, folding wedges, and horizontal shore straining pieces. A double or compound flying shore may be given when the distance between the walls is more.
How Are Flying Shores Installed? The process of installing a flying shore is intricate. In some instances, a trusted framework may be used to act as a flying shore. Below are a few steps explaining, in brief, the method of erecting the flying shore.
- The process starts with setting the ground before the flying shore erection. That includes getting the angles and measurements correct. The cleats are nailed to the wall plates. Ensure the first pair supports the horizontal shore while the others help add strength to the struts.
- Note that the horizontal beam’s cleat should be thick for the wedges and provide a nice overlay by the beam. Check to see that the horizontal beam has an equal clear-bearing surface at each end.
- Place the struts at an angle that is not more than 45 degrees to the horizontal beam. Keep the mounts apart on the horizontal beam using the straining pieces. The length of the horizontal beam determines the length of the straining pieces.
- Put the horizontal beams and the straining pieces and ensure they are tightened by the folding wedges between the wall plate and shore.
- The final step is to fix the struts into position between the top part of the lower struts and lower cleats.
In cases where there’s a structural gap between two buildings because an old building has been removed, a flying shore is inserted. The shore is removed after the construction of a new structure.
Secant Pile Shoring
Secant pile shoring is another method of shoring used when there’s a need to interlock walls. This shoring type seeks to link two walls to make a continuous wall to prevent unstable structures’ collapse.However, a few things need to be done before interlocking can happen. Secant pile shoring requires an intersection of two combinations of piles. The first pile is intersected to the un-reinforced pile, and the other is the reinforced pile.
Secant pile shoring is risky. You need to consider the surcharge load and proximity before installation. This type of shoring is often used when there’s little to no room for excavation to occur. Intersecting two walls forms a continuous wall to create an opening for the excavation process to happen.
How Is Secant Pile Shoring Done? Secant pile shoring is done by intersecting two combinations of piles, including the un-reinforced or the primary pile and the reinforced pile, also known as a secondary pile. Some of the steps that need to be followed for secant pile shoring include:
- Interlocking the primary and secondary piles to form a continuous wall.
- A guide beam is then made before the installation to ensure the alignment stays in place. The beam comes in handy during deep excavations.
- The provisional casing is extracted after casting the primary pile.
- The secondary piles are instantly drilled. The reinforced piles are placed inside, and the concrete is poured around the structure to form a continuous wall.
Secant piles are an ideal choice when there’s no space for open excavation or when the room is limited. That could be due to the proximity of an existing structure. In such a case, the extra loads are considered in the design due to the adjacent form.
Using this type of shoring has its advantages as it provides increased wall stiffness, offers improved construction alignment, and is less noisy than other methods. Secant pile walls can also be installed in hard soil or land.
Secant pile shoring has its drawbacks as well. It’s challenging to get vertical tolerance when dealing with deep piles. It’s also challenging to achieve complete waterproofing in joints. Cost is another limiting factor, as secant pile walls are more expensive than sheet pile walls.
A raking shore is a structure that supports walls that aren’t structurally stable within a building. This shoring method uses needles, cleats, sole plates, inclined members, and bracing/wall plates. Raking shoring is meant to keep the walls intact to reduce damage to the existing structure or building.
The method consists of a wall plate that is placed vertically along the wall’s face. It’s then secured using needles.
The needles penetrate the wall by about 4-6in (10-15cm). Cleats are used to strengthen the nails to ensure they don’t get sheared off because of the raker’s thrust.
A construction worker places the raker so that the centerline and the wall meet at the floor level. That is done to ensure that there will be a raker that corresponds to every floor.
The inclined soleplate is placed into the ground on which the rakers’ feet are connected. A hoop iron is then used to stiffen the feet of rakers at the soleplate. The wall plate distributes the pressure to the wall uniformly.
Raking shoring becomes effective when the raker meets the wall at an angle of 60 degrees. The wall plates increase the area of support.
Points to Note When Using the Raking Shoring Method: Rakers provide sideways support to the walls. While using raking shores, you need to ensure that the rakes are disclosed at 45 degrees in the ground. The length of the trackers can be reduced in tall buildings. Ensure that rakers are braced at intervals.
Hydraulic shoring involves using hydraulic pistons that are pumped outward until they press up against the trench walls. These pistons are combined with plywood that can be 1-⅛ inches (2.9 cm) thick or a steel plate special heavy with ⅞ inch (2.2 cm) thickness. Prefabricated aluminum and struts are used in this shoring method.
One of the reasons why hydraulic shoring is popular is because it’s simpler and quicker to use. Other shoring methods are used for extensive excavations and long-term applications. Other reasons why hydraulic shoring stands out include:
- Digging trenches of different depths and widths.
- Being safe than timber shoring as workers don’t need to go into the trench.
- Hydraulic systems are light and can be easily installed by a worker.
- The pressure is distributed evenly along the trench as they are gauge regulated.
- The method prevents preloading, and the movement of trench faces by using the natural cohesion of the soil.
What to Know When Using the Hydraulic Shoring Method: With this method, the shoring is installed from the top and the bottom is removed. The shoring needs to be monitored in every shift. Sometimes there may be cracked or leaking cylinders, bent bases, broken connections, and other defective parts that require immediate attention.Hydraulic shoring is also excellent for waterline and sewer repair. It can also be used to lay pipes when crossing utilities becomes a problem. The shoring method allows for open-cut trenches to remain open for control density fill pipe zone applications.
Soldier Pile Walls/H or I-Beam Shoring
Soldier piles are one of the ancient ways of retaining wall systems used in deep excavations. The method has been used since the 18th century. When timber lagging and street piles are used, the technique is referred to as a Berlin Shoring Wall system. In some cases, concrete piles, caissons, and circular pipes can also be used like soldier piles, but this could increase the overall cost. Lagging materials include steel plating, precast concrete panels, shotcrete, and timber.
Soldier piles and lagging can be applied to residential and commercial use for foundation repairs, home construction, and archaeological digs.
Timber lagging is mostly used, although reinforced concrete panels can also be used for permanent conditions. The soldier piles help with moment resistance in lagging walls and soldier pile. Embedding the soldier piles below the excavation grade helps to achieve passive soil resistance.
How Are Soldier Pile Walls Installed? Soldier pile and lagging consists of steel piles placed or driven in drilled holes. When additional lateral resistance is needed, tiebacks can be installed depending on the soil conditions and the wall’s geometry. Here are the steps when installing soldier pile walls.
- Start by constructing soldier piles at intervals of 6ft-12ft.
- Drive the piles into the soil on both sides of the trench using an impact hammer or hydraulic vibrator. Pile distance guides can be used to ensure the piles are in the right longitudinal distance.
- After ensuring the piles are in place, the excavator is used to cut depending on the ground conditions. It installs the two shoring plates between the piles on both trench sides.
- The plates are pushed down to the stated depth by the excavator.
- To support the soil pressure and plates, bracings or heavy-duty trench struts are placed between the piles.
Soldier pile and lagging walls are one of the affordable ways to keep walls in place. They are fast and straightforward to construct. Adjustments can be made to the soldier pile installation, thanks to its versatile nature. Construction of soldier piles and lagging walls do not need advanced construction techniques like other shoring methods.
Some soil varieties require the use of conventional wall retaining strategies. That is essential when dealing with soil types that are easy to drain. While installing soldier piles is labor-intensive, the process is quiet and does not cause disturbance than other wall retaining solutions.
Some of the drawbacks of soldier pile and lagging systems include the fact that they are not as sturdy as other retaining systems. They are limited to temporary construction and cannot be used in places with high water table conditions. Any bad backfilling can lead to surface settlements. It can also be challenging to control basal soil movements as only the soldier pile’s flange is embedded beneath the subgrade.
While soldier pile and lagging installations extend along the horizontal plane indefinitely, they become unstable when installed higher than six yards above the ground. Nonetheless, it’s possible to get around this by placing the piles closer together, but this may end up being costly.
What to Know About Soldier Piles and Lagging: Installing soldier piles requires the experience of a professional who conducts structural load analyses and studies the soil structure. Specialized equipment is used and requires extensive training. Some states require certification and licensing when using the equipment. Removing the vertical piles or horizontal lagging also requires close supervision.
Contiguous Pile Shoring
Contiguous pile shoring is also referred to as tangent pile shoring. This method involves the use of tightly spaced piles. The piles lie tangent to each other, hence the name tangent pile shoring.
These pile walls are constructed using CFA technology. Adjacent pile walls have reinforced piles, with the gap between the piles being 2-6in (50-150mm). In some instances, a permanent wall can be created to resemble a structural concrete facing sprayed concrete.
In areas with minimal water pressure or places where water isn’t as important, contiguous pile shoring comes in handy. That’s because it helps to retain dry granular material. When dealing with water-bearing soil, this shoring enables water seepage through the pile gaps. Note that you can’t use this shoring method for a high groundwater table, mainly where there aren’t dewatering works.
How Is Contiguous Pile Shoring Done? Contiguous pile walls are an economical and straightforward supporting system. Apart from being affordable, this shoring method ensures a shorter construction period when handling small to medium depths of excavations. Some of the steps involved include:
- Construct a pile using continuous flight auger technique or the shoring, rotary technique.
- Place the pile cage reinforcement to enable the pile to handle the bending forces.
- Let the concrete gain its strength.
- Install a capping beam to the tie piles while making sure that the wall mimics a monolithic structure.
- Resume level digging to formation level.
- Install permanent or temporary propping if the design calls for it.
Contiguous pile shoring works well for embankment cuttings, bridge abutments with horizontal loads, and new basement structures, particularly in urban settings. This type of shoring can also be used to provide extra support for highways prone to embankment slippage.
Some of the advantages of contiguous pile walls include affordability, unlike diaphragm walls, it’s simpler to build in load variations, and they can be used for flexible geometry. The piles can also be installed in difficult ground conditions and work well in urban areas where conventional retaining methods would encroach the adjacent properties. The footings on underground utilities and adjacent buildings make contiguous pile walls an excellent choice for supporting an excavation. These piles have a quicker speed of installation, unlike the secant piled walls.
Sheet piles are a fantastic type of shoring used to isolate the excavation from bodies of water like a seaside, a pond, or a creek. This type of shoring is common in harbor construction. This retention system involves the steel sheets with interlocking edges to create a wall. The wall offers lateral support and can be permanent or temporary.
How Are Sheet Pile Walls Installed? Installing sheet piles may be done in two ways. Both methods use granular soil, but the ground below the dredge line may be clayey or sandy. The surface of the earth on the water is known as the dredge line or mud line. These construction methods are categorized into a dredged structure and a backfilled structure.
A backfilled structure follows a sequence of construction that involves:
- Dredging the soil in front and back of the proposed structure and driving the sheet piles.
- A backfill is done to the level of the anchor, and the anchor system is placed.
- The final process is backfilling up to the top of the wall to create a backfilled structure.
For a dredged structure, the process involves:
- Driving the sheet piles.
- Backfilling up to the anchor level and placing the anchor system.
- Backfilling up to the top.
- Dredging the front side of the wall.
Steel sheet piling is lightweight, offers high resistance to driving stresses, and it can be used on multiple projects. You can adapt the pile length by bolting or welding, and you get to enjoy a long service life with minimal protection.
On the downside, this type of shoring is noisy and may cause a disturbance. Installing these pies may be challenging in soils with cobbles or boulders.
Construction workers have to deal with the threat of an unstable structure collapse at any time. Moreover, any collapsed structure interferes with completing the construction work and could lead to higher costs. Using the right shoring method can help stabilize an insatiable structure until the construction process is complete.
Any of the above shoring methods can be effectively used depending on the construction type to ensure the structure remains stable throughout.