Shoring is the process of providing temporary support to construction projects.
This is usually provided with sheet piles, steel H beams or screw piles (steel anchors capable of sustaining dead shore system and lateral loading). Sheet pile walls are generally driven in groups called panels, which are interconnected laterally employing secondary piles and tiebacks. All forms of pile shoring construction have the primary purpose of keeping soil from entering trench walls that have been dug for foundation work or other purposes. Conventionally, this is done using wooden planks or soldier pile walls. A more modern way to prevent soil entry would be to use geotextile systems, flying shoring or soldier piles.
Sheet piles are rigid contiguous wall plates made from steel/iron sheets, usually driven into intervening pile locations cutting into the ground to form retaining walls around an excavation area. The height and length can be adjusted as per the construction project. Its main advantage over other systems is that it allows for deep excavation, which can be used later for backfill purposes once construction work starts again on the retaining wall.
However, sheet piles have lower capacities because they are driven in by manual labour compared with screw piles, or H-beam system types, so require more space. They need secure soils below them for adequate load-bearing capacity. It. It. It is not ideal for use in areas where the ground conditions are not suitable for excavation and construction work.Screw piles are made of large diameter threaded rods, which are screwed into the soil existing structure directly below the secant piles without disturbing it. This prevents any further subsidence of the plate steel I-beams and gives better stability to steel reinforcing bars compared with traditional systems since there is no need for structural concrete or grout fill. They can be installed at very high speeds (around 1m/min), they do not require extensive site preparation from construction workers, and they make use of existing soils to provide support. The disadvantage would be that they are fixed at one end, which means they do not work well in soft soils or clays that will flow around them; their capacity diminishes as soil adjacent structure conditions become progressively weaker.
H-beams are rigid steel beams that can be driven into sandy or soft soil quickly and easily and provide a stable and safe vertical structure for supporting collapsed structures. They use the existing ground to bear their weight like screw piles which help in the speedy installation of diaphragm walls. However, they do need extensive shoring methods for site preparation since the interlock walls requires a shoring wall before installation. The main disadvantage of this method is that it makes the design process more complicated because its dimensions must be carefully calculated for each case otherwise, there may not be enough unreinforced pile to support the continuous wall safely or the temporary structure.
Caisson shoring is a type of sheet piling used during deep excavations of footings and foundations for buildings. H-beam, sheet piling or screw piles are placed vertically around the excavation. The soil below the foundation is excavated, a platform of reinforcement is set up on top of these secant pile walls, and a watertight box structure (the caisson) is lowered into the excavation by hydraulic jacks until it rests on the reinforced concrete.
The primary purpose of shoring excavations is to prevent an existing wall from collapsing.
These systems are inexpensive and quick to install. The metal prop does not require a high skilled workforce and can be used effectively for shallow trenches with low shoring loads. They can also handle large volumes of soil, which means faster backfilling once the construction work has finished. On the other hand, it is labour-intensive as a lot of time is required for installation and removal of props on each section, the steel sections cannot be deformed (which limits their capacity to about 2 tons), and they are susceptible to corrosion over time especially in areas where saltwater intrusion occurs regularly.
Unlike hydraulic backfill systems that use steel props attached with chains to hold up the excavated soil, hydraulic struts support excavation walls using a single steel column inserted into the trench by hydraulic pistons and then filled with a grout mixture to provide added stability. Struts are typically used when the hydraulic shoring depth is more than 1 metre. Compared to other primary pile interlocking systems, they can be costly due to the high installation costs because of their labour-intensive nature. Still, struts prevent unstable structures from being eroded, which saves additional money on backfilling.
This shoring system functions by placing hydraulically driven vertical sheet piles around an edge of a trench to prevent collapse. These sheets are very strong and have good corrosion resistance. Therefore, they tend to occupy smaller areas and require less time for installation and removal while still providing a relatively high degree of safety to lagging walls. However, these systems can get expensive and may not be ideal for projects without a detailed design plan.
The installation time of a sheeting system is difficult to determine because it varies from project to project. On average, an experienced crew will be able to install between 500 and 800 metres in a day. This also depends on the soil conditions and excavation depth at construction sites, because soft soils can add an additional hour to your excavation process, whereas undisturbed dry soils may reduce installation time by half.
Various factors must be taken into consideration when installing tangent pile shoring, depending on whether it is being installed manually or with a machine.
Steps for doing manual shore installation include:
Inspecting the trench for any obstructions such as underground services/pipes before starting excavation.
Preparing the edges of the excavation by raking shores of the adjacent pile and backfilling around it before adding fresh concrete.
Installing wooden planks (timber shoring) between the trench sidewalls of adjacent buildings.
Hydro-seeding with water-bearing granular soils or clay. This can be done to cover open joints, which allows water to seep in, making the ground more cohesive when wet.
Removal of excess granular fill/earth.
Backfilling and compaction of excavated soil using either manual labour or machines such as small dumpers etc.
Applying desiccant dust on exposed earth before hydro-seeding is used for added protection against moisture entering into the soil.
This method requires less preparation time and, when combined with high-pressure water jets to remove excess soil, also reduces work time.
Preparing site by removing loose earth around trench edges using high-pressure nozzles.
Installing rubber edge protection along the trench edges for extra safety.
Installing a steel plate support through hydraulic operation.
Hydroseeding that retains dry granular material or clay. This can be done to cover open joints, which allows water to seep in, making the ground more cohesive when wet.
Backfilling and compaction of excavated soil.
Hydro-seeding is a process that involves applying a slurry or clay slurry to the exposed earth. This creates a protective layer around the soil, which prevents any water from entering into it and causing further erosion of the sidewalls. The granular material used for hydro-seeding must be able to suit the soil conditions at hand while being cost-effective enough to meet budget requirements.
Various types of grouts can be used for this purpose, including bentonite, Portland cement and resin pre-mixed slurries etc. Excavating is highly dangerous work and heaivly regulated. For more information, take a look at the SafeWork NSW wesbsite . Check to see if any laws apply to your area.