Piling is a broad term and refers to numerous foundation-building & reinforcing techniques. Foundations of any construction project must be flawless to ensure that the superstructure and all that traverse it are safe. The type and measurements of foundations are decided by engineers who perform a series of calculations and carry out a detailed study of the site soil. Depending on these factors, it is determined whether a project should have a shallow or a deep foundation. Engineers usually go for shallow foundations if the site soil is suitable and has adequate load-bearing capacity. However, engineers will go for deep foundations if the LBV (load-bearing value) of the surface layers and the soil characteristics are not ideal. There are numerous methods of building deep foundations, and piling is one of them. Once it is understood that piling is the preferable method, engineers must sit together to identify the type of piling required. Several factors must be considered, including cost, time, regulations, and site conditions, before they agree on the method. Let us read about five of the most common piling techniques used by construction companies for residential, commercial, industrial, and public projects.
Replacement piles/ Bored pile foundations are usually poured in place for supporting infrastructure by transferring their weight/load to rock or soil layers with good settlement characteristics and high load-bearing capacity. The process involves drilling vertical holes into the ground with the help of a piling machine. Steel cylinders or sleeves are drilled into the ground, followed by concrete pouring. SFA (Sectional flight auger) and CFA (Continuous Flight Auger) are the two most common methods for preparing bored foundations.
Applications of Bored Piles
Bored pile foundations are ideal for challenging soil conditions and well suited to tolerating considerably heavy loads. Apart from being used for building foundations, they are often used for building structural underground walls for earth retention. Secant pile walls (overlapping piles) are often used for controlling groundwater migration.
Bored Pile Advantages
- Different lengths of piles can be created for passing through compressible, soft, and unsuitable soil to stronger bearing strata.
- They can be extended much deeper to protect from moisture variation and frost penetration.
- Less disruptive to nearby soil.
- Minimal disturbance to nearby structures because of low vibration.
- High capacity and economics.
Driven piles are built using vibration by driving or hammering steel casings (permanent or temporary) into the ground. They are ideal for building foundations at construction sites with highly cohesive or contaminated soil and for areas with high water tables. They can be prepared both on-site and off-site. The former uses pre-cast piles and can be fabricated from concrete, wood, composite, or steel. Steel-driven piles are of several types, including H-section (used for marine structures), screw piles (sand and soft silt), and tube piles (soft subsoils, marine structures). Concrete-driven piles can have several shapes, including sheets, cylindrical, octagonal, or square. They are driven into the ground using percussion. They are highly suitable for extremely loose soils and soils with running water. Timber piles are also percussion driven and available in various shapes. They are used for construction near estuaries and river banks.
Advantages of Driven Piles
- Driven Piles can be prepared off-site, reducing chances of errors and installation time.
- Driven piles do not require soil extraction and do not lead to structural problems or subsidence.
- Their installation displaces and compacts the soil, which enhances the pile’s bearing capacity.
- They are highly cost-effective as they can be constructed in different shapes from different materials.
- They have high structural strength.
- They have high bending and lateral resistance, which makes them suitable for complex conditions such as seismic loading, water, wind, etc.
Screw piles look like huge screws with helices attached to them. The pile shafts are usually circular and hollow and are mainly constructed from galvanised steel. Just like the screws you use, screw piles are fastened into the soil with the help of rotary hydraulic tools fitted on earthmoving machines. Screw piles are ground anchoring systems highly suitable for deep foundations, and they transfer the infrastructure’s load onto the pile.
Screw piles minimise the spoil (excavated soil), usually created using other methods. This makes it more cost-effective in several situations. Screw pile foundations for various projects, including roads, telecommunications, rail, retaining structures, masts, and several others.
Advantages of Screw Piles
- The installation time of screw piles is much lower than many other piling methods.
- The installation cost is much lower than other piling methods
- A range of screw sizes can be used.
- Screw piles leave a much lower carbon footprint.
- Their usage eliminates the need for excavation and therefore backfilling.
- They can be installed close to other structures without causing any damage.
- They can be easily removed if they are not required.
Sheet piling is a type of drive piling. The sheets are usually constructed from steel and have interlocking edges. Sheets can also be built from concrete or timber. The sheets are driven into the earth to provide excavation support. They are also often used for creating temporary or permanent retaining walls at construction sites where extensive excavations must be carried out. Other applications include building underground structures such as car parking, basements, and tunnels., They are also used for land reclamation, cofferdams, seawalls, and many more. Timber sheets are mainly used temporarily or for resisting mild lateral loads. Reinforced concrete sheets are manufactured by linking together pre-cast concrete. Steel sheets are preferred when a higher resistance is required. They are available in several forms, including straight web sections, box sections, composite and normal sections.
Advantages of Sheet Piling
- Sheet piles are reusable and recyclable.
- They come in a wide variety of lengths and sizes.
- Both permanent and temporary structures can be built.
- Low-vibration methods can be used to install them in highly populated areas.
- The construction site remains clean, as there is no spoilage.
- Sheet piling installation time and cost are considerably low.
- They are highly suitable for both below and above-water usage.
Mini piling is a subclass of piling and used piles with a much narrower diameter. This is why it is often called micro piling. These piles are extremely light and highly cost-effective. They can support considerable loads and can be used in various ground conditions. Among piling techniques, it is considered to be one of the most versatile and highly adaptable methods for building new foundations and reinforcing existing ones(underpinning). They are highly suitable for building foundations at sites with weak surface soil. The most common installation method involves drilling/screwing hollow steel shafts into the ground. Concrete or grout is poured to form a pile while the soil is supported by the shaft. This makes the process considerably more convenient than conventional boring methods where extra support is required. Micro piling is also used when construction sites have restricted access, such as low headroom.
Advantages of Mini Piling
- Many piling techniques can be performed with the help of piling rigs which reduce labour requirements and cut down construction time.
- As the rigs can perform much of the work, your construction cost reduces considerably. Micro piling is often used even when the site conditions permit shallow foundations because of the low construction cost.
- The compact piles are ideal for building foundations in soils with low LBV (load-bearing value), high moisture, and if the ground is highly reactive to climatic conditions.
- Construction sites that cannot permit the passage of heavy machinery and a large labour force can benefit significantly from micro piling as the rigs are considerably small.
- Low headroom, such as in the case of upper floors or basements, tunnels, and under the bridges, can all benefit from micro piling.
- The rigs cause minimum noise and can be used for construction in sensitive properties such as hospitals, schools, and colleges.
- Micro piling is the least disruptive and can help businesses carry out construction projects without disturbing their operations.
- Mini piling causes the least vibration and is highly suitable for construction near historical and archaeological sites.
- The life of existing infrastructures can be increased by reinforcing their foundations using micro pilling.