Where the bearing capacity of the soil is poor or imposed loads are very heavy, pile foundations and Geotechnical engineering may be required.
Piling is a form of foundation stabilisation where either concrete, timber or steel piles are used to stabilise a structure. There are two main types of pile – end bearing piles, where the pile acts as a column carrying the load down to the bearing strata, and friction piles, where the load is gradually transferred along the length of the pile.
Piled Foundations provide support for structures by transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics.
• Where large axial, horizontal and tension loads are applied to a structure or member
• Where existing structures or members require alteration or improvement
• Weak/ soft ground conditions
• Building on ‘made’ ground
Considerations When Deciding On Piling Types
There are a very wide range and type of pile foundation types available, suitable for different applications, depending on considerations, such as:
• The nature of the load requiring support
• Areas of limited access, such as house extensions, basements or other domestic work
• Ground conditions
• The presence of water or contamination
• Sensitivity to noise and vibration
• Proximity to other structures
Subsidence Main Causes
- The building or structure has been built on compressible clay soil
- Soil under the building/structure has not been compacted properly during construction
- Water damage has weakened underlying soil and foundations
- Movement of varying soil structures underneath foundations
- Vibrations & moving of soil at nearby excavations
- Vibration from passing traffic
- Incomplete/poor quality foundation works
- Changes in environmental or surrounding circumstances
- Natural decomposition of soil, such as peat
- Vegetation growth – Oak, Willow and Poplar are all very effective at sucking up moisture from the soil
Water escaping from damaged drains can sometimes soften, or even wash away the ground beneath the foundations, resulting in ground movement and, therefore, building movement. This issue usually affects sandy or gravelly soil.
Areas where there was heavy coal mining will have several open areas underneath the ground, which can lead to subsidence. Traffic and building work nearby can cause heavy and extended vibration which can lead to the soil moving and subsidence.
Vegetation adjacent and close to the foundations can be a cause of subsidence. Roots extract the moisture from the soil, causing it to shrink.
This is more of a risk during long periods of dry weather as thirsty plants can advance their roots through existing foundations to extract water.
Often subsidence is related to the moisture content of the soils and in particular the soils underneath the foundations. Certain soil types are more susceptible than others. Cohesive soils, such as clay and silt are particularly vulnerable as they shrink and swell in relation to their moisture content, with the weather having an enormous impact on their composition.
Non-cohesive soils, like sand and gravel, are less susceptible to shrinkage and expansion, but are more susceptible to settlement and risk being washed away by water flow such as damaged, old drainage, leaking water pipes or poor site drainage.
O Organic – Also called humus, this is the top-most layer of any soil with a significant amount of plant life above it. Humus is a layer of organic material (hence the ‘O’), like dead grass, fallen leaves, etc. that collects on the ground’s surface.
A Surface – The A Surface is topsoil, the upper layer of actual dirt. It’s made of broken up bits of rock and dust as well as organic matter. If a soil has a deep A surface, that likely means it is older and has had a lot of plants growing in it over time. In terms of plants and farming, this is the nutrient-rich layer that plants love to get their roots into.
B Subsoil – This layer is also made of finely ground up rock bits (AKA dirt and dust!) and some organic matter, though much less than in the A surface. The subsoil is also hard-packed and dense. In some tropical areas with a lot of rainfall, heavy minerals such as iron and nickel can get washed out of the upper soil layers (“leaching”) and deposit in the subsoil, causing it to be heavy and hard, and also to take on a different colour.
C Substratum – The C substratum is the parent material from which the soil formed by erosion and plant activity. This usually means large chunks of partially broken-up rock, very little organic material. In sedimentary deposits, the C substratum can include a sedimentary rock layer if it is the parent material of the soil and a different type of rock than the bedrock.
R Bedrock – ‘R’ stands for rock, and in this case, bedrock. Bedrock is considered to be solid rock that formed in place and is the underlying foundation of an area. It will be the bottom-most layer, above which soil development takes place.
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