Structural design

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Foundation design

Beam design

Foundation design

A lot of our work is foundation design. Below are some of the factors that mean that something more than a traditional strip footing will be required.

Sloping sites
On sloping sites (especially on steep slopes) it is important to ensure that the house is protected from sliding down the slope and that any retaining walls are adequately designed. Where space is at a premium it is often required that some rooms are built into the slope and this will require a retaining wall.

We work closely with Architects and Clients to ensure that we provide them with the most cost effective solution to achieve what they want.

Deep foundations have been specified here to counteract the effect of trees. We warn Clients to test how the ground will stand up before excavating. These will now need piling.

Building near trees
Trees are only a problem when building on clay. However, where this is the case the design takes account of:

  • The type of tree
  • The height the tree only if it is being removed (if it is staying it is assumed to be its mature height regardless of size)
  • The type of clay
  • The distance between the tree and the building

The principle of the design is to ensure that foundations are deep enough that they cannot be affected by expansion or contraction of the ground. This can happen, for example, in very dry weather when the tree continues to extract water from the clay causing it to shrink.

Building over shallow mine workings
We are based just outside Chester and are surrounded by areas of shallow mine workings. This can lead to problems if the extent of any mine workings is not fully established prior to building. We work closely with local geologists who have extensive experience of the area.

The usual solution after any drilling and grouting of the site has been done is to build the house on a raft which is designed to span over any localised soft spots that may occur.

The steel reinforcement in a ground beam. This is now ready for pouring the concrete.

Piled foundations
(Building on poor or filled ground)

Most houses are built on natural clay or sand. While the properties of each is different they are known and predictable. Where the ground is made up of material that has been disturbed (we would call this fill) the properties of it are unknown and probably variable across the site. In such cases we would often propose a piled design. The most common type of pile we specify are 150mm or 220mm diameter steel tubes that are driven into the ground and filed with concrete. The steel tubes are about 2m long and are welded together as they are hammered or drilled into the ground until they are supported by firm ground. A reinforced concrete beam (known as ground beam) is built over the top of the piles to support the building. We have a photo gallery of the installation of mini piles for an extension being built on filled ground.

Building in areas subject to flooding
This is quite straight forward from a foundation point of view. The effect of flooding it to reduce the load that the ground can support so the foundations must be designed so as to put a reduced pressure on the ground to compensate.

Buildings which include basements
There has been an increase in the number of basements we have designed recently. This is presumably a reflection of the cost of land. Basements can be expensive to build because of the need to build retaining walls around them. The design must also allow for adequate tanking (waterproofing) to be installed to ensure the basement is damp free.

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