Ground Condition

Types of soil;

Before you buy a site or start building on an existing site, you need to find out the type of the soil you are going to be dealing with and what effect it would have, if any on the foundation of your house. This is not something that you can do yourself unless you are a professional land surveyor, so get a full report done with the right people.

There is a lot of variation on load bearing capability of different soils, what this means is that when you place your foundation and the house on the soil it should be able to take the weight.

If the soil’s bearing capacity is too low, you will need to have special foundation designed by a qualified architect or an engineer. This could be a raft, piles or other options.

An average two storey house has a bearing capacity of approximately 75 KN/m2.

The following is a guide to the load bearing capability of different soils:

Rock has a very good load bearing, but the foundation must be carried down to unweathered rock and stand on even bearing.

Types of subsoil Bearing Capacity KN/m2 Limestone 4000 Slates 3000 Hard Shale’s 2000

Sand & Gravel usually has an acceptable bearing capacity, however a full site test must be done to insure that the bearing level is not effected by things like the water level. In cases of loose sand or loose gravel and loose silty/clayey sand, there might be a need for a raft foundation.

Types of subsoil Bearing Capacity KN/m2 Compact Sand Greater than 600 Compact Gravel Greater than 300 Loose Gravel Less than   200 Loose Sand Less than   100 Loose silty/clayey sand Less than   100

Clays & Silty Clays are generally very bad soil conditions for foundations and house constructions as all clays and silts are susceptible to long term settlement. It is therefore highly possible that you need a special foundation like a raft instead of a ordinary strip.

Types of subsoil Bearing Capacity KN/m2 Hard/Stiff Clay 300 - 600 Stiff Sand / Clay 150 - 300 Firm Sand / Clay 75 - 150 Soft Clay/Silt/Sand 75 Very soft Clay/Silt/Sand Less than 75

Peat is very bad news when it comes to foundations and advice should be taken from an expert in the field to the required procedure before any construction work is done. Peat could be very soft or firm and before any attempt is made on the foundation, all peat and organic soil should be removed up to a reliable bearing level below.

Please note: The above information is only for guidance purposes and for any type of soil, an expert in the field should be approached for advice.