Task 1 - Why Should We Do A Site Investigation!
As being a long standing member at Bogsworth Sports & Leisure club and also having a lot of knowledge about the construction industry, I have been asked to explain to the chairmen of the club about why we should do a site investigation prior to the commencement of construction to build a new club house and cricket pitch. Unfortunately earlier this year one of the clubs long-time established members passed away, in his will the land he owned was to be offered at a very small price to the club if they wished to relocate the club and pitch.
With the club taking up the offer i will inform the club why the site investigation is crucial prior to construction and the effects on the job if they decided not to partake in one.
Site surveys can tell us a lot about the area of land that we propose to build on. For example;
- the nature of the soil
- the thickness of the layers of different types of soil at the test location
- the strength of the soil
- the existence of contaminants in the soil
- the degree of moisture present
- the existence of a water table
- the location of existing services
The first stop to a desk top survey being the "desktop survey" with things like Ordinance Survey maps, to see exactly were the site is and what public footpaths that could cross your land. Libraries, historians and local authorities could tell you exactly what the land has been used for in previous years and the surrounding areas that could have contaminated the land. This could be very useful as it could save a lot of time and money in the long run. Also previous site investigations, Ariel photographs and utilities/service drawings can show information that could help, With the information you gathered from the desktop survey you now know more about the type of land and possible contaminants.
The next step is to do a "Walk over survey" this helps with finding out potential problem ground and ground water often like wet land or ponds. This type of survey can also flag up things like old foundations, drainage and contaminants. Backfilled areas are also noticeable too, which helps with the previous uses of the land. The walk over can also show if access to the land is viable, and also if plant and wagons can access the site.
After the "walk over survey" a more detailed site survey is put into place this involves; Pitting, trenching and drilling. These techniques help to see how the ground lies on the site and the different layers of earth. Soil and water samples are also taken so that tests can be done to check for contaminated land. The land is tested also to see the layers of the earth and this can also effect which type of foundation is later used on the job.
The ground investigation is the next step this involves
- trial pits
Trial Pits are usually dug to no more then 6m this usually helps notice any existing services and any possible obstructions before the boreholes are drilled.
The borehole test is usually drilled into the ground while being struck by a hydraulic ram, the type of bore is usually affected by the conditions of the land.
After the samples have been taken they can be analysed to see how the land lye's and what conditions the land is in. The samples also show how much water the land holds to help with planning the foundation type.
With the more detailed information gathered from the previous surveys the next step is to do "remedial treatment" which is based on the sites final usage, its cost benefit and possible pollution present on the land as well as the water regime permit.
And finally the last thing is "Long term monitoring" is usually the groundwater monitoring which tells how the site has done in remediation and how the land has settled after construction.
So eventually after the site investigation has concluded it will tell the client weather or not the land is suitable to build on, Also with the information it will give the architect a better understanding on which type of foundation to use. The results from the tests on the land could also point out if the land has any contaminants.
2. Substructure & Foundations
Substructure is the type of construction level under the dpc (damp proof course) of a building; The substructure is the main element that carries the load of the building which is usually called the foundations. The foundations are one of the most important things of a building; failure in the foundations could cause major effects on the building and may end up in demolition.
The foundations safely hold the load of the structure to the ground and they also have to refer and stick by to the Building regulations approved document A. The foundations may also be required to prevent the structure being pushed up. Undue settlement refers to the amount and nature of settlement permissible.
When the foundations have been laid it will cause immediate settlement under the soil and will also carry on for many years with the fine sands. The long term compression of the soil is called consolidation. The land will also settle when water is pushed out of the clay. The three basic types of settlement are uniform settlement, tilt and non-uniform settlement.
The uniform settlement is usually when the foundation vertically settles. The structure should not be affected but the services could be.
Tilt settlement usually means the structure settles on a tilt, this can lead to cracking around the window and door frames.
The more serious of settlement is Non uniform; this could have serious affects on your structure and could be possibly end up in structural failure.
Foundations can also prevent upward movment in the building were ground water pressure could be excessive.
There are many different types and types of foundations which all depend on what the ground is like, type of construction ect. Soild types are split between 2 main titles, Cohesive and granular.
Cohesive soil is usually types of clay were the soil sticks together and granular is more of a sandy type of soil which is loose and easily compacted.
Load on the foundations also has a major effect on the construction and the three elements are dead load, imposed load and wind load.
Dead load is the is the force attributed to the total structural mass of the building materials multiplied by 9.81 to give Newton's. Imposed loads are the force that will be imposed on the property in the way of people, furniture and fittings. The loading of snow (snow load) will come into this category and an allowance for this in all foundation design will be included in the calculations. Wind load is relatively low rise, in a normal, reasonably sheltered environment, a figure of 1 kN/ square metre is acceptable.