Site Investigation

The site investigation has to be carried out for the successful implementation of the project. This information will generally comprise : 

1. The nature and composition of the subsoil 
2. The presence of any filling or natural strata of less strength and cohesion, than the bulk of the  subsoil itself. 
3. The presence of my variations in subsoil across the site due to me presence of natural fault lines or beds of material laid down by climatic conditions or natural features such as streams now no longer in existence. 
4. The level of the existing water table at the date of the investigation and the presence of any springs or movement in the flow of ground water. 

A number of methods may be utilized to determiner the depth and composition of the subsoil of a building site.'These range with the size or complexity  of the project and also the financial resources available for the investigation. 

For small residential or similar projects it may be sufficient to determine the type of approximate  bearing value of the subsoil by one of the following methods : 

1. By digging a number of small holes about 600 mm deep found the approximate perimeter of the proposed building. 
2. By drilling a number of similar holes with a hand auger, which produces a hole, about 150 mm diameter and when extracted produces a cone or plug of the  , material through which the auger has passed.   
3. By driving appointed steel crowbar into the ground and gaudily the dear& of resistance to the bar. 

Probably, the best of these is the use of a hand auger lo attract soil samples followed by the insertions of a crowbar to clandestine tile resistance of the subsoil to penetration at  foundation depth. 

For rather large projects more expensive  methods may be used. 

1. The extraction of a series or trail holes about 1 m square x 1.5 m deep. The depth should be at least 0.5 below the proposed level of any foundations to ensure that the subsoil strata penetrated is continuous. Driving a crowbar the bottom for a further 0.5 111 will assist in controlling  this continuity. This method is relatively inexpensive, labour only being employed. 
2. By setting up a mechanical rig and drilling a hole either by percussion methods, which uses a chisel pointed steel bit screwed Lo  a steel rod, or by the use of a hollow tube which lifts a core of subsoil upto the surface's. These methods 'are used when the investigation is carried out at depths greater trillium those at which trail holes are economic. 
3. By loading a reinforced concrete slab with increasing  weight at 2 hour intervals and levelling up the upper surface with an optical level. From the amount of settlement the bearing value of the subsoil can be calculated in relation to the area of the slab.