What is Site Investigation?

Site Investigation means the various investigations that determine if the site will be suitable for its intended use based on structural, economical and environmental factors. Site Investigation is not limited to preliminary works alone. It is also undertaking to investigate defects, failure or safety of existing works.

Types of site investigation

Investigation of site for new works:

The investigation could involve determination of the overall suitability of the soil for the construction work.

The economical and environmental impact the proposed new works will have on existing infrastructure.

Proper preliminary site investigation will help determine the correct financial implications, material as well as equipment  necessary for a successful project.

Investigation of defects or failure of existing works.

This type of investigation may be  mandatory to establish cause of failure and provide remedy. For instance, in the case of a building collapse after several years, soil investigation may reveal reduction of the bearing capacity of the soil which may have been caused by changes in level of ground water.

Investigation of the safety of existing works.

When proposed new works are being planned, it will be necessary to assess the impact it will have on existing works or infrastructure. Structurally, situations that may be investigated are;

Will excavation reduce ground support of the existing structure or not?

Will groundwater lowering cause settlement.?

Will  disturbed drainage cause flooding or instability to the existing structures?

Environmentally, situations that may be investigated include impact of noise and waste that will be  generated by the proposed structure.

This type of investigation is not only limited to preconstruction it is also necessary after construction and during use of the structure.

Investigation as to the suitability and availability of materials for construction.

If the soil material on site is to be used for construction works,  support structure or both, then its suitability must be determined.

This is usually done by visual inspection and standardized tests.

Importance of soil investigation in civil engineering

Civil engineering works have some form of foundation which is supported by the ground. The interaction between a civil engineering structure and the ground that holds it is complex. Hence it is appropriate that proper soil study and investigation is carried out before structure is built in it.

It is standard practice to examine any soil on which a structure is intended to be erected in order to determine the following:

• The suitability of the soil site for the proposed work.
• Adequate and economic foundation design.
• Difficulties that may arise during construction.
• Situations that may occur after construction.

Rock types

Rock types can be classified by their method of excavation. That is, whether blasting is required, by load bearing or other physical properties.

From a civil engineer’s point of view, A rock is a solid mass composed of soil material in a very stable position of which it’s removal is only possible after blasting, or breaking by compressed air and hydraulic tools or by breaking tools such a wedges or sledge hammer.

Rocks can be placed into 3 basic categories, the are:

Igneous, sedimentary and metamorphic.

Igneous rocks include basalt and granite. They are formed by the solidification of molten material from the hot lower levels of the earth crust which have ascended towards the surface. They have very high bearing capacities about 3 times that of sedimentary rocks and 40 times that of alluvial clays and sand.

Sedimentary rocks includes, Limestone and sandstone.They were formed by stratification and cementation of earth materials over time.Their strength depends on properties such as angle of stratification and cementation as well as behaviour under wet conditions.

Metamorphic rocks are any sedimentary or igneous rock deposits which after consolidation have become changed by heat and pressure. Examples of metamorphic rocks are gneisses, slates, schists.

The most suitable type of  rock for civil engineering  foundation work is the igneous rock. Sedimentary rocks have lower  load bearing capacity due to the presence of soft clay material in their deposits. However, the load bearing capacity of all types of rock is greatly reduced as a result of weathering and earth movements.

Soil types

Types of soil includes;

• Residual soil ( too soil)
• Detrital sediments ( sands, gravel, slits)
• Organic deposits (peat)
• Calcareous deposits ( shell, coral)
• Uncemented volcanic dust.

Soil types are identified by;

• Size and nature of soil particles
• Density and structural properties

You can download the table of Field Identification and Description of Soils. (BS 5930:2015) HERE

The table can be found in page 110 of BS 5930: 2015.