WHAT IS SITE INVESTIGATION

Site Investigations

Site investigation or sub surface explorations are done for obtaining the information about subsurface conditions at the site of proposed construction.Site investigation consist of determining the profile of the natural soil deposits at the site, taking the soil samples and determining the engineering properties of the soils.It also includes in-situ testing of the soils.

Site investigation are performed to obtain information on the physical properties of soil and rock around a site to design earthworks and foundations for proposed structure and for repair of distress to earthworks and structures caused by subsurface conditions.This type of investigation is called a site investigation.Additionally site investigations are also used to measure the thermal resistivity of the soils or backfill materials required for underground transmission lines, oil and gas pipelines, radioactive waste disposal and solar thermal storage facilities.

Site investigation are generally done to obtain the information that is useful for one or more of the following purposes:

• To determine the bearing capacity of the soil.
• To select the type of foundation for a given structure.
• To select the depth of the foundation  a given structure.
• To select the suitable construction techniques.
• To determine the ground water level and properties of water.
• To predict the lateral earth pressure against retaining walls.
• To estimate the probable maximum and differential settlements.
• To investigate the safety of the existing structures and to suggest the remedial measures.

Stages Of Site Investigation

1. Site Reconnaissance 
2. Preliminary Explorations
3. Detailed Explorations

Site Reconnaissance

Site reconnaissance is the first step in a site investigation.It includes a vist to the site and to study the maps and other relevant records.It helps in deciding future programme of site investigation, scope of work, methods of exploration to be adopted, type of sample to be taken and the laboratory testing and in-situ testing.

Preliminary Exploration

The main purpose of preliminary exploration is to determine the depth, thickness, extent and composition of each soil stratum at the site.The depth of the bed rock and the ground water table is also determined.The preliminary explorations are generally in the form of a few borings or test pits.Tests are conducted with cone penetrometers and sounding rods to obtain information about the strength and compressibility of soils.

Preliminary site exploration is carried out for small projects, light structures, highways, airfields, etc. The main objective of preliminary exploration is to obtain an approximate picture of sub-soil conditions at low cost. It is also called general site exploration.

Detailed Explorations

The main purpose of detailed explorations is to determine the engineering properties of the soils in different strata.It includes an extensive boring programme, sampling and testing of the sample in a laboratory.Detailed exploration is preferred for complex projects, major engineering works, heavy structures like dams, bridges, high rise buildings, etc. A huge amount of capital is required for a detailed site exploration hence, it is not recommended for minor engineering works where the budget is limited. For such type of works, data collected through preliminary site exploration is enough.

In this stage, numerous field test such as Vane shear test, plate load test and permeability tests are conducted to determine the properties of the soils in natural state.