Soil Investigation : Purposes and Stages

Soil Exploration or Soil Investigation -

Soil Exploration or Soil Investigation are done for obtaining the information about subsurface conditions at the site of proposed construction. Site investigation is generally required for every big engineering project.

Purposes of Soil Investigation -

Site investigations are generally done to obtain the information that is used for one or more of the following Purposes –

• To select the type and depth of foundation for a given structure.

• To determine the bearing capacity of the soil.

• To estimate the probable maximum and differential settlements.

• To estimate the groundwater level and to determine the properties of water.

• To predict the lateral earth pressure against retaining walls and abutments.

• To select suitable construction techniques.

• To predict and to solve potential foundation problem.

•  To ascertain the suitability of soil as a construction material.

• To investigate the safety of the existing structure and to suggest the remedial measures.

 

 

Stages in sub surface exploration or soil exploration -

 Soil exploration or Soil investigation is generally carried out in three stages -

1. Reconnaissance
2. Preliminary exploration
3. Detailed exploration

1. Reconnaissance -

Site Reconnaissance is the first step in a sub-surface exploration program. It includes a visit to the site and to study the maps and other relevant records. 

It helps in deciding future program of site investigations, scope of work, method of exploration to be avoid adapted, type of samples to be taken and the laboratory testing and in-situ testing.

 

2. Preliminary exploration -

The aim of a Preliminary exploration is to determine the depth, thickness, extent and composition of each soil stratum at the site. The depth of the bedrock and the groundwater table is also determined.

The preliminary exploration is 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 soil. Geophysical methods are also used in preliminary exploration for locating the boundaries of different strata.

 

3. Detailed exploration -

The purpose of the detailed exploration is to determine the engineering properties of the soil in different strata. It includes an expensive boring program, sampling and testing of soil samples in a laboratory.

Field tests such as vane shear tests, plate load tests and permeability test are conducted to determine the properties of the soils in natural state. The tests for determination of dynamic properties, are also carried out if required,

For complex projects involving heavy structures such as bridges, dams, multi-story buildings, it is essential to have detailed exploration.

Methods of Soil Exploration: Open -

excavation, boring & Geophysical methods