Explain briefly types and method of Geological Investigation:

The types of geological investigation are as follows:

1. Surface Investigation and

2. Subsurface investigation

Surface investigation:

 In this type of site investigation, data are collected from the surface which can be done by two methods:

1. Direct method and 

2. Indirect method

Direct methods:

 In this method, direct field visits are made and data are collected by observations, measurements and photography. The data includes information about:

1.  Lithology

2.  Soil and rock types, strength etc.

3.  Weathering grade of rocks.

4.  Folds, faults, joints etc.

5.  Landslides and geohazards .

Indirect methods:

Investigation in which preliminary data are obtained about any specific site without visiting directly in the site is....Show More

The types of geological investigation are as follows:

1. Surface Investigation and

2. Subsurface investigation

Surface investigation:

 In this type of site investigation, data are collected from the surface which can be done by two methods:

1. Direct method and 

2. Indirect method

Direct methods:

 In this method, direct field visits are made and data are collected by observations, measurements and photography. The data includes information about:

1.  Lithology

2.  Soil and rock types, strength etc.

3.  Weathering grade of rocks.

4.  Folds, faults, joints etc.

5.  Landslides and geohazards .

Indirect methods:

Investigation in which preliminary data are obtained about any specific site without visiting directly in the site is termed as indirect method. There may be different means by which such investigation can be carried out:

 Literature review:

The study of existing books, articles, maps and previous reports of project area is known as literature review.

 Map analysis:

The study and analysis of available topographic map, aerial photographs and satellite images to evaluate terrain, slope orientation, drainage and other geomorphic feature is known as map analysis.

 Subsurface investigation:

 In this type of Investigation, subsurface details are done. This is generally done after site investigation. It is done by two methods:

1.  Direct subsurface investigation and

2.  Indirect subsurface investigation

 Direct subsurface investigation:

Direct contact with the subsurface details are made in this method. This method helps in:

1. Determination of depth, thickness, types of rocks and soil.

2. Identification of weathering grade.

3. Prediction of GWT conditions.

4. Prediction of presence of aquifers.

 This method includes the following parameters:

1. Excavation works.

2. Drilling of boreholes.

Indirect Subsurface Investigation:
It is the type of Investigation in which  sub-surface data are obtained without direct contact with subsurface materials and structures. This method helps in:

1. Predictions of presence of aquifers.

2. Determination of GWT.

3. Finding discontinuities.

 Various indirect methods of site investigations are:

  Seismic method:

 The velocity of Elastic waves produced by shocks are analysed and compared for different subsurface structure to obtain the information or data.

 Gravity survey:

 The normal `g` calculated using altitude and the observed `g` by experiment are compared. Considerable difference shows the presence of unusual rock mass below the place.

 Electrical method:

 Resistivity, electro-chemical activity and dielectric constant are compared to obtain the data.

 Magnetic method:
The observed and theoretical values of magnetic intensity are compared to obtain and interpret the data.