Indirect methods of soil exploration:
The magnetic and gravitational methods are less preferable with the viewpoint of geotechnical investigation. The reason is that these methods are used for very large areas. In geotechnical investigations geophysical methods are more frequently preferred. The efficiency of these methods depends upon our ability to locate the boundaries of strata of different distinct compositions, with the detection of the wave velocity or the electrical resistivity of the soil.
Thus indirect methods of soil exploration do not provide us any information about the engineering properties of the materials that are encountered. They are to be used in conjunction with the boring. The names of these methods are given below:
- Seismic methods:
This method cannot be used when lower stratum velocity is less than the upper material.
- Electrical resistivity methods:
It is based on difference of ER.