**5. Structural mapping of the Bedrock**

The structural setting of the bedrock (possible fault location, fracture, joints, buried river channels etc.) can be investigated with the seismic and electrical resistivity method. Fractures in bedrock occur most often in competent rocks unable to adjust to the stresses placed upon them. Fractures in bedrock are characterized by moisture making them more electrically conductive than a non-fractured bedrock. Fractured region may be topographically more depressed than the surrounding unfractured bedrock.

### **6. Location of construction materials**

Electrical resistivity profiling method is mainly used in the search for sand and gravel deposits needed for construction projects. The data can be inverted to depict the resistivity variation, both laterally and vertically, against depth. The lowresistivity area (less than 20 ohm-m) corresponds to clay layers and high-resistivity zones (greater than 100 ohm-m) correspond to sand and gravel lenses.

*Geophysical Investigations for Design Parameters Related to Geotechnical Engineering DOI: http://dx.doi.org/10.5772/intechopen.108712*

### **7. Soil corrosivity**

Corrosivity is defined as soil's ability to corrode a material that may be buried in it. As soils at building site would normally host metallic pipes etc., it becomes mandatory that a well-organized site testing exercise be carried out to evaluate soil aggressivity (corrosivity) taking into consideration the type of materials to be buried in it. The degree of corrosivity of the soil can be predicted using the electrical resistivity values. The electrical resistivity values of the top soil at the site can be used to assess the corrosivity of the soil of that site. Soils with resistivity values of less or equal to 10 ohm-m are strongly corrosive. Soils with resistivity values ranging between 10 and 60 ohm-m are moderately corrosive while those with resistivity between 60 and 180 ohm-m are slightly corrosive. Soils with resistivity values greater than 180 ohm-m are practically non corrosive.

### **8. Site subsoil competence**

The strength of any geological material is influenced by several factors such as the mineralogy of its particles, the character of the particle contrast and agents of weathering. However, in a given locality, apparent resistivity values can be used for the evaluation of earth materials and their competence. Materials underlying a site can be judged to be generally competent or incompetent. High apparent resistivity zones are said to be competent in comparison with regions of relatively low resistivity values. Certain ranges of apparent resistivity values can be correlated with lithologic competence.

### **9. Mapping of seepage zones**

Earth and rock-fill dams are large civil engineering structures designed to impound surface water. The design of dams makes provisions for control seepage and spillage. In spite of advances made in the field of geotechnical engineering, it is not possible to have 100% leak-proof structure. Anomalous seepages may sometimes occur through permeable soils, rock aquifers controlled by their structural bedrock topography and fault/joints structures. Geophysical method play an important role in mapping seepage paths and monitoring the changes of the seepage with time, enabling to plan technically and economically worthwhile remedial measures

### **10. Magnetic prospecting method**

The origin of the earth's magnetism is commonly believed to be the liquid part of the earth's core, which cools at the outside as a result of which material becomes denser and sinks towards the inside of the outer core and new warm liquid matter rises to the outside; thus, convection currents are generated by liquid metallic matter which move through a weak cosmic magnetic field which subsequently generates induction currents. It is this induction current that generate the earth's crust magnetic field. Most rocks of the earth's crust contain crystals with magnetic minerals; thus most rocks have a certain amount of magnetism, which usually has two components induced by the magnetic field present while taking measurement, and remanent

which is formed during geologic history [8]. The aim of magnetic survey is to investigate subsurface geology on the basis of anomalies in the Earth's magnetic field resulting from the magnetic properties of the rocks [9]. Although most rock-forming minerals are effectively nonmagnetic, certain rock types contain sufficient magnetic minerals to produce significant magnetic anomalies. An observed anomalous magnetization might be associated with buried magnetic objects that are potentially of commercial interest. Anomalies recorded in the measured field are interpreted in terms of variations in magnetic susceptibility and/or remanent magnetism, the physical rock properties affecting the measurements. Magnetic susceptibility is the physical property on which the response of magnetic method is based, and it is the property whose distribution we are trying to investigate.
