Abstract
This chapter focusses on geophysical survey techniques, employed in engineering geological investigations and it includes case studies. Goal of a geophysical study in an engineering geological research is to display discontinuities in the rock masses, physico-mechanical properties of soils and rocks, groundwater exploration, faults, landslides, etc. It is also helpful to learn type and thickness of soil, layer inclination. These techniques include engineering geological surface mapping, geotechnical drilling and in situ testing.Then the obtained geophysical field data are analyzed and interpreted in conjunction with the results of geological information.The most common geophysical methods namely seismic, magnetometric, vertical electrical sounding (VES), Very Low Frequency (VLF) Electromagnetics methods, ground penetration radar (GPR) provide sufficient information about the subsurface although they have their limitations, setting up the minimum tests requirements in relation to the type of the geological formations.
Top1. Introduction
This chapter focusses on geophysical survey techniques, employed in engineering geological investigations and it includes case studies. Goal of a geophysical study in an engineering geological research is to display discontinuities in the rock masses, physico-mechanical properties of soils and rocks, groundwater exploration, faults, landslides etc. This chapter is beneficial not only for students but also the geological/geotechnical engineers and the contractors to find out the relevant geophysical method(s). Using the geophysical methods in such problems can clear the static and dynamic geotechnical parameters. It is also helpful to learn type and thickness of soil, layer inclination. These techniques include engineering geology surface mapping, geotechnical drilling and in situ testing.
In order to analysis the geophysical studies assume that the medium are homogeneous and the obtained geotechnical parameters reflect the average values of the related medium. Then the obtained geophysical field data are analyzed and interpreted in conjunction with the results of geological information.
The most common geophysical methods namely seismic, magnetometric, vertical electrical sounding (VES), Very Low Frequency (VLF) Electromagnetics methods, ground penetration radar (GPR) provide sufficient information about the subsurface although they have their limitations, setting up the minimum tests requirements in relation to the type of the geological formations. The weakness zones with a nearly vertical orientation are defined by these methods. The VES and seismic methods are most appropriate for vertical delineation of discontinuities. Weathering zones are recognized by lower wave propagation velocities, whereas the resistivity may differ depends on fluctuating hydrogeological conditions. There are different groundwater exploration methods in geophysics and hydrogeology. Groundwater exploration in these disciplines is based on the identifying underground formations, hydrologic cycle, groundwater quality, and detection of nature, number and type of aquifers. Surface geophysical methods, especially electrical and electromagnetic techniques are also commonly employed the groundwater investigation methods.
Geophysical tecniques applied by geophysic engineers are becoming popular in the geology, environmental, archeological and civil engineering fields. We will give some field applications samples that where the geophysical techniques are effectively use such as problems. Geophysical tecniques can solve the problems of engineering and hydrogeology works are used very effective. However, we prepare this chapter with using geophysical tecniques such as magnetic, resistivity, electromagnetic, seismic refraction tecniques applied in engineering problems such as in enginering geology, geotechnics, soil-rock mechanics, water and environmental engineering areas. Some data like depth of underground water and subsurface layers, thickness of soils-rocks in the related engineering branchs can be tracked and assessed by the geophysical tecniques of which commonly gravity, resistivity, magnetic, seismic, electromagnetic and ground penetration radar (GPR).
The physico-mechanical properties of ground can be obtained by the geophysical tecniques relatively in short times and economically. Inherently, a geophysical survey planning could be implemented by a geophysicst. This chapter was prepared different engineering problems the geophysical tecniques of resistivity, magnetic, seismic, electromagnetic and ground penetration radar (GPR), which can be applied in engineering geology, Geotechnical Engineering, Rock Mechanics and Engineering.
The methods employed in the case studies of engineering geology and geotecnical works were performed in Denizli, Turkey. The engaged geophysical methods in this chapter are magnetic susceptibility, vibrators, resistivity and seismic refraction methods.
Key Terms in this Chapter
Weathering Zones: A distinctive layer of weathered material that extends roughly parallel to the ground surface. It differs physically, chemically, and mineralogically from the layers above and/or below. A broad distinction may be drawn between the weathering zones in drift, which are normally distinguished by degrees of oxidation and by carbonate content, and those on bedrock, which are usually separated according to the relative proportions of corestones and weathered matrix.
Denizli: Is an industrial city in the southwestern part of Turkey and the eastern end of the alluvial valley formed by the river Büyük Menderes, where the plain reaches an elevation of about three hundred and fifty metres (1,148 ft). Denizli is located in the country's Aegean Region.
Vertical Electrical Sounding (VES): Is a geophysical method for investigation of a geological medium. The method is based on the estimation of the electrical conductivity or resistivity of the medium. Electromagnetics methods.
Dynamic Geotechnical Parameters: Geotechnical investigations are performed by geotechnical engineers or engineering geologists to obtain information on the physical properties of soil and rock around a site to design earthworks and foundations for proposed structures and for repair of distress to earthworks and structures caused by subsurface conditions.
Seismic Tecniques: Reflection seismology (or seismic reflection) is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflected seismic waves.
Magnetic Tecniques: These tecniques are that dimensions, and amplitude of an induced magnetic anomaly is a function of the orientation, geometry, size, depth, and magneticsusceptibility of the body as well as the intensity and inclination of the earth's magnetic field in the survey area.
Geophysical Tecniques: Exploration geophysics is an applied branch of geophysics, which uses physical methods, such as seismic, gravitational, magnetic, electrical and electromagnetic at the surface of the Earth to measure the physical properties of the subsurface, along with the anomalies in those properties.
The Groundwater Investigation: Groundwater Exploration project pass through various surveys. The main objective of these surveys is to study and understand the hydrological cycle of the region, to understand overall concept of type, nature, no: aquifers and quality of groundwater.
Ground-Penetrating Radar (GPR): Is a geophysical method that uses radar pulses to image the subsurface. This nondestructive method uses electromagnetic radiation in the microwave band (UHF/VHF frequencies) of the radio spectrum, and detects the reflected signals from subsurface structures.