The x-t coordinate system in Figure 2 shows times of first arrivals of waves to individual geophones from the moment the wave was generated. Analysis of thus changed properties of seismic waves therefore allows determining the tectonic structure of the underground, lithological composition of underground strata, and in favorable circumstances also directly locating reservoirs of oil and gas. Successful application of seismic methods is based on the fact that underground layers have different elastic properties and density that directly depend on their lithological composition. įigure 1 The principle of seismic refraction To initiate mechanical force, explosives, hammer, weight drop or other source of impulse are used.
Waves along paths of their propagation from the source to refractor (or reflector) to receivers. Times elapsed from sending to receiving a seismic wave depend on depths of studied structures and velocities of propagation of seismic 1 In other words, under the influence of an impulse, particles of matter in the underground begin to vibrate in the direction of seismic wave propagation, if waves are longitudinal or P-waves, or perpendicularly to this direction, in case of transverse or S-waves, while not changing their positions in the medium through which the elastic waves propagate and transmit mechanical energy from one point to another (Figure 1).
Under the influence of an external impulse, particles of matter in the underground move from their original positions toward each other and collide, and thereby transmit mechanical motion underground from one point to another. The applied seismic methods comprise sending impulses underground and registering the consequent arrivals, refracted from subsurface interfaces by a number of detectors laid out at or near the surface. The big advantage of geophysical methods is that instruments are relatively inexpensive, and investigations are much faster and cheaper than conventional investigations - exploratory drilling. INTRODUCTION Geophysical studies are measurements of physical quantities (resistance, speed of propagation of sound, density, magnetism, conductivity, etc.) aimed at identifying comprehensively the rock mass structure and lithology characteristics to be used in geotechnical studies, water investigations, etc. Results of geophysical investigations should be included in the data obtained by geological mapping, which will in correlation with drilling results complete the picture of geological structure of terrain and facilitate categorization of materials and rocks for the purpose of developing the engineering and hydrogeological profile as a base for designers in the project execution stage. Both examples are presentations of an optimum program of exploratory boring supplemented by results of deep seismic refraction studies. This paper presents two examples of preparation of seismic sections as a basis for geotechnical design of foundations.
Times elapsed from sending to receiving seismic waves depend on depths of studied structures and propagation velocities of seismic waves along paths of their propagation from the source to the refractor (or reflector) to the receiver. Applied seismic methods comprise sending impulses underground and registering the resulting refracted arrivals from subsurface interfaces on a number of receivers positioned on or near the surface. Seismic Refraction Method Ivana Lukić1, Davor Barać2, Danijela Zovko3 1įaculty of Civil Engineering, University of Mostar, Bosnia and Herzegovina Department of Planning, Studies and Environmental Protection, Institut IGH, d.d.,Croatia 3 Integra d.o.o., Mostar, Bosnia and Herzegovina 2ĪBSTRACT Seismic methods are applied primarily in order to determine quasi-homogeneous zones according to parameters of fragmentation, physical and chemical weathering and deformability of rock masses and cohesionless soil. International Balkans Conference on Challenges of Civil Engineering, BCCCE, 19-, EPOKA University, Tirana, ALBANIA.
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