Module 1 : Site Exploration and Geotechnical Investigation
Lecture 2 : Boring Methods of Exploration [ Section 2.1 : Different Types of Boring Methods ]
These waves are classified as direct, reflected and refracted waves. The direct wave travel in approximately straight line from the source of impulse. The reflected and refracted wave undergoes a change in direction when they encounter a boundary separating media of different seismic velocities (Refer fig. 1.7). This method is more suited to the shallow explorations for civil engineering purpose. The time required for the impulse to travel from the shot point to various points on the ground surface is determined by means of geophones which transform the vibrations into electrical currents and transmit them to a recording unit or oscillograph, equipped with a timing mechanism.
Assumptions
The various assumptions involved are:
All soil layers are horizontal.
The layer is sufficiently thick to produce a response.
Each layer is homogeneous and isotropic.
Velocity should increase with depth, following the Snell's law as given in fig. 1.6.
is the angle of incidence, 
is the angle of refraction, 
and 
are the velocity in two different mediums. 
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