Stanford Rock Physics Laboratory - Gary Mavko. Parameters That Influence Seismic Velocity. Replace Gas with Water. Gas Water Difference. Increase Pp by. PDF | Rippability or ease of excavation in sedimentary rocks is a significant site for the development of a water reservoir and related infrastructure in Kampus Pauh with the seismic velocity method to provide appropriate correlation. The seismic velocity profile obtained was used to interpret rock layers. site for the development of a water reservoir and related infrastructure in Kampus Pauh The seismic velocity profile obtained was used to interpret rock layers within the . methods were conducted to establish correlation between the rock.
Frequent planes of weakness such as fractures, faults, and laminations. Rocks with moisture permeating the formations. Rocks with low "shear strength. Conditions that make ripping difficult are as follows: Rocks with no planes of weakness. Non-brittle energy absorbing rock fabrics. Rocks with high "shear strengths. The above rippability criteria are presented by The Caterpillar Company in a book titled Handbook of Ripping. Rippability versus seismic velocity.
Handbook of Ripping, 8 th Edition Figure 1 shows the rippability of various rock types for different seismic velocities using a D9 Caterpillar tractor. Seismic Refraction Basic Concept: The seismic refraction method can be used to find rock velocities. The method requires a seismic energy source, usually a hammer for depths of less than 15 meters and explosives for depths to 30 meters. The seismic waves then propagate through the overburden and refract along the bedrock surface.
While they are traveling along this surface, they continually refract seismic waves back to the ground surface. These refractions are then detected by geophones placed on the ground surface.
Figure 2 shows the layout of the instrument, the geometry of the seismic refraction procedure, and the corresponding time-distance graph that is used in data processing. The design of a seismic refraction survey involves 1 location of survey, 2 geophone spacing, and 3 the spread cable length. Surveys should be recorded on days with little wind, away from traffic and other sources of noise and vibrations.
In addition, since some of the noise travels as airwaves, covering the geophones with sound- absorbing material partially filled sandbag may help dampen unwanted noise and enhance coupling of the geophones to the ground.
In general, refraction spreads need to have a length at least three times the desired depth of investigation, which, if investigating to depths of 20 meters, will be 60 meters. If a 24 channel seismic system is used, a geophone spacing of 3 meters, giving a spread length of about 70 meters, will be sufficient, and will also provide velocities for shallower bedrock layers.
Both refractor depth and velocity can be obtained from the seismic data. Generally, geophones having a natural frequency of less than about 10 Hz will be used. A plot is then made showing the arrival times against distance between the shot and geophone. This is called a time-distance graph.
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Correlation between P-wave velocity and some mechanical properties for sedimentary rocks
Note the relatively large lateral velocity changes in the chalk. This is a fairly large data set for an engineering project. How many geophones were used for each spread, and what was their spacing? How many spreads were involved in the entire survey? How many of the shots fired into the eastern-most spread were located further east from location 0?
How many shots were detected by the geophone at location 0? Shear wave refraction This record was recorded using geophones mounted horizontally and transverse to the profile. To generate the shear wave signal a metal bar with fins to anchor it to the ground was placed transverse to the profile, then struck with a hammer on either end. Records from these two shots were subtracted so as to increase signal-to-noise ratio.