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Disadvantages : |
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Blind zone effect: If  >  , then wave refracts more towards normal then the thickness of the strata is neglected. |
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Error also introduced due to some dissipation of the velocity as longer the path of travel, geophone receives the errorous readings. |
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Error lies in all the assumptions. |
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| 2.1.3 |
Role of geophysical methods in solving geotechnical problems |
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Gravitational and magnetic methods are used in mining and petroleum engineering. In geotechnical engineering, the gravitational method has very limited use for survey of unconsolidated sediments over the dense bedrock. |
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Magnetic method is applied to locate dikes, faults and buried pipes and other concealed magnetic metal works. |
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For dam and bridge sites, to locate depth of the solid rock, seismic and resistivity methods are used. |
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For design of the underwater foundation resistivity method is used. |
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For building sites to locate hard rock strata/ soft strata seismic method is used. |
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Slope design and the landslide investigation can be done using seismic and the resistivity methods. |
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To locate the shallow deposits, seismic and the resistivity methods can be used as in excavation work in sand, gravel deposits etc. |
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Ground water investigation can be done using seismic and resistivity method. |
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In the evaluation of insitu concrete, geophysical methods are used to determine uniformity of concrete. detection of cracking, assessment of rate of corrosion etc. |
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