Estimation of the thickness of the fractured zone when blasting rock foundations: Fid-Bau Portal

Estimation of the thickness of the fractured zone when blasting rock foundations

Kornilov, A. M. / Panenkov, A. S. / Postnikov, A. T.

Conclusions Strict observance of the technology of drilling and blasting operations on foundation areas adjacent to the planned profile of the cut, proper estimation of the thickness of the fractured zone, and effective organization of operations for the finishing of rock in this zone are quite important conditions for high-quality preparation of the foundation for concreting, on the performance of which depend the strength, stability, longevity, and economic indices of the structure.Of all the methods investigated the seismoacoustic methods are the most rapid and sufficiently reliable for determining the thickness of the fractured zone.Ultrasonic well logging and interhole sound testing permit obtaining the character of the change of the state and properties of the rocks with depth and determining the lower boundary of the fractured zone. In this case the method of ultrasonic interhole testing, which provides the necessary accuracy of determining the thickness of this zone, requires minimum preparatory work, and is highly effective, can be recommended as a rapid method.Seismic profiling in the case of relatively small thicknesses of the fractured zone and comparatively low gradients of the foundation rocks (as is usually the case with the hole method of blasting) can give distorted results.It is best to use the seismic profiling method for estimating the depth for removal of weathered rocks and thickness of the fractured zone when excavating a foundation pit by means of large blasts. In this case the thickness of the manual finishing zone should be determined more exactly by the ultrasonic interhole sound-testing method.