- Email: [email protected]
Crosshole seismics and seismic tomography
275
The project includes the development of the most appropriate source and field procedure. Furthermore, software for data-processing with a microcomputer has been prepared. Examples of the main problems of the practical interpretation of the processed seismic sections are given.
Seismic Crosshole Measurements in Crystalline Rock MONICA HAMMARSTROM,
SVEN IVANSSON, PER MORfiN and JORGEN PIHL
Division of Applied Seismology, National Defence Research Institute, Stockholm (Sweden)
Box 27322, S-102 54
Seismic crosshole techniques for detection of fracture zones in crystalline rock have been developed and tested as a part of the International Stripa project. Seismic signals are generated in one borehole by microexplosions and recorded in another hole by an array of receiving units, separated by 10 m. Each unit consists of three accelerometers for measurements in the three principal directions. Seismic crosshole measurements have been performed in granite in the Stripa mine. The recording distances are up to 250 m. Tomographic inversion applied to the P-wave traveltimes gives a map of the velocity structures of the rock volume. The results are compared with other geophysical crosshole methods, geophysical borehole-loggings and with geological observations.
Crosshole Seismics and Seismic Tomography T.L. BY Norwegian Geotechnical Institute,
P.O.B. 40 Taasen, 0801 Oslo 8 (Norway)
The crosshole seismic method represents a unique opportunity to explore the interior of the ground. The method is especially favourable where one wishes to assess poor quality zones within rockmasses. By means of seismic tomography, features with variable rock qualities can easily be detected through careful interpretation of the tomographic plots. The quality criteria are normally the seismic P- and S-wave velocities, or more correctly the travel times of the transferred waves. Other parameters as first arrival amplitude, rise time, rise velocity and frequency content of transferred waves are used to complete the information.
276
A complete crosshole seismic set-up consists of a pulse transmitter, one or several receivers and a data acquisition and processing system. Seismic tomography is completed in 8 profiles along the two projected future main road tunnels crossing from east to west under the city of Oslo. Crosshole seismic measurements are performed to evaluate the overburden and the ground conditions. Conclusions from this investigation are included in the decision base concerning the exact location of the tunnels.
Measurements
of Vibrations
from Rock Blasting
SIGURD LUNESTAD Norges Geotekniske Institutt, Postboks 40 Tmsen, 0801 Oslo 8 (Norway,J
In rock blasting, seismic waves are generated. The explosive charges are initiated by delayed detonators with intervals of 25-500 ms. The duration of a round is 500-600 ms at surface blasting, 5-6 s at underground blasting. From experience and theoretical considerations there are criteria for vibrations levels that can be tolerated without damage to buildings, defects in instrumentations and complaints from people. Several proposals to standards are made (i.e. DIN 4150, ISO/DIS 2631/2) concerning vibrations of buildings and the influence on people. Producers of sensitive equipment (i.e. EDB) recommend limits of environmental vibrations. For buildings and structures peak particle velocity (ppv - mm/s) and peak particle displacements (A - ,um ) are recommended parameters to be measured. Limiting values are in the order of 2-100 mm/s and lo-200 pm. The frequencies vary from 4-5 up to 400-500 Hz. Concerning sensitive equipment (EDB etc.) acceleration measurements are often recommended. An acceleration limit of 0.25 g has been widely used. In Sweden a limit of 20 mm/s ppv is proposed. Estimation of vibration levels, is based on the relation: v=kQ”.@se
-yR
which can be simplified u = /z,, 7&
(velocity)
to:
or A = k, 7&
(displacement)
A short revue of the vibration measurements proposed to be carried out at the tunnel works for the E 18 through Oslo, will be given.
The project includes the development of the most appropriate source and field procedure. Furthermore, software for data-processing with a microcomputer has been prepared. Examples of the main problems of the practical interpretation of the processed seismic sections are given.
Seismic Crosshole Measurements in Crystalline Rock MONICA HAMMARSTROM,
SVEN IVANSSON, PER MORfiN and JORGEN PIHL
Division of Applied Seismology, National Defence Research Institute, Stockholm (Sweden)
Box 27322, S-102 54
Seismic crosshole techniques for detection of fracture zones in crystalline rock have been developed and tested as a part of the International Stripa project. Seismic signals are generated in one borehole by microexplosions and recorded in another hole by an array of receiving units, separated by 10 m. Each unit consists of three accelerometers for measurements in the three principal directions. Seismic crosshole measurements have been performed in granite in the Stripa mine. The recording distances are up to 250 m. Tomographic inversion applied to the P-wave traveltimes gives a map of the velocity structures of the rock volume. The results are compared with other geophysical crosshole methods, geophysical borehole-loggings and with geological observations.
Crosshole Seismics and Seismic Tomography T.L. BY Norwegian Geotechnical Institute,
P.O.B. 40 Taasen, 0801 Oslo 8 (Norway)
The crosshole seismic method represents a unique opportunity to explore the interior of the ground. The method is especially favourable where one wishes to assess poor quality zones within rockmasses. By means of seismic tomography, features with variable rock qualities can easily be detected through careful interpretation of the tomographic plots. The quality criteria are normally the seismic P- and S-wave velocities, or more correctly the travel times of the transferred waves. Other parameters as first arrival amplitude, rise time, rise velocity and frequency content of transferred waves are used to complete the information.
276
A complete crosshole seismic set-up consists of a pulse transmitter, one or several receivers and a data acquisition and processing system. Seismic tomography is completed in 8 profiles along the two projected future main road tunnels crossing from east to west under the city of Oslo. Crosshole seismic measurements are performed to evaluate the overburden and the ground conditions. Conclusions from this investigation are included in the decision base concerning the exact location of the tunnels.
Measurements
of Vibrations
from Rock Blasting
SIGURD LUNESTAD Norges Geotekniske Institutt, Postboks 40 Tmsen, 0801 Oslo 8 (Norway,J
In rock blasting, seismic waves are generated. The explosive charges are initiated by delayed detonators with intervals of 25-500 ms. The duration of a round is 500-600 ms at surface blasting, 5-6 s at underground blasting. From experience and theoretical considerations there are criteria for vibrations levels that can be tolerated without damage to buildings, defects in instrumentations and complaints from people. Several proposals to standards are made (i.e. DIN 4150, ISO/DIS 2631/2) concerning vibrations of buildings and the influence on people. Producers of sensitive equipment (i.e. EDB) recommend limits of environmental vibrations. For buildings and structures peak particle velocity (ppv - mm/s) and peak particle displacements (A - ,um ) are recommended parameters to be measured. Limiting values are in the order of 2-100 mm/s and lo-200 pm. The frequencies vary from 4-5 up to 400-500 Hz. Concerning sensitive equipment (EDB etc.) acceleration measurements are often recommended. An acceleration limit of 0.25 g has been widely used. In Sweden a limit of 20 mm/s ppv is proposed. Estimation of vibration levels, is based on the relation: v=kQ”.@se
-yR
which can be simplified u = /z,, 7&
(velocity)
to:
or A = k, 7&
(displacement)
A short revue of the vibration measurements proposed to be carried out at the tunnel works for the E 18 through Oslo, will be given.