This code of practice outlines the methodology for conducting seismic tests on rock masses situated between boreholes, commonly called the crosshole seismic technique. It provides guidelines for determining P-wave and S-wave velocities, attenuation, and dynamic elastic properties, critical for geotechnical and seismic engineering evaluations. The standard serves as a reference for specialists performing in-situ seismic assessments to characterize rock mass mechanical behavior.
Overview
This code of practice outlines the methodology for conducting seismic tests on rock masses situated between boreholes, commonly called the crosshole seismic technique. It provides guidelines for determining P-wave and S-wave velocities, attenuation, and dynamic elastic properties, critical for geotechnical and seismic engineering evaluations. The standard serves as a reference for specialists performing in-situ seismic assessments to characterize rock mass mechanical behavior.
Audience
Contents
Structure
Frequently Asked
The standard advises selecting seismic sources based on the wave type required. For P-waves, suitable sources include air guns, explosives, sparkers, downhole hammers, piezoelectric vibrators, and magnetostrictive devices. SH-waves are typically generated using downhole hammers or piezoelectric vibrators. SV-waves can be produced by explosives, air guns, sparkers, downhole hammers, or piezoelectric vibrators. The chosen source depends on the wave type, site conditions, and desired frequency range, generally between 10 Hz and 2 kHz.
Velocities of P and S waves are determined by measuring the travel time of seismic waves between source and receiver points in boreholes. The travel time is recorded from the initiation of the seismic source to the arrival of the first break of the corresponding wave on the seismogram. Distances between source and receiver are precisely surveyed. Velocity is then calculated using the formula V = D/t, where D is distance and t is travel time. Measurements often involve multiple receivers spaced at intervals of 0.5 to 5 meters to ensure accuracy.
Critical equipment includes seismic sources tailored to the required wave type (P, SH, SV) such as explosives, air guns, sparkers, downhole hammers, piezoelectric vibrators, and magnetostrictive sources. Receivers comprise geophones (sensitive to particle velocity), piezoelectric accelerometers (sensitive to acceleration), and hydrophones (for water-filled boreholes detecting pressure variations). A triaxial receiver array, consisting of one vertical and two orthogonal horizontal sensors, is recommended for wave identification. Additional apparatus includes mounting and surveying tools, amplifiers with gains between 70 to 130 dB, signal enhancement units, precise timing devices with intervals of 0.1, 1, or 10 ms, a time break unit, and analog or digital recording devices such as electromagnetic oscillographs.
The dynamic elastic modulus is calculated using measured P-wave and S-wave velocities along with the rock density. First, the dynamic Poisson's ratio is computed via the ratio of these velocities. Shear modulus (Gd) is determined from the product of density and squared S-wave velocity. Bulk modulus (Kd) is derived from density times the difference between squared P-wave velocity and four-thirds of squared S-wave velocity. Finally, the dynamic Young's modulus (Ed) can be calculated either as twice the shear modulus times one plus Poisson's ratio or thrice the bulk modulus times one minus twice Poisson's ratio. This process yields reliable estimates of the rock mass's elastic properties.
Boreholes should be strategically drilled considering geological and topographical factors. Uncased holes are preferred; if casing is necessary, low-velocity materials like high-impact PVC should be used and properly grouted for intimate contact with the rock. Borehole spacing must balance coverage and avoid excessive distances that may capture refracted waves. Precise surveying of hole location, depth, inclination, and deviation is essential. Receivers should be firmly placed against borehole walls, except in water-filled holes where suspension receivers may be employed. A triaxial receiver configuration—one vertical and two horizontal sensors at right angles—is recommended. Measurement intervals between receivers commonly range from 0.5 to 5 meters to ensure accurate velocity determination.
Ask AI about any clause, requirement, or provision in IS 13372 PART 2. Get instant, clause-cited responses powered by our indexed library.
Free tier includes 150 queries (50 AI + 100 Reference) · No credit card required