This standard outlines the code of practice for conducting in-situ seismic tests within boreholes to determine the compressional (P-wave) and shear (S-wave) velocities of rock mass. These velocities are used to calculate dynamic elastic properties like Young's modulus, shear modulus, and Poisson's ratio, which are critical for the design of major structures founded on or in rock, such as dams, tunnels, and power plants.
Code of practice for seismic testing of rock mass, Part 1: Within a borehole
Quick Reference Values
Typical P-wave velocity in competent rock3000-6000 m/s
Typical S-wave velocity in competent rock1500-3500 m/s
Typical Dynamic Poisson's Ratio in rock0.15 - 0.35
Key Formulas
Vp = L/t_p — P-wave velocity from travel time
μd = [ (Vp/Vs)^2 - 2 ] / [ 2 * ( (Vp/Vs)^2 - 1 ) ] — Dynamic Poisson's Ratio
Ed = ρ * Vs^2 * (3*Vp^2 - 4*Vs^2) / (Vp^2 - Vs^2) — Dynamic Young's Modulus
Practical Notes
Proper coupling of geophones to the borehole wall is critical for good signal quality.
Accurate surveying of borehole deviation is essential, as velocity calculations depend on the precise source-to-receiver distance.
The energy source (e.g., sparker, mechanical hammer) should be chosen based on rock conditions and required penetration depth.