Rock mass assessment from seismic measurements

Abstract

An important part of many site investigations is the geomechanical assessment of the rock mass in terms of a classification system which is independent of the user. All classification systems used to date are based on observation of the rock mass and the determination of simple engineering parameters on intact rock specimens. In this paper, the use of the seismic properties of the rock mass to assess the geomechanical performance of the rock mass are examined and illustrated by three case histories. It is shown that precise values of uniaxial compressive strength cannot be predicted from compressional wave velocity determinations, although rock types can be classified qualitatively (for example, weak to very weak or strong to very strong). For a specific lithology, the compressional wave velocity can be related to the degree of fracturing and an approximate relationship with RQD established.

The Relationships between Effective Porosity, Uniaxial Compressive Strength and Sonic Velocity of Intact Borrowdale Volcanic Group Core Samples from Sellafield

“…The regression coefficients (r 2 ) of the three relationships (Table 3) are all above 0.7 for 256 points. The highest r 2 value is for the Log 10 regression line, which is plotted on (1965) and McCann et al (1990). The plot suggests that the sonic velocity may be used to find a limiting maximum strength.…”

“…discontinuities caused for example by fractures, jointing and infilled mineral veins, it can be used as a part of the assessment of the rock mass such as Rock Quality Designation (RQD) (Glenn & Nelson, 1979, McCann 1990. McCann et al (1981) introduced the concept of a simplified rock mass classification system based on the dynamic bulk modulus of the rock mass from sonic and shear velocity.…”

“…To this end, data from the laboratory tests described in this paper have been analysed for a series of relationships between the parameters including effective porosity, sonic velocity, effective porosity and uniaxial compressive strength. The relationship between uniaxial compressive strength and sonic velocity was investigated by D'Andrea et al (1965) for various rock types from the United States of America and by McCann et al (1990) for a wide range of British rock types. McCann et al (1990) found a good coefficient of regression (r 2 of 0.88, 150 data points) for a power model (y = ax b ).…”

“…The relationship between uniaxial compressive strength and sonic velocity was investigated by D'Andrea et al (1965) for various rock types from the United States of America and by McCann et al (1990) for a wide range of British rock types. McCann et al (1990) found a good coefficient of regression (r 2 of 0.88, 150 data points) for a power model (y = ax b ). However, the individual points were well scattered, particularly at low porosity values.…”

Field testing methods for engineering geological investigations

“…D' Andrea et al (1965) compared the compressional wave velocities measured for a range of American rocks with their uniaxial compressive strengths. Whilst a correlation can be obtained, a similar comparison for a wider range of British rocks showed that a broad range of velocities can be obtained for weak rocks of fairly uniform strength and, conversely, for very strong rocks, velocity remains fairly constant despite large variations in strength values (McCann et al 1990). (1983) as one of the parameters for the determination of liquefaction potential.…”