2.8.2.1 MARBLE ROCK MASS CLASSIFICATION
The karst morphology of a marble rock mass may be interpreted using the marble rock mass classification system given in Table 2.5. Under this system, the marble rock mass is classified in terms of MQD, which is an index devised to measure the degree of dissolution voids and the physical and mechanical implications of fractures or cavity-affected rock mass. MQD should be calculated for each drill hole according to the definition and illustration given in Figure 2.6.
Table 2.5 Classification of Marble Rock Mass
| Marble Class | MQD Range (%) | Rock Mass Quality | Features |
| I | 75 < MQD ≤ 100 | Very Good | Rock with widely spaced fractures and unaffected by dissolution |
| II | 50 < MQD ≤ 75 | Good | Rock slightly affected by dissolution, or slightly fractured rock essentially unaffected by dissolution |
| III | 25 < MQD ≤ 50 | Fair | Fractured rock or rock moderately affected by dissolution |
| IV | 10 < MQD ≤ 25 | Poor | Very fractured rock or rock seriously affected by dissolution |
| V | MQD ≤ 10 | Very Poor | Rock similar to Class IV marble except that cavities can be very large and continuous |
Notes :
- In this system, Class I and Class II rock masses are considered to be a good bearing stratum for foundation purposes, and Class IV and Class V rock masses are generally unsuitable.
- Class III rock mass is of marginal rock quality. At one extreme, the Class III rating may purely be the result of close joint spacings in which case the rock may be able to withstand the usual range of imposed stresses. At the other extreme, the Class III rating may be the result of moderately large cavities in a widely- jointed rock mass. The significance of Class III rock mass would need to be considered in relation to the adjacent drill hole sections in the context of a 3 dimensional model.
- Table 2.5 is not applicable to the marble clast-bearing volcaniclastic rocks.
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