What is the primary formula for SMR?

SMR = RMR_basic + (F1 × F2 × F3) + F4, where RMR_basic is from IS 13365 (Part 1). (Clause 4.1)

How are the adjustment factors F1, F2, and F3 determined?

They depend on the geometric relationship between the strike and dip of discontinuities and the slope face, as detailed in Table 1.

What does the F4 factor represent?

F4 is an adjustment for the method of excavation, accounting for disturbance. It ranges from +15 for a natural slope to -8 for poor blasting. (Table 2)

What is a 'Fair' slope according to SMR?

A slope with an SMR value between 41 and 60 is classified as 'Fair' (Class III), indicating it is partially stable. (Table 3)

IS 13365

: 2000

The quantitative classification system of rock mass - Guidelines, Part 1: RMR for predicting engineering properties

CurrentSpecializedGuidelinesBIMGeotechnical · Rock Mechanics

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This guideline establishes the Rock Mass Rating (RMR) system, a standardized method for classifying rock masses. It details the process of assigning a numerical rating based on five key parameters: rock strength, RQD, discontinuity spacing, discontinuity condition, and groundwater. The final RMR value helps in determining rock mass quality, predicting its engineering behavior, and providing initial guidelines for excavation and support systems in tunnels and other structures.

The quantitative classification system of rock mass - Guidelines, Part 1: RMR for predicting engineering properties

Quick Reference Values

SMR Class I (Very Good) Range> 80

SMR Class II (Good) Range61 - 80

SMR Class III (Fair) Range41 - 60

SMR Class IV (Poor) Range21 - 40

SMR Class V (Very Poor) Range< 21

F4 Adjustment for Natural Slope+15

F4 Adjustment for Poor Blasting-8

Key Formulas

SMR = RMR_basic + (F1 * F2 * F3) + F4 — Slope Mass Rating Calculation

Practical Notes

The SMR system is an empirical method; its results should always be validated with kinematic analysis and, where necessary, numerical modeling.

Accurate measurement of joint and slope orientation in the field is critical for a reliable SMR calculation.

The RMR_basic value used as input is obtained from IS 13365 (Part 1).