PSI - Issue 32

Ivan Pankov et al. / Procedia Structural Integrity 32 (2021) 166–172 Author name / StructuralIntegrity Procedia 00 (2019) 000 – 000

169

4

in which A is the strength criterion parameter; k 1 , k 2 , k 3 are the influence coefficients, in general, depending on values of the principal stresses and rock strength indicators with different load patterns. The coefficient k 1 is determined by expression ͳ ൌ ͳ ሺ ͳ ൅ ሻ . Accordingly, the strength criterion is accepted in the following form: ͳ ʹ ሺ ͳ ൅ ሻ ൌ А ൅ ʹ ʹ ൅ ͵ ͵ Ǥ ሺͷሻ One of the variants of criterion (5) is an expression with the constant influence coefficients k 2 = C and k 3 = 1 (Pankov, 2020), which is as follows: ͳ ʹ ሺ ͳ ൅ ሻ ൌ ൅ ʹ ൅ ͵ ǡ ሺ͸ሻ in which ǡ ǡ are the strength criterions parameters. According to the conditions (1) – (3), the strength criterion parameters are determined by the formulas: ൌ − Ǣ ሺ͹ሻ ൌ − ͳ ͳ ൅ ͳ Ǣ ሺͺሻ С ൌ ʹ ሺ ʹ − ͳ ሺ ͳ ൅ ͳሻሻ ൅ ʹ Ǥ ሺͻሻ 4. Results and Discussion The developed method has been experimentally verified on various rock types of mining sites in Russia and Kazakhstan. The average results of the complex strength indicator determination, as well as the values of the strength criterion (6) parameters calculated using formulas (7) – (9) are presented in the Table.

Table.The results of a complex determination of the strength indicators and strength criterion parameters for various rock types

Rock

The number of samples

Strength indicators Criterion parameters ǡ ƒ ͳ ǡ ƒ ʹ ǡ ƒ ǡ ƒ ǡ ƒ

Siltstone

8

− 7.1

59.4 99.6 51.1 60.8 34.6 16.9 20.2 23.1

113.6 135.2

7.1

437.6 520.4 384.1 244.7 183.1

0.14 0.09 0.10 0.17 0.19 0.14 0.18 0.31 0.17

Diorite

16

− 16.0

16.0

Sandstone

5 4

− 6.0

79.5 99.5 67.6 25.2 43.5 92.1 17.5

6.0

Andesitic porphyrite Marbleised limestone Carbonaceous siltsotne

− 12.1

12.1

18

− 5.5 − 3.5 − 2.5 − 2.6 − 0.3

5.5 3.5 2.5 2.6 0.3

5 3 6 3

64.7

Rock salt Sylvinite Carnallite

143.0 182.1

4.9

75.1

The tests have been conducted on 9 rock types, 68 samples have been tested. The weakest rocks have been carnallite and carbonaceous siltstone, the strongest ones have been diorite, siltstone and andesitic porphyrite. The analysis has revealed the tendency of ʹ ͳ value to increase when the uniaxial compression strength becomes