PSI - Issue 32

Artem Udartsev et al. / Procedia Structural Integrity 32 (2021) 187–193 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

191

5

Fig. 6. An example of typical carnallite creep curvesobtained at different values of the lateral pressure

The deformation rate of the salt specimens was estimated at the stage of the steady-state creep, characterized by a constant rate. The results related to the rates of the steady-state creep of sylvinite and carnallite are given in Table 2.

Deformation rate ( ͳ ), 10 -2 · day -1 Silvinite

Table 2. Rates of the steady-state creep of the specimens of sylvinite and carnallite, GPD

Loading degree

Carnallite  3 =0 MPa

 3 =0 MPa

 3 =5.0 MPa

 3 =7.5 MPa

 3 =5.0 MPa

 3 =7.5 MPa

0.3 0.4 0.5 0.6 0.7 0.8

0.0047 0.0037 0.0129

0.0499

0.105 0.231 0.832 1.376

0.104 0.156 0.546 1.038 3.605 10.45

0.0107

0.3709

0.123 0.255 0.541

0.258 1.693 3.445 5.502 13.63

1.032 3.059

0.150 0.397 3.557

- - -

2.35 4.26

-

6.21

4. Analysis of Results Analysis of the results of the conditional instantaneous tests under uniaxial and volumetric compression (Table 1) of sylvinite and carnallite specimens showed that almost all the obtained values of the main mechanical indicators, i.e. ultimate strength and failure strain at ultimate strength, increase when the lateral pressure is increased. Dependences of the change in the obtained parameters on the level of the lateral pressure are given below (Fig. 7). The dependences shown in Fig. 7 reflect the nonlinear nature of changes in the considered mechanical parameters depending on the level of the lateral pressure. An increase in the conditional instantaneous ultimate strength with an increase in the level of the lateral pressure by 5.0 and 7.5 MPa for sylvinite rocks occurs by 3.3 and 3.6 times (relative to the uniaxial ultimate strength σ 3 = 0 MPa), and for carnallite rocks it happens by 3.6 and 4.2 times, respectively. The increase in fracture strain with the increasing lateral pressure for sylvinite rocks is more intense than for carnallite ones. Analysis of the creep curves shown in Fig. 5 revealed that under long-term uniaxial and volumetric loading, almost all the tested sylvinite specimens switched to the stage of the decaying creep in the load r ange (0.3÷0.4) σ str . At load levels in the range (0.4÷0.8) σ str , the steady or progressive creep took place for all sylvinite specimens. For carnallite specimens (Fig. 6), the decaying stage was observed only at volumetric creep ( σ 3 = 5.0 MPa) with a load of 0.3 σ str . The rest of the specimens switched to the stage of the progressive creep, or were in the stage of the steady-state creep with an assumed tendency to a transition to the progressive phase.