A new method of investigating the rheological properties of semirocks in different stress states characterized by Nadai-Lode parameter, Mό, ranging from −1 to +1 has been developed by Kubetsky (1981). The determination of rheological properties of rocks by laboratory and field tests is done according to the new method under quite the same loading conditions.
One of the feasible test schemes making it possible to set up in an investigated rock mass a stress state characterized by the parameter Mό= −0.5 to-land Mό =0,as well as the test procedure and results obtained in investigating the rheological properties of several semirocks are given in the following.
(Figure in full paper)
A principal feature of the method is that determining the rheological properties is made with the use of results obtained in vertical loading and subsequent torsion of a ring pillar or a ring concrete test plate inseparably bound with the base. The principal difference of the new method, as compared to the ring shear method, Bishop et al. (1971), is in the fact that no ring specimen is tested, but a ring load is applied to the surface of an undisturbed semirock massif. The ring pillar or a ring concrete test plate are used only to transfer an applied force to the base. The determination of deformability of the rock at different stress states is done through an interpretation of the test data by proper solutions of three dimensional problems pertaining to the theory of elasticity or creep.
Depending on the aim of the investigation different sequences of applying the loads to the monolith or massif may be accepted which offer a possibility to study how the trajectory of loading influences the characteristics in question. When vertical loads are applied to an investigated massif the creep parameters in compression can be determined by the method described in the paper by Kubetsky (1979). In this case the stress state in the rock is charaçterized by the parameter Mό = −0.5 to −1.0 with a sufficient for practical purposes accuracy. As field plate tests have shown the dependence of settlement for different time moments on the mean stress in the footing of the test plate has, in general, a non-linear character. On the. other hand, if a stress interval of 4.0 to 10.0 MPa is considered, a linear or piecewise-linear approximation of the "settlement-mean stress" relation may be used with sufficient for practical purposes accuracy. Under this condition variation of settlement S (r;t) with time can be found from the following formula:
Where Dt; vt- time operators characteriding creep properties of the rock; 6 (t) - mean normal stress in the footing of the ring pillar; wc - coefficient which depends on relation ε = r 1 /r2, location of the point on the bane surface, and thickness of the compressed layer H; r1,r2 - inner and outer radii of the pillar; t - time.