PSI - Issue 32

N.A. Samodelkina et al. / Procedia Structural Integrity 32 (2021) 173–179 N.A. Samodelkina / Structural Integrity Procedia 00 (2019) 000 – 000

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Figure 3 shows the distribution of the normal and tangential stresses over the contact between the OSR and CSZ, depending on the goaf boundary position in relation to the wedge-out zone and maximum subsidence of the earth surface. An increase in the normal stress is noted during the subsidence increase in the boundary part of the undermined mass(Fig. 3b); this reflects the formation of a zone of the abutment rock pressure. At the same time, shear stresses on the contact increase (Fig. 3d). A change in the goaf boundary position has almost no effect on the nature of the distribution of both the normal (Fig. 3a) and tangential (Fig. 3c) stresses: their maximum value simply moves along the contact of the wedge-out zone. Thus, the analysis of the stress state of the contact between the OSR and the CSZ does not give an unambiguous answer about the degree of danger of its undermining (an increase in shear stresses causes an increase in the normal stresses too). At the same time, some conclusions can still be made. It is worth noting that an increase in shear stress (with a sign change), although not a very significant one, takes place at the contact behind the abutment rock pressure. Meanwhile, the normal stresses hardly differ from the stresses in the undisturbed mass. This creates certain prerequisites for shear displacements in this part of the contact.

Fig. 4. Distribution of relative shear displacements along the upper contact of the CSZ at different goaf positions

Let us consider the nature of the changes in the shear displacements along the contact between the OSR and CSZ. As an illustration, Fig. 4 shows their distribution,normalised to the displacement corresponding to the peak strength of contact p  at three positions of the goaf boundary, relative to the section of the wedging-outOSR and TFM. It should be noted that p  is not a constant value, it is found in each contact element, based on the Coulomb