Numerical simulation is performed for the changes of stress field at consecutive extraction of a diamond ore deposit, The features of stress distribution around openings are examined. Failure zones of rock mass are determined With using of Coulomb-Mohr criterion. The results of calculations were compared with the experimental data of observations in situ. Geomechanical recommendations are proposed for placing of technological workings.
Open-pit mining method is used for excavation of ore at Siberian diamond deposits. The maximum depths of open-pits are reached. Last years the deep mining IS applied, The features of stress distribution around openings are examined at experimental industrial block of the "International" kimberlite pipe, which is mined at the depth onOO-800 m. Cut-and-fill mining 111 slices about3.5–5 m in height and about 5 m in width is applied in various variants of room and pillar mining with a combine. As a result some cylindrical mined out spaces with a diameter 60 m and a height 10- 70 m were filled with the solidifying fillings. Under these conditions a number of geomechanical problems arises. The main of them is the possible rock fall into workings. The experience of application of geomechanical investigations in practice is discussed. Numerical simulation is performed for the changes of stresses in ore mass and in country rock at consecutive extraction of the diamond deposit. Character of failure in rock mass is researched. Strength of rock has a wide rage of values. The difference in mechanical properties sets a limit of accuracy of analysis. The finite element method was applied for forecasting the stress state of rock mass near the mined out spaces during development of mining works.
The results of experimental investigations showed the Initial principal horizontal stresses are approximately equal to 0.7–0.8 of vertical pressure been due to a weight of overlying rock thickness at this depth (Baryshnikov et al. 2003). Therefore the numerical solutions of axisymmetrical problems were used. The initial stress state of rock mass is following
(Equation in full paper)
where z is a distance from the surface of the earth, γ is specific gravity of rock (27 KN/m3), λ - ratio of initial horizontal stress to vertical one at the depth H (800 m).The problems were solved in terms additional displacements (Boltengagen 1999) under the following boundary conditions on the external boundary (the surface of the cylinder with a diameter 4 km and a height 2 km): the upper horizontal boundary is free from stresses, additional displacements are equal to zero on the lower horizontal boundary, additional horizontal displacements and tangential stresses are equal to zero on the vertical boundary. Elastic modulus of rock was taken equal to 10 GPa, Poisson's ratio of rock γ is equal to 0.25. The height of mined-out spaces (cylinders with the diameters 60 m) are quoted on the corresponding illustrations of problems. Elastic modulus of artificial fillings is one-tenth or one-hundredth of elastic modulus of rock.
