Effect of Dynamic Stress Produced by Rock Blasting on the Optimal Dimensioning of Room and Pillars in Horizontal Layers

Abstract

An optimal dimensioning of the room and pillars of the square or rectangular section is finding adequate transversal section support for the pillar; in that sense, all forces acting on the pillar must be evaluated. The pillar has its ends subjected to normal (σ) and shear stresses (τ). In addition, the pillar can also be subjected to dynamic stresses from the seismic waves generated by rock blasting. Thus, when calculating the dimensions of a mine pillar, the stresses imposed by seismic waves must be considered. The combination of lithostatic and dynamic stresses generated by blasting can affect the pillar, generating regions, or areas that will exhibit the formation of cracks, microcracks, chipping, and other detrimental processes for its stability. In that regard, it is appropriate to assess the dynamic effects of the energy delivered in each wave pulse so that these dynamic quantities can be included in the dimensioning of the pillars. This paper presents the physical and mathematical formulation describing the dimensioning issues of room and pillars and its solution using numerical modeling. The numerical modeling is performed using nonlinear mathematical programming and simulation with FLAC 3D (Fast Lagrangian Analysis of Continua in 3D). In this study, it was proven that the stress generated by the seismic wave represents a dynamic stress of nearly 5.5 MPa. 'Dimensioned pillars considering wave stresses allows it to recover an average 1.6% less when it is compared with pillars only under overlying rock mass'.