Stability of boundary pillars in transition from open pit to underground mining

ZHAO Xing-dong(赵兴东)^1,2, LI Lian-chong(李连崇)³, TANG Chun-an(唐春安)³, ZHANG Hong-xun(张洪训)¹

(1. College of Resources & Civil Engineering, Northeastern University, Shenyang 110004, China;
2. State Key Laboratory for Geomechanics & Deep Underground Engineering
(Chinese University of Mining and Technology), Beijing 100083, China;
3. School of Civil Engineering, Dalian University of Technology, Dalian 116024, China;)

Abstract:Based on the height of back-filled materials, thickness of ore body, height of boundary pillar and dipping angle of ore body and water pressure, the safety factors of all the pillars are calculated with the limit equilibrium method. The calculation results present that the safety factors of pillars in Sections 19, 20, 24, 28 are less than 1.3, and those of unstable sections are identified preliminarily. Further, a numerical investigation in Sections 18, 20, 22, 24, 25 and 28 implemented with numerical code RFPA^2D is employed to further validate the pillar performance and the stability of stopes. The numerical results show the pillars in Sections 18, 22 and 24 are stable and the designed pillar size is suitable. The width of the ore body near Section 28 averages 20 m, failure occurs in the left stope, but the boundary pillars near Section 28 maintain good performance. The pillars in Sections 20 and 25 are unstable which are mainly affected by the Faults F8 and F18. The existence of faults alters the stress distribution, failure mode and water inrush pathway. This work provides a meaningful standard for boundary pillar and stope design in a mine as it transitions from an open pit to underground.

Key words:boundary pillar; stability; underground mining; numerical simulation; case study