For citation: Pham D., Vitcalov V.G. DETERMINATION OF OPTIMAL BLOCK LENGTH ALONG THE STRIKE TO PROVIDE SAFETY AND EFFICIENCY WHEN EXTRACTING MEDIUM-THICK IN-CLINED COAL SEAMS USING ROOM-AND-PILLAR METHOD IN QUANG NINH COAL BASIN. Gornye nauki i tekhnologii = Mining Science and Technology (Russia). 2018;(2):3-8. https://doi.org/10.17073/2500-0632-2018-2-3-7