In coal mining terms, a lowwall is the up-dip face/slope which is excavated along the limit/line of oxidation (LOX line) during the boxcut mine development stage. As the boxcut and pit advances down-dip with each successive strip, overburden material (or spoil) is progressively in-pit dumped on the lowwall. In this article, we introduce some of the key concepts surrounding lowwall geotechnical and mine design.
Lowwalls mine slopes are typically constructed via free-dig excavator and truck in soil and weathered rock overburden. Drilling and blasting practices are subsequently used to excavate through the fresh, intact overburden material until the target coal seam is reached and and the first strip's highwall is established.
During the initial boxcut mine development stage, the overburden waste is excavated and truck-dumped in external dumps (i.e., ex-pit dumps) until the boxcut is advanced enough to accommodate in-pit dumping.
Given blasted overburden material is subject to swelling and bulking, designing and constructing optimal in-pit lowwall spoil dumps is fundamental to mining economics in open strip coal mining.
Lowwall slope stability is one of the most important considerations in geotechnical design and mine planning, owing to the fact that mining equipment and personnel are often working in the active strip, down-dip of the progressing lowwall in-pit spoil dumps.
Some of the most critical factors affecting lowwall in-pit spoil dump stability are floor dip, immediate floor lithology type, geomechanical properties (e.g., effective cohesion and friction), and the presence of water and/or mud prior to spoil emplacement.
A combination of pit floor ripping, trenching, and/or blasting may be required to adequately disrupt low strength materials before emplacement of in-pit spoil.
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