Highwall Bench Width and Overall Slope Angle

Stack benches and the wall gets flatter overall even though every face is steep, and quoting the face angle understates it badly. Each bench contributes its own horizontal setback -- the face's own run plus the bench width -- and the overall angle is the total height over the total run. Forty-foot benches with 30 ft catch benches cut at 65 degrees run 48.65 ft each, and the wall comes out at 39.4 degrees overall: TWENTY-SIX DEGREES flatter than the face, entirely from the benches. The overall angle is what a slope stability analysis evaluates, and giving a regulator or an engineer the face angle instead is a materially different wall. The lever runs both ways. Narrow the benches to 20 ft and the wall steepens to 46.0 degrees -- more ore recovered, less catchment, and a steeper wall to justify. Widen to 40 ft and it flattens to 34.3 degrees. Ten feet of bench width is worth about seven degrees of overall angle here, which costs stripping and buys stability and catchment. BENCH WIDTH DOES TWO JOBS AND THEY ARE WORTH SEPARATING. Geometrically it sets the overall angle. Operationally it is the CATCH bench that has to stop rock falling from above from reaching people and equipment below, and that requirement -- the Ritchie criterion and the modern work refining it -- often demands a wider bench than the stability analysis alone would. A bench too narrow to catch anything is a bench that only exists on the plan. Slope geometry only. It says NOTHING about whether the wall is stable, which depends on rock mass strength, discontinuity orientation and persistence, groundwater pressure, blast damage to the face, and the failure mode that geometry permits -- planar, wedge, toppling, or circular. A geometrically modest wall in adversely oriented jointing can be far more dangerous than a steep one in massive rock, and only a slope stability analysis by a qualified engineer distinguishes them. It does not evaluate catch bench effectiveness against rockfall, which needs the Ritchie criterion or a rockfall simulation and depends on bench face condition as much as width, and it does not address ramp design, drainage, scaling, monitoring, or the ground control plan. MSHA ground control requirements, the site's ground control plan, and a qualified geotechnical engineer govern.

horizontal run per bench = bench height / tan(face angle) + bench width; overall slope angle = arctan(bench height / run per bench); the bench width for a target overall angle = bench height / tan(target) - the face run.

The bench-stacking geometry by name. Geometry only: MSHA ground control requirements, the site's ground control plan, and a qualified geotechnical engineer govern whether a wall is stable.

Trigonometry on the user's own bench dimensions; no ground control standard is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: bench_height_ft, bench_width_ft, face_angle_deg, bench_count, alternative_bench_width_ft, target_overall_angle_deg, face_run_ft, run_per_bench_ft, overall_angle_deg, total_height_ft, alternative_overall_angle_deg, width_for_target_ft

• The overall angle is what gets analysed the face angle is a different and much steeper numberslope engineering practice
• Bench width buys catchment as well as angle and the catchment requirement often governs the wider oneRitchie criterion and successors
• Geometry is not stability adverse jointing makes a flat wall dangerous and massive rock makes a steep one safegeotechnical engineering