Double benching is an open-pit mining technique where two benches are excavated at once, creating a “double bench” or a single bench face with a combined height of two standard benches. This method increases productivity by allowing an excavator on the upper bench to load material directly into trucks on a lower level or on the bench below, reducing machine repositioning and loading costs.
When conducting double-benching in open pits, several safety considerations are critical to minimize risk and ensure operational efficiency:
- Bench height control: the upper bench height should not exceed the cab height of the excavator. If material is not free-rilling, a Job Safety Analysis (JSA) should determine an appropriate upper bench height to prevent instability and hazards at the working face.
- Excavation practices: benches should be excavated to correct levels, with the advancing face excavated in a controlled manner (approximately a 45° arc) ensuring the face is free-rolling into the trough without undermining or burrowing. This prevents material from unexpectedly falling onto equipment or personnel.
- Bench surface maintenance: the bench surface must be level and smooth to avoid material dragging onto excavator tracks or the center track frame, reducing the risk of equipment damage and hazards.
- Catch drains and safety berms: a catch drain alongside the upper bench protects excavators from rilling material striking the track frame. Additionally, safety berms along bench crests prevent equipment from driving accidentally over edges and catch falling rocks, critical for preventing accidents.
- Controlled material pull-down: when material needs to be pulled down, it should be done in a controlled manner using bucket cylinders fully closed to avoid uncontrolled rock falls or face collapse.
- Safe access and equipment movement:excavators must be moved safely from the dig face to tail benches with proper access and safety bund walls in place when servicing is conducted on benches.
- Operational spacing and progressive loading: maintaining appropriate roll sizes and excavator bucket positioning when advancing the bench face helps avoid equipment damage and facilitates safe progression.
These measures ensure the structural stability of benches during double-benching, protect personnel and equipment from falling debris and machine hazards, and promote controlled material handling in the open pit environment.
To sum up, safety in double-benching centers around careful bench height management, controlled excavation face design, stable bench surfaces, protective structures like berms and drains, and disciplined equipment operation and movement protocols to prevent accidents and equipment damage.
