Performance of chain trenchers in mixed ground

Chain trenchers were used to cut moderately strong sandstone bedrock, compressive strength 6-9,000 psi (41-62 MN/m2), of varying thickness up to 17 ft (5,1 m), beneath desert alluvium in Sedona, Arizona. Data from the case history indicated an inverse relation between trencher performance expressed as a cutting rate or volume excavation rate and the thickness of rock cut. This was compared with curves derived from a simple balance of the cutting energy available from the trencher and the energy required to break a unit volume of rock. The closeness of the fit provides a basis for understanding the mechanics of chain-trencher cutting performance and for the prediction of performance in rocks of different strengths and thicknesses. The main conclusions are that: (1) The design of chain trenchers is such that power available for cutting remains constant and low; and (2) machine productivity in terms of traverse speed or excavation rate is inversely proportional to the strength and thickness of any rock cut.