ABSTRACT: This paper defines the principal aspects of primary and secondary rock fracture by impact. It discusses mechanical rock fragmentation and cutting tool design. And it investigates those physical rock properties that can be used to predict excavation rate performance. Items that are referred to for specific discussion are:
- Viability of the impact-kerf-cutting (IKC) concept
- Impact rate of a tool and its effect on rock penetration within a velocity range of 10 to 20 ft/sec.
- Use of Schmidt Hammer for estimating unconfined compressive strength (UCS).
- The reliability of using UCS for production rate predictions.
- Production rate estimating procedures.
This paper covers laboratory and field testing pertaining to the development of an impact slot-cutting/ridge breaking tool for excavating rock. This tool was developed for use on a hydraulic breaker with the intent of reducing the use of explosives in short or irregular shaped excavations. Laboratory drop testing was conducted at the Mining Equipment Research Facility (METF) of the US Bureau of Mines (Now NIOSH). Full-scale field tests were then conducted at two rock quarries and one foundation excavation project. It was found that the IKC tool, when mounted on a properly sized hydraulic breaker and operated by experienced people, can be production rate competitive with explosives for trenching, tunneling, vein mining