Talking about underground rock excavation, we have mining with the aim of extracting minerals from underground. At first, we excavate (non-valuable) waste rock in order to gain access to the mineral deposit.
In underground mines hydraulic breakers mounted on pedestal booms near to grizzly crushers are used for breaking oversized rocks (secondary breaking). Another very common application is scaling (roof support) after drilling and blasting.
Drum Cutters are used successfully as a primary excavation machine in Soft to Medium rock formations like gypsum or salt. Drum Cutters provide excellent accuracy and performance in scaling or profiling.
Another kind of underground rock excavation is construction (tunneling) where the main aim is to develop underground tunnels, shafts, chambers and passageways for civil engineering use. Depending on the rock properties Hydraulic Breakers or Drum Cutters can be used as a primary excavation method or in combination with Drilling and Blasting.
The combination is sometimes required when roof conditions don't allow blasting because of collapse risk of the surface area. A common practice as well is to use hydraulic attachment tools at the entrance area of a tunnel to protect surrounding rocks for better stability.
Scaling of the face, roof and walls is a process that heavily depends on the rock conditions. In good rock conditions, the roof and walls will not yield any falling rock, and the need for scaling will be minimal. In poor conditions, all surfaces will require scaling, which is much more time-consuming.
The selection of the right tool is depending on the rock type and its properties. The size of hydraulic attachment tools is limited to the excavator size and available space.
While it is true that boulders are created by insufficient blasting or blasting difficulties due
to hole deviation, they are a reality and must be broken up into smaller, more manageable pieces through haulage or crushing. There are only two ways of dealing with these unwanted boulders. They can either be drilled and blasted or broken down using hydraulic breakers.
Tunneling with hydraulic breakers or drum cutters is a common method when drilling and blasting is forbidden, restricted or economically unviable for example, for short tunnels.
Another example is a combination of using a breaker in the starting phase of the tunnel when the roof conditions are too weak and then switching to drilling and blasting once the roof is more stable. Depending on the size of the tunnel and the mobile equipment that can be driven in one-step as a full face or sequential as partial face. For working in low roofed tunnels, there are special excavators equipped with front linkage.
Tunneling and rock excavation with breakers is a cost efficient method because it produces the required size of boulders without secondary reduction or problems on a crusher feeding. Normally there is no need for separate scaling after excavation, which reduces the need for carriers and special machines.
A similar tunneling process can be conducted using drum cutters instead of breakers.
Compared to using breakers, drum cutters produce much smaller rocks which are easier to handle. However cutting also produces more dust, so it is highly recommended that water spraying is used to minimize the dust on site.
One standard application is secondary reduction of oversize boulders in the rock pile. The use of hydraulic breakers has made safety problems a thing of the past.
Selective mining with heavy-duty hydraulic breakers is a worthwhile consideration in many quarries, as it frequently allows improved material grades to be excavated that bring higher sales revenue. Using hydraulic breakers can also reduce the amount of fine grain material that may be unsuitable for use in applications such as road construction, compared to blasting.
Using hydraulic breakers to remove the overburden allows the entire deposit to be utilized.
Quarry operations or open pits are long-term projects where deposits are usually mined over several decades. These quarries are part of the landscape, and during operation residential developments often expand up to the edges of the site. It can become impossible to use explosives in these areas because of the safety risks and reduced tolerance for noise and vibration. In some countries the tough regulations around using explosives has made blasting difficult and expensive resulting in an increased competitiveness for blast free methods:
The performance capacity and adaptability of heavy duty hydraulic breakers or drum cutters make them an interesting alternative for rock excavation.
Selective excavation allows different rock grades to be removed separately from an inhomogeneous deposit. Deposits with high impurity levels and distinct fault zones can be very difficult to excavate and result in raw materials of sharply differing grades.
Using hydraulic attachment tools as flexible excavation units, deposits can be mined selectively regardless of the complexity or direction of the seams. Comparing drum cutters with breakers, breakers cause a lower percentage of fine grain material.
Whenever the blasted rock is too big to be loaded or fed through the crusher, secondary reduction is required. Even with the most advanced blasting techniques, it is inevitable that there will be oversize boulders, and these need to be broken as economically as possible.
Hydraulic breakers are particularly suitable for all quarries and mines where secondary reduction is needed. Our wide range of breaker models together with capabilities of modern carriers makes our breakers competitive in all secondary reduction applications. The excavator – breaker combination is a flexible unit which can be used at several points in the quarry for various tasks like digging, loading & carrying. In many cases, oversize boulders can be sold profitably for use in embankments, dry walls or as breakwater rocks. In suitable rock types, hydraulic breakers can be used to create appropriate blocks.