Stripping or strip mining is the removal of overburden or waste materials from open-pit surface mines. The process involves machines such as stripping shovels, bucketwheel excavators, or draglines to strip away the rock and uncover the valuable ore that is being mined.
Valuable minerals such as coal, ironstone, or limestone are uncovered by a shovel that digs long strips or a machine that cuts and casts the overburden from the pit in order to expose the ore. The stripping shovel typically sits atop of the surface it is mining and is propelled forward as the digging advances.
The process begins with careful planning because of the high pressure that the crawlers of these large machines are dealing with. The ground must always be tested for stability because the machine’s crawlers could cause it to sink if the surface is not completely solid. If it does sink, it may take several days and numerous scrapers and bulldozers to push it out. Coalbeds provide the best stability for strip mining.
A large ramp has to be built so the machines can get from the ground’s surface to the pit floor. Usually, a ramp is built as steep as possible to reduce the amount of materials and time it takes to construct.
Bulldozers push down trees and bushes that reside in the area and any dirt or sand is removed. The next step involves drilling holes into the rock or overburden that covers the mineral. When the position of the mineral is found, some miners may use dynamite to blast it. What is left is strip mined with a large stripping machine. The ore is dug up in long narrow strips, one after another, until the top layer is removed. Each subsequent layer that has to be is removed until the ore is exposed. Once the ore is removed, the waste strips are used as backfill.
Once the machine is ready to strip, there are several people employed to ensure that the operation runs smoothly. This includes the driver or operator, an oiler, a ground man, and those responsible for operating other machines.
The operator drives the machine and controls the machine’s movements with two hand levers and two foot pedals. The hand levers control the hoisting of the dipper and the extension/retraction movement. The foot pedals allow the dipper to swing from right to left.
The oiler must keep the machine well oiled and clean. He also takes over the operator’s role whenever the operator takes a break.
The ground man is in charge of leading the lower machine. The role includes keeping the power cable away from falling rocks. He also operates a bulldozer that is sometimes used to remove the overburden.
Once stripped or cut, the overburden is placed in piles behind the work area.
The stripping process can be very costly, as the machines used for this application are among some of the largest earthmoving machines in the world. They are also expensive because each application usually requires the work of just one to complete the job. Large surface mines may employ more, but this is not common.
One of the common problems encountered in strip mining is pit wall failure. If the wall of the pit becomes unstable, it may bury the stripping machine, making it unsafe and difficult to escape.