Shaft Loading Clamshell vs Crawler-Mounted Loader

In the past few years changes have taken place in shaft sinking. Progress has been made with types of machinery designed, developed, and made available to shaft sinking contractors. This is particularly true of drilling and mucking equipment. Compared with conventional clamshell loading, mucking or loading with a crawler-mounted overshot loader is a new technique for shaft work. There are several methods of clamshell loading. Dravo Construction Co. mounts an air tugger on the clamshell to operate the closing line. The load, or holding line, is attached to the hoist of a crane or whirler at the shaft collar. The clamshell is raised or lowered by the hoist when a signal is given by a bell or light system operated by men at the bottom of the shaft. Two men control the drift of the clamshell with tag lines, pulling it to any position in the shaft for loading, or over the shaft muck bucket for emptying. One man operates the air tugger to open and close the clamshell by means of two lines attached to the operating air valve, just as reins are used to drive a horse. One man operates the signal telling the hoist operator when to raise or lower the clamshell. This method requires two hoisting lines in the shaft-the line from the mine hoist that lifts