Performance Characteristics of Earth moving Equipment

In this section, the performance characteristics of the following types of equipment used for earthmoving are discussed. 

1. Power shovels 
2. Drag lines 
3. Scrapers 

Power Shovels 

The performance characteristics of power shovels depends on : 

(i)  Class of Material : The output of a power shovel handling earth varies with the class of material being handled. The following materials are arranged in the increasing order of shovel output : 

• moist loam or light sandy clay or sand and gravel; 
• good common earth; 
• hard, tough clay or wet, sticky clay; 
• poorly blasted rock; and 
• well blasted rock. 

(ii)  Depth of Cut : If the depth of the face from which a shovel is excavating material is too shallow, it will be difficult or impossible to fill the dipper in one pass up the face. The operator will either have to make more than one pass to fill the dipper, which increase the time per cycle, or he may canny partly filled dipper to the hauling unit in each cycle. In either case the effect will be to reduce the output of the shovel. 

If the depth of the face is greater than the minimum required to fill the dipper, with favorably crowding and hoisting forces, the operator may do one of three things. He may reduce the depth of penetration of the dipper into the face in order to fill the dipper in one full stroke. This will increase the time for a cycle. He may start digger-above the base of the face, and remove the lower portion of the face later. The may run the dipper the full height of the face and let the excess earth spill down to the bottom of the face, to be picked up later. The choice of any one of the three methods will result in some lost time, based on the time required to fill the dipper when it is digging at optimum depth. 

(iii) Angle of Swing :  The angle of swing of a power shovel is the horizontal angle, expressed in degrees, between the position of the dipper when it is excavating and the position when it is discharging the load. The total time in a cycle includes digging, swinging to the dumping position, dumping, and returning to the digging position. If the angle of swing is increased, the time for a cycle will be increased, while if the angle of swing is demeased, the time for a cycle will be decreased. 

(iv)  Job Conditions : A shovel may operate in a large, open pit, with a firm, well drained floor, where trucks can be spotted on either side of the shovel to eliminate lost time waiting for hauling units. The terrain of the natural ground may be uniformly level, so that the depth of cut will always be optimum. The haul road is not affected by climatic conditions, such as rains. A job of this type is large enough to justify the selection of balanced hauling units. Such a projecr can be classified as having excellent job conditioils. 

Another shovel may be used to excavate material for a highway cut through a hill. The depth of cut may v,uy from zero to considerably more than the optimum depth. The sides of the cut must be carefully sloped. The cut may be  so narrow that a loaded truck  must move out before an empty truck can back into the loading position. As the truck must be spotted behind Uie shovel, the angle of swing will be almost 180". The floor of the cut may be muddy, which will delay the movement of trucks. Light rains niay delay operations for several 

days. A project of this type may be termed as having poor job cvnditions. 

In excavating a basement that requires the trucks to travel up an earth ramp, a power shovel may be delayed considerably by the ground water or rain, by difficulty of getting haul units in and out, and by the difficulty of excavating the corners. 

Job conditions may be termed as excellent, good, fair and poor. There is no uniform standard that may he used as a guide for classifying a job. Each job planner must use his own judgement and experience in deciding each contrition. 

(v)  Management Conditions :  Tl~e  attitude of the owner of a shovel in establishing the conditions under which a shovel is operated will affect the output of the shovel. While the owner may not be able to improve job conditions, he may take several steps to improve ungentle conditions, including the following : 

• Greasing and lubricating the shovel influentially. 
• Checking the shovel parts that arc subject to the greatest wear, and replacing worn parts while the shovel is not being operable, as at the end of a shift. 
• Replacing badly worn wire rope between shifts. 
• Replacing dull dipper teeth with sharp ones, as necessary. 
• Giving the shovel a major overhaul between jobs, if necessary. 
• Keeping at the job extra parts that are subject to the greatest wear. 
• Keeping the pit clean and smooth to permit better truck spotting and to reduce the angle of swing. 
• Providing adequate trucks of the correct size to eliminate lost time in loading and waiting for trucks. 
• Paying a bonus to the crew for production in excess of an agreed amount to encourage high production. 
• Providing a competent supervisor to keep the job running smoothly. 

(vi)  Size of Haul Units :  If the size of the haul unit is a multiple of full dipper capacity, the loading will be efficient. However, if the size is some fraction of the dipper capacity, there will be spilling of the material over the sides of the haul units, thus increasing working effort and affecting the job conditions. 

(vii) Skill of the Operator : With experience the operator can operate the shovel more efficiently and quickly or combine two or more actions like swinging the dipper while raising the dip stick. 

(viii)Physical Condition of the Shovel : A new machine would be stiff to operate for some time. Then the parts become smooth and move more readily. Towards the end there would be frequent breakdowns. All these affect the output of the shovel.