It is important to select the right machine for the job to be acted. defective choice will affect in underutilization of machine or is strange for the activity. These approached in damaging age additionally resources. Furthermore the progress of the job or project will be effected. 

An excavator ( back hoe ) loading a hauling unit 

What are the factors to consider then during the selection process? The two basic factors which should be taken into consideration are: - 

1.        The cost per unit of excavation and 

2.        The job condition the machine will work in 

Lets discuss more in details these two factors. The meaning of cost per unit of excavation means how much does it cost to excavate per unit volume of the material found in the job site. The factors to take into account when working out the cost per unit of excavation are :- 

•        The size of the job, as a larger job may justify the higher cost of a large machine. 

•        The cost of transportation ( larger ones more cost) 

•        In quarry works, there is the combined cost of drilling or blasting to be considered. If a large excavator is used, these costs may be less than if a small one as a large machine will handle bigger rocks better than a small one. Hence a large machine may permit savings in drilling and blasting costs. 

Normally it works out that the unit cost per volume of excavation is less for large excavators than small ones. 

As for the job considerations, this determine the type of bucket or the size of machines to be used. There are different types of buckets in terms of size and make. Hence if the material to be excavated is hard and tough, the bucket of a large machine which can exert higher digging pressure will handle the material more easily. If blasted rock is to be excavated, the large-size bucket will handle bigger individual pieces better and easily. Then if the project time is short and a high production is required, either multiple small machines or a single large one can be used. 

Another factor which is often missed is the type of hauling units available. If small hauling units are used then the size of the excavator should be small, where as if large or heavy hauling units are used then a large excavator should be used. Finally it is also important to take into account the maximum dumping height of the excavator when loading hauling units. 

As for back hoes, beside the above, there are additional factors to consider and these are:- 

•        Maximum digging depth required 

•        Minimum digging depth available 

•        Working radius for digging and dumping 

•        dumping height required 

•        digging width required ( trench operation) 

•        clearance for carrier, superstructure and boom 

•        hosting capability. 

If the work is a trenching operation, then the primary concern is to match the hoe's ability to excavate linear length per unit of time with the pipe / cable laying production. Usually, the volume of material moved is not the question. 

Thus the above are factors to be taken into when selecting the right excavators for the work and it is also advisable to always consult manufacturers specification in the planning and selection.