Earth moving equipment names can easily be confused with each other, so let’s briefly list and describe them here:
- Dozers: Dozers are general use, probably the most basic type of equipment in construction. They can be used in land clearing, dozing, scraper loading assistance for earthwork and also for general use for purposes other than earthwork, where push or pull effort is needed with high traction, which is highly important during construction. The blades can change for different needs. For example a blade for clearing trees would not be suitable for moving earth, and still a different blade would be needed for scraping an unsuitable top soil layer or a different one for side hill cut of a hill to clear the path for a road curve. Not only the blade type but blade angle with respect to the surface being worked on (called angle of attack) also have a great affect on how operations are performed. It is also possible to attach single or multiple rippers at the back of a dozer, depending on soil type, condition and the required task, for soil ripping or existing asphalt or concrete paving ripping operations, to loosen the soil or to demolish the paving and easily remove later.
- Scrapers: They are specific equipment to haul, dump, spread or load loose soil materials.
- Trucks: Trucks are used to haul materials over long distances. For short distances, dozers and scrapers can haul some material to a certain degree, but as the distances get bigger, this becomes inefficient as far as cost and schedule. In these cases, making use of trucks makes more sense, even if it means a separate equipment such as a loader is needed to load the truck.
- Graders: They serve a lot of purposes in earthwork operations, including grading, creating ditches or banks, and general shaping of the route or area that is being worked on. The different tasks that require highly variable cutting angles can be performed, thanks to the highly adjustable blade which can cut or sweep over the soil not only at different elevations, but also rotate to a considerable degree around all three axis, in other words, highly flexible position and pitch. Examples include not only usual grading, spreading of material and leveling but also cutting v-ditches, sloping high banks near the road, which require a high degree of blade angle flexibility. Of course, due to highly adjustable blade location and angle, the traction power can not be as high as a dozer, so these are not suitable to perform dozer work (but the opposite is not true: as long as a dozer blade is capable of cutting similar to a grader with required angles, a dozer can also perform as grader or even better due to higher traction). Therefore, graders can move smaller amounts of material in comparison to dozers, but they can work at a wider variety of angles. In front of the blade, there is also a scarifier (made of partially removable teeth, depending on operation) attached to the grader, to soften the material that would be too hard for the blade to cut.
- Hydraulic Excavators: Unlike loaders that excavate approximately at the same level of its wheels, hydraulic excavators can excavate well below its wheel level. This allows them suitable for especially digging narrow trenches, but they could still be used for general excavation work as well.
- Loaders: One of the most frequently used equipment type among the ones listed here, loaders are used extensively in construction to load trucks, or any other container, excavate, striping, stockpiling materials, backfilling, carry things around, push or pull miscellaneous things when needed, such as lifting forms or rebar for concrete, moving and carrying around large pipes and manholes, towing things, with its strong hydraulic activated bucket that can move up to a considerable height or down. Loaders are also faster than almost any equipment we talked about in this section, except trucks, which allows them to move around freely all over a jobsite doing a large variety of primary or supplementary tasks. Instead of buckets, forks can also sometimes be attached in the front, so loaders can also serve as forklifts. For excavation, which is one of the most frequent usage areas of loaders, soft to medium hard materials are fine, but hard soil can not be excavated with loaders with reasonable efficiency.
- Roller: These are used to compact soil, by running a heavy cylindrical weight over the soil. There are different types, that are called with many names and a few are: sheepsfoot roller, pneumatic tire roller, smooth drum vibratory rollers, dual drum vibratory rollers… All these variations are used for different types of soil conditions. For example a sheepsfoot roller is suitable for clay, while a vibratory roller is suitable for sandy soils, since the vibration action will mean nothing for clay but it will cause a lot of interparticle arrangement in sand which also causes finer particles to fill voids between larger particles which means better compaction. For gravel dominant soils, a dual drum vibratory roller would be more appropriate where it can deliver strong vibratory and pressing action to gravel. In all cases, the soil must be brought to wet condition as close as possible to its optimum water content, as recommended from the lab tests of that soil. It means, if the original water content is less than optimum, watering the soil, or if the original water content is more than optimum, drying of the soil may be needed, such as by scarifying the soil surface for allowing water to easily evaporate.
For all equipment mentioned above, production estimates are made, in order to come up with the budget and schedule. These estimates take into account factors such as:
- Estimated efficiency, such as actual working minutes per hour for each equipment
- Travel, haul distance for one cycle
- Travel speed of equipment
- Total weight of load
- Number of passes required if more than one, for completing a full cycle
- Density of soil
- Width of the area covered in one pass
- Moisture content of soil
- Loading time
- Tire contact area and wheel load
- Rolling resistance, which is the ground force that resists the movement of the vehicle. For example on soft ground, as the wheels penetrate deeper into the soil, there is more contact with soil and the wheel, which means more friction, which means higher rolling resistance. To give an idea, on a hard, smooth, well maintained road surface, the resistance could be around 40 pounds per ton of loaded equipment, while on a soft muddy roadway, with considerable tire penetration, this value could be as high as 400 pounds per ton.
- Correction factors for soil material type, grade, operator, bucket fill, or even operating techniques
- and all other relevant variables based on job specific requirements.
Not all of the items above apply to every equipment, so the list is given as a general list to cover for all equipment. After calculation, this production estimate result can be related to the required total work or available total time to find out the number of machines needed, or the time can be estimated for how long it would take to finish a certain amount of work with certain number of available equipment or operator.
In the next post of this series, we will discuss “Foundations”