2.1. Components of Pusher Cycle Time

Cycle time = LT+HT+DT+RT+ST+TT+ADBT (Where, LT-Load, HT-Haul, DT-Dump, RT-Return, ST-Spot, TT-Turn, ADBT-Acceleration, Deceleration, and Braking)

Cycle time is the total duration for completing one full cycle of work performed by a machine, in this case, a scraper assisted by a pusher. The formula includes various components: loading time (LT), which is how long it takes to load the material; haul time (HT), the duration for transporting the material; dump time (DT), the time taken to unload the material; return time (RT), which accounts for the time taken to return to the starting position; spotting time (ST), to correctly position the pusher loader for the next load; turning time (TT), to change direction; and ADBT, which encompasses the time for acceleration, deceleration, and braking during this cycle. Each component contributes to the overall efficiency and productivity of the operation.

Think of cycle time as a recipe for baking a cake. Just as each step in the recipe contributes to the final cake—mixing ingredients, baking, cooling, and decorating—each component of the cycle time works together to determine how quickly and efficiently a scraper can operate within its task.

You can split the cycle time into 2 parts: fixed time and variable time. Fixed time does not depend on travel distance, while variable time depends on distance and speed.

Cycle time can be divided into fixed and variable components. Fixed time includes activities that do not change regardless of how far the machine travels. For example, loading and unloading always takes a specific amount of time, irrespective of distance. In contrast, variable time relates to the haul and return journeys—these are influenced by distance and the speed of the machine, which may change based on various site conditions such as terrain and machine type.

Imagine you're planning a road trip. Fixed time could represent the duration of pit stops—fueling, eating—always taking about the same time. Variable time, however, would change based on how far you’re driving; if you have to drive a longer route, the traveling time increases.

Loading time of the scraper is fairly consistent, regardless of scraper size, due to assistance from a pusher. The average load time for the pusher loaded scraper in common earth is about 0.8 minutes.

The loading time for a scraper tends to remain stable because it is often assisted by a pusher. Whether the scraper is small or large, the loading time does not vary significantly because the pusher aids in the efficiency of the loading process. This consistency allows project managers to predict loading times accurately based on machinery rather than dispositional differences in the scrapers.

Think of loading a truck: smaller and larger trucks might have different capacities, but if a fork-lift is consistently available to help load both, you can clock the loading time reliably. Like packing a backpack for school, it may take consistent time regardless of size when there's a helping hand involved.

Loading scrapers to maximum capacity will reduce rather than increase the rate of production due to incoming earth encountering resistance from material already in the bowl.

The load growth curve reveals an important insight: as you fill the scraper's bowl, the efficiency of loading decreases after reaching a certain capacity (around 85%). Beyond this threshold, the material inside the bowl becomes a barrier to the incoming loads, creating resistance that slows down the loading process. This diminishing return means you’re better off filling to an optimal level rather than maxing out the bowl.

Picture trying to pour more cereal into a full bowl of milk. The cereal simply cannot enter fast enough because the milk is already full. You’d be pouring slower and making a mess, illustrating how too much load decreases efficiency instead of increasing it.

Haul and return time are variable; they depend on both travel distance and machine speed, which is affected by site conditions and machine type.

Haul and return times differ based on how far the scraper needs to go to deliver its load and the speed it can achieve on the way. For instance, when the scraper is hauling a load, it travels more slowly compared to the return trip when it is empty. Maintaining good conditions on the haul route (like having a smooth road) is crucial as it influences the machine's speed and therefore affects cycle time. Regular maintenance of these routes leads to higher productivity and lower operational costs.

Consider how quickly you can walk on a paved sidewalk versus uneven gravel. The distance remains the same, but the smoother the surface, the faster you can go. Similarly, maintaining the haul route allows scrapers to work more efficiently, saving both time and resources.

Dump time depends on scraper size, material type, and constraints in the dump area as well as operating conditions.

The time it takes to dump the scraper’s load varies largely based on the size of the scraper and the type of material being dumped. Larger scrapers will naturally take a bit longer for dumping due to more volume, and handling cohesive materials (like clay) may require more time compared to loose materials. Moreover, if there are space constraints at the dump area—like nearby machinery congestion—the dump time can also increase.

Think of a waste collection truck. If it arrives at a site where the dumpster is easily accessible, it can unload quickly. However, if there are obstacles, like other vehicles or a narrow alley, unloading takes much longer. Similarly, the conditions dictate how quickly or slowly a scraper can unload.

Turn time is influenced by the type and size of the scraper and may vary between the fill area and cut area.

The time it takes for a scraper to turn varies depending on its current load and the specific area within the project site. Turns made in the fill area tend to take less time compared to the cut area due to less congestion and fewer obstacles. In the cut area, more machines often compete for space, making turning more complex and time-consuming.

Imagine driving a car in a parking lot versus a busy intersection. In the parking lot (fill area), you can make quick turns without interference, but at an intersection filled with cars (cut area), you must navigate carefully and wait for safe openings, thereby taking longer to complete the turn.

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