6. Balancing Scraper and Pusher Operations

So, now let us work on the first problem on productivity estimation of the scraper. So, a scraper with the assistance of the pusher is moving the dry earth soil having unit weight of 1660 kg per bank meter cube.

In this section, we are discussing the operation of scrapers and pushers in earth-moving projects. Scrapers are heavy machinery used to collect and haul materials like soil. When they work with pushers, they can move larger quantities of material efficiently. The unit weight of the dry earth soil being moved by the scraper is mentioned as 1660 kg per bank meter cube, which helps estimate the load and productivity. This figure is significant because it influences the calculations for the load the scraper can carry and the overall efficiency. Understanding the relationship between scrapers and pushers lays the foundation for estimating productivity in construction operations.

Think of scrapers as trucks carrying goods, while pushers are like loaders that help load more goods onto these trucks. Just like how the weight of the goods affects how much the truck can carry and how efficiently it can drive, knowing the weight of the soil helps in calculating how much the scraper can effectively move on a construction site.

So, hope you remember what is swell factor? We have defined what is swell factor in early lecture, it is a ratio of loose dry unit weight of the material by bank dry unit weight of the material. So, particularly for the push loaded scrapers your swell factor, the unit weight will increase by 10%, because of the additional pressure which we received from the pusher to the material inside the bowl.

The swell factor is crucial in understanding material volume during excavation and hauling. It quantifies how much the volume of material increases once it is disturbed or loosened, typically from being compacted in the ground. For push-loaded scrapers, this factor increases by about 10% due to the additional pressure applied by the pusher. This means when a pusher applies force, more material can be packed into the scraper bowl, increasing its effective weight and density, which is vital for calculations regarding load and efficiency.

Imagine trying to fit as many marbles as possible into a jar. When the marbles are packed tightly together (bank), you can fit a certain number. However, if you shake the jar (disturb the soil), the marbles spread out, and you can fit in more (loose volume). Now, if a friend helps you pack the marbles in tightly (similar to a pusher), you can fit even more than before because of that added pressure.

So, now the next step is we have to determine what are all the resistance in the haul route? The rolling resistance is uniform throughout the haul route. Is given in the question is 50 kg per ton or equivalent gradient as 5%.

To ensure the scraper operates efficiently, it's essential to calculate the total resistance encountered during operation. Rolling resistance refers to the force resisting the motion of a vehicle on a surface. In this scenario, it is given as 50 kg per ton, or a 5% equivalent gradient, indicating the slope the scraper must overcome while hauling materials. Both rolling resistance and grade resistance (which changes according to the slope of the haul route) are crucial for calculating the speed and power requirements of the scraper.

Imagine pushing a shopping cart up a slight hill. The effort it takes to push the cart forward while going up represents rolling resistance. If the hill gets steeper, it becomes even harder to push, showing how gradient affects force. Similarly, knowing the resistance helps engineers ensure the scraper can handle what’s being carried without unnecessary strain.

Now let us see the balanced number of scrapers which are served by one pusher. So, that is equal to n is nothing but number of scrapers served by one pusher. It is equal to cycle time of the scraper by cycle time of the pusher.

Balancing the number of scrapers and pushers ensures smooth operation and minimizes delays in material handling. Each machine has a cycle time, which is the total time taken to complete a loading, hauling, and dumping cycle. By calculating the ratio of the scraper’s cycle time to the pusher’s cycle time, we can determine how many scrapers one pusher can effectively assist without causing downtime. In this case, the cycle times were previously calculated as 7.78 minutes for the scraper and 1.37 minutes for the pusher, leading to a balanced number of approximately 5.68 scrapers.

Think of a restaurant where a waiter serves multiple tables. If the waiter can serve each table in 5 minutes (equating to the scraper) but takes only 1 minute to refill drinks at another table (equating to the pusher), we can determine how many tables the waiter can handle at any given time. Efficiently balancing these operations ensures that customers (in this case, the scrapers) are served quickly without waiting too long.

--