4.1. Cycle Time Analysis

So, once the loading of scraper 1 is completed, the pusher will back-track return back and spot the next a scraper, scraper 2 and start pushing it in the same direction. So, that is what is a back-track loading. So, first it is pushing the scraper 1, as a scraper 1 is completely loaded it will start moving on its own. Once the scraper 1 is loaded, your pusher will get detached and return that is backtracking, backtrack and it has to travel some distance and spot the next scraper 2. And then start pushing again in the same direction, it starts moving again in the same direction. So, that is what is your back-track loading method. So, one limitation of this back-track loading method is it needs additional time for returning back backtracking. So, that is why we call this as a slowest method. So, this is the slowest of all the methods which we are going to discuss now.

The back-track loading method involves a series of steps where a pusher loads a scraper, and then, after unloading, returns to fetch the next scraper. This method is considered slow because the pusher needs to make a return journey which adds more time to the overall cycle. In essence, the loading process starts with the pusher engaging the first scraper (scraper 1), which, once fully loaded, moves on its own. The pusher then detaches and backtracks to find scraper 2, introducing a time delay associated with the additional travel needed for backtracking.

Imagine a waiter serving food at a restaurant. After serving a table, the waiter has to return to the kitchen for another order before serving the next table. Just like the waiter, the pusher has to travel back to pick up the next scraper and this traveling time makes the process slower.

So, here you can see that the return time is more, return time is more because of the backtracking. So, everything the actual value will depend upon your project site. So, we cannot tell the exact value but basically your back-track method takes longer time because the pusher has to return back, it has to back-track and spot the next scraper and then start pushing it again in the same direction. But this is more commonly adopted by everyone because the people prefer the cutting in the same direction.

The effectiveness of the back-track method is influenced by the physical layout of the project site; longer distances between scrapers and varying terrain can increase backtrack time significantly. Therefore, while this method is slower, it is often preferred due to its simplicity and because it allows for continuous cutting in a uniform direction, reducing complications during the operation.

Think about a train traveling on a circular track. If it has to take a detour to return to the start before picking up passengers at a new station, it is slower than if there were direct stops along the way. Operators choose this method for its straightforwardness, much like how the train operates continuously on the same track.

So, the next method which we are going to discuss is your chain loading method. So, this we commonly follow for long cuts, long narrow cuts like your roads, we can follow the chain loading method, say here your pusher is pushing the scraper 1, once a scraper 1 is completely loaded the scraper 1 is now in fully loaded condition. Now your pusher will get detached from the scraper 1 and the pusher start pushing the next scraper. But here is what happens the scraper 2 will come and wait near the pusher. Your pusher may not backtrack again; it may not return back again and spot the next scraper.

In the chain loading method, the process is more efficient compared to back-track loading. Once scraper 1 is loaded, instead of the pusher traveling back to grab the next scraper, scraper 2 is already positioned near the pusher. This reduces the return time significantly, making the cycle time shorter. Thus, this method is particularly beneficial for long and narrow projects such as roads where scrapers can be lined up waiting for the pusher.

Imagine a production line in a factory where workers pass items from one to another. Instead of going back to pick up new items, the next worker in the line is already ready to receive and process the previous item. This keeps the line moving smoothly and efficiently, just like how chain loading minimizes waiting time.

The next one is shuttle loading, this is not commonly followed, but you can follow it when you have 2 fill areas. That means you have a fill area in this direction as well as you have fill area in this direction. If you have fill areas in both the direction, then you can follow the shuttle loading. So, what happens here is the pusher is pushing the scraper 1. The scraper 1 is now completely fully loaded, it is fully loaded. After that your pusher is getting detached from the scraper 1 and it starts pushing another scraper in the opposite direction.

The shuttle loading method is advantageous when there are fill areas available in both directions. Once the pusher finishes loading scraper 1, instead of returning to one direction to pick up another scraper, it switches and pushes a scraper in the opposite direction. This method further reduces return time and consequently, the overall cycle time. However, its application is limited since it requires specific site conditions.

Think about a swing that can go back and forth. If one side of the swing is full of kids waiting to go, the swing can just continue back and forth without stopping to return to the starting point. This efficiency showcases how shuttle loading maximizes operations in settings where multiple loading zones are available.

So, when you compare all these 3 methods, you can see that your back-track is the slowest method, the cycle time is relatively higher because it has to backtrack or return to support the next scraper but your chain and shuttle loading though they are not commonly followed so, but they are having the lesser cycle time and we know the reasons already.

In summary, the back-track loading method is the slowest due to the necessary return journey, leading to greater cycle times compared to chain and shuttle loading methods. The latter two methods are more efficient as they reduce the return travel distance, ensuring that scrapers are continually loaded and unloaded with minimal downtime.

Consider different delivery methods in a shipping company. A delivery truck that has to return to the warehouse for each drop-off will take longer than one that can deliver multiple items in a single round, similar to how chain and shuttle loading optimize the loading and unloading process.

So, to summarize back-track loading method is the slowest of all the methods because of the additional pusher travel time for backtracking on returning. But most commonly followed because people prefer cutting in the same direction. Chain loading, it is suited for long and a narrow cut, here the return time is reduced. Shuttle loading requests 2 separate fill areas in both direction. So, you can see scrapers moving in both directions, this is also having shorter cycle, but this is the one which is commonly followed.

To determine the cycle time of the pusher, one can use a formula based on the loading time of the scraper. The relationship between the two is given as Tp = 1.4Lt + 0.25, where Tp is the cycle time of the pusher and Lt is the loading time. Understanding this relationship is crucial for planning and optimizing the loading processes on construction sites.

Think about calculating the time it takes to bake cookies. If you know how long it takes to bake one batch (loading time), you can estimate how many batches you can manage in a day (cycle time). This helps bakers optimize their workflow to get the most cookies baked efficiently.

Another important thing as I mentioned earlier, we need to balance the interdependent machines, your scraper and pusher are interdependent machines, they work together. So, we have to balance them, we have to choose the correct number of scrapers and pushers, so that one need not wait for the other. So, we have to reduce the waiting time of the machines, so that we can reduce the cycle time, increase the productivity and reduce the production cost.

To achieve a harmonious operation between scrapers and pushers, it is essential to maintain a balance in their numbers. A pusher should ideally serve multiple scrapers (4 to 5), based on their respective cycle times. By calculating the number of scrapers that can effectively be served by one pusher, waiting times can be minimized, leading to improved productivity and reduced costs.

Just like a restaurant must balance the number of chefs and waitstaff to ensure customers are served promptly, construction teams must manage the number of scrapers and pushers. If there are too many scrapers for each pusher, they will be idle, wasting both time and resources, similar to customers waiting too long for their meals.

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