2.2.1. Back-Track Loading

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) So, cycle time of a scraper, it is nothing but load time, hauling time, dumping time, return time spotting because most of the conventional scrapers a pusher loader scraper. So, it has to spot the pusher, that spotting time is also included then turning, then ADBT that means the time needed for increasing your speed or decreasing the speed, time needed for applying the brakes. So, all this manure comes under this ADBT acceleration deceleration and the braking.

The cycle time of a scraper is broken down into several components, each represented by an abbreviation. This includes loading time (LT), hauling time (HT), dumping time (DT), return time (RT), spotting time (ST), turning time (TT), and ADBT which accounts for acceleration, deceleration, and braking. Understanding these components helps in specifying how long the scraper takes to complete its entire operation from loading to returning empty.

Imagine a school bus. The time it takes for the bus to make a full round — from picking up kids, driving to school, dropping them off, returning back, and then parking — can be compared to the cycle time of a scraper. Each step (picking up, driving, dropping off, etc.) takes a certain amount of time that sums up to the total bus round's duration.

So, basically you can split the cycle time into 2 parts. One is fixed time, other one is variable time. Fixed in the sense this part of the cycle time does not depend upon your travel distance. So, that is called as fixed time, say your loading, dumping, turning, your accelerating, decelerating. All these things comes under the fixed time. So, it is not dependent upon the distance travelled. The other one is a variable time, your haul and return is a variable time because it is significantly dependent on your travel distance.

Cycle time can be categorized into fixed time and variable time. Fixed time includes components like loading, dumping, and turning, which remain constant regardless of how far the scraper travels. In contrast, variable time encompasses hauling and returning, which are heavily dependent on the distance traveled and the speed of the scraper.

Consider baking a cake. The time taken to prepare the batter and bake it is fixed; it won't change regardless of how many cakes you decide to bake. However, if you decide to deliver the cakes to a different location, the time it takes to get there varies based on traffic and distance. Similarly, in a scraper's operation, some tasks (like loading) have a fixed duration, while others (like hauling) may change.

So, basically the loading time of the scraper is fairly consistent irrespective of the scraper size. So, that means whether it is going to be a smaller scraper or bigger scraper in both cases. So, commonly we can say that we are going to assist this scraper with the help of a pusher according to the size of the scraper the compatible size of the pusher you have to select and we are going to supplement the loading power.

The loading time for scrapers remains relatively uniform whether the scraper is large or small. This is largely because scrapers are often assisted by pushers, which help in the loading process. The size of the pusher must correspond to the size of the scraper for effective operation.

Think of a friend helping you carry boxes to a car. Whether it's a small box or a big one, your friend can help out in a similar timeframe. Similarly, a pusher assists scrapers regardless of their size, making the loading process steady and efficient.

Another important concept which we need to know is about the load growth curve for scraper loading. So, we commonly believed that when we load this scraper when we fill the bowl of the scraper to the maximum capacity we are going to maximize a production. So, this is what is a common belief this is what is a common assumption, but that is not true.

The load growth curve indicates that loading a scraper to its maximum capacity can actually reduce production. Early loading occurs efficiently, but as the bowl fills (around 85% capacity), resistance increases because the incoming material struggles against what is already in the bowl. This results in a decrease in the rate of loading, illustrating a principle known as the 'law of diminishing returns.'

Imagine trying to stuff too many clothes into a suitcase. At first, you can fit many shirts and pants easily, but as it gets closer to full, you find it increasingly difficult to add more. Each piece you try to add meets resistance from the clothes already there, which is similar to how loading too much material in a scraper decreases efficiency.

the next important component of the cycle time of the scraper is your haul and return time, as I told you it is a variable time, it is going to depend upon your travel distance and the speed of your machine.

Haul and return times are variable components of the scraper's cycle time. These durations depend on the distance traveled and the speed at which the scraper operates, which can be influenced by project site conditions, such as rolling resistance and grading.

If you're running a race, the time it takes you to complete it will depend on how far the race is and how fast you can run. Similarly, a scraper's haul and return time relies on how far it needs to travel and how quickly it can move based on the terrain.

So, the next important thing which we are going to see as a component of your cycle time is your dump time. So, your dump time of your scraper it depends upon your scraper size obviously, bigger the scraper your dumping time will be more.

Dump time, which is the duration taken to unload material, is influenced by the size of the scraper and the type of material being dumped. Looser materials can be dumped quickly, while cohesive, sticky materials require more time. Additionally, site constraints, such as congestion, can further affect the dumping process.

Imagine trying to pour sand out of a bag versus trying to pour molasses. Sand (a loose material) flows out quickly, while molasses (a sticky material) takes significantly longer to pour out. This highlights how material characteristics affect dumping times.

So, you can see that the turn time is basically not affected by the type or the size of the scraper. So, hope you remember the picture which I have shown to show the production cycle of the scraper, you can see the scraper commonly you can see that 2 turnings are done by the scraper.

Turn time is an important aspect of the scraper's cycle time, and it is generally consistent, regardless of the scraper's type or size. However, turn times can vary depending on the environment, such as whether the turn occurs in a congested area (cut area) or a more open area (fill area), with congestion typically increasing turn durations.

Think of driving a car. Making a wide turn in an open parking lot is quick, but doing the same turn in a crowded space with several obstacles takes much longer. This serves to illustrate how site conditions can influence turn times for scrapers.

As we discussed earlier when you use a pusher for assisting your scraper, you can reduce the loading time of the scraper, it will help you to increase the productivity of the scraper and reducing unit production cost of the scraper.

Using a pusher to assist scrapers during loading can decrease loading time, thereby enhancing overall productivity and reducing costs. However, it is critical to balance the number of scrapers with pushers to avoid either machine waiting for the other, which would lower operational efficiency and increase costs.

Imagine having a team for a relay race. If one runner gets tired and can't hand off the baton on time, the entire team's performance suffers. Similarly, balancing scrapers and pushers ensures smooth operations, maximizing efficiency and minimizing idle time.

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