2.3. Excavating Below Ground Level

They have poor mobility. So, that is why it is preferable to place a truck very close to the excavator. So, very commonly you can see that the truck is placed at 90 degrees. So, the truck is placed at 90 degrees, this will be 90 to the bucket position. This is a common position. Basically, angle of swing is nothing but the horizontal angle between the digging and the dumping positions between the loading and the dumping positions.

When excavators need to load material onto a truck, having the truck positioned nearby is crucial since excavators cannot move quickly. An ideal positioning at a 90-degree angle enables efficient material transfer. The angle of swing refers to the horizontal angle that the excavator’s bucket must pivot between the digging action and the dumping action onto the truck. This positioning allows for a smoother and faster workflow in excavation tasks.

Think of it like a basketball player making a layup. If the hoop is directly in front of them, they can score easily, just like the excavator loading material directly into the truck without excess movement. But if the hoop is positioned to the side, the player has to adjust their stance and angle, increasing the time and effort to score—similar to how the excavator must swing more if the truck isn’t positioned correctly.

As the truck moves further away, your angle of swing would increase. As the angle of swing increases, your cycle time will increase, and productivity will decrease. The ideal production of a shovel is based on a 90-degree swing.

When the truck is not positioned optimally, the excavator has to swing its bucket at a larger angle to load the truck. This increases the cycle time—the amount of time it takes to complete one loading operation—and thus decreases overall productivity. Therefore, maintaining a 90-degree angle of swing is crucial for maximizing efficiency during the material handling process.

Imagine trying to throw a ball to a target. If you're directly facing the target, you can throw it quickly and accurately. But if you have to twist your body to reach the target, it will take longer and require more effort. In the same way, a greater angle of swing means more energy and time used, which isn't efficient.

Now, let us see what are all the adjustment factors we have to apply while doing the productivity estimation based upon the height of the cut of material…If the actual height of cut is the same as optimum height of cut, it means the percentage is 100%. So, in that case, you need not apply any correction factor.

When estimating productivity, it’s important to consider both the actual height of the material being excavated and the angle of swing. If these parameters deviate from ideal conditions (like the optimum height of cut and a 90-degree angle), correction factors must be applied to ensure accurate productivity calculations. For instance, if the actual height of cut is below the optimum, productivity decreases and a correction factor will account for this loss.

Think of a student preparing for an exam. If they study exactly the way they were taught (ideal conditions), they do well. But if they study too little or in a chaotic environment (not ideal), their performance drops. Similarly, if the excavation conditions aren’t ideal, the productivity will face a decline.

Now, another thing to be noted is truck spotting clearance… there should be some space left for the tail swing of the shovel.

While positioning the truck close to the excavator, it's essential to leave sufficient space for the excavator's tail to swing without hitting the truck. This clearance ensures safe operation, preventing accidents and allowing the excavator to function without obstruction.

Imagine a swing set. When swinging forward, you need to ensure there's enough space around you so you don’t hit anything. Just like kids need space to swing safely, excavators also require space to operate effectively without risking injury or damage.

Another important factor is haul unit exchange time… If your truck is not readily available for the loader to load the material or to dump the material into the truck, if you do not have a truck readily available, then the loader has to wait for the truck.

Haul unit exchange time refers to the duration required for a loaded truck to clear its position and for an empty truck to take its place. If the trucks aren't efficiently managed, excavation and loading operations can be delayed, increasing overall cycle time and reducing productivity. Minimizing this time requires careful planning and balancing the number of trucks and machinery involved in excavation.

Think of a fast-food restaurant's drive-thru. If the cars move quickly, customers get their orders faster. But if one car is slow in clearing out or preparing their order, it slows down everyone behind them. Similarly, efficient truck exchange ensures smooth operations at an excavation site.

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