Stock Pile Segregation
This post will primarily focus on how to deal with segregation of a stockpile after you have already made the product.
Lets say you have a segregated aggregate base pile like the one I showed you in my last post. Your boss probably won't be keen on throwing out all of that material and starting over so how do you fix the problem once you already have a segregated stockpile? I'd say with a good loader operator and a few extra minutes before load out. When moving a stockpile to another location or loading material out of a stockpile and into trucks, the loader operator can perform an action called "fluffing the pile" to mix the material back up and de-segregate it. Your plant may call this by another name, I've heard it called "bucking the pile" and "mixing the pile" as well and I'm sure there are a hundred other names to it depending on where the plant is located. The important thing is how it is done.
The loader operator will take three vertical cuts of the stockpile. His first cut will be in the middle of the pile and then to the right or left of the first cut as seen in the picture below. It is tempting to take only one big cut to fill the loader's bucket but the more cuts you take, the less segregated the load will be.
To execute these cuts effectively, the loader operator must position the bucket as close to the ground as possible without making contact. It is imperative to prevent the loader bucket from scraping the ground when extracting material from the stockpile. The plant floor differs in material type, size, and gradation from the stockpile, and any contact between the bucket and the ground would result in contamination of the material being collected. Additionally, it should be noted that the lower 2 feet of the stockpile can potentially be contaminated with native soil, particularly in the case of clean, fine products like concrete sand. Mud can infiltrate the stockpile, compromising its purity and reducing the cleanliness of the material in the lower section. This is one of the reasons why many plants are transitioning to concrete or paved floors beneath their wash plant stockpiles.
Once the loader bucket is positioned near the base of the stockpile, the operator should push the bucket into the pile while simultaneously raising it towards the top, following the procedure depicted in the accompanying image. It is crucial that the operator avoids merely skimming the outer layers of the pile and instead pushes the bucket as deep as possible into the pile. This ensures the collection of both coarse material from the outer layers and fine material from the interior, guaranteeing comprehensive mixing and de-segregation.
Following each cut, the loader operator will redistribute the material onto the side of the pile and proceed to the next designated section. This approach facilitates the thorough blending of the materials before loading them into trucks, ensuring the attainment of a homogeneous product. When loading trucks, it is crucial for the loader operator to maneuver around the outer perimeter of the pile instead of continuously digging deeper into a single section. Apart from safety considerations, progressing towards the center of the pile results in finer material, underscoring the significance of ongoing mixing between the outer and inner regions while circling the stockpile. To maintain a consistent loading process, the loader should initiate operations from the midpoint of one side of the stockpile, fluff that particular section, and subsequently proceed to each adjacent side as trucks are being loaded. This rotational movement along the side of the pile, spanning a 180-degree arc as illustrated in the accompanying image, ensures uniformity in the loaded material. By consistently scooping similar material for each load, the practice prevents scenarios where one truck receives an excessively coarse product followed by another truck receiving an extremely fine material. Furthermore, it is vital to continue fluffing the stockpile as the loader progresses towards untouched sections. Just as the initial section required mixing, these unprocessed areas demand the same level of attention and blending.
The method described above represents a single approach for addressing stockpile segregation issues within an aggregate plant. I invite you to share your own solutions, as I value your input and insights. As an extension of this ongoing discussion, my forthcoming post will concentrate on techniques for the movement and stockpiling of aggregates that mitigate both segregation and degradation.