What class of stones for riprap ranges from 15 kgs to a maximum of 25 kgs with at least 50% weighing more than 20 kgs?

Riprap is a method used in civil engineering for stabilizing shorelines, streambanks, and slopes against erosion. The classification of riprap stones is typically based on their weight and size to ensure proper effectiveness in their application.

The criteria outlined in the question describe a specific range and distribution of weights for riprap stones. The correct class, identified as Class A, specifies stones that weigh between 15 kg and a maximum of 25 kg, with the requirement that at least 50% of those stones must be heavier than 20 kg. This means the majority of the material used for the riprap needs to have adequate weight to resist moving under the influence of water flow, which is crucial for the structural integrity of the project.

In contrast, the other classifications—Class B, Class C, and Class D—have different weight ranges and characteristics. Class B typically involves heavier stones than what is specified in the question, while Class C may have a wider range, and Class D could involve lighter materials or requirements that do not meet the specific criteria set by the question. Understanding these classifications and their specifications is essential for selecting the appropriate stone for various engineering needs, emphasizing the importance of weight in ensuring stability and effectiveness in erosion control applications.