What is riprapin construction?

Both appear on drawings and bid forms, and quarries sell by the ton, so estimators routinely convert between them. The conversion uses placed unit weight, which includes the voids between stones and is meaningfully lower than solid rock density; an illustrative working figure is on the order of 1.3 to 1.5 tons per cy depending on the stone and gradation. Whatever number you use, state it on the takeoff so the conversion is auditable.

Without a filter layer, flowing water moves through the voids between stones and washes the underlying soil out from beneath the blanket, a failure mode called piping. The stone then settles, the protection unravels from the bottom, and the outfall scours anyway. A nonwoven geotextile filter fabric (or a granular filter layer) holds the soil in place while letting water pass, which is why nearly every riprap detail shows fabric and why the takeoff should always carry it.

A class is a specified gradation, a range of allowable stone sizes usually described by weight or dimension around a median stone size. The catch is that class names are not national: each state DOT defines its own, so the same class number means different stone in different states. Price the gradation in the project spec, confirm your quarry can produce it, and remember that larger classes cost more to haul and place per ton.