of the debris (n.碎屑片,堆积层). The accepted procedure is to remove practically all vegetable matter from the original ground and from fill material , since , if allowed to remain , it may decay and leave voids that result in settlement. Selective clearing in adjoining areas may at times be required.
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For hauls of considerable length or over the public highways where axle loads are limited, rear- dump trucks (后卸式货车)or bottom-dump trucks (底卸式货车) loaded by front-end loaders (前端装载机), power shovels(挖土机), or belt conveyors may be cheapest. At times, weather may be a controlling factor. For example, the rubber-tired tractor units have difficulty in operating on wet, slippery roadbeds. Thus, in areas subject to heavy rainstorms, scrapers pulled by track-type tractors may bemore satisfactory.