Figure 5-9.-Layout and development of a pit, using a dragline.PIT OPERATIONSSand, gravel, and other construction materials areextracted from pits with scrapers that can move hugevolumes of material in a relatively short period of time.The material is removed from the floor of the pit insuccessive thin layers over its entire width.During excavation, scrapers should be carefullyspotted to maintain an even downgrade and preventcutting holes below the general level of the pit floor.When the pit is longer than 100 feet in the direction ofloading, the scraper spots should be staggered along thelength of the cut as well as across the width of the zone.Figure 5-8 depicts the layout and development of ascraper pit with lines A-A and B-B showing the limitsof the pit. Lines A-A and B-B divide the area into threezones for current excavating, stripping, and clearing.Zone 1 is being excavated at the same time Zone 2 isbeing stripped and Zone 3 is being cleared. Threescrapers in staggered formation load downhill in Zone1, and a dozer strips downhill in Zone 2.In consolidated gravel or soft rock, when scrapersassisted by pusher tractors (Push Cat) will not pickup aheaping load within 150 feet, a ripper should be used toloosen the material, thereby increasing the loadingefficiency of the scrapers. Rippers should be operateddownhill, and an entire zone should be ripped at one timewhile the scrapers are hauling from another zone.The dragline is the most practical piece ofconstruction equipment for underwater digging and isparticularly adapted to submerged gravel pit operations.Draglines can efficiently recover sand, gravel, laterite,or coral from beaches, the beds of streams, and thebottoms of lakes and lagoons. Figure 5-9 depicts thelayout and development of a pit being excavated with adragline.Clamshells are capable of excavating loose sand,gravel, and crushed stone at, above, or below groundlevel. The clamshell can be raised and loads dumped atheights equal to the distance from the tip of the boom tothe ground, minus the length of the clamshell bucket, toallow adequate clearance for the bucket when it isopening.Material removed from pits can seldom be used inits inplace state. In most cases, pit material must beprocessed (crushed and screened) to meet jobspecifications. But, before the material can beprocessed, it must be loaded and delivered to theprocessing equipment. Loading and delivery mayrequire additional handling equipment, such asfront-end loaders equiped with either a rollback bucketor 4-in-1 bucket and conveyers that may be used singlyor in series to load vehicles, construction equipment, orhoppers from stockpiled material. Bucket loaders mayalso be used. They consist of a power-driven endlesschain to which buckets are attached so material is loadedon the downward travel. Handling equipment is used to5-11
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business