driving cap is used, the chamfered butt must fit the cap.When a cap is not used, the top end of the pile is wrappedwith 10 or 12 turns of wire rope at a distance of aboutone diameter below the head of the pile (fig, 10-9, viewsA and B). When a hole is bored in the butt of the pile,double wrappings are used (view C). The pile can alsobe wrapped or clamped if the butt is crushed or split. Asan alternative to wrapping, two half-rings of 3/8-inchsteel are clamped around the butt (view D).The tip of the pile is cut off perpendicular to its axis.When driven into soft or moderately compressible soil,the tip of the pile may be left unpointed. A blunt-endpile provides a larger bearing surface than a pointed-endpile when used as an end-bearing pile. When driven, ablunt-end pile that strikes a root or small obstructionmay break through it.Where soil is only slightly compressible and mustbe displaced, the tip of the pile is usually sharpened tothe shape of an inverted truncated pyramid (fig. 10-9,view A). The blunt end is about 4 to 6 inches square;the length of the point is 1 1/2 to 2 times the diameterof the pile at its foot. A crooked pile maybe pointed fordriving, as shown in view B.For hard driving, steel shoes are used to protectthe pile tips. A manufactured shoe is shown in viewC, and an improvised steel shoe is shown in view D.Steel BearingSteel ranks next to timber in importance,especially where the construction must accommodateheavy loads or the foundations are expected to be usedover a long period of time. Steel is best suited for useas bearing piles where piles must be driven under anyof the following conditions:Piles are longer than 80 feet.Column strength exceeds the compressivestrength of timber.To reach bedrock for maximum bearing surfacethrough overlying layers of partially decom-posed rock.To penetrate layers of coarse gravel or soft rock,such as coral.To attain great depth of penetration for stability(for example, driving piles in a rock-bedded,swiftly flowing stream where timber piles can-not be driven deeply enough for stability).One of the most common types of steel bearingpiles is the pipe pile. An open-end pipe pile is open atthe bottom. A closed-rid pipe pile is closed at thebottom. Another common type of steel pile is theH-type, often seen as HP. When driving HPs, a specialdriving cap (shown in fig. 10-10) is used.Figure 10-9.-Preparation of timber piles for driving.Figure 10-10.-HP-bearing pile and special cap for driving10-5
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