Quantcast Types of Piles

 
  
 
Figure 12-73.—Aligning and capping steel pile bents. driving, or that is to be salvaged (steel sheet piles are frequently salvaged for reuse) is usually  extracted (pulled). Pulling should be done as soon as possible after driving; the longer the pile stays in the soil, the more compact the soil becomes, and the greater the resistance  to  pulling  will  be.  Methods  of  pulling  piles are as follows: 1. In a direct lift method, a crane palls the pile. The crane hoist line is rigged to the pile through the use of wire rope rigging, and an increase in pull is gradually applied to the pile. Lateral blows from a  skull  cracker (heavy steel ball swung on a crane line to demolish walls) or a few light blows on the butt or head with the pile-driving hammer are given to break the skin friction, and the crane pull is then increased. If the pile still refuses to extract, it may be loosened by jetting, air extractors,  or  beam  pullers. 2. The 5,000-pound pneumatic, or steam, hammer may be used in an inverted position to pull piles. The hammer is turned over and the wire rope rigging is attached to it and the pile is extracted. A pneumatic extractor may also be used. The crane line, holding the hammer  or  extractor,  is  hoisted  taut;  and  the  upward blows of the hammer ram on the sling, plus the pull of the crane hoist, are usually enough to pull the pile. 3. Tidal lift is often used to pull piles driven in tidewater.  Rigging,  wrapped  around  the  piles,  is attached to barges or pontoons at low tide; the rising tide pulls the piles as it lifts the barges or pontoons. Types of Piles The  principal  use  of  piles  is  for  the  support  of bridges,  buildings,  wharves,  docks  and  other  structures, and in temporary construction. A pile transfers the load into an underlying bearing stratum by either of the following: 1. Friction along the embedded length of the pile 2. Point bearing plus any bearing from the taper of the pile A pile maybe classified roughly as friction or end bearing, according to the manner in which they develop support. The load must be carried ultimately by the soil layers around and below the points of the piles, and accurate knowledge of the compressibility of these soil layers is of utmost importance. Some of the common terms used with piles are as follows: 1. Piles. A pile is a load-bearing member made of timber,  steel,  concrete,  or  a  combination  of  these materials, usually forced into the ground to transfer the load to underlying soil or rock layers when the surface soils at a proposed site are too weak or compressible to provide  enough  support. 2. Pile foundation. A pile foundation is a group of piles that supports a superstructure or a number of piles distributed over a large area to support a mat foundation. 3. Bearing piles.    Piles that are driven vertically and used for the direct support of vertical loads are called  bearing  piles. Bearing  piles  transfer  the  load through a soft soil to an underlying firm stratum. They also distribute the load through relatively soft soils that are  not  capable  of  supporting  concentrated  loads. 4. End-bearing piles. Typical end-bearing piles are driven through very soft soil, such as a loose silt-bearing stratum  underlain  by  compressible  strata.  Remember this factor when determining the load the piles can support  safely. 5. Friction piles. When a pile is driven into soil of fairly uniform consistency and the tip is not seated in a hard layer, the load-carrying capacity of the pile is developed by skin friction. The load is transferred to the adjoining  soil  by  friction  between  the  pile  and  the surrounding soil. The load is transferred downward and laterally to the soil. 6.  Combination  end-bearing  and  friction  piles. Many piles carry loads by a combination of friction and end bearing. For example, a pile may pass through a 12-51


 


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