Pile Foundation Functions


When the soil beneath the level at which a footing or raft would normally be established is too weak or too compressible to provide adequate support, the loads are transferred to more suitable material at a greater depth by means of piles or piers. The distinction between the two is somewhat arbitrary.

Piles

Piles are the structural members of small cross-sectional area compared to their length, and are usually instated by a driver consisting of a hammer or a vibrator. They are often grouped into clusters or rows, each containing enough piles to support the load delivered by a single column or wall.

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Important Factors To Consider During Pile Design

A lightly loaded column may, in some instances, require only a single pile. However, since under field conditions the actual position of a pile may be  as much as several inches from its planned location, an eccentric loading can hardly be avoided. Consequently, the heads of single piles are usually braced in two directions by grade beams. If only two piles are needed, their heads may be connected by a concrete cap braced by grade means in only one direction, perpendicular to the line joining the two piles Fig.1(b). Clusters containing three or more piles are provided with reinforced concrete caps, as shown in Fig.1(c), and are considered stable without support by grade beams.

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Vertical piles may also be used to resist lateral loads as for example, beneath a tall chimney subject to wind. Compared to their axial capacity, the lateral capacity is usually small. Where large lateral loads are to be used (Fig.1d.) Batters of 4 horizontal : 12 vertical represent about the greatest inclination that can be achieved with ordinary driving equipment. Economy usually favors smaller inclinations even if more piles have to be battered.

Functions of Pile Foundation

Piles are used if the bearing capacity of soil at shallow depth is not enough to withstand the structural load. So the piles are driven  to transfer the loads from the structure to the high bearing capacity soil/rock stratum. The main functions of using pile foundations are listed below in short.

  • To transfer the load from the structure to the foundation at a greater depth where the \bearing capacity of soil is efficient to withhold the structure loads.
  • Pile controls the soil settlement which can be accompanied by surface foundations.
  • Piles are used to increase the safety factor for high loaded structures.
  • Piles enable the scope of construction in very low bearing capacity soils

Note : Article Courtesy : http://civilengineersforum.com/function-of-pile-foundation/

IMPACT OF SEDIMENT MANAGEMENT ON RESERVOIR LIFE


As shown in Figure, the Initial Reservoir Storage is the sum of Future Storage Requirements, Active Storage, and Dead Storage. The line designated as Today is the point at which sediment mitigation is implemented.

Impact Of Sediment Management On Reservoir Life

The Reservoir Capacity line indicates the steady decline of the reservoir’s storage capacity as sediment accumulates over time. This storage loss begins the moment water is stored. The rate of capacity decline (slope of the line) depends on local conditions. In reality, the decline of reservoir capacity is an irregular process with the greatest sediment accumulation taking place during annual spring runoff and during rainfall events. Both of these change over the years too. The rate of capacity decline is estimated as a straight line from the time the reservoir is built until today, and projected into the future.

The Required Storage Capacity line indicates the minimum storage necessary for the water system, of which the reservoir is a part, to function. Notice the intersection of the Reservoir Capacity line and the Required Storage Capacity line. This is the time when the reservoir capacity can no longer meet the requirements for which the reservoir was built. This occurs long before the reservoir is completely filled with sediment.

As time passes beyond this point, reservoir uses can become more and more restricted. The restrictions can pass unnoticed due to the normal variations in the water supply and reservoir usage. With sufficient data, this point can be estimated to plan for the future and help determine the urgency for sediment mitigation actions. This typically varies from when 15 to 40 percent of the reservoir storage is lost.

Case 1 – shows the reservoir capacity over time if no action is taken and sediment is allowed to accumulate with no mitigation.

Case 2 – shows the reservoir capacity if one, or more, sediment mitigation strategies are implemented, resulting in a slower rate of sediment accumulation in the reservoir. Notice the resulting extension of the reservoir’s useful life.

Case 3 – shows the reservoir capacity after removing a certain volume of sediment from the reservoirand simultaneously enacting one, or more, sediment mitigation strategies that results in slowing the rate of sediment accumulation. Notice the greater extension of the reservoir’s useful life than Case 2.

Case 4 – shows the reservoir capacity after enacting one, or more, sediment mitigation strategies that result in stopping sediment accumulation in the reservoir completely. Depending on local conditions, this may or may not be possible. When it is possible, the Reservoir Capacity and Required Storage Capacity lines never intersect and the reservoir’s useful life is potentially extended indefinitely. One scenario to achieve this is a combination of bypassing sediment during spring runoff and hydrosuction removal of previously accumulated sediment. Hydrosuction or another single method alone could also accomplish this.