Selection of Deep Foundations.

Deep foundations provide an efficient foundation system for soils  that do not have a shallow, stable bearing stratum. Selection  of a deep foundation requires knowledge of its characteristics and capacity.

a.   Characteristics.  Information adequate for reaching preliminary conclusions about types of driven piles or drilledshafts to be selected for a project is given in Table 1-4.  This table  lists major types of deep foundations with respect to capacity, application, relative dimensions, and advantages and disadvantages.  Refer to Foundations (Pile Buck Inc. 1992) for additional  information.  Information in the table provides general guidelines in the selection of a type of deep foundation. Relevant...

b.  Capacity.  Deep foundations transmit structural loads to deep strata that are capable of sustaining the applied loads.Accurate predictions of load capacity and settlement are not always possible.  Adequate safety factors are therefore used to avoid excessive movement that would be detrimental to the structure that is supported and to avoid excessive stress in the foundation.   Driven piles or drilled shafts are often used to resist vertical inclined, lateral, or uplift forces and overturning...

c.   Applications.  Driven pile groups are typicallyused by the Corps  of  Engineers to support locks, dry docks, and other facilities constructed  in river systems, lakes, lagoons, and other offshore applications.   Drilled shafts typically support many permanent onshore structures such as administrat ive buildings, warehouses, dormitories, and clinics.    Drilled  shafts are divided into two groups: displacement and mnondisplacement. (1)  Displacement.  Dri...

d.  Location and topography.  Location and topo-graphy strongly influence selection of the foundation.  Local practice is usually an excellent guide.  Driven piles are often undesirable in congested urban locations because of noise, inadequate clearance for pile driving, and the potential for damage caused by vibration, soil densification, and ground heave.  Prefabricated piles may also be undesirable if storage space is not available.  Other variables may restrict the utilization of deep foundation: (1)...

e.  Economy.  (1) Driven piles. Costs will depend on driving rig rental, local labor rates, fuel, tools, supplies, cost and freight of pile materials, driving resistance, handling, cutoffs, caps, splicing, and jetting.  Jetting is the injection of water under pressure, usually from jets located on opposite sides of the pile, to preexcavate a hole and to assist pile penetration.  Costs are also influenced  by downtime for maintenance and repairs, insurance, overhead, and profit margin.  An...

f.  Length.  The length of the deep foundation is generally dependent on topography and soil conditions of the site.(1) Driven piles. Pile length is controlled by soil conditions and location of a suitable bearing stratum,availability and suitability of driving equipment, total pile offshore.  Piles up to 150 feet are technically and economically weight, and cost.  Piles exceeding 300 feet have been installed acceptable for onshore installation. (2) Drilled shafts. Shaft length depends on the depth...

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