What is group action of piles?
Group action. Piles driven in clay derive their capacity from friction. They are commonly driven in groups or clusters beneath individual footings or as single large groups beneath mats or rafts.
How is Downdrag calculated in piles?
Downdrag load on pile is the sum of the negative shaft resistance along the length of the pile where the soil is m oving downward relative to the pile.
What is group capacity of piles?
Capacity of pile group is the sum of the individual capacities of piles, but it is influenced by the spacing between the piles. If piles are spaced sufficient distance apart, then the capacity of pile group is the sum of the individual capacities of piles.
What is negative skin friction in piles?
Negative skin friction occurs when concrete piles are situated in soft soils, consolidating soil-mass, etc., resulting in a downward force that increases loading on shaft piles and reduces the bearing capacity of the piles.
What are the factors affecting selection of piles?
Factors affecting the selection of Pile Foundation Soil conditions. Loads from structures. Nature of loads. Number of piles to be used.
How many piles do I need?
At least three capped piles are needed to ensure stability against lateral forces (with the exception of caisson piles). Capping beams are also suitable for distributing the weight of a load-bearing wall, or of close-centred columns to a line of piles.
What is Downdrag on a pile?
Downdrag is pile settlement in response to settlement of the surrounding soil. In fact, downdrag can limit structure settlement by pre-compressing the pile and the soil at the pile tip prior to application of the structure load.
What is Downdrag?
Downdrag is pile settlement in response to settlement of the surrounding soil. The bearing capacity approach to downdrag leads to erroneous design calculations and the implementation of unnecessary construction mitigation techniques.
What is pile working load?
Working load : the load which the pile is designed to carry without exceeding the allowable settlement requirement.
How do you know if skin friction is negative?
Calculating Negative Skin Friction A = horizontal area bounded by the pile group or cross-sectional area of piles and enclosed soil. N = no. of piles in pile group. g = unit weight of fill or compressible soil layers.
What are the conditions of soils that require pile foundation?
Conditions That Require the Use of Pile Foundation
- Compressible or Weak Upper Soil Layer.
- Presence of Horizontal Forces.
- Presence of Expansive Soils.
- Subjected to Uplifting Forces.
- Soil Erosion.
Why pile foundation is used in clay soil?
Clay and silt are especially vulnerable if they’re saturated since they liquefy easily. However, anywhere that has a high water table or shows signs of being marshy are potentially vulnerable, and piling should be considered.
How do group effects affect the downdrag force in a pile?
It is found that group effects lead to a reduction in downdrag force in a pile, as compared with a single isolated pile, and that inner piles in a group develop less downdrag force than the outer piles.
What causes downdrag friction in piles?
Long-term consolidation, seismic dry sand and liquefaction-induced settlements of a soil deposit can impart significant amount of downward load to piles. This load, called downdrag or negative skin friction, is caused by the friction between the pile and the downward moving soil.
Do group effects affect the behavior of end‐bearing piles under negative friction?
This paper describes a boundary element analysis for analyzing the behavior of a group of end‐bearing piles subjected to negative friction. It is found that group effects lead to a reduction in downdrag force in a pile, as compared with a single isolated pile, and that inner piles in a group develop less downdrag force than the outer piles.
What is downdrag or negative skin friction?
This load, called downdrag or negative skin friction, is caused by the friction between the pile and the downward moving soil. The magnitude of this force can be estimated by using neutral plane method which was briefly described in my previous post (click here).