Karteikarten
Deep Foundations
Karten in diesem Stapel (14)
- 1When are deep pile foundations used and why?1. The soil at the surface is soft-deep foundations can transmit load down to more competent strata.
- 2When are deep pile foundations used and why?2. There are high horiz wind loads present or uplifting-shallow foundations can not take high horizntal loads relative to their vertical loads. They are vulnerable to sliding failure, whereas deep foundations can. (Wind turbines). Uplift is where the foundation is pulled vertically upward (off shore tension-leg platforms)
- 3When are deep pile foundations used and why?3. Scour can occur- Below water, in a region of high sediment transport (seabeds, rivers), foundations can be vulnerable to scour and erosion. This effects deep foundations less than shallow.
- 4What is a pile?Relatively long and slender members used to transmit foundation loads through soil strata of low bearing capacity to deeper soil or rock having a higher bearing capacity.
- 5What is an end-bearing pile?When the bearing stratum is a hard and relatively impenetrable material such as rock or very dense sand/gravel. In this case the pile derives much of its carrying capacity from the resistance of the stratum at the toe of the pile.
- 6What is a sheet pile?Used to support earth or water in cofferdams for foundation excavations or as retaining walls.
- 7What is a friction pile?If a pile does not reach an impenetrable stratum but is driven for some distance into the soil, it derives its carrying capacity partly from the end-bearing and partly from skin friction between the pile shaft and the surrounding soil.
- 8What is a displacement pile?A pile that pushes the soil out radially and down vertically when it is installed. This leads to high horizontal stresses in the soil acting on the pile shaft which improves the shaft resistance.
- 9What are the different displacement piles?Driven- preformed units driven into the soils by the blows of a hammer.
Driven & cast-formed by driving a tube witha closed end into the soil and then filling with concrete. Tube may or may not be withdrawn.
Jacked or pressed. - 10What is a non-displacement pile?Constructed by boring a hole in the ground and then filling it with concrete, reinforced with steel reinforcement if on-shore or by a steel tube if off shore.
- 11What are some types of non-displacement piles?Bored & cast - a hole bored into the ground and filled with concrete.
Concrete/grout intruded piles - hole is formed by a hollow stemmed flight auger. The concrete grout is placed as the auger is extracted. - 12Explain the differences between how displacement and non-displacement piles carry load?Displacement piles are stiffer than for bored since the installation process causes compaction and hence stiffening of the surrounding soil. For bored piles, in situ soil stresses can be relieved during the excavation process if not maintained by a drilling fluid resulting in a softer initial response
- 13Explain the differences between how displacement and non-displacement piles carry load?The soil at the base of a displacement pile has been preloaded beyond in situ conditions so it tends to be on an unload-reload loop which is stiffer. The soil at the base of a bored pile has not been preloaded so tends to be less stiff. Base grouting can improve stiffness.
- 14Where can piles derive their stiffness from?Axial capacity from shaft and base resistance. Lateral capacity from the horizontal soil pressure acting alongside the shaft. This must not create a bending moment that would exceed the plastic moment capacity of the shaft.
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- Geotechnical Engineering Karteikarten am Deep Foundations, erstellt von Billie Santos am 13/04/2017.
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- Billie Santos
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