Recent Advances In Pile Foundation - Bcm Seminar

Recent Advances in Pile Foundation

Asha N M Manali Hegde Ritu Susan Kurien

Recent Advances • Micropiles • Soldier Piles • Suction Piles • Adfreeze Piles

Micropiles • Micropiles can be defined as small diameter piles, typically less than 150mm, where the pile load is carried structurally predominantly by the pile reinforcement. Hence micropiling is often relatively heavily reinforced with a substantial full length central reinforcement bar. Micropiles are normally grouted due to small volumes. • Micropiles, also called mini piles, are used for underpinning. Micropiles are normally made of steel with diameters of 60 to 200 mm. Installation of micropiles can be achieved using drilling, impact driving, jacking, vibrating or screwing machinery.

Micropiling Advantages • • • • • • • • • •

Small lightweight equipment Low noise and vibration Suitable for tension loads Minimal site preparation Can be installed successfully into most ground conditions including rock High output - combined drilling and grouting make high piling outputs possible Limited headroom, restricted access capability Rapid mobilisation and setup High loads in restricted access and low headroom sites Suitable for refurbishment projects, bridgework, tunnel work and basement works.

Soldier Piles The soldier pile wall is a temporary or permanent retaining wall commonly used for excavations in urban areas. The soldier pile wall is the archetype of quick, inexpensive shoring. It is, however, only applicable in the absence of groundwater (or with only small quantities of water) and in cohesive soils. The soldier pile wall provides first and foremost temporary shoring but can be made permanent with certain adaptations. The method consists of : 1. Drilling regularly spaced boreholes in which metal beams are sunk 2. Installing cladding (wood, shotcrete, steel plates) between the beams as the excavation progresses The stability of the retaining wall is temporarily provided by struts or anchors except in shallow excavations where the wall may be self-supporting.

Construction • • • • • • • • • • • •

Construction of a soldier pile wall is practically free of ground disturbance. It involves 5 main stages : 1 • Drilling of large diameter boreholes 2 • Sinking of a beam embedded with concrete or slurry at the bottom and filling from the top 3 • Continuing the excavation in successive layers 4 • Installing the cladding, which may consist of planks, railway sleepers, shotcrete or concrete cast in situ 5 • Stabilising of the curtain wall for depths of more than 3 m by anchors or struts

Use This type of wall is used mainly for : • Shoring of excavations where no displacement is possible • Shoring of narrow excavations (underground railways and sewers) at varying depths, combined with strut bracing. • Shoring of buildings or structures without settlement

Suction Piles • •

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Suction piles are used underwater to secure floating platforms. Tubular piles are driven into the seabed (or more commonly dropped a few metres into a soft seabed) and then a pump sucks water out the top of the tubular, pulling the pile further down. The proportions of the pile (diameter to height) are dependent upon the soil type: Sand is difficult to penetrate but provides good holding capacity, so the height may be as short as half the diameter; Clays and muds are easy to penetrate but provide poor holding capacity, so the height may be as much as eight times the diameter. The open nature of gravel means that water would flow through the ground during installation, causing 'piping' flow (where water boils up through weaker paths through the soil). Therefore suction piles cannot be used in gravel seabeds. Once the pile is positioned using suction, the holding capacity is simply a function of the friction between the pile skin and the soil, along with the self-weight and weight of soil held within the pile. The suction plays no part in holding capacity because it relieves over time. The wall friction may increase slightly as pore pressure is relieved. One notable failure occurred (pullout) because there was poor contact between steel and soil, due to a combination of internal ring stiffeners and protective painting of the steel walls.

Adfreeze piles • •

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In extreme latitudes where the ground is continuously frozen, adfreeze piles are used as the primary structural foundation method. Adfreeze piles derive their strength from the bond of the frozen ground around them to the surface of the pile. Typically the pile is installed in a pre-drilled hole 6"-12" larger then the diameter of the pile. A slurry mixture of sand and water is then pumped into the hole to fill the space between the pile and the frozen ground. Once this slurry mixture freezes it is the shear strength between the frozen ground and the pile, or the adfreeze strength, which support the applied loads. Adfreeze pile foundations are particularly sensitive in conditions which cause the permafrost to melt. If a building is constructed improperly, it will heat the ground below resulting in a failure of the foundation system. Another ongoing concern for adfreeze pile foundations is climate change. As the climate warms, these foundations lose their strength and will eventually fail.

Bibliography • http:// en.wikipedia.org/wiki/Deep_foundation • www.ensoftinc.com/new-jaa/products/m_ suctionpile1.pdf