spectra
Spectra Geotechnologies Foundations Contracting L.L.C
Spectra Geotechnologies Foundations Contracting L.L.C

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+971 2 6766116

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+971 2 5840645

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Piling & Foundation Contracting
By virtue of the geographic & geologic setting of the UAE and Gulf region at large; in terms of; prevalent eolian dune environment, proximity to the marine environment (in plan and elevation) and recent tectonic history of the region; the predominance of; loose dune sands, soft tidal sabkha deposits, soft fractured rock deposits & their residual soil derivatives as well as their soluble (evaporate) content has availed weak and compressible material in association with high groundwater levels near the ground surface. This is in addition to the excessive hydraulic conductivity of near-surface deposits and that has made it incumbent on constructors in the vicinity to deal with foundation piles, shoring systems and dewatering as a matter of routine practice.

 

 

Piles
Piles are reinforced concrete (RC), steel and composite slender members of high strength and thus; in a very broad sense, designed to carry loads axially (in compression and tension) as well as laterally in bending. The exact mechanisms of load transfer between a pile and ground are quite complex and statically in determinant but generally are a combination of vertical end-bearing (downwards & upwards) and shaft (skin) friction (upward and downward shear resistance) as well as lateral bearing (compression) in the case of laterally loaded and slender compression piles.

The strength, stiffness, dimensions, distribution, surface characteristics and orientation of piles with respect to the applied loads in collaboration with the prevailing ground conditions, determine the safe load capacity of piles and pile groups (axially and laterally).Types of foundation piles SGFCs offer are:

  • Drilled - Cast In-situ Concrete Piles

These are RC concrete piles normally drilled within a common diameter of 450-1500mm. The weak, collapsible soil section is normally cased (temporarily or permanently) while the rock is not; as it is self–supporting. The pile bottom (end bearing surface) is usually cleaned up properly prior to casting, the steel cage is lowered in a centralized manner and placed in position (with the designed concrete cover allowance) and the concrete is either gravity-casted using a shoot or hopper connected to a gravity tremie pipe or pressure-tremied using a concrete pump and hose. The concrete is first placed at the bottom and allowed to displace any contaminating soil cuttings, collapse debris, groundwater and drilling fluid upwards until fresh, uncontaminated concrete emerges at the surface. 

  • Micro-Mini Piles

This system involves drilling a large number of small diameter (100-250mm) holes to depths ranging between 3m and 15m and installing central reinforcement (rebar, steel rods or other rolled steel sections), adequately centered to acquire the designated cover. The hole is subsequently grouted or else micro-concreted using a suitable tremie hose displacing water, drilling circulation media, cuttings and sediment from the bottom upwards and out of the hole and until uncontaminated grout or micro-concrete exits the hole.

In particular cases, the central steel reinforcement is the tremie pipe itself and in other cases the central reinforcement is the drilling rod, the tremie and sacrificial bits may also be used too. In yet other cases the hole is first grouted or filled with flowable micro-concrete and the reinforcing element subsequently dropped in position in a centralized manner and pushed down statically or using vibratory methods. In some cases, casings are used to reinforce the section with or without central reinforcement.

Holes may be cased permanently or temporarily using steel or polymer-based casing pipes. Of particular interest in temporary steel casing is Symmetrix / Robit type of drilling in which the casing and drilling string with the drilling bit proceed simultaneously and once the hole is partially or fully drilled and cased, the string and bit retracted, the hole cleaned and reinforced, concreted (or grouted) followed by retraction of the casing. Hollow stem augers of different inner and outer diameters may also be used for similar applications. 

Micro-piles and mini-piles are considered highly slender deep foundation members and therefore buckling, P-δ effects and lateral forces are very important to be considered in their design. Group design is more important to reckon with for such slender pile systems.