Tower Crane, Foundation and Excavation Methods Explained

Tower Crane

The tower crane lifts and moves horizontal and vertical loads, assembles structural elements, and performs heavy lifting work. Its main parts are the base, which may sit on rails or embedded footings, the tower or mast, the jib (horizontal arm), the crown with rotation mechanism, the counter-jib and the ballast.

Key characteristics include the maximum and minimum height, the maximum reach, the crane power, and the useful load, which varies with the reach. The maximum load applies at the minimum reach. Loading tip: always check the load chart before lifting.

Automontable Crane

Self-erecting cranes are characterized by a fast assembly speed and good load capacity for short reaches. They have a small turning radius and occupy little ground space, and they can easily be towed or moved from site to site.

Hydraulic Crane

Hydraulic cranes are used where tower cranes are difficult to assemble or place, for prefabricated assembly, for introducing loads into interior spaces, and for access to courtyards.

Telescopic truck crane: it includes a sturdy chassis, a diesel engine, suspension, stabilizers and a superstructure. The crane's rotation, boom elevation and extension, hook lowering, and rotating crown and/or machinery are all hydraulically controlled.

Deep Foundations

Deep foundations include pile caps and piles, including micropiles (under 20 cm), normal piles (20-60 cm) and large piles (80-150 cm).

• Continuous flight auger (CFA): the earth is extracted continuously while grout is simultaneously injected, producing little vibration.
• Driven steel piles: steel tubes are driven into the ground using a hammer, with the first tip either open or closed. They compact the soil with low noise and vibration.
• Injected piles: grout is injected through the tube, forming a bulb at the tip.
• Prefabricated piles: driven piles of concrete or steel, installed with a hammer, though they generate noise.

Diaphragm Wall

A diaphragm wall has a small relative thickness and great depth. It is excavated in panels using thixotropic fluid (bentonite) and consists of overlapping piles or walls.

Procedure: guide wall construction, panel excavation, placement of reinforcement cages, concrete pouring through a tremie pipe, construction of the capping beam, excavation, and internal bracing with anchors, followed by final construction and stabilization.

Tablestacking

Interlocking sheet piles allow overlapping and delimit an area that can be excavated waterproof. They are driven with a hammer, drilled, or installed with hydraulic vibrators.

• Full embedment: used where the depth of the wall is greater or the water table is high, and where the piles are clipped.
• Overlapping piles: used for shallow depths without a high water table.

Wellpoint Dewatering

Wellpoint systems lower the underground water table, drawing it down quickly through suction pipes.

Components: galvanized steel pipes with a filter at the end, a depth of about 1 m, and an absorbent length. Flexible hoses connect the pipes to the suction collector. The collector is a flexible tube connected to each pipe and carries the water to a pump.

Foundation Calculations

The best foundation performance is achieved by expanding the surface area through enlarged footings or by founding on a strong, resistant stratum.

Systems include: enlarged footings, micropiling, jet grouting, and mortar injection to increase strength. Large-diameter columns are heavily intermingled with the surrounding soil to prevent collapse.