Piling it on

Those good times extend to having a very active industry body, the Piling and Foundation Specialists Federation, representing the interests of its members.The industry is also in an interesting phase, with some of the established players of the past now being part of the Keller Group, although they generally act independently. There is an emerging group of local contractors that may be relatively new in years, but have experienced people in charge and are not afraid to adopt new methods when required.It all speaks of a very healthy industry.Steel screw piles aren’t for every application, but there are a lot of applications where they can be appropriate. The have some distinct advantages in their ability to be removed without being destroyed, which is great for temporary works, their absence of vibration, noise and displaced soil, and the minimal needs for specialised equipment.The principal item of specialised equipment is a planetary drive head, and these have a number of sources. One of the beauties of these drive heads, apart from their ability to impart the necessary torque, is that a while ago someone determined there was a correlation between the installation torque of a pile and its capacity. This means the planetary drives can be instrumented to enable piles to be readily installed with the correct torque to allow them to have the required capacity.Digga is the largest manufacturer of planetary drives in Australia and was early to see the potential of steel screw piles. However, the company also realised this application had slightly different requirements to a typical planetary drive application, and it has worked with the industry to adapt its product accordingly.Hydraulic motor failures as a result of kick back were a problem in the early days of screw piling. When this was identified as an issue, Digga recommended that installers fit variable foot controls to their hydraulic circuits to control the release of built-up inertia in the pile. This has progressed to Digga developing a Swoosh Valve integrated in the drive head, which detects reverse inertia and grabs hold of it before slowly releasing the kick back – saving costly damage to the motor, drive unit and machine.Other refinements were designed to assist in the accurate installation of screw piles. Diggalign is an alignment indicator that allows the operator to correctly align the pile for accurate installation. The centring function also works for inclined (raker) piles, allowing them to be installed at a predetermined angle.A more recent innovation is the I-Drive planetary system that has been designed to cope with the high flows and hydraulic horsepower of the latest closed-centre hydraulic systems. Digga I-Drive systems do not require the use of a case drain and are highly resistant to contamination. They require no additional filtration, which contributes to their compact design. They are claimed to be the most compact drives available on the worldwide market, allowing maximum clearance for installing a pile or anchor.The system makes full use of the hydraulic system of the host machine, allowing for quicker installation. The I-Drive has a range of speeds to match the torque and speed (rpm) requirements of the installation.Where a pile has a final installation torque requirement of 200,000 newton-metres, it can be started at 100,000Nm, allowing installation at twice the rotational speed until the point where more than 100,000Nm is required to continue. This significantly speeds overall installation time for the piles. I-Drive units are available in single, dual and three-speed models and can handle flows up to 500 litres per minute. The most recent Digga development is a specialised screw anchor hitch called the Rhino Hitch. This allows the operator to traverse over the pile, pick it up and support both the drive and pile at the required installation angle. The Rhino Hitch allows for additional height to maximise vertical reach. The hitch also allows for control over positioning of pile when drilling starts. While the 300,000Nm torque of the largest unit built to date seems enormous, Digga managing director Suzie Wright says the industry has already foreshadowed a need for installation torques as high as 500,000Nm and Digga is already working on development of gearboxes that will handle these massive torques.

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