KELLER is continually investing in research and development to make its ground engineering techniques more efficient.
The focus recently has been on Continuous Flight Auger (CFA) piling where innovations have improved performance by an impressive 30%, creating savings which will ultimately be passed on to our customers.
The CFA market is highly competitive with many smaller, low-cost operators offering their services. So the challenge facing the Keller research team leading this work was to improve the efficiency of current CFA techniques to drive down costs while improving overall performance.
Research leader Serge Lambert, Technical Director of Keller France, explains the solution: “The CFA piling system is very fast and economical but can lead to a necking at the slightest jolt when the tool is raised.
“The CFA pile has seen continuous improvement in recent years. The first CFA piles (Type 1) had no monitoring. The type 2 pile had monitoring equipment included to provide an ongoing verification of concrete quality. However, regardless of these improvements, the operating standards restrict concrete stress. To overcome these restrictions we have developed the Type 3 pile by adding a tremie pipe, with two openings in its base, driven 80 cm into the concrete.”
“The new technique combines the advantages of conventional concrete casting with casting under pressure. The grouting volume and pressure are permanently monitored and controlled. A special scraping mechanism clears the spoils automatically as the tremie pipe is raised.”
The higher compression strength of the concrete means piles (Cmax = 40 MPa are expected) can be 30% shorter when compared with conventional CFA piles. Since piles are sold by the metre there is a proportional saving to the client. This research will also allow us to define as precisely as possible, the friction and resistance values which are often too conservative in the standards.
The next stage of the work is to manufacture the tool and collect load test data.
“We are going to run feasibility tests in rock and very compacted soils,” said Serge.
“Using high pressure pressiometers, we will be able to demonstrate the anchoring performance of the technique in different ground conditions. This is important because the use of this type of pile is often limited due to very compact soil layers.”
The final stage of the research, working in collaboration with the Keller Auger Cast Pile Global Project Team is to perform comprehensive loading tests. In addition to superior concrete quality when compared to the classical CFA approach, a key goal of this work is to give Keller a robust statistical method to define shaft fractions and tip resistance for the new tool.
“By collaborating across a number of countries, including Canada, Poland and France, Keller will have the most comprehensive load data of any company. I am convinced this work puts Keller at the forefront of the next generation of CFA piling. The plan is have the new tool available for on-site use later in 2017,” said Serge.