Improving the Cost-efficiency of Large Diameter Bored Piles
Niemeläinen, Matias (2017)
2017
Rakennustekniikka
Talouden ja rakentamisen tiedekunta - Faculty of Business and Built Environment
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Hyväksymispäivämäärä
2017-05-03
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201704201330
https://urn.fi/URN:NBN:fi:tty-201704201330
Tiivistelmä
The main goal of this Thesis was to create a more effective way to install piles using the Down-the-Hole-method (DTH-method). Side objectives included the study of drilling parameters, design principles and regulations regarding pile installation. The main research materials were the Finnish instructions and standards that discuss piling, such as Paalutusohje 2016 (RIL 254-2016) and standard SFS-EN 1536 + A1 (Execution of Special Geotechnical Work. Bored Piles).
Often the main single cost in DTH-piles is the steel casing. Generally, it can be up to 40 % of the total installment costs. On top of that, for example in bridge foundation piles, the casing is not included in the bearing capacity calculation and it works only as a concrete casting mold. The idea of a new method was to extract the casing after pile concreting and thus decrease the costs of DTH-piles. This pile installation method was originally an idea of CEO Arto Niemeläinen from Destia Engineering Oy, and the method was designed in co-operation with drilling specialists from Destia Engineering Oy.
The designed method was tested by drilling, concreting and excavating two RD711/12,5 piles at the company grounds. The purpose of the field test was to determine the properties of a pile installed using this method and to make improvements in the working technique. The main improvement in the working technique was the vibration and adding of concrete in the beginning of the casing extraction.
Both of the piles were installed successfully as the key measurements were the concrete cover of the reinforcement, the diameter of the formed pile and the compressive strength of the concrete. These results were then compared to the standards. As the design value of the pile diameter was 652mm and the smallest realized value was 710mm and the concrete cover of the reinforcement was according to standards the pile installation can be considered acceptable. After concrete testing it was noted that the concrete had not yet fully developed its compressive strength due to cold soil surrounding the pile. It was calculated that the piles had compressive capacities of 11450kN and 12550kN, compared to a design value of 12350kN. Although further research is needed, by evaluating the results of this test there should be no reason why a pile installed using this method could not be successful.
Often the main single cost in DTH-piles is the steel casing. Generally, it can be up to 40 % of the total installment costs. On top of that, for example in bridge foundation piles, the casing is not included in the bearing capacity calculation and it works only as a concrete casting mold. The idea of a new method was to extract the casing after pile concreting and thus decrease the costs of DTH-piles. This pile installation method was originally an idea of CEO Arto Niemeläinen from Destia Engineering Oy, and the method was designed in co-operation with drilling specialists from Destia Engineering Oy.
The designed method was tested by drilling, concreting and excavating two RD711/12,5 piles at the company grounds. The purpose of the field test was to determine the properties of a pile installed using this method and to make improvements in the working technique. The main improvement in the working technique was the vibration and adding of concrete in the beginning of the casing extraction.
Both of the piles were installed successfully as the key measurements were the concrete cover of the reinforcement, the diameter of the formed pile and the compressive strength of the concrete. These results were then compared to the standards. As the design value of the pile diameter was 652mm and the smallest realized value was 710mm and the concrete cover of the reinforcement was according to standards the pile installation can be considered acceptable. After concrete testing it was noted that the concrete had not yet fully developed its compressive strength due to cold soil surrounding the pile. It was calculated that the piles had compressive capacities of 11450kN and 12550kN, compared to a design value of 12350kN. Although further research is needed, by evaluating the results of this test there should be no reason why a pile installed using this method could not be successful.