Tensile capacity of the grooved steel pipe pile
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Uritetun paalun vetokapasiteetti
Anchors are often used to resist tensile forces on tall and narrow structures where steel pipe piles are used to restrain compressive force. It has been studied that by grooving the steel pipe pile and by drilling and grouting the pile to the bedrock it could also resist tensile forces. The grooved tensile pipe pile could thus replace the anchors and increase the cost-effectiveness of the design. This master`s thesis was funded by SSAB and is based on the previous research “The tensile capacity of steel pipe piles drilled into the bedrock” published in 2015. In this research grooved steel pipe piles drilled and grouted into the bedrock to resist tensile forces are studied by literature review and field test. The main focus was to develop the design of grooved tensile steel pipe pile, implement theory on the field test and compare the results to previous studies. This research can be divided in two parts. In the first part instructions and theory concerning tensile piles are studied by literature review. In the second part grooved tensile steel pipe pile design are tested by the field test. From the literature review it was found that the material properties, size of the annulus, size of the reamer, friction and mechanical interlocking affects to the bond strength and design of the grooved tensile pipe pile. With the aid of the literature review and previous research the design was modified by increasing the wall thickness of the pile and by selecting oversized reamer for some of the piles. Otherwise similar grooved tensile pipe pile design was used in the loading test as in previous studies. In this research the piles were tested from the ground level in construction like situation. The achieved bond strength stayed between 0.24 to 0.88 MPa. The highest tensile capacity was 3068 kN. Failure was assumed to happen on steel to grout surface. The highest values were obtained on piles with wider annulus between rock and pile surface. It is assumed that this enabled a better flushing and grouting resulting in higher capacity. Therefore base on the tested piles, the RDs 220/12.5 pile with grooves and 273 mm ring bit is recommended to be used as tensile pile. Results were finally compared to the present instructions and previous studies. It was found that capacity of the grooved tensile pipe pile was over five times higher than it is allowed to use for the design according to present instructions.