Experimental study for effects of water-swelling friction reducing materials on pulling out of temporary structures

Water-swelling friction reducing materials (WSFRMs) are more frequently used as a "pull-out assisting material" for temporary sheet-piles or piles that are required to be removed and collected after use. Generally, WSFRMs are applied to the steel sheet-piles, piles or H-steel piles before the piles are driven into the ground or placed in the mortar fluid. The WSFRMs absorb moisture in the ground or mortar to swell and form a swelling membrane over the piles. Then, the membrane works also as a lubricating membrane and as a result it can reduce friction. The authors pay attention to these characteristics of WSFRMs and try to develop a special material that can swell only when soaked in an alkaline moisture environment without swelling in acid or a neutral water environment, in addition to the conventional material that swells in any type of moisture environment. In this paper, given that the amphoteric and alkaline WSFRM is coated to temporary materials, to facilitate the pull-out, the authors carry out some experiments to evaluate the fundamental characteristics such as the swelling ratios of the amphoteric and alkaline WSFRMs and the forces to pull out the iron flat bars on which such WSFRMs were coated in advance. As one of the findings, the amphoteric and alkaline WSFRMs coated in advance reduce the friction on the contact surface between the flat bar and the mortar and enables the pull-out with less force.