Discharging Characteristics by Screw Auger of Gravel Drain Pile as a Reinforcing Measure againstEarthquakes

摘要

APG (auger pressure grouted) piling or CFA (continuous flightrnauger) piling, which is a typical foundation piling techniquernused in Europe or the USA, involves drilling a hole with a flightrnauger, filling concrete or grout through the hollow center of thernauger pipe and inserting reinforcement cages in the ground. ForrnAPG piling, when the rotational speed of the auger is greaterrnthan the penetration rate, it discharges too much soil onto thernground and causes displacement or subsidence. AppropriaternAPG piling therefore requires the right amount of soil to berndischarged onto the ground.rnFor the gravel drain method, which is widely used in Japan, arnhelical shaft is attached around the outer surface of the casingrnpipe to discharge the soil onto the ground in order to mitigaterndisplacement of the surrounding ground. Considering that thernamount of soil discharged onto the ground has a major impactrnon the displacement of the surrounding ground, it is extremelyrnimportant to make an accurate estimation of the discharged soilrnfor appropriate control when carrying out the work. In this paperrnthe authors clarify the soil discharging characteristics of therngravel drain method in the sandy ground, propose an equation tornestimate the discharged soil, and demonstrate the validity of thernequation based on the field measurement of the discharged soil.