Horizontal Deformation Efficiency of a Pile Controlled by the Capsuled Expansion Technique: A Field Trial and Numerical Analysis

The capsule expansion technique (CET) is a novel active measure to control the deformation of subsurface structures induced by underground engineering construction. CET has been applied to tunnel deformation control, but its application in pile foundations is rarely reported. In this paper, a field trial and three-dimensional coupled consolidation finite-element analysis were performed to study the interaction of capsule-soil-pile and control efficiency of CET. Field trial results verify the feasibility of CET in controlling pile horizontal deformation, and the control efficiency is 60% higher than that of Tube-a-Manchette grouting with 40%. Numerical back analyses indicate that the pile maximum displacement increases almost linearly with the expansion diameter, while the control efficiency of CET hardly changes. The total stress of the soil in front of the pile is significantly reduced by 20.3% due to the dissipation of excess pore-water pressure, resulting in the reverse displacement of the pile. High excess pore pressure induced by CET would cause the soil to bear additional stress after dissipating, leading to the reverse displacement of the soil and further diminishing the control efficiency. Moreover, control efficiency can be improved by reducing the surrounding excess pore-water pressure induced by expansion and increasing the excess pore-water pressure at the back side of the pile.