Performance of screw piles in bio-stabilized slope based on field monitoring and finite element modelling

A novel slope stabilization technique was recently developed incorporating screw piles with vegetated flapped soilbags. These screw piles are subjected to lateral stress from soil slope and their deformation can be difficult to quantify, given the fluctuating pore-water pressure and heterogeneous soil conditions. This study proposes the use of in-situ spectral analysis of surface waves (SASW) test to estimate the small-strain soil stiffness which can then be factored to calculate the lateral deformation of the pile in finite element modelling based on prescribed pore-water pressure change. A case of bioengineered slope in Kanchanaburi province, Western Thailand was studied, involving field monitoring of pile head tilt, pore-water pressure, suction, and soil moisture over one year. The findings revealed pile head tilt of up to 0.2 degrees in response to rainfall and rise in pore-water pressure and soil moisture over one year period. A series of finite element modelling were performed using factored shear moduli from in-situ SASW test and the monitored pore-water pressure variation to reproduce the amount of pile head tilting as observed in the field during one year. It was revealed that by assuming operational shear modulus ranging between 0.0075 and 0.01 times small-strain soil stiffness, a satisfactory agreement was obtained between field measurement and analysis of pile movement. This findings provides a basis for further studies on performance of bioengineered slope utilizing screw piles.