Assessment of Stress in the Soil Surrounding the Axially Loaded Model Pile by Thin, Flexible Sensors

Abstract

Foundation piles transfer the applied vertical load to the surrounding soil by skin friction and base resistance. These two components induce stress in the soil. The load transfer is still not fully recognized, and some pile load tests analyses have raised many doubts. The present paper aimed to measure the stress levels during pile load tests in laboratory conditions. This research examined the possibilities of using thin, flexible sensors in measuring the stress in soil. Two sensors were used: tactile pressure sensor with mapping system and color film pressure sensors with digital analyzing. Calibration and preliminary tests of the sensors have been described. This calibration proved that this kind of sensor could measure the stress in the soil in laboratory conditions. The results of stress distribution in the soil, shown as pressure maps, have been presented. Significant stress changes were observed in pile load tests. Rough and smooth piles were compared in the analyses. Stress distribution was the result of simultaneous interaction of pile skin and base. The knowledge about stresses surrounding the pile allows us to carry out a deeper analysis of the pile–soil interaction.

Archives of Civil Engineering

“…According to laboratory experiments by [8], the particle size distribution near the pile can be changed, reducing the interface friction angle at large deformations. The behavior of the sandy soil surrounding the pile during the pile installation is complex, and different laboratory tests on sandy soil properties, interface parameters, and experiments, including calibration chamber or centrifuge test, should be used to model the entire system [9][10][11].…”

“…During pile jacking, stress changes in the sandy soil are significant near the pile, but they also extend a significant radial distance. Model tests and field measurements have been conducted during pile installation with pressure cells in the sandy soil mass [3,11].…”

Tactile Pressure Sensors Calibration with the Use of High Pressure Zones

“…The sensors manufactured by Tekscan have been used in the studies on the pressures in the soil [ 3 , 4 , 5 , 6 , 7 ], railroad track pressure [ 8 ], pressure in the joints [ 9 , 10 ], pressure by medical pressure garments and socks [ 11 , 12 , 13 ], pressure when gripping tools and handles [ 14 , 15 , 16 ], pressures between rolling elements [ 17 ] and others. This variability of applications is provided by the very small thickness of the sensors (usually 0.1–0.3 mm), their flexibility and relative unpretentiousness to external conditions.…”

“…Another widespread application of tactile sensors with challenging calibration is measuring pressures caused by soils and granular matters [ 3 , 6 , 7 , 22 ]. In particular, in [ 3 ], the loads exerted by soil on a pipe moved by a horizontally directed force have been experimentally studied.…”

“…Large variation in values over the loaded patch is a typical feature of pressures measured in the experiments with granular matters. The study [ 7 ] demonstrates the calibration of sensors under loading applied to a sample with a contact surface representing medium sand. The presented images of the pressure distribution over the area show significant inhomogeneity with the presence of spot-like high-pressure zones.…”