A 50-mm-diameter circular aluminium tube was instrumented with two optical fibres that consist of 13 Fibre Bragg Grating sensors (FBGS) for each. The performance of the FBGS was evaluated by applying a series of increasing transversal loads at 1×g level and comparing the strains measured by FBGS with those calculated from the Euler-Bernoulli beam theory. Centrifuge test was then conducted at 100×g to estimate the transversal response of the calibrated model pile that had been jacked 450 mm into saturated sand and horizontally loaded at 500 mm above the ground. The profiles of the normal strain, bending moment, soil reaction and pile deflection were measured or determined, allowing to construct the soil reaction-pile deflection (P-y) curves. The results confirmed the reliability of the FBGS at 100×g by giving satisfactory measurements on bending moments and coherent measurements on shear force at the ground level.

Water plays a vital role on the hydromechanical behavior of unsaturated soils. An important concern in unsaturated soil mechanics is to determine the distribution of water within voids and its interaction with soil grains. This paper presents some results of the spatial distribution of water in different soils using the synchrotron-based X-ray microcomputed tomography (μ-CT). Three materials (glass beads, natural sand, and clay) were first prepared at a water content of about 10%, statically compacted under vertical total stress of 500 kPa, and then scanned by synchrotron X-rays at an energy of 18 or 20 keV. The three-dimensional (3D) microstructure of the samples including air, liquid, and solid phases was reconstructed, and some new observations were obtained: (i) the iodine-based contrast medium (KI) can increase the peak greyscale value of water from 110 to 122, enhance the air-water contrast, and thus facilitate the segmentation of water phase; (ii) in the compacted glass beads and sand, water distribution is characterized using the μ-CT and image reconstruction technique. The water contents obtained by phase segmentation, i.e., 10.2% and 9.3%, are comparable with those measured by the oven-drying method, i.e., 9.7% and 9.4% for the glass beads and sand, respectively; (iii) water is preferably distributed within aggregates when it is mixed with the oven-dried particles, and an aggregate-dominated 3D structure is observed. However, it is impossible to determine the water phase for the studied material even with the resolution of 0.65 μm/pixel.

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