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ABSTRACT:The present study explored the efficacy of pile shaft surface treatment on the improvement of soil-pile frictional resistance for floating or friction piles. 4 surface conditions of model piles measuring 200 mm long and 20 mm in diameter were examined, namely smooth (control), roughened, fishbone and checked shafts. A pile cap made of plywood was fixed to the top of the pile with 10 mm embedment depth, leaving 190 mm clearance for installation in the sand bed. The test chamber was a see-through glass tank with a footprint of 100 mm x 200 mm and 300 mm height. Coarse sand of D50 = 1.5 mm were loosely placed in the chamber by layers up to 200 mm height before the piles were installed either in single or triple group formations. The incremental load test of conducted via application of dead load ranging between 0.01-0.08 kPa on the pile cap, and the corresponding settlement was recorded. The test results revealed settlement to be reduced by the piles in the order of roughened > fishbone > checked > smooth for the single pile configuration, with maximum reduction of 40 % recorded by the roughened pile. As for the pile group, settlement reduction of the piles with surface treatment clearly outperformed the control pile by almost 50 %, though differences between the former were marginal with seemingly overlapping stress-strain plots. All in all the surface treatment of pile shaft enhanced the shaft friction for the piles installed in sand, but field implementation would require further examination of the pile-driving efficiency as the improved piles could cause additional resistance during installation.

Slope failures occur when the shear resistance along the slip plane is exceeded. This can be caused by excessive load imposed at the slope crest or compromised stability of the slope, e.g. disturbed dimensions of the slope. In order to prevent slope failure, stabilisation or reinforcement measures need to be taken. A common solution is to intercept the slope failure plane with reinforcement elements, such as soil nails and ground anchors. In soil nailing, reinforcement bars are installed on the slope to effectively resist the additional shear forces from the imposed loads, hence reducing the probability of failure in the long run. This paper describes the innovation of soil nail with screw-in installation mechanism instead of the conventional push-in approach. The screw-in installation ensures better soil-nail grip and less disturbance during the slope stabilisation procedure, especially in terms of noise and spoils. In addition, the novel nail has a hollow stem which improves shear resistance with greater soil-nail surface contact on the inner wall. The opening at the nail head also enables displaced air to escape as the nail is screwed into the slope and soil pushed into the inner hollow cavity. The prototype nails were tested in a slope model with different configurations, and were found to reduce the Angular Distortion Ratio by 37 % and the Volumetric Deformation Index as much as 33 % respectively. The novel screw-in soil nail could be potentially used to stabilize natural and man-made slopes, though full-scale simulations are recommended to formulate the installation procedure and to validate the effectiveness.

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