Experimental investigation on the seismic behavior of helical-soil nailed walls

Abstract

Helical nails are a new type of reinforcement element that has been widely used during the last decade. This has caused that despite their widespread use, the seismic behavior of geotechnical structures reinforced by them is still unknown. Therefore, the present attempted study to evaluate the effects of some structural parameters on the dynamic performance of helical soil-nailed walls (HSNWs) using shaking table tests. For this purpose, eight reduced-scale wall models were constructed with different inclinations, lengths, and arrangements of helical nails and then subjected to input excitations with different durations. The response of each model to base excitation was determined in the form of fundamental frequency, acceleration amplification, facing displacement, and failure mechanism. The results showed that although a uniform increase in the nail length along the wall height significantly improved the seismic performance of the HSNWs, this improvement could also be achieved to some extent by increasing the length of the nails locally in the lower and upper halves of the walls reinforced by horizontal and inclined nails, respectively. The use of inclined nails instead of horizontal ones was an efficient solution to reduce the lateral displacement, acceleration amplification, and changes in the frequency content. The effectiveness of this solution was reduced with the use of shorter nails in the upper half of the wall and eventually minimized by reducing the length of the nails across the wall height. The nails located in the lower half of the wall were identified as having the greatest effect on the seismic performance of HSNWs when horizontal nails were used. The opposite occurred when inclined nails were used. A parabolic failure surface with a specific inflection point was observed to be the potential failure surface of the HSNW. The dimensions of the potential failure surface increased with an increase in the length and inclination of the nails. Also, a combination of overturning and base sliding was identified as the predominant deformation mode in HSNWs, although the base sliding mode faded with an increase in nail inclination.

Keywords

• helical soil-nailed wall
• shaking table test
• failure mechanism
• seismic performance