The Shaking Table Experimental Study On Liquefiable Sand Soil Improved By Granular Sand Pile

Liquefaction of saturated sand soil during earthquake is an important subject in geotechnical engineering. Granular material pile has been widely used in liquefiable ground due to its effectiveness and adaptability. At present, some knowledge about anti-liquefaction mechanism of granular material pile has been acquired, but it is quite limited. The design and anti-liquefaction judgement in practical engineering mainly focus on the effect of densification, either it is too conservative or the risk of liquefaction still exists. Research related is lack of experimental data.In view of this, under the support of National Science Fund Project "The experimental study on mechanism of piles improving liquefiable soil" (No.50578104), in this paper, shaking table tests were designed and carried out to analyze the effectiveness of granular sand pile, it includes two parts: (1) Explore the difference of development of excess pore water pressure in non-improved soil and improved soil by sand piles; (2) The influence of different parameters (pile length, pile spacing) on the effectiveness. The results are as follows:1. In non-improved soil, with depth decreasing, excess pore water pressure decreased while the pore pressure ratio increased; the liquefaction region firstly appeared in shallow soil, then spreaded to the deeper; at last, the entire layer liquefied.2. In non-improved soil, 6s after the start of vibration, the excess pore water pressure arised and reached peak at about 16s; In improved soil by 3D pile spacing, 14s after the start of vibration, the excess pore water pressure arised and reached peak at about 40s; In improved soil by 3.5D pile spacing, 12s after the start of vibration, the excess pore water pressure arised and reached peak at about 36s; In improved soil by 4D pile spacing, 10s after the start of vibration, the excess pore water pressure arised and reached peak at about 32s. The smaller the pile spacing is, the slower the excess pore water pressure arised and reached its peak.3. In improved and non-improved soil, when its peak was arrived, excess pore water pressure began to dissipate, particularly the dissipation became slower and slower with the decrease of depth.4. In the improved soil with pile length of 10cm, with the depth increasing, the pore water pressure ratio increased, the liquefaction region firstly appeared in the deeper soil, then spreaded to the shallow, at last the entire layer liquefied.5. In the improved soil with pile length of 20cm, with the depth increasing, the excess pore water pressure decreased. Because, 20cm pile length improved the dissipation of pore water in the deeper soil, when it flowed towards the shallow, the shallow excess pore water pressure increased.6 Among the improved models, the one with 4D pile spacing and 10cm pile length liquefied in the entire layer; the one with 3D pile spacing and 20cm pile length had the best result, liquefaction did not happen; the ones with 3.5D pile spacing, 10cm pile length and 4D pile spacing, 30cm pile length also had better effect; in the other ones, liquefaction occurred either in shallow soil or deeper soil. So not always the longest piles or the closest piles have the best function. Sometimes, in practical engineering, good results could be gotten by using mix of long and short piles.