Study On Transverse Dynamic Response Of Liquefied Soil Foundation Model Reinforced By Different Piles Based On Shaking Table Test

The liquefaction of saturated sand has been the important research topic ofscholars in the field of geotechnical engineering. Seismic action is the mainreason of the liquefaction of saturated sandy soil, and, in recent years, all partsof the world frequently suffer from large and small earthquakes, directlybringing the great threat to people’s life and property safety, and the secondarydisasters caused by earthquake exacerbate the losses of the people’s life andproperty. Since the wenchuan earthquake, our country strengthenes theawareness of disaster prevention and mitigation engineering in constructionareas, therefore, liquefaction research of the saturated soil caused by theearthquake effect is more important. At present, gravel pile in the liquefied soilbecause of its good capability of dissipation of pore water pressure is widelyadopted by engineering, and cement-soil pile, the rigid pile reinforcing foundation in improving the bearing capacity of foundation and eliminating theuneven settlement of foundation have significant effects and is also used inliquefied soil reinforcement in practical engineering, but there is few researchdone regarding its mechanism theory. Therefore, based on shaking table test,and from the perspective of the lateral dynamic response of liquefied soilresearch, systematically studying mechanism and reinforcement effect of theliquefied soil foundation under different reinforcement form, analyzing theinternal relation between each parameter and improving pile reinforcementtheory of liquefied soil, is of great significance in the application of practicalengineering.In this paper, based on the national natural fund project (No.50578104)"Study on reinforcement mechanism of liquefacted sandy soil reinforced bypiles", Shanxi bureau of science and technology project (No.10-1-06)"Study onthe mechanism of liquefaction resistance of sand reinforced by piles in the loessarea ", and the loess research laboratory of Shanxi Province open fund project(KLTLR-Y13-3)" Study on pile foundation bearing in the liquefied soil",6groups of liquefied soil model is un-reinforced foundation, reinforcedfoundation by single gravel pile, reinforced foundation by single cement-soilpile, reinforced foundation by four gravel piles, reinforced foundation by fourcement-soil pile and reinforced foundation by gravel piles and cement-soil pilesare studyed by shaking table test, and the time history curves of super static porewater pressure, earth pressure and soil acceleration in liquefied soil reinforced by different piles in different depth are received, and comparing the test data andcomprehensive analysis, come to the conclusions as follows:(1) The excess static pore water pressure of un-reinforced foundation andreinforced foundation by different piles are increasing with the growth of burieddepth. Excess static pore water pressure of reinforced foundation by cement-soilpile after the peak remains the same as the growth of the vibration time,instructing cement-soil pile in dissipating pore water pressure does not work;excess static pore water pressure of reinforced foundation by gravel pile issignificantly decreased after the peak, and less than other reinforced foundation,showing the effect of gravel pile in dissipating pore water pressure is remarkable.According to the curve of excess static pore water pressure of each test modelpeak curve along with the change of buried depth, the relation is fitted out: U=-kD (type: U-excess static pore water pressure peak value, unit: kPa; D-burieddepth of soil, unit: cm; k-factor), and by the relation the super static pore waterpressure value of arbitrary buried deep can be predicted.(2) Earth pressure of un-reinforced foundation and reinforced foundation bydifferent pile along the depth shows the trend of the middle largest, the uppertimes and the lower minimum. Earth pressure of reinforced foundation bycement-soil pile at the beginning of the test rapidly reaches the peak, declinesand maintains stable, and in the same deep earth pressure value of reinforcedfoundation by cement-soil pile compared with other forms of reinforcedfoundation is small, showing the cement-soil pile in lateral horizontal force has very good effect; in reinforced foundation by gravel pile, the soil pressurereaches the peak, then decline back slightly, and keep until the end of thevibration; because gravel pile soil drainage making the soil destiny, the earthpressure model are larger than reinforced foundation by cement-soil pile.According to earth pressure peak value of each test model along with the changeof buried depth curve, the relation is fitted out: P=-aD2-bD (type: P-horizontal earth pressure peak value, unit: kPa; D-depth of soil, unit: cm; a, b-factor), through the relation, the earth pressure value of the arbitrary depth canbe calculated.(3) Soil acceleration of un-reinforcement model in the different depthsdecreases with the increase of depth, which is much larger than reinforcementmodel by piles; soil acceleration values of reinforced foundation by gravel pileshows the changing rule of the middle larger, the deep and shallow smaller; soilacceleration of reinforced foundation by single cement-soil pile in differentdepth decreases with the increase of buried depth; soil acceleration in the samedepth of reinforced foundation by cement-soil pile is much smaller than that ofun-reinforced foundation. According to the soil peak acceleration curve alongwith the change of depth of each model, the relation is fitted out: A=kD+e, A=-aD2-bD+c (type: A–soil peak acceleration, unit: m/s2; D-depth of soil,unit: cm; k, A, b, c, e-factor), through two equations,the soil accelerationvalues in the arbitrary depth of un-reinforced foundation, reinforced foundation by cement-soil pile, reinforced foundation by gravel pile are measuredrespectively.To sum up, gravel pile has very good effect in dissipating pore waterpressure and soil compaction. Although cement-soil pile does not work indissipating excess static pore water pressure, but can share the horizontalseismic force effectively; reinforcing liquefied soil by different pile, horizontalseismic force in the middle of the pile are biggest, and the middle of the pile isprone to fracture phenomenon and must attach importance to it in actualengineering; pile reinforcing soil liquefied soil on the lateral dynamic responsehas a certain effect, and the weakening effect of the gravel pile in shallowfoundation soil is particularly obvious. Therefore, in the actual project,cement-soil pile and gravel pile composite reinforcement of liquefied soil canconsidered, and it would have attain better reinforcement effect.