Study On The Characteristics Of Liquefied Sand Reinforced By Different Pile Based On The Shaking Table Test

Earthquake is the main disaster bringing great loss to people’s life andproperty throughout the domestic and foreign natural disaster, and it is also themajor problem we are facing to be solved. Saturated sand is liquefied underseismic loads, causing the ground to take water and sand blasting, unevensettlement, carrying capacity decreased, foundation failure, resulting inbuildings cracking, tilting, even collapse. It increases earthquake disaster loss.Reinforcing liquefied soil has been a hot and difficulty to geotechnical to study.Earthquakes occur frequently in recent years. The soil has been reinforced alsooccurs instability due to the liquefied. Therefore, studying the mechanism ofdifferent reinforcement methods of liquefied soil is urgent. The theory ofreinforcing soft foundation by cement pile improving the bearing capacity,reducing uneven settlement has been relatively mature, and it has been widelyused in practical engineering. But the research on reinforcing liquefied soil is few. Gravel pile is recognized as the most effective method to reinforce liquefiedsoil, and it is widely used in practical engineering. But the study onreinforcement mechanism of liquefied soil of different dry density is less. Sostudying on the reinforcement effect of different dry density liquefied soilfoundation reinforced by cement pile and gravel pile, and analyzing internalrelations of liquefied soil each parameter, and improving the reinforcementtheory of cement pile and gravel pile reinforcing liquefied soil are of greatsignificance to its application in practical engineering.The paper relies on the National Natural Science Foundation-fundedprojects “the test study on the reinforcement mechanism of liquefied sandreinforced by pile”(Project Number:50578104), and Shanxi CommunicationDepartment Science and Technology projects “Study on the mechanism ofresistance to liquefaction of the sand reinforced by pile in the Loessregion”(Contract Number:10-1-06) and Key Laboratory Projects of LoessArea Highway Construction and Maintenance Technology Transport Sectorprojects “The test study on pile foundation capacity of liquefied soil”(ContractNumber: KLTLR-Y13-3) simulating seismic loads, and expanding a series ofstudies on un-reinforced liquefied soil model and reinforced liquefied soil modelby cement pile and reinforced liquefied soil model by gravel pile through theshaking table test. Each of these models include three groups of test, and thepacking sand dry density of the test is1.5g/cm3,1.6g/cm3,1.7g/cm3. Themacroscopic phenomena in each group test model is observed. Test data of excess pore water pressure and earth pressure and settlement in different burieddeeps are gathered. Sorting test data. Drawing the time curve of each parameterin different buried deeps. And sorting the characteristic values-peak, values in60s of the parameters. Drawing contrast time curve and making analysis. Thevariation is Summarized. Conclusions are following:(1) Excess pore water pressure peak increases with depth increasing inun-reinforced liquefied soil model and reinforced liquefied soil model by cementpile, gravel pile. Excess pore water pressure peak decreases with the dry densityincreasing in the same reinforced liquefied soil model. Excess pore waterpressure peak of un-reinforced liquefied soil model is maximum with the samedry density. Liquefied soil model reinforced by cement pile follows. Andliquefied soil model reinforced by gravel pile is minimum. Gravel pile providesdrainage channel for reinforced liquefied soil model. At the end of the testexcess pore water pressure has been dissipated. Soil strength is enhanced. Therelational expressions of excess pore water pressure peaks and depths are fittedout according to the excess pore water pressure peak curves: U=－aZ (In theFormula: U-excess pore water pressure peak (kPa);Z-Soil buried depth (cm);a-Scaling factor). Any depth excess pore water pressure peak can be determinedaccording to the relationship.(2) The earth pressure peak along the depth curve of the three kinds ofliquefied soil model is parabola opening to the left and covering the coordinateorigin. Earth pressure peak of the depth24cm is maximum. The shallow follows. The deeper is minimum. Earth pressure peak at different depth of reinforcedliquefied soil model by gravel pile with the same dry density. Un-reinforcedliquefied soil model is minimum. Reinforced liquefied soil model by cement pilein the middle. Earth pressure peak increases with the dry density increasing inthe same reinforced liquefied soil model. The increase speed of theun-reinforced model is the fastest. Reinforced model by cement pile follows.Reinforced model by gravel pile is the slowest. Earth pressure of reinforcedliquefied soil model by gravel pile is the maximum with the same dry densitywhen the test to the60s. Reinforced model by cement pile is minimum.Un-reinforced model is in the middle. The relational expressions of earthpressure peaks and depths are fitted out according to the earth pressure peakcurves: P=－bZ2－cZ(In the Formula: P-Earth pressure peak (kPa); Z-Soilburied depth (cm); b, c-factor). Any depth earth pressure peak can bedetermined according to the relationship.(3) Settlement peak decreases with the depth increasing in the each groupof test models. Settlement of soil surface is maximum. Settlement at differentdepths of un-reinforced liquefied soil model is maximum with the same drydensity. Reinforced liquefied soil model by cement pile follows. Reinforcedliquefied soil model by gravel pile is minimum. Settlement peak decreases withthe dry density increasing in the same reinforced liquefied soil model. Therelational expressions of settlement peaks and depths are fitted out according tothe settlement peak curves: Z=mS－n(In the Formula: S-settlement(mm); Z-Soil buried depth (cm); m, n-factor). Any depth settlement peak can be determinedaccording to the relationship. The form of reinforced by pile makes a greaterimpact on settlement to liquefied soil with a small dry density. Surfacesettlement of un-reinforced soil liquefied model, and reinforced soil liquefiedmodel by cement pile and gravel pile have a small difference when the drydensity increases to a certain extent. Showing that the form of pile has littleinfluence on settlement of liquefied soil.In summary, whatever the form of pile reinforced liquefied soil it suffers amaximum level seismic force at the middle portion. So it can result in broken atthe middle portion of pile. It must draw the actual project’s attention. Gravelpiles provides a good drainage channel for liquefied soil model, dissipatingexcess pore water pressure, enhancing model soil compactness, and reducingsettlement of soil. Cement pile can not dissipate excess pore water pressure, buthas some effect on reducing the settlement, sharing horizontal seismic forces. Sothat designing liquefied soil composite reinforced by cement pile and gravel pilecan be considered in the actual engineering. It will get a better reinforcementeffect.