Experimental Study On Liquefiction Of Sand And Comparison Between Chinese And Foreign Codes For Padma Bridge In Bangladesh

Padma bridge project in Bangladesh is a key project of "the Belt and Road initiative",Which will bring convenient transportation in Bangladesh,enhance the economic and cultural exchanges between countries along the line,and promote the development of economic globalization.Earthquakes often occur in Bangladesh and the project is located in the Ganges River Delta region,which deposits deep sand that is easy to liquefy.Liquefaction is a serious earthquake disaster phenomenon,so it is very important to do a good job in seismic design of structures and foundation reinforcement.The premise of seismic design of structures and reinforcement of foundation is to identify the liquefaction of construction site,and the accuracy of liquefaction identification method directly affects the safety of structures and the economy of engineering.The American code and European code are often used in Bangladesh for liquefaction identification,whose accuracy of American and European codes for liquefaction identification in Bangladesh is questionable.Therefore,it is of great significance to study and develop liquefaction identification method suitable for Bangladesh sand,which is important to ensure the safety of the project and improve the economic performance of the project.Based on the dynamic triaxial test,this paper studies the pore pressure growth trend,strain development characteristics,stress-strain curve and dynamic strength characteristics of Bangladesh sand under different σ’3c,CSR and Dr,and proposes a new liquefaction identification method suitable for this area.The main work and results are as follows:1.Carring out a series of dynamic triaxial tests to study the liquefaction characteristics of Bangladesh sand.The increase of pore pressure ratio of Bangladesh sand is negatively correlated with confining pressure and relative density.The development curve of pore pressure conforms to A-type growth curve.The strain development curve conforms to the Monismith power function model.The stress-strain curve is elliptical,and the larger the vibration times,the smaller the area of hysteresis stress-strain curve.Under the same conditions,Bangladesh sand is easier to liquefy than standard sand.2.Based on the results of dynamic triaxial tests,proposing a new formula for liquefaction identification of Bengal sand.The results show that the calculating result for liquefaction depth of the proposed method is significantly less than that of NCEER.3.Based on new liquefaction identification method proposed in this paper,the construction site of the project is basically not liquefied under the earthquakes of magnitude 6 and 7;for grade 7.5,the recommended liquefaction depth is 4.36m;for grade 8,that is 10.07m;for grade 8.5,that is 12.95m.When the groundwater level is low,the site will not liquefy when the magnitude is 6～8,and recommends liquefaction depth is 9.38m under the magnitude 8.5 earthquake.4.Summarizing and comparing the codes of different countries and regions,and founding that the codes based on the critical standard penetration test blow count method is the safest,followed by the codes based on the anti-liquefaction safety factor method,and the codes method based on the cyclic stress method has the highest risk.5.Calculating typical boreholes near Padma bridge in Bangladesh by different codes,and comparing the conservative of different codes for liquefaction identification in this area.The results show that,the depth is 6～10m,the security of each code is:SDCRE>SDCHE>SDCB>JSDRS>NCEER>EGEP>EERC,the depth is 10～20m,the security of each code is:SDCRE>SDCHE>SDCB>JSDRS>NCEER>EERC>EGEP.