| Improved the soft foundation with the enhanced sand bag wells is a new way, which is put forward by the specialists of Guangdong Province Hangsheng Construction Group CO.LTD to reinforce synthetically the silt and liquefiable sand interbeds foundation, which abound in Shan(tou)-Jie(yang) express way. The dissertation studies its mechanism by laboratory test, engineering test, theoretical derivation and numerical simulation.With vibration direct sheat test, vibration liquefaction test, and so on, the dissertation analyzes the rule of the vibration impacting the intensity of the sand, the rule of the vibration changing the pore water pressure, and the rule of the vibration liquefying the sand. It could educe that, (1) with vibration, (?) could depress 1°～3°, c could depress more than 50%; (2) all of swing, vibration frequency, excitation technique and vibration velocity could impact the shear strength of sand; (3) with vibration, the pore water pressure could rise quickly, and then go to tranquilization, at the same time, the changing of the pore water pressure shows undulatory property; (4) when the pore water pressure rise to a degree, the seeping upwards could minish the effective stress to zero, which could make the sand liquified. All of these validate the vibration could weaken the strength of sand evidently.With the four schemes engineering test in the testing field for the enhanced sand bag wells in the soft foundation trial lot of the section Shanshui-huaiji, Guangzhou-Hezhou express way, by measuring the surface subsidence and standard penetration test, the effect of consolidating to the loose-middling close-grained sand by the enhanced sand bag wells is validated, which could eliminate the sand from liquified.With the seven schemes engineering test in the testing section for the enhanced sand bag wells in the soft foundation trial lot of the seventh bid package, Shan(tou)-Jie(yang) express way. By static sounding and standard penetration test, the effect of consolidating to the thin sand layer is not obvious. But by testing with surface wave prospecting method, the changing from the soft soils (silt) layer and liquefiable sand layer interbeds foundation to a homogeneous foundation was very obvious. It could be considered that much sand in the layers upper has been pressfitted into the silt subjacent and upper. At the same time, by monitoring the pore water pressure during the course of the CFG piling works, the increscent pore water perssure could make the sand liquefied. These validate that the enhanced sand bag wells could improve the liquefiable sand by consolidating the sand and pressfiting the sand into the silt layer subjacent. At the end, with monitoring the surface subsidence during the course of filling the roadbed, the effection of consolidating the soft foundation was very good. Therefore, it got to the purpose of reinforcing synthetically the soft soils (silt) layer and liquefiable sand layer interbeds foundation.With wave equation, the dynamics of vibration immersed pipe is analyzed. Combining with the results of vibration testing indoor, it could be demonstrated from the theroy that the increscent pore water perssure during the course of vibration immersed pipe could make the sand liquefied, which could also help the pipe sinked and the foundation consolidated.With the method of ultimate bearing resistance, the dynamic resistance at the end of the pipe and around the pipe are analyzed. With the dynamic resistance at the end of the pipe as the source of the expansionary force for the cylindrical hole expanding, the horizontal shift caused by vibration immersed pipe has been analysed with the theory of cylindrical hole expanding. The mechanism of horizontal consolidation for the enhanced sand bag wells has also been demonstrated.By citing several scholastic results of the vertical shift in the interbed foundation for the vibration immersed pipe, the engineering testing result of much sand in the layers upper has been pressfitted into the silt subjacent has been demonstrated.By analysing the mechanics state after pulling out the pipe from the interbed foundation, some interspace between the sand bag and the well wall has been demonstrated to be filled with the soil in the same layer which sprung back after consolated by cylindrical hole expanding and some to be left for the silt falling from the layers upper.By also citing several scholastic results of the direction of the main stress changing would affect the pore water pressure, and analysing the changing rule of the pore water pressure with the relevant theory of dynamics groundwater, the mechanism of the vibration immersed pipe affecting the pore water pressure has been demonstrated ulteriorly, and some matting has been analysed for analysing the mechanism of the interbed foundation drainage concreting with the enhanced sand bag wells.By analysing the mechanism of the drainage concreting for the interbed foundation with the enhanced sand bag well in, and monitoring the foundation during the cource of filling the road with the methods summarized by the specialists of Guangdong Province Hangsheng Construction Group CO.LTD with years of their practical experience, also with the new method to judge the steady, AGO, and the analysing the methods of calculate the ultimate settlement, the mechanism of reinforcing synthetically silt layer and liquefiable sand layer interbeds foundation with the enhanced sand bag wells has been demonstrated.With Abaqus, the course of the concreting has been numerical simulated. Contrasting the results with the results monitoring the surface subsidence in the testing section of the seventh bid package, Shantou-Jieyang express way, the results are analogical. At the same time, the mechanism of drainage concreting soon with more sand in the soft foundation has been found. Therefore, the mechanism of reinforcing synthetically the soft soils (silt) layer and liquefiable sand layer interbeds foundation with the enhanced sand bag wells has been demonstrated more.
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