| The chongwan section of the West dyke of the canal in Yangzhou has the most serious potential safety hazard.There are a lot of soft soil layers in the dyke body and under the dyke foundation,with a depth of 20m,large thickness,high water content,low strength,and unstable settlement of the dyke body.Although the reinforcement measures have been taken for many times,the fundamental problem has not been completely solved.In this paper,two kinds of vacuum preloading reinforcement technology are tested for the settlement of chongwan section.The principle is as follows:traditional vacuum preloading sets up vertical drainage board in the foundation,lays sand cushion,and then seals the site with sealing film Then,vacuum is pumped under the film by jet pump to form vacuum negative pressure in the sand layer,And through the negative pressure drainage function of the drainage plate,the soft soil foundation can be protected.Variable vacuum preloading method is to set up vertical drainage board in the foundation,arrange booster pipe,and then seal the whole site with sealing film.The jet vacuum pump is directly connected with the drainage plate through the pipeline to pump water to form the vacuum under the membrane.At the same time,the pressurization system is opened to split the reinforced soil to form a new drainage channel to realize the reinforcement.The main findings are as follows(1)Through the field comparative test of the project,it is found that compared with the traditional vacuum preloading method,the variable vacuum preloading method can not only improve the final stable vacuum degree by 54.5%,but also extend the vacuum transfer depth by 44.4%.These parameters monitoring show that the variable vacuum preloading method is better than the traditional vacuum preloading method in improving the vacuum degree under the membrane and the reinforcement depth.In addition,with the increase of depth,the excess pore water pressure gradually decreases,but at the same depth,the excess pore water pressure in the variable vacuum area is about 20 kPa lower than that in the traditional vacuum area,which is conducive to accelerating the dissipation of soil pore water pressure and foundation reinforcement.Furthermore,it is found that the method of variable vacuum preloading can not only improve the settlement effect,but also significantly enhance the bearing capacity of foundation.(2)By optimizing the design scheme,the variable vacuum preloading reinforcement technology is applied in chongwan embankment foundation reinforcement project.Based on the analysis of the cross plate strength monitoring data,the mechanical properties of the soil layer and the bearing capacity of the foundation in the South and North concave sections of the embankment foundation after variable vacuum preloading are significantly improved,which are generally greater than the design requirements.Moreover,combined with the analysis of surface settlement monitoring data,it is found that the average consolidation degree of the South concave section and the North concave section is increased by 28.3%and 27.7%respectively compared with that before the variable vacuum preloading reinforcement,which provides a guarantee for the subsequent construction.In general,the monitoring results of both field test and practical application show that the variable vacuum preloading reinforcement technology has more advantages than the traditional vacuum method in the vacuum degree under membrane and foundation consolidation reinforcement,and its pressurization system can effectively transfer the reinforcement depth and the consolidation effect of the foundation,greatly improving the construction efficiency,It provides a guarantee for the smooth progress of the follow-up construction. |
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