Effect Analysis And Settlement Prediction Of Vacuum Preloading Hydraulic Fill With Or Without Sand Cushion

Engineering characteristics were changed a lot of hydraulic fill which formed from dredging silt in land reclamation project.Hydraulic fill foundation can be used for the subsequent project after strengthening treatment.Vacuum preloading method is one of good methods to reinforce hydraulic fill foundation.Taked the land reclamation project in Wen Zhou as background and based on a large number of monitoring data,test data and some previous data,this paper studies engineering characteristics of hydraulic fill,analyzes the effect of vacuum preloading hydraulic fill with sand cushion or not,predicts its settlement.The main work and research findings are described as follow:(1)Through summarizing the test data of Engineering characteristics of hydraulic fill in this based engineering and some previous data,showing that engineering characteristics of hydraulic fill is poor,there are more disadvantages than engineering characteristics of the natural soft soil;clay is accompanied when the hydraulic fill are formed from undisturbed natural soft soil.(2)Through analyzing the monitoring data and the test data of vacuum preloading hydraulic fill without sand cushion,expounding the features of change in vacuum degree under membrane,pore water pressure and surface settlement of vacuum preloading hydraulic fill without sand cushion.Finding that preloading effect in the shallow field is better than deep field.(3)Through analyzing the monitoring data and the test data of vacuum preloading hydraulic fill with sand cushion,expounding the features of change in vacuum degree under membrane,pore water pressure,surface settlement of vacuum preloading hydraulic fill with sand cushion.The depth of drains has effects on hydraulic fill compression deformation,the influence of vacuum preloading method with sand cushion can reach the bottom of drains more than 10 m.The deeper drains,the worse preloading effect in shallow field,the drains were fighted too deep to play high efficiency.(4)Comparing the reinforcement effect of vacuum preloading hydraulic fill with or without sand cushion,show that the existence of sand cuhion makes the pore water pressure more sensitive to the change of vacuum degree under membrane.The eitence of sand cushion and increasing the length of drains are more advantageous to transmit the vacuum.The pore water pressure dissipates soon in initial vacuuming and dissipates slowly in late vacuuming of the vacuum preloading method with sand cushion,but the vacuum preloading method without sand cushion is just opposite.The features of change in surface settlement and sedimentation rate of vacuum preloading hydraulic fill with or without sand cushion are similar.(5)Based on the measured settlement data,using hyperbola method and three-point method to predict the settlement of vacuum preloading hydraulic fill and putting forward a new companion method(coupling hyperbola method and three-point method).The calculation results show that the accuracy and stability of new companion method is best in the three methods,the accuracy and stability of hyperbola method is better,the accuracy and stability of three-point method is worst.