Research On Consolidation Technology Of Soft Soil Foundation By Vacuum-surcharge Preloading

With the rapid development of the construction industry and the rapid development of coastal cities along the Yangtze River,the development of soft soil foundation is increasing.How to control the stability and settlement of soft soil as foundation has become one of the important factors affecting the quality,duration and cost of the project.Vacuum combined with surcharge preloading technology has great cost performance and advantages in strengthening soft soil foundation,cost and environmental protection.Based on the practical application project,this paper further summarizes the construction technology by studying the soft foundation reinforcement technology of vacuum combined with surcharge preloading.The consolidation test of soft soil foundation is carried out by comprehensively using sand blowing and filling loading methods,and the consolidation effect of vacuum combined with surcharge preloading is discussed and comprehensively evaluated.The main research contents are as follows:(1)Compared with the soft foundation reinforcement scheme,the vacuum combined with surcharge preloading technology has the characteristics of simple process,wide application range,fast implementation speed and remarkable reinforcement effect compared with the common composite foundation method and drainage preloading method.Vacuum combined with surcharge preloading adopts the methods of "rushing" and "sucking" to form a larger water level difference,and "squeezing" and "discharging" the pore water in soft soil to achieve better consolidation effect.In the actual project,this technology can complete the reinforcement of soft foundation within 3 months,and the settlement after construction is within 100 mm,which meets the project requirements.(2)Aiming at the preloading technology of vacuum combined with sand blowing and fill loading,carried out the observation of vacuum degree,settlement and water level and indoor geotechnical tests.The results show that the vacuum combined with surcharge preloading technology has obvious reinforcement effect on soft soil foundation.Based on the law of "the average settlement velocity is hyperbolic decreasing",Through hyperbolic method,the consolidation degree of each area can reach 90%,and the post-construction settlement is about 50 mm.This technology is the superposition of vacuum preloading and surcharge preloading,and the reinforcement effect is not only proportional to the effective weight of surcharge,but also related to the vertical transmission of vacuum.Due to the downward transmission of vacuum degree along the drainage plate,the reinforcement effect will also decrease,and the general effective depth is less than 20 m,especially within 0-8m,and the shear strength of soil increases by 150%..(3)Contrast and analyze the consolidation effect of vacuum combined with surcharge preloading by sand blowing and filling.The results show that the effect of vacuum combined with sand blasting is better,and the increase of shear strength before and after reinforcement with a depth of 2m is about twice as much as that of vacuum combined with filling.In comparison,sand blasting can complete the loading in a short time,and the water in the sand also acts as a part of the load,which can make the soft soil consolidate quickly in the early stage and the effective superposition time is longer.And in terms of construction organization,sand blasting is more convenient to implement,does not need a lot of mechanical equipment,and is not affected by the weather.Compared with the average consolidation of filled soil,the sand blowing loading has obvious differences.Because of the sand blowing construction technology,the closer to the sand blowing port,the greater the load and the longer the time,and the more obvious the reinforcement effect.