The Application Research On Highway Soft Subgrade By Vacuum And Surcharge Preloading Method

Soft soil foundation is of wide distribution in China. Given that construction limits, numerous roads were built on the soft soil foundation. Owing to the disadvantage, like heavy moisture content, high compressibility and low foundation capability, of the soft soil, obstacles in road constructions are of great presence. In light of this issue, solutions like Surcharge Preloading Method, DJM Method, Plastic Drainage Method and Vacuum Preloading Method have been conducted to cope with the problems. However, the mentioned methods can still not sufficiently meet the requirements, for instance, the stability of construction, construction duration post-construction settlement and so on. Focusing upon this problem, Vacuum Combined Surcharge Preloading Method boasts the potential preponderances.This thesis, linked with the research on experimental project of Vacuum Combined Surcharge Preloading Method for soft soil foundation in Sangtiandao region, Suzhou City, specifies in following concerns:1) Theoretical analysis of surcharge preloading and reinforce mechanism of vacuum preloading with a further illustration of the features after the two methods are combined will be carried out.2) Indoor conventional experiments of the soil mass on the spot before and after loading, comparative analysis of the physical mechanics quality index of soil mass after reinforced, and evaluation of the effectiveness will be implemented.3) Discussion over regulation and vacuum influence basin of the quantity of settlement, pore pressure and horizontal movement after reinforced in such manner will be held with statistics from project monitoring, while Layerwise Summation Method and Usher-Spillman Model will be taken to predicate the settlement.The findings and further understandings in the research are provided as follows:1) The moisture content shrinks in clear form after the application of Vacuum Combined Surcharge Preloading Method, and the change rate of moisture content presents the most at the depth of14.0～14.3m. In this way, the effectiveness of this method can be clearly seen. 2) In accordance with the comparative study over experiment result of the physical mechanic quality of soil mass before and after the use of Vacuum Combined Surcharge Preloading Method, the finding is that, after preloading, the density of soil enlarged while the moisture content shrunk, the tightness of soil enhanced. Among other things, the internal friction angle in soil mass is relatively widened and its cohesion is intensified.3) After Vacuum Combined Surcharge Preloading Method,0-16mm area in soil mass moves apparently from both sides of the road towards the center of it with "centripetalism";16-26mm area, the "centripetence" presents less effectiveness as the distance of the reinforced region is enlarged.4) Calculations settlement in manner of Layerwise Summation on sections, namely, K1+480, k1+580,k1+680, are154.31cm,138.70cm,129.20cm respectively. When the vacuum to reach200d model shows User-Spillman Model is suitable after comparative analysis..The research with sufficient monitoring statistics in soft soil foundation of Sangtiandao region in Suzhou City is of great assistance for project design, construction, in the meantime, it offers reference and guidance to those resembling projects that are or will be implemented in Suzhou city, moreover, it enriches the theoretical and practical basis for further research.