Vacuum-Surchargepreloading: Experiment And Theory

Vacuum preloading and vacuum-surcharge preloading are effective methods to improve soft foundation.In recent years, these method was extensively used to treat soft clay ground such as harbor yard,airport,electric power plant,express highway, highway at bridge-head and etc.There have been great deep developments of improvement mechanism,construction techniques and design theory, whereas the development of theory for vacuum preloading and vacuum-surcharge preloading has lagged hehind a lot the engineering practice. Many problems such as the difference between vacuum preloading and surcharge preloading, the feasibility of soft clay with confined water by vacuum preloading,the rule of underground water during vacuum preloading, the stabibility of vacuum-surcharge preloading,the environment effect of vacuum preloading, its control method and etc still exist.This status has limited the more and more application and development of these two methods,which largely provokes more both academic and engineering researchers at home and abroad.Based on the former researchers' achievement, this dissertation focused on the mechanism and theory of vacuum preloading and vacuum-surcharge preloading through laboratory test,field experiment and theoretical study. The main aspects of this dissertation were studied as follows:1. Based on the improved Rowe's consolidation apparatus, the laboratory tests of vacuum preloading, surcharge preloading and vacuum-surcharge preloading were conducted.2. Field experiment of soft ground with confined water at Gangwan 220kV was performed. The results showed that it's safe and economic that the technology of 'tearing membrane' was combined with the 'non-tearing membrane' while driving PVDs.The main settlements could be eliminated effectively by vacuum-surcharge preloading at soft foundation with confined water, the degree of consolidation of total soft soil was 83% and that prediction post-construction which would last for more than 100 years was acceptable.3. According to the principle of equality of degree of consolidation, based on the negative pressure distribution pattern of twice exponential decay, the formula of equality for sand drains was deduced.The solutions about soft foundation with confined water by vacuum preloading and vacuum-surcharge preloading were derived from the previous research of other people.4. With ABAQUS FEA program, the stability of soft soil foundation treated with vacuum-surcharge preloading was studied.The results showed that the stability of soft soil foundation was related to the degree of vacuum, the depth of treatment,...