Theory And Model Test Study Of Recently Reclaimed Soil Foundation

With the development and construction of Tianjin Binhai New Area, more and more land is made up with reclaimed soil. In the past the reclaimed soil foundation is dried in 2 to 3 years, and then it was reinforced in vacuum preloading method. But with the development and construction of Tianjin Binhai New Area, there is new technics of vacuum preloading, so the reclaimed soil can be reinforced without dried, the object was changed to recently reclaimed soil. Vacuum preloading method is an effective reinforcement to soft soil foundation; and this method is suitable for reclaimed soil foundation. Many foreign and domestic scholars and engineers have done a lot of research and made many interesting research results in the Vacuum preloading mechanism. However, the recently reclaimed soil characterized by low-intensity, high water content, large thickness, there is many problems due to these characters in vacuum preloading method. The theory and calculation method is not accurate to the recently reclaimed soil foundation. In order to solve these problems the paper did some studies on the calculation theory and test as followings:First, the settlement calculation method of recently reclaimed soil foundation was put forward. The formation process and character of the recently reclaimed soil are analyzed, and it was proposed that the reclaimed soil is unconsolidated soil, there is excessive pore water pressure which is caused by the self weight in it before the reinforcement. So there will be settlement during the PVDs installment. It is considered that the vacuum preloading settlement include the settlement during the PVDs installment and the settlement during the vacuum preloading. The settlement calculation method was put forward, and at the same time, the calculation result was compared to the field test data, it shows that the method is feasible.The indoor model test study was conducted to the recently reclaimed soil.The reclaimed soil have the water content of 80% and it is super-soft soil. With the development of land of Reclamation, the bottom elevation of the reclaimed area getting lower and lower, the thickness of the reclaimed soil reached 10m from the original thickness of 2m now, so that a great deformation occured in the course of the vacuum preloading. There are some phenomena that hard to explain. In order to solve these problems, this paper carried out an ultra-soft soil vacuum preloading indoor model test. Some research have been done through the experiments: (1)Though the indoor model experiment it was found that the PVDs has undergone a drastic distortion and even part of it was breaken due to large deformation of the ultra-soft soil during the vacuum preloading, this result the efficiency of the PVDs reduced, so that the soil reinforcement is ineffective and can not achieve the desired bearing capacity of foundation requirements. (2) in order to make secondary reinforcement, secondary PVDs installation was carried out, results show that the settlement was further developed,water content was further reduce,vane strength was further improved, and the Vane strength decline rate greatly developed. the distribution of vacuum degree along the PVDs and in the soil was also be studied. The test result provide reference to explore a more effective method of reinforcing the deep reclaimed soil foundation.Though the analysis of the the character of reclaimed soil and the consolidation process, the FE calculation method was put forward. The recently reclaimed soil foundation vacuum preloading is divided into two processes, the consolidation during PVDs installing and vacuum preloading. The paper incorporates the nonlinearity constitutive relation (Duncan-Chang's model) into the Biot's consolidation theory program. Considering different load conditions, a general-purpose program was compiled to analyze the behavior of the soft clay consolidation with plain strain FEM. Two actual projects were calculated using this program. Comparing to the field measurements data, it indicates that the method reflects very well the developing trend of settlement and pore water pressure for the projects. At the same time, the vacuum preloading of reclaimed soil foundation was analyzed using ABAQUS FE soft ware, the result goes well with the field data.At last, the paper presents a new method of vacuum preloading by improving the drainage system. An indoor experiment was made to compare the ventilating vacuum preloading with the ordinary vacuum preloading. On the basis of test data, described the theory of the ventilating vacuum preloading.