Analytical Theories Of Consolidationand Seepage Of Soft Ground With Vacuum Preloading

There were large areas of soft clay whose engineering behavior was poor in China, and with the development of national economy, construction of infrastructure projects such as ports, terminals, airports and highways entered into a period of rapid development; in order to protect structures in the construction and eliminate excessive settlement, therefore, it was necessary to carry out the necessary processing method of soft ground.As a kind of drainage consolidation methods, vacuum preloading in soft ground with and have a greater advantage for its cost, duration, effects, environmental protection campreing to other traditional methods and then had a wide range of applications.Based on the former researchers's work, this theis researched the questions above via field experiment and thoretical analysis. All the work done was as follows:(1) Solutions for settlement and consolidation calculation of soft ground with vacuum preloading were studied by considering the loss of vacuum. Firstly, an axisymmetric deformation model was developed under equal strain condition according to the vacuum pressure condition of sand drain with vacuum preloading, formulae of deformation and volumetric strain were derived from spatial axisymmetric displacement control functions by using the displacement method.(2) Then connecting the obtained volumetric strain functions and the existing Hansbo's sand drain foundation consolidation theory, and modifying some boundary conditions with vacuum preloading, analytical solutions for consolidation of soft ground under vacuum preloading was conducted when vertical water flow in soil was neglected.(3) Analysis of the dynamic of fluid motion and Absorption principle and law of pore pressure drop of plastic vertical drain (PVD) were made, and then the analytical solution for groundwater level changes in reinforcement zone of soft ground with vacuum preloading was investigated by using one-dimensional transient seepage flow model according to the classical theory of kinematics of groundwater, using average groundwater zero pressure line in reinforced zone as the boundary condintion, solution of one-dimensional transient seepage flow model was also conducted when reducation of water pressure in drainage boundary was changing over time.(4) Finally, a comparison between the present solution and some previous solutions was made, and those theoretical solutions and test data in situ for comparison at the same time. The results show that volumetric strain has great effects on pore pressure and consolidation calculations, it would lead to large errors in consolidation calculation of vacuum preloading while quoting the volume strain formula of surcharge preloading directly. And by using Hansbo's approximate method to calculate degree of consolidation can meet the requirements of precision.Through on-site monitoring, monitoring of field test results and field vane test and cone penetration test results are summarized, indicating that vacuum preloading of soft clay foundation treatment can achieve better reinforcement effect through the comparative analysis of all these test results.