The Engineering Application And Mechanism Of Vacuum-Piled-load Preloading Method

There distribute the soft soil in great quantities in the seaside district, medium downstream of Yangtze river and Pearl river downstream etc. in our country . It has the following engineering feature: high water content, high compress, low water permeability and low strength. Constructing various important engineering structure , the soft soil foundation must be processed in order to insure engineering safety and normally performing.To process above-mentioned this soft soil foundation, must to consider thus three basic problems:1. Settlement problem, the building doesn't produce harmful settlement and differential settlement during the period of application.2. Stability problem, accelerate to increase shear strength of the foundation soil, raise the bearing capacity and stability.3. Under the premise of resolving two above-mentioned problems, it can shorten the work period, lower the engineering cost, obtain the best processing effect.With preloading method to process the foundation is valid and this method is a kind of method that use extensively in current engineering. Based on vacuum preloading method and piled-load preloading method, the vacuum-piled-load preloading method which is the new generation effective soft soil processing method is developed. Currently, many important engineering, such as the piling field of extensive wharf, airport runway and expressway etc., all of them adopt the vacuum-piled-load preloading method to process the soft soil foundation, and carried on a great deal of trial research, obtain satisfactory processing effect.This thesis describes the problem first how to be put forward, which adopt the vacuum-piled-load preloading method to process the soft soil foundation. When the load of this soft foundation is great, the higher bearing capacity is required, the author puts forward the technique route of this problem whether we can adopt the vacuum-piled-load preloading method to process the soft soil foundation or not.This thesis reviews the development of preloading method, discuss mainly the applying condition and basic principles of vacuum preloading method and piled-load preloading method. At the same time, it is introduced the design calculation and the construction technology of twomethods in detail.Based on the consolidation mechanism of vacuum preloading method and piled-load preloading method, the possibility of applying the vacuum-piled-load preloading method is discussed furthermore. Based on the former researchers' work, the consolidation mechanism of vacuum-piled-load preloading method is studied out from the principle of effective stress. According to the test data of some soft soil reinforcing engineering of Tianjin harbor, the rationality of this mechanism is argued, get a beneficial conclusion is obtained. It is shown that the stress is added up under the positive pressure and negative pressure, the consolidating effect is added up from the engineering. When take out the vacuum, vacuum pressure force pore water pressure to lower quickly in the foundation soil, the shrinkage of soil body will happen, the piled-load can add quickly, the side extrusion of soil body don't happen, the foundation can avoid losing stability.In the end, the design calculation and construction technology of the vacuum-piled-load preloading method is introduced in detail. Currently, in the road and bridge engineering, many expressway are constructed on the wet soft foundation. Many regions adopt the vacuum-piled-load preloading method to process the foundation. Combined the practical engineering, this thesis analyze the consolidating effect and get the conclusion. With this method, the growth of subsoil strength is very effective to compare with vacuum preloading method and piled-load preloading method, and the construction technology is simple, the construction is convenient, the engineering cost is lowered, the work period is shortened, the engineering is economic.