Studying The Impact Of Groundwater Changes On The Subgrade Deformation And Line Regularity Of Column-Net Structure And Ballastless Track High-speed Railway

In recent years, with the rapid development of the national economy, the amount of groundwater exploitation increased year by year, resulting our country not only exists a very serious regional settlement, but also the differential subsidence in ground along the high-speed railway caused by groundwater exploitation is also very prominent, and it not only affects the normal function of the line, excessive settlement, differential settlement will directly affect the running safety. Based on the extensive research and gathering a lot of data, a systematic research about the typical high-speed railway subgrade-column-net structure subgrade settlement caused by exploitation of groundwater have been carried out. The main contents are as follows:(1) Revealed the mechanism of the settlement caused by groundwater drawdown. Based on the classic Terzaghi effective stress principle, the theoretical calculation that groundwater decline leads to ground subsidence has been derived. Combined the theoretical analysis and finite element numerical simulate method got the mechanism which is about exploited groundwater caused land subsidence. The mechanism is that in the process of groundwater tables falling pore pressure decreases, while the effective stress of soil is increasing which lead to soil consolidation and compression(2) Fortran was used to developing groundwater integral rising and falling module, combining the actual variation of groundwater level in North China, studying the subgrade settlement and piles in force which is under lunar cycle and annual cycle changes of the groundwater level. The result shows that:the subgrade settlement linearly increased with the groundwater depth decreased, when the groundwater level rises, subgrade settlement accordingly reduced, but not completely restored to the situation prior to precipitation. Negative skin friction and axial force are gradually increased with the decline of groundwater tables, while the neutral point position in pile are linearly decline with the groundwater tables decreases, and maximum axial force occurs in neutral position.(3) Established a high-speed railway column-net structure fluid-solid coupling model, analyzed column-net structure subgrade settlement in three different types groundwater exploitation,which are agricultural water, industrial water and domestic water, studied the subgrade settlement changes in shallow and deep groundwater exploration, calculated the influence of the pumping distance and pumping rate for the subgrade settlements. The results show that:the main difference between seasonal agricultural water and non-seasonal industrial and domestic water for the subgrade settlement lies in its pumping rate, seasonal factors has little influence on it. Comparison of shallow groundwater exploitation and deep groundwater exploitation for the subgrade settlements can be seen that in the same pumping rate, in spite of deep groundwater exploitation subgrade settlement is more larger, but it mainly a wide range of regional settlement and the value of shallow groundwater exploitation settlement is smaller, but its influence for the line regularity is bigger. As the pumping distance became shorter the subgrade settlement became larger, the amount of subgrade settlement produced by pumping rate of 1250m3/d is 3.4 times of 250m3/d, the amount of pumping rate is more greater the subgrade settlement is more larger.(5) The track irregularity produced by different pumping distance and pumping rate are imported into the high-speed railway vehicle-track-column-net structure subgrade dynamic coupled model, by using two-step approach to get the runnning safety characteristics, dynamic response of track and column-net structure which are produced by different pumping distance and pumping rate. The results show that:when the pumping rate is certain, pumping distance become shorter while running safety and dynamic response of the column-net structure become larger. When pumping distance is 200m, the wheel unloading rate is 0.55; when pumping distance is 150m, the wheel unloading rate reached 0.58; when pumping distance is 100m the wheel unloading rate reached 0.62, so as to ensure the running safety of high-speed railway, within 200m of the center line groundwater exploitation should be prohibited. When pumping distance is 200m, increasing pumping rate has a certain impact on the running safety, but no bigger than the impact of pumping distance.