Research In Evolvement Of Channel And Character Of Confined Water Of Paleochannel Of Qiantangjiang River

In the area with confined water, separation layer under the base will be thinner and thinner with the increasing depth of the foundation pit. Confined water may rush forth and upheave, causing the exterior protected construction unbalance and finally bringing up the most dangerous accident in the construction of the foundation pit.The Qiantangjiang River crossing tunnel in Qingchun Road in Hangzhou was facing the serious problem which is caused by the confined water in the paleochannel of Qiantangjiang River. The shield TBM launching shaft of the Qiantangjiang River crossing tunnel is one of the deepest foundation pit close to the Qiantangjiang River. There is no reference experience to take as it is the first construction. Hence there is no more completely information about the the paleochannel of Qiantangjiang River.This thesis firstly gave a brief introduction to the theory of paleochannel and the evolvement of paleochannel. Including the study objects, contents, methods and meanings of the theory of paleochannel, then drew a conclusion for the evolvement style of paleochannel and all kinds of factors that effect it as well. This thesis use many analysis methods such as analysis with document of historical geography(including official history, chorography and pertinent historical literature); relief map in doors, striograph(including aerial photo, satellite photo, color infrared film )to identification and pointillism; physiognomy inspection in wild and method of access to introduce the current situation and the process of its forming, including inspection in the riverhead and the estuary position of Qiantangjiang River, the formation of the estuary and the history transition as well. According to the document investigation and data analysis, determined the relatively exact position of the estuary and riverhead. According to the document investigation, introduce the formation of geologic environment and diverging riverhead, the transition of bilateral shoreline along Hangzhou Bay and stream, the recent changes of marginal bank in the riverhead as well as the reasons leading to the riverway' s transition. Synthesizing the results of the document investigation, estimate the position and range of the confined water saved and study on the character of the confined water. According to the problem of confined water in Qiantangjiang paleochannel faced, get a conclusion on the characteristics and impact factors on the foundation pit engineer with confined water. On the base of the introduction to the stable calculation method and their separate advantage for safety coefficient of piping of foundation pit with confined water. Combine with classics pressure equilibrium that the shield TBM launching shaft in north of Qiantangjiang River of the Qiantangjiang River crossing tunnel adopted to calculation, analyzed whether the method is suitable or not, and analyze the reason why adopt this method finally. When the safety coefficient of piping is not satisfaction to the request, we should take the actions to the confined water. And also introduce the basic theory of dewatering of confined water and the processing method of the gutter drainage and well point precipitation. And also the relative merits and applicable condition of kinds methods. The shield TBM launching shaft in south of Qiantangjiang River adopted the impervious curtain synthesizing with well point precipitation to deal with the problem, avoiding the weakness of impervious curtain or well point precipitation adopted singly. It makes a good effect of the two aspects in economy and safety. Also offer an excellent reference experience to the similar construction in the same area in the near future.