The Research On The Support Design And Leak Block Construction Technology In The Deep Pit With Confined Water

Ultra-deep foundation pit construction has been studied a lot at home and abroad, but the construction of 30m-deep pit rich of silty sand is the first time at the side of Qiantang River. This article discusses the research on the southern working deep pit of the passing-through -tunnel at Hangzhou Qing-chun road, because of the 30m depth and the location near the Qiantang River, it faced with high pressure water treatment issues in strong powder sand and highly permeable gravel layer deep foundation works for the first time. For the wide range of ancient Qiantang river, the average sand thickness is over 22m distributed at the ups and downs of gravel layer.It is highly risky confined aquifer for the complex Geological and hydro-geological. The on-site water pressure survey shows that: it contributed to the higher initial water head, the larger single well flow and the water level restore and larger fluctuations, and it lead to dynamic balance of the entire underground water pressure with sufficient water supply from the upper reaches.The final construction program of the southern working deep pit solved the highly water pressure problem with curtain riser combined with dewatering program, to avoid single curtain riser with highly cost and difficult construction or the unsafe single dewatering program, It got both the good economy and security results and provided a very good experience for similar projects.The forms and features of the aquifer stratum in the old Qiantang River channel was described, the treatment of the aquifer and the design method of trench retaining structure was put forward. Also we summarized and consummated the construction technology and other technical works timely, and assured well technical support for later underground construction related to similar geology condition in the region of Hangzhou.The treatment to confined water was a great important technical problem in the trench engineering. In this paper, we researched on it through the pumping test and numerical calculation in detail, also we optimized the design value and put forwarded feasible scheme of construction based on the comparing of observed data and the calculated result by FEM.