Pipe Well Working Under Vacuum Condition Dewatering System & Its Use In The Construction Of Beijing Subway

In the process of excavating the foundation pit and tunnel of the subway, it isdifficult to deal with the perched water, the saturated water in the aquiclude, as wellas the remaining water on the aquifer surface. Currently, the subway construction inBeijing basically uses pumping pipe wells and self-seepage wells combined todewater;and only few sections use big-caliber radial wells, due to the limits of thesites. And the water mentioned above is hard to be drained with regular methods likeusing pipe wells;as a result, constructing with "water" happens in all the sections ofconstruction;however, this is not a good choice in terms of costs and safety.In view of this fact, it is necessary to design a pipe well vacuum compounddewatering system, which combines the use of well-developed dewatering andvacuuation techniques. And this compound system contains two independent yetmutually complementary systems, namely, the pumping system and the vacuuationsystem. The principle is: one hand, to impose negative pressure to cause the waterlevel of the well different from that of the stratum, so that the gravity water can beseparated out;on the other hand, under the negative pressure condition, the capillarywater which cannot be separated out under common pressure can be separated out,this is the most advantage of the vacuuation system to other methods.The experiment conducted in Line No.2 of the subway (from JinSong to finaldestination) witnesses the successful completion of such compound system: pipewells are sealed on a sectional basis;special sets for well-sealing are designed;andimportant data is obtained, including the minimum vacuum degree of the well thatconstruction requires, as well as the maximum impacted distance and the effectiveimpacted radius in the course of vacuuation on a single well. And this system provesto work well in solving the "water" problem in construction.