一、前言 北京地下铁道复兴门底层站折返线,属于北京一、二期地下铁道的续建配套工程。一期地铁西起苹果园,东至北京站,自1971年初建成运营以来,日平均运量达390 000人次,已趋饱和。二期地铁西起复兴门,经西直门、东直门等站,沿着北京二环路成马蹄形运行至建国门。由于二期工程未能与一期地铁的北京站、 I. Introduction The re-entry line of the Fuyang Gate at the basement of the Beijing Subway is a continuation of the first and second phase of the Beijing Mass Transit Railway. Since the first phase of the MTR westbound from the apple orchard and east to Beijing Railway Station, the average daily traffic volume has reached 390,000 since it was put into operation in early 1971 and has become saturated. The second phase of Metro west Fuxingmen, Xizhimen, Dongzhimen station, along the Beijing Second Ring Road into a horseshoe-shaped operation to the Jianguomen. As the second phase of the project failed with a subway station in Beijing,