既有线改建和修建复线时常遇到“合拢”施工。为达到施工生产与运输生产两不误，本文提出了影响 “合拢”准确性的因素及其消除这些不利因素的方法。

The construction of the closure for railway often occurred during reconstruction of existing railway line and construction of double line railways. In order to be unaffected both in the construction of closure and the operation of traffic，the paper proposes the factors which influence the accuracy of the closure and the methods to eliminate those unfavourable factors.