Application of a combined precast and in-situ-cast construction method for large-span underground vaults

Abstract

Exploitation of large underground space calls for innovative structures and construction methods. In this paper, a combined precast and in-situ-cast method for construction of large-span underground vaults is proposed. It was applied to an engineering example in the form of the vault of the Wuzhong Road Metro Station in Shanghai. This vault consists of 56 elements. Construction of an element involves the following steps. Firstly, upper ribbed arch segments are precast in a factory. After hardening, they are transported to the site and then assembled to three-hinged arches. The latter serve as a permanent formwork. Then, steel cages are made, followed by in-situ casting of concrete. As the concrete hardens, an integral arch, representing an element of the vault, is obtained. It carries the dead load of the covering soil and the overload on top of it. Structural analysis of this example is based on transfer relations, representing analytical solutions of the linear theory of slender circular arches. From the viewpoint of engineering practice and computational analysis, the advantages of the combined precast and in-situ-cast method over the in-situ-cast method are as follows: (i) the construction period is shortened by 50%, (ii) a fair-faced concrete surface of the vault is produced, rendering decoration work superfluous, and (iii) the maximum bending moment of an element of the studied vault is reduced by 40%.