Analysis On Covered Top-down Excavation Technique Adopted In Practical

Covered Top-down Excavation method is a comparatively ideal method for metro construction. It has relatively little impact to its surroundings. Since the structure itself can be used as supporting system for enclosure construction, its rigidity is higher and that prevents possible deformation for enclosure construction and its surroundings evidently. Compared with other metro construction method, it enjoys lower cost also. These comparatively ideal indexes establish its proper place in modern urban subway station construction.Combined with Nanjing Xinjiekou subway station project, the biggest Asian station were built by Covered Top-down Excavation method, to introduce large-scale construction by the method. In this paper, the general construction methods and procedures had been illustrated, especially some technologies of slurry wall,templates and central pile-columns whose designed plan and quality management were also been discussed in detail. During construction, integrated technologies of surface steel tube concrete columns with underground drill-pouring piles, a systematical Covered Top-down Excavation method for permanent steel pipe concrete columns had been won. Some steel pipe column installation technologies such as sleeve technology, orientation, concrete filling and sleeve reclaim technologies were even initiated here. Its characteristics of high precision orientation, high efficiency, low cost and large development fulfilled the theory and practise of steel pipe concrete columns construction and provided an valuable reference for other similar projects in China.