Abstract:

The rational crosssection form and optimization idea of the super largespan opencut tunnel with large overburden should be carefully studied. Hence, the north section of the second highway of Guangzhou New Baiyun International Airport with the covered soil thickness of 5 m and singlehole span of 31 m is taken for an example to carry out analysis on the structural mechanical behavior, technical economy, construction technology, etc. It is concluded that the crosssection form of the folded plate of straight wall is the optimum for the largespan tunnel with large overburden according to the finite element modeling and calculation. In addition, the optimal folded plate size (2 m×1.25 m) scheme is obtained by discussing the influence of different sizes of folded plate of straight wall on the internal force of tunnel structure. At the same time, by setting different crosssection heights and adding diaphragm beam, the measure of 1.5 m raising of the crosssection with the tunnel roof covering soil more than 5 m is put forward. Based on the analysis of the crosssection of the super largespan tunnel, it is difficult to increase the thickness of the roof of the tunnel structure to satisfy the bearing requirements of the deep cover soil. As a result, the structural design scheme of hollow slab at the roof of the tunnel is formulated.

Key words: expressway, opencut tunnel, deep overburden, superlarge crosssection, crosssection form, deflection angle, hollow slab