Abstract
Peck method and stochastic medium method are the two most commonly used methods to estimate surface settlement caused by tunnel excavation. However, the Peck method was not suitable for a shallow‐buried tunnel, and the calculation process of the stochastic medium theory was complicated. To solve this problem, in this paper, a simple and accurate prediction approach for surface settlement was obtained by improving the Peck method based on the basic idea of stochastic medium theory. In detail, the over‐excavation area of the tunnel was divided into n independent units, and the surface settlement caused by the collapse of each unit was calculated, respectively. Then, the total surface settlement can be obtained by superimposing surface settlement induced by each unit. Taking the shallow‐buried section of Mulingguan tunnel entrance as a case, the surface settlement calculated by the modified Peck formula and original Peck formula was compared with the observed data, respectively. The comparison results indicated that the surface settlement calculated by the modified Peck formula is closer to the observed data than that calculated by the original Peck formula in the calculation process of surface settlement of shallow‐buried tunnel. The table of recommendation for the number of units can be obtained by a discussion of reasonable n values. Finally, the difference between the original Peck formula and the modified Peck formula was analysed, and the results showed that the change rule of the surface settlement is consistent under the tunnel depth, internal friction angle, and ground loss of the tunnel. However, the calculation error of the surface settlements calculated by the original Peck formula is more significant than that calculated by modified Peck formula under the tunnel diameter ratio being less than 1.75. The modified Peck formula is more suitable for calculating the surface settlement under internal angle friction being less than 20° or greater than 40°. The research results expand the scope of application of the original Peck formula and enrich the calculation approach of surface settlement induced by underground excavation in tunnel construction.
Highlights
Han et al evaluated the applicability of the Peck formula in different regions by discussed and analysed surface settlement observed data collected from more than 30 groups of subway construction in China; the results showed that the Peck method was not suitable for shallow-buried tunnels [32]
It shows that the modified Peck formula can better predict the surface settlement of singleline tunnel, but there will be some errors for the double-line tunnel
In this study, a simple and accurate prediction method for surface settlement was obtained by improving Peck method based on the basic idea of stochastic medium theory. e modified Peck formula was verified by an engineering example. e obtained conclusions are summarised as follows: (1) e Peck formula is an approximate algorithm of the stochastic medium theory under the condition of large depth and a small section of the tunnel by comparing the calculation principle of surface settlement with the stochastic medium theory and the Peck formula
Summary
Subway tunnels and other public facility tunnels are often constructed by the subsurface excavation method due to the problem of traffic congestion and the environmental quality requirements. e underground excavation of urban subway tunnels is bound to cause surface settlement and even cause surface collapse, affecting the safety of driving and pedestrians [1,2,3,4,5,6,7,8]. erefore, it is of great practical significance to predict surface settlement induced by the underground excavation of urban subway tunnels to prevent excessive surface settlement or surface collapse. Han et al evaluated the applicability of the Peck formula in different regions by discussed and analysed surface settlement observed data collected from more than 30 groups of subway construction in China; the results showed that the Peck method was not suitable for shallow-buried tunnels [32]. Another method to predict surface settlement and deformation induced by tunnel construction is the stochastic medium theory. Compared with the Peck method, stochastic medium theory can be applied to a shallow-buried tunnel and various excavation sections, which has more advantages [35, 36]. The difference between the modified Peck formula and original Peck formula is discussed, which further verified the rationality of the modified Peck formula
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