Abstract
Loess is a kind of special soil with structure and hydrocollapse behavior; due to the particularity of loess, the deformation regularity of the tunnel in loess shows different characteristics from those in rock. To ensure the safety of construction, crown settlement (CS) and horizontal convergence (HC) are widely used to assess the stability of the tunnel structural system. Based on statistical analysis, this study focused on analyzing the influence of cover depth on the deformation of surrounding rock of loess tunnels by ANOVA, and relationships between them were presented by regression analysis. The achieved results indicated that the influence of cover depth on deformation was not obvious in shallow tunnels, while the cover depth had a significant effect on deformation in deep tunnels. Based on the difference of influence of cover depth on deformation between shallow tunnels and deep tunnels, a method for determining the cover depth threshold (CDT) in the tunnel by statistical analysis was proposed. The horizontal and vertical deformations in shallow tunnels were discrete and obeyed the positive distribution, mainly concentrated within 200 mm. The deformation allowance in shallow tunnels was recommended to be 200 mm. In deep tunnels, as the cover depth increased, the deformation increased linearly, while the CS/HC decreased.
Highlights
Loess is widely distributed and accounts for 1/6 of China territory as shown in Figure 1 [1], necessitating the construction of tunnels in loess regions
During the tunnel construction in loess ground, the sequential excavation method (SEM) is widely applied to promote the tunnel face stability, such as both-side drift method (BSDM), bench excavation method (BEM), central diaphragm method (CD), and cross diaphragm method (CRD), as shown in Figure 2. e BEM is adopted in the regions with ordinary surrounding rock, while the CD and CRD are mainly used in the sections with weathering rock, poor geology, or tunnel portal
Statistical analysis, as an important approach to study regularity, is widely used to analyze monitoring data of deformation in rock tunnels, whereas rarely in loess tunnels [46,47,48]. is paper studies the influence of cover depth on the deformation of surrounding rock of loess tunnels by analysis of variance (ANOVA) and relationships between them were presented by regression analysis, providing a more reliable theoretical basis for the deformation law of surrounding rock in the design and construction of loess tunnels
Summary
Loess is widely distributed and accounts for 1/6 of China territory as shown in Figure 1 [1], necessitating the construction of tunnels in loess regions. Statistical analysis, as an important approach to study regularity, is widely used to analyze monitoring data of deformation in rock tunnels, whereas rarely in loess tunnels [46,47,48]. Is paper studies the influence of cover depth on the deformation of surrounding rock of loess tunnels by ANOVA and relationships between them were presented by regression analysis, providing a more reliable theoretical basis for the deformation law of surrounding rock in the design and construction of loess tunnels. E analysis of variance (ANOVA) was used to study whether the tunnel deformation was significantly different at different levels under specific spans, to study whether the influence of cover depth on deformation was significant. (1) According to the data of cover depth and deformation, the regression equation is initially set (2) Solving regression coefficient (3) Perform a correlation test and determine the correlation coefficient (4) After meeting the relevant requirements, the regression equation and the specific conditions can be combined to determine the trend of the deformation with the cover depth, and the confidence interval of the predicted value can be calculated
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