Mechanical Characteristics of the Combination System of Medium-Diameter Anti-Slide Piles and Tunnel-Under-Landslide Loading

Abstract

Landslides have significant impacts on the stress and deformation of existing tunnel that can damage the existing tunnel lining structures and thus affect normal traffic operation. It is of importance to study the mechanical mechanism of tunnel–landslide support systems. However, there are few studies on the mechanical mechanism of existing tunnels in landslide areas. The combination of medium-diameter anti-slide piles (300 mm ≤ D ≤ 800 mm) overcomes the disadvantages of the complex construction process and higher site requirements for large-diameter anti-slide piles (D > 800 mm) and the disadvantage of lower support with micro anti-slide piles (D < 300 mm). In this study, considering the influence of landslides on existing tunnel deformation, a new type of medium-diameter anti-slide pile reinforcement system for existing tunnels is proposed based on the Nanping Tunnel project. In order to study the influence of pile spacing on tunnel support, first, the maximum pile spacing of 12.5 d (25 cm) was calculated by the mathematical geometric method, and then, three physical models were established for experimental comparison and analysis, including three different spacing cases of 7.5 d (15 cm), 10 d (20 cm), and 12.5 d (25 cm). In addition, numerical simulation was used to analyze the landslide and tunnel deformation under three pile spacing working conditions. The following conclusions are reached: As the distance between the combined pile increased, the deformation of the pile body and the tunnel lining structure also increased gradually, and the earth pressure and bending moments acting on the tunnel and the pile body increased progressively. However, when the pile spacing was increased from 7.5 d to 10 d, the increase in tunnel bending moment (52.9% increase in tunnel lining moment) was much more significant than when the pile spacing was increased from 10 d to 12.5 d (28.1% increase in tunnel lining moment). The results showed that if the landslide thrust is small, the pile spacing can be increased to 12.5 d or more in the design of combined medium-diameter anti-slide piles; if the landslide thrust is large, the pile spacing should be reduced to 7.5 d or less. Whether the landslide’s thrust is large or small, the combined medium-diameter anti-slide piles with a 10 d pile spacing are less cost-effective for landslide control. The new combined medium-diameter anti-slide piles have high loading capacity and stability, which can further improve the strength of existing tunnels.

Mechanical properties of the combined medium-diameter anti-slide piles and tunnels under landslide loads at different sliding zone angles

“…The models for the bedrock, sliding mass, and sliding zones adopt the Mohr-Coulomb model, while the models for the lining and pile bodies adopt the Elasticity model [20,24,27]. All model nodes are fixed in the Y-axis direction.…”

“…These contact elements have a maximum shear force limit of 0.99 kN/m and a normal stiffness coefficient of 999 kN/m. The stiffness modulus of the contact elements for the pile-soil and tunnel interfaces is 2.45 MPa in the normal direction and 0.245 MPa in the shear direction [24]. Through the application of similarity scaling, the loads obtained from the model experiments are successfully converted to loads that accurately represent the actual working conditions.…”

“…The simulation of the sliding zone is carried out using a dual-layered polyethylene film that is filled with talcum powder. Back-calculation using the Bishop method yielded values of c=5.3kPa and φ=12.6° [24]. The tunnel model has dimensions of 25cm in height and 70cm in length.…”

“…Additionally, some scholars [22,23] have explored the mechanism of tunnel deformation in the secondary excavation support of existing tunnels and proposed appropriate support methods. Some scholars [24,25] have also analysed different support factors to obtain the force characteristics of tunnel lining under different support conditions. The tunnel-landslide system has been extensively studied by experts and scholars.…”

“…2 [24]. The combined medium-diameter anti-slide pile overcomes the challenges of complex construction, high cost, and demanding site requirements associated with large-diameter anti-slide piles.…”