Parametric study of structural parameters affecting seismic stability in slopes reinforced by pile-anchor structures

Highlights

• Dynamic finite analysis and the Newmark method are used to evaluate slope seismic stability.

• Parametric study of structural parameters affecting the pile-anchor structure is performed for seismic design.

• Newmark permanent displacement is an effective evaluation index for slope seismic stability assessment.

Abstract

Parametric study was performed on the seismic stability of pile-anchor slope reinforcement structures for earth retaining wall with different structural parameters. Dynamic finite element analysis and the Newmark permanent displacement method were combined to derive the dynamic time-history response of the pile-anchor structure and evaluate slope seismic stability. The effects of pile embedment, pile thickness, anchor position on the pile, anchor free length, anchor direction and anchor prestress were investigated by batch calculation under different structural conditions, and optimized design suggestions are proposed based on the numerical study. The quantitative analysis indicates that Newmark permanent displacement can effectively evaluate slope stability under seismic loading and provide an accessible approach to improve the performance-based design of pile-anchor structures. For the generalized vertical soil slope prevalent in actual slope engineering, considering the maximum factor of safety and minimum permanent displacement, it was found that the most optimized embedded depth occupies approximately 30% of the whole pile length in the soil slope, and the pile thickness is set as 1.5–2 m for superior shear and bending strength. In addition, there is a critical anchor position 3 m beneath the pile top, a threshold free length of the anchor cable of 9.5 m, as well as an optimal direction within the range of 15°–20°. Furthermore, the pile-anchor structure shows better sliding resistance with rational anchor prestress accounting for 20% of the sliding force. The slope seismic stability evaluation based on dynamic finite element analysis with different pile-anchor structural parameter conditions performed in this paper may lay a foundation for the design optimization of pile-anchor reinforcement structures for better dynamic performance.

Introduction

Landslides are among the most problematic natural disasters in the world. Massive landslides have occurred worldwide with high frequency and across large areas in recent years, threatening human life and influencing the social and economic development conditions of many countries. In particular, earthquake-induced landslides have resulted in numerous casualties and considerable financial repercussions. Thus, with the increasing frequency of landslide disasters and the difficulty of slope treatment, slope dynamic response analysis and the stabilization of slope reinforcement structures have remained hot issues. Anti-slide pile and anchor structures have been regarded as an effective treatment retention method in slope treatment in areas that are prone to earthquakes [1]. The working mechanism of the pile uses the soil resistance in front of the pile and the anchoring effect of the stable ground under the sliding surface on the pile to resist the sliding force of the sliding body [[2], [3], [4]]. For anchoring, the sliding load of unstable rock and soil on the surface of the slope can be transmitted to the stable ground below the sliding surface by the tensile force [5,6]. For large-scale landslides distributed in mountainous regions, a single pile or anchor treatment may be insufficient to resist the sliding force, or the cost may be prohibitively high for larger and stronger reinforcement structures [[7], [8], [9]]. Under such circumstances, a pile-anchor structure may be used to combine the pile and anchor together to substantially reduce the cost and difficulty of slope treatment by overcoming the problems of excessive bending moment of the pile body, poor anchoring formation, and insufficient treatment scope when the slope is supported by a single anti-slide pile or anchor [10,11]. In recent years, the pile-anchor structure has played an increasingly irreplaceable role in slope treatment at a large scale for high, steep, and deep slopes [2,[12], [13], [14], [15], [16]]. For example, pile-anchor structures have been widely used in slope treatment in the Three Gorges Reservoir Region, high-cut slope reinforcement for large-scale water conservancy construction such as Jinping and Xiluodu, and slope repair in the Wenchuan–Yingxiu area, which is prone to earthquakes [17,18].

Regarding slope reinforcement design, recently, some researchers have focused on the mechanical performance of the retaining structures and the stability of the reinforced slopes. Kourkoulis, Gelagoti, Anastasopoulos and Gazetas [19] presented a parametric study taking the pile spacing, thickness of the stable soil mass, depth of pile embedment, pile diameter, and pile group configuration into account to evaluate the lateral resisting force in each case. A photoelastic technique was applied by Li, Xu, Yang, Li, Yang and Zhang [20] to study the distribution of landslide thrust in pile-anchor structures under the conditions of different pile materials and lengths. Li, Su, He and Xu [21] evaluated the seismic stability of a slope reinforced with a row of piles by applying limit equilibrium analysis in conjunction with a pseudo-static method in the cases of different pile locations. In addition, both the finite element method and the limit equilibrium method were employed by Li, He and Wu [22] to analyze slope seismic stability considering the effects of anchor orientation and anchor position. Moreover, the Newmark permanent displacement method has been widely used to evaluate the seismic stability of reinforced slopes [[23], [24], [25]].

In this study, a parametric investigation of pile-anchor reinforcement structures for earth retaining wall under seismic loading was performed to evaluate slope seismic stability under the conditions of different structural parameters. Dynamic finite element analysis was conducted to derive the dynamic time-history response of the pile-anchor structure, and Newmark permanent displacement was applied as an index to evaluate the structural parameters affecting the seismic stability of the reinforced slope considering the pile embedment, pile thickness, anchor position on the pile, anchor free length, anchor direction and anchor prestress.