Research On Reinforcement & Anti-slide Mechanism And Key Technologies Of Engineering Application Of Continuous Pile-plug Structure

In view of the application limitation of conventional single retaining structure in certain cases, this paper proposes a new-style anti-slide structure with better applicability, which is called continuous pile-plug structure. This structure is constructed by excavating multistage underground adits and shafts continuously and then backfilled with reinforced concrete, consequently forming a stair-shaped anti-slide structure by multistage horizontal limbs and vertical limbs connected end to end. It is expected to take advantage of the integrated reinforcement and retaining function and result in anti-slip effect.Presently, there is neither effective application experience and monitoring data nor mature analysis theory and computational method for continuous pile-plug structure. Therefore, concerning engineering application, this paper adopts numerical analysis method to perform a thorough study on its anti-slide mechanism, reinforcement effects and principal design parameter effect. The key technologies of engineering application are then studied and summarized synthetically based on theoretical analysis and engineering practices. Finally, the continuous pile-plug structure is applied to the Houzishi landslide control engineering in Three Gorges Reservoir Region. The main contents and conclusions are as follows.(1) On the basis of choosing the appropriate physical models of landslide and continuous pile-plug structure, a FLAC-procedure-based plane strain numerical analysis model is built. The rock-soil materials is simulate by ideal elastoplastic constitutive model with Mohr-Coulomb criterion, the continuous pile-plug structure is simulated by pile structural elements and the safety factor and mechanical characteristics of limit state are solved with strength reduction method. The interaction effects between structure and landslide are simulated for three different conditions, i.e. not using continuous pile-plug structure, using continuous pile-plug structure and using conventional anti-slide pile.(2) The indexes, including shear strain increment, displacement vector, plastic zone distribution and safety factor of landslide, are calculated for the landslides with & without continuous pile-plug structure. It is indicated that the internal anti-slide mechanism of continuous pile-plug structure is to reduce shear deformation, depress plastic zones, block slide displacement, mobilize rock-soil resistance, and improve bedrock stress state. The external anti-slide mechanism includes reinforcement effect and retaining function. Therefore continuous pile-plug structure combines retaining plug and anti-slide pile and has a wider range of application for landslide control.By comparing the internal forces and the displacement vectors of continuous pile-plug structure and anti-slide pile, it is showed that continuous pile-plug structure works in a complex stress state involving bending moment, shear force and axial force and has obvious holistic resistant behavior and relatively small and uniform deformation. It is concluded that continuous pile-plug structure works well because of the interactions between the connected parts, which help to optimize bending and shear distribution, strengthen axial force and harmonize deformation.(3) The influence of main design parameters on anti-slide effect are studied, including sectional dimension, lateral spacing, structural style, concrete strength and shear strength. It is indicated that they all have influences on reinforcement effect, which vary in pattern, extent and tendency. Comparatively speaking, shear strength and structural style have the most significant effect while concrete strength has the smallest effect.(4) Based on theoretical analysis and engineering practices, the key technology of structure application are studied and summarized in terms of structural arrangement way, key construction technique, key constructional measures and effect monitoring measures. Structural arrangement way should follow the implementation principle of dynamic design and informational construction, the localization method of arranging adits and shafts by tracing slippery belt, the excavation procedure of layered parallel construction, and the function classification of different adits and shafts. Key construction technique mainly includes maintaining cavern stability, protecting surrounding rock integrity and guaranteeing concrete backfill quality. Key constructional measures mainly include rebar mechanical splicing, quick-acting anchor and backfill grouting of adit. Effect monitoring measures mainly include landslide deformation, structure stress and seepage.(5) For the first time, continuous pile-plug structure is applied to the Houzishi landslide control engineering in Three Gorges Reservoir Region. The macroscopic signs and monitoring data show that the landslide is stable and the structure is in good load-bearing condition. However, long-term continuous monitoring is still needed to have the landslide deformation process and the structure stress situation for ensuring their security.