| China is one of the typical countries with a great number of people suffering from serious landslide hazards,making the prevention of landslide hazards a significant demand of China.With numerous water resource and hydropower engineering projects such as Gezhouba,Three Gorges and Baihetan built in succession,landslides in reservoir regions severely threaten the safety and properties of residents,and safe operation of these projects as well.Three Gorges Project is the largest and the most extensive water resource and hydropower engineering project,there are over 5,000 geological hazards in the Three Gorges Reservoir(TGR)region,among which the Zigui basin is a typical region prone to landslides,partially due to the widespread Jurassic sliding-prone strata(interbedded weak and hard strata).Consequently,the water-rock interaction,evolution mechanisms,prevention and optimization of landslides are key scientific problems of research associated with reservoir landslides in similar regions,and are also important geological guarantees for national development.In this dissertation,the scientific problems of reservoir landslides in Jurassic strata of Zigui Basin,TGR region,i.e.,water induced multi-scale deterioration mechanisms of physical and mechanical properties of rock mass,and the embedded mechanisms of stabilizing piles in interbedded weak and hard strata,were studied in detail.Comprehensive research methods including site investigation,laboratory experiments,and theoretical analysis were employed to systematically study the distribution features and development mechanisms of reservoir landslides in the study area,the water induced multi-scale deterioration mechanisms and quantitative characterization of probabilistic properties of rock mass in interbedded Jurassic strata,and the embedded mechanisms and multi-objective optimization of stabilizing piles embedded in such strata.The major achievements of this study are summarized below:(1)Distribution features and spatiotemporal deformation characteristics of reservoir landslides in Jurassic strata of Zigui basin,TGR region were studied,and the development and deformation mechanisms of reservoir landslides were revealed.Distribution features and development mechanisms of reservoir landslides are important scientific premises of regional landslide research.Through site investigation and literature review,the distribution map of landslides in Zigui basin of TGR region were produced.The distribution characteristics of reservoir landslides in this region were studied,and the corresponding development mechanisms were then proposed considering regional geological environment and anthropogenic activities.Understandings of deformation characteristics and mechanisms of landslides are important for studies including evolution,forecasting and prevention of landslides.Using Baijiabao landslide,Majiagou landslide and Bazimen landslide as examples,spatiotemporal deformation characteristics of typical reservoir landslides were studied combining site investigation and in-situ monitoring data,the triggering factors responsible for landslide deformation were then identified through an attribution reduction method based on neighborhood rough set theory.With the deformation differences of monitoring data with various precision discussed,the deformation characteristics and mechanisms of Baijiabao landslide were presented.(2)Multi-scale deterioration mechanisms of cyclic wetting-drying of Yangtze River water on physical and mechanical properties of rock mass were studied,and the probabilistic properties of rock mass were quantitatively characterized.Yangtze River water(river water)contains complicated chemical and microorganism compositions,long term cyclic wetting-drying of river water can affect the physical and mechanical properties of rock mass.Using three types of water,i.e.,the river water,the ionized water having similar ion compositions with the river water,and the distilled water,numerous laboratory tests were conducted to study the influence of cyclic wetting-drying of different water types on multi-scale physical and mechanical properties of sandstone and argillaceous siltstone(i.e.,rock of interbedded Jurassic strata).The effect differences of different water types were discussed,and the deterioration mechanisms of river water on sandstone and argillaceous siltstone were further proposed.Structural parameters of rock mass show significant variability and uncertainty,the water induced deterioration and structural features of rock mass should be considered during quantitative characterization of geotechnical parameters.With prior knowledge,multi-source data(from multiple estimation models)and probabilistic characteristics of model uncertainty integrated,a modified Bayesian sequential updating method for estimation of geological strength index(GSI)of rock mass was proposed,characterization models for GSI of sandstone and argillaceous siltstone were established.Considering deterioration effect of cyclic wetting-drying of river water on physical and mechanical properties of rock mass,the probabilistic characteristics of strength of rock mass were analyzed based on generalized Hoek-Brown criterion.(3)The embedded mechanisms of stabilizing piles in interbedded Jurassic strata were studied,and a multi-objective optimization framework algorithm for stabilizing piles was developed.Structural properties of bedrock and influence of river water on rock mass should be considered in studies of embedded mechanisms of stabilizing piles in the study area.Based on the probabilistic characteristics of horizontal foundation coefficient(K)of interbedded Jurassic strata,the Majiagou landslide was demonstrated to study the deflection and internal stress of stabilizing piles embedded in interbedded Jurassic strata via the multi-K method.The effect of geological structure,river water induced deterioration and design parameters(e.g.,cross-sectional size and embedded depth)on responses of stabilizing piles were analyzed,and the embedded mechanisms of stabilizing piles in interbedded Jurassic strata were proposed.Design of stabilizing piles should meet balance among safety,engineering cost and system robustness.The characterization models for performance indexes of landslide-stabilizing pile system including system stability and life-cycle cost were established,and a multi-objective optimization framework for stabilizing piles considering system stability,life-cycle cost and system robustness was developed.The Majiagou landslide was used as an example and its optimal design of stabilizing piles was obtained,then the influence of the deterioration of river water on rock mass,the influence of performance indexes on the optimal design,and the influence of design parameters of stabilizing piles and water type on system performance of landslide-stabilizing pile system were further discussed.The research of this study may enrich the information of landslide distribution in the TGR region,deepen the understanding of water-rock interaction,improve the estimation accuracy of rock mass parameters,and develop the design theory of landslide prevention.The research may also provide theoretical and practical reference for studies of deterioration mechanisms of water on rock and soil masses,and mechanisms and prevention of landslide hazards. |
PDF Full Text Request