Research On Deformation Mechanism And Control Technology Of Tunnel-Landslide System

In this thesis, on the basis of Traffic Construction Science and Technology Project inGansu Province–"Mechanism and Control Technology of Tunnel Hazards induced byTypical Landslide along Wu-Guan Expressway "(No:200813), it is that "DeformationMechanism and Control Technology of Tunnel-Landslide System." be selected as theresearch subject combined with our experience of decades in traffic engineering geologicaldisaster prevention. The combination method is used for research, such as informationresearch, theoretical analysis, numerical simulation experiments, geomechanical model testand on-site monitoring. Focusing on the construction period, the author discusses thefollowing aspects of the problems: the deformation characteristics, interactional mechanism,engineering security evaluation, and deformation control technology of Tunnel-LandslideSystem.(1) Owing to complex topographic and geologic conditions and development process ofgeologic structure along Wu-Guan Expressway, there are a large number of landslides,collapses, mud-rock flows and other disasters. It had a greater influence along theexpressway, as a whole belonging to the unstable sites. The survey shows that there arelandslides54with various types, the collapse of scattered47and other dangerous rockdiseases along the expressway. Ma-Ya-Zi mountain range is the regional north-southwatershed. Loessial landslides mainly develop in the northern section with large andmedium-sized shallow. Loose Quaternary deposits landslide, bedding rock and antidip rocklandslide with huge-scale, develop generally in the southern section. According to thespecific characteristics of tunnel-landslide along Wu-Guan Expressway, the slope structuretypes of the tunnel-landslide along expressway are divided into the following fourcategories: accumulation layer-bedding rock slope structure, accumulation layer-antidip rockslope structure, steeply bedding slope structure and steeply antidip rock slope structure. Inresponse to these types, the slope structural characteristics of selected typical worksites wereanalyzed separately, and it is laid foundation for further analysis of landslide failure modeduring excavation.(2) Emphasised on typical tunnel-landslides on Wu-Guan Expressway, the concept of"Tunnel-Landslide System" is initially established. Considering these aspects such as slopestructure, disaster predisposing factors and spatial composing relations between tunnel andlandslide, the relative perfect mode of deformation is established with the parallel system, the orthogonal system and the bias system as the core. Taking "Tunnel passing through thesliding zone, tunnel passing beneath landslide, tunnel passing through under the sliding bodyin parallel system and that in orthogonal system" as four representative patterns, the loadingmode of system is set up, with tunnel as mainsupporting body. Differential equations for thesimplified model have been established, and then displacement function is gained by theintroduction of boundary conditions. The theoretical solution of tunnel supporting loads anddeformation might be got by differential relationof displacement, rotation, bending momentand shear.(One of the innovations, shown in Chapter3&4)(3) During evaluation of the security of tunnel surrounding rock and stability oflandslide, the stress or deformation in the surrounding rock (slope) mihgt be neededconstantly to evaluate the state of security and stability. This study explores an unifiedassessment criteria of Point Safety Factor for the tunnel safety and landslide stability, wemay get hold of the spatial distribution regularity and develop processes of the evaluationindicator by tracking excavation process. It lays the theoretical foundation for securityevaluation and supporting structure optimization design of Tunnel-Landslide System.Numerical analysis and model test results show that the entire slope is overall stable in eachscheduled test conditions, but the partial destruction would be some impact of the project.Therefore it is more reasonable to use Point Safety Factor for evaluating the deformationmechanism and control technolog of Tunnel-Landslide System.(One of the innovations,shown in Chapter5&6)(4) As to Tunnel-landslide Parallel System, it can be conclued that the main aspects ofunderstanding as follows by using integrated application of numerical simulation,geomechanical model test and field monitoring.①On the basis of three-dimensionalnumerical calculation results, the Point Safety Factor of Stress State of tunnel surroundingrock and the Point Safety Factor on Interface of landslide have been defined. According todistribution of Point Safety Factor, the stability of the different parts of the rock and slopecan be determined, and then deformation mechanism of tunnel surrounding rock andlandslides would be analyzed;②The landslide steady state and geotechnical physicalproperties changes on account of tunnel excavation, and slope becomes more unstable owingto rainfall;③The necessary advanced distance between the two holes should be kept duringtunnel excavation, so that the scope of the construction disturbance can be effectivelyreduced;④Whlie passing though special geological area such as the sliding zone, it is bestto take pre-reinforcement measures, at least emergency response plans should do a good job.(5) Mechanism of pre-reinforcement is described and the deformation controltechnology based on the conception of pre-reinforcement is provided by taking Tunnel-Landslide Parallel System as main study object. Controlling or reducing thedeformation during excavation is the key to control progressive destruction of Tunnel-Landslide System. Therefore the use of pre-reinforcement techniques is required, includingpre-reinforcement engineering and scientific construction technology. By comprehensiveanalysis of the numerical analysis and geomechanical model test, it shows that as the impactof the excavation and rainfall on landslide acts on within a certain range to stability ofTunnel-Landslide System. The role of pre-reinforcement engineering is the most obvious dueto significantly improving and optimizing of the nature of original system, but it should benoted that the supporting structure to design in a suitable position. To some extent,excavation also determines the steady state of the system, thus the forward excavation isbetter than reverse excavation, and the forward excavation without pre-reinforcement is mostunfavorable to stability of Tunnel-Landslide System.(One of the innovations, shown inChapter6)...