| China is a country with a wide distribution of weak and hard strata,such as the Baihetan Hydropower Station and Three Gorges Hydropower Station located in the southwest of China,where weak and hard composite stratified geological structures are common near the dam area.The construction of large-scale hydropower projects in such geological environments with low stability makes geotechnical engineering problems more complex,which brings great challenges to the slope prevention and control work.In previous anchorage support designs,the traditional homogeneous rock assumptions were often used to simplify calculations,without considering the influence of the composite layered rock structure on the anchoring mechanism,and the dynamic changes in the anchorage affect of the slope under the influence of external factors.The geological background of the vicinity area of Baihetan Hydropower Station,a major project in China,was taken in this paper,and the slope project of the outlet field was used as the object of study.Based on the field investigation and previous studies,a shear-slip modified model considering the residual stress stage was constructed,and the mechanical properties of the anchorage interface were theoretically investigated.Using similar materials,multiple samples of composite layered anchored rock mass with joints were prepared,and the pull-out test under axial load was carried out.As the same time,PFC2D numerical simulation was used to analyze the stress and strain distribution at the anchorage interface,and the failure law of the anchored rock mass was discussed from macroscopic and microscopic perspectives,respectively.On this basis,in order to study the anchorage mechanism at the slope scale,a physical model test platform for composite layered rock slope was constructed.The influence of rock structure and mechanical properties,anchorage angle and loading mode on the anchoring mechanism were systematically studied.The slope deformation and evolution stages were divided according to its failure mode.Finally,a new Adam-DAG combined prediction model was proposed,which was used to predict the slope surface displacement of the outlet field slope.The anchoring effect of the slope of the outlet yard was analyzed,and the optimal anchoring angle and anchoring length were determined by optimizing the design.The above research shows that:（1）Based on the existing shear-slip model,a modified model considering the residual stress state was constructed,and the stress distribution of the anchoring interface was theoretically analyzed.The shear stress value of the anchoring interface calculated by the shear-slip modified model,it drops after reaching the extreme value and then tends to stabilize.Compared with the traditional mechanical model,the correction model can more accurately reflect the nonlinear change trend of the bolt during the whole force process.By changing the rock mass structure,anchoring parameters and pulling force for theoretical calculation,it was concluded that the stress"abrupt"phenomenon will occur at the position of the weak interlayer,and the axial force increases with the increase of the pulling force,and the diameter of the anchor solid was proportional to the axial force and inversely proportional to the shear stress.（2）Specimens of"hard-weak-hard"composite layered rock mass with joints were prepared using similar materials and subjected to axial load indoor pull-out tests.The anchorage specimens of four rock structures and three joint plane dips were tested,which to visualize the stress and strain distribution characteristics at the anchorage interface.According to the load-displacement curve characteristics of the specimen,the four stress stages experienced by the anchoring interface were divided,namely,the quasi-linear increase stage,the nonlinear increase stage,the sharply decreasing stage and the residual stress stage.The shear stress value and distribution morphology of the anchoring interface were directly related to hardness ratio of weak and hard rock,the smaller the hardness ratio,the smaller the peak shear stress,and the larger the distribution range.The 70%mudstone interlayer thickness and the 60°dip of joint plane were the critical point of the ultimate pulling force,beyond which the ultimate pull-out force will no longer change.（3）The PFC2D numerical simulation technique was used to apply both continuous and cyclic loads to the anchored specimens,and the influence of the loading method on the anchorage mechanism of the composite laminated rock was investigated from microscopic perspective.The cyclic load acts as a"time accelerator"for the rock mass anchoring system,which consumes more energy than the continuous load.The vertical displacement field was symmetrically distributed in a"U"shape on both sides of the rod body,and the bonded fault zone forms a rectangular fault zone distributed around the anchor solid and at the interface with the bolt.In addition,mudstone was more affected by cyclic load than sandstone,and when the number of cycles reaches 50 times,the deformation feature of"uplift"on both sides of the mudstone was the first to occur.（4）Based on similar theory,rock mechanics and similar materials research,a physical model test platform for composite layered rock slopes was constructed.Physical model tests were conducted to analyse the effects of anchoring inclinationθ（20°,25°,30°）,mudstone thickness h（0 mm,15 mm,30 mm）,and loading mode（continuous loading,cyclic loading）on the stress and strain at the anchorage interface.The anchor force and slope deformation evolution characteristics were also analyzed.Based on the stress characteristics of the bolt,25°was determined as the optimal anchoring angle among the three anchor angles.The influence of mudstone thickness on the slope failure mode was analyzed according to the slope deformation characteristics,and four deformation evolution stages of the slope were divided,which were the micro-crack,macro-crack,near-slip and slip damage stages.（5）Taking the slope of the right bank of Baihetan Hydropower Station as the engineering case,the Adam-DAG combined prediction model was used to accurately predict the slope surface shift change pattern of the slope from June 28,2019 to December25,2021.According to the geometric similarity ratio,the slope surface deformation of the actual outlet field slope at each deformation evolution stage was calculated.Based on the unified strength theory,the original anchoring support design of the outbound slope was optimized,and the optimal anchoring angle of the slope was determined to be 29°,and the corresponding optimal anchoring length was 26.6 m.The study of this thesis has the following innovations:（1）The anchorage mechanism of composite layered rock masses with joints was revealed.Through indoor pull-out tests and numerical simulations,the stress characteristics of the rock anchorage structure system of composite layered rock masses with joints were analyzed from macroscopic and fine view points,and the trend of the anchorage interface stresses along the anchor rod axial direction was explored.（2）The deformation evolution stages of composite layered rock slope with anchor were distinguished.Taking the slope of the right bank outlet field of Baihetan Hydropower Station as an engineering case,a similar theory of composite layered rock slope was established,building a physical model test platform composed of loading system,monitoring system and data acquisition system.The anchoring mechanism and deformation evolution characteristics of the composite layered rock slope with anchors were revealed.（3）The deformation prediction model of the composite layered rock slope with anchorage structure was constructed.A more accurate Adam-DAG slope displacement prediction model was proposed from the characteristics of the actual slope deformation data.The prediction model was used to evaluate the effect of slope anchoring and its stability.The original slope support scheme was optimized and designed to determine the optimum anchorage angle and anchorage length for the slope. |
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