| High rockfill dams are extensively built on deep overburden layer in China.The technology of building earth and rockfill dams has been mature after decades of development.However,it must be mentioned that when it comes to building high rockfill dams in deep alluvial overburdens,we are still in the primary stage with little engineering experiences.Consequently,this bring us many technical problems,especially for the safety evaluation of the anti-seepage systems of engineers.The anti-seepage system of high core rockfill dams on deep overburden generally includes core,cutoff wall and the connecting gallery between them.Because the stiffness of the core and the cutoff wall is quite different,uneven deformation and stress concentration may be observed in the gallery.Therefore,the gallery is the weak part of the anti-seepage system.In China,some galleries,such as the galleries in Pubugou,Maoergai and Qiaoqi dams,have been troubled by water leakage due to the gallery damage.In addition,the core and cutoff wall are also crucial parts for the dam body and foundation overburden.Once the damage occurs,the safety of the whole project will be threatened.Some existing gallery analyses always has certain limitations.Only focusing on a specific project or a single effecting factor,general laws of stress behavior of the gallery is difficult to learn.At the same time,there is quite few knowledge about the gallery cracking behavior.The cutoff wall in the deep overburden is thin.There is a big deformation difference between the cutoff wall and the overburden layer,as the overburden layer has a significantly small stiffness than the cutoff wall.The cutoff wall is in complex 3 dimensional stress condition,and the deformation and stress characteristics need to be analyzed in detail.When asphalt core is used as an impervious water barrier in rockfill dams,there is a strong interaction at the interface between the core and the adjacent transition zones,as the core has a significantly small stiffness than the neighboring transition layer.It is important to understand the behavior of the interface,since it plays a significant role in the asphalt core response.In conventional FEM softwares,highly nonlinear contact mechanics methods are applied to treat the interface.Numerical difficulties always exists in computational procedure when using these methods,and the calculation may be not convergent.In view of the above problems,the main contents of this paper are as follows:1.The comprehensive method for gallery stress and deformation calculation is established.The gallery structure is complex,and the stress behavior is affected by many factors.The detailed simulation meshing,the creep of concrete,the contact between the gallery and surrounding soils,and the yield condition of bedrock are all considered comprehensively,and then the gallery calculation method considering multiple factors is proposed.The general law and mechanism of stress distribution in gallery are revealed.The calculated stress distribution of the gallery is consistent with the stress distribution reflected by the monitoring data.This prove that the method can reasonably reflect the stress and deformation characteristics of the gallery.2.An incremental nonlinear elastic concrete model and submodel method are used to simulate and analyze the whole gallery cracking process of elastic-elastoplastic-crackingsteel yield-structura failure.The cracking range,yield range,cracking development law and cracking direction of gallery are analyzed,and the cracking mechanism is clarified.The calculated reinforcement stress and structural joint deformation are compared with the actual monitoring data,and the reasonability of this method is verified.The results show that the non-uniform settlements result in the microcracks firstly appear near the bedrock surface,approximately at an angle of 45 ° with the bedrock surface.The angle indicats that the cracks are mainly caused by shear stress.With the dam construction,large transverse compressive stresses are appeared on the upstream surface,which causes peeling cracks.After the impoundment,the circumferential cracks on the downstream surface develop from the two banks to the riverbed section,and the crack direction changes from 45 ° angle with the bedrock to the vertical direction.Generally speaking,longitudinal cracks may appear in the inner side of the top arch and the bottom plate of the whole gallery.Circumferential cracks may appear on the downstream surface and bottom plate near the 1/4 span of the gallery.The entire gallery section near the bedrock is in danger of cracks.3.It is difficult to predict the behavior of the cutoff wall in complex 3 dimensional stress condition.The deformation and stress characteristics of the cutoff wall are analyzed,and the possible position and mechanism of tensile stress are described.A bunch of finite element analysis is carried out to study the influence mechanism of valley shape on the deformation and stress distribution of the cutoff wall.The results show that the slope of bedrock in the overburden,the width of river valley and the asymmetry of the left and right banks of bedrock have great influence on the deformation and stress characteristics of the cutoff wall.4.Under the dynamic condition,the seepage control system is usually under more complex stress states.Based on the general finite element software platform,the HardinDrnevich model is integrated to analyze the dynamic response of Huangjinping rockfill dam,which was a dam built on a thick alluviaum layer more than 100 m.The dynamic response characteristics of the gallery and cutoff wall are explored,and the dynamic safety of the seepage control system is evaluated.Under dynamic condition,the area of tensile stress caused by bending deformation in the downstream surface of the gallery has expanded,and the area of tensile stress in the cutoff wall has also expanded.5.Based on general finite element software platform,a three-dimensional contact thinlayer element is developed to simulate the interaction between asphalt core and adjacent transition zones,and its validity is verified.In the thin-layer element,hyperbolic model is applied.On this basis,the interaction at the interface between the core and the adjacent transition zones in Huangjinping dam is analyzed by finite element method and monitoring data.The comparison between the calculation results and the actual observation data proves that the developed thin-layer element method can well simulate the interaction between the asphalt core and the adjacent transition zones,and the real behavior characteristics at the surface are obtained.The calculation results are used to evaluate the safety of the asphalt core.At the same time,the dynamic response characteristics of the core wall is analyzed. |
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