Study On The Composite Element Method For Anchorage Rock Masses

With the development of infrastructure construction in the south-west of china, high and steep rock slope, dam foundation and other complex problems usually become the important issues in the construction, the reinforcement quality is directly related to project quality, time limit for a project and benefit, even with respect to the safety of engineering. Rock reinforcement measures such as pre-stressed anchor cable and bolt are adopted. Analysis of anchorage theory of rock and the design method are lagging behind the engineering practice from the application situation. Therefore, researching on analysis method of rock mass anchorage technique has a very important theoretical and practical significance for the anchorage optimization and design guidance.The composite element method is a new numerical analysis method in recent years, which is proposed by Wuhan University professor Chen Shenghong. Researching on the jointed rock masses reinforced by bolts, seepage drainage pipe, water cooling pipes of mass concrete temperature control has made gratifying achievements, but the application in large scale and complex engineering still has a lot of work to improve. Therefore, this paper will take the rock anchorage measures as the study object and carry out research on the composite element method in order to explore a reliable, efficient, scientific approach for analysis of rock mass anchorage measures. The main research work and achievements of this paper are as follows:(1) Pre-stressed anchor cable has three parts which are inner anchor section, free segment and the anchor head, the inner segment of pre-stressed anchor cable is contained in the element and considered as a composite element, free section and anchor head draw are considered as finite element by the idea of implicit bolt element, the related basic assumptions and each sub element of the coordinate system are established. According to the elastic-viscoplastic theory, the constitutive equation of each sub element is established, based on the principle of virtual work, algorithm of the inner anchor section composite element, the free section and anchor head finite element is derived. The results of examples show that results of this algorithm are in good agreement with the traditional analysis results.(2) On the basis of contrastive analyzing the features and consolidation mechanism of the ordinary mortar anchor, hollow bolt and grouting hollow, taking the hollow grouting anchor as the main body, according to the deformation compatibility principle, the displacement-strain equations in composite element are derived, based on the principle of virtual work, balance equations of nodal displacement-load is derived, composite element generalized algorithm of bolt is established. When this generalized algorithm were degraded, it can analysis other2types of bolt, the results of examples show that results of this algorithm are in good agreement with the traditional analysis results.(3) Based on some key technical problems such as pre-stressed anchor cable force influence factors, mechanism, shear stress distribution, the steel strand, mortar, interface mechanics, material damage process, damage mechanics and viscoelastic plastic potential theory, taking the equivalent visco-plastic accumulated deviation strain as sub element mechanics parameters, making an appropriate selection of damage variable, the relation between the pre-stressed anchor evolution equation of damage and injury and composite element method is integrated, a composite element damage algorithm of pre-stressed anchor is established; The results of examples show that it can well reflect the transfer and stress distribution of the anchorage segment load and consistent with existing research results.(4) According to the principle of the dynamics analysis method and composite element method, the derivate process of anchoring quality of composite element method matrix, stiffness matrix and damping matrix is introduced, the composite element dynamics method control equation and solving scheme analysis of jointed rock mass reinforced by bolt are established; Some key technical problems in dynamic analysis of composite element method under the action of earthquake are discussed. The viscous elastic artificial boundary, the realization of artificial seismic wave generation, acceleration integral method and seismic displacement baseline drift are applied to the composite element method analysis; Finally, a preliminary study and analysis are carried out through some simple examples.(5) Based on the research results of the second and fifth chapters, the finite-composite element coupling calculation program is developed, it has been successfully applied in Kala hydropower station high rock slope stability analysis and reinforcement effect evaluation,the research results have been adopted by design department.