In this paper, a three dimensional finite element analysis of Jintan arch dam abutments using fracture damage model is described. A damage mechanics model which involves in statistical parameters of rock strength is proposed. For jointed rock mass, the damage principles and tensors, and the damage propagation function are discussed. They are based on the triaxial test results of rockmass. In this paper, the numerical analysis results show that the damage model agrees very well with the phenomena of physical model.
Dans ce document, a ete faite une analyse d'element limite de trois dimensions du fondement de construction de roche faisant appel au modele de 1'endommagement à fracture, analyse appliquee au fondement du bar rage-voûte de Jinshuitan. Un modèle de la mecanique de 1'endimmagement est propose, modèle qui concerne les paramètres statistiques de la puissance de la roche. Le document aborde egalement la methode repetitive moderne quant à 1'èspace de 1'usage excessif. Une analyse du fondement du barrage-voûte de Jinshuitan a ete utilisee dans Ie programme mentionne ci-dessus.
In der vorliegenden Arbeit wird eine dreidimensionale finite element Analyse fuer die seitlichen Gesteinsauflager mittels dem Bruchmodell Vorgestellt, das fuer Jinshitan Bogenstaumauer angewandet wird. Ein Bruchmechanismusmodell einschliesslich der statistischen Parameter der Gesteinfestigkeit wird entwickelt.
Stability analysis of dam abutments is of paramount importance in dam design. In China, jointed rocks with deficient geological conditions are often encountered in dam sites. The problems to be studied in the stability analysis of dam abutments are mainly involved in mechanical behavior and strength of jointed rock mass. In this paper, a damage mechanics model is proposed. It treats the rock mass as a macroscopically nonhomogeneous one and leads to the possibility of globally modelling the nucleation and the propagation of these discontinuities, including their effects on the stress-strain relations. In this paper, presented there are the general theory and applications of damage model to the dam abutments. The generalization for tridimensional conditions which takes the anisotropic damage effects into consideration and some new proposals are made for evaluating the deterioration of rock masses.
It is obvious that for rockmass, its geological formations form the main factors in mechanical characteristics. Generally, the rock mass behaves as mechanically anisotropic owing to the existence of a few sets of discontinuties which have their own specific orientations. From the results of rock specimen tests, the failure configurations of the specimens have shown that the failure surfaces are dependent on the pre-existing discontinuities in the rockmass. The fracture cracks would develop along some joints, bedding planes, fissures or faults under some loading conditions. In Fig. 1, the fracture tests of multijoint gypsum specimens are shown. The cracks in these specimens, of which the fracture intensity factor ratios are greater than 5.0, initiated and propagated along the pre-existing joints apparently. Here the ratio is de fined between the intact rock and the weak joint surface. In Jintan projects, three sets of joints are assumed in abutment rockmasses, of which the fracture toughness KlC and KIIC are much smaller along the joint orientations than those deviate from them. For example, from tests in laboratory, along joints, Ku=15TM-3/2 Kbl=5.4TM-3/2, whereas in intact rock K,,=160TM-3/2, Kbl=98Tm -3/2. This implies that the cracks are apt to extend along joint orientations. From the above experiment results, some important conclusions could be drawn as follows: -In rockmass, several pre-existing discontinuities could be found, which is refered to primary damage. -These discontinuities form the weak links along which the fracture toughness is much smaller than those in intact rock. Hence, the damage effects of rock should be considered along these surfaces. In rock masses, their damage propagations only involve in these weak links, i.e., the extension of weak joints. If a damage tensor is specified for a rock mass, it implies that the damage configuration is prescribed. A damage model may be defined to describe this damage phenomenon. Discontinuities in the rock mass such as joints, bedding planes flaws of certain-sized discontinuities in rock mass are assumed as a damage to intact' rock. The damage effect may be considered as an deduction of area of rock mass or a deduction of modulus of elasticity.
In case of anisotropic development of deterioration, the damage parameter is defined with a scalar D bearing upon the area of cross section. The cross sectional area of the rock mass is expressed as follows: S = So (1-D) Where D = 0 corresponds to intact rock D = 1 corresponds to collapse S and So represent the damaged and 0 riginal area respectively. As shown Fig.2, the tetrahydron has an surface area S.
