Study On Seismic Safety Of High Rockfill Dam With Earth Core On The Thick Overburden Layer

With the progress of the hydropower resources development in western China, there will appear a batch of200m and even300m high earth-rockfill dams, which will be located in the area of high seismic intensity, thick overburden and even adverse geological conditions. So far, however, the highest dam on thick overburden in the world is the Pubugou dam with only186meter dam height. For building the high dam more than200m on the thick overburden layer, both the seepage control design for dam and foundation and the anti-seismic measures have no experience to draw on, which bring worldwide challenges to the design, construction and operation. The seismic safety of the high earth-rockfill dams more than200m on the thick overburden foundation was studied; the main contents are as follows:1. The material parameters of the earth-rockfill dams are strongly dependent on confining pressure. The widely used Hardin-Drnevich model can reflect the effect of confining pressure partly. A new improved constitutive model that could accurately consider the confining pressure was put forward based on the traditional Hardin-Drnevich model in this paper. The new model can fit the experimental data better, response the dynamic properties of the material accurately. Each parameter in the new constitutive model still retains their physical meaning and easy to be defined. The model would not reduce the computational efficiency though the number of material parameters in the model is big. The relevant calculated procedure with the new model was programmed based on the program of ADINA, which are applied to the calculation and analysis of seismic dynamic response of240m high Cnanghe dam on the thick overburden foundation. The conclusion can be got that the result was conservative without considering the effect of confining pressure when analyzing high rockfill dam, which will have a certain influence on the economics of engineering.2. Seepage prevention system is the most important structure in high rockfill dam with earth core. The joint of the dam seepage structure and foundation seepage control structure is the weakest part in the seismic safety of dams. Taking high core rockfill Changhe dam as background, the seismic safety of seepage prevention system of high rockfill dam on thick overburden layer was studied using the improved Hardin-Drnevich model considering confining pressure and the advanced sub-model technology. The dynamic responses on the core wall of high rockfill dam and the cutoff wall and the corridor on thick overburden layer were analyzed. Used nonlinear constructive model of concrete cracking, the nonlinear changes in the cracks development process of the corridor in process of reservoir impounding and dam construction were analyzed. At last, seismic safety of the dam seepage core wall, the dam foundation cutoff wall, the joint of core wall and cutoff wall was evaluated. The feature of dynamic response on the high core rockfill dam with thick overburden was summarized. Combined with engineering experience, safety measures of seepage control system were put forward.3. The calculation and analysis were carried out on the aspects of reinforcement mechanisms, effects and application characteristics for anti-seismic measures of geogrid and concrete beam grillage used in the crest of high earth-rockfill dam. But some problems exist in the anti-seismic measures, so a new kind of rockfill dam seismic strengthening measure has been put forward:Hardfill seismic strengthening measure. The reinforcement effect and the possibility of implementing of Hardfill seismic strengthening measure were discussed based on the Changheba project. The results show that the Hardfill seismic strengthening measure can enhance the overall stability, inhibit the permanent deformation and improve the dynamic strength safety coefficient, bring no adverse effect to the operation of the dam. The new measure has the advantages such as, the simple construction process, low cost as well as no interference with construction schedule of the dam and has a good application prospect.4. Some of the traditional classical vibration pore pressure models were obtained based on the testing of sand, which cannot be directly applied to seismic pore pressure computation of the cohesive soil and gravel of high earth-rockfill dam. A new vibration pore pressure model for cohesive soil and gravel was put forward in this paper according to the results of saturated undrained dynamic triaxial test. The new vibration pore pressure model considered the influence of dynamic shear stress ratio and can fit the experimental data better, response the dynamic strength properties of the material more accurately. The model parameters were determined conveniently and the model would not reduce the computational efficiency though the number of material parameters in the model is added. Based on the program of ADINA, the effective stress algorithm program with the new vibration pore pressure model was implemented. The new model was used in the calculation and analysis of Changheba dam. The pattern of the accumulation process of excess pore pressure during earthquake and the dissipation as well as diffusion of excess pore pressure after earthquake were understanded through the calculation and analysis.