Research Of Unsteady Seepage-Stress Coupling On High Concrete Face Sand-gravel Dam

The concrete faced rockfill dam has the advantages of safety,economy and adaptability.It has great competitive and development prospects.At present,sand gravel is a kind of natural materials which are widely distributed in the river and floodplain.It has the advantages of low cost,simple construction,and easy crushing,etc.Which is often chosen as the material of the CFRD compared with the blasting rockfill material.There are more than 100 meters of concrete faced rockfill dam in the northwest area of China,some seismic design intensity is greater than or equal to 8 degrees.The natural sandy gravel has the characteristics of poor dispersion of gradation,discontinuity and easy separation of construction,and it pose a threat to security if the dam’s anti-seepage body is destroyed under strong earthquake.At present,scholars at home and abroad are mostly studying the failure of concrete face rockfill dam from the fluid and solid two different angles,and assess the safety of the dam just condidering the damage of anti-seepage body and the seepage state after earthquake.However,once the anti-seepage body crack after earthquake,the reservoir water may leakage,causing seepage-gravel-face slab interaction.There may be a worse impact on the safety of the dam,which in previous studies are not reported.Under the action of unsteady seepage field,the stress and deformation of the dam will inevitably change.The effect of this unsteady seepage-stress coupling on dam and face slab should be studied deeply.Therefore,it has important theoretical and engineering significance to evaluate the dam safety basing on the calculation method of unsteady seepage-stress coupling.In this paper,the plastic damage model of concrete and the generalized plastic model of rockfill are adopted to to analyze the stress and deformation of the dam under the unsteady seepage.The main work of this paper:(1)Based on the plastic damage model of concrete and the generalized plastic model of rockfill,a distinctive coupled unsteady seepage and stress method is established.Write program by self to form a complete set with geotechnical engineering software system-GeoStudio.Map the pore water pressure calculated by Seep/w to the solid mesh.Sort out the generalized plasticity model parameters basing on the results of static and dynamic three axis test of a gravel dam which provide the basis for static and dynamic stress analysis of the dam.(2)The method established in this paper is adopted to conduct two dimension unsteady seepage-stress coupling finite element analysis,finite element stability analysis under the extreme conditions and the normal conditions.The rationality of the calculation method,the reliability of the calculation program and calculation parameters is verified by this means.The results show: the water of the reservoir extends along the interface between coarse and fine particles and spreads around under the action of gravity,reaches a steady state finally.It is not safe for the stability of downstream dam slope when dam material is evidently stratified and poor drainage under the extreme conditions.The seepage flow of the dam is controlled by the cushion layer and most of the head losses in it.The tensile stress is small at the local failure of the face slab,which will not cause the damage further,and the water depth has little effect on it.(3)The two dimension static and dynamic finite element analysis is carried out for the 200 m high weak permeability dam.According to the damage distribution of the face slab,the change of the permeability coefficient is determined.Considering the failure of cushion layer and the evidently stratified of dam material,the unsteady seepage of the dam is calculated,and the variation of stress and deformation of dam under the action of unsteady seepage is analyzed.The results show that: the deformation of the dam and face slab rebound;The 3rd principal stress(compressive stress)of the dam and the face slab is significantly reduced.The face slab occurs tensile stress locally,the damage value of is larger under the unsteady seepage after earthquake;It is necessary to consider not only the damage state of the slab after earthquake,but also the influence of unsteady seepage development on the stress field when evaluating the maximum aseismic capability of dam.