Advances in seismic design of earth-rockfill dams and foundations in China and revision of code based on lessons from Wenchuan Earthquake

The advances in seismic design of earth-rockfill dams and foundations and the revision of code for seismic design of hydraulic structures in China (SL203-97/DL5073-2000) are presented based on research results and lessons from Wenchuan Earthquake disasters. The main revisions and advances focus on four aspects: (1) Seismic fortification criterion and its basic principles, in which the seismic design criterion, design parameters of ground motions and method for determining seismic waves are revised. For especially important projects, the seismic safety margins of the structures under MCE shall be assessed in order to prevent any collapse resulting in reservoir water discharging catastrophically. The near-field effect, hanging wall effect and unsteadiness of the frequency spectrum shall be considered when determining the design earthquake response spectrum. Earthquake prevention and disaster mitigation emergency contingency plans are required for the structures with engineering seismic fortification category of Class A. The seismic response spectrum for earth-rockfill dams is stipulated, and the value of the maximum acceleration response spectrum ( ) is taken as 1.60, whose corresponding damping ratio is 20%. (2) Site and foundation, in which the criterion for classification of site soils and site itself are revised. Site soils are classified into 5 types instead of 4 types in the old code according to the shear wave velocity of soil layer, and are classified in more detail than before according to the type of site soil and overburden thickness. For the liquefaction potential evaluation method, the formula for determining the critical standard penetration test N-values (SPT N-values) and the formula for correcting the influence of the effective overburden stress on SPT N-values are revised. (3) Seismic calculation and safety evaluation of earth-rockfill dams, in which contents for seismic calculation are supplemented. Seismic calculation should include seismic stability calculation, permanent deformation calculation, safety evaluation of the anti-seepage body and liquefaction potential evaluation. The scope for adopting the dynamic analysis method for the analysis of seismic effect and safety evaluation is supplemented. For the earth-rockfill dams with the following conditions: a) higher than 150 m and with a design intensity of VII; b) higher than 70 m and with a design intensity of Ⅷ or Ⅸ; and c) presence of liquefiable soils in the foundation based on finite element method is necessary for dynamic analysis to comprehensively evaluate its seismic stability. For the earth-rockfill dams with deposits thicker than 40 m, finite element dynamic analysis is recommended, and the principles for dynamic analysis of earth-rockfill dams are provided, including selection of constitutive model and determination of model parameters, calculation of the permanent deformation and requirement for stability analysis. The basic principles for evaluating seismic safety of earth-rockfill dams according to the dynamic results are provided. (4) Earthquake resistant measures for earth-rockfill dams and foundations, in which earthquake resistant measures for CFRD are proposed according to the experience of the design, construction and lessons from earthquake damages of Zipingpu Dam in Wenchuan Earthquake, including seismic deformation control, protection of dam crest and nearby slope, anti-squeezing of vertical joints, anti-dislocation of horizontal construction joints and detailed structure design of joints.