Statistical Analysis And 3D Elasto-plastic Numerical Simulation Of Embankment Dam Damages In Wenchuan Earthquake

Seismic damages of embankment dams in 12 May, 2008 Whenchuan earthquake had characteristics of large quantity, wide spreading, severe damage and diversified damage type. After this earthquake, seismic safeties of embankment dams were receiving increased concern in China. 3D elasto-plastic seismic response analysis of embankment dam had always been one of the focuses and frontier topics in geotechnical earthquake engineering. The aims of this study were to investigate and analyze the typical earthquake damage phenomena and failure characteristics of embankment dams in Whenchuan earthquake, establish the calculation model of a representative severely damaged dam and perform the 3D elasto-plastic seismic response analysis of this selected embankment dam. Therefore, this thesis studied the following five key scientific issues.(1) Investigation and analysis of seismic damages of embankment dams in Whenchuan earthquakeBased on the field survey, the typical earthquake damage phenomena and failure characteristics of embankment dams in Whenchuan earthquake were summarized, and the influence factors for seismic disasters of embankment dams were analyzed.Numerous embankment dams has suffered serious damage during this earthquake, and even broken in some serious case. More than 90% of the 379 serious damage dams were embankment dams, and the 69 failure dams were all embankment dams.The typical damages included cracks, slips of dam slopes, leakages of dam bodies and damages or destructions of release works and other accessory facilities. Most of the failure embankment dams were located at the southeast of seismogenic fault, which was a long and narrow transition zone from mountain to basin. Local uneven complex topography and site effect could affect the spatial distribution of ground motions, and then affected the seismic response of embankment dam.(2) Improvement and application of elasto-plastic constitutive model for soilBased on the CM model, a modified elastoplastic model with rotation hardening which could systematically describe the monotonic and cyclic mechanical behaviors of soils combining the subloading, normal and superloading yield surfaces, was employed in the static and seismic stability analysis of embankment dam. By using the degree of saturation as independent state variable, this model could unified describe the behavior of unsaturated soil and saturated soil. By the transform stress method, this model could uniquely describe the overall mechanical properties of soils under general stress states,without changing the values of parameters. The model were suitable for three-dimensional static- dynamic analysis for complex embankment dam and foundation dynamic interaction system. Thus, this laid a good theoretical foundation for the simulation of embankment dam disaster process in earthquake.(3) Secondary development of numerical calculation program DBLEAVESThe secondary development of a finite element-finite difference coupled numerical solution program DBLEAVES which can be used for large deformation analysis was conducted. The improved elasto-plastic constitutive model was introduced into the soil-water-air three-phase coupled field theory, and the artificial boundary which was composed of bottom boundary and lateral boundary was also introduced into the DBLEAVES. Thus, the DBLEAVES can more suitable for 3D elasto-plastic seismic response analysis of embankment dam.(4) Establishment of the 3D numerical computation model of a typical embankment damA complex 3D numerical model for a typical embankment dam which was damaged seriously in the Wenchuan earthquake along with its surrounding sites was developed. The operating status before earthquake, damage state after earthquake and damage generation process of a typical embankment dam was immediately investigated after the 2008 Ms 8.0 Wenchuan earthquake. The geological, topographic and hydrological data and material and status parameters of dam and its local site were also obtained through the field investigation and laboratory tests, respectively. Based on the above data, a 3D numerical model of embankment dam along with its surrounding local site which is closed to the real situation was established(5) 3D elasto-plastic seismic response analysis of a typical embankment damThis simulation reappeared the disaster process of typical embankment dam in Wenchuan earthquake, and gave the spatial and temporal distribution of PGA and residual deformation. The results agreed well with the phenomena of field survey, which indicated that the proposed method was sufficient for simulating seismic disaster process of embankment dam. The present work shown that the local site effect has a significant influence on the seismic response of earth dam. The ground motion intensity would increase in the foundation below the earth dam when the dynamic interaction was considered. However, the influence of dam existence on dynamic response of site which away from the dam was lightly. Local site and topographic effects controlled the damage level and pattern on embankment dam. The ground motion was most easily to focus at middle of dam crest where the wave reached finally. Here, the ground motion magnified about three times compared to that on bedrock, thus leaded to serious collapse at the middle of the dam crest. Furthermore, the influence of characteristics of input ground motion on the elasto-plastic seismic response analysis of embankment dam was studied.