The Regional Environment Of Forming Microstructure Of Loess And Mechanisms Of Its Seismic Subsidence

Loess with more holes and weak cementation has the unique micro-structurecharacteristics, which is the main internal factors to induce sudden subsidence underadditional seismic loading. Loess in different regions has the different micro-structure, andresults in different seismic subsidence. In this paper, by many regions and kinds of formingenvironment in the Loess Plateau to study the micro-structure, through the high magnifymultiples of scanning electron microscopy image analysis and spectrum analysis, numericalsimulation of seismic subsidence test theory and related analysis to research questions asbelow: the different environment of loess micro-structural features; loess seismic subsidencemechanism of micro-structure and dynamic constitutive relation; loess ground motioncharacteristics of the venue; loess seismic subsidence evaluation method of micro-structureand subsidence of loess foundation by acid improved technologies. The thesis carried out thefollowing three structural characteristics of loess research: the diversity character, theparticles character, and the three-phase quality. And in the following progress has been madeof innovation:1) The paper studied the loess micro-structure and its characteristics of different climateenvironment and forming ages in China's Loess Plateau. It analyzed comprehensivly theformation of the regional loess environment characterized on regional climate, from theformation of loess both the breadth and depth to investigation. After research on the actualareas loess micro-structures, the paper accomplished the analysis and summary the loessphotographs characteristics of micro-structure on its regional differences, as well as differentforming ages of loess. It tested and analyzed in detail the differences physical and mechanicalparameters with its different micro-structure froming. Then it research on the micro-structuralfeatures changed by different regions and differences forming climate. It also respectivelyinterpreted and judged that those loess micro-structure characteristics could resulted in whatkinds of seismic disasters on preliminariy.2) Based on the pore size and the stress parameters and three-phase characteristics ofloess, the paper set up seismic subsidence coefficient formula to calculate residual strain andthe stress- strain constitutive model. The formula for calculating residual strain is proved to be closed to most regions loess by test result. Further derived the dynamic stress-residualstrain general process formula, derived from the large deformation process, such as thehardening phase (elastic stage, plastic stage of filling, shear and compaction) and thesoftening phase (broken softening stage, the yield rheological phase, strain-hardening stage),which is proved to apply for different loess micro-structure. In addition, the paper alsoobtained and verified the loess dynamic stress - strain of one-dimensional constitutiveformular.3) It bring forward the loess particle damping theory, and found the damping of the loessmodel and one-dimensional nonlinear time-history ground motion fluctuations equation.Compared with the loess Site with strong motion records of the actual data validation, itprove that the fluctuations of time-space equation is consistent with the simulation results offrequency spectrum characteristics of the actual site, and can respond to the different loessmicrostructure characteristics of nonlinear dynamics.4) The paper also put forward the micro-theory methods and evaluation indicators usedto determine the loess seismic subsidence damage. Through micro-structure characteristics todetermine the loess site damage likely to be strong or weak; in accordance with the indicatorsof energy spectrum elements to determine the formation of loess and climatic conditions;Proposed damage indicator parameters: Ca / Mg ratio, Ca / Fe ratio, K/Al ratio, Si/Al ratio.,etc chemical indicators; gravel particle size; gravel sedimentation rate; size distributionskewness; impracticable holes; and loess depth., etc.5) The paper put forward the acidic chemical treatment method to defend the seismicsubsidence of loess foundation. It researched how to use micro-structure and energy spectrumanalysis method to improve the structural strength of loess. The added filling is calciummaterial, boron compound and phosphoric acid. After compared with different test projectby seismic subsidence test and its loess microstructure, the paper proposed a better resolvedproject to elimination loess foundation subsidence. Tests showed that this approach has theeconomical benefit and environmental protected excellence.