Breakage Mechanism With Lateral Unloading Study Of Red Clay And Its Application In Engineering

With the rapid development of economy,society and accelerating urbanization process in China,the development and utilization of underground space have become increasingly demanding for the social development.Since red clay is a special soil widespread,which engineering and mechanical properties are specific and special,therefore,the deep excavation and high slope engineering of red clay are not only the important part of urban construction in China,but also become the focus and difficulty of engineering construction.Excavation and supportion of deep foundation excavation and high slope engineering,and development of deep foundation pit of red clay have become the main content of various construction projects of the red clay regions.In urban construction,scientific construction and rational utilization of deep foundation pit of high-rise building is one of the most common forms of urban underground space development.Red clay is one of the special soils and it distributed more widely.To meet the engineering requirements of underground space development for urban and treatment of high side slope for red clay in red clay areas,a more in-depth study has been accomplished by the ways of theoretical analysis,chemical analysis,methods microscopic structures observation,experiment and numerical simulation analysis on the red clay for the breakage mechanism at the lateral unloading conditions and the stability problems of deep foundation pit as the research background for the stability and the excavation of the foundation pit for a high building in Guiyang.The main research content and conclusions are as following:(1)The geology distribution of red clay,geological origin and geological environment were analyzed by geological environment analysis,and test analysis had been accomplished using spectrum analysis,SEM scanning and other modern analytical techniques for the chemical composition and properties of microscopic structure for red clay at different locations in the same cross-sectional,the chemical composition of red clay ratio was obtained,and proposed the microscopic grain structure model of red clay,and discussed the mechanical effect of the chemical composition of red clay and microstructure.(2)True triaxial tests were accomplished for the red clay at different locations on the same cross-section simulated the lateral stress path under unloading real load conditions by using the true triaxial apparatus,and compared with the test results of the true triaxial loading conditions.The changes in laws were obtained that the strength of the red clay at the same confining pressure changes with the main stress ratio variation b values have increased after the first decrease compression,and the soil at lateral unloading damaged easier than that at vertical pressure in the event of structure breakage.(3)By using the thinking ways combining of the property of macroscopic deformation and microstructure damage,analytical methods were proposed for the structural deformation breakage on the lateral unloading of red clay,and the soil deformation and destruction of the theoretical model were analyzed,and then two structural damage model of different sections of the brittle shear pressure and plastic deformation of tension and shear slip were proposed for different location of the cross-section of red clay under lateral unloading.The mechanics mechanism were proposed for the microscopic deformation and break of the excavation damaged for red clay.(4)The image of microscopic structures under different loading conditions for red clay were processed by using the special digital image processing system,the test data were computed and processed by regression analysis using SPSS software.It was studied for the quantitative relationship between microscopic structural parameters and the stress,deformation of the red clay and determined the key micro structural parameters for the macroscopic deformation,and then it was analzed the intrinsic relationship of macroscopic deformation and break and micro structural parameters for red clay.(5)According to the true triaxial test results,the method studied for the stability analysis of deep foundation pit under lateral unloading conditions of the red clay,the method was proposed for the reduction of dynamic double strength parameters,then the parameters of the constitutive model were modified and M-C constitutive model was established which based on lateral unloading red clay,then the calculation method proposed for the deep Foundation stability safety factor of red clay by using the major geotechnical engineering calculation software FLAC3 D.(6)It was compared for the adaptability of the different yield criteria,and analyzed the analysis methods for constitutive model,then discussed the methods of the establishment of the constitutive model based on the analysis of structural damage mechanics mechanism for red clay and defines the damage parameter.The structural strength parameters indicators on red clay were proposed and derived structural damage constitutive equation for red clay,and then proposed the ideas and methods to verify elasto-plastic damage constitutive model for red clay,and had the preliminary validation.(7)The numerical analysis for deep excavation stability of red clay had been done by using the method of double strength reduction dynamic parameters and the applications of FLAC3 D and other computing software,and choosing the M-C constitutive model and the secondary development elastio-plastic damage constitutive model.The changes in law were obtained for the parameters of different excavation depth of shear stress increments,horizontal displacement increment,safety factor,damage parameter,plastic region and others.The analytic network model established for support schemes of deep excavation in red clay,and the most unsafe site and its reasonable critical excavational depth were determined for the foundation pit.(8)The support schemes were optimized for the calculation and evaluation by using Super Decisions calculation software,and selected the optimal support scheme.With the using of the methods such as overall optimal controlling,gradual optimization approaches and sensitive analysis,the control system for the engineering cost and project risk were established for the deep foundation fit in red clay,and further confirmed and applied the results of the theoretical analysis and test.