Nanping Tunnel Of Da-Zhun Railway Experimental Study On Unsaturated Creep Behavior Of Slip Zone Soil

There is a long incubation process before landslide formation.The creep of sliding zone soil is an important process and mechanism in the process of landslide incubation.The creep characteristics determine the development process of landslide.In this paper,based on the landslide of Nanping Tunnel of Da-Zhun Railway,unsaturated creep characteristics of sliding zone soil are studied.Firstly,the paper finds out the geological environment conditions of Nanping tunnel landslide area,analyses the nature and genesis mechanism of landslide.On this basis,triaxial test,unloading test and creep test of unsaturated soil are carried out,and creep model of unsaturated soil is analyzed.The influence of water suction on creep is explored,and unsaturated creep model reflecting water action is established.The purpose of quantitatively studying the effect of water on the deformation mechanism of landslide is to study the mechanism of landslide deformation.(1)Introduce the geological characteristics of Nanping Tunnel landslide and the influence of hydrological weather on the formation of landslide.Taking the landslide sliding zone soil as the research object,a series of indoor routine physical and mechanical properties tests were carried out,and the basic physical properties of soil samples were obtained.(2)Triaxial test and unloading test of sliding zone soil are carried out by using triaxial strain gauge.The influence of unloading effect and initial confining pressure on specimen deformation after unloading is studied.The variation trend of tangential and axial strain rates in unloading stage is analyzed.The linear relationship between confining pressure and peak strain,strain rate and total deformation at unloading stage.The test results are helpful to further study the influence mechanism of other related factors on landslide deformation and fracture morphology.(3)Using unsaturated triaxial creep tester and Chen’s loading method,creep curves,stressstrain isochronism curves and matrix suction of landslide sliding zone soils in Nanping Tunnel under different net confining pressures,matric suction and biased stresses were obtained in triaxial consolidation drainage creep tests of unsaturated soils under different confining pressures,matric suction and biased stress levels.Stress-strain curves under force are analyzed and summarized.(4)Based on creep test results and classical creep model,a classical creep model reflecting the influence of matrix suction on creep characteristics is established according to the characteristics of creep curve changing with matrix suction.The relationship between model parameters,stress-strain and time is presented.The model curve is drawn and compared with the test curve.The model can provide good creep properties of anti-unsaturated soils.(5)On the basis of fractional calculus,the formula of fractional Laplace transform,the software components based on fractional calculus and their constitutive equation are given according to the creep curve obtained from the test.Using Able clay pot instead of Newton element in the model,the corresponding fractional order model is obtained.The constitutive relation of the fractional model is deduced by using the fractional Laplace transform,and its creep equation and relaxation equation are obtained by introducing a special function.The results show that the fitting accuracy of the fractional model is higher than that of the general combined rheological model,which can overcome the disadvantage of the mismatch between the classical model and the test data near the inflection point of the creep curve.It reflects the non-linear creep process and can describe the rheological constitutive properties of sliding zone soils more effectively.On this basis,the non-linear creep theory of sliding zone soils will be further improved.It has important theoretical guiding significance and engineering application value for the design and construction of specific projects such as foundation settlement with sliding zone soil,underground tunnel excavation,foundation pit excavation,slope instability,landslide treatment and so on.