Creep Characteristics And Long-term Strength Of L₂/S₂ Contact Zone Loess Of Zhaitou Landslide At South Jingyang Plateau

With the development and construction of loess area in Western China,the creep problem of loess has become a research subject of special concern for geotechnical scholars.Intensive study of the creep deformation characteristics of the loess plays an important role in the stability and safety of engineering construction of loess area and it is profound significance to control and prevention the Loess geological disasters.The loess shows different creep deformation characteristics because of influence of the factors such as moisture content,stress state,confining pressure condition and material composition.This paper takes the landslide of Zhaitou Village at South Jingyang plateau as the research object.It is,through the collection of data,concluded that the occurrence of landslide of the south Jingyang plateau is caused by the creep deformation of contact zone loess.Therefore,triaxial creep tests on the contact zone loess of landslide in the Zhaitou Village were conducted under considering the influence of factors such as moisture content,confining pressure,and stress state.At the same time,the creep characteristics of contact zone loess were analyzed,the creep model of contact zone loess was established and the long-term strength parameters of contact zone loess were determined and applied for the engineering application.The main research content and research results are as follows:The contact zone loess of Zhaitou landslide at south plateau was selected as the creep test samples and the natural samples and saturated samples were made for three axis creep test.The confining pressure of the test consists of five pressure conditions: 100 kpa,150kpa,200 kpa,250kpa and 300 kpa.We could obtain the creep curves of various confining pressure conditions through creep test and draw the stress-strain isochronous curves and the curves of the relationship between the strain rate and the time.By studying the creep curves of the test results show that the creep curves have similar characteristics under the axial stress at all levels,all of which show the stage of deceleration creep and stable creep.The final failure form of the tests sample show type of middle bulging,which without obvious fracture surface and the smaller confining pressure,the greater the bulging deformation;under the action of all levels axial stress at the same confining pressure,the creep deformation gradually increases with the time increasing and the stress-strain isochronous curves become more and more deflection to the strain axis,which shows that the nonlinear visco-elastic properties of the soil;Under the action of axial stress at all levels,all of the test sample will produce certain instantaneous elastic deformation and the creep rate of soil decreases and approaches to zero eventually with the time increasing,which process of deformation shows deceleration creep.It could be concluded that confining pressure and water content are crucial important on creep behavior of soil from rheological test.In this paper,through the research on the creep behavior of the contact zone loess,first of all,we could identify the creep model of landslide creep deformation characteristics of the Burgers model based on the element model theory and draw the curves of creep model,then by comparing curves of creep model with curves of test creep,it is found that the curves of model can be better reflecting curves of in test creep by comparison;At the same time,it is found that the change of the model parameters is reasonable through the research and analysis on the parameters of creep model,which shows that the Burgers model can reflect the creep properties of the contact zone loess well.Secondly,It is revealed that the logarithmic function and the power function of empirical model can better reflect the change law of the creep curve through the fitting creep curve of the empirical equation method.Meanwhile,the parameter values of the empirical creep model equation would be obtained,and the description of the creep law of the contact zone loess has a certain meaning.According to analysis the creep deformation curves and the stress-strain isochronous curves and the curves of the relationship between the strain rate and the time,studying the long-term strength value on contact zone loess of different confining pressure through the method of isochronous curve,the first inflection point method of creep curve and the method of steady state on creep rate and stress.By comparing the values of long-term strength determined by the comparison of the three methods,it is discovered that the long-term strength increases with the increase of the confining pressure and the long-term strength values obtained by the three methods are relatively close and stable.Because of the means and methods for processing data are different from each other,and the various methods for understanding the physical basis of long-term strength are different.Therefore,the long-term strength values of the contact zone loess obtained by different method must not be the same.In this article,three methods are used to find out the maximum and minimum values of the long-term strength as the change interval of the long-term strength value,which is used for reference for practical engineering application analysis.Through analysing the curve change relations of long-term strength parameter values with the change of time based on the creep curve and applying the rule of long-term strength parameters change with time to the stability analysis of slope engineering.Meanwhile,research and analysis on influence characteristics of parameter change on the stability coefficient of slope and analysis the change characteristics of slope stability coefficient influenced by time factors.