Study On Creep Constitutive Model Of Rich Frozen Sand Soil On Qinghai-Tibetan Plateau

As the "One Belt And One Road" cooperation initiative continues to advance,a large number of infrastructure projects have been launched in alpine regions such as the QinghaiTibet Plateau.The soil in the frozen cold area is highly sensitive and unstable.The Gera section of Qinghai-Tibet Railway has been in operation for more than 10 years since 2006.On-site monitoring data show that the thickness of the track bed in some sections in the permafrost area is as high as 1.70m due to continuous patching and lifting of the track.Subgrade filling and permafrost characteristics have significant effects on subgrade settlement and deformation.Therefore,it is urgent to conduct in-depth study on frozen sand soil with high ice content for the maintenance of Qinghai-Tibet railway and highway and the construction of Qinghai-Tibet expressway in the future.In view of the above,this article with the qinghai-tibet permafrost area roadbed disease control theory as the background,focus on the quantitative evaluation of rail traffic load long-term effects of permafrost with high ice content subgrade affect scientific problems,based on the frozen soil to carry out a series of triaxial creep test,the frozen soil in a variety of ice content,dry density,stress level and temperature creep properties of conditions,A three-dimensional equation was established to describe the creep characteristics of frozen sand with high ice content.Meanwhile,the rigor and applicability of the modified creep equation were verified based on the test results.The main research contents,conclusions and innovations of this paper are as follows:(1)In this paper,the traditional method for preparing frozen soil samples with high ice content was improved by developing a low-cost method for preparing frozen soil samples with high ice content under laboratory conditions at room temperature.The test results showed little variability and few errors,which created conditions for the study of mechanical properties of saturated frozen sand with high ice content.Based on the deformation characteristics of rail transit roadbed in the high-altitude frozen region of Qinghai-Tibet Plateau,the effects of various ice content(ω),dry density(ρd),stress level(σ)and temperature(t)on the creep law were investigated by using the laboratory test method of constant temperature-consolidation-creep.The results show that the creep law of frozen sand is sensitive to the change of ice content(ω)and temperature(t).(2)Based on the theoretical framework of the Nishihara model,the rheological parameters of frozen sand are regarded as variables determined by time and stress,and the influence of ice content on the creep characteristics of frozen sand is explored,and damage variables and hardening parameters are introduced to reflect the frozen sand For the hardening and damage effects that exist in the creep process,the shear modulus in the constitutive model element is corrected to a function with the stress level as the independent variable,and the steady viscosity coefficient in the viscoelastic and viscoplastic elements is corrected to Taking time and shear stress as functions of independent variables,a modified Nishihara model that can describe the creep law of frozen sand is established.(3)An improved Nishihara model,which is suitable to describe the creep phenomenon of frozen sand with high ice content and takes into account the damage and damage effects during the creep process of frozen soil as well as the factors of the variation of parameters not involved in the classical Nishihara model with time and stress level,is established.Based on the test data,the modified Nishihara model is verified.This equation can well reflect the attenuation,steady and accelerated creep characteristics of frozen sand under different ice content,stress level and temperature conditions.The fitting results are in good agreement with the experimental data.The research results of this paper can accumulate basic data for permafrost mechanics,and have a positive guiding significance for the maintenance of roadbed engineering in high altitude areas,and also have a certain reference value for the construction of Qinghai-Tibet Expressway.