Study On The Dynamic And Static Characteristics Of Warm And Ice-Rich Frozen Sandy Soil In Qinghai-Tibet Plateau

In order to meet the needs of economic construction in cold regions,the state focus on the development of the highway transportation in the Qinghai-Tibet Plateau.However,due to the complex mechanical properties of frozen soils,the subgrade diseases of road traffic in this area are extremely serious under the background of global temperature rise and human engineering disturbance.Due to the permafrost thawing and frost heaving,the poor section of the QinghaiTibet Highway subgrade is much higher than the subgrade in general areas.The second phase of Gongyu Highway,which opened to traffic in 2017,has a maximum subgrade settlement of20 cm in the ice-rich road section.The Qinghai-Tibet Expressway has not opened to traffic because the construction and protection technology of the wide roadbed is still being explored.The strength of frozen soil is weakened and the deformation capacity is increased under the conditions of high temperature and high moisture content.Therefore,the subgrade disasters mainly occur in warm and ice-rich frozen soil sections,The success of the roadbed mainly depends on the treatment of the warm and ice-rich frozen soil.As the foundation of road traffic in cold regions,frozen soil is not only subjected to constant static loads,but also to long-term vibratory loads of heavy-duty traffic.Therefore,taking the sandy soil of highway subgrade in Nagqu region of Qinghai-Tibet Plateau as the research object,to clarify the mechanical properties and changing laws of warm and ice-rich sandy soil under the dynamic and static loads,has an important theoretical and practical significance for designing and construction in the early stage,operation and maintenance in the later stage of the project in cold area.In this study,an indoor dynamic and static triaxial test of warm and ice-rich frozen sandy soil was carried out.The purpose is to study the dynamic and static properties of warm and ice-rich frozen sandy soil.The specific content and main results of this research are as follows:1)Under the conditions of different temperatures(-0.5 °C,-1 °C,-1.5 °C,-2 °C),different moisture contents(20%,40%,60%,80%)and different confining pressures(0.1MPa,0.3 MPa,0.5 MPa,0.7 MPa,1 MPa)the static triaxial test of the frozen sand was carried out,and the results showed that: under each test condition,the stress-strain curve of the frozen sand was strain softening;the static elastic modulus of the frozen sand decreased linearly with the increase of water content and temperature;The static strength of sand is most sensitive to temperature changes,followed by water content and confining pressure.The static strength decreases rapidly with the increase of temperature,and decreases linearly with the increase of water content.The Duncan-Chang model calculation parameters are determined by the stressstrain curve,study the law and regression relationship of parameters changing with temperature,establish a modified Duncan-Zhang model with temperature as the influencing factor.(2)Under the condition of-1.5 °C and the moisture content of 20%,changing the confining pressure(0.1 MPa,0.3 MPa,0.5 MPa,0.7 MPa)and loading frequency(0.5 Hz,1Hz,1.5 Hz,2 Hz)to load the frozen sand in stages.The dynamic triaxial test results show that the dynamic stress-strain curves of frozen sand show nonlinearity,hysteresis and strain accumulation under all test conditions;the backbone curve of frozen sand can be well fitted by the H-D model,The dynamic elastic modulus of frozen sand decreases with the increase of dynamic strain amplitude,and the maximum dynamic elastic modulus increases linearly with the increase of confining pressure and frequency;The damping ratio first decreased and then increased with the increase of the dynamic strain amplitude,and finally tended to be stable.The maximum damping ratio increased linearly with the increase of confining pressure,and decreased nonlinearly with the increase of frequency.(3)Under the assumption that the physical properties(temperature,moisture content)of the frozen soil are the same,the conversion relationship of the starting static elastic modulus is established through multiple regression analysis.