冻结砂土在动荷载下的蠕变特征

通过分析不同试验条件下的蠕变过程曲线,探讨了冻结砂土在动荷载下的蠕变模型,分析了最大加载应力,温度及加载频率对冻土蠕变破坏应变,破坏时间和最小蠕变速率的影响.结果表明,当最大加载应力变大时,破坏应变增加,破坏时间缩短,最小蠕变速率变快;加载条件相同时,温度越低,破坏应变越小,破坏时间越长,最小蠕变速率越小;加载频率变化时,最小蠕变速率的变化无明显规律,都在一个量级范围内,当频率变大时,最小蠕变速率略有变小的趋势.频率增加,破坏时间缩短,破坏应变减小.频率小于7Hz时,频率对破坏应变和破坏时间影响较大,而当频率大于7Hz时,随频率加快,破坏时间和破坏应变只略有减小.

Creep Characteristics of Frozen Sand under Dynamic Loading

Determining creep indices and developing creep model are two main tasks of the research on creep behavior of frozen soil, one important part of frozen soil mechanics. Many researchers have engaged in this field. As a result, some creep models, such as attenuation creep model, steady creep model, gradual flowing creep model and tertiary creep model, were developed. The influence of confining pressure, maximum axial stress and loading frequency on creep properties was evaluated. The creep yield criteria were presented. However, most of these works involve the creep behavior of frozen soil under static loading condition, and involve the frozen silt under dynamic loading condition. Fewer documents involve the creep characteristics of frozen sand under dynamic loading, which will be discussed in this paper. A series of creep experiments under various conditions, namely different temperature, various frequency and different maximum axial stress, were conducted on MTS, then creep curves were drawn and creep modal was put forward. The primary creep model ε=Aσ^mt^λ (Vyalov) was used to analyze the first and second stages of creep. Then, referring to the creep models under static loading condition and considering the features of dynamic loading, equation ε/σⁿ=B₁+B₂t^1/3+B₃t was used to predict the whole creep process. Comparing the two analysis methods, it can be noticed that the coefficients of two regression methods are similar. However, the latter method has the advantage of predicting whole creep process. The influence of loading, temperature and loading frequency on creep failure factors (failure strain, time to failure and minimum creep rate) was evaluated. The test results indicate: (1) Failure strain increases, time to failure shortens and the minimum creep ratio quickens with increasing axial stress. The variation rate of creep factors is different between stress less than 2 MPa and stress more than 2 MPa. (2) The lower the temperature is, the less the failure strain, the longer the time to failure and the less the minimum creep ratio will be. The variation rate of creep factors is different between temperatures lower than -10℃ and higher than -10℃. (3) No obvious frequency dependent change of the minimum creep rate was found, which seems varying within a range. But there is a trend that the minimum creep rate slightly decreases with increasing frequency. Time to failure shortens and failure strain lessens with increasing frequency. When it is less than 7 Hz, the frequency greatly influences the failure strain and time to failure. But the failure strain and time to failure slightly decrease with increasing frequency when frequency is greater than 7 Hz.