冻融饱和粉砂动力性能试验

Experimental study on dynamic cumulative axial strain performance of artificial frost-thawed saturated silty sand

摘要:

在软土地区,例如上海,98%的地铁联络通道、地下泵房以及越江隧道采用冻结法施工,但土体的冻胀融沉对地下建筑及周围环境的影响显著.尽管冻土的物理、力学特性得到较多关注,关于饱和冻融土动力特性的研究还不是很充分.试验设计了制样-脱模装置和饱和-冻融方法,采用动三轴系统进行冻融饱和粉砂动力试验.结果表明:制样-脱模装置和冻融、饱和方法满足粉砂制样、冻融和饱和要求.重塑粉砂高度、体积冻胀率随温度降低而增大,原状粉砂规律不明显.轴向应变与动孔隙水压力密切相关,动孔隙水压力前期迅速增加,随后震荡调整,约275次附近出现峰值,随后下降并维持一个相对恒定值.冻结温度-30 ℃时,土样累积塑性变形最大,冻结温度-20 ℃时,土样累积塑性变形最小,-10 ℃取得中间值.总体上,累积塑性应变随振动频率增加而减小,围压增大、动应力幅值减少能显著减小粉砂的累积塑性变形.提出的改进Stewart半对数累积塑性变形模型可以预测冻融饱和粉砂的累积塑性变形.

Abstract:

In the soft soil areas, such as Shanghai, artificial freezing method is adopted for constructing 98% underground engineering of metro side channel, pumping stations, and cross-river tunnels, but the method also causes notable problems of frost heaving and thaw collapsing on subway tunnel and surrounding geology environment. Although physical and mechanical properties of frozen soils have been studied, it is hardly sufficient for the research on the dynamic plastic deformation of freezing-thawing saturated silty sand. A remold-striping equipment was designed, and a method of saturating and freezing-thawing was proposed. The dynamic cumulated axial strain characteristics of freezing-thawing saturated Shanghai silty sand was studied using triaxial testing system. The experimental results reveal that compared with traditional compaction method, the remold-stripping equipment and proposed test methods provide an effect way for remolding, saturating, and freezing-thawing silty sand. The height and volume frost heaving ratio of intact saturated silty sand sample showed less influence with freezing temperature, but remolded silty sand frost heaving ratio increased as freezing temperature decreased. The axial permanent axial strain was closely related to the dynamic pore water pressure and less influenced by freezing temperature. Reducing vibration frequency resulted in smaller cumulated plastic strain. Increasing effect cell pressure and dynamic stress amplitude can significantly reduce the dynamic cumulated axial plastic strain of remolded freeing-thawing saturated sandy silt. Improved semi-logarithmic mode of cumulated permanent axial strain on freeing-thawing saturated silty sand was proposed and verified by experimental data, which could exactly forecast development trend of dynamic permanent axial strain.