各向均匀与单向冻结条件下饱和岩石冻胀变形特性对比试验研究

Comparative experimental study on frost deformation characteristics of saturated rock under uniform freezing and uni-directional freezing conditions

寒区隧道围岩的冻结是沿隧道径向的单向冻结,而不是常规岩石冻胀试验中的各向均匀冻结。为研究岩石在不同冻结条件下的冻胀变形规律,进而证实寒区隧道围岩单向冻结条件下具有不均匀冻胀性,分别进行封闭条件下饱和砂岩各向均匀和单向冻结时冻胀特性的对比试验。其中单向冻结试验利用自行设计的装置成功地进行。试验表明,封闭条件下饱和砂岩各向均匀冻结时,冻胀变形各向相等,变形过程可以划分为冷缩、冻胀、稳定3个阶段;而单向冻结时,沿冻结方向冻胀应变明显大于垂直冻结方向冻胀变形,且沿冻结方向冻胀应变变化过程也不同于垂直冻结方向冻胀应变,垂直冻结方向变形过程仍为冷缩、冻胀、稳定3个阶段,而沿冻结方向变形过程表现为冷缩、快速冻胀、冻胀量降低、稳定4个阶段,岩石表现出明显的不均匀冻胀性。试验测得饱和砂岩在0.7~2.2℃/cm温度梯度下的冻结不均匀冻胀系数在2.20~2.71范围。在试验的温度梯度范围内,不均匀冻胀系数与平均温度梯度呈线性关系,温度梯度越大,不均匀冻胀系数越大。为考虑围岩不均匀冻胀性的寒区隧道围岩冻胀力计算中不均匀冻胀系数的取值提供了试验依据,从而可合理地计算寒区隧道围岩冻胀力。

The freezing process of rock surrounding tunnels in cold regions is uni-directional along the radius,which is different from the uniform freezing in normal frost heave experiments of rock.A series of freezing experiments on saturated sandstone under uniform freezing and uni-directional freezing conditions were thus conducted in a closed system respectively.The test results show that the frost heave of saturated sandstone is uniform in different directions under uniform freezing condition,and that the variation process can be divided into three stages：a thermal contraction stage,a frost heave stage and a stable stage.However,under uni-directional freezing condition,the frost heave parallel to the freezing direction is much larger than that perpendicular to the freezing condition.Moreover,the variation process of the frost heave perpendicular to the freezing direction can still be divided into three stages as above.However,in the variation process of the frost heave parallel to the freezing direction,four stages are observed：a thermal contraction stage,a frost heave stage,a frost heave declining stage and a stable stage.The non-uniform frost heaving coefficient is in the range of 2.20 to 2.71 when the temperature gradient is in the range of 0.7 to 2.2 ℃/cm and the non-uniform frost heaving coefficient has the linear relationship with the temperature gradient.The greater the temperature gradient is,the greater the non-uniform frost heaving coefficient is.