Research on ground characteristics of permafrost in Mongolia

第一年在指定区域设置测量点，对蒙古地面进行季节性冻胀测量。根据2003年10月至2004年10月的观测结果，得出以下结论：1)无论冻土是否存在，在高水位的地面上都观测到较大的隆起。2)易受影响的地面如粘土可产生较大的隆起，而不易受影响的地面如沙子可产生较小的隆起。而下层砂土和上层粘土的地基也会产生很大的隆起，因为砂土层会促进水的吸力，在粘土层中形成冰透镜。3)冻结速度慢，升沉大。另一方面，对现场取样进行室内试验，确定冻胀比等参数在Takashi方程中。结果表明，地面的升沉与冻结速度密切相关。此外，从对Takashi方程的敏感性分析中也发现，超载和冻结速度是方程中的主导参数。最后，可以说，可以通过对现场样品进行室内试验来进行冻胀估算，这一事实可以应用于多年冻土区的管道设计。

During the first year measurement site is set on the designated area to measure seasonal frost heaves in Mongolian ground. Based on the measurement from Oct.2003 to Oct.2004, the following conclusions are obtained :1)large heaves are observed in the ground with high water level, regardless of permafrost's existence.2)Susceptible ground such as clay can yield large heave, while unsusceptible ground such as sand can yield small heave. However, the ground of sand in lower layer and clay in upper layer also can yield much heave because sand layer may promote suction of water to form ice lens in clay layer.3)Slow freezing speed gives large heave.On the other hand, laboratory test on the samples taken from the site is conducted to define frost heave ratio and other parameters in Takashi equation. As a result, it is found that heave of the ground strongly depends on freezing speed. Additionally from the sensitivity analysis for the Takashi equation, it is also found that over load and freezing speed are dominant parameters in the equation.Finally, it can be said that the frost heave estimation can be done by conducting laboratory test on the samples in site, and this fact can be applied to the pipeline design in permafrost area.