Research on ground characteristics of permafrost in Mongolia

第一年在指定区域设置测点，对蒙古国地面季节性冻胀进行测量。根据2003年10月至2004年10月的实测资料，得出以下结论：1)无论是否存在冻土层，高水位地基都会出现较大的隆起；2)粘土等敏感地基会产生较大的隆起，而砂土等不敏感的地基会产生较小的隆起。但下层砂土和上层粘土地基也会产生较大的冻胀，因为砂层会促进水在粘土层中形成冰透镜。3)冻结速度慢会产生较大的冻胀。另一方面，通过对现场取样的室内试验确定了Takashi方程中的冻胀率等参数。结果表明，土体的隆起强烈依赖于冻结速度。此外，通过对Takashi方程的敏感性分析，还发现超载和冻结速度是方程中的主要参数，可以通过对现场样品进行室内试验来估算冻胀，这一事实可以应用于多年冻土地区的管道设计。

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.