The freeze-thaw circle will result in loess deterioration, reduce the shear strength of loess. Loess samples with different moisture contents were prepared from Shanxi Yangquan No. l tunnel as the research object, do height variation test, direct shear test, moisture content test and dry density variation test on different moisture content loess samples after freeze-thaw circle. The results showed that:

  1. The height of the samples increase after freeze-thaw circle, samples which has high moisture changes greater than which has low moisture content. However, the final height of the samples tends to a constant value.

  2. Freeze-thaw circle cause the water migration in soil, due to the freezing and thawing effect is different, making the water migration from the inside to outside cannot return to inside fully and accumulate in the surface of samples, resulting in the moisture content is reduced, and this phenomenon is more obvious in initial high moisture content loess.

  3. Freeze-thaw circle cause the volume changes and migration through the action of water, thus acting on the soil particles, undermine the role of the connection between soil particles, in turn caused the height of sample increased and the volume changed, dry density decreases;

  4. The cohesion c reduced significantly with the increase of freeze-thaw circle. The extent of migration is sharpest before 3 circle freeze-thaw circle, the extent of migration is slower after 5 circle freeze-thaw circle.

  5. With the increased moisture content of loess, the magnitude of the change increase with the freeze-thaw circle, loess deterioration is more obvious when freeze-thaw circle effects, the internal friction angel showing a gradually decreasing trend, but the change is much less than the values that moisture content impact on cohesion.

  6. Freeze-thaw circle and moisture content increase resulting in the shear strength reduced. The affect cohesion impact on shear strength is greater than the inter friction angle impact on shear strength. Hope this paper can provide construction reference in loess distributed area of Yangqu even in Shanxi.

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