| Loess, is widely distributed in China and it plays an important role in the development of agricultural production, construction and ecological environment. The gully and tableland formed by water erosion in the loess are prone to landslides, because water is one of the important factors of loess landslides. The solid, liquid and air gas attribute to moisture migration, then the increase or decrease of the groundwater level can cause wet and dry conversion in loess strata. In addition, dry-wet cycling can change the structure of loess, affect the permeability of loess and air in pore space can affect water movement as well.According to the field investigation of Jingyang loess landslide group, this paper has found the fundamental situation. Based on the indoor experiments, it analyzes permeability, porosity and dry density changes of the undisturbed soil and the remolded soil under dry-wet cycling, researches water and air movement law in the remolded loess column. The following conclusions can be obtained:(1) Under the effect of dry-wet cycling, interspace of undisturbed soil reduces while interspace of remolded soil increase. Dry soil will loss water and crack in the end, remolded soil is easier to crack than the undisturbed soil and the cracks width of remolded soil also are large. The soil of small dry density is prone to produce large cracks; when there is water seepage in the soil column, remolded soil generated horizontal cracks under its own weight. The width of cracks is related to the position of cracks, upper soil of the column is easier to produce the large cracks than the lower; water movement under confinement is slower than open conditions.(2) According to the results of the dry-wet cycling penetration test, the initial permeability of undisturbed soil is random, the differences is in one of magnitude; after six cycles of wet and dry, permeability of 10 undisturbed soil samples decreases, the permeability curve of 10 remolded soil samples tends to go up.(3) Under confined conditions, moisture in the upper transported moves faster than the lower; the connectivity of pore space in the soil column is good for air, the air can response to changes in pressure quickly; when pore space of air is occupied by the water, the water pressure and air pressure of pore space will increase with the phenomenon of air overflowing to release pressure. Obstruction of air to water movement is the dynamic process of increase to decrease and then increase, the shocks of pressure curve illustrates this rule. The Water moves from top to bottom, the gas moves from bottom to top. Under open conditions, the air resistance movement mainly occurs at the beginning of the water infiltration, the air will enter the atmosphere through the bleed hole which results air resistance reduces.(4) The pore space of unsaturated loess and remolded loess are occupied by air, there were good connectivity and poor connectivity between the pore space, so the good connectivity of pores space is not easy to form a gas piston when the water infiltrates, air resistance is small. By contrast, the poor connectivity of pores space is easy to form a gas piston, air resistance is lager and there will be accompanied with continuing pressure releasing.(5) Under natural conditions, wet and dry cycles would affect the formation of loess shrinkage crack, while the hydraulic conductivity of remolded soil would increase. And the moisture can not be hindered by air in communicating interspace. Therefore some advantage channels for moisture transport in loess could form.The water table of loess slope zone will be raised by water through the advantage channels, which would accelerate the potential landslide occurrence; the remolded soil slope are prone to loess gully and internal erosion due to the soil erosion, which can accelerate loess landslides and collapse process. |
