Study On The Law Of Water Migration And Settlement At The Interface Of Loess Filled Area Under Rainfall

In order to increase the area of high-quality standard farmland,improve the food supply rate and improve the quality of ecological environment in hilly and gully areas,China has implemented the project of "gully control and land creation".Excavating-filling interface,new-old interface and interface between different compaction degrees often cause disasters such as piping,collapse,landslide,uneven settlement and crack in the duration of gully control and land creation projects in the Loess Plateau area.The present study established physical models of interfaces of different compaction degrees,different angles and different ladder layers in loess fill area.In this paper,the method of artificial simulation rainfall and numerical simulation are used to reveal the law of water migration and settlement at interface of loess fill area under rainfall.At the same time,the engineering suggestions are put forward.The conclusions are as follows:(1)Under certain conditions,the maximum depth of wetting front is linear with time during rainfall,and exponential after rainfall.The results of rainfall model test and numerical simulation show that the wetting front has an obvious transition zone near the interface,where a rainwater dominant flow channel is available.The pore water pressure value at interface increases greatly,and the interface has the potential of piping and collapse.(2)The total settlement of soil above the interface is nonlinearly related to the filling thickness,and the maximum local inclination is close to the upper edge of the interface.The vertical displacement and horizontal displacement of the soil near the interface between the original backfill area and the low-pressure solid new backfill area appear,and the displacement of the shallow soil is larger.There is a trend of shear failure at the interface,and the direction is oblique down along the interface.The large settlement of the low pressure solid filling area and the uneven settlement of the soil on both sides of the filling interface are often accompanied by surface cracks,and the maximum cracks appear near the upper edge of the interface.(3)The compaction degree of the original backfill is 80%,the slope angle of the interface is 45° and there is no step.When the compaction degree of the new backfill increases from60% to 70% and 80%,the rainwater infiltration rate decreases,the increase or decrease near the peak value of water content and pore water pressure decreases,and the peak value of pore water pressure obviously lags behind the volumetric water content.The maximum settlement of soil decreased from 14.8cm to 5.9cm and 0.1cm,the maximum local inclination decreased from 19.39% to 10.00% and 0.94%,and the distance of transition section decreased from110 cm to 90 cm and 0cm.The trend of shear failure at the interface decreased,and the maximum width of cracks near the upper edge of the interface decreased from 3.6cm to 0.5cm and 0cm.In conclusion,the compaction degree of filling soil has great influence on the interface of loess filling area.(4)The compactness of the original backfill is 80%,the compactness of the new backfill is 60%,and there is no ladder at the interface.When the slope angle of the interface increases from 45° to 60° and 75°,the change range of pore water pressure at the interface position decreases gradually.The uneven settlement near the interface gradually changes from’inclined’ to ’stepped’,and the ’stepped’ shear failure is more and more serious.The crack width decreases from 3.6cm to 3cm and 2.5cm,and the number of cracks gradually decreases and closer to the upper edge of the interface.(5)The compaction degree of the original backfill is 80%,the compaction degree of the new backfill is 60%,and the slope angle of the interface is 45°.When setting 1 ladder at the interface,the maximum settlement of the soil decreases from 14.8cm to 14.7cm.The local slope value at the interface of the filling area increases greatly and changes sharply,and the maximum width of the crack decreases from 3.6cm to 2.9cm.When setting 3 ladders at the interface,the maximum settlement of the soil decreases from 14.8cm to 11.9cm,the maximum local inclination decreases from 19.39% to 18.22%,the distance of the transition section decreases from 110 cm to 80 cm,and the maximum crack width decreases from 3.6cm to 2.1cm.Setting steps and anti-angles at the interface may form water accumulation at the anti-angle of shallow steps in the fill area,but it has little effect on the change of volumetric water content of rainfall infiltration in the fill area.(6)It is suggested that the engineering hazards such as uneven settlement caused by rainfall at the interface of the filling area should be reduced by improving the compactness of backfill soil,controlling the uniformity of both sides of the interface,reducing the slope of the interface,and setting multi-layer ladder and anti-angle interfaces.