The Numerical Analysis On Moisture Field And Deformation Characteristics Of Collapsible Loess Subgrade

Collapsible loess,which has the nature of large pore structure,the high intensity and the week compressibility,can easily lose its structure under the intrusion of rain.In highway engineering,the phenomenon of roadbed-subsidence is often occurred more seriously.In combination with the expressway engineering construction from Guyuan to Xiji,the features of water distribution and the collapse deformation of the subgrade is studied.Main work's contents and conclusions are as follows:(1)According to the physical-experience model(Arya-Paris model)as well as the physical and mechanical parameters of collapsible loess in Guyuan,by the way of the GEOSTUDIO platform,some kinds of SWCC under the different dry density of soil were fitted.And then through the VG model,the permeability functions have been calculated.In order to analyze the reasons(saturated water content,dry density and soil type)that affect the development of the capillary water rising in the subgrade,the model of soil column has been builded.(2)Considering different compaction degrees,and the weather standard in Guyuan,and the rainwater conditions for runoff formation,as well as the side ditch for draining water,under these cases,different rainfall conditions,different groundwater tables and different rainfall patterns are all applied to the numerical model of infiltration in Guyuan.Numerical analysis result shows that,1)under the condition of light rain,the rainfall infiltration usually happened at the toe of subgrade,after the rain,the distribution of the pore water pressure come to be more balanced than before.2)With the increase of rainfall,the rainwater can easily gathered at the toe of subgrade,and the surface is transiently saturated.3)Influenced by the compression degree,the new saturation line is appeared,and the zone of moisture in soil is divided.(3)Three kinds of inhomogeneity(the inclination of the subgrade's surface,heterogeneous material when filling embankment,the uneven distribution of the initial water content of the foundation)has been considered to study the distribution of the moisture field.Numerical analysis result shows that: 1)When the rain immerses with a tilt direction,the depth and direction of the rain infiltration have changed,which causes a change to the saturation line and water content in subgrade.2)The different filling materials has different infiltration characteristics and water-holding capacity,which leads to the phenomenon that the value of pore water pressure and water content in subgrade alternating between the maxima and the minima.3)The different distribution of initial water content under the foundation influenced the path of raining infiltration.And it lead to a small effect on the water content in shallow soils,but a large effect on the water content in the bottom of the subgrade.(4)Through the method of numerical simulation,the effects of subgrade treatments(replacement of soil,soil compaction pile,lime-soil compaction pile)after the rainfall has been studied.As the result: 1)In filling area,the maximal coefficient variation of the water contents in the horizontal direction is 8%,and the maximal average moisture content is about 20%,which means that the distribution of moisture in the horizontal direction is even and changes with a low water content.The minimum coefficient variation of the water contents in the vertical direction is 40%,and the maximal average moisture content is about 13%,which means that the distribution of moisture in the vertical direction is uneven but it changes with low water content.Through the method of ‘replacement',the maximal settlement on the surface of subgrade is reduced about 10 cm.2)The method of the ‘soil compaction pile' has changed the seepage direction of rainwater,and the average water content of wet area is reduced about 2%.The water content reaches the maximum at the bottom of the soil compaction pile,and the saturation line drops from the collapse area into the non-collapse area.The average coefficient variation of the water contents in the vertical direction is 14%,it means that the distribution of the water contents in the vertical direction is even.And the maximum value of settlement is about 8.3cm on the surface of the subgrade.3)Through the method of ‘lime-soil compaction pile',the position of the saturation line has been dropped after the rainfall.In the compaction area,the average coefficient variation of the water contents in the vertical direction is 23%,and the average water content is 12%,it means that the distribution of the water content in the vertical direction is uneven but changes with a low water content.In contrast with the ‘soil compaction pile',the maximal settlement of subgrade has reduced about 1.3cm after the rainfall.(5)The indicators,such as water content and settlement of subgrade,are monitored at the construction site.Through the comparison and analysis,the results of numerical simulation are consistent with the practical condition of engineering.