Study On Seepage Law And Collapse Characteeistics Of Loess Foundation Under Rainfall Infiltration

The collapsible loess foundation is very’sens.itive to water,especially the long-terrm rainfall will cause the obvious change of the matrix suction,and cause the attenuation of the shear strength of soil,which will lead to the foundation disaster.Therefore,the study on the infiltration and collapsibi lity of rainwater in loess foundation under the action of continuous rainfall is not only of important guiding significance to practical engineering problems such as foundation stability,but also can effectively reduce the occurrence of disasters and the loss of economic property.In this paper,physical test and numerical test are combined.Through physical experiments,the seepage law of remolded and undisturbed loess foundation is explored,and the key elements(parameters,boundary and flow)of rainfall infiltration numerical simulation are verified.By using the method of hydrology statistics,the rainfall characteristics of continuous rain in xi’an city and the total rainfall amount under different recurrence periods were obtained,which was taken as the boundary condition.The existing data were excavated and the effects of different measured soil-water characteristic curves and permeability coefficients on the foundation seepage field were analyzed by numerical simulation.Based on the simplified principle of collapsible d eformation of loess,the collapsible deformation of loess foundation is analyzed by using finite element software.The main contents and conclusions are as follows:(1)The calibration of SWR soil moisture sensor was carried out with self-designed tools,and the calibration method and cubic calibration relation of S WR sensor were summarized.A set of large-size indoor water infiltration device was designed to investigate the seepage law of remolded loess foundation.It was concluded that the water content first increased and then decreased with time and then tended to be stable.The migration rate of wet front decreased with the increase of migration distance.(2)SEEP/W is used to simulate the field infiltration test,and the infiltration law of undisturbed loess foundation is discussed:during the immersion process,the shape of the immersion line was always approximately symmetrically distributed.The turbulent range mainly occurred in the lower foundation after the water supply was stopped.Application platform for secondary development of ABAQUS,the loess collapsibility deformation model was applied to numerical simulations,it is concluded that the loess collapsibility deformation law,and compared with the measured result is found that the deformation decreases with depth increasing,the collapse occurs mainly in the upper area,and reduce the rate of fast,collapsible deformation from the trial pit center to try the pit direction gradually reduced,thus verified the developed program used to simulate the feasibility and rationality of collapsible deformation.(3)The measured daily rainfall from 1981 to 2015 in xi ’an was sorted out,and it was found that the days of continuous cloudy rain in xi’an were distributed in 4～12 days,with an average rainfall of 5.6 days.The total rainfall was distributed in 20.3～186.7mm,with an average rainfall of 71.6mm.Application of hydrological frequency calculation software,the computer optimization optimal line method to map the Pearson Ⅲ frequency curve,through curves obtained under different return period xian sounds total rainfall.(4)In view of the loess foundation treatment in practical engineering,according to the continuous rain of different return period,the calculation of rainfall infiltration by SEEP/W analysis out of the can reflect the actual situation of different rainfall,rainfall duration,soil-water characteristic curve,the permeability coefficient and different depth of foundation treatment in the process of rainfall the impact of foundation seepage field change to some extent.At the end of rainfall,the deformation of foundation surface is larger than that of treated foundation surface.For the foundation surface,the deformation near the side of the foundation pit is smaller than that far away from the side of the foundation pit.For the treated foundation surface,the deformation at the corner of the foundation pit is greater than that far away from the corner of the foundation pit.