The Centrifuge Modeling Test And Numerical Analysis Of Irrigation-induced Loess Landslide

This paper presents a centrifugal model test with both physical and numerical simulation,which takes the jiaojiayatou loess landslide at Heifangtai as an example. The methods used inthis paper overcome sever disadvantages in the previous studies, such as, the size effects,unclear process of groundwater movement and slope deformation, and representativeness ofdisturbed loess. Experiments were carried out with the centrifugal model test, which simulatesthe deformation and failure process of the loess landslide and its characteristics underirrigation condition. The numerical simulation software of FLAC3D is used to analysis slopedeformation and failure under different groundwater level. The deformation and failuremechanism of irrigation induced loess landslide are obtained with physical and numericalsimulation as follows:(1) Two groups of centrifugal model test of undisturbed loess and disturbed loess underirrigation condition were conducted. Under200g acceleration condition, centrifugal modelachieves a good fitting with the geological prototype for both the stress state and thegroundwater level. The test results compensate gravity loss due to the model scale andovercome size effect. It also shows the interaction process of groundwater movement andslope deformation and failure, and reflects the structural characteristics of undisturbed loess.(2) Based on the centrifugal experiment, the curves of different monitoring data withacceleration change similarly. The top soil start to collapse with the natural self gravity first,then, the open and closed fractures alternatively appeared on the slope with the increasingacceleration There are several dropdown for both the earth pressure and pore-water pressurewith there increase. Fractures accelerate the speed of groundwater infiltration and migration.Therefore, the groundwater level increased gradually, and the soil changed from unsaturatedto saturated state. Due to seepage and water softening, the mechanical properties of the soilchange, slope started to destroy at the toe and top of the slope, and developed throughout thewhole slope in the end. Settlement mainly occurred on the top of slope Displacement decreasewith the increase of depth. With the increase of groundwater level， the speed ofdisplacement accelerates until the maximum vertical displacement achieves.. Maximum lateral displacement occurs in the upper middle position for the remolded loess slope, at thetoe for the undisturbed loess slope.(3) In the centrifugal experiment, the subsidence curve of loess and stress curves changesimilarly. The disturbed loess is uniform, but its original structure is destroyed. So there isdeviation between the monitoring curve and the site investigation. Undisturbed loess has thestructure characteristics, and curve has multiple mutations but matches field investigation inthe change process.(4) Analysis of numerical simulation results show that, the plastic zone of the slope is inunstable state. The maximum principal stress is mainly concentrated in the slope toe and shearfailure appears. At the top, the maximum principal stress is in tensile stress state and tensioncrack appears here. Maximum vertical displacement occurs at the top of the slope. Themaximum total displacement occurs at the slope toe. The Shear failure occurs mainly in theshallow part of the loess slope.(5) Based on centrifugal modeling, numerical simulation and field survey, the first phaseis in the natural state, compression cracking–Collapse, the second stage under the action ofwater for shear sliding mechanism, comprehensive analysis of the failure mechanism of thelandslide is compression cracking-shear slipping mechanism.