Study On The Influence Of Priority Flow To The Widened Embankment Of Silty Sand

Preferential flow is a common natural phenomenon in soil matrices.Preferential flow means that the water bypasses the soil rapidly and massively moving along the preferential channelinside.In the road extension project,the old roadbed has been completely consolidated becauseof long-term traffic load,and the new roadbed will still have some settlement on account of the load and its own gravity in the short term.Due to the difference in settlement between the old and new roadbed,which will have a negative impact on the stability of the roadbed,affecting the traffic safety and the using function of the road.The physical-mechanical properties experiments of silty soil were measured by laboratory experiments,which measured the optimum moisture content of silty soil.The preferential flow test was carried out in the field to observe the characteristics of the preferential flow and test the preferred flow moisture content.With indoor freeze-thaw cycle test,the effects of freeze-thaw cycles,freezing temperatures and influence of water content on the shear strength of soil samples were analyzed.The results of the indoor tests were used in the finite element simulation of the subgrade extension project to analyze the influence of the preferential flow channel on the stability of the subgrade under the freeze-thaw cycle.The main research contents were as follows:(1)Basic mechanical properties of silty sand.The particle sizing curve and plasticity index of the silt soil were measured,and the maximum dry density and the optimum moisture content of the soil sample were measured by compaction test.(2)The preferential flow moisture content of the soil sample under the seepage flow was measured by the outdoor preferential flow test.The horizontally and vertically section dyed images were processed and analyzed using image processing software of Photoshop and Image-Pro Plus.The percolation characteristics of the preferential flow image were evaluated and analyzed by using the priority flow dyed area ratio and other evaluation indicators.(3)The direct shear test pieces were made according to the optimum moisture content and the priority flow obtained according to the preliminary test.Referring to the historical winter temperature in the Kaifeng area,the freezing temperature was set as-5℃、-10℃and-15℃,the cycles of freeze-thaw cycles of 1,3,5,7,9 and 11 times were carried out on the test block.The direct shear test of the test pieces after the freeze-thaw cycles was carried out to study the effects of moisture content,freezing temperatures and times of freeze-thaw cycles on the shear strength index,internal friction angle and cohesion,were studied.(4)SIGMA/W module in the GEO-STUDIO software was used to establish a finite element model for the widening subgrade and explore the impact of the priority flow channel at the junction of the new and old subgrade on the stability of the subgrade.(5)SLOPE/W module in the GEO-STUDIO software was used to establish a finite element model for the expansion of the embankment,calculate and analyze the position of the slope slip surface and the embankment stability coefficient with different freeze-thaw cycles and different freezing temperatures.The anchorage reinforcement measures are used to strengthen the widened embankment,and the influence of anchor length and anchorage angle on the stability of the embankment is analyzed.