Research On The Seepage Failure Of The Remolded Loess Interface

In order to alleviate the current situation of land shortage and soil erosion,under the guidance of national policies,Yan'an has carried out a vigorous project to control land and make land.In the course of the project,due to the continuous backfilling of the earthwork,a large area of remolded loess filling area was formed.Due to the huge amount of engineering,the filling area is not compacted at one time,and there are a lot of remolded loess contact surfaces.Due to the difference in compaction,porosity and particle gradation of the remolded loess on both sides of the contact surface,coupled with rainfall erosion and infiltration,the surface of the contact surface is damaged by cracks and gullies.In the long run,the contact surface may even produce landslides,Ground subsidence and other phenomena.Therefore,the remolding of the loess contact surface in the fill area is the key part to maintain the stability of the trench management project.In this paper,the loess in Yan'an is taken as the research object,using the infiltration sample and infiltration failure experiment and other research methods to study the influence and law of the degree of compaction and fine particle content on the permeability and impermeability of the remolded loess interface.The particle flow analysis software PFC2 D reveals the mechanism of seepage failure at the contact surface from a microscopic perspective.The research conclusion is as follows:(1)The permeability coefficient of the remolded loess shows a power function decrease with the increase of the compaction coefficient,and the deceleration is fast and then slow.With the increase of compaction coefficient,the seepage resistance of remolded loess soil samples showed a linear increase trend.Under the same compactness coefficient,the seepage failure slope of the soil sample with the contact surface is smaller than that of the soil sample without the contact surface.When the compaction coefficient on one side of the contact surface is fixed,the seepage failure slope of the soil sample increases linearly with the increase of the compaction coefficient on the other side.However,the seepage failure slope of the samples with the same degree of compaction coefficient on both sides of the contact surface is higher than that of the adjacent soil samples.(2)The permeability coefficient of remolded loess decreases with the increase of fine particle content,80% fine particle content is the critical point,when <80%,the permeability coefficient decreases linearly;> 80%,the permeability coefficient decreases slowly,Tending to a constant value.When the compactness coefficient and fine particle content are the same on both sides of the contact surface,the presence or absence of the contact surface does notaffect the permeability coefficient of the soil sample.However,the presence of the contact surface will reduce the seepage resistance of the soil sample.The seepage failure slope of the soil sample with the contact surface is smaller than that of the soil sample without the contact surface.When the content of fixed fine-grained soil on one side of the contact surface is not less than 80%,the seepage failure slope of the remolded loess sample shows a regularity consistent with the above analysis as the content of fine-grained soil on the other side increases.When the fixed fine-grained soil content on one side of the contact surface is less than 80%,the seepage failure slope of the remolded loess sample decreases linearly with the decrease of the fine-grained soil content on the other side.(3)The penetration channels of the seepage-damaged soil samples without contact surfaces are all cracks at the bottom of the soil samples and connected to the cracks around the soil samples to form the penetration channels.The infiltration channels of the soil sample with contact surface penetration are all cracks at the bottom of the soil sample contact surface and the cracks of the soil sample side wall form the infiltration channel.At the same time,the top of the soil sample with a small compaction coefficient or a small fine particle content first cracks,Osmotic damage occurs.(4)After analyzing the mechanical mechanism of loess seepage failure,it is found that the crack appears in the tensile stress area,and the formation of the crack is the result of the contact stress changing from compressive stress to tensile stress and gradually increasing.It is preliminarily stated that the seepage failure of loess should belong to the tensile failure between particles,not the shear failure.The main mechanical reason for the failure is that the tensile stress in the soil sample exceeds the tensile strength of the soil.Moreover,the infiltration channels of the seepage failure soil samples and the numerical simulation of seepage failure soil samples are both the infiltration channels formed by the cracks on the bottom of the contact surface and the cracks around the side walls.Using PFC2 D to simulate the seepage failure of cohesive soil,although the results are inconsistent with the results of the laboratory test,the larger range is about 15%,and the numerical simulation results are consistent with the laws reflected by the results of the seepage failure physical test.