Experimental Study On Deformation Mechanism Of Overlying Subgrade In Local Subsidence Area Based On Reinforcement Effect

The local subsidence area of subgrade formed by rainfall or pipeline rupture is the main cause of frequent urban collapse accidents.The existing treatment methods are not perfect,and even lead to repeated collapse.Geotextiles can increase the stability of subgrade,reduce the loss of filler and prevent the development of deformation zone by virtue of their excellent physical and mechanical properties.In order to further explore the deformation mechanism of subgrade reinforced by geotextile in local subsidence area,the indoor model tests of two kinds of fillers with different reinforcement length,reinforcement type,vertical spacing and reinforcement layer number were carried out by using the self-designed movable door model device.At the same time,based on digital image correlation(DIC),the deformation evolution law of overlying soil layer in local subsidence area is revealed,and the deformation behavior and mechanical response of reinforcement and filler are quantified.The research results can provide some theoretical support for optimizing the design of subgrade structure in local subsidence area reinforced by geotextile.The main research contents and results are as follows:(1)The model test of subgrade in local subsidence area under different working conditions was carried out,and the deformation evolution law of the whole subgrade was analyzed.The results show that the failure modes of different types of fillers are similar,but the sand will break through first.Geotextile reinforcement can effectively slow down the development of local subsidence area to the top of subgrade,and with the increase of reinforcement length,the shear zone on the left and right sides of the filling above the subsidence area is gradually not obvious,and the vertical deformation range of the filling in the subsidence area is gradually reduced.Compared with non-woven geotextiles,woven geotextiles have better reinforcement effect in reducing the deformation of filling soil in local subsidence area.With the increase of the vertical spacing of the double-layer reinforcement,the overall deformation range of the subgrade increases first and then decreases.The main deformation area of the subgrade changes from the upper subgrade filler of the upper reinforcement to the subgrade filler between the two layers of reinforcement.With the increase of the number of reinforcement layers,the overall deformation range and deformation height of the subgrade gradually decrease.(2)In addition to the qualitative evolution law of subgrade deformation,this study also obtained the quantitative vertical displacement distribution law of representative soil layers.In the model test of unreinforced subgrade,the sand filler is easy to produce vertical displacement,but the maximum vertical displacement is smaller than that of gravel soil filler.In the model test of geotextile reinforced subgrade,with the increase of the length of the reinforcement,the vertical displacement of the filler can be effectively reduced,but when the reinforcement reaches a certain length,the reinforcement effect is relatively limited.Compared with the two kinds of geotextiles,in the early stage of local collapse development,nonwoven geotextile reinforcement can effectively improve the mechanical behavior between fillers and reduce the vertical displacement of fillers,especially in reinforced sand subgrade.In the later stage of local collapse development,the coordinated deformation ability of woven geotextiles and fillers is better than that of nonwoven geotextiles,and the effect of reducing the vertical displacement of fillers is remarkable.With the increase of the vertical spacing of the double-layer reinforcement,the vertical displacement of the filler increases first and then decreases.With the increase of the number of reinforcement layers,the vertical displacement of each layer of filler decreases obviously.(3)In addition to the evolution law of subgrade deformation,this study used the soil pressure acquisition instrument to obtain the distribution law of soil pressure at the bottom of the model box during the test.The increase of soil pressure in the stable area of sand filler is greater than that of gravel soil filler,and the soil arching effect is more obvious.Increasing the length of the reinforcement can improve the load transfer effect of the reinforcement and promote the load transfer from the subsidence area to the stable area.Compared with non-woven geotextiles,when reinforced with woven geotextiles,the load transfer effect of reinforcement is more significant,which can effectively increase the load transferred to the stable area,especially at the edge of the stable area.When double-layer reinforcement is used,the appropriate vertical spacing can effectively improve the bearing or transfer load capacity of the bottom reinforcement.The more the number of reinforcement layers,the greater the increase of soil pressure in the stable area,and the more significant the effect of load transfer from the collapse area to the stable area.