Experimental Study On The Protection Measures Of Subgrade Seepage Ditch Blockage

With the vigorous development of highway construction in China,the water damage of highways has been increasing year by year.The failure of drainage facilities on highways in rainy areas of the south is a major reason for water damage to highways.The pipe-type permeable trench is one of the most effective methods for underground drainage of highways,and the southern filling soil is mostly powdery clay with a high content of fine particles.The active fine particles in the powdery clay can fill the pores of the geotextile under the action of water flow,making the permeable trench prone to blockage and even failure.This study investigates the anti-clogging performance of permeable trench structures through field surveys and indoor and outdoor experiments,and proposes an optimized design for permeable trench structures to provide theoretical basis and technical support for the optimal design of seepage trenches.First of all,this article conducted on-site investigations on multiple expressways in Hunan Province,such as Changyee Expressway,Nanyue Expressway,Hengzao Expressway,Liuleng Expressway,Litang Expressway,Tanshao Expressway,and Liyi Expressway,analyzed the water damage and causes of underground drainage facilities.Secondly,through the indoor siltation test,the flow rate and flow attenuation degree of the infiltration ditch under different anti-filter siltation protection measures are revealed,and the following conclusions are obtained:the penetration test shows that the risk of geotextile being silted up is much greater than the risk of soil particle loss,and selecting the maximum effective pore size of geotextile according to FHWA soil preservation criteria can effectively reduce the occurrence of siltation and will not lead to the destruction of soil structure.The permeability coefficient affecting the reverse filter is mainly the lower geo textile,the larger the effective pore size of the lower geotextile,the larger the permeability coefficient of the system and the larger the flow rate;After comprehensive analysis,the scheme of laying geotextiles with a thickness of less than 100g/cm2(MBD,MBA)under or above and below the medium coarse sand reverse filter material can be preferred as the scheme for the design of the trench reverse filter layer.Based on hydraulic calculations of the permeable trench and drainage capacity calculations,compressive strength tests,and vertical deformation calculations of drainage pipes(perforated PVC pipes,rigid permeable pipes,and plastic blind trenches)in the permeable trench structure,this article proposes applicable conditions for each drainage pipe.Each drainage pipe with a pipe diameter between 110 mm and 200 mm can meet the drainage requirements of the seepage ditch.When the permeable trench is laid under the roadbed ditch,PVC pipes and white plastic blind trenches are suitable for burial depths less than 4.4m,while rigid permeable pipes and black plastic blind trenches are suitable for burial depths less than 3.5m.When the permeable trench is laid under the roadbed,PVC pipes and white plastic blind trenches are suitable for burial depths less than 4.0m,while rigid permeable pipes and black plastic blind trenches are suitable for burial depths less than 3.0m.indoor model box tests were conducted to simulate the drainage process of infiltration trench structures and reveal the variations in drainage flow under three combinations of drainage pipes and anti-filtering materials.The experimental results showed that the drainage efficiency of pipes with larger void ratios was higher;water pressure had little influence on the drainage efficiency of drainage pipes,and the drainage performance of infiltration trenches was mainly controlled by the water passage performance of drainage pipes.The drainage efficiency of PVC pipes with smaller surface void ratios was greatly affected by the structural type.The drainage efficiency of medium-coarse sand filtering layer(B infiltration trench)structure was generally better than that of crushed stone filtering layer(A infiltration trench)structure.Therefore,it is recommended to use a combination of 150mm diameter plastic blind trenches and medium-coarse sand anti-filtering materials as clogging prevention measures for infiltration trench structures and apply them to solid engineering.Finally,the new permeable trench structure was applied in the physical engineering of the Beinei to Ganshan Expressway in Hunan Province.Compared with the permeable trench structures in other parts of the expressway,the new structure showed a significant improvement in drainage effect,indicating that the new permeable trench structure has certain practical value.This article proposes measures for preventing siltation in roadbed infiltration ditches through a combination of field surveys,theoretical calculations,and indoor experiments,which have been verified in engineering examples.It has good guiding significance for improving the quality of underground drainage facilities on highways in rainy areas of southern China,and provides theoretical and technical support for the development of underground drainage facilities on highways in China.