Study On The Seepage Of Grass Ditch And Settlement Of Subgrade Of Municipal Road Collapsible Loess Area

In recent years,with the continuous promotion of the national strategy of "new urbanization",the construction of sponge city has also been vigorously promoted in the northwest of China.However,the collapsibility of loess brings great challenges to the construction of sponge City aiming at the comprehensive utilization of rainwater.How to develop sponge city in collapsible loess area has become a widespread concern in engineering and academic circles.Based on the scientific research subject of "Seepage Prevention Evaluation and Optimization of Near Sponge Rainwater Facilities in Typical Application Scenarios of Collapsible Loess Site",this paper studied the grass planting ditch rainwater infiltration and subgrade deformation in collapsible loess site through model test,field in-situ test and numerical analysis.The research contents and achievements are as follows:(1)Through the physical model test of geometric similarity ratio 1:4,the infiltration path and influence range of rainwater in the grass planting ditch on collapsible loess site were studied.The results show that the infiltration of rainwater in the grass planting ditch is mainly concentrated in the soil under the grass planting ditch,mainly vertical infiltration,and the influence range of lateral infiltration is limited.(2)Based on the in-situ test of rainwater infiltration in grass planting ditch in typical collapsible loess field,the influence law of rainwater infiltration in grass planting ditch on the change of soil moisture content was analyzed.The rainwater infiltration rate and influence range of three types of grass planting ditch were compared.Combined with the formula of soil moisture deformation fitted by indoor moisture deformation test,the calculation method of subgrade moisture settlement caused by rainwater infiltration of grass planting ditch is proposed.(3)In the collapsible loess field,the final soil water movement patterns of the three types of infiltration caused by rainwater infiltration are similar to "pear shape" : the vertical infiltration depth is larger than the influence range of the lateral infiltration,which is relatively limited.Under the same conditions,the influence range of the rainwater infiltration of the two types of stagnant infiltration is relatively consistent,which is significantly greater than that of the transmission infiltration.The rainwater infiltration rate of stagnant infiltration type is more than 80% faster than that of transmission type and the depth of rainwater infiltration is less than 2.5m in this experiment.(4)The extension length of impervious membrane at the bottom of grass planting ditch has an effect on both the vertical infiltration depth and horizontal infiltration range of rainwater in loess,but it has a more significant effect on the horizontal infiltration range(with a good inhibition effect).The humidification settlement caused by rainwater infiltration in the transmission type is smaller than that in the stagnant type,and the subgrade settlement caused by rainwater infiltration can be effectively reduced by increasing the extension length of impervious membrane at the bottom of the trench.(5)During the construction of the grass planting ditch,it is suggested to eliminate the loess collapsibility within a certain range at the bottom of the stagnant type grass planting ditch or increase the extension length of the impervious membrane at the bottom of the ditch,so as to prevent the damage or functional failure of the grass planting ditch caused by the humidification settlement.At the same time,the supervision of the stagnant type grass planting ditch and the surrounding important buildings or structures should be strengthened in the engineering construction.