Study On The Influence Of Road Sponge Biological Retention Facilities On The Stability Of Subgrade Slope

Road bio-retention facilities in sponge cities are important environmental protection infrastructure,which plays an important role in controlling road runoff pollution,reducing road runoff flood peak and prolonging the time of runoff flood peak.But road sponge biological stranded facilities set and its operation will affect the roadbed slope stability,because the sponge city construction in our country,the rise time is shorter,specific biological stranded facilities of subgrade slope stability,the influence mechanism is unclear,the existing in the construction of practical engineering application of biological stranded facilities more conservative,lack of effective theory as the technical support,Aiming at the above technical requirements,this paper uses the theoretical basis of environmental engineering and geotechnical engineering,and adopts the scientific research methods such as finite element numerical simulation analysis,orthogonal test design,data fitting and variance analysis.The influences of factors such as the width and depth of biological retention facility structure layer,rainfall intensity and edge slope rate on the hydrological parameters,mechanical phenomena and runoff control of the subgrade slope of sponge city road are systematically studied,and the prediction model of the hydrological parameters and mechanical phenomena characteristic objects of the subgrade slope is established.The evaluation method of the influence of biological detention facilities on the roadbed slope stability of sponge city is put forward,which provides theoretical basis and technical support for the road construction,planning and design of sponge city.The main research contents and conclusions are as follows:【1】The three dimensional finite element numerical model of sponge city road is constructed,and the influence law of biological retention facilities on hydrologic parameters and mechanical phenomena at different control points of subgrade slope is clarified.The results show that the hydrological parameters of the subgrade slope will increase under the condition of heavy rain,and the hydrological parameters of the soil under the sidewalk and the roadway will increase significantly under the influence of the biological detention facilities.Mechanics phenomenon in slope foot through the coupling of seepage field and stress field under the effect of stress concentration significantly increased,slope toe the first principal stress by compressive stress changes for the tensile stress,easy to make the tension failure of soil slope foot,biological stranded facilities of rainwater infiltration on slope stability of the foot of the failure mode for the horizontal slip damage;However,biological detention facilities had the greatest effect on the vertical displacement of the subgrade under the sidewalk and the roadway,indicating that the failure mode of rainwater infiltration of biological detention facilities on the stability of the subgrade under the sidewalk and the roadway was vertical settlement failure.【2】The influence law of structure of biological detention facility,rainfall intensity and side slope rate on the stability of subgrade slope with biological detention facility was studied.The finite element numerical simulation results show that the width of biological detention facilities has a certain increase on the hydrological parameters of the embankment slope.Compared with the side slope surface and the foot of the slope,the width of facilities at the bottom of the sidewalk and the roadway is more affected by the hydrological parameters.The horizontal displacement under the sidewalks and driveways is significantly affected by the width of the bio-retention facilities,but has little effect on the mechanical phenomena at other locations.In terms of runoff regulation,the larger the width of biological detention facilities,the greater the reduction rate of runoff water quantity and runoff pollutant SS.In terms of hydrological parameters,the influence law of biological detention facility depth is basically consistent with that of width,and the influence degree is lower than that of width.In terms of mechanical phenomena,the influence on the control points of the subgrade slope is not obvious,and the influence on the reduction rate of runoff water quantity and SS reduction rate of runoff pollutants is also not obvious.The effect of rainfall intensity on the hydrological parameters and mechanical phenomena of subgrade slope increases obviously.The increase of rainfall intensity increases the increase of hydrological parameters and mechanical phenomena.At the same time,the hydrological parameters and mechanical phenomena of slope surface and slope foot are more obviously affected by rainfall intensity during the whole rainfall process.The increase of rainfall intensity will advance the time of overflow phenomenon of biological detention facilities,and the reduction rate of runoff water quantity and runoff pollutant SS will change from increasing to decreasing at an earlier stage,and the decline rate is faster in the middle and later period of rainfall.The slope rate has a significant influence on the mechanical phenomena of the subgrade slope.The steeper the slope rate is,the larger the horizontal and vertical displacements of the subgrade slope are,and the increase degree of the horizontal displacements is greater than the vertical displacements.At the same time,the mechanical phenomena of the slope surface and the slope foot are more obviously affected by the slope rate than those under the sidewalk and the roadway.The edge slope rate has no obvious effect on runoff water quantity reduction rate and runoff pollutant SS reduction rate.【3】The evaluation method of the effect of biological detention facilities on the stability of subgrade slope is put forward and applied in practical engineering.Based on hydrological parameters affect the characteristics of pore water pressure and mechanical phenomena influence characteristics horizontal displacement orthogonal experiment design,using the finite element numerical simulation,combined with analysis of variance,the influence of subgrade slope hydrology parameters and mechanical characteristics of the sensitivity of various factors are studied,the results showed that slope foot pore water pressure affected by rainfall intensity is the largest,The pore water pressure under the sidewalk is most affected by the width of biological detention facility.However,the horizontal displacement of the two places is most affected by the slope rate,and the depth of biological detention facility has the least effect on the horizontal displacement.A prediction model of pore water pressure and horizontal displacement of sponge city roadbed slope based on BP neural network is established,and an evaluation method of the influence of biological retention facilities on the stability of sponge city roadbed slope is obtained by using the prediction model.The applicability of the evaluation method is verified by its application in practical projects.It provides a theoretical basis and application method for road slope stability design of high-fill sponge city in mountain city,and provides technical support for promoting the construction of whole-area sponge city and reducing urban runoff pollution load.