Study On Seepage Failure Mode Of The Double-Deck River In Sponge City Under Different Drainage Measures

The double-deck river is a new type of urban river.It absorbs the construction concept of storage and drainage of the sponge city,and has unique advantages in urban river regulation.Seepage failure is a potential threat to the safety of the double-deck river.Based on the River control project in Longzhou Bay,Banan District,Chongqing,this paper studies the seepage failure mode of the double-deck river under different drainage measures through theoretical analysis,indoor test and numerical simulation.The main research contents and related research conclusions are as follows:?1?By consulting relevant documents and referring to the engineering examples,the basic characteristics of the double-deck river are studied,and the functions,applicable conditions,section features and seepage prevention and drainage measures of the double channel are described in detail.?2?Based on the seepage theory and the theory of seepage deformation,combined with the structural characteristics of the double-deck river,the main factors affecting the seepage stability of the double-deck river and the main forms of the seepage failure in the double-deck river are systematically analyzed.?3?The backfill soil in the construction site of the River control project in Longzhou Bay,Banan District is selected as raw material,and the permeability characteristics of backfill soil are investigated in laboratory.It is concluded that the degree of compaction has a great influence on seepage properties of backfill soil..When the compaction degree reaches 95%,the permeability coefficient can reach 10^-4cm/s magnitude,critical gradient is about 1.0,the maximum damage gradient is about3.0.With the improvement of the compactness,the seepage failure type of transitional soil can be transformed from piping types into soil flow.?4?Based on unsaturated seepage theory,three-dimensional and two-dimensional seepage analysis of the double-deck River under different drainage measures is carried out by using ABAQUS and GeoStudio finite element software.The following conclusions are drawn:?1?The direction of cross section is the main direction of seepage.?2?In the absence of seepage prevention and drainage measures,the seepage of the upper course leads to the continuous rise of the groundwater level and the larger pore water pressure on the outside of the box culvert,which is not conducive to the stability of the structure of the box culvert,and the contact surface between box culverts and backfill soils is at risk of contact erosion.?3?The drainage holes are arranged on the side wall and roof of the box culvert,which is beneficial to reducing the groundwater level and reducing the seepage pressure on the outside of the box culvert,but the hydraulic gradient at the outlet of the drainage hole exceeds the impervious critical hydraulic gradient of the backfill soil,and there is a danger of escaped seepage failure.?4?The arrangement of graded crushed stone drainage body on the outside of the box culvert is beneficial to further improve the drainage capacity of the box culvert,reduce the groundwater level and reduce the hydraulic gradient of the seepage flow,but there is still a risk of seepage failure at the foot of the upper river bank slope and the drainage orifice of the drainage hole of the lower box culvert.?5?Laying the geomembrane in the upper channel can significantly reduce the leakage,effectively control the groundwater level and reduce the hydraulic gradient of the percolation outlet.The hydraulic gradient of the seepage flow can be controlled within the allowable range of safety,which is beneficial to the landscape of the upper river and the seepage stability of the backfilling area.?5?On the basis of the results of indoor test and numerical analysis,the prevention and control measures of seepage failure in double-deck river are discussed,and the four aspects,such as anti seepage ability,seepage prevention measures,drainage measures and the filtration facilities for percolation outlet,are put forward to prevent the seepage failure of the double-deck river in the design and construction.