| Multi-layered soft grounds are one of the problematic grounds in subgrade engineering,its consolidation and stability have always been a focus in engineering.Based on the Padma Bridge project in Bangladesh,this paper contributes to the problem of embankments stability and its relationship with consolidation degree of multi-layered soft grounds,and the theoretical analyse of vertical consolidation of multi-layered soft grounds and its overall stability analysis method of embankment-multi layered soft grounds considering the consolidation degree are studied via one-dimensional consolidation theory,limit equilibrium method and numerical simulation.The main research results are as follows:(1)A theoretical analytical method for one-dimensional consolidation of multi-layered soft grounds is established.Based on the basic governing equation of vertical consolidation of two-layered grounds,vertical consolidation problem of three-layered and four-layered grounds are extended and analyzed via its boundary conditions,interlayer continuity conditions and initial conditions,and the theoretical calculation formula is derived.For multi-layered soft grounds under the load of railway embankment,the excess pore water pressure increases first and then decreases in a "step type" with the increase of time.Analysis results of practical example shows that the theoretical calculation is consistent with the distribution pattern of excess pore water pressure and consolidation degree simulated by FLAC3 D,and the results are within 15%.(2)The method for stability analysis of embankment-multi layered soft grounds considering the consolidation degree is proposed.Based on the effective stress principle and the method of plane stress state analysis,the function expression of shear strength,consolidation degree and direction of failure at any point in grounds is derived,and the function expression is introduced into three classical section methods,Fellenius method,simplified Bishop method and Morgenstern-Price method,by limit equilibrium analysis,to form the embankment-multi layered soft grounds stability analysis method.Analysis results of practical example shows that the factor of safety calculated by Bishop method is 23% higher when the consolidation degree is 90% than when the consolidation degree is unconsolidated.The factor of safety of Morgenstern-Price method is closest to the numerical simulation value,and the deviation between the two is less than10%.(3)The differences between the proposed method and the current railway standard method and the reasons are compared and analyzed.Compared with the standard method,the results of the proposed method are consistent only when the consolidation degree reaches 90% or above.As the consolidation degree decreases,the factor of safety by proposed method is significantly higher than that of the standard method.The reasons for the difference are as follows: on the one hand,in the case of long embankment construction process,the shear strength index of foundation soil in this paper is taken as consolidation fast shear value,which is usually greater than the quick shear value of standard method;On the other hand,when calculating the strength increase of the sliding surface caused by consolidation of grounds,only the gravity of the sliding surface passing through the corresponding embankment filling is considered in the standard method,and the influence of the gravity of the grounds in the section is ignored,which is fully considered by the method in this paper.(4)The influences of cohesion,internal friction Angle,slope ratio,embankment height,grounds thickness,transmission coefficient and consolidation coefficient on the factor of safety of embankment-multi layered soft grounds and the most dangerous slip surface are given.For multi-layered soft grounds,the thickness of the ground determines the distribution pattern of the most dangerous slip surface.When the surface grounds thickness exceeds a certain small depth,the most dangerous slip surface only passes through this ground.With the increase of transmission coefficient and consolidation coefficient,the factor of safety of embankment-multi layered soft grounds increases,and the depth of the most dangerous slip surface becomes shallow.Compared with transmission coefficient,consolidation coefficient has more obvious influence on the factor of safety of embankment-multi layered soft grounds and the most dangerous slip surface.Analytical method of vertical consolidation degree of railway embankment multi-layered soft grounds and the overall stability analysis method of embankment-multi layered soft grounds established in this paper can provide theoretical guidance and reference for practical engineering,which has important theoretical significance and application value. |
