Reseach On Creep And Pavement Failure Characteristics Of Soft Soil Roadbed With Inclined Hard Layer Or Rock Layer

Highways along the coast,along the river,along the lake,or along the depression often encounter with soft soil foundations where there is inclined hard layer or a step under it.Due to the poor engineering properties and obvious creep of soft soil,the soft soil foundations with inclined hard layer or a step will change the thickness of the soft soil.And this will lead to excessive uneven settlement,excessive lateral displacement,and excessive road structural stress on the road which is building on the soft soil.This paper takes a road along the coast of eastern Zhejiang,which is built on the soft soil foundations with inclined hard layer and a step,as the research object.Field investigation,theoretical analysis and numerical calculation were used to study the creep of soft soil foundations with inclined hard layer or a step,and the stress of a road which is built on the soft soil.The main research contents include the following aspects.Firstly,according to the mechanism and characteristics of soft soil creep and the theory of viscoelastic mechanics,a suitable viscoelastic constitutive model is used to fit the constitutive model of soft soil creep which is taken from a certain coastal area of eastern Zhejiang Province.The relevant parameters of the soft soil are obtained,which provide the basis for the theoretical derivation and numerical simulation.Secondly,using the Winkel foundation model,the variable thickness of the viscoelastic foundation is transformed into the uniform thickness viscoelastic foundation whose relevant ground parameters is changed by assuming that the ground reaction coefficient of the viscoelastic foundation in the Laplace space changes with the thickness of the viscoelastic foundation.Simultaneously,the cross section of an infinite long road is treated as a beam on a variable thickness viscoelastic foundation and a finite length road is treated as a plate on a variable thickness viscoelastic foundation,then the corresponding deformation analysis is performed.The derived content includes:(1)Under the Laplace space and the actual conditions,the analytical solution for the simply supported elastic beam on the viscoelastic foundation with variable thickness,which is subjected to uniform load,is derived respectively.The influence of the slope of the soft soil base and the loading time on the deflection of the beam is analyzed.(2)Under the Laplace space condition,the solution of elastic plate on variable thickness viscoelastic foundation,which is subjected to uniform load,is derived,then the numerical solution is given by the inverse Laplace numerical transformation method.Thirdly,by establishing a numerical analysis model of the soft soil foundation with inclined hard layer,the settlement of road surface obtained by numerical analysis and theoretical solution results of beams on variable thickness viscoelastic foundation are compared,and the effects of the average depth of soft soil,the load time and the slope of the underlying hard layer on the creep of soft soil foundation and the stress of pavement structure are discussed.The results show that: the numerical analysis results are in good agreement with the analytical solution of the beam on the variable thickness viscoelastic foundation;the inclined hard layer which is under the soft soil layer will increase the uneven settlement of the subgrade,the uneven settlement of the soft soil foundation,the lateral displacement of the soil which is located at the foot of the road on the deeper side of the soft soil,the tensile stress of the upper layer of the pavement structure and the tensile stress of the base layer;when the depth of the soft soil layer is greater than a certain depth,the influence of the inclined hard layer on the road deformation can be ignored.Finally,according to the field investigation of the researched section and the engineering geological exploration report,the three locations where the steps may appear are analyzed.By establishing three-dimensional numerical analysis models,the soft soil foundation with a step and the soft soil foundation with inclined hard layer and step are analyzed.The creep of soft soil foundation and road structure stress under this terrain condition are analyzed.And according to the road deformation and the stress distribution of the pavement structure,the causes of the disease in the road section studied in this paper are analyzed.The results show that: when the steps are in different positions,the location of the cracking of the surface layer and the cracking of the base layer are different;the soft soil foundation with inclined hard layer and step under it will result in greater uneven settlement and uneven lateral displacement of the shoulder;thereby aggravating the deformation and damage of the road;the distribution of the disease,which is caused by the soft soil foundation with inclined hard layer and step under it,is similar to the soft soil foundation with only step under it;the reason for the occurrence of cracks and guardrail offsets in the research section is that the hard layer under the soft soil layer is inclined and there are steps,the slope is about 9%,and the step is located near the position B.