| Transport infrastructure construction has been one of indispensable part in modern industrialization,and the important guarantee of economic circulations both at home and abroad.In recent years,the rapid developed highway and high-speed railway have been basic pillars to support domestic economic growth and social development.The potential impact on public safety and social economics from transport infrastructures including highways and high-speed railways highlights the necessity and the significance of the long-term monitoring of subgrade performances in life cycle,and the identification of failure precursors as well as the early safety warning of subgrade internal failure.However,there are some technical challenges.The first challenge is that traditional monitoring methods mostly focused on external stability indicators such as settlements and lateral displacements,while the deformations inside subgrades are not valued.The second is that some measurement methods for internal deformations of subgrades have limitations to varying degrees in terms of in-situ and long-term monitoring.These limitations include poor durability,installation effect,high cost and low range.The third challenge is that traditional measurement methods could only provide single information of local deformation,which is difficult for distributed measurements of internal deformations,highly possible resulting in the missing,false or delayed warning of subgrade internal failure.This thesis offers an alternative for these challenges based on experimental study on an innovative sensor-enabled geobelts(SEGB),which is developed based on the tensoresistivity of conductive polymers.With multiple methods including theoretical analysis,laboratory tests,full-scale model tests,finite element methods and in-situ tests,SEGB is utilized to study the precursor identification and early warning methods of subgrade internal failure.The conductive polymer SEGB can realize distributed measurements for self-deformations when interacted with surrounding soil.Further,combined with multiple constitutive models including tensoresistivity model,full stress-strain constitutive model,SEGB-soil interfacial constitutive model and rheological constitutive model,the distributed measurement of SEGB could provide multiple information including stress distribution,strain distribution,displacement distribution and interfacial shear stress distribution.These multiple informations from SEGB are helpful to investigate the nonlinear behaviour distribution law in surrounding soils considering the viscoplastic deformation of SEGB.The deformation characteristics of SEGB before the failure are analyzed,and the methods of precursor identification and early warning methods for the subgrade internal failure is proposed from the perspective of long-term performances of subgrade.The main conclusions are drawn as follows:(1).Laboratory tests are carried out to investigate the full stress-strain property of SEGB,tensoresistivity of SEGB,SEGB-soil interfacial property and rheological property of SEGB.Based on test results,multiple constitutive models including the stress-strain constitutive models considering the viscoplastic deformation of SEGB,tensoresistivity constitutive model considering temperature,strain hardening and strain softening interfacial constitutive models and the rheological constitutive models developed on Kelvin elements are established,repectively.All these constitutive models are combined in the positioning,precursor identification and early warning methods for subgrade internal failure.(2).Incorporating the full stress-strain constitutive models of SEGB and interfacial constitutive models,load tranfer equations in strain hardening interfaces and strain softening interfaces are deduced and solved by finite difference method.Based on the distributed measurement and multiple information from SEGB,the validity of the load transfer equations is verified by pullout test results,and the distribution law of nonlinear behavior of SEGB in pullout process is investigated.(3).Pullout tests are carried out considering various effective lengths of SEGB and various normal pressures.The relationship between the distributed deformations of SEGB and the two failure modes-tensile break and pullout,is mainly investigated,and the deformation characteristics of SEGB under different failure modes are analyzed Based on the pullout test results,a critical state equation considering the effective length of SEGB and normal pressure is proposed to describe the transition between two failure modes-tensile failure and pullout.The critical equation could be utilized for preliminary prediction of failure mode of SEGB.(4).Benefitting from multiple constitutive models,the multiple information including stress distribution,strain distribution,displacement distribution and interfacial shear stress distribution are available.Taking advantages of the distributed deformations and multiple information of SEGB,the positioning,precursor identification and early warning methods of subgrade internal failure are proposed.Further,software and hardware of safety monitoring and early warning system is developed based on SEGB aiming at the long-term performance monitoring and failure warning of subgrade.The developed system achieves the functions of automatic collection,automatic transmission,cloud storage,real-time monitoring,backend querry and multi-level warning message of the distributed measurement data from SEGB.(5).With the applications of developed safety monitoring and early warning system,full-scale models of retaining walls reinforced by SEGB and in-situ field test of high fill quarry subgrade reinforced by SEGB are carried out to verify the proposed positioning,precursor identification and early warning method of subgrade internal failure.Finite element modelling is utilized and the rheological property of SEGB are considered in UMAT subroutine to analyze the long-term performances of subgrade and provide guidance for the long-term safety monitoring of the subgrade. |
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