Research On Influence Of Gravel Pile Group On Hydrothermal Condition And Deformation Of Highway Foundation In Permafrost Swamp

This dissertation aims to explore the relationship between the stress field,the moisture field and the temperature field in the process of permafrost degradation over time when the gravel pile group in the warm permafrost swamp area treats the highway foundation.Analyze the effect and influence of gravel piles on the permafrost in the degraded area of warm permafrost.First,based on the assumption of continuous porous media and Biot’s consolidation theory,the two types of stress field governing equations are derived based on the assumption of large strain and small strain respectively,combined with the three-dimensional unsteady heat transfer equation considering convective heat transfer.The governing equations of the hydro-thermal-mechanical coupling model describing the physical field changes of the warm frozen soil are established,and the multi-physics field is unified.In view of the characteristic that the stiffness of warm frozen soil is more sensitive to temperature changes,the stress field parameters of the frozen part are further refined,and the stress-temperature coupled damage constitutive model of warm frozen soil is established.Considering the deteriorating effect of temperature changes on the stiffness and strength of warm frozen soils,a statistical damage model based on Weibull distribution is used to establish the stress damage factor,and the temperature damage factor is determined by the degree of attenuation of the initial elastic modulus caused by temperature.The stress damage factor and the temperature damage factor are coupled by the compound damage factor.Through frozen sand and frozen silty clay,the accuracy of the prediction results of the constitutive model for strain-softening materials and strain-hardened materials was verified respectively.At the same time,two methods for solving the shape parameters and scale parameters of the stress damage factor are derived,and the parameters obtained by different methods are respectively brought into the constitutive model calculation,and the results are compared with the measured stress-strain curve.The influence of the two parameters on the final prediction results of the constitutive model is analyzed,and the results show that the semi-theoretical and semi-fitting method has certain advantages compared with the full-fitting method.Furthermore,through the secondary development of general multi-physics finite element software,the hydro-thermal-mechanical coupling model is numerically realized.A triaxial test with constant axial pressure,which controls the temperature change of the confining chamber,is used to verify the validity of the prediction results of the hydro-thermal-mechanical coupling model.Comparing the three sets of experimental results of different degrees of axial deformation caused by different deviatoric stresses,the necessity of considering the geometric nonlinearity in the governing equation of the model stress field is demonstrated.Through the simulation results,the interaction of the three physical fields in the process of thawing and consolidation of warm frozen soil is analyzed,and the dynamic balance,mutual restriction and mutual promotion among them are discussed.Finally,through the aforementioned hydro-thermal-mechanical coupling model,a simulation analysis of an old road widening project near Sunwu County on the Bei’an-Heihe section of the G1211 expressway was carried out.The validity of the simulation results is verified by the measured settlement data and ground temperature data.The simulation results are used to discuss the relationship between the internal stress field,moisture field and temperature field of the foundation over time.Comparing the simulation results of untreated ground with gravel piles,the impact of gravel piles on the physical fields of warm and ice-rich permafrost foundations is further discussed.Through the above analysis,the mechanism of the gravel pile group is explained.Through multi-physics coupling analysis,it is concluded that the impact of gravel piles on warm permafrost foundations mainly includes the following three aspects:accelerating the dissipation of excess pore water pressure;improving the integrity and stiffness of the foundation;accelerating the initial melting of warm permafrost,and will not cause long-term disturbance to the ground temperature field.At the same time,it is demonstrated from the numerical level,which provides theoretical support for its application in permafrost degradation areas.