| The Hanjiang to Weihe River Valley Water Diversion Project is known as the "South to North Water Diversion" project in Shaanxi Province,which is of great significance in solving the water supply shortage problem in Guanzhong plain urban agglomerations such as Xi’an.However,the loess yuan area in the north of the Weihe river where the Hanjiang to Weihe River Valley Water Diversion Project passes through has a relatively thick loess cover layer,and there is a potential risk of loess foundation humidifying during the operation of the water transmission pipeline project.In addition,earthquake disaster frequently occur in the loess area.Under the superposition of earthquake load and water,the loess foundation under the pipeline is prone to large deformation,which poses a serious threat to the safe operation of the project.Therefore,this article takes collapsible loess from a typical site of the north main line of the Phase II of the Hanjiang to Weihe River Valley Water Diversion Project as the research object.Through consolidated undrained dynamic triaxial tests,the dynamic characteristics and seismic deformation laws of loess under humidification are studied.The changes in hysteresis curves,backbone curves,dynamic shear modulus,damping ratio,and seismic subsidence coefficient curves of loess under different humidification states and consolidation confining pressures are analyzed.The dynamic deformation characteristics of undisturbed loess and remolded loess are compared and analyzed,and the effect of compaction treatment on seismic subsidence deformation is studied.Based on the Hardin-Drnevich model and elastic-plastic theory,a parameter formula is proposed to describe the dynamic deformation characteristics of undisturbed loess under the action of humidification.A modified Hardin-Drnevich model is established,and a formula for calculating the seismic subsidence coefficient of undisturbed loess is derived.A humidification seismic subsidence model of undisturbed loess is established.The research results can provide theoretical basis for the construction of the Hanjiang to Weihe River Valley Water Diversion Project.The main research achievements are as follows:(1)Under cyclic loading,loess exhibits obvious strain accumulation phenomenon.With the development of dynamic shear strain,the hysteresis curve gradually moves towards the direction of increasing dynamic shear strain,and the area of the hysteresis curves also gradually increase.The degree of strain accumulation in loess increases with the increase of water content and weakens with the increase of confining pressure.The strain accumulation and energy dissipation capacity of remolded loess after compaction are gradually weakened.(2)The backbone curves of loess are mainly hyperbolic,and its dynamic shear stress gradually increases with the development of dynamic shear strain,and finally tends to be stable.The maximum dynamic shear stress of loess gradually increases with the increase of confining pressure and decreases with the increase of water content.Under the same confining pressure and water content,the maximum dynamic shear stress of remolded loess is greater than that of undisturbed loess,and its strain hardening characteristics are more obvious.(3)The dynamic shear modulus of loess decreases continuously with the development of dynamic shear strain under different water content and consolidation confining pressure conditions.As the confining pressure increases,the dynamic shear modulus gradually decreases.As the water content increases,the dynamic shear modulus gradually increases.In the case of low water content and high confining pressure,the initial decay rate of dynamic shear modulus of loess is faster,and compaction treatment improves the ability of remolded loess to resist shear deformation.(4)The damping ratio dynamic shear strain relationship curves of loess with different water contents have different shapes: at low water contents,the relationship between damping ratio and dynamic shear strain of undisturbed loess is "S-shaped",and the remolded loess is "bell shaped".When the water content is high,the relationship between damping ratio and dynamic shear strain of both undisturbed and remolded loess are linear.However,the damping ratio of loess is not sensitive to changes in confining pressure,and the damping ratio of remolded loess is generally smaller than that of undisturbed loess.(5)Based on the Hardin-Drnevich model,a parameter formula considering humidification and different consolidation confining pressures are proposed,and a modified Hardin-Drnevich model is established.After verification,it is found that the relative errors between the predicted values of the model and measured values are less than13%.The modified model can effectively predict the backbone curves of undisturbed loess under humidification.(6)The overall seismic subsidence coefficient of loess increases slowly and then rapidly with the increase of dynamic shear stress.The seismic subsidence coefficient of loess significantly increases with the increase of water content and decreases with the increase of confining pressure.When the water content is low and under high confining pressure conditions,the seismic subsidence curves of loess are close to a straight line.Compared to undisturbed loess,the seismic subsidence of compacted and reshaped loess is significantly weakened.(7)Based on the elastic-plastic theory,combined with the parameters of the modified Hardin-Drnevich model,the formula of the seismic subsidence coefficient of undisturbed loess is derived,and a three-parameter model of undisturbed loess humidifying seismic subsidence is established.It is verified that the relative errors between the predicted values and the measured values are concentrated between 0.83 %-22.57 %,and the model can better describe the seismic subsidence characteristics of undisturbed loess under humidification.(8)The dynamic shear stress characteristics of the undisturbed loess seismic subsidence under the action of humidification and the seismic subsidence amount of the loess foundation of the water pipeline after humidification are calculated using humidifying seismic subsidence model of undisturbed loess.It was found that the characteristic dynamic shear stress of undisturbed loess increases linearly with the increase of consolidation confining pressure,and decreases nonlinearly with the increase of water content.The seismic subsidence of the loess foundation of the water pipeline increases exponentially with the increase of water content.In practical engineering,it is necessary to bury it as deep as possible and pay attention to the waterproofing of the base to reduce the impact of seismic subsidence on water pipelines. |
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