Research On Subgrade Deformation Control Technology Of Widening The Existing Intercity Railway To Build High-speed Railway

The newly-built Zhongwei-Lanzhou Railway is connected to the Zhongchuan Intercity Railway as a new line project,which requires widening and filling of the existing Zhongchuan Railway subgrade.However,there are differences between the construction of the new line and the Zhongchuan Intercity Railway line design standards,subgrade filling material selection,and filling compaction control standards.Therefore,it is necessary to consider the impact of the filling construction process and the application of the new line train load on the existing subgrade.And seek a reasonable subgrade lap structure to improve the deformation stability of the existing-wide subgrade.Based on site investigation,construction theory analysis and finite element numerical simulation,this paper reveals the influence of subgrade lap structure form,construction method,and physical and mechanical properties of filler on the deformation of existing-wide subgrade.Based on the purpose of reducing the uneven deformation of the existing-wide subgrade,a subgrade lap structure form suitable for engineering practice is proposed,and corresponding suggestions are provided for the construction of the subgrade.The main research content and conclusions are as follows:(1)The ABAQUS finite element software simulates the layered filling process of widening roadbeds and reveals the law of influence of layered filling construction on the changes of existing roadbed.The results show that the lateral compression of the existing subgrade on both sides of the subgrade will increase with the increase of the filling height.The horizontal displacement and additional settlement of the shoulders on both sides of the existing subgrade are greater than the center of the subgrade,and when the height of the subgrade is 3m,the filling speed should be controlled,and attention should be paid to leveling of the subgrade junction during the filling process.At the same time,a reasonable subgrade lap structure should be set up,and the construction method and filler parameters of the widening filling construction should be optimized.(2)Construct different working condition models to analyze the influence of step excavation size on the deformation characteristics of existing-widening subgrade.The analysis shows that when the step height-to-width ratio is 1:1.5,the step height is set to0.6～1.0m,and the step width is 0.9～ 1.5m is good.Reasonable step size is beneficial to reduce the impact of the filling construction on the deformation of the existing subgrade,and reduce the deformation of the filling subgrade.The step size is too large or too small,which will have a negative impact on the deformation coordination of the roadbed.(3)Considering the two-stage state of the filling construction process and the application of the train load,the influence of the design form of the subgrade reinforcement on the displacement and deformation characteristics of the existing-wide subgrade is revealed.The results show that the recommended reinforcement spacing is 0.6m and the reinforcement length is 7m to 10 m,the bar modulus is 2GPa to 4GPa.The deformation,differential settlement,and horizontal displacement of the existing-broadband roadbed all decrease with the increase of the number of stiffened layers,the length of the stiffener,and the modulus of the stiffener,with the decrease of the stiffener spacing.The improvement of the subgrade deformation by the number of reinforced layers,reinforced spacing,reinforced length,and reinforced material modulus does not show a linear relationship,and there is a better reasonable interval.In terms of the position of reinforcement,as a subgrade reinforcement material,the geogrid has a deformation constraint influence area.Different reinforcement positions have different influences on the horizontal displacement and settlement deformation of the existing-wide subgrade.The reinforcement can be added to the corresponding area according to the actual situation to reduce the displacement and deformation.(4)Analyzing the influence of different stages of filling construction methods on the deformation characteristics of the existing-side-wide subgrade,the results show that the disturbance deformation of the existing subgrade by the symmetrical filling construction on both sides is less than that of the other side after the filling is completed on one side.In the selection of the filling method,the horizontal displacement and deformation of the existing subgrade are more sensitive than the additional settlement of the existing subgrade.When construction conditions are restricted and cannot be symmetrically filled at the same time,the existing roadbed deformation monitoring should be strengthened and isolation measures should be taken to ensure the safe operation of the existing line.(5)Considering the influence of the strength and rigidity of the widened subgrade on the deformation stability of the existing-widened subgrade,the results show that increasing the rigidity and strength of the subgrade effectively enhances the overall resistance to deformation of the subgrade and reduces the differential settlement of the existing-widened subgrade.But it does not change the relationship linearly.Subgrade filling works should use fillers with larger internal friction angles and appropriately increase the compaction of subgrade fillings.During the construction process,the moisture content and compaction coefficient of the paving fillers should be strictly controlled to improve the deformation stability of the existing-widened subgrade.