Study On The Design Parameters Of Jet Grouting Piles To Control The Settlement Of Existing Subgrade Subjected To Train Speed Increasing

The design standards of railway subgrades built early in China were relatively low.As the speed of trains continued to increase,the existing subgrade settlement problems became more and more serious,and the corresponding reinforcement measures emerge in large quantities.Among them,the high-pressure jet grouting pile construction method is simple and does not affect the normal operation of the line,and is widely used in practical engineering.However,the mechanism and law of subgrade reinforcement by jet grouting pile is not perfect,it is necessary to further study its controlling law of the subgrade settlement and explore design and improvement scheme for it.This paper based on the subgrade settlement treatment engineering in the west section of the Lan-Xin Railway,combines geological survey and experimental monitoring data,and the following four aspects are studied by numerical method:(1)The numerical simulation model of the subgrade in the test section is established.First,the settlement law of the original subgrade is calculated and analyzed,and then the effects of the lateral limit frame hoop,the frame anchor cable and the high-pressure jet grouting pile to control the subgrade settlement under the condition of increasing speed are calculated and analyzed,and the corresponding selection suggestions are given.It is found that the settlement increases linearly with the increase of train speed before subgrade reinforcement,but the increase rate is different.The rotary jet grouting pile has significant advantages in strengthening the existing subgrade.(2)Under different speed-up conditions,the paper makes a detailed sensitivity analysis of the reinforcement parameters of the inclined jet grouting pile,including the vertical inclination,pile length,pile diameter,pile spacing and different layout forms,etc.,nearly100 geometric models have been established and more than 400 working conditions have been calculated.It is found that in order to improve the reinforcement efficiency,the length of the inclined jet grouting pile should not exceed 10 m,and the optimal vertical inclination is related to the speed-up of the train.When the speed of the train is raised to less than about140 km / h,the optimal vertical inclination is about 80 °,while when the speed of the train is raised to about 160 km / h or higher,the optimal inclination is about 70 °.When the pile arrangement changes from fine to coarse,the subgrade settlement changes decrease first and then increased.Under the condition of controlling the displacement volume of piles,the optimal design parameters such as pile diameter and pile spacing are obtained.(3)In order to eliminate the triangle soft subgrade in the lower part of the ballast,the horizontal jet grouting pile is used to strengthen the road base.Under different speed-up conditions,the control variable method is used to carry out a detailed sensitivity analysis on the reinforcement parameters of horizontal jet grouting pile,including pile length,pile diameter,pile spacing and different layout forms.More than 80 geometric models have been established and more than 300 working conditions have been calculated.And the limitations of horizontal jet grouting pile are analyzed in combination with specific construction.It is found that in order to improve the reinforcement efficiency,the length of horizontal jet grouting pile should not exceed 6m.When the pile diameter is less than 0.2m or the pile spacing is more than 2m,the reinforcement effect is not obvious.The number of rows should not exceed 2.When strengthening the low embankment,attention should be paid to the prevention and control of slurry seepage at the top of the subgrade.(4)In view of the advantages and disadvantages of the oblique and horizontal jet grouting piles,this paper explores the measure of the combination of the oblique and horizontal jet grouting piles,and based on the limitations of the construction of the horizontal jet grouting piles,further optimize the measure through adding the horizontal steel pipe,more than 60 geometric models have been established and nearly 300 working conditions have been calculated.It is found that the combined jet grouting pile can effectively reduce the area of triangle blind area under the reinforcement of oblique jet grouting pile,and break through the limitation of strengthening subgrade base with horizontal jet grouting pile.The optimal combination design is basically the combination of the optimal design of oblique and horizontal jet grouting pile.For the low embankment,the horizontal steel pipe can be added to improve the reinforcement efficiency by about 80%,but after the improvement,the slope toe uplift increases slightly,the maximum amplitude is about 0.5mm.