Research On The Reinforcing Design To The Subgrade Disease Of Dazhun Railway

Dazhun railway is located in a region with seasonally frozen soils. As such, the railway is exposed to severe and wide spread road diseases. Typical subgrade diseases such as frost heaving, mud pumping, subgrade settlement and other diseases had severely affected the safe and stable operation of the railway. A comprehensive treatment must be put forward to effectively solve the problem, and at the same time, not interfering with the operation of the existing railway.This article analyzed the mechanism of frost heaving, mud pumping and the settlement of subgrade from the aspects of soil, water and temperature. However, due to the difficulty in manually controlling the temperature condition, we proposed to tackle the problem from the angle of drainage and soil improvement.Dewatering holes are used with respect to hydrophobic drainage. Numerical analysis was carried out on the gravity drainage mode, which is then compared with the calculated results of negative pressure drainage method. This comparison established the advantage of negative pressure drainage over gravity drainage. Secondly, sensitivity analysis of the influence factors of negative pressure drainage treatment was performed by adjusting the dewatering holes about the embedment depth, spacing, aperture and the negative pressure. Finally, proving that the required drainage time for when the frost range for saturation is lower than the critical value of frost heaving of soil is most sensitive to the change of negative pressure, less sensitive to the change of drainage hole depth and spacing, and least sensitive to the change of aperture.On the aspects of soil improvement, a reinforcement scheme utilizing oblique lime soil piles is proposed. Numerical analysis was carried out on different reinforcement schemes, and the results were compared with the calculated results of unreinforced embankment analysis. The results showed that when the depth of reinforcement is equal, oblique piles provided superior support over vertical and horizontal piles. The sensitivity analysis of the influence factors on the performance of oblique lime soil pile composite subgrade were also conducted by changing the pile slope angle, pile length, pile diameter and vertical spacing. The test showed oblique lime soil pile composite subgrade deformation to be most sensitive to the change in pile length, followed by the change in pile diameter. Sensitivity to the change in the pile angle and distance were not obvious.Finally, this paper established the drainage design parameters and the design of oblique lime soil piles, recommending a comprehensive design scheme of Dazhun railways from the aspect of drainage and soil improvement.