Abstract
The settlement of the widening of soft soil subgrade highways is typically associated with different treatment positions of cement mixed piles. In order to overcome this, in the current paper we employ the finite element method to simulate and analyze the influence of piles under an existing road slope and under an existing subgrade and new embankment on the settlement characteristics of the subgrade and foundation. In particular, we focus on the influence of the pile length and pile spacing on the subgrade and foundation settlements based on a northern high-speed reconstruction and expansion project. The subgrade and foundation soils in the finite element analysis are considered to be homogeneous, continuous, and isotropic elastoplastic materials. The Mohr–Coulomb ideal elastoplastic constitutive model is implemented as the constitutive soil model. The impact of piles under an existing subgrade and new embankment on the settlement is observed to be more significant than that of piles under the existing road slope. Moreover, the subgrade and foundation settlements increase with the pile spacing under the existing road slope and under the existing subgrade and new embankment. More specifically, an increase of the pile spacing from 200% to 400% of the pile diameter is associated with an increase in the maximum settlement of the foundation surface from 1.76 to 1.85 cm (existing road slope) and from 1.44 to 1.96 cm (existing subgrade and new embankment). In addition, the subgrade and foundation settlements decrease for increasing pile lengths under the existing road slope and under the existing subgrade and new embankment, the pile length increases from 4.7 to 9.2 m, and the maximum foundation surface settlement is reduced from 6.2 to 5.52 cm and from 9.73 to 5.43 cm, respectively. The results can provide reference for future subgrade widening projects.
Highlights
Advances in Civil Engineering reconstruction and expansion of the Shian Section project of Beijing, Hong Kong, and Macao and simulated the additional stress of the subgrade widening under varying settlements [10]
In order to analyze the influence of the cement mixed pile spacing on the settlement of the new and old subgrade, we investigate the following two conditions. (1) e pile spacing of the cement mixed piles under the existing road slope is fixed to 300% of the pile diameter, while the pile spacing of the cement mixed piles under the existing subgrade and new embankment varies
The foundation deformation is similar across different depths and the settlement curve follows an approximate basin-shape. e maximum settlement at the cross section of the subgrade appears near the toe of the old subgrade
Summary
Following a 7 m widening on both sides, the new subgrade has a height of 4.1 m, with a stone soil filling. E muddy clay foundation is reinforced by cement mixed piles of a 7.2 m length and 0.5 m diameter. The muddy clay foundation is strengthened by cement mixed piles with an elastic modulus of 100 MPa and Poisson’s ratio of 0.25 [26, 27]. 4.1 m cement mixing pile m 14 m old subgrade new subgrade transverse settlement observation tube medium sand the non-slope pile length. We adopt the Technical Specification for Construction of Highway Subgrades (JTG/T 3610-2019) and consider the actual construction of the reconstruction and expansion project to determine the filling thickness and filling time of each layer as 20–30 cm and 1-2 d, respectively [32]. Initial setting Final setting Soundness 3 days’ rupture 28 days’ rupture 3 days’ compressive 28 days’ compressive time (min) time (min) (mm) strength (MPa) strength (MPa) strength (MPa) strength (MPa)
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