Numerical investigation of the mechanical response of semi-rigid base asphalt pavement under traffic load and nonlinear temperature gradient effect

Understanding the structural behavior of layered asphalt pavements subjected to dynamic moving wheel loads is a crucial requirement for the future design of more-durable pavement structures...

Finite-Element Simulation of Instrumented Asphalt Pavement Response under Moving Vehicular Load

Problematic soils exist almost everywhere on the globe. State-of-the-art solutions to make civil engineering infrastructures built on them are still highly sought. The CFG (cement-fly ash-gravel) pile composite foundation system has been widely used in buildings, highways, railways, and bridge transition sections owing to its proven engineering characteristics in soft ground treatment. This paper discusses about the development and achievements of its engineering applications, along with possible future research directions. The remarkable evolution took place in the past to address projects’ strict differential and postconstruction settlement control requirements including embedding the geosynthetic layer into the load transfer platform and combining it with rigid slabs, as seen implemented in few CFG pile-supported embankments. It was also observed that the interaction of the existing CFG pile composite foundation with an adjacent new foundation pit excavation inevitably presents a complex soil-structure interaction mechanism among the fundamental components—the retaining wall, mat, piles, cushion, and soil.

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CFG Pile Composite Foundation: Its Engineering Applications and Research Advances

Railway transportation is one of the most advantageous modes of transportation because of its high capacity, which obviates the increasing demand for conveying passengers and cargo. However, high initial costs and ongoing maintenance costs (partially resulting from the degradation of the subgrade and embankments) are drawbacks. Besides, railway subgrade soil experiences a high impact load and alternate drying-wetting and freeze-thawing cycles. In order to counter these problems, various kinds of soil improvement have been employed to improve the engineering properties of soils and minimise embankment and subgrade degradation. Chemical, mechanical, and geosynthetic techniques are currently being used to improve railway embankments. Some methods, such as columnar systems and deep mixing, fortify embankment foundations or subsoil, while others (e.g. chemical binders) can be used as mixed material to stabilise embankments and subgrade soil to a shallow depth. Hence, this review paper first discusses the correlation between railway track elements, failures, and the degradation of embankments in railway networks, and then compares the soil stabilisation techniques from multiple aspects. 

Improved methods to prevent railway embankment failure and subgrade degradation: A review

Tunnel lining stiffness, grout strength and shield-driven speed are important parameters that influence ground surface settlement during tunnel excavation. Optimising these parameters would allow effective control of ground settlement during tunnel construction, specifically the maximum settlement. This paper investigated the influence of tunnel lining stiffness, grout strength and shield-driven speed on ground settlement in heterogeneous soil. Consequently, a 3D nonlinear finite element model was developed using Abaqus which accurately predicted the ground settlement during the construction of the Nanjing WeiSanLu tunnel. Furthermore, the influence of the shield-driven speed, modulus of elasticity of grout and tunnel lining stiffness on ground surface settlement was studied. Statistical analysis was performed to investigate the level of impact of each influencing factor and their two-way interaction on the maximum ground settlement. It was revealed that ground surface settlement is greatly influenced by the properties of tail voids grouting and stiffness of tunnel lining. The result also indicated that the relationship between the prediction factor and the maximum settlement on the ground differs according to the level of the studied factors.

Numerical Investigation of Ground Settlements Induced by the Construction of Nanjing WeiSanLu Tunnel and Parametric Analysis

The performance of railroad structure has a tremendous influence on the safety and stable operation of high-speed trains. Strong vibrations and the degradation rate of the track are the main factors affecting the transport safety of a railroad built over a weak soil. Geogrid reinforced embankment supported by pile structure is a new efficient construction technique used to ensure the stability and enhance the performance of the railroad system; but only a few studies are oriented to its behavior under train operation. This paper investigates the dynamic response of geogrid reinforced embankment supported by cement fly-ash gravel pile structure during a high-speed train operation. The establishment of a realistic simulation model for railroad subjected to a moving train load, is an important first step towards the reliable design of geogrid reinforced embankment supported by pile structure. Thus, a 3D nonlinear FEM has been established to simulate the instrumented Harbin-Dalian railway test section. Each train carriage was modeled as a transient dynamic load through a user-defined Dload subroutine. The developed model was successfully validated by the dynamic response recorded from the field test section. The improvement of the railroad structure by the CFG piles and geogrids contributed significantly to the reduction of the vibration in the structure, which attenuates 1.2 times faster with the structure depth, even under overload conditions. Moreover, the phenomenon of resonance observed when the train reaches speeds of 100 and 260 km/h were annihilated. The analysis of the stress distribution within the embankment revealed that a dynamic arch is formed in the embankment at 2 m from the ground. The stress onto the pile was 16 times greater than that acted on the soil and the tensile stress developed in the geogrid was high at the piles edge below. In addition, the coupling effect of geogrid with various tensile strengths and the piles with different strength grades indicated that the combination of a high-strength pile and geogrid significantly reduces the displacement gap due to the variation of train speed. As a result, the vibrations of the track were almost constant during the train operation; thus, ensuring comfort to passengers and reducing the risk of derailment.

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Muhan Yan

Papers

Dynamic Response Analysis of Geogrid Reinforced Embankment Supported by CFG Pile Structure During a High-Speed Train Operation