Justification of the parameters of a flexible grillage to strengthen the soft foundations of the subgrade of high-speed highways

Abstract

The paper analyzes the determination of the parameters of a flexible pile grillage according to the British standard BS 8006 and according to the methodology set out in the “Manual for the design of the subgrade of roads on soft soils”. The BS 8006 methodology does not take into account the characteristics of the soft soil of the inter-pile space, while the methodology for designing the subgrade of roads on soft soils does not take into account the change in the load on the pile grillage from the height of the embankment. At the same time, the maximum tensile forces for the considered cases, obtained by various methods, turned out to be similar. The results of modeling the operation of a flexible pile grillage by the finite element method are presented. To assess the forces arising in the geosynthetic material of a flexible grillage, numerical modeling of embankments reinforced with CFG piles, sand drain piles, and Jet-Grouting piles was performed in the Plaxis software package. Modeling was carried out for embankments with a height of 6, 8 and 10 m on a soft foundation. In the course of modeling, the values ​​of forces in the geosynthetic material were obtained. The obtained values ​​of tensile forces in a flexible grillage with concrete piles of the CFG type, determined by numerical simulation, turned out to be approximately 2 times less than those calculated by analytical methods. The values ​​of tensile forces in the flexible grillage for Jet-Grouting piles and sand piles in a geotextile shell are approximately 1.8 times higher than the forces arising from the reinforcement with CFG piles. The influence of the characteristics of the soft soil of the inter-pile space on the values ​​of tensile forces in the flexible grillage has been determined. The tensile forces that occur in geosynthetics, in all the cases considered, do not exceed the allowable values. Therefore, it can be recommended as a flexible pile grillage for the subgrade of high-speed highways.