Deformation of rail transit infrastructure subjected to traffic loads considering bi-directional principal stress rotation (PSR)

Abstract

In engineering practice, soil is often subjected to complex loads, such as traffic loads, leading to complicated stress paths that include the principal stresses rotation (PSR). Under these complex stress paths, soil exhibits sophisticated stress-strain behavior. Over recent decades, significant research has been devoted to investigating the influence of PSR on the mechanical behavior of soils.
Traffic loading is a typical complex dynamic load. Under traffic loads, a soil element is subjected not only to vertical dynamic stress but also to dynamic shear stresses in two horizontal directions (typically the direction of travel and the direction perpendicular to it). This results in a bi-directional PSR. However, conventional geotechnical dynamic testing apparatuses, such as dynamic triaxial devices and Hollow Cylinder Apparatuses (HCA), have limitations in simulating this bi-directional shear stress. While dynamic triaxial devices generally cannot independently control shear in the two horizontal directions, the HCA, although capable of achieving continuous rotation of the principal stress axes, still falls short in simulating bi-directional shear stress.

This study employs the Variable Direction Dynamic Cyclic Simple Shear (VDDCSS) system, manufactured by the UK company GDS Instruments, to replicate the complex stress paths under cyclic traffic loading, including bi-directional PSR. The VDDCSS system utilizes three independent electro-servo actuators to apply dynamic loads independently along three orthogonal directions (one vertical and two horizontal). This effectively simulates the complex stress state induced in soil under actual traffic loading conditions, providing an advanced experimental means for investigating the mechanical response of soil under the influence of bi-directional PSR.

The Leighton Buzzard sand (Fraction E) was tested under cyclic loading.
Three series of experiments were conducted to investigate the mechanical behavior of soil under cyclic traffic loading in different scenarios according to the stress path extracted from the numerical simulations: a single-track single-tunnel subway, a single-track heavy-haul railway embankment, and a double-track heavy-haul railway embankment. Under drained conditions, cyclic traffic loads were applied to these three scenarios, and their long-term deformation behaviors were observed

In the subsequent discussion, the key parameters for evaluating the effects of traffic loads are the characteristics of vertical deformation and shear deformation.

Significant effects of bi-directional PSR were observed through experiments. From the perspective of traditional geotechnical engineering tests, each test was discussed, including stress-strain response, vertical deformation, and shear deformation.

Date of Award	18 Jul 2026
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Yung-Tsang Chen (Supervisor) & Dariusz Wanatowski (Supervisor)