## 1 Introduction  
Brake failure in heavy trucks significantly contributes to severe traffic accidents [1]. A type of auxiliary lane, referred to as a truck escape ramp (TER), has been developed to mitigate these accidents. Figure 1 illustrates the fundamental design of the TER, which aims to decelerate trucks through the rolling resistance induced between the truck tires and the arrester beds, typically composed of pebble aggregates. Since the construction of the first TER in California, research on TERs has mainly focused on predicting brake drum temperatures [2], determining truck departure angles [3], exploring alternative materials for arrester bed pavements [4] and other related aspects. However, a significant knowledge gap exists regarding the load-bearing capacity of irregularly shaped, randomly distributed pebble aggregates in arrester beds, which directly influences the safety performance of trucks navigating through these beds. Figure 1: Truck escape ramp. Advancements in computational technology have significantly enhanced the recognition of the discrete element method (DEM) as an exceptionally effective approach for investigating interaction mechanisms within pebble aggregates [5]. The DEM leverages Newtonian mechanics to analyse the contact forces amongst these elements by representing particles as discrete entities, offering a detailed perspective at the particle level. This method utilises time steps to accurately compute the resultant forces and motions of particles, thus facilitating an extensive understanding of their dynamics. The DEM, originally developed by [PERSON] to address rock mechanics [6], has been extensively applied across various fields. The DEM application spans from analysing road materials in highway engineering [7; 8], to investigating soil interaction mechanics [9; 10; 11], to constructing simplified models for trucks on roads with discrete pebble surfaces [12; 13]. This diverse application spectrum not only demonstrates the DEM's versatility but also significantly underscores its efficacy in assessing the load-bearing capacities of pebble aggregates. The DEM provides a framework for the construction of particle shapes through three principal methodologies. The fundamental element construction method (Figure 2a) [14] converts basic geometric shapes, predominantly spheres, into diverse forms, such as triangles, cylinders and ellipsoids. This method enhances computational efficiency by lowering the computational requirements. Nonetheless, the application of the DEM is typically confined to regularly shaped pebbles, necessitating precise adjustments to the software's contact parameters for accommodating the varied geometries of different pebbles. The tangent element construction method (Figure 2b) [15] facilitates the modelling of intricate particle shapes with a precision that is dependent on the quantity of the basic elements utilized. This dependency significantly influences the computational load required for the modelling process. The overlapping element construction method (Figure 2c) [16] constructs the desired object by stacking basic elements. This approach skillfully balances computational efficiency with modelling precision. However, this approach demands careful consideration of the algorithm for computing the coordinates of these basic elements. Experimental methodologies play a crucial role in validating numerical simulations, especially in the domain of DEM simulations [17]. These methods are essential for calibrating and verifying the accuracy of DEM simulations, ensuring the reliability of their outcomes. The triaxial compression test [18; 19] provides a detailed assessment of the pebble properties and their interaction dynamics. However, the effectiveness of this test in measuring the load-bearing capacity of pebble beds is limited due to the potential interference from the boundary walls. The shear test method [20; 21] effectively examines the influence of pebble attributes on contact mechanisms.