## 3 External Loads over Haul Roads  
The vehicles considered in this article, shown in Table 1, are mining trucks that transport the material to the primary crushing area. The road along which they circulate, called a mining haul road (see Figure 14), is normally an exclusive road built with highly resistant materials [34]. Several layers of crushed gravel, pit-run gravel and sand are arranged. An example of a haul road section in shown in Figure 15.  
Currently, international standards and recommendations for calculation and design of buried steel pipelines only consider the effects of live loads on the pipe for HS-20 type vehicles whose load does not exceed 35 tons [1,2]. One of the main contributions of this study is to analyse vehicles with a weight much higher than the weight contemplated in  
Figure 14: Haul road design profile (Komatsu 980 t truck), (dimensions in meters). Figure 13: Validation results: circumferential deformations. FEM vs. experimental test (final stage of construction). the standards. Therefore, this article evaluates the behaviour of a group of pipes subjected to higher magnitude loads. The finite element calculation procedure described in Section 2 has been used for the study. Construction materials for haul road pavement require high durability. The determination of the height of the road layer depends on the vehicles that circulate on it. The elasticity modulus on the top layer (surface) is approximately 500 MPa, on the second layer (base) is in the range of 150 to 350 MPa and in the layer below the base (subbase) the value ranges between 100 to 150 MPa (Table 2). To simplify the parametric analysis, all layers with an elasticity modulus of 150 MPa are considered. This hypothesis is consistent with the fact that the thickness of the top layer is very small. The tire print has an elliptical shape. The model has been simulated according to the work developed by several researchers [35; 36; 37; 38]. Other authors, in order to simplify the calculation of the contact area, consider a circumference whose equivalent radius is half the real width of the tire [34]. To simplify the analysis, the tire print has been considered to be rectangular with a width equal to the width of the wheel \(A^{\prime}\) and length \(L\) (tire contact length). Its calculation is carried out using Equation (7), where:  
* \(a_{c}\) is the equivalent area of the tire print on the trench. It is determined using the equivalent radius \(r_{e}\) (which is half the width of the wheel);
* the width of the wheel is \(A^{\prime}\). \[L=\frac{a_{c}}{A^{\prime}} \tag{7}\]  
The Figure 16 shows the representation of the tire prints of the vehicle. For the vehicles used in this article, the front axles are single and the rear axles double. According to the manufacturers' technical sheets, the greatest load is exerted on the rear axle. Therefore, the contact pressure under the rear wheel area is taken into account. As described in Section 1 of this article, there are equations that estimate the surface loads of rectangular sections. These loads are applied on the buried pipe and that are a function of the burial height. [PERSON] [39] has validated, through finite element models, the Spangler equation, which does not depend on the soil properties, but only on the burial height of the pipe. \begin{table}
\begin{tabular}{c c c c c} \hline  & **Material** & **Thickness (m)** & **Bearing Capacity (MPa)** & **Young’s Modulus (MPa)** \\ \hline Surface & Gravel GW or crushed rock & 0.3 to 0.6 & 0.7 to 0.9 & Note 1 \\ Base & Gravel (GW) or pit run sand & 1 & 0.3 to 0.65 & 150 to 350 \\ Subbase & Gravel (GW) or till, mine spoil & 1.5 & 0.1 to 0.2 & 100 to 150 \\ \hline \end{tabular} Note 1: Consider 500 MPa for design.  
\end{table} 
Table 2: Minimum bearing capacity and Young’s modulus of haul road construction materials [34]. Figure 15: Typical section of a section of a haul road for 320 t trucks [4].