*2.1. Cost Function Formulation*

The concerned scheduling scheme is inherently a combinational optimization problem, aiming to minimize overall energy consumption, maximize transport capability, and reduce vehicle idle times, for Nstep tasks assigned to each of the Ntruck unmanned dump trucks. The cost function of the combinational optimization problem, as described in Equation (1), is a weighted sum of three terms: each truck's transport capability, energy consumption, and the total time spent when the last truck among all the Ntruck ones finishes its Nstep-th task. The three terms are summed up after being multiplied by weighting coefficients w1, w2, and w3: Ntruck

$$\sum\_{i=1}^{l\_{\text{track}}} \left( \frac{\mathbf{w}\_1}{Q\_i} + \mathbf{w}\_2 \times E\_i \right) + \mathbf{w}\_3 \times T\_\prime \tag{1}$$

where *Qi* denotes the gross transport capability of unmanned dump truck *i* after finishing all of its Nstep tasks, *Ei* denotes the consumed energies of unmanned dump truck *i* after it finishes all of its Nstep tasks, and *T* denotes the earliest moment that all of the Ntruck trucks finish their Nstep tasks. Details behind these variables are defined as follows.

#### *2.2. Transport Capability Composition*

In Equation (2), *Qi* is defined as the product of the basic loading capability of the truck *i* (i.e., Ci) and *N*unloading, the steps among all of the Nstep ones that involve unloading actions. Notably, *N*unloading is determined according to a specific solution.

$$Q\_i = \mathbb{C}\_i \times N\_{\text{unloading}}.\tag{2}$$

#### *2.3. Energy Consumption Composition*

Equation (3) shows that the energy consumption of each unmanned dump truck is composed of the energy consumption during the on-road cruising process, the energy consumption during the loading actions, and the energy consumption during the unloading actions:

$$E\_i = E\_{\text{cruisiring}} + E\_{\text{loading}} + E\_{\text{urloading}} \,\text{s} \tag{3}$$

Herein, *E*cruising sums up the energy consumption of unmanned dump truck *i* during its cruising process. *E*loading sums up the energy consumption of unmanned dump truck *i* during all of its loading actions. *E*unloading sums up the energy consumption of unmanned dump truck *i* during its unloading actions.

*E*cruising consists of two components: energy consumed by the drive system and that of the accessory system [32]. According to the classical vehicle dynamics principle [33], the energy consumption of an unmanned dump truck is defined as

$$E\_{\text{cruising}} = \mathbf{w}\_4 \times \mathbf{v}\_i^3 \times T\_{\text{cruising}} + \mathbf{w}\_5 \times \mathbf{v}\_i \times T\_{\text{cruising}} \tag{4}$$

where *T*cruising is the driving time of unmanned dump truck *i* to complete Nstep tasks, which is determined as per a specific solution candidate. v*<sup>i</sup>* denotes the average speed of unmanned dump truck *i* during cruising process. w4 and w5 are weighting parameters.

Equations (5) and (6) define the energy consumption during loading and unloading actions, respectively:

$$E\_{\text{losing}} = \mathbf{w}\_6 \times T\_{\text{losing}}.\tag{5}$$

$$E\_{\text{unloading}} = \mathbf{w}\_6 \times T\_{\text{unloading}}.\tag{6}$$

Herein, *T*loading is the loading time of unmanned dump truck *i* during loading tasks; *T*unloading is the unloading time of unmanned dump truck *i* during its unloading tasks. w6 is the coefficient that converts loading/unloading time to energy consumption.
