*3.2. Objective Function*

In this work, the initial construction cost *CC*RCRW of the RCRW was considered the single objective function of the optimization problem, to be minimized. The objective function was defined as follows:

$$\rm{CC}\_{\rm{RCRW}} = \rm{C}\_{\rm{c}} V\_{\rm{c}} + \rm{C}\_{\rm{st}} \mathcal{W}\_{\rm{st}} \tag{24}$$

where *C*c and *C*st are the cost per unit volume of concrete and the cost per unit weight of steel reinforcement, respectively; *V*c and *W*st are the volume of concrete and weight of steel per unit length of the retaining wall, respectively. It is worth noting that the cost of the formwork, casting concrete, vibration, and generally all related labor costs were taken into consideration in the parameter *C*c. In addition, the earthwork cost was not considered in the calculation of the total cost of the RCRWs.
