# Sustainability Analysis of the M-30 Madrid Tunnels and Madrid Rio after 14 years of Service Life
## 2 The MIVES Method and Its Application to the Renovation of the South-West Section of M-30  
Considering the large number of heterogeneous factors that must be taken into account to perform this sustainability analysis, experience has shown the use of a multi-criteria decision-making method (MCDM) as the most suitable given that MCDM breaks down the problem studied into its elemental pieces so as to completely understand the evaluation process [25; 26]. It is also noticeable that the selected method must be versatile enough to be applied to the great complexity of the infrastructure when analyzing socio-economic and environmental factors [5]. Additionally, it has been stated that sustainable engineering is an adequate field to use MCDM [27]. There are a wide range of methods to assess the sustainability of a building or a civil engineering work, but they have different scopes and approaches [22; 25]. For instance, Life Cycle Assessment (LCA) [16; 22; 28; 29; 30; 31; 32; 33; 34] evaluates the sustainability of a building analyzing its environmental burden during its life cycle, namely, it considers the environmental inputs, outputs and impact during the life service of an infrastructure. Another kind of analysis is the one carried out by Life Cycle Cost (LCC) [16; 22; 35] which performs an economic study taking into account the purchasing and operating phases of the infrastructure in a period of time. Other complementary methods are: Life Cycle Energy Analysis (LCEA) [22; 36] which studies the energy inputs over the service life of a infrastructure; Material Flow Analysis (MFA) [22; 37] which analyses transformation, transport or storage of construction materials and Energy Flow Analysis (MEFA) [22; 38] which adds the energy flow to the study. However, previous researchers came to the conclusion that the methods mentioned above are not fully appropriate to evaluate the sustainability of infrastructures [26; 27; 39]. In addition, there are some MCDM used in the construction sector such as ANP, DEA/ELECTRE, TOPSIS, or PROMETHEE which are only used in some geographical frameworks [30; 31]. In this context, MIVES is a genuine MCDM as it combines a holistic discriminatory tree of requirements, criteria and indicators [5; 22; 40]; the value function concept [41] and seminars delivered by experts to evaluate the functions and weights using the Analytic Hierarchy Process (AHP) [22; 26; 42]. Therefore, this method allows researchers to obtain a scientific and sustainability-based rationale to make a decision between different alternatives [26]. Nevertheless, the main drawback of the method is that, as it involves an exhaustive and rigorous process and seminars delivered by experts on each field, it might not be suitable for urgent assessments [22]. Also, the MIVES method has already been used in several sustainability analysis of both architectural and civil works [16; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35], so taking into account the similarities between these projects and the case study of the M-30 burial, and considering the strengths of the method, MIVES was the chosen MCDM to perform this analysis. It is also remarkable that MIVES is the proposed method to evaluate the sustainability of concrete structures in the Spanish Structural Concrete Code EHE-08 [19; 22; 56; 57]. As mentioned above, the MIVES method combines qualitative and quantitative factors for sustainability assessments in order to obtain a single general and non-dimensional sustainability index (SI, [58]). Therefore, before starting the process, an awareness of the problem and solutions should be obtained [22; 23; 58]. Once defined, a holistic decision tree with three levels (that is to say, requirements, criteria, and indicators) is required as shown in Figure 2. The indicators are evaluated by using value functions which turn the qualitative factors into quantitative variables with the same unitsand scales.