## 1 Introduction  
The increasing number of catastrophic accidents in tailing storage facilities (e.g., tailing dams or dry stacks) highlights the need to reinforce these structures. The use of heavy ground improvement technologies such as Jet Grouting or Dynamic Compaction is not possible in these structures due to the risk of static liquefaction induced by vibrations. The reinforcement of existing tailing deposits at risk or the improvement of dry stacks can be performed by building external structural zones capable of containing the possible liquefaction failure of the unstable material. One possibility is to build those structural zones with cemented filtered tailings, improving stability and avoiding the migration of fine particles to the bottom part of the embankment, where, due to very high overburden stresses, they tend to contract upon shear being very prone to liquefaction [1]. [PERSON] et al. [2] proposed the use of Portland cement to stabilize dry stacks. However, the use of Portland cement (OPC) in large-scale projects is environmentally criticized, as its production is highly energy-intensive, it requires a significant number of natural aggregates, and it is responsible for a large part of world's greenhouse gas emissions. Alternative binder research is increasingly moving towards replacing OPC in a significant part of future binder applications [3]. Alkali-activated binders (AABs) can significantly increase the strength and stiffness of stabilized soils not only at the laboratory scale [4,5] but also in large-scale tests [6]. AAB is generated by the reaction of a precursor (e.g., aluminosilicate) with an alkaline solution (activator). Since industrial by-products (such as ashes or slags) can be used as precursors, the binder's global-warming potential is reduced, and the circular economy is favored [7]. AAB has been used to recycle tailings into several applications [8] not only in cement and mortars [9] but also for more geotechnical problems such as backfill or cover materials [10], road base courses [11], or tailing-binder mixtures for stacking [12]. As highlighted by [PERSON] [13], in the cases where mine tailings exhibit a low level of reactivity to be used as precursors, some pre-treatment methodologies (thermal treatment, mechanical activation, alkaline fusion, etc.) or additional precursors (e.g., ashes, slags, metkaolin, etc.) can be used to enhance alkaline activation. However, the AAB binder optimization can take a significant experimental effort especially when the number of variables is large. To overcome this limitation, [PERSON] et al. [14] used machine-learning and data-transformation methods to predict the strength of an AAB made with tailings, with fewer experiments. A generalized application of AAB in soil improvement requires a rational methodology to define mixture dosage depending on the desired performance and in situ conditions. For soils stabilized with OPC, a ratio between porosity and volumetric cement content was developed [15,16] called the porosity cement index. [PERSON] et al. [17] applied this index to gold tailing-AAB mixtures, and [PERSON] et al. [18] also used this index to compare three types of binders to stabilize iron tailings. However, in these works, there was no development of a binder index capable of adjusting the AAB components to tailings in an in situ water content, as this variable was fixed. This is essential because, in mining operations, the tailings conditions may vary significantly [19]. Statistical models based on the Design of Experiments [20] have been applied to cementitious materials [21], to soil-cement mixtures [22], and to AAB-tailing mixtures [23] to reduce the number of experiments but not with the purpose of obtaining a mixture index that could summarize the contribution of each AAB component (precursor, alkaline activator, tailings, and water).