## 1 Introduction  
The word \"bentonite\" was first applied by [PERSON] (1966) to refer to Cretaceous clay deposits with highly plastic properties. The term was later redefined by [PERSON] and [PERSON] [PERSON] and [PERSON] (1966) to designate those clays produced by in situ alteration of volcanic ashes, with smectite as the main component. Subsequently, [PERSON] (1966) defined bentonite as that clay with a significant smectite content (specifically montmorillonite), regardless of its origin; this is the most widely adopted definition, especially in the radioactive waste management community. The problem of radioactive waste storage leads to the need to find safe containment systems that prevent the release and diffusion of radionuclides from inside the containers to the surrounding environment. In this sense, due to their physicochemical properties, such as low hydraulic conductivity, high specific surface, remarkable ion exchange capacity, swelling behavior, and high sorption capacity [PERSON] (1966), the use of an Engineered Barrier System (EBS) integrating compacted bentonite has aroused a strong interest in the last decades as a sealing element [PERSON] (1966). Thus, the main function of the bentonite barrier is to protect and isolate the canister containing the residues from any type of geochemical or physical stress to maintain its integrity. In addition, the bentonite works as a hydraulic barrier that limits the mobilization of radioactive contaminants that could be released if the metallic container fails. These functions can be enhanced through blending with other materials, such as sand-bentonite mixtures [4]. Among the different types of bentonites, the application of MX-80 or Wyoming bentonites (in honor of their origin) has been the object of study in several countries in EBS for radioactive repositories [6]. Particularly well known are the studies being carried out to use this type of bentonite as a barrier in KBS-3-type repositories, a deposition concept considered in Sweden and Finland. The waste is sealed inside metal canisters, which are deposited in vertical holes constructed at great depth, surrounded by compacted MX-80 bentonite, which, either alone or mixed with other filler materials, is also used to seal the access tunnel [5]. Although the properties of EBS-bentonites have been extensively studied, no systematic procedure has been proposed to characterize the stability of their macrostructure. Stability is considered to critically affect the long-term integrity of the compacted bentonite, which has motivated its experimental characterization by in situ tests such as the BeLLT (Bentonite Large Scale Load Test) and the BLL (Bentonite Long-Term Load Test), both within the framework of the full-scale emplacement experiment [7; 8]. These studies show a growing interest in defining a laboratory-scale protocol that ensures repeatability and contributes quantitative data toward the assessment of the effect of compaction on macrostructural stability. Several methods are currently in use, the suitability of which depends on the processes to be studied, since each methodology can provide different information [9; 10]. The most common methods are based on measuring the size distribution of the fragments or, more generally, macrostructural units (MU) generated after the application of a disaggregation effort. Such effort can be applied internally (e.g., by wetting) and also externally (mechanical agitation, tillage, etc. ), resulting in the fracturing of the MU. Accordingly, the failure areas provide relevant information about the voids, pores, and solid phases of the soil and its MU [11]. Most of these fragmentation procedures are performed in two stages. First, the MU are generated, and subsequently, a sieving measurement is performed. Two different methods of sieving are considered: dry sieving (the process is carried out in the air) and wet sieving (the process is carried out in water or another liquid) [12; 13].