## 1 Introduction  
The safety concept of a geological repository for the disposal of radioactive waste is based on a multibarrier system that includes the natural geological barrier and engineeredbarrier system (EBS) [1]. The natural geological barrier is provided by the repository host rock and its surroundings, whereas the EBS comprises the waste form, waste canisters, buffer materials, and backfill [2; 3; 4]. The multibarrier system is expected to perform its desired functions to isolate waste from the biosphere. The buffer should have the following characteristics: low water permeability, microporous structure, canister support, high swelling capacity, colloid filtering, inhibition of microbial development, resistance to rock shear movements, retardation of radionuclides, self-sealing ability, and ability to effectively isolate waste for at least 100,000 years [1; 5]. The EBS must produce a tightness for canisters. Obviously, the embedded clay must be used to protect canisters from mechanical impact and must be very taut and almost free of groundwater permeation. These are the primary objectives of the buffer zone, and preventing the migration of discharging radionuclides is a secondary objective. Therefore, the disposal system mainly requires that the buffer material should maintain its tightness and ductility and should not shear or bend the disposal container. Currently, based on the SKB concept, the disposal system's buffer zone design has been proposed, which is called KBS-3 V [6]. The design principle was introduced as early as the late 1970s. Later, other countries, such as Canada, South Korea, Finland, and Japan, also implemented it as the standard concept. Moreover, it possesses good characteristics that allow intermittent waste placement, providing enormous time for preparing deposition holes and placing buffers and containers [6]. The manufacturing and placement of the buffers must ensure the high homogeneity and high density of mature clay for the ions to be transported by diffusion rather than flow, affording the standard that the minimum final density of the mature buffer zone should be 1950 Kg/m\({}^{3}\). However, literature indicates that the thermal-hydraulic-mechanical (THM) model, which is used to predict the soil mechanical properties of the buffer zone, states that the final density will be uneven, which has been verified by field tests. This is because internal friction prevents the initial, very significant density difference [6; 7]. Bentonite is used as a buffer material in most high-level radioactive waste (HLW) repository designs. Smectite clay is the main mineral component of bentonite and plays a key role in controlling the buffer's physical and chemical behaviors [6; 8]. According to the concept of Sweden and several other concepts, a buffer zone comprising highly compacted smectite clay blocks is used as the main component. This denotes that these blocks will expand via hydration and combine with water from the host rock to close the gap between the block and host rock, which is required to place the block. A question that is often speculated upon: are the joints between the blocks used as paths for rapid water inflow, causing local expansion and irregular uplift and fracture of individual block? Clearly, dry cracks are formed in the hottest part of the buffer zone after a block's hydration swelling. Another question is whether the density in the final maturation buffer is lower than the specified 1950 Kg/m\({}^{3}\). This risk can be minimized through careful material control, but risk still exists. In other words, water seeps into the waste canisters, which may cause high vapor pressure, causing the compression of the buffer material. [PERSON] [6] indicated that these phenomena are the evolution and possible deterioration of the buffer materials in radioactive waste disposal facilities [6]. To provide the necessary performance over a period of time, the buffer material is required to not undergo mineralogical change, desiccation, or cementation.