## 5 Summary and Conclusions  
This study investigated how diatom content, diatom crushing degree, and pore fluid ionic concentration influence the consistency limits of DS, along with the underlying microscopic mechanism. The main conclusions are as follows:  
Diatom frustules have a porous microstructure with massive skeletal and intra-skeletal pores, which provide space to store water. The crushed diatom fragments form chain-like connective skeletons and have no intra-skeletal pores. The microstructure of a DKM is characterized by diatom-kaolin aggregates, with the pores of the diatom frustules surrounded or filled by clay particles. The pore size distribution curve of kaolin changes from unimodal to trimodal with increasing diatom content because of the introduction of skeletal and intra-skeletal pores. With increasing diatom content in a DKM, the volume proportion of tiny and medium pores increases, and that of small pores decreases, which is closer to the pore characteristics of diatoms than those of kaolin. A DKM with a diatom content of over 60% is silt-dominated; otherwise, it is clay-dominated. With an increasing diatom proportion, the clay fraction of a DKM decreases approximately linearly, but its activity increases with the clay fraction. The diatom frustules are active silt-sized particles, in effect, like clay particles in the soil. The \(w_{\rm L}\) and \(w_{\rm P}\) values increase significantly with increasing diatom content, but \(I_{\rm P}\) remains almost constant. The extremely high \(w_{\rm L}\) and \(w_{\rm P}\) values of DS are associated with the intact diatom frustules: the \(w_{\rm L}\) and \(w_{\rm P}\) values of a crushed DKM are lower than those of an uncrushed one because the collapsed intra-skeletal pores in the former can no longer  
Figure 15: Classification of DS according to pore fluid sensitivity: (**a**) permittivity and conductivity of the samples; (**b**) electrical sensitivity of the samples. Data sources: DKMs [7]. retain water; however, the water stored in the intra-skeletal pores of diatom frustules contributes little to the plasticity of the soil. The Atterberg limits of kaolin are affected by NaCl concentration, whereas those of pure diatoms are almost unaffected. Similar to the consistency limits of pure diatoms, the \(w_{\rm L}\), \(w_{\rm P}\), and \(I_{\rm P}\) values for a DKM with even a small proportion of diatoms (20%) are insensitive to NaCl concentration. The plasticity and pore fluid sensitivity charts fail to classify DS accurately, especially when the diatom content is high. Further investigations are needed to establish a more reasonable classification system for DS, considering its unique microstructure and diatom content. This study considered the effect of geological burial in the marine environment during the forming process of DS by investigating the influences of diatom content, diatom crushing degree, and pore fluid ionic concentration on Atterberg limits. Additionally, the microstructure and pore characteristics of DS were examined via microscopic tests. Through the test results of Atterberg limits and microstructure of DS, this study revealed the micro-level mechanism of the high Atterberg limits of DS. In this study, only disk-shaped diatoms are considered, which means the results of this work may not apply to DS dominating other diatom species. More diatom species and other factors, such as complex mineral components of natural DS, should be considered in further research. Conceptualization, X.Z. and X.L. ; Methodology, Y.X., X.L. and A.Y. ; Validation, Y.X. ; Formal analysis, Y.X., G.W. and X.L. ; Writing--original draft, Y.X. and X.L. ; Writing--review & editing, X.Z. and G.W. ; Supervision, X.Z. ; Project administration, X.Z. ; Funding acquisition, X.Z. All authors have read and agreed to the published version of the manuscript. This work was supported by the National Natural Science Foundation of China (Nos. 41972285, 42177148, 41972293), the Youth Innovation Promotion Association CAS (No.