## 1 Introduction  
As a distinct type of soil, marine sedimentary soil is widely distributed in the foundations of marine engineering structures. With the extensive construction of offshore infrastructure and the rapid development of reclamation projects, engineering challenges related to the properties of marine soils continue to emerge. The compressibility of marine sedimentary, a critical soil property for evaluating foundation settlement, is influenced by a variety of factors, including mineral composition, soil structure, and pH value of seawater. Among these factors, the pore water salt concentration is noteworthy and cannot be neglected [1; 2; 3; 4]. Marine soil has long been subjected to a high-salinity seawater environment, with the chemical composition of its pore water solution closely resembling that of seawater. However, due to fluctuations in climate, topography, ocean currents, and other factors, the actual salt concentration of seawater can vary between 0.2% and 7% [5], rather than remaining constant. Therefore, it is of significant practical importance to investigate the influence of pore water salt concentration on the compression characteristics of marine soils. It has been reported that variations in pore water salinity can significantly influence the compression parameters of reconstituted marine clay [6]. Among different types of clays, montmorillonite-based mineral clays exhibit a particularly pronounced response to changes in pore water salt concentration. Studies have shown that as the pore water NaCl concentration increases, the liquid limit [7; 8] and water-holding capacity [9] of clays primarily composed of montmorillonite decrease. Consequently, the soil's and compressibility are also reduced [10; 11; 12]. [PERSON] et al. [13] and [PERSON] et al. [7] employed X-ray diffraction technology to reveal that, under the influence of chemical solutions, the development of the double-electron layer of soil particles is inhibited. The thickness of the adsorption double-electron layer becomes thinner [14], the repulsive forces between particles are reduced, the gaps between soil particles gradually decrease [15], and particle flocculation is promoted [16]. Ultimately, these changes lead to a reduction in the soil's water-holding capacity. However, for inactive clays dominated by illite and kaolinite, their physical and mechanical properties are relatively less affected by pore water salinity [17; 18], and they may even exhibit the opposite trend [19; 20]. The double-electron layer theory, being an idealized model, does not account for the mechanical structure of soil particles, making it unsuitable for this type of clay. To address this, some researchers have proposed alternative clay models. [PERSON] et al. [21] and [PERSON] et al. [22] suggest that the negative charge on the surface of clay minerals is influenced by the solution concentration. Under low and high salinity pore water conditions, clay particles form edge-to-edge and edge-to-surface structures, respectively. However, in pore water with moderate salinity, clay particles exhibit a surface-to-surface structure. This arrangement increases the pore size between aggregates while decreasing the pore size within the aggregates. In this clay model, the compression process primarily involves the reduction of pores between aggregates. Existing research on the salt effect primarily focused on how salt concentration impacts the engineering properties of clays with specific mineral compositions. However, studies examining the salt response of real marine sedimentary clays are relatively scarce [6; 7; 8; 9; 10; 11]. Moreover, the changes in the physical and mechanical properties of clay due to variations in pore water chemistry are not consistent across different studies, and the explanations for these phenomena remain inconclusive [21; 22; 23; 24]. Given these gaps, it is essential to explore the salt response laws that are applicable to the engineering characteristics of marine sedimentary soils.