## 1 Introduction  
In the Loess Plateau of China, the loess primarily consists of silt-sized sediments with a highly porous and unstable structure, formed from the accumulation of wind-blown dust [1, 2, 3]. The region is characterized by intricate valleys and scarce land resources with severe soil erosion [4]. Nowadays, land demand for accommodating the increasing population and for agriculture has been rising, exacerbating conflicts over limited land availability in gullies and ravines. To achieve sustainable socioeconomic and agricultural development on the Loess Plateau, projects such as the mountain excavation and city construction (MECC) project, and the gully management and land reclamation (GMLR)project, have emerged [5; 6; 7; 8]. MECC involves cutting down mountains, filling in gullies, and creating new land to expand urban areas, during which the soil filling in the gully is carefully compacted (Figure 1a). GMLR involves new methods for slope management and soil conservation in the hilly gully, primarily using modern machinery for slope cutting, gully filling to make new arable land, complemented by drainage channels and slope protection measures (Figure 1b). The aforementioned measures are significant initiatives to increase urban/arable land resources, alleviating the pressure on urban/arable land use [9]. However, these projects have disrupted the hydrogeological and engineering geological balance, leading to a series of geotechnical issues such as differential settlement [10; 11; 12], highlighting the necessity to investigate the macro-level hydraulic and mechanical behavior of the remolded loess [8; 13; 14; 15; 16; 17; 18]. The remolded loess of backfilled area which is excavated from intact loess of excavation area in the MECC project and GMLR project is a special type of remolded soil. In the construction process, the remolded loess underwent operations of layered excavation and mechanical compaction. At the same time, natural intact loess from different locations and different age strata were mixed together and then directly compacted into new remolded soil layers. Since the newly compacted loess layer has not undergone long-term geological evolution after artificial filling, the characteristics of remolded loess have significant heterogeneity compared with natural intact loess. Recently, numerous studies have investigated the hydraulic and mechanical properties of both intact and compacted loess, revealing significant differences between them [19; 20; 21; 22; 23; 24; 25]. Laboratory experiments have demonstrated that, despite compaction efforts, compacted loess often exhibits collapsibility that can surpass that of the intact loess [26; 27; 28]. Additionally, for the hydraulic behavior, intact loess shows higher hydraulic conductivity [20] and higher water retention behavior in the low suction ranges [19]. It is widely acknowledged that the macro-level hydraulic and mechanical behavior of soils, either in the compacted or intact state, is governed by their microstructure [14; 16; 19; 21]. Quantitative characterization of the soil microstructure is increasingly crucial for interpreting the micro-level hydraulic and mechanical behavior and developing constitutive models that consider the structural effects [10; 17; 29; 30; 31]. Numerous studies have been conducted to investigate soil fabric using techniques such as scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) [2; 32; 33; 34]. Several studies have compared the microstructures of intact and compacted loess using  
Figure 1: Two typical engineering projects in the Loess Plateau of China: (**a**) Mountain excavation and city creation (MECC) project; (**b**) Gully management and land reclamation (GMLR) project. MIP and SEM techniques [19; 22; 25; 35]. Naturally deposited loess typically exhibits a loose arrangement of particles and inter-particle bonding, such as clay particles, soluble salts, and calcium carbonate [1; 14; 28; 36].