Stress release of the surrounding soil is the fundamental reason for many accidents in tunnel engineering. There have been a great number of numerical simulations and analytical solutions that study the tunneling-induced ground stress. This paper conducts a series of physical model tests to measure the stress state evolution of the surrounding soil during the tunnel advancing process. The ground compactness, as the most critical factor that determines the mechanical properties of sand, is the control variable in different groups of tests. The measurement results show that at the tunnel crown, the minor principal stress sigma 3, which is along the vertical direction, decreases to 0 kPa when the relative density (Dr) of the ground is 35% or 55%. Therefore, we can deduce that the sand above the crown collapses. When Dr = 80%, sigma 3 does not reach 0 kPa but its variation gradient is very fast. At the shoulder, the direction angles of three principal stresses are calculated to confirm the existence of the principal stress rotation during tunnel excavation. As the ground becomes denser, the degree of the principal stress rotation gradually decreases. According to the limited variation of the normal stress components and short stress paths at the springline, the loosened region is found to be concentrated near the excavation section, especially in dense ground. As a result, different measures should be taken to deal with the tunnel excavation problem in the ground with different compactness.

The relationships between soil aggregates, aggregate-associated carbon (C), and soil compaction indices in pomegranate orchards of varying ages (0-30 years) in Assiut, Egypt, were investigated. Soil bulk density (Bd) and organic carbon (OC) content increased with orchard age in both the surface (0.00-0.20 m) and subsurface (0.20-0.40 m) layers 0.20-0.40 m). The percentage of macroaggregates (R-0.25) and their OC content in the aggregate fraction > 0.250 mm increased as the pomegranate orchard ages increased in the surface layer (0.00-0.20 m). Older pomegranate orchards show improved soil structure, indicated by higher mean weight diameter (MWD) and geometric mean diameter (GMD), alongside reduced fractal dimension (D) and erodibility (K). As orchard ages increased, maximum bulk density (BMax) decreased due to an increase in OC, while the degree of compactness (DC) increased, reaching a maximum at both soil layers for the 30 Y orchards. Soil organic carbon and aggregate-associated C significantly influenced BMax, which led to reducing the soil compaction risk. Multivariate analyses identified the >2 mm aggregate fraction as the most critical factor influencing the DC, soil compaction, and K indices in pomegranate orchards. The OC content in the >2 mm aggregates negatively correlated with BMax, DC, and K but was positively associated with MWD and GMD. Moreover, DC and Bd decreased with higher proportions of >2 mm aggregates, whereas DC increased with a higher fraction of 2-0.250 mm aggregation. These findings highlight the role of aggregate size fractions and their associated C in enhancing soil structure stability, mitigating compaction, and reducing erosion risks in pomegranate orchards.