# Ground Deformation Associated with Deep Excavations in Beijing, China
## 4 Discussion
As the strength of a dense specimen increases with an increase in particle size when particles are uncrushable or strong (have a high reference strength), at the microscale, the relationship between strength and particle size is positively related to the friction utilization ratio. This means that it has the capacity to resist interparticle sliding. This ratio generally increases with the increase in particle size, which results in an increasing peak shear strength [21]. Otherwise, the strength of a dense specimen, as well as the friction utilization ratio, reduces as the particle size becomes smaller. Moreover, damage onset, damage development, and failure may occur during the entire process wherein soft clay is subjected to loading during the support system's construction. The total volume and number of pores increase, and the distributions within the soil, comprising aggregated particles and pores, become looser due to loading, which may also lead to the destruction of the soil fabric [22; 23; 24]. The embedded depth ratio is much lower than that of Shanghai soft soil [31], Hong Kong mixed soil, and Taipei soil clay [2], which is closer to that of silty clay and clay soils in Japan [30]. The final deformation for different strata conditions in different sites varies, but ground movements are relatively consistent in all cases [32]. Ground movements have obvious temporal and spatial laws. The deformation is reduced from the middle transect to the corner. Although the influencing zone is influenced by the excavation level to an extent, and it reaches a distance of about 2.5\(H\)-3\(H\) (approximately 25-40 m), the location of \(\delta vm\) seems not to be influenced by workmanship, and generally, it shows a progressive trend in locations where the value is 0.42-0.6\(H\) (approximately 10-15m), and when it's position moves away from the wall. Little variation in terms of settlement is found outside of the range during excavation. Analogical results were found in other sites, which also seem to be independent. Throughout all stages of excavation, stress consistently accumulates in the soil surrounding the retaining wall and near the surface being excavated [3]. This may explain why the position of the deformation on the maximum ground surface seems to not be moving in accordance with the excavating depth. The maximum surface settlement occurs when the 1-2 struts above the bottom plate are removed. The removal of the brace can result in significant ground movements [33]. In this study, the removal of bottom supports (i.e., struts) to construct the internal structure, induces additional surface settlements and an inward bulging of the wall; this is because of the large soil pressure on the pit wall and the low stiffness of the internal structure. With the completion of the internal structure, it has greater stiffness, and gradually and effectively, it bears the soil pressure acting upon it. Thus, the deformation is reduced and it converges. Since the removal of the struts of the upper half, the wall system exhibited adequate lateral stiffness with the presence of a few slabs, resulting in minimal additional settlements. Some minor upheaval appears during post-excavation, which may be partly attributed to the rebound of both soil and wall due to the reduced vertical load [15]. The deformation at the corner is restrained by the soil and maintenance structure on both sides, whereas the buttressing effect of the excavation corner helps reduce settlements. Groove patterns are found on the ground surface around deep excavations in Beijing. During the initial phase of excavation, there is minimal lateral displacement observed in the wall due to the presence of adequate lateral support or sufficient stiffness in its upper section. However, as the excavation progresses, the upper part of the wall becomes constrained, and it experiences inward deformation around the excavation site (significant inward movement).