# Ground Deformation Associated with Deep Excavations in Beijing, China
## 4 Discussion  
Ground performances associated with excavation mainly exhibit themselves in terms of surface settlements, \(83.9\%\) of which generally range from \(0\) mm and \(-30\) mm, and slight upheavals were found near the corner. Since deep foundation pits are excavated in a hard stratum, soils at the bottom will rise due to the unloading effect, which also drives the surrounding soil upward together. Moreover, the lateral soil of a foundation pit produces a movement trend of displacement and sinking. However, because of the support system, this trend is restrained. The two motions interact with each other. Upheaval predominantly appears in terms of upward movements. We can observe a noticeable reduction in settlements adjacent to the wall that have been embraced locally. This may be attributed to the friction and potential intermingling occurring along the interface between the contiguous pile wall and soil [15]. In this study, maximum surface settlements appear more convergent than those in cases from other areas. \(\delta vm\) develops with increasing \(H\), and it generally ranges from \(0.04\%H\) to \(0.12\%H\), with an average value of \(0.089\%H\) (generally\(<30\) mm). The magnitude of \(\delta vm\) is similar to the records in cases involving a certain thickness of soft soils overlying stiff and hard strata, such as stiff clays, residual soils, sands, and weathered rocks [2; 7; 8; 14; 15], or in stiff strata [20]. The geological condition of bottom strata may determine the influence of the overlying soft soil of a certain thickness on \(\delta vm\) as stiffer materials predominate, otherwise, the \(\delta vm\) is much lower than that in soft soils or in mixed  
Figure 13: Final ground deformation normalized by the maximum settlement. Note: the design settlement profiles for sand, clays, and mixed soil were proposed by [PERSON] et al. (1990) and [PERSON] et al. (2007). soil conditions; this is because soft materials predominate, since soil has a high reference strength when particles are uncrushable or strong [21]. The support stiffness and \(EDR\) can also affect the \(\delta vm\), and the opposite tends to occur when the maximum ground surface settlement is exhibits an increasing EDR and support stiffness. The restriction of the angular particle movement in granular soils may be stronger under the same support force [22]. The \(\delta vm\) decreases until it is not obvious, which is when the EDR reaches 0.4, or the support system has achieved a certain stiffness (>20,000). It seems that a further increase in stiffness for support, nor the penetration depth of the wall, can influence the performance of the excavation, since the stability of excavation is guaranteed. The EDR and support stiffness increase the bearing capacity factor to an extent, and the effect may diminish beyond it [27; 28]. It is suggested that an increase in the EMR and support stiffness cannot contribute to a corresponding decrease in settlement if the excavation has become stable. In Shanghai soft soil areas, the maximum EDR was 1.52, the minimum was 0.45, and the average value was 0.88. In Hong Kong, there is a maximum EDR of 1.6, a minimum of 0.28, and an average value of 0.96. The average EDR of 13 foundation pits in the sandy soil stratum was 0.47, whereas that of the clay stratum was 0.44 in Japan. The average EDR of 14 foundation pits in Chinese Taipei was 0.65. In this study, the maximum and minimum EDR of bored piles in the collected foundation pits are 0.44 and 0.28, respectively. Numerous studies have shown that the EDR is greatly affected by strata conditions [29]. The main soil layers in Beijing are silty soil, silty clay, medium-coarse sand, and gravel, which have a strong embedded effect upon pile toes, and they provide more support against the base upheaval [7; 30].