# Study on Shielding Effect of the Pile Group in a Soft-Soil Foundation
## 4 Conclusions  
The mechanism of shielding effects of a pile group-soft soil system was investigated through a numerical study. Using FLAC[33] and the cavity expansion theory, a three-dimensional numerical model was created. Multiple response characteristics including displacement, stress and strain were combined to systematically study the mechanisms of shielding effects. The following are the particular conclusions:  
1. Displacement field analysis revealed that the \"actual accumulative displacement\" considering the shielding effect was 21.43% less than the \"superimposed displacement\" without the shielding effect, indicating the pronounced presence of superposition and shielding effects in the pile group. A further examination of the displacement trajectories of pile heads and ground surface soil revealed that each penetration of a pile induces a directional disturbance both on the soil and piles, and the pile itself contributes to the shielding effect. Specifically, on both sides of the pile group, the displacement of soil near the existing piles (W direction) exhibited a relatively smaller superposition effect. This observation highlights the effective role of the existing piles in controlling deformation.
2. Stress field indicates that pile installation caused a redistribution of soil stress. For a newly installed row of piles, there is a connected zone of stress increase in the Y direction between piles. After piling in order, this high-stress connected zone extends in the X direction, with the stress between piles in the same row decreasing; the original stress ring of soil in the outermost ring of the pile body is deflected, and a stress-increasing zone is formed along the W-E direction. In the meantime, stress increases along the N-E direction and S-E direction, which indicates that both piles and the local soil around may contribute to shielding the soil behind the pile.
3. The X-direction strain increase in the soil between the piles is larger than that near the piles. This result generally demonstrates a distinction between the strain distribution of the soil near the pile and between the piles and implies that the uneven pattern is correlated to \"shielding\".
4. Through a synthetical analysis of displacement, stress and strain fields, the mechanism of the shielding effect induced by pile construction is proposed, and is attributed to the direct obstruction effect of piles and the \"soil arching effect\" caused by the soil between piles. The former is reflected in the direct barrier of the existing pile to the soil displacement caused by the installation of the new piles. The latter is reflected in the obstruction of soil between the two existing piles to the displacement of the soil passing through the two existing piles.  
Conceptualization, C.L.; methodology, Q.T.; software, M.H.; validation, L.H. and R.W.; formal analysis, L.H.; investigation, L.H. and S.C.; resources, C.L. and Q.T.; writing--original draft preparation, C.L.; writing--review and editing, Q.T.; visualization, M.H. supervision, S.C. All authors have read and agreed to the published version of the manuscript.  
This work was funded by the Research Project of China Railway Siyuan Survey and Design Group Co., Ltd. (No. 2022K003), the National Natural Science Foundation of China (No. 42007268), postdoctoral innovation practice positions in Hubei Province (No. RCXM2022002) and the China Postdoctoral Science Foundation (No. 2021M703002).  
Not applicable.