# Study on Shielding Effect of the Pile Group in a Soft-Soil Foundation
## 3 Results
### Shielding Effect Mechanism  
A row of pile bodies and the soil between them have been proved to contribute to shielding effects, and the simulated response characteristics of stress and the displacement of the foundation are essentially consistent with other research results [33; 37], thereby indirectly validating the rationality of the model. Nonetheless, how the soil in between piles behaves as a shield remained unsolved. Consequently, this section will synthetically analyze the formation mechanism of the shielding effect from the pile group, based on the above studies. Figure 13 displays an interesting phenomenon that in the B-B\({}^{\prime}\) profile, the soil stress between the piles is obviously smaller than that out of the pile group. To explain this phenomenon, an analysis of the strain characteristics is needed. As depicted in Figure 14, the strain increases relative to the initial state after the installation of the first pile row are extracted. The soil between the piles displays positive strain (tensile strain) increases in the X direction, as shown in Figure 14a, but has negative strain (compressive strain) increases in the Y direction, as shown in Figure 14b. Figure 15 further depicts the soil strain variations between piles of the first row following the installation of subsequent rows. In Figure 15, the green line denotes the difference in soil strain increments between the installation of the second and first rows of piles, while the red line represents the difference between the installation of the third and second rows of piles. According to the results, the X-direction strain increase in soil between the piles is larger than that near the piles (Figure 15a), which corresponds to the result of Figure 14. This result generally demonstrates a distinction between the strain distribution of soil near the pile and between the piles and implies that the uneven pattern is correlated to \"shielding\". Figure 14: Contour maps of soil strain increments at a depth of 5 m after the first row of piles is installed; (**a**) Strain increment in the X direction; (**b**) Strain increment in the Y direction. Figure 13: Variation in soil stress-XX along the B-B\({}^{\prime}\) profile at a depth of 5 m.  
Based on the comprehensive analysis, during pile group installation, the shielding effect of an existing row of piles on new rows of piles is caused by two factors: a. the direct obstruction effect from the existing piles, and b. the obstruction from the soil between the existing 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, as explicated in the analysis of Figures 7 and 10-12. The latter is reflected in the obstruction of the soil between two existing piles to the displacement of the soil passing through two existing piles, as depicted in Figures 13-15. In fact, the principle of the obstruction from the soil between existing piles is similar to the \"soil arch effect\". When the soil is compressed laterally and tends to pass through adjacent piles, it may produce relative movement with the soil near the pile shaft, thus transmitting the soil thrust to the soil near piles and finally producing a soil arch. Figure 16 exhibits the X-direction stress distribution in the soil between piles. The stress between two adjacent piles (region B) is relatively lower than that of the soil near pile shafts (region A), where the stress is concentrated. The stress contours resemble an arch (indicated by yellow dashed lines) with obvious arching bodies and feet (see Figure 16). This conclusion is firmly supported by the results of Figures 10 and 13.