# Model Experiment Study on Vertical Bearing Characteristics of Large-Diameter Ring Piles
## 3 Analysis of Model Experimental Results
### Analysis of Pile Compression Law in Model Experiment  
The compression-load curve (Figure 9) can be obtained by extracting the data within 30 min before the load changes and taking the average value. The pile wall thickness has a significant impact on pile compression. The general rule is that the smaller the value of \(K\), the smaller the wall thickness, \(T\), and the greater the compression amount. The compression of Ring Pile No. 4 was slightly larger, at 10 kN, whereas the compression of the other four piles was small, less than 0.1 mm. The compression of Ring Pile No. 2 changed slightly when the load increased to 30 kN, reaching 0.4 mm. The compression of the five piles increased significantly, within the inflection point range, at a load of 40 kN. The total settlement of a single pile consists of the compression of the pile subsoil and compression of the pile body. The pile body does not undergo large compression, owing to the structure and material strength of the traditional solid pile. Because the inner wall of the ring pile is against an empty space and the cross-sectional area of the pile body under stress is small, pile body compression is more likely to occur. Table 4 shows the pile compression within the inflection point range. Obvious anomalies were observed in the data of Ring Pile No. 2, and these points were excluded from the analysis. Within the load range of the inflection point, the pile compression increased gradually as the value of \(K\) decreased. However, the compression remained less than 0.8 mm as the load increased to 60 kN. In addition to Ring Pile No. 4, the other four piles reached their peak displacement. As the load increased further, the pile-end bearing capacity and pile-side friction reached their maximum limits, and pile-end pierce damage occurred; the soil at the pile endpoint compressed rapidly, and stress was released to the surrounding soil. Then pile compression tended to decrease. Figure 9: Pile compression curve. Figure 14: Pile strain of Ring Pile No. 4. Figure 12: Pile strain of Solid Pile No. 2. Figure 13: Pile strain of Ring Pile No. 3. In the experiment, the strain gauge was attached to the pile surface, and the strain gauge at the bottom of the pile was close to the edge. The confined soil at the bottom of the pile was sand with low relative strength, which could be regarded as a weak cushion. In addition, because the pile bottom was flat, the stress distribution was uniform, with a small strain value. However, part of the strain gauge at the bottom edge of the pile will inevitably press small stones, resulting in stress concentration and strain increase. As shown in Figure 12, there was a sudden increase of strain at the bottom. The strain development law of the four ring piles with different wall thicknesses was similar to that of the solid piles. A general law was observed: the smaller the value of \(K\), the larger the strain at the top of the pile. The strain at the top of Ring Pile No. 5 was significantly larger and was five times that of other piles under the same load. At approximately 0.75 m away from the pile top, with a variation in the value of \(K\), strain growth showed a large variation: The change in strain growth of Ring Pile No. 2 (\(K=0.6\)) was similar to that of the solid pile but decreased or increased slightly. The strains of Ring Pile No. 3 (\(K=0.4\)) and Ring Pile No. 5 (\(K=0.2\)) showed an obvious surge at this point, whereas the strain of Solid Pile No. 5 was approximately ten times that of the other piles. At the middle position of the pile, the strains of all four ring piles decreased by different amounts. After passing through the middle position, the strains of the four ring piles and solid piles increased with depth. At approximately 0.4 m away from the pile bottom, the strain decreased gradually. A 300 mm seal was placed at the bottom of the pile. Because the cross-sectional area of the pile and stressed area increased, the strain in this part decreased.