## 4 Analysis of Test Results
### Deep Foundation Horizontal Stress  
The stress shovel test can obtain the variation law for the horizontal earth pressure of the deep foundation between two subgrades, as shown in Figures 10 and 11. The following is known: (1) During the excavation stage, the existing line foundation forms a slope, and the soil gradually changes from exhibiting static earth pressure to exhibiting active earth pressure. The test data showed that the stress of the existing line was released, the lateral earth pressure of the old line toward the new line increased significantly, and the  
Figure 9: Test and calculated conversion coefficient, a.  
micro-strain of the element reached 6.8 \(\varepsilon\mu\) (dimensionless, \(\varepsilon\mu\) = (\(\Delta L/L\)) \(\times\) 10\({}^{-6}\)), which is about 3 kPa. The foundation soil was expressed as the extrusion of the existing roadbed to the new line. (2) In the process of pile formation, the compressive stress generated by the pile body squeezed the soil, causing the lateral earth pressure to fluctuate (reduce) toward the new line. (3) With an increase in the fill load of the new line, the additional stress in the deep soil increased, the existing line foundation squeezed the new line, the lateral earth pressure reversed, the pressure toward the new line decreased sharply, and the new line affected the existing line. The compressive stress of the line increased; in the later stage, with the stability of the fill load, the lateral stress level of the deep foundation did not change significantly.  
When further comparing the pressure distribution in the opposite direction, by examining the two-way lateral stress distribution, we can observe in Figure 12 that the extrusion effect of the existing line on the new line was more obvious. This was caused by the load of the trains on the line foundation, which mainly occurred in the shallow foundation. The lateral earth pressure in this test remained less than 10 kPa, which was far less than the highest level (60-70%),\(f\), of the alarm value for monitoring foundation pit deformation, and \(f\) was the designed limit value. The upward pressure did not pose a threat to the existing line base.  
Figure 11: Lateral stress curves for new lines.  
Figure 10: Lateral stress curves for existing lines.  
When analyzing the data curves of three indicators such as horizontal stress, lateral displacement, and displacement of existing line foundation slope toe, it can be seen that the most obvious data change occurred in the stage of foundation excavation during the construction process near the existing line. The change trend slows down in the stage of pile formation and paving. The results show that the excavation and unloading of the foundation soil has the greatest impact on the stress field and displacement field distribution of the existing line foundation, and the dynamic stress of the accessories generated by the train load aggravates the trend. The deformation observation of the existing line base should be strengthened to ensure the stability of the embankment, because the existing road foundation is in the most unfavorable state at this stage.