## 3 Field Measurement of the Deformation of Shaft Tower Foundation during DHS Process
### Inclination of the Shaft Tower Foundation  
The inclination value of the shaft tower foundation can be calculated from the high-precision levels' monitoring results. The results in the DHS process are shown in Figure 5, where a positive value means that the shaft tower inclines to the south or west, and a negative value means it tilts to the north or east. Figure 5 shows that the shaft tower foundation first inclines northeastward at the drilling stage, and then recovers towards southwest due to frost heaving, and the shaft tower tilts further eastward at the thaw settlement stage.  
Figure 4: Settlement curve of each monitoring point at the shaft tower foundation in the process of drilling, frost heaving and thaw settlement (DHS process). (**a**) Monitoring point J1; (**b**) monitoring point J2; (**c**) monitoring point J3; (**d**) monitoring point J4.  
(1) Drilling stage  
After drilling, the shaft tower foundation began to sink and the shaft tower started to incline due to the inconsistency of the settlement speed at the four corners of the shaft tower. Figure 5 shows that the shaft tower inclines towards northeast immediately after the drilling operation. The maximum inclination rate in the north-south direction is \(-0.343\) mm/m (5 January 2020), and that in the east-west direction is \(-0.171\) mm/m (5 January 2020), which are less than the allowable value (2.5 mm/m) for the inclination of the shaft tower foundation. Measured against the shaft tower height (71 m), the maximum inclination value towards the north at the top of the shaft tower is 24.4 mm, and the maximum value towards the east is 12.1 mm in the drilling stage.  
(2) Soil freezing stage  
During the freezing construction period, the northeastward inclination of the shaft tower continued to decrease, which means the shaft tower was returning to the southwest direction. After the freezing construction, the inclination value of the shaft tower in the north-south direction was close to 0 mm/m (5 July 2020). Although the soil strength and expansion in the frozen area continued to increase, which prevented the shaft tower foundation from sinking, the decrease in the inclination value was not under human control, but the result of a combination of factors.  
(3) Soil melting stage  
At the soil melting stage, the inclination value of the shaft tower foundation in the north-south direction increased first and then decreased. After 281 days of soil melting (13 April 2021), the inclination value of the shaft tower in the north-south direction almost decreased to 0 mm/m. In addition, at the stage of soil melting, the shaft tower foundation further inclined to the east, and the maximum inclination was \(-0.406\) mm/m (10 January 2021). Measured against the shaft tower height (71 m), the maximum inclination value towards the north at the top of the shaft tower was 11.6 mm, and the maximum value towards the east was 28.83 mm.  
Benefiting from the protective measures, such as symmetrical drilling, partial freezing and hot water circulation in temperature-control holes, the stability of the shaft tower foundation was ensured with the maximum inclination value (\(-0.406\) mm/m) well below the allowable value (2.5 mm/m) in the DHS process.