## 3 Field Measurement of the Deformation of Shaft Tower Foundation during DHS Process
### Shift Tower Foundation Settlement  
We choose a reference point far away from the tower, which is not affected by freezing method construction, and determine the elevation of each measuring point of the tower foundation by round-trip leveling. The measurement starts with drilling, and the settlement data of each monitoring point is shown in Figure 4. The blue solid points in Figure 4 are the monitoring results of the high-precision level, and the red circles are the results of the DS-3. The data analysis is mainly based on the test results of DL-2007, supplemented by the DS-3. It can be seen from Figure 4 that at the drilling stage (A), soil freezing stage (B) and soil melting stage (C), the shaft tower foundation experiences a process of slow settlement, slight heaving, fast settlement and finally, stabilization.  
(1) Drilling stage  
The drilling stage began on 21 October 2019 and lasted 88 days. A total of 120 holes of various types were drilled, with a total drilling footage of 31,111 m. At the drilling stage, the flushing fluid carried rock powder and sediment away from the stratum, and the rock and soil volume, according to the diameter of the boreholes was estimated at about 950 m\({}^{3}\), which caused the settlement of the shaft tower foundation. It can be seen from Figure 4 that at stage A, monitoring points J1 to J4 sank 3 mm, 4 mm, 7 mm, and 7 mm, respectively. The settlement is therefore very limited at the end of stage A, leading to little tilting and disorder in the tower.  
(2) Soil freezing stage  
The freezing stage was put into trial operation on 22 January 2020, and after 164 days, the freezing station was shut down on 4 July 2020. It can be seen from Figure 4 that in the first 58 to 61 days of soil freezing, the elevation of the monitoring points was still decreasing, indicating that the shaft tower foundation settlement caused by drilling did not stop. The rock-soil expansion that was caused by soil freezing slowed down the settlement of the shaft tower foundation but did not compensate the settlement from drilling. Compared with the starting point of drilling construction, J1 to J4 sank 8 mm, 9 mm, 10 mm, and 10 mm, respectively. After 61 days of freezing operation, the foundation of the shaft tower trended in reverse, starting to rise at all four monitoring points. This phenomenon showed that after the soil was frozen for 61 days, the frozen walls began to form a complete circle, and the soil strength and expansion in the frozen area continued to increase, which stopped the drilling-induced settlement of the foundation.  
Figure 3: Layout of monitoring points and measuring instruments. (**a**) Layout of monitoring points; (**b**) DL-2007; (**c**) DS-3.  
(3) Soil melting stage  
On 4 July 2020, the repair project stopped freezing and entered the thaw settlement stage. After the freezing station was shut down, the elevation of the shaft tower foundation started to show some typical features of the settlement stage (the blue point on the timeline is the result of 5 July). In the early stage of soil melting, the settlement rate of the shaft tower foundation was relatively fast, but 113 days after soil melting (26 October 2020), it began to slow down, and 281 days after soil melting (13 April 2021) the settlement stopped. During the whole melting period, monitoring points J1 to J4 sank 39.2 mm, 46.0 mm, 40.0 mm, and 43.7 mm, respectively. From the monitoring results of foundation settlement, it can be seen that the thaw settlement amount is much greater than the frost-heating amount.