# Study of the Load-Bearing Characteristics of Bolts under Asymmetric Freezing Conditions
## 3 Results and Analyses
### Study on the Bearing Characteristics of Bolts in a Cold Environment
#### 3.2.1 Effect of Frost Heave on Anchored Soil Stress  
To explore the internal stress changes in frozen soil, a microscale earth pressure box was used to collect stress of soil at key positions around the bolt. The collected data are shown in Figures 10 and 11, where the abscissa is the temperature at the centre of the bolt.  
Figure 9: Cloud maps of soil temperature at different freezing times.  
According to the analysis of Figure 10, the horizontal frost heave force at each monitoring point increased to different degrees with decreasing temperature. Because monitoring point No. 1 was first affected by the negative temperature load, it entered the freezing state earlier than the other monitoring points, and the horizontal stress increased first. Because monitoring point No. 5 was farthest from the cold source, it had the latest contact with the negative temperature load and remained unfrozen for a long time; the horizontal stress developed last.  
When the core temperature of the bolt was reduced to 0 \({}^{\circ}\)C, the surface of the shaft was subjected to a frost heave confining pressure of 5.54 kPa, and when it was reduced to \(-3\)\({}^{\circ}\)C and \(-7\)\({}^{\circ}\)C, the pressure around the rod increased to 11.09 kPa and 162 kPa, increases of 55.5 kPa (100.1%) and 106.6 kPa (192.4%), respectively.  
Because soil at different locations entered the frozen state at different times, the retaining pressure of the bolt was asymmetrical. When the temperature at the centre of the bolt was 5\({}^{\circ}\)C, the soil around the rod had not yet frozen, but the soil to the right had undergone frost heaving, and the frost heaving force reached 3.89 kPa. The soil mass was compacted under the action of horizontal force, and the horizontal stress slightly increased. It was difficult for the unfrozen weak soil on the left side of the bolt to provide horizontal support, and thus, the bolt was displaced to the left by the asymmetric force.  
When the temperature dropped to 0 \({}^{\circ}\)C, the stress difference between the two sides was 11.05 kPa, then the compressive strength of the soil on the left side of the bolt gradually increased as it entered the frozen state. The stress difference down to \(-3\)\({}^{\circ}\)C was 12.18 kPa, while the difference was 5.74 kPa at \(-7\)\({}^{\circ}\)C. Under the condition of lateral freezing, the bolt would be in an asymmetric confining pressure state for a long time.  
Figure 11: Vertical stress curve.  
Figure 10: Horizontal stress curve.  
Figure 11 shows that the vertical frost heaving force of each monitoring point increases with decreasing temperature. The upper soil mass has already entered the freezing state before the centre dropped to the negative temperature and had a vertical frost pull-out force. When the centre temperature was 0 \({}^{\circ}\)C, the freezing stresses at 50 and 150 mm above the centre, i.e., monitoring points Nos. 7 and 6, reached 4.54 and 7.7 kPa, respectively, while the soil below did not freeze and was only self-weight stress. When the temperature dropped to \(-7\)\({}^{\circ}\)C, the stresses at the monitoring points from top to bottom, i.e., Nos. 6, 7, 8 and 9, were 19.6, 15.2, 10.0 and 5.9 kPa, with increases of 154.5, 234.8, 566.7 and 227.8%, respectively, compared with 0 \({}^{\circ}\)C. The vertical stress growth in the soil around the anchor rod was in the form of \"diffusion\" from top to bottom.