# Internal Force Analysis of Buried-boring Piles in the Yuanzishan Landslide
## 3 Application of Buried-Boring Piles in the Yanzishan Landslide
### Application of Buried-Boring Piles to the Yanzishan Landslide  
The cross-section from A to A\({}^{\prime}\) of the Yanzishan landslide was selected in order to design the buried-boring piles in the calculation. The spacing between the piles was 1 m. The diameter of the pile, \(D\), was 0.5 m. The moment of inertia of the buried-boring pile, \(I\), was \(3.066\times 10^{-2}\) m\({}^{4}\). The Young modulus, \(E\), of the buried-boring pile was 30 GPa. The driving force of the landslide, \(p\), was 300 kN/m. The angle of the slip surface, \(a\), was 5\({}^{\circ}\). For the value of c, we can use equivalent soil strength to transform the integrated internal friction angle [37]. If the value of c is not large, the friction angle (\(\varphi\)) of the soil can be directly used, which is more conducive to engineering safety. A soil safety factor of  
Figure 4: Geology conditions pertaining to the cross-section AA\({}^{\prime}\) of the Yanzishan landslide obtained via engineering geological survey.  
Figure 3: Yanzishan landslide and slope deformation: (**a**) The range of the Yanzishan landslide; (**b**) cracking observed at the front edge of the slope; and (**c**) cracking in the middle of the slope.  
1.3 was used, along with a driving force distribution coefficient of 0.4, when the slope slid along the EB surface (Figure 1). The minimum pile length above the slip surface was 0.86 m, based on Equations (1) and (9). When the slope body slid along the DB surface (Figure 1), the minimum pile length above the slip surface was calculated to be 2.12 m, based on Equations (4) and (9). Therefore, in the design of the bored piles for emergency landslide control, the pile length above the slip surface should be at least 2.5 m.  
In order to study the ratio of the pushing force of the landslide acting on the buried pile to the residual driving force of the landslide, a buried depth ratio, \(R_{\rm s}\)[28], was defined as the pile length above the slip surface, \(h\), divided by the depth of the slip surface (H, Figure 1). The ratio of the driving force across the shared piles, \(P_{s}\), was defined as the driving force of the landslide acting on the piles divided by the driving force of the landslide at a specific pile location. If the pile length above the slip surface was 2.5 m and the depth of the slip surface was 10 m in engineering design, \(R_{\rm s}\) = 25%. Using Equations (10)\(and\)(11), the driving force at the top of the pile, \(q_{0}\), was 36.43 kPa, and the driving force strength at the slip surface, \(q_{1}\), was 42.86 kPa. In this case, the driving force of the landslide acting across the piles was calculated to be 99.1 kN, such that \(P_{\rm s}\) = 33%. For varying \(h\) values of 5, 7.5, and 10 m, different \(R_{s}\) values and corresponding \(P_{s}\) values were calculated (Figure 5).  
The ratio of the driving force across the shared piles increased quadratically as the buried depth ratio increased. When \(R_{\rm s}\) = 50%, \(P_{\rm s}\) = 60.7% (Figure 5). [PERSON] [28] used driving force experiments to study the force distribution law of buried piles at large depths and measured that, for \(R_{\rm s}\) = 54%, the driving force of the landslide acting on the bored pile accounted for 59% of the total driving force of the landslide, which is consistent with our calculations (60.7%).