## 4 Design Methodology of Composite-Anchor Uplift Piles
### The Use of Load-Bearing Capacity Design Formulas in Engineering Examples
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Soil Layer**} & \multirow{2}{*}{**Perimeter of File u\({}_{i}\) (m)**} & \multirow{2}{*}{**Thickness**} & \multicolumn{2}{c}{**Pile-Side Ultimate**} & \multirow{2}{*}{**Pull-Out Coefficient**} & \multicolumn{2}{c}{**Standard Value of Pile-Side**} \\  & & & & **Friction q\({}_{sk}\)** & \(\lambda_{ip}\)** & **Resistance per Layer (kN)** \\ \hline
1 & 2.512 & 1.60 & 25.0 & 0.8 & 80.38 \\
2 & 2.512 & 1.40 & 27.5 & 0.7 & 67.70 \\
3 & 2.512 & 2.50 & 30.0 & 0.7 & 131.88 \\
4 & 2.512 & 0.30 & 30.0 & 0.8 & 18.09 \\
5 & 2.512 & 0.50 & 30.0 & 0.7 & 26.38 \\
6 & 2.512 & 2.70 & 70.0 & 0.7 & 332.34 \\
7 & 2.512 & 1.80 & 30.0 & 0.8 & 108.52 \\
8 & 2.512 & 0.70 & 70.0 & 0.7 & 86.16 \\
9 & 2.512 & 2.50 & 50.0 & 0.8 & 251.20 \\
10 & 2.512 & 3.00 & 70.0 & 0.7 & 369.26 \\ \(\Sigma\) & & 17.00 & & & 1471.91 \\ \multicolumn{5}{c}{Characteristic value of uplift bearing capacity (kN)} & 1400 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The calculation table of composite-anchor pile. Figure 8: Anti-floating pile layout plan. (3) Design of the number of composite-anchor piles. The original design of anti-floating piles has a diameter of 800 mm and a length of 18.00 m. The main reinforcement consists of 20 third-grade steel strands (HRB400) with a diameter of 25 mm, arranged in 135 piles. The characteristic value of the uplift bearing capacity of each pile is 1400 kN. After optimization calculation, the length of fully bonded piles is 17.00 m, the diameter is 800 mm, and the characteristic value of uplift bearing capacity is 1400 kN. The number and location are the same as those of the original anti-floating piles. (4) Design of reinforcement for the rod body of composite-anchor piles. For this, \(1\times 7\phi\)s17.8 steel strand is used, with a design tensile strength of 1320 MPa; a total area of the anchor cable body \(A_{8}=1400000\times 2/1320=2121\) mm\({}^{2}\); and a single bundle of \(1\times 7\phi\)s17.8 steel strand with a cross-sectional area of 191 mm\({}^{2}\). The number of steel strands \(n=2121/191=12\). (5) Verification of the anticorrosion service life for single-side coated welded pipes. According to the provisions of 4.1.18 in the Technical Code for Building Pile Foundations (JGJ 94-2008) [24], \"When the inner wall of the steel pipe pile is isolated from the outside world, the anti-corrosion of the inner wall can be ignored\" and the steel strands in the steel pipe of this project can be ignored for anti-corrosion. The composite uplift piles in this project are located below the groundwater level, and the medium for isolation from the outside world is DN65 welded pipe with a wall thickness of 3 mm. According to Table 4.1.18 of the Technical Code for Building Pile Foundations (JGJ 94-2008) [24], the corrosion rate on one side below the water level is 0.03 mm/y. The single-sided corrosion life of DN65 welded pipe = 3 mm/0.03 mm/y = 100 \(\times\) y \(>\) 50 \(\times\) y  
The single-side corrosion life of welded pipe meets the design requirements. (6) Parameters of composite-anchor pile. After the above preliminary design stage and considering the construction method of fully bonded piles, the parameters of the uplift piles are finally determined in this chapter:  
1 The pile body diameter is 800 mm, the effective pile length is 17.0 m, and the pile body concrete strength is C25. 2 The number of piles is 135. 3 There are 4 composite-anchor cables set up as the main reinforcement, each consisting of 3 \(1\times 7\phi\)s17.8 steel strands. The effective length of the main reinforcement is 17.7 m, consisting of DN65 high-strength steel pipes, grout, and 4 \(\times\) 3\(\phi\)s17.8 steel strands. 4 Each bundle of composite-anchor cables is provided with a DN65 high-strength steel pipe on the outside, with the bottom tapered and sealed. The steel pipes are connected by 150 mm-long DN80 high-strength steel pipe sleeve welds.