## 4 Analysis of the Force of the Inclined-Straight Combination Pile  
The displacement diagram of the front and rear rows of piles when the excavation reaches 10 m is shown in Figure 10. The results indicated that when the deep foundation pit is excavated by inclined and straight combination pile support, the difference between the horizontal displacement of the front and rear rows of piles at the same depth is small, and they are all within the error range. That is, it can be considered that when the deep foundation pit is excavated by inclined and straight combination piles, the relative displacement between the soil and the pile body does not occur, and the pile side frictional resistance only appears in the front and rear rows of piles near the soil side outside the pile. [PERSON] et al. [28] used indoor experiments to simulate the sliding surface of the inclined pile-supported foundation pit when it is close to the overturning damage, and the simulation results showed that for the inclined straight combination pile support structure with an inclination angle \(\leq\)20\({}^{\circ}\), there is no damage to the sliding surface of the soil between the piles when the overturning damage occurs. Therefore, when conducting force analysis, the support structure and the soil between the piles can be analyzed as a whole. The force analysis behavior of the support structure can be drawn as shown in Figure 11.  
Figure 11: The behavior of force analysis of inclined-straight pile. Where, (G is the gravity of soil between combined piles).  
Figure 10: Horizontal displacement of front and rear rows of piles.  
For the force analysis of the inclined straight combination pile, the overturning rotation point can be approximated at the foot of the front row of inclined piles. Then, the moment of overturning rotation point should be taken:  
\[E_{a}b_{a}\leq E_{p}b_{p}+F_{n}b_{n}+G \tag{1}\]  
From the force analysis, compared with the straight pile, when the inclined pile support structure is tilted to the pit, the overturning force distance consisting of the active soil pressure outside the pit will be balanced with the overturning force distance consisting of the passive soil pressure, active zone frictional resistance and the gravity of the soil between the piles and the gravity of the combined pile. In addition, the larger the inclination angle of the front pile, the larger the overturning resistance distance is, so the stability of the inclined straight combination pile is greatly improved compared with the straight pile. However, when the inclination angle is \(\geq\)20\({}^{\circ}\), the soil between the piles will have a sliding damage surface, and the back row of straight piles will have upward frictional resistance near the side between the piles, and the stability of the support structure may be reduced instead.  
Therefore, in the actual project, a suitable inclined pile inclination angle should be selected with the geological condition and other factors, so that the stability of the support structure can be optimized. At the same time, because the overturning resistance of the inclined pile is greatly improved compared with that of the straight pile, the soil deformation and horizontal displacement outside the pit is smaller when the deep foundation excavation of inclined and straight combined supporting pile is carried out, and the influence on the pile foundation of the adjacent structure outside the pit is also smaller.