# Review of the Double-Row Pile Supporting Structure and Its Force and Deformation Characteristics
## 2 Study of Double-Row Pile Structures  
The design of basic parameters such as the pile diameter, the pile length, the size of the crown beam and connecting beam, the pile spacing, and the row spacing of double-row pile supporting systems is very important. A double-row pile structure model is shown in Figure 1. The change of these basic structural design parameters will often have a great impact on the whole pull pile supporting structure. Using reasonable structural design parameters will play an important role in the deformation control of the whole system. The use of reasonable structural design parameters will play a significant role in the deformation control of the entire system [55, 56]. In the design of a double-row pile supporting system, the design of optimal row spacing plays an important role, and the change in row spacing directly affects the horizontal bearing capacity of the front pile. For example, [PERSON] et al. [57], [PERSON] et al. [58], and [PERSON] et al. [59] studied the horizontal displacement of double-row pile supporting structures under different row spacings and found that the appropriate increase in row spacing had a good control effect in reducing the horizontal displacement of the double-row pile structure. However, the internal force of the double-row pile supporting structure will increase with the increase in row distance between the front and back piles, and the retaining effect of the back pile will also decline [60]. The maximum horizontal displacement of piles can be effectively reduced by reducing the row spacing of double-row piles. However, when the row spacing is too small, the supporting role of the back row pile may be greatly reduced, and its anti-lateral movement ability cannot be fully brought into play. At this time, the double-row pile can be regarded as a single-row pile in terms of its supporting effect [38]. Because it is difficult to obtain actual engineering monitoring data, finite element software can be used to conduct numerical simulation research and qualitative analysis of the optimal row and pile spacing. Through numerical modeling  
Figure 1: Schematic diagram of a double-row pile supporting structure model. analysis, optimal structural design parameters with certain reliability can be obtained, and the structural parameters with reasonable economy can be given in combination with engineering practice [61; 62; 63]. However, optimal row spacing has regional and project limitations in engineering, and different scholars place different emphases on the value of optimal row spacing based on the qualitative analysis of the numerical simulation model established. For example, [PERSON] et al. [64] believed that when the pile diameter of a double-row pile in a deep foundation pit is 600-1200 mm, the most reasonable row spacing of the double-row pile supporting structure is three to four times the pile diameter. [PERSON] et al. [65] believed that the horizontal displacement is most significantly controlled when the row spacing between the front and back piles is four to five times the pile diameter. [PERSON] et al. [66] comprehensively considered that, from the perspectives of technology and economy, the optimal row spacing between the front and back piles was 1.6-2 times the pile diameter. For the study of horizontal pile spacing of front and back piles, it is generally believed that increasing pile spacing can reduce the lateral displacement of double-row pile supporting structures, but the greater pile spacing means that greater earth pressure will be borne. Therefore, the pile spacing cannot be increased without restraint to support the control effect [67; 68]. [PERSON] et al. [69] found, through finite element numerical model analysis, that the displacement of double-row pile supporting structures could be reduced to a certain extent by appropriately reducing the distance between horizontal piles in the back row. However, reducing the horizontal pile spacing of the back row piles is equivalent to increasing the overall stiffness of the back row piles.