# Review of the Double-Row Pile Supporting Structure and Its Force and Deformation Characteristics
## 2 Study of Double-Row Pile Structures
At this time, the earth pressure on the back of the row piles will also increase, which will also increase the project cost. In summary, the deformation control function of a double-row pile structure can only be fully brought into play by matching the distance between rows and piles and having a reasonable construction scheme [70]. When the supporting structure is in the optimal row and pile spacing, the control effect of the connecting beam becomes a new research object. When there is no connecting beam, the supporting structure system only acts as the single-row pile supporting structure, and the deformation characteristics of the structure are not significantly different from those of the single-row pile supporting structure. For the pile row support structure with connected beams, connected beams can not only reduce the range of soil stress concentration between two groups of double-row piles, but also increase the overall mechanical performance of the load section and the overall stiffness of the structure [71; 72; 73]. In addition, increasing the stiffness of the beam can control the horizontal displacement of the supporting structure. However, the increase in the stiffness of connected beams has a node, and when the node is exceeded, the control effect of connected beams on the horizontal displacement and lateral torsion of the double-row pile supporting structure is no longer obvious, which also plays a certain reference role in the cost control [74; 75]. In a study on crown beams, [PERSON] et al. [59] found that reducing the stiffness of crown beams greatly increases the lateral displacement of double-row pile supporting structures. However, the effect of increasing the stiffness of the crown beam on reducing the lateral displacement of the double-row pile supporting structure was not obvious. Later, [PERSON] et al. [76] studied the crown beam and connecting beam, considering their integrity based on their rigid connection. The rigid connection between the crown beam and the connecting beam makes the two a whole, which can effectively improve the lateral support stiffness coefficient of the rectangular double-row pile double beam and also plays a good control role in the lateral displacement constraint of the double-row pile supporting structure. Drawing from a large amount of the literature and field monitoring data, it can be understood that the soil pressure of the front pile and the back pile in the double-row pile support system is different. For this reason, many scholars have carried out a lot of research on the characteristics of double-row pile support systems. Through the establishment of a numerical model to carry out numerical simulation analysis, it was found that the different embedment depths of the rear pile have an effect on the internal force distribution of the front and back piles, which further leads to the conclusion that the combination of long and short piles can give full play to the overall performance of the row pile structure [77; 78; 79]. However, [PERSON] et al. [80] and [PERSON] et al. [81] successively found, through physical simulation tests, that when the double-row pile structure adopts the front long and back short composite pile structure, the change of the back short pile length does not significantly improve the overall stability of the double-row pile support structure. The selection of the pile section size is also one of the parameters that cannot be ignored in the control of foundation pit deformation and engineering costs. With the increase in the height-diameter ratio of the supporting pile, the horizontal displacement of the pile top of a double-row pile also increases. The excessive height-diameter ratio will pose a serious threat to the stability of the double-row pile retaining structure itself [82].