## 1 Introduction  
As one of the most common natural disasters worldwide, landslides are mainly caused by human engineering construction and natural environmental factors. Frequent landslide disasters in recent years have resulted in enormous losses to lives and properties. When it comes to landslide treatment, anti-slide piles can penetrate the landslide bed to resist landslide mass and keep a slope stable, which works as a widespread measure against landslides [1, 2]. As for research on slope reinforcement by a traditional single-row pile-supporting structure, many domestic and foreign scholars have analyzed the influence of pile layout, pile spacing, and geotechnical properties upon slope stability and acquired a great number of research findings [3, 4, 5, 6]. [PERSON] et al. [7] theoretically derived a formula for pile-spacing calculation under an equilibrium condition that the side friction of the pile was equivalent to the landslide thrust between piles. [PERSON] proposed a method to calculate the pile top burial depth through the ultimate balance theory, derived the calculation formula through the transfer coefficient method, and validated the formula [8]. However, single-row piles exert a limited effect on slope reinforcement during practical engineering applications,and in particular, double-row and even the multi-row piles are often adopted for medium- or large-sized landslide treatment. [PERSON] et al. [9] put forward a new layout of double-row piles, with the top of the back-row piles embedded in the slope at a certain depth, and the top of the front-row piles was placed on the slope surface. [PERSON] et al. [10] researched the difference in slope reinforcement between double- and the single-row piles and indicated that their failure modes were significantly different. [PERSON] et al. [11] proposed a simplified model of double-row piles to analyze the influence from the shear strength of soil on the slope stability under a seismic effect. [PERSON] et al. [12] analyzed the mechanical transfer effect between double-row piles and proposed a calculation method to distribute the landslide thrust among different piles. Based on the particle image velocity (PIV) measurement and image-processing technology, [PERSON] et al. [13] advised that the row spacing of double-row piles should be three to five times the pile diameter, and that the pile spacing should be four times the pile diameter. It can thus be seen that the theoretical research on and the engineering applications of both single-row and multi-row piles are relatively sufficient. However, in view of slope stability and other factors, slope reinforcement through single-row and multiple-row anti-slide piles is largely limited, so as to avoid soil excavation in a large area. The landslide thrust is mainly carried by the upper part of a pile. In order to optimize the mechanical behavior of single-row and the multiple-row piles, the pile top can be formed as a whole by a straight crown beam made of concrete, which can substantially improve slope stability. In particular, the upper part of the pile body should be further strengthened under a seismic effect [14; 15]. [PERSON] showed that the pile top displacement of front-row piles in a portal frame composite structure was significantly smaller than that of single-row cantilever piles and crown beam-free double-row piles [16]. Some scholars indicated that the crown beam plays a significant role in coordinating the deformation of anti-slip piles, and the back-row piles had a greater impact on slope stability than the front-row piles [17; 18]. Reliability and economic efficiency are two important factors for portal frame composite structure, and excessively large pile spacing and crown beam size leads to the failure in the slope reinforced by anti-slide piles, which may weaken the soil arching effect [19; 20; 21]. Because of the mechanical characteristics of the arched beam, the compression resistance of concrete can be given full play by an arched beam instead of a traditional straight crown beam.