## 1 Introduction  
Lateral spreading of saturated sand is a common seismic damage phenomenon. A large number of earthquake disaster studies have shown that liquefaction lateral spreading is the main cause of structural earthquake damage [1; 2; 3; 4; 5; 6]. For example, [PERSON] et al. [7] proposed that the main reason for the collapse of Showa Bridge in the 1964 Niigata earthquake was that the pile group foundation in the liquefaction lateral spreading site had excessive horizontal displacement at the top of the pile. [PERSON] et al. [8] found that in the 2008 Wenchuan earthquake, the horizontal motion load of the bridge increased due to the liquefaction and expansion of soil mass, which led to beam cracks and the separation of beams and columns of Bailua Bridge. [PERSON] et al. [9] reported lateral spreading around the foundation of a bridge near Port au Prince in the 2010 Haiti earthquake which led to horizontal movement of the bridge's pile foundation. The above studies on earthquake disasters have shown that liquefaction-induced lateral spreading can severely damage bridge foundations. Therefore, the question of how to reduce the damage caused by liquefaction-induced lateral spreading on bridge pile foundations as a result of earthquakes has become a scientific problem of concern in bridge engineering. The liquefaction-induced lateral spreading of foundation soil is mainly caused by excess pore water pressure in the soil that cannot be reduced quickly enough. Therefore, scholars have conducted many experimental studies with the aim of preventing liquefaction by reducing pore water pressure. [PERSON] et al. [10; 11] studied whether a rigid-drainage pile with a porous channel was effective at preventing sand liquefaction and reducing the loss of soil strength. The results showed that a rigid-drainage pile could effectively reduce the settlement of the embankment and the lateral displacement of soil when used with a cofferdam embankment. [PERSON] et al. [12] proposed a new drainage pipe design composed of multilayer horizontal steel rings and vertical drainage pipes which could reduce the excess pore water pressure in soil during earthquake by collecting water in the steel rings and draining it through the steel pipes. [PERSON] et al. [13] proposed a new drainage pile design that fixes the drainage structure to the pile body. Their research showed that the new drainage pile could dissipate excess pore water pressure in time through the drainage channel and reduce the degree of liquefaction at the site. [PERSON] et al. [14] studied the influence of different groundwater levels on the structures of buildings equipped with multidirectional drainage pipes and sheet-pile walls. The results showed that the liquefaction resistance of foundations that had drainage pipes was significantly higher than that of conventional foundations. The above research mainly focused on seismic research into bridge pile foundations, but research on composite systems similar to superstructure sheet-pile walls--that is, pile group systems in liquefied lateral spreading sites--requires further study. To date, scholars have studied the effects of earthquakes on structures using various methods, such as shaking table tests [15; 16; 17], FEM (finite element method) analyses [18; 19; 20; 21], etc. Following previous studies' methodology [22; 23; 24; 25; 26; 27; 28], a series of shaking table tests was conducted and the seismic response of a bridge foundation strengthened with drainage sheet piles in liquefied inclined sites was investigated. Various parameters of the response of laterally spreading foundations, such as excess pore water pressure ratio and acceleration, were tested. Parameters associated with the sheet-pile wall, including bending moments and lateral displacement, were also tested, and the lateral displacement of the bridge superstructure was recorded. The results are analyzed and discussed below.