## 1 Introduction  
Jointless bridge has a continuous superstructure without moveable deck joint (MDJ), which includes integral abtment jointless bridge (IAJB), semi-integral abtment jointless bridge (SAJB) and deck-extension abtment jointless bridge (DAJB), etc. IAJB with the most favorable integrality has been widely used in North America, Europe and Australia [1; 2; 3; 4; 5]. Compared to the conventional bridges,the advantages of IAJBs involve: (1) decreasing cost of installation and maintenance of joints, (2) reducing impact and damage on bridge deck caused by bump, (3) enhancing the earthquake resistance with better redundancy. However, the superstructure would be moved (expansion/contraction) along the longitudinal direction of bridge under temperature variations, creep and shrinkage effects, or earthquake excitations [6]. These movements would inevitably cause the abutment and pile foundation to move back and forth and induce soil-structures interaction (including soil-pile, soil-abutment, abutment-pile, and soil-abutment-pile). It is well-known that when the abutment moves away from the embankment, it is subjected to active earth pressure; whereas when it moves towards the embankment, it is subjected to passive earth pressure. The researches on interaction of soil-pile foundation in IAJB were widely and comprehensively studied [7; 8; 9; 10]. The results indicate that the piles supporting on the abutment in IAJB should have reasonable flexibility to accommodate the horizontal movement. For the researches of soil-abutment interaction, some researchers carried out the tests in Lab or in filed to study the effects of temperature or seismic movements on IAJBs. [PERSON] et al. [11] and [PERSON] et al. [12] reported that when abutment moved towards the embankment, the earth pressure was equal to about two-thirds of the Rankine passive earth pressure after several cycles. [PERSON] et al. [13] observed that the distribution of earth pressure was in the shape of a trapezoid under cyclic load, and suggested that the passive earth pressure coefficient was only related to the height and longitudinal displacement of abutment. Other researchers analyzed the interaction of soil-abutment by finite element model. [PERSON] et al. [14; 15] analyzed a 137-m-long IAJB using ANSYS software, and concluded that the earth pressure behind abutment was 0.478 times that of the Rankine passive earth pressure when temperature rose about 15 degrees Celsius. [PERSON] et al. [16] also studied the ratcheting effect with the aid of the finite element model and concluded that the earth pressure behind the abutment increased year by year under the seasonal temperature cycling. For example, when the integral abutment bridge was subjected to a temperature increase of 30 degrees Celsius, the earth pressure increased by 23% after 5 years. [PERSON] et al. [17] analyzed a computer model of a 64-m-long bridge using the TDV software [18], and inferred that the earth pressure behind abutment was 0.161 times the Rankine passive earth pressure when temperature rose about 20 degrees Celsius. [PERSON] et al. [19] implemented a finite element model that incorporated nonlinear soil behavior and linear structural response considering various loading conditions and concluded that the depth of the pile would influence the behavior of the abutment. The researchers indicate that the earth pressure behind the abutment in IAJBs increases gradually with the periodical and seasonal temperature over the years. This phenomenon of increasing earth pressure is called the ratcheting effect of soil [20]. Nevertheless, these studies were mainly focused on the soil-abutment interaction rather than the soil-abutment-pile interaction, which need to be further investigated. In addition, [PERSON] et al. [21] conducted a test of monolithic abutment integrated with steel H-pile to estimate the lateral displacement capacity and the seismic performance of integral abutment bridges. However, it is only focused on the interaction of abutment-pile, ignored the effect of soil.