Abstract: A soil arch would be generated in the expressway embankment reinforced by rigid piles under the dead weight of the fill,and the external load could be transferred through the arch.The load transfer mechanism of the shallow layer directly influenced the coordination work of piles and soil and the effect of reinforcement.However,research on vertical soil arching effect and character of soil arch was not well enough.By experiment in situ and analysis on the data of the pore water pressure and the pile-soil relative displacement,the existence of the soil arch was approved.The experimental data also reflected that certain equilibrium mechanical structure was formed under given load.Every time the load was increased by 20 kPa,the original structure was destroyed once and then generated again.The data also reflected that the arch generated in coarse aggregate could bear more load increment and the arching effect was stronger when the embankment was reinforced by piles with caps.