侧向堆载下斜桩长度影响斜-直双排桩受力响应试验研究

Experimental Study on Influence of Inclined Pile Length on Mechanical Response of Inclined-straight Double-row Piles under Lateral Surcharge

深厚软土地基上修建高速公路(铁路),路堤荷载传递至坡脚将产生水平荷载,路基可能产生滑移破坏。为减少该水平荷载产生的不利影响,提出在坡脚处设置斜-直双排桩。采用模型试验研究均质砂土地基侧向加载下,9°斜桩长度为直桩长度的0,0.75,1,1.25倍时,斜-直双排桩桩侧土压力、桩身弯矩及直桩水平位移,揭示路堤荷载下坡脚斜桩长度对斜-直双排桩变位规律与破坏模式的影响规律。结果表明:单直桩整体侧移呈"平移+绕桩底转动"模式,侧移峰值在桩顶,土压力、弯矩峰值在桩身中部;斜-直桩土压力峰值出现在桩身中下部且内侧直桩土压力大于外侧斜桩,直桩侧移峰值出现在桩身中部,弯矩峰值出现在内侧直桩中部和外侧斜桩顶部,内侧直桩弯矩峰值大于外侧斜桩弯矩峰值;随着桩长比增大,斜-直桩土压力峰值缓慢增大,内侧直桩产生的侧移峰值缓慢减少,内侧直桩弯矩峰值缓慢增大、外侧斜桩弯矩峰值快速增大。路堤荷载作用下,内侧直桩的中部、外侧斜桩的顶部易发生弯曲破坏,直桩先于斜桩破坏。工程中,为了提高坡脚抗滑移能力,建议设置斜-直双排桩,并增加外侧斜桩的长度,使内侧直桩与外侧斜桩的抗弯刚度比大于2。

When the expressway(railway) is built on the deep and thick soft soil foundation, the horizontal load will be generated when the embankment load is transferred to the foot of the slope, and the roadbed may slip and destroy. In order to reduce the adverse effect of the horizontal load, it is proposed to set up inclined-straight double-row piles at the foot of the slope. Under the lateral loading on homogeneous sand foundation, when the length of 9° inclined pile is 0, 0.75, 1, 1.25 times of the length of straight pile, the lateral soil pressure on inclined-straight double-row piles, the bending moment of pile body and the horizontal displacement of straight pile are studied by model test. The influence of the length of inclined pile on the displacement and failure mode of inclined-straight double-row piles under embankment load is revealed. The result shows that(1) the whole side shift of the single straight pile is in the mode of "translation+turning around the bottom of the pile", the peak value of the side shift is at the top of the pile, and the peak values of soil pressure and bending moment are at the middle of the pile body;(2) the peak value of inclined-straight pile soil pressure appears in the middle and lower part of pile body and the soil pressure on inner straight pile is greater than that on outer inclined pile;(3) with the increase of pile length ratio, the peak value of soil pressure on inclined-straight pile increases slowly, the peak value of lateral displacement of inner straight pile decreases slowly, the peak value of bending moment of inner straight pile increases slowly, and the peak moment of the outer inclined pile increases rapidly;(3) under the embankment load, the middle of the inner straight pile and the top of the outer inclined pile are prone to bending failure, and the straight pile is broken ahead of the inclined pile. In the project, to improve the anti-slip ability of slope foot, it is suggested to set up inclined-straight double row piles and increase the length of the outer inclined piles to let the bending stiffness ratio of the inner straight pile to the outer inclined pile be greater than 2.