倾斜软基上斜直桩组合结构单侧受力破坏模式试验

Experimental Study on the Failure Mode of Inclined-straight Pile Composite Structure on Declining Soft Foundation Under Single Side Load

倾斜软基上修建高速公路(铁路)时,地基容易出现差异沉降、滑移甚至垮塌。提出坡脚斜直桩组合结构+桩体复合地基加固倾斜软基,采用模型试验,对比测试倾斜软基上桩体复合地基受压时,坡脚处插入硬层的双单桩、双直桩组合结构以及斜直桩组合结构的桩侧土压力、桩身应变和外侧桩水平位移,揭示倾斜软基上插入硬层的斜直桩组合结构单侧受力变形机制与破坏模式,为倾斜软基上斜直桩组合结构的设计提供试验依据。结果表明:①内、外侧桩在桩身中部偏上位置呈现桩侧土压力峰值;外侧桩倾斜度增大,其桩侧土压力峰值快速减小,内侧桩桩侧土压力大于外侧桩;②外侧桩在桩身中部偏上位置呈现侧移峰值,桩顶嵌固连梁外侧桩的桩身水平位移及其峰值均随倾斜度增大而减小,总是小于桩顶自由的外侧桩,峰值位置也较低;③桩身中上部出现弯矩峰值,外侧桩弯矩峰值位置略低,外侧桩倾斜度增大导致内侧桩弯矩增大、外侧桩弯矩减小;④单侧受载时,斜直桩发生水平位移,随后弯曲变形,内侧桩率先破坏、外侧桩后破坏,具有关联性,而双直桩的破坏荷载介于斜直桩的内侧桩和外侧桩之间。加大内侧桩的抗弯刚度和外侧桩的倾斜度将大幅度提高斜直桩组合结构的整体稳定性。工程中,建议外侧桩倾斜度为10%~20%,并根据路堤高度(荷载)选择内侧桩与外侧桩刚度之比大于2。

When a highway(railway)is built on inclined soft soil,the foundation is prone to differential settlement,slippage,and even collapse.To strengthen the declining soft foundation,a joint program of an inclined-straight pile composite structure and pile composite foundation is proposed in this study.In the model test,the lateral earth pressure,pile strain,and horizontal displacement of the outside piles for double single piles,double-straight piles composite structure,and inclined-straight piles composite structure inserted into a hard layer were measured and compared when the pile composite foundation in declining soft soil was compressed.The deformation mechanism and failure mode of the inclined-straight piles composite structure inserted into a hard layer on declining soft soil were identified,which provided an experimental basis for design.The results show the following.①The upper middle position of the inside and outside piles appears peak values of the soil pressure.With an increase in the inclination of the outside pile,the peak value of the earth pressure on the outside pile decreases rapidly.The lateral earth pressure of the inside pile is greater than that of the outside pile.②The outside pile shows a peak lateral displacement at the upper-middle position of the pile body.The horizontal displacement and peak value of the outside pile with a fixed beam at the top of the pile decrease with an increase in the inclination,which is always smaller than that of the free top pile,and the peak position is also lower.③Peak values of the bending moment are observed in the upper-middle part of the pile body,whereas the bending moment peak position of the outside pile is slightly lower.The bending moment of the inside pile increases,and the bending moment of the outside pile decreases with an increase in the inclination angle of the outside pile.④Under a single side load,the inclined-straight piles initially undergo horizontal displacement and then exhibit bending deformation.The outside pile is destroyed following internal pile failure,which is related.The failure load of the double straight pile is between the inside and outside piles.In the project,increasing the bending stiffness of the inside pile and the inclination angle of the outside pile,will greatly improve the overall stability of the inclined-straight piles composite structure.According to the height(load)of the embankment in engineering,an inclination of 10%-20%of the outer pile is proposed,and the stiffness ratio of the inside pile to the outside pile should be controlled above 2.