预应力锚索复合土钉支护的现场测试研究

结合北京熊猫环岛地铁车站深基坑支护工程,通过对预应力锚索与土钉联合使用条件下土钉轴力随时间变化、土钉轴力沿长度的分布、土钉轴力最大值的分布、锚索预应力的变化等现场测试及分析,从力学机制上研究了预应力锚索复合土钉的工作机理,研究表明:(1)土钉受力具有时间效应及开挖效应;(2)土钉轴力形成和空间分布与基坑潜在滑动趋势有关;(3)预应力锚索对作用范围内土钉轴力空间分布有一定影响;(4)预应力锚索可减小坡体位移,使得各土钉轴力相对减小,改善坡体应力状态;(5)工作状态下,土钉和预应力锚索的受力状态变化相互影响较小,各自发挥作用。

VARIATIONS OF IN-SITU FORCES IN SOIL NAILS AND PRE-STRESSED GROUND ANCHORS AS COMBINED STRUCTURE FOR EXCAVATION OF A SUBWAY STATION FOUNDATION PIT IN BEIJING

This field test used the supporting structure for excavation of foundation pit at the PANDA annular island subway station in Beijing.The supporting structure combined pre-stressed ground anchor and soil nails.The field test results included the axial force variation of the soil nails with time,the axial force distribution of the soil nails along its length,the maximum axial force distribution of the soil nails,the pre-stress variation of the cable and so on.The principle of the pre-stressed composite soil nailed reinforcement structure is studied from the aspect of mechanical mechanisms.The results show that:(1) The tensile force in soil nails is variable with time and excavation;(2) The development and distribution of the axial force in soil nails are relevant to the potential slide trend of the foundation pit;(3) The influence of the pre-stress ground anchor on the axial force distribution of the soil nails is rather large;(4) The usage of the pre-stress ground anchor can reduce the displacement and improve the stress state of the pit slope,as well as reduce the axial force of the soil nails;(5) in the initial stage of being used,the variation of the load condition in the soil nailing has less effect on that of pre-stress ground anchor.They function independently.