桩端后注浆嵌岩灌注桩竖向承载性状现场试验研究

Field test investigation of the vertical bearing behavior of post-grouting and rock-socketed piles

在南京河西地区开展了桩径1100 mm,有效桩长50.9〜55.9 m,以中风化泥岩为桩端持力层共6组大吨位桩端后注浆嵌岩灌注桩竖向静载荷试验,深入研究了该地区大直径后注浆嵌岩桩竖向承载特性及荷载传递机制。试验结果表明:4根试桩Q-s曲线为缓变型,2根试桩为陡变型,桩顶回弹率达63.6%〜83.4%,桩端阻力占总荷载比例不到5%;注浆质量差、桩端沉渣厚的试桩极限承载力明显偏低,嵌岩部分的桩侧摩阻力比正常工作的试桩小25.7%〜30.8%;相比嵌岩较深试桩,嵌岩较浅试桩的极限承载力偏小,但端阻发挥更多,且在桩端附近的桩侧摩阻力发挥程度也更高,嵌岩段承担荷载的占比更高;随着桩顶荷载增大,试桩的嵌岩段总阻力近似线性增长,且基本大于桩周土总侧摩阻力。本试验研究成果为后注浆嵌岩桩设计提供了依据,同时也为类似地区大直径嵌岩桩实践与理论研究提供了参考。

In Hexi area of Nanjing,six groups of large tonnage static load tests were carried out to study the vertical bearing characteristics and load transfer mechanism of large diameter post-grouting and rock-socketed piles.The test piles were embedded in moderately weathered mudstone with different rock-socketed length,and their diameter was 1100 mm and the effective pile length was 50.9〜55.9 m.The results show that the load-settlement curves of the 4 piles are mild ones and the other 2 piles are steep ones.The rebound rate of the pile top is 63.6%~83.4%,and the tip resistance accounts for less than 5%of the total load.In addition,the ultimate bearing capacity of the test piles with poor grouting quality and thick sediment under the pile tip are obviously smaller,and the shaft friction of the rock-socketed part of the piles is 25.7%〜30.8%smaller than that of the normal test piles.The shaft frictions located in the end of the pile are 25.7%〜30.8%smaller than those of the normal working test piles.Compared with the piles with larger rock-socketed length,the ultimate bearing capacity of the test piles with smaller rock-socketed length is smaller,whereas the tip resistance plays a major role.The shaft friction near pile tip is higher,and the proportion of the load carried by the rock-socketed section is also higher.With the increase of the load,the total resistance of the rock-socketed section increases approximately linearly,and is basically larger than the total shaft friction of soil layer.The experimental research results can provide a basis for the design of postgrouting and rock-socketed piles and give a significant reference for the practice and theoretical research of large-diameter rock-socketed piles in similar areas.