摘要
本文通过厦门某项目大直径(超)长灌注桩桩端有无注浆、不同持力层的对比静载试验以及基坑底大吨位(6000kN)抗拔试验,分析研究大直径(超)长灌注桩的竖向承载性能,得出以下结论和建议:抗压桩、抗拔桩均存在侧阻力时间效应因素的影响而降低桩侧摩阻力,当暴孔约9d,抗压桩桩侧摩阻力降低约23%,抗拔桩桩侧摩阻力降低约1/3;采用S-lgP法和经验参数法(结合静载试验)分离桩侧摩阻力和桩端阻力,表明大直径超长灌注桩即使是嵌岩桩通常也属于端承摩擦桩,侧摩阻力先于端阻力发挥,故应先满足桩身压屈变形,才能保证桩端阻力的发挥;不管是抗压桩还是抗拔桩,可优先考虑桩侧注浆,可较大幅度提高桩侧摩阻力,而不要盲目增加桩长或嵌岩深度;桩侧抗拔土阻力峰值对应的桩顶上拔量同样约为0.02D,当桩周土层为全风化岩—强风化岩时,抗拔系数约为0.60。
Based on the static loading tests with the post grouting or not for the cast-in-situ piles for a project in Xiamen with large diameter and（super） long bored piles,the contrast static loading tests on pile tip in different soils,and the uplift static loading tests in foundation pit with big load 6000kN,the vertical bearing performance of the large diameter and（super） long bored piles is analyzed on the basis of many groups of contrast vertical loading tests.The conclusions and suggestions are as follows： the pile side friction resistance of compressive pile or uplift pile is reduced because of the time effect;when the finished bore hole is in air for 9 days,the side friction resistance of compressive pile is reduced about 23%,and the uplift pile is reduced about 1/3;with the S-lgP method or the empirical coefficient method（combined with loading tests）,the pile side friction and the pile tip resistance are separated,which shows that large diameter and super long bored piles usually belong to the end bearing friction pile,and the pile side friction resistance is brought into play before the pile tip resistance,so it should be met the pile shaft buckling deformation firstly to ensure the display of the pile tip resistance;for compressive pile and uplift pile,the pile side friction resistance is greatly improved by pile grouting rather than blindly increasing pile length;the peak value of the side uplift soil resistance of the large diameter bored pile corresponding to the uplift value of the top pile is also about 0.02D and when the soil around the pile is the weathered rock and the strongly weathered rock,the uplift factor is about 0.60.
出处
《工程勘察》
2013年第9期7-13,18,共8页
Geotechnical Investigation & Surveying
