砂土地基强夯影响因素及振动规律的现场试验研究

Field Test on Influencing Factors and Vibration Law of Dynamic Compaction for Sand Foundation

针对某些大型建筑工程地基软土地质发育,下卧地层常为高含水量、高压缩性、低强度土层的情况,开展了砂土地基强夯的现场试验。根据试验结果,分析了地下水位、软土夹层、满夯遍数及振动碾压对砂土地基强夯加固效果的影响,探讨了不同能级强夯振动规律。研究结果表明：地下水位对强夯加固深度和效果有明显影响,砂土地基强夯时,若地下水位过高,需将地下水位降至地面下2～3 m后再施工;加固深度内若有软土夹层,则会明显减小强夯夯能向下传递效果,因此需提高单击夯能来提高强夯加固效果;第二遍满夯的加固效果不明显,可与第一遍满夯合并,或者用具有相同加固效果的振动碾压方式来替代;通过对不同级别强夯振动的现场试验,提出了不同能级强夯振动的三向加速度峰值衰减系数和当量系数值,并给出了不同能级强夯振动的安全距离。

Aimed at the condition of soft foundation and underlying stratum with high water content,high compressibility and low strength in some large scale construction projects,the field test of sand foundation dynamic compaction was conducted. Based on the test results, the influences of underground water depth, soft soil interlayer, number of full-compaction and vibro-rolling on foundation reinforcement effect have been analyzed. Vibration law of different energy-level dynamic compaction has been investigated. Some conclusions have been drawn. Firstly, underground water depth has an obvious influence on reinforcement depth and effect. For dynamic compaction in sand foundation,if the underground water level is high,the water level should be reduced to 2 ～ 3 m under the ground surface. Secondly,when soft soil interlayer exists in reinforcement depth,the transmitting effect of compaction energy will be weakened and single compaction energy should be increased to improve reinforcement effect. Thirdly, reinforcement effect of the second time full-compaction is not very obvious. Therefore,the second time full-compaction can be combined with the first time full-compaction or substituded by vibro-rolling which has the same reinforcement effect as the second time full-compaction. Based on vibro test of different energy-level dynamic compaction,attenuation coefficients and equivalent coefficients of peak accelerations in three directions are proposed. And vibration safety distance of different energy-level dynamic compaction in fine sand foundation is also proposed.