强夯法加固可液化砂质粉土地基试验研究

Experimental investigation on dynamic compaction for reinforcement of liquefiable sandy silt foundation

针对北京大兴机场飞行区地基存在可液化砂质粉土层,研究采用低能级、小夯距和少击数的强夯法对其进行处理。为了评价夯击效果,确定强夯过程中的夯击参数,选择1000 kN·m和2000 kN·m两个能级的夯击能,每个夯击能级设定4、6、8、10和12击数。同时,设置夯击能1000 kN·m条件下夯击数4、6和8,用以研究地表冻土层对夯击效果的影响,在试验区分别进行了全深度标准贯入、面波、干密度试验检测。试验结果表明:强夯后的砂质粉土地基具有更大的密实度、传播波速和抗液化能力。其中,夯击能1000 kN·m和2000 kN·m作用下的最佳夯击数分别为10和8,对应的强夯影响深度为4.5 m和5.5 m,消除液化的深度则为4.3 m和5.3 m。而在检测指标上,标准贯入试验要求在1000 kN·m和2000 kN·m夯击能作用下,4.5 m和5.5 m全深度标准贯入击数平均值不少于10和12。最佳夯击次数作用下原地基表层的干密度不低于1.45 g/cm3。研究结果推荐在机场跑道区域采用2000 kN·m强夯能级进行地基处理,而停机坪和滑行道区域采用1000 kN·m强夯能级进行地基处理。

In light of the significant presence of liquefiable sandy silt layers in the foundation of the airfield area at the Beijing Daxing airport,this study employed a low-energy,small spacing,and low blow count dynamic compaction method to treat it.To assess the compaction effects and determin the parameters of the compaction process,two energy levels of 1000 kN·m and 2000 kN·m were selected,with each energy level tested at 4,6,8,10,and 12 blow counts.Additionally,the effect of the surface frozen soil layer on compaction was investigated using 1000 kN·m energy level with 4,6,and 8 blow counts.The full depth standard penetration,surface wave and dry density tests were carried out in the dynamic compaction test area.The experimental results revealed that the sandy silt soil foundation exhibited increased compaction,propagation wave velocity,and enhanced liquefaction resistance after dynamic compaction.Optimal blow counts were determined as 10 and 8 for energy levels of 1000 kN·m and 2000 kN·m,the corresponding dynamic consolidation depth is 4.5m and 5.5m,and the eliminating liquefaction depth is 4.3m and 5.3m,respectively.Besides,the standard penetration test requires a minimum of 10 and 12 blows in the depth range of 4.5 m and 5.5 m for energy levels of 1000 kN·m and 2000 kN·m.At the optimal blow counts,the dry density of the surface layer of the original foundation should not be less than 1.45 g/cm3.The experimental results suggest that,for foundation treatment in the runway area,the dynamic compaction level of 2000 kN·m is suitable,and 1000 kN·m dynamic compaction level is used for foundation treatment in the apron and taxiway area.