Experimental investigation on dynamic compaction for reinforcement of liquefiable sandy silt foundation
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摘要:
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1 000 kN·m和2 000 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1 000 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1 000 kN·m和2 000 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1 000 kN·m和2 000 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2 000 kN·m强夯能级进行地基处理，而停机坪和滑行道区域采用1 000 kN·m强夯能级进行地基处理。
Abstract: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 1 000 kN·m and 2 000 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 1 000 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 1 000 kN·m and 2 000 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 1 000 kN·m and 2 000 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 2 000 kN·m is suitable, and 1 000 kN·m dynamic compaction level is used for foundation treatment in the apron and taxiway area.
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图 2 强夯法检测方案示意图
Figure 2. Schematic diagram of dynamic compaction method detection scheme
图 3 夯击次数与夯沉量变化曲线
Figure 3. The relationship between compacting times and tamping volume
图 4 单击夯能1 000 kN·m条件下强夯前后标准贯入击数与标准贯入深度关系
Figure 4. Relationship between standard penetration blow count and depth before and after dynamic compaction under single impact energy of 1 000 kN·m
图 5 单击夯能2 000 kN·m条件下强夯前后标准贯入击数与标准贯入深度关系
Figure 5. Relationship between standard penetration blow count and depth before and after dynamic compaction under single impact energy of 2 000 kN·m
图 6 强夯前后不同深度的面波波速曲线
Figure 6. Surface wave velocity curves at different depths before and after dynamic compaction
表 1 可液化土层主要物理力学性质统计表
Table 1. Statistical table of key physical and mechanical properties of liquefiable soil layers
岩土层名称 含水率
w/%天然密度
ρ/g·cm-3孔隙比n 饱和度
Sr/%压缩模量
E100~200s/MPa塑性指数
Ip液性指数IL 标贯击数N ②砂质粉土(液化层) 47.55 1.69 1.267 97.5 4.2 27.6 0.59 6 ②1黏质粉土(液化层) 19.42 1.82 0.761 69.2 6.35 8.3 0.39 6 ②2粉细砂(液化层) — — — — — — — 8 
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表 2 可液化地基土层强夯处理参数
Table 2. Construction plan for dynamic compaction of liquefiable soil strata in subgrade
试验区 单击夯能/
(kN·m)夯点间距/
m单点击数 冻土层情况 1区 1 000 3.0 4 未挖除 2区 1 000 3.0 6 未挖除 3区 1 000 3.0 8 未挖除 4区 1 000 3.0 10 未挖除 5区 1 000 3.0 12 未挖除 6区 1 000 3.0 4 挖除 7区 1 000 3.0 6 挖除 8区 1 000 3.0 8 挖除 9区 2 000 4.0 4 无冻土层 10区 2 000 4.0 6 无冻土层 11区 2 000 4.0 8 无冻土层 12区 2 000 4.0 10 无冻土层 13区 2 000 4.0 12 无冻土层
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表 3 强夯前后液化土样数量对比
Table 3. Comparison of liquefied soil sample quantities before and after dynamic compaction
单击夯击能/
(kN·m)液化判别深度/m 液化土样数量 强夯前 强夯后 1 000 1.3~4.3 13 0 5.3 6 6 2 000 1.3~4.3 8 0 5.3 7 0 6.3 2 2
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表 4 强夯法综合应用参数
Table 4. Comprehensive application parameters for dynamic compaction construction
夯击能/
(kN·m)适用场地分区 强夯应用参数 标准贯入试验 干密度检测 最佳夯击数 夯点布设 夯间距/m 有效加固深度/m 消除液化深度/m 标贯击数/击 干密度/(g·cm-3) 1 000 滑行道、停机坪区域 10 正方形 3 4.5 4.3 ≥10
(4.5 m深度内)≥1.45
(0.3 m深度内)2 000 跑道区域 8 正方形 4 5.5 5.3 ≥12
(5.5 m深度内)≥1.45
(0.3 m深度内)
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