Behaviour of embankment on composite foundation with geosynthetic-encased stone columns under freeze-thaw condition
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摘要: 制作了一套加筋碎石桩复合地基冷冻试验系统,开展了1组加筋碎石桩复合地基路堤冻融离心模型试验和1组未冻融的对比试验,以研究加筋碎石桩复合地基经历季节性冻土后填筑的路堤在冻融条件下的性状。研究结果表明：冻融条件下加筋碎石桩复合地基在地基土未融化前,其桩顶和桩间土沉降基本一致,而在地基土全部融化后,桩间土沉降显著增大；冻融条件下路堤边坡基本保持初始坡度,路堤下地基沉降比较均匀,而未冻融组路堤边坡明显变缓,路堤下地基不均匀沉降明显；在复合地基和桩体均处于冰冻状态时,其桩顶和桩间土应力一致,当桩体先于桩间土融化后,桩顶应力减小而桩间土应力增大,而当地基土开始全部融化后,桩间土应力快速下降而桩顶应力快速增大,冻融条件下复合地基沉降稳定时的桩土应力比是未冻融条件下桩土应力比的2/3左右；冻融条件下由于路堤加载过程中桩顶周围土体处于冰冻状态,限制了桩顶侧向位移,而冻土层以下土体推动下部桩体向外位移,使得靠近路堤边坡下的桩体向路堤内弯曲,但弯曲变形量较小,而未冻融条件下的桩体则向路堤外弯曲且弯曲变形量较大；加筋碎石桩适合用于季节性冻土区湿地软土地基处理,其复合地基经历季节性冻土后填筑的路堤整体性能较好。Abstract: A set of freezing test system for composite foundation with geosynthetic-encased stone columns (GESCs) is developed. The centrifugal model tests are conducted on an embankment on composite foundation with GESCs under freeze-thaw condition, and the comparative tests under non-freezing condition are also conducted. The behavior of embankment built on composite foundation with GESCs subjected to seasonal freezing is studied under freeze-thaw condition. The results show that under freeze-thaw condition, the consistent settlement is found on the top of the columns and on the soil when the soil and the columns are in the frozen state, while that on the soil increases significantly after complete melting. The embankment slope remains the original slope angle and has relatively uniform settlement under freeze-thaw condition, while the significant decrease in slope angle and differential settlement are observed under non-freezing condition. When the soil and the columns are in the frozen state, the stresses on the top of the columns and on the soil between the columns are consistent. However, columns melt before the soil, the stress on the top of the columns decreases while that on the soil increases. After the soil melts completely, the stress on the soil decreases rapidly while that on the top of the columns increases rapidly. Under the freeze-thaw condition, the stress concentration ratio is relatively small, which is about 2/3 of that under non-freezing condition. Because the soil around the top of the columns is in a frozen state during the embankment loading, the lateral displacement of the top of the columns is restricted. However, the soil below the frozen soil layer pushes the lower part of the columns outward that makes the columns under the embankment slope bend inward, but small bending deformation is observed. Inversely, the columns bend outward under non-freezing condition, and the bending deformation is obvious. The GESCs are suitable for the soft soil foundation treatment of wetlands in the seasonal frozen soil areas, and the overall performance of embankment built on the composite foundation with GESCs subjected to seasonal freezing is satisfactory.
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表 1 桩顶和桩间土沉降
Table 1 Settlements on top of columns and soil
(mm) 试验 桩顶沉降 桩间土沉降 差异沉降 加载期末 休止期末 加载期末 休止期末 加载期末 休止期末 冻融组 12 42 14 54 2 12 未冻融组 19 22 37 42 18 20 
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