深层振动密实对湿陷性黄土层水平应力变化的影响

深层垂直振动不仅会增加土体刚度，还会增加其水平有效应力。结合深层振动密实技术在我国西北地区处理湿陷性黄土地基的首次实践，探讨了深层振动密实对湿陷性黄土地基土层水平应力变化的影响，同时揭示了湿陷性黄土振动密实的机制。现场试验结果表明，处理深度范围内（–8 m）土层的锥尖阻力和侧壁阻力平均提高了2倍以上，摩阻比增加了20%～50%。–3 m以上范围内土层的侧壁阻力比值较大，且对应较高的水平应力变化值（ ），土层水平应力增加显著。深度–3～–7 m范围内土层的侧壁阻力比保持在4左右，对应 值在3～4之间。–7 m以下土层的 值逐渐减小并趋于1。水平应力变化受土层侧壁阻力比的影响较大，受有效内摩擦角的影响小。分析认为，水平应力的增加，导致土层产生“预固结”效应，在微观上表现为黄土由疏松多孔的粒状结构趋向于镶嵌结构，以架空孔隙为主导的大孔隙或消失或演变为镶嵌孔隙等小孔隙，土体逐渐变得密实。

Influence of deep vibratory compaction on the horizontal stress change of collapsible loess

Compaction by deep vertical vibration increases not only the soil stiffness but also the horizontal effective stress. Based on the first practice of deep vibratory compaction in the treatment of collapsible loess foundation in northwest China, this paper discusses the influence of deep vibration compaction on the change of horizontal stress of collapsible loess and reveals the mechanism of compaction of collapsible loess by vibration. The results obtained from the field test showed that the cone stress and the sleeve resistance of the soil increased by more than 2 times within the treatment depth(–8 m), and the friction ratio increased by 20%–50%. The value of the sleeve resistance ratio was relatively large above –3 m depth, and corresponding to a higher horizontal stress change(K₀₁/K₀₀), indicating an increase of horizontal stress after compaction. At the depth from –3 m to –7 m, the sleeve resistance ratio was maintained at about 4, and the corresponding K₀₁/K₀₀ was between 3 and 4. The value of the soil below –7 m gradually decreased and became close to 1. The horizontal stress change was greatly affected by the sleeve resistance ratio but was less affected by the effective friction angle. The increase of horizontal stress caused the “pre-consolidation” effect of the soil, which was manifested in the microscopic view that loess changed from a granular structure to a mosaic structure. The large pores dominated by trellis pores disappeared or evolved into small pores such as mosaic pores, and the soil layer gradually became dense.