Shear characteristics of foamed flowable stabilized soil under triaxial compression conditions
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摘要: 发泡流态固化土（FFSS）已广泛应用于回填工程中，但其性能评价多基于无侧限抗压强度，缺乏对侧向约束作用的研究。本文通过不固结不排水（UU）三轴剪切试验，重点探究了湿密度、粉土掺量和围压等因素对FFSS力学特性的影响规律。结果表明：试样的应力−应变曲线具有明显的弹塑性特征，符合莫尔–库仑准则；围压和湿密度的增加均可提升材料的三轴压缩强度，当湿密度从600 kg/m3提高至1200 kg/m3时，黏聚力增长超250%，内摩擦角随密度增加而降低；围压可延缓强度劣化，脆性指数降低40%～60%；粉土掺量以35%为临界值，此时强度与变形性能最佳。此外，本文基于试验数据构建了抗剪强度的多元回归模型，可为FFSS的工程设计与性能预测提供支持。Abstract: Foamed Flowable Stabilized Soil (FFSS) is widely used in backfill engineering. However, its performance evaluation is mostly based on unconfined compressive strength, with limited studies addressing the influence of lateral confinement. In this study, a series of Unconsolidated Undrained (UU) triaxial shear tests were conducted to systematically investigate the effects of wet density, silt content, and confining pressure on the mechanical behavior of FFSS. The results show that the stress–strain curves of the specimens exhibit distinct elastoplastic characteristics and conform to the Mohr–Coulomb failure criterion. Both increased confining pressure and wet density contribute to enhanced triaxial compressive strength. Specifically, when wet density increased from 600 kg/m3 to 1200 kg/m3, cohesion increased by over 250%, while the internal friction angle decreased with increasing density. Confining pressure was also found to delay post-peak strength degradation, reducing the brittleness index by 40%~60%. A critical silt content of 35% was identified, at which the material achieved optimal strength and deformation performance. Moreover, a multiple regression model for shear strength was developed based on the test data, offering valuable support for the engineering design and performance prediction of FFSS.
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图 4 无侧限抗压强度下的FFSS破坏形态
Figure 4. Failure modes of FFSS in the unconfined compressive strength test
图 9 不同湿密度下FFSS的力学响应
Figure 9. Mechanical response of FFSS under different wet densities
图 10 不同围压下FFSS的力学响应
Figure 10. Mechanical response of FFSS under different confining pressures
图 11 不同粉土掺量FFSS的力学响应
Figure 11. Mechanical response of FFSS with different silt contents
图 12 不同粉土掺量FFSS的微观结构图
Figure 12. Microstructure images of FFSS with different silt contents
图 14 抗剪强度参数随粉土掺量的变化规律
Figure 14. Variation of shear strength parameters with silt content
表 1 水泥的物理力学性能
Table 1. Physical and mechanical properties of cement
比表面积
/（m2∙kg−1）标准
稠度/%凝结时间
/min抗压强度
/MPa抗折强度
/MPa初凝 终凝 3 d 28 d 3 d 28d 358 28.2 192 231 28.1 50.7 6.5 9.6 
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表 2 发泡剂性能指标
Table 2. Properties of the foaming agent
稀释
倍数发泡
倍数气泡群密度
/（kg∙m−3）1 h泌水量
/mL1 h沉降距
/mm60 20 51 22 2
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表 3 FFSS配合比
Table 3. Mix proportions of FFSS
湿密度
/（kg∙m−3）固体质量
/（kg∙m−3）水泥用量
/（kg∙m−3）粉土用量
/（kg∙m−3）用水量
/（kg∙m−3）泡沫用量
/（kg∙m−3）600 384.71 308.35 77.09 173.44 40.61 800 527.20 422.55 105.64 237.68 33.42 1000 669.69 536.75 134.19 301.92 26.24 1200 812.17 650.95 162.74 366.16 20.15
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表 4 试验方案设计
Table 4. Design of the test scheme
湿密度 /(kg·m−3) 粉土掺量/% 试验围压/kPa 600，800，1000，1200 0，20，35，50，65 100，200，300 注：为便于比较分析，FFSS-800-20-100表示湿密度800 kg/m3、粉土掺量20%、围压为100 kPa时的试样，其余试样命名类推。
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