Study on Creep Characteristics and Long-Term Strength of Soil in Loess-Red Clay Composite Slopes Under Excavation Conditions
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摘要:
在黄土高原地区，开挖卸荷易引发边坡失稳灾害，而黄土的水敏性与蠕变特性是开挖边坡变形的关键因素. 为探究开挖工况下黄土、红黏土和复合土体的蠕变特性及长期强度，依托天水市中梁镇某开挖边坡工程，通过三轴卸荷蠕变试验，研究了黄土、红黏土及界面试样在不同含水率（12%、18%和24%）和围压（100 kPa、200 kPa和300 kPa）条件下的卸荷蠕变特性. 结果表明：（1）试样均呈现“衰减蠕变-稳态蠕变-加速蠕变”三阶段蠕变特征，围压越大土体对卸荷越敏感，含水率升高加剧了试样蠕变，并使试样更易破坏；相同卸荷条件下，红黏土应变略低于黄土，界面会增加蠕变应变；界面试样临界卸荷量最低，且试样更易沿界面破裂；（2）长期强度指标（c、φ）随围压增大而提高、随含水率升高而降低，界面试样φ最小，为12.54°；（3）界面试样的蠕变应变随着卸荷量的加剧而加速增加，界面是抗剪薄弱环节. 研究可为开挖工况下黄土-红黏土复合边坡稳定性防控提供试验依据.
Abstract:In the Loess Plateau region, excavation-induced unloading is prone to triggering slope instability disasters, and the water sensitivity and creep characteristics of loess are key factors governing the deformation of excavated slopes. To investigate the creep characteristics and long-term strength of loess, red clay, and composite soil under excavation conditions, this study relies on an excavated slope project in Zhongliang Town, Tianshui City. Through triaxial unloading creep tests, the unloading creep behaviors of loess, red clay, and interface specimens were studied under different moisture contents (12%, 18%, and 24%) and confining pressures (100 kPa, 200 kPa, and 300 kPa). The results show that: (1) All specimens exhibit three-stage creep characteristics, namely attenuated creep, steady-state creep, and accelerated creep. Higher confining pressure makes the soil more sensitive to unloading; an increase in moisture content exacerbates the creep of specimens and renders them more susceptible to failure. Under the same unloading conditions, the creep strain of red clay is slightly lower than that of loess, while the interface increases the creep strain. The interface specimens have the lowest critical unloading amount and are more likely to fracture along the interface. (2) The long-term strength parameters (cohesion c, internal friction angle φ) increase with the rise in confining pressure and decrease with the increase in moisture content. The φ value of the interface specimens is the smallest, reaching 12.54°. (3) The creep strain of the interface specimens increases acceleratively with the intensification of unloading amount, and the interface is a shear-weak zone. This study can provide experimental basis for the stability control and prevention of loess-red clay composite slopes under excavation conditions.
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Key words:
- excavation /
- unloading creep test /
- composite slope /
- creep curve /
- long-term strength /
- slope stability
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图 4 红黏土试样的卸荷蠕变应变-时间关系曲线
Fig. 4. Unloading creep strain-time curves of red clay samples
图 5 18%含水率下界面试样的卸荷蠕变应变-时间关系曲线
Fig. 5. Unloading creep strain-time curves of bounded interface samples under 18% moisture content
表 1 试验土样的基本物理性质
Table 1. The basic physical properties of the test soilsamples
试样类型 天然密度(g/cm3) 含水率(%) 干密度(g/cm3) 土粒相对密度 孔隙比 黄土 1.631 12.11 1.455 2.68 0.976 红黏土 1.656 11.75 1.482 2.73 0.982 
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表 2 三轴卸荷蠕变试验方案
Table 2. Unloading Creep Test Scheme
试样类型 含水率(%) 围压（kPa） 卸荷量（kPa/级） 黄土试样 12/18/24 100 12.5 200 25.0 300 37.5 红黏土试样 12/18/24 100 12.5 200 25.0 300 37.5 界面试样 18 100 12.5 200 25.0 300 37.5
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