Design method for active slope reinforcement: A case study of excavated slopes
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摘要:目的
边坡失稳破坏具有较强的时空特征，现有被动设计方法造成大量挖方边坡工程失稳。分析边坡开挖时空演化规律，探讨边坡主动加固设计方法，对边坡信息化施工和安全控制尤为重要。
方法采用现场调研和数值模拟手段，分析高边坡开挖破坏原因和滑带主应力演化规律，揭示边坡开挖渐进破坏机制，进一步构建以加固时机、加固深度、加固力为核心三要素的边坡主动加固设计方法体系，并通过典型挖方边坡工程检验方法的可行性。
结果和结论结果表明：(1)挖方边坡开挖失稳破坏过程可划分为：破坏应力孕育期、稳定发展期和急速发展期。(2)建立挖方边坡变形阶段和安全系数(Fs)与开挖步的表征关系，可控弹塑性变形阶段1.05≤Fs≤Fst(设计安全系数)为最佳加固时机；临界坡高计算方法可以更加方便地确定加固时机，0.4 Hcr~0.7Hcr(临界坡高)为最佳加固时机。(3)提出主动加固深度上下界的界定方法，主动加固时锚固段的深度需在锚固上界之下，且达到锚固下界。(4)考虑开挖损失应力补偿，提出每级坡主动加固力的确定方法，保证开挖过程中边坡稳定性。(5)通过工程案例进行主动和被动加固设计比较，得出采用提出的主动加固设计方法只需要相对较小的加固力即可较好地约束边坡变形和塑性区扩展。研究成果可为挖方边坡工程信息化施工和加固设计提供指导。
Abstract:ObjectiveSlope instability and failure exhibit extinct spatiotemporal characteristics. Existing design methods for passive reinforcement have resulted in the engineering instability of numerous excavated slopes. Therefore, analyzing the spatiotemporal evolutionary patterns of slopes during excavation and exploring the design methods for active slope reinforcement are particularly important for the information technology (IT)-based construction and safety control of slopes.
MethodsUsing on-site investigations and numerical simulations, this study analyzed the causes of excavation-induced failure of high slopes, as well as the evolutionary pattern of the principal stresses in the sliding zone. Consequently, this study revealed the progressive failure mechanism of slopes during excavation and developed a design system for active slope reinforcement with reinforcement timing, depth, and force as key factors. Finally, this study verified the feasibility of the system using typical slope excavation engineering.
Results and ConclusionsThe results indicate that the excavation-induced failure process of a slope can be divided into three periods: the incubation, stable development, and rapid development periods of failure stress. The characterization of the deformation stage and safety factor (Fs) of the excavated slope using the excavation steps was established, revealing that the optimal reinforcement timing was the time when 1.05≤Fs≤Fst (design safety factor) in the controllable elastic and plastic deformation stage. The reinforcement timing can be more conveniently determined using the calculation method for the critical slope height, which indicates that 0.4‒0.7 Hcr (critical slope height) represents the optimal reinforcement time. The method for determining the upper and lower boundaries of the active reinforcement depth indicates that the depth of the anchorage segment should be positioned below the upper boundary of the anchorage segment and extend to its lower boundary. Considering the compensation for excavation-induced stress loss, this study proposed a method for determining the active reinforcement force of each grade of a slope to ensure slope stability during excavation. The comparison of active and passive reinforcement designs for an engineering case suggests that the proposed design method for active reinforcement allows for the effective restriction of slope deformations and plastic zone expansion using a relatively small reinforcement force. The results of this study can serve as a guide for the IT-based construction and reinforcement design of slope excavation engineering.
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图 1 高速公路沿线的挖方边坡破坏情况实例
Fig. 1 Examples of excavation-induced slope failure along expressways
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图 5 预定滑带上应力提取点位布设
Fig. 5 Layout of stress extraction points on the predetermined sliding zone
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图 6 预定滑带上最大最小主应力比变化情况
Fig. 6 Variations in the maximum and minimum principal stress ratio of the sliding zone
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图 7 预定滑带上最大最小主应力云图
Fig. 7 Nephograms showing the maximum and minimum principal stresses in the sliding zone
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图 8 挖方边坡开挖变形阶段特征
Fig. 8 Diagram showing the characteristics of excavation deformation stages of excavated slope
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图 15 开挖前后水平应力变化情况
Fig. 15 Variations in the horizontal stress before and after excavation
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图 16 不同加固方法下边坡稳定性与开挖步关系
Fig. 16 Relationship between slope stability and excavation steps under different reinforcement methods
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图 17 不同加固方法的水平位移和塑性区云图
Fig. 17 Contour maps showing the horizontal displacement and plastic zones in different reinforcement methods
表 1 边坡物理力学参数
Table 1 Physical and mechanical parameters of a slope
土层 γ/(kN·m−3) E/MPa c/kPa φ/(º) υ 黏土 19 50 15 46 0.38 
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表 2 岩土层物理力学参数
Table 2 Physical and mechanical parameters of the soil layer
岩土层 γ/
(kN·m−3)E/
MPaυ 峰值强度 残余强度 c/kPa φ/(º) c/kPa φ/(º) 粉质黏土 20 50 0.38 24 23 8 17 强风化泥岩 23 100 0.33 68 33 13 31 中风化泥岩 24 500 0.30 78 35 18 33.5
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表 3 计算过程中各级边坡涉及的主要的力
Table 3 Primary forces involved in various slope grades in the calculation
单位：kN/m 坡级 被动加固力 分级主动加固力 分段主动加固力 剩余推力 7 200 150 150 6 400 250 250 5 650 300 300 4 800 600 600 3 900 800 900 2 1100 1000 1100 1 450 350 400 总和 4500 3450 3700 4473
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