Model test on stability of soft rock slopes composed of nearly horizontal redbeds with cracks
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摘要:
针对川东地区含裂隙近水平红层软岩边坡在长时强降雨条件下易产生滑坡灾害的问题，依托含双软弱夹层的此类典型坡体实例，以弹性模量和抗拉强度为主控因素制备可表征软岩遇水软化开裂特性的相似材料，构建了含裂隙近水平红层软岩边坡的室内物理试验模型，研究了边坡在长期雨水入渗作用下的坡体变形、裂隙扩展和稳定性演变规律。结果表明：（1）坡体变形发展可分为初始变形阶段、匀速变形阶段、加速变形破坏阶段；（2）坡体裂隙扩展主要包括在坡体后部的自下而上发育的“上窄下宽”裂隙，以及在坡体前部的自上而下发育的“上宽下窄”裂隙。裂隙扩展区域主要集中在上、下软弱夹层之间，其中易产生超孔隙水压力；（3）试验模型的FLAC3D数值模拟再现了该推移式滑坡的渗流过程，超孔隙水压力随时间呈现先增大后逐渐趋于稳定的变化特征，在软弱夹层和竖向裂隙处，超孔隙水压力呈累计增大的特征；（4）坡体滑面形成及失稳破坏演变过程可划分为浅表层裂隙发育贯通阶段、裂隙向软弱夹层延伸发育并逐步贯通阶段、裂隙扩展与坡体滑动失稳阶段。长期雨水入渗致岩体强度弱化，以及裂隙逐渐向坡体深部发育并与软弱夹层贯通形成多级阶梯式滑裂面，是造成含裂隙近水平红层软岩边坡滑动失稳的根本原因。
Abstract:Regarding to the problem that soft rock slopes composed of nearly horizontal redbeds with cracks in the eastern Sichuan area is prone to sliding failure under long-term heavy rainfall conditions, based on a typical slope example with double weak interlayers, similar materials that can characterize the softening and cracking characteristics of the soft rock in water are prepared with elastic modulus and tensile strength as the main control factors. A laboratory physical test model on a soft rock slope with fissured nearly horizontal redbeds was constructed, and the deformation, crack propagation and stability evolution of the slope under long-term rainwater infiltration was investigated. The results show that (1) the development of slope deformation can be divided into three stages - initial deformation, uniform deformation and accelerated deformation failure; (2) the crack propagation of the slope mainly includes the ‘upper-narrow and lower-wide’ cracks developed from bottom to top in the rear of the slope, and the related cracks developed from top to bottom in the front of the slope. The crack propagation area is mainly concentrated between the upper and lower weak interlayers, where excess pore water pressure is easily gathered; (3) a numerical simulation of the test model via FLAC3D presents the seepage process of the thrust landslide, and shows that the excess pore pressure increases initially and then stabilizes gradually with time. At the weak interlayers and vertical cracks, the excess pore water pressure increases cumulatively; (4) the evolution process of the sliding surface and slope instability can be divided into three stages: shallow fracture development and penetration, fracture spreading to deep weak interlayers and gradual penetrating, fracture further extension and slope failure. The weakening of rock mass caused by long-term rainwater infiltration, together with the gradual development of cracks to the deep zone of the slope and their connections with the soft interlayers to form the multi-stage stepped sliding surface are fundamental reason of slope failure for the soft rock slopes composed of nearly horizontal redbeds with cracks.
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Key words:
- nearly horizontal redbeds /
- soft rock slope /
- stability permeability /
- model test /
- cracks
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表 1 岩层原型与模型材料的主控力学参数
Table 1. Main mechanical parameters of rock prototype and model materials
岩层 σt/MPa σc/MPa E/MPa c/kPa φ/（°） 粉砂岩 原型 1.440 44.95 4803.24 6630.0 59.6 设计 0.029 0.90 96.07 132.6 59.6 试验 0.027 0.66 82.07 128.2 58.9 泥岩 原型 0.300 3.20 588.00 280.0 34.3 设计 0.006 0.06 11.76 5.6 34.3 试验 0.005 0.06 10.92 5.0 33.1 
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表 2 数值模型主要物理力学参数
Table 2. Main physical and mechanical parameters of the numerical model
材料 c/kPa φ/（°） σt/kPa E/MPa k/（cm·s−1） 软弱层 23.5 15.2 30 0.459 6E-3 岩层 132 41 800 82.7 0 裂隙 23.5 15.2 30 0.459 1E-1
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表 3 坡体模型稳定性分析的滑面参数取值
Table 3. Parameters of the sliding surface in the slope model for stability analysis
阶段 φ/（°） c/kPa PJ/kPa V/kPa L/m S/m2 I 16.4 31 17.53 3 0.85 0.2 Ⅱ 15.8 28 31.58 5 1.3 0.31 Ⅲ 15.2 25 33.88 6 1.4 0.6
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表 4 坡体稳定性分析结果
Table 4. Analysis results of the slope stability
阶段 滑面 R/（kN·m−1） F/（kN·m−1） K I I 27.30 12.42 2.20 Ⅱ Ⅱ 37.67 27.36 1.38 Ⅲ Ⅲ 37.68 42.26 0.89
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