EXPERIMENTAL STUDY ON THE LATERAL FLOW SLIDE MECHANISM OF SATURATED LOESS MASS
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摘要: 1920年海原Ms 8.5地震诱发了大量黄土液化型滑坡，多表现为低角度、长距离、流态化运动特征，甚至出现大范围近水平侧向扩展流滑现象，其特殊的成因机制颇受争议。为此，在对海原地震诱发的石碑塬滑坡遗迹详细勘查的基础上，借助DPRI-5大型环剪仪，进行饱和黄土稳态变形特性试验研究，探讨了固结压力、饱和度和剪切速率等因素对黄土稳态强度的影响规律。结果表明：黄土稳态强度受到固结压力、饱和度及加载速率等因素的影响。在不排水剪切条件下，固结压力越大，黄土孔压响应越慢，稳态强度越高；黄土的饱和度越高，黄土孔压响应越快，稳态强度越低；剪切速率对黄土强度具有一定弱化效应，当剪切速率＜0.1 mm/s时，剪切速率对强度影响较小；当剪切速率介于0.1~1 mm/s范围时，随着剪切速率的提高，稳态强度有不同程度的降低；当剪切速率＞1.0 mm/s时，随着剪切速率的增大，影响程度降低，稳态强度趋于恒定，总体上看来，饱和度越高，剪切速率对强度的弱化影响越明显。研究成果揭示了石碑塬饱和黄土层在低稳态强度下发生侧向流滑的致灾机理。Abstract: In 1920, the Haiyuan Ms 8.5 strong earthquake induced many loess liquefaction landslides, which were characterized by low angle, long distance, fluidization, and even phenomenon of large-scale horizontal lateral spreading flow slide happened, and the special formation mechanism is quite controversial. The Shibeiyuan landslide was one of the most typical examples of these landslides. Based on the detailed exploration of Shibeiyuan landslide remains, with the application of the DPRI-5 ring shear apparatus, the stability deformation characteristics of the liquefied saturation loess was studied and the influence laws of factors like consolidation pressure, saturability and shearing speed on the steady state strength of loess was discussed. The research indicates that the dynamic load level and its action mode affect considerably the stress-strain of loess and the developing law of pore water pressure; at the same void ratio, the steady state strength of saturated loess is not affected by early stress path, but related to consolidation pressure, saturation, loading rate and so on. The main conclusions are as follows:1Under the undrained shear condition, the higher the consolidation pressure gets, the slower the pore pressure response, and the higher the steady state strength gets2 The higher the saturation of loess gets, the faster the pore pressure response and the lower the steady state strength gets. 3 Shearing rate has a certain weakening effect on loess strength. When the shearing rate is within the scale of 0.1 mm/s, it poses little effect on the steady state strength; when the shearing rate ranges from 0.1 to 1 mm/s, the steady state strength reduces to various degree as the shearing rate increases; when the shearing rate is more than 1mm/s, the steady state strength tends to be constant because the increase of shearing rate would reduce the effects. In general, the higher the saturation degree is, the greater of the weakening effect of the shearing rate poses on the steady state strength. It reveals that steady deformation characteristics and the disaster-inducing mechanism of horizontal lateral flow slide of the Shibeiyuan saturated loess layer under low steady state strength.
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图 1 石碑塬滑坡全貌
a—石碑塬滑坡全貌；b—液化形成的波浪起伏状堆积地貌
Figure 1. The picture of the Shibeiyuan landslide
图 2 石碑塬滑坡工程地质平面图
1—房屋；2—道路；3—沟道；4—剖面线；5—钻孔及编号；6—探井及编号；7—泉；8—地层界限；9—滑坡区边界; 10—滑源区边界；11—推测滑坡剪出口；12—被滑坡掩埋的沟道；13—马兰黄土；14—第四系全新统冲洪积层；15—滑坡堆积层
Figure 2. Engineering geological map of the Shibeiyuan landslide
图 3 石碑塬滑坡工程地质纵剖面图(Ⅱ-Ⅱ')
Figure 3. Engineering geological longitudinal section of the shibeiyuan landslide
图 4 不同正应力下环剪试验时程曲线
Figure 4. Time-history curves of the ring shear test under different normal stress
图 5 环剪试验的应力路径关系曲线
Figure 5. Stress path curves under different initial strains of the ring shear test
图 6 环剪试验的黄土峰值强度和稳态强度
Figure 6. Losses peak strength and steady state strength of the ring shear test
图 7 不同饱和度黄土环剪试验时程曲线
Figure 7. Time-history curves of the losses ring shear test under different saturabilities
图 8 不同饱和度黄土的孔压时程曲线
Figure 8. Time-history curves of losses pore pressure of different saturabilities
图 9 不同饱和度黄土的峰值强度和稳态强度
Figure 9. Losses peak strength and steady state strength under different saturabilities
表 1 试验黄土的基本物性指标
Table 1. The basic physical parameters of the test loess
取样深度/m 土的天然状态物性指标 塑性指数Ip 粒度组成/% 天然密度ρ/(g·cm-3) 含水率ω/% 孔隙比e0 粘粒＜0.005/mm 粉粒0.005~0.075/mm 砂粒0.075~2.0/mm 14.10 1.47 5.30 1.02 4.56 8.52 78.64 12.84 
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