饱和黄土体侧向流滑机制的试验研究

EXPERIMENTAL STUDY ON THE LATERAL FLOW SLIDE MECHANISM OF SATURATED LOESS MASS

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。

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. ③Shearing rate has a certain weakening eftect 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 O. 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 lmm/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.