公路勘察中滑坡体的地球物理特征与分析——以张榆线公路勘察为例

Geophysical Characteristics of Landslide Body in Highway Reconnaissance: A Case Study in Highway Prospecting of Zhangyu Line

滑坡是影响路桥安全的重要隐伏地质灾害。地球物理方法作为一种无损高效的勘察方法,可有效查明滑坡体内部的地质构造及滑面等特征。本文以张榆线崇礼隧道出口段滑坡为例,采用高密度电阻率法和剪切波速测试,并结合钻孔资料对滑坡体的地球物理特征进行了分析。该滑坡体视电阻率值和剪切波速值具有明显的垂向差异性,一定程度反映了该滑坡体岩土体性质、密实度、含水率的垂向差异性,综合分析认为视电阻率值和剪切波速值较高的强风化流纹岩顶面为潜在滑面。在此基础之上,基本确定了滑坡体由冲洪积体和坡积物组成,附着于流纹岩体之上,横向长度达300 m,纵向长度260 m,滑坡体厚度达20~30 m。同时,根据高密度电阻率三维剖面分析,认为滑坡体底部滑趾处为剪出口位置。最后,基于滑坡体地球物理特征建立了滑坡体地质模型。

Landslide is important hidden geological disasters that effect on the safety of roads and bridges. As a nondestructive and efficient investigation method, geophysical methods can effectively find out the features of geological structures and sliding surfaces inside the landslide body. By taking the landslide at the exit of Chongli tunnel of Zhangyu line as an example, the geophysical characteristics were analyzed by means of high-density resistivity method and shear wave velocity test combined with borehole data. The apparent resistivity and shear wave velocity of the landslide have obvious vertical differences, which reflect the differences in the vertical rock properties, density, and moisture of the landslide. The result shows that the top surface of the highly weathered rhyolite with high apparent resistivity and shear wave velocity is the potential sliding surface. On this basis, it can basically be inferred that the landslide body is composed of alluvial and alluvial deposits, attached to the rhyolite rock body, with a transverse length of 300 m, a longitudinal length of 260 m, and a sliding body thickness of 20-30 m. Simultaneously, according to the analysis of the high-density resistivity of the three-dimensional profile, it is considered that the slide toe at the bottom of the sliding body is the shear outlet position. Based on the above characteristics, the geological model of the landslide is established.