基于探地雷达的水库坝前淤积土沉积规律研究

宁夏南部黄土丘陵山区水库除险加固工程中普遍采用"坝前淤积面加坝"工法进行施工,而淤积层的分布规律对评价坝基稳定性至关重要。为勘察淤积土剖面分层情况和空间分布特征,利用探地雷达(GPR)对固原市西吉县大沙河水库坝前淤积土进行探测试验。在选定的坝前淤积土探测区域内,布设了10条测线,首先确定了雷达探测最佳图像效果的叠加次数,然后在所有测线上每隔0.5 m (共计794个测点)进行了探测。同时开挖深度为1.5 m的探槽观察淤积层剖面状况,并在不同深度剖面上取土样进行室内基本物理性质试验。结果表明:雷达探测的最佳叠加次数为512次;雷达波谱图显示在深度为0～2.5 m范围内,坝前淤积土有6层明显的沉积层理;在深度为4～9 m范围内,有清晰连续的河道河床轮廓,各测线上淤泥的沉积厚度范围为3.7～8.2 m;在探槽深度约50 cm处可以观察到明显的砂质粉土—黏质粉土的层理,与探地雷达在该位置的图像解析一致。探测试验为坝前淤积层沉降计算及工程处理措施提供了基础数据。

Study on Sedimentation Regulation of Silted Soil in the Front of Reservoir Dam Based on GPR

In the reservoirs eliminating danger and reinforcement engineering in severe soil erosion area of the Loess Plateau in southern Ningxia of China, the construction technique of "raising earth dam from upstream deposited mud" is generally adopted. And the distribution rule of deposit layers is very important to evaluate the stability of the dam foundation. In order to investigate the profile stratification and spatial distribution characteristics of the upstream silted soil, the ground penetrating radar (GPR) was used to detect the silted soil in front of Dashahe reservoir in Xiji County, Guyuan City. In the selected detection area of the silted soil in front of the dam, 10 survey lines were laid. First, the number of superimpositions for the best image effect of radar detection was determined, and then detection was carried out at 0.5 m intervals (a total of 794 detection points) on all test lines. At the same time, a 1.5 m deep trench was excavated to observe the profile of the silting layer. And soil samples were taken from different depth profiles for laboratory experiments of basic physical-mechanical properties. The results showed that the optimal number of superpositions of radar detection was 512. Radar spectrum showed that there were six obvious sedimentary bedding layers in the range of 0 to 2.5 m. In the depth range of 4 m to 9 m, there was a clear and continuous outline of the river-bed profile, and the sedimentary thickness of the silt on each survey line ranged from 3.7 m to 8.2 m. Obvious sandy silt-clay silt bedding could be observed at the depth of about 50 cm in the trench, which was consistent with the image analysis of GPR at this position. These findings could provide a basis for the settlement calculation and engineering treatment measures of the silting layer in front of the earth-filled dam.