Influence of foundation pit dewatering on sonar seepage detection accuracy
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摘要: 随着声纳渗流检测技术在水文地质勘探中的应用，其测量结果精度的高低对获取的水文地质参数的准确性起着至关重要的作用。文章依托南宁某基坑工程，采用现场试验方法，同时考虑天然流场和人工流场，分三个阶段对基坑止水帷幕进行声纳渗流检测，对比不同阶段渗漏缺陷暴露的情况，同时根据渗透流速量级变化判断其检测结果精度的高低，并在实际工程中验证其准确性。研究结果表明：不同降水阶段的渗透流速大小变化显著，基坑地下水位降深每增加10 m，声纳检测到的渗透流速平均提高1~2个量级。其原因为降水导致基坑内外水头差增大，水力坡度的增加使渗漏缺陷附近的渗流场发生变化，高水头作用下渗透流速变化明显，渗漏缺陷定位更加精准，声纳检测精度也越高。可见，抬高基坑内外水头差对墙体渗漏缺陷的精准定位十分必要。因此，在对基坑止水帷幕采取声纳渗流检测时，建议将地下水位降至基坑底板以下，以提高检测结果的精度，有效探测止水帷幕渗漏风险。Abstract: With the application of sonar seepage detection technology in hydrogeological exploration, the accuracy of the measurement results plays an important role in obtaining accurate hydrologic parameters. Based on a foundation pit project in Nanning of Guangxi, this paper adopts the method of field test and considers the combination of natural flow field and artificial flow field. Sonar seepage detection was carried out on the foundation pit waterproof curtain in three stages, and the exposure of leakage defects at different stages is compared. The accuracy of the measured results is judged according to the change of the magnitude of osmotic velocity. The correctness is verified in the actual engineering progress. The research results show that the permeability velocity varied significantly in different precipitation stages, and with each 10 m increase in the depth of foundation pit water level, the seepage velocity detected by sonar seepage increases by an average of 1 to 2 orders of magnitude. The reason is that the difference between the water head inside and outside the foundation pit is increased due to precipitation, and the increase of hydraulic gradient makes the seepage field near the leakage defect change. Under the action of high water head, the seepage velocity changes obviously, so the location of the leakage defect is more accurate, and the accuracy of sonar detection is also higher. Therefore, it is very necessary to raise the head difference between the inside and outside of the foundation pit to accurately locate the wall leakage defects. When the sonar seepage detection is adopted, it is recommended to lower the groundwater level below the foundation pit floor, so as to effectively detect the risk of seepage of waterproof curtain.
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