基于瑞雷面波技术的芒洪八角塔倾斜成因无损探测

Abstract

瑞雷面波探测技术具有无损、浅层分辨率高、经济高效等优势，已广泛应用于探测各类建筑的地基结构信息。始建于清朝康熙年间的芒洪八角塔位于云南省澜沧县，是全国重要保护文物。现今八角塔整体向北倾斜，并出现了开裂现象，为保护文物，迫切需要采用无损探测方法探明塔基础结构信息，分析塔身倾斜的原因。本篇文章研究应用瑞雷面波技术高分辨率探测塔基础地层的剪切波速度结构，据此结合工程地质信息推断塔身倾斜原因，为保护文物提供依据。通过在塔基础布置两条瑞雷面波测线获取剪切波速度结构信息，推断八角塔基础浅地表层回填土厚度约为1 m，其下基岩为砂砾岩，塔基坐落在相对凸起的基岩面上，塔基础的北侧有剪切波低速异常区，持力层相对较弱.综合探测结果，总结得出以下内容：1) 塔北侧存在局部破碎带；2) 持力层对塔基产生的支持力不均匀导致塔向北侧倾斜。 Rayleigh wave detection technique has been used widely to detect the structural information of tower foundation for engineering constructions. There are many advantages, including nondestructive, near surface high resolution, cheapness and quickness, etc. The Manghong Octagonal tower was built in Kangxi period of Qing dynasty, located in Lancang county, Yunnan province and became one of the most important historical sites in China. At present, Manghong Octagonal Tower is inclining to north and the tower appears some cracks at the bricks on tower body. In order to protect cultural relics, nondestructive detection method has to be utilized to ascertain the structural information of tower foundation, and analyze the reason why the tower was inclined. In this paper, we used Rayleigh wave exploration technique with high resolution to obtain shear wave velocity structure of tower foundation. Combining with the engineering geological information, we can deduce the reason why the tower was inclined, and provide some basic advices for the protection of cultural relics. We processed the Rayleigh wave data from the two survey lines at the tower foundation, and obtained the information of the shear wave velocity structure. From there, we can deduce the backfill soil thickness is about 1 m near surface of tower foundation and the bedrock is sandy conglomerate. The tower foundation is located on the relative prominent bedrock surface, and a shear wave low-velocity area can be found on the north of foundation with weaker bearing stratum. We can conclude from the result of detection as follow: 1) the local fracture zone exist on the north of the tower; 2) the uneven supported power between the bearing stratum and tower foundation would lead the tower to inline north.