Damaged Mechanism and Improvement Countermeasures of Monitoring Wells

• Main Authors: Wen-Kwei Jean, 簡文奎
• Other Authors: 廖朝軒
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/03141178427469755134

碩士 === 國立臺灣海洋大學 === 河海工程學系 === 93 === This study first collects the data associated with the well break, discusses the reasons of the well break and performs the case study of the recent monitoring well break. In the past, the establishment of monitoring wells did not consider the influence of environmental adverse factors, such as areas of land subsidence and the vicinity of faults, resulting that many monitoring wells were broken under different mechanisms with different levels. Monitoring wells in Changhwa and Yunlin counties were regarded as an example in this study. The wells were affected seriously by the land subsidence and the 921 Chi-Chi earthquake and caused the break of many wells. Therefore, an analysis-of-variance technique was used to analyze the physical break of wells associated with the change of co-seismic groundwater levels due to the 921 Chi-Chi earthquake and pumping rates in groundwater right databases. The study result reveals that the physical break of wells in the groundwater constraint zone correlates with pumping rates. Over-pumping in this zone typically causes land subsidence to compress well tubes, causing the deflection and fracture of well tubes and screens and the damage of well buildings. Furthermore, the physical break of wells out the groundwater constraint zone correlates with the change of co-seismic groundwater levels due to Chi-Chi earthquake. The earth crust is compassed in the western area from the Changhwa fault. The soil volume stress due to the 921 Chi-Chi earthquake causes the damage of wells. This work suggests that the elevation of monitoring wells should be re-measured in the area of the land subsidence and after the occurrence of the Chi-Chi earthquake. Additionally, this study proposes methods of the examination and maintenance of monitoring wells. After the occurrence of large earthquakes, the examination and maintenance of monitoring wells are performed using a television inspection system to find the location of the well break. The frequency of the examination and maintenance of monitoring wells should be increased when the monitoring wells are located in the area of the land subsidence and after the occurrence of the earthquake. If a new monitoring well is constructed in areas of land subsidence and the vicinity of faults, its well building and facility should be enhanced, such as increasing the thickness of well tubes, using high stiff materials and strengthening well bodies.