邊坡地錨抽樣檢測與整體風險度評估之研究

Study on maintenance examination and reinforcement percentage of slope ground anchors and overall risk assessments

鄭清江(Ching-Jiang Jheng) ； 卿建業(Jian-Ye Ching) ； 游友友(Yo-Yo Yo)

《華梵藝術與設計學報》 10期 (2015/07) Pp. 125-139

摘要

自國道3 號發生大規模坍方事件後，高速公路之地錨邊坡均已全面安全檢測及補強。現行地錨檢測共分為四種項目，分別為外觀檢測、鑿開檢視、內視鏡檢測與揚起試驗等，其檢測抽樣比率各有不同，而不同項目檢測結果所顯示的彼此關係大都呈現不定趨勢，且各種檢測項目的結果最後如何顯示出整體邊坡的安全風險度，尚未見有具體的探討。以至於後續執行的維修補強是不是恰當，有無過當浪費或是不足的疑慮。本文針對不同邊坡分別由整體中間、兩端與隨機抽樣三種方式，每10%進行檢測結果之統計，其結果顯示地錨支數越少時抽樣10%時誤差越高，約抽樣達40%才漸趨穩定；從旁邊開始抽樣之地錨10%時容易低估地錨檢測分數，約達40%才漸趨穩定；PLAXIS 與STABL 分析結果顯示，常時情況安全係數約1.50~1.52、暴雨情況安全係數約1.28~1.45。因此當抽樣率低時建議從中間開始抽樣，抽測比率約採30%以上，比較符合整體地錨坡面性能評分之情況。並考量統計的不確定性之標準偏差，以及邊坡穩定分析常時情況與暴雨情況標準偏差之不同，則建議地錨檢測抽樣比率應以達到30%為較佳之選擇。

關鍵字

地錨檢測 ； 抽樣檢測比率 ； 坡面穩定分析

並列摘要

After the large-scale landslide which buried the Formosa Freeway (sta. 3.1 k) in northern Taiwan occurred on April 25, 2010, all slopes stabilized by ground anchor along the freeways have been comprehensively examined and reinforced. The existing four ground anchor examinations are: visual inspection, scuttling detection, endoscopy detection and lift-up test. Sampling ratio of the examinations differs from each other and results of each examination do not show consistent trend. Moreover, concrete discussions of safety risk of entire slope revealed by the each examination have not been made. As a result, misgivings of insufficiency and wasting of subsequent maintenance and reinforcement arise. This study focuses on statistic results of 10% of the examinations on the middle, both ends, and random samples of an entire slope. The results point out that larger errors appear with less numbers of ground anchors when only 10% of the samples are examined. When 40% of the samples are examined, the errors become stable. When examinations for the ground anchors from both ends are executed, the score are easily underestimated, which become stable when 40% of the samples are examined. Therefore, it is suggested that sampling is made from the middle part of the slope when sampling rate is low, and the quality of the entire ground anchor slope would be consistent with the score when sampling rate is over 30%. Standard deviation (σMS) of statistic uncertainties are also to be considered, as well as the differences in standard deviation between normal and storm conditions of slope stability analyses. It is accordingly suggested that the best choice would be 30% of the sa mpling ratio for ground anchor examinations.

並列關鍵字

Ground anchor examination ； sampling examination ratio ； slope stability analysis