時域反射法於土釘工程品質檢測技術研發

Abstract

近年來台灣地區使用土釘來加強邊坡穩定上較為頻繁，但國內尚無一套簡易的土釘檢測方法以檢測土釘施工品質，包含土釘長度與灌漿的品質。因此，本研究為提供一土釘檢測方法，並提升其可靠、效率與經濟性，嘗試利用時域反射法（Time Domain Reflectometry, TDR）傳輸線式之優勢，同時參考香港之經驗，企圖研發改善適用於土釘工程品質檢測方法。依香港相關文獻建議，其係利用一單心電纜線平行固定於土釘側邊，以單心電纜線與土釘形成TDR的導線，藉以檢測土釘長度與回填品質，但其技術經本研究評估仍其有纏繞弊端以及無法區分長度和孔洞限制。為此，本研究改採同軸纜線替換既有單心電纜線，除利用預埋之同軸纜線可確實且快速檢核土釘的長度，並可藉由纜線的外導體與鋼筋形成之TDR導線，檢核混凝土灌漿品質是否完整，有無包含孔洞情形。目前相關的室內試驗長度量測的部分設計三組不同長度的試體，其量測誤差百分比結果均在百分之一以內，結果相當準確，而在回填灌漿的部分，設計兩組不同孔洞大小的試體，其量測的結果均在百分之五以內，結果顯示透過預埋之同軸纜線可確實且快速的檢測土釘長度及其回填灌漿的品質。目前已有現場初步案例應用測試。本研究冀後續改善能落實工程實務應用，並提供一標準土釘檢測方法與作業程序，藉以提升相關工程施工品質。

Soil nail method is frequently employed to enhance slope stability in Taiwan in recent years. But there is no simple method to verify the soil nails quality in domestic constructions area. Therefore, this study aims to provide a soil nail inspection method to meet the requirements of reliability, efficiency and economic feasibility. This research is based upon the time domain reflectometry (TDR) method and refers to the experiences of Hong Kong researches in order to improve the quality of the soil nail works. According to the Hong Kong researches suggestions, the standard configuration of the TDR soil nail inspection is analogous with a parallel transmission line if the single electric core wire is pre-installed along a steel soil nail. The twin conductors act as the TDR transmission line to detect the soil nail length and grouted quality simultaneously. However, the preliminary technical evaluation revealed by this study points out the practical limitations from the Hong Kong existing method. To solve the aforementioned problems, this study proposes using a coaxial cable to replace the single electric core wire. The development can provide the quick soil nail length check by measuring the coaxial cable length. Meanwhile, it also can use the outer conductor of the coaxial cable and steel bar to form a TDR waveguide and detect soil nail grouted quality. Our research trial have shown that the three different length soil nails measurement error are all in less than one percent and the two different void sizes soil nails measure result are all less than five percent , the results show that the embedded-through coaxial cable can reliably and quickly detect soil nail length and its backfill grouting quality. We have some initial test case in field. Based on these verifications, this study provide a standard TDR soil nail testing method in order to enhance the quality of related constructions.