以大型直接剪力試驗探討地工格網剪力介面行為之研究

以大型直剪試驗各種土壤與地工材料相關介面摩擦係數以被廣泛的使用在各種加勁結構物設計介面參數，但大多數剪力試驗研究利用相同土壤材料與格網組合進行直剪試驗，在試驗上觀察剪力介面帶上之土壤顆粒變化研究仍然是缺乏的。因此本研究將利用透明大型直剪盒與五種近似方形開孔格網與四種不同粒徑土壤搭配觀察剪力帶介面間土壤顆粒流動特性，並在試驗過程中採用數位照相機拍攝剪力介面變化，分析不同格網特性與土壤顆粒之關係，與加勁土體間介面剪力帶變化之情形。研究結果顯示，觀察三分石、一分礫石顆粒與格網有良好的互制行為，破壞面將會遠離格網，介面剪力帶寬約(9.2mm-26mm)、(8.7mm-13.4mm)。越南矽砂置入格網之介面剪力帶寬約(4mm-6mm)介於礫石與標準砂間。觀察標準砂介面剪力帶範圍約(1.2mm-2.6mm)受砂顆粒尺寸效應影響介面上剪力帶範圍最小。上述四種不同粒徑土壤與不同型式地工材料試驗之介面觀測結果，介面剪力帶大小依序為三分礫石＞一分礫石＞越南矽砂＞標準砂。可了解在不同粒徑土壤所呈現出不同之介面行為，不論是加勁土壤與未加勁土壤條件下，礫石試體皆比越南砂、標準砂有較明顯的剪力帶的發生，在相同的條件下礫石較越南砂、標準砂有較高之剪力強度，且土體膨脹量亦較大。在本研究中探討剪力介面觀測來了解土壤在格網勒條間之發展，試驗中發現格網勒條表面與格網張力強度對介面上土壤顆粒流動是有相當大的影響。

關鍵字

介面剪力帶；直剪試驗；格網肋條

並列摘要

The interface friction coefficient between different soils and geosynthetics by obtaining from large-scale direct shear test has been widely used in designing of reinforced earth structure. Most of the direct shear tests are usually performed the geogrid and same soil at upper and lower layer of shear box. The lack of research by using direct shear test to observe the shear band of soil particles. Therefore this study adopt a transparent large-scale direct shear box with five opening size of grid and four different soil particle size to observe the flow characeteristics of soil particle at interface shear band by using a digital camera. Recording interface friction changes and analyize the change of different geogrid characteristics and between soil particles. The testing results show gravel particles and geogrid have good interaction behavior. Failure surface of shear band will be far away from the location of geogrid and interface area. The bandwidth is about (9.2mm-26mm)、(8.7mm-13.4mm) that is measured at Vietnam sand. The interface shear band bandwidth is about (4mm-6mm) at Ottawa sand and gravel. Observation of Ottawa sand interface shear band bandwidth about (1.2mm-2.6mm),effect of sand particle size on the interface shear band with the scope of the smallest. The result of interface shear observation use four different soil particle size and five different kinds of type geogrid of the above mentioned, the interface shear band ranked in descending order are as follows: gravel＞Vietnam sand＞Ottawa sand. Understandably, the different soil particle size can show the different interface behavior, despite in reinforced soil condition or in unreinforced soil condition, gravel specimen has more visible shear band than Vietnam sand and Ottawa sand. Under the same conditions, the gravel has the higher shear strength more than Vietnam sand and standard sand, soil dilation behavior also more pronounced. This study is to explore Interface shear observation and to understand the soil in the geogrid rib development, in this test can found that geogrid surface and geogrid rib tensile strength with soil particle mobile has the quite Obviously influence.