| Summary: | 碩士 === 逢甲大學 === 土木工程所 === 100 === Due to vast and expansive slope terrains in Taiwan, ground anchors have been widely used to support the stability of side slopes during constructions of collective housings, roads, and dams in mountainous areas. Every time a disaster took place at the side slopes supported by the ground anchors, relevant appraisal reports have always blamed it on the ground anchor construction or ground anchor corrosion. After the disaster of Lincoln Mansion on August 18th, 1997, the disaster investigation report commissioned by Shihlin District Prosecutors Office has concluded that the causes of disaster were poor quality of ground anchor construction and loose fixture. However, based on the characteristics of this disaster, my adviser concluded that the cause should be the effect of weakness of expanded basement space.
The purpose of this study is to investigate the landslide disaster that took place at 3.1 km of National Highway No.3 on April 25th, 2010. With this disaster taking place under a special condition with no wind, nor rain, nor earthquake, the professional cause of land slide should be separated from the engineering judgment to be performed by the civil engineer. In other words, as an expert, the civil engineer must have the professional knowledge to conduct all kinds of engineering judgments based on information gathered at various stages such as planning, investigation, measurement, testing, analysis, design, construction, and operation management in order to ensure the safety of this construction project. If we regard the content of engineering judgment as the cause of disaster, we are in fact accusing civil engineers of making the wrong engineering judgment thus failing to ensure the safety of construction project.
After excluding engineering judgment from the possible causes of disaster, based on the mechanisms of reducing tensile strength of ground anchor along with shear band sliding, and the reducing shear resistance at the sliding surface along with the increasing sliding speed, in this study we found the tensile strength of ground anchor has been greatly reduced by 88.9% when the relative displacement of ground anchor through shear band has reached the inner diameter D of ground anchor. During shear band sliding, the contact between sliding block and sliding surface will change from surface contact to point contact such that the shear resistance at the sliding surface will be greatly reduced along with the increasing sliding speed. As for the side slope supported by ground anchor at 3.1 km of National Highway No.3 where the ground anchor tensile strength was only designed to provide 9.3% of sliding resistance, there is actually no direct correlation between ground anchor corrosion and the land slide disaster.
Currently the ground anchor has been leaning toward performance oriented design, and the ground anchor performance reduction over time according to past literatures actually follows the downward bending parabolic model. Since this kind of parabolic model has totally neglected the influence of shear band sliding, it cannot be used to evaluate the greatly reduced performance of ground anchors due to shear band sliding during various previous disasters. In light of this, the author of this dissertation has eventually included the influence of shear band sliding in the aforementioned parabolic model such that the correlation of reducing ground anchor performance over time can be completed gradually.
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