In order to investigate the anchorage ability of a concrete trench, field pull-out tests were conducted. Section sizes of trench were varied ranging from 200 mm by 200 mm to 600 mm by 600 mm. The geomembrane were draped on the shoulder of its edge being placed on the bottom of trench. The trenches were filled with concrete. From the experiments, failure mechanism of concrete anchorages can be classified into four modes.