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Nanan Elementary School is located at Ta Di Village, Mituo District, Kaohsiung City. The reason why it is called ‘Ta Di Village’ is that this is a place where is usually filled with water. Also, the surface soil in the village is easily washed away by water. It often makes the holes of the synthetic-rubber sports track and the grass at the school collapse without any warnings. Although the school has filled the collapsing areas and paved the sports track many times, it is still dangerous for students and people who use these areas as long as the real reason is not fully understood. This study tends to analyze that the collapsing of the earth is attributed to the seepage layer of the underground stream (above GL.-15m). The study is done by collecting the data about the geology and hydrology of the school, drilling the existing soil, examining the physics and mechanics of the soil, pumping the water and observing the level of the underground water. In addition, the study samples the diffused soil to process the pinhole test and bicapillarypycnometer test. By doing these tests, it finds out that the soil of Nanan Elementary is the kind of highly diffused soil that is easily damaged by running water andit leads to the destruction of the piping. From the geology data analysis of BH-1~BH-9 drilling holes at the school, it conforms with the mode of the water flowing up and down from an earth-filled dam and this is the reason why the collapsing of Nanan Elementary happens. Besides, through the dropping water (BH-4、BH-6) from the pumping well (PW1) and the well of observing water level, it is known that the water flow above the GL.-15m underground is from south to north. However, according to the distribution of the underground stream, BH-1~BH-9, the flow of the underground water is from southeast to northwest. As a result, it is highly recommended to build the retaining walls, the gutters, and the cut water facilities at the east and south side of the school. In this way, it can filter the underground river and reduce the possibility of the underground stream taking away the surface soil. By doing these, it can improve the problem of the collapsing at school.
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