[O-08] Poster presentations by senior high school students

[O08-P85] Gravel extraction and gravel pits around the Tama River

*Ryota Toyama¹, Oisi Kazuki¹ (1.Metropolitan Tachikawa High School)

Keywords:gravel pits, Tama River, liquefaction

During an earth science class, we learned about the existence of gravel extraction sites along the Tama River known as "gravel pits" and became interested. Gravel from the Tama River was extensively used in Tokyo's buildings and roads during the Meiji era, leading to a lowering of the riverbed and a ban on extraction in the 1930s. This led to a shift towards land-based gravel extraction, resulting in numerous gravel pits being dug along the river basin. However, during the land reclamation process, waste and garbage were often put in gravel pits, leading to pollution issues. Concerned about the seismic vulnerability of the ground, we investigated and learned about liquefaction damage occurred in gravel extraction and landfill sites in Ibaraki Prefecture during the Great East Japan Earthquake. Through analysis of old maps, aerial photographs, literature, and field surveys, it was discovered that gravel extraction also took place in the floodplains and terraces of the Tama River, where residential areas and schools were subsequently built on landfill sites. Furthermore, N-value investigations at several gravel pit sites revealed weak ground conditions.