Abstract This report describes the damage and ground movements observed in the residential area of Satozuka 1-Jo, Sapporo, Japan during the 2018 Eastern Iburi Earthquake as triggered by the liquefaction of pumice sand with which a valley had been filled. The geographical setting and the on-ground and aerial reconnaissance and soil characterization results are reported, leading to a possible scenario of the state of the pumice fill from its formation to the earthquake. This report focuses on the liquefaction disaster in Satozuka 1-Jo and summarizes it as follows: (a) The Satozuka residential area is located at the end of a plateau consisting of pyroclastic flow deposits, pumice sand called Spfl, deriving from the Lake Shikotsu caldera (30 to 40 thousand years ago), and some valleys that formed by erosion. (b) To develop level residential land, the pumice sand ridges were cut and the valleys were filled in with the pumice sand in the 1970s. The gradual loss of drainage capability might have led to a rise in the long-term groundwater level. (c) Liquefaction of the pumice sand fill was triggered and the fluidized fill flowed downwards along the sloped topography. Where the slope angle became steeper, asphalt pavements seem to have been pushed upwards and broken through by the liquefied soil, and the liquefied soil flowed out to the ground. (d) Physical and mechanical tests were conducted on the pumice sand fill, and its characteristics were reported with particular emphasis on its volumetric behaviour upon compaction, wetting, and pre- and post-liquefaction compression. Undrained cyclic triaxial tests showed the low liquefaction resistance of the pumice fill despite its high fines content (around 40%, non-plastic). (e) The laboratory test results and field evidence suggest that the potential key factor of the liquefaction at this site was the loosely compacted pumice sand fill, which easily forms a loose soil structure with macropores even when compacted on the wet side of optimum.

中文翻译：

---

2018 年北海道伊武里东部地震导致札幌里冢地区的地面运动和破坏

摘要 本报告描述了在 2018 年日本札幌 Satozuka 1-Jo 居民区观察到的损坏和地面运动，该地震是由填充山谷的浮石液化引发的。报告了地理环境以及地面和空中侦察以及土壤表征结果，从而得出了从形成到地震的浮石填充状态的可能情景。本报告重点关注 Satozuka 1-Jo 的液化灾难，并将其总结如下： (a) Satozuka 住宅区位于由火山碎屑流沉积物、称为 Spfl 的浮石砂组成的高原尽头，源自支笏湖火山口（30至4万年前），以及一些由侵蚀形成的山谷。(b) 开发水平住宅用地，1970 年代，浮石沙脊被切割，山谷被浮石沙填满。排水能力的逐渐丧失可能导致长期地下水位上升。(c) 浮石砂填料液化被触发，流化填料沿倾斜地形向下流动。在坡度变大的地方，沥青路面似乎被液化土向上推破，液化土流向地面。(d) 对浮石砂填料进行了物理和机械测试，报告了其特性，特别强调了其在压实、润湿以及液化前后压缩时的体积行为。不排水循环三轴试验表明，尽管细粉含量高（约 40%，非塑料），但浮石填料的耐液化性较低。(e) 实验室测试结果和现场证据表明，该地点液化的潜在关键因素是松散压实的浮石砂填料，即使在最佳湿侧压实，也很容易形成具有大孔隙的松散土壤结构。