以振動台試驗探討土壤液化引致地下管線上浮之機制

Abstract

臺灣位於環太平洋地震帶，地震頻繁發生。由於地震振動，飽和的砂土可能因超額孔隙水壓力的產生，砂土強度降低導致土壤液化的發生。土壤液化發生時，建築物下沉、地層下陷、噴砂、地下維生管線及結構物上浮或破壞等災害常伴隨著土壤液化發生。本研究利用剛性盒於1g 振動台上進行一系列的縮尺模型試驗，以研究土壤液化發生期間的土壤運動行為、地下管線的垂直位移量以及地表沉陷量，並探究其相關機制。剛性盒的長、寬、高尺寸分別為121、35及35.5公分，並於長邊開設了一個壓克力透明窗口，透過攝影機記錄，分析試驗期間管線及土壤的運動行為趨勢。本研究所使用的試驗材料為石英矽砂，其統一土壤分類為不良及配砂土 (SP)，管線模型為高密度聚乙烯 (HDPE) 管，縮尺比例為1：3。本研究共進行了七組試驗，所有試驗之試體厚度均為30公分。管線模型埋設至試體中央地表下15公分處，並保持管線內部中空無水，加速度及水壓感測器則距離管線模型水平10公分處垂直埋設，用以測量試驗期間之加速度和孔隙水壓歷時。本研究輸入振動台之振動訊號為正弦波，並透過改變不同輸入振動頻率及檯面水平位移、最大運動加速度及愛式強度 (Arias Intensity) 探討對管線上浮量、地表沉陷量之影響。試驗結果顯示在輸入相同檯面水平位移下，輸入越高的振動頻率，管線上浮量越低，地表沉陷量則有上升的趨勢；而在輸入相同振動頻率下，輸入越高的檯面水平位移，管線上浮量及地表沉陷量均有上升的趨勢，而隨著最大運動加速度及愛式強度的增加，管線上浮量及地表沉陷量也均有提升的趨勢。本研究亦根據各學者所提出之上浮理論公式檢核本研究之試驗結果，且利用粒子圖像測速法 (Particle Image Velocimetry, PIV) 分析土壤於管線上浮期間之運動行為趨勢。

Taiwan is located in the Circum-Pacific Seismic Belt, where earthquakes occur frequently. Due to seismic shaking, excess pore water pressure may develop at shallow depths in saturated sandy soil strata, resulting in soil liquefaction and disasters such as building and ground settlement, sand boiling, and uplift or damage to underground pipelines and structures. This study aims to use a rigid box to conduct a series of scaled model tests on a 1-g shaking table to investigate the soil behavior, the uplift of an underground pipeline, and ground settlement during soil liquefaction. The dimensions of the rigid box are 121 cm  35 cm  35.5 cm, and an acrylic window is installed on the long side to record the movement behavior of the pipeline model and soil through a GoPro. The tested material is poorly graded silica sand (SP), and the pipeline model is made of high-density polyethylene (HDPE) and a scale 1:3 of the prototype. Seven tests were conducted with a sample thickness of 30 cm, and the hollow pipeline model was buried 15 cm below the ground surface. The horizontally buried sensors at 10 cm from the pipeline model recorded acceleration and pore water pressure during the test. The input motion was a sine wave, and by varying the input frequency and table displacement, maximum input acceleration, and Arias intensity, the effects on pipeline uplift and ground settlement were explored. The results of the tests showed that, under the same input amplitude, higher input frequencies led to lower pipeline uplift and an increase in ground settlement. Similarly, under the same input frequency, higher input amplitudes resulted in increased pipeline uplift and ground settlement. Moreover, with the increase in maximum input acceleration and Arias intensity, both pipeline uplift and ground settlement showed an increasing trend. This study also verified the test results using the uplift theories proposed by various researchers and analyzed the soil movement behavior during pipeline uplift using Particle Image Velocimetry (PIV).