液化引致地下管線上浮量之影像分析及解析模型

Abstract

地震誘發之土壤液化現象對地下結構物安全構成重大威脅，尤其在飽和鬆散砂土中，孔隙水壓迅速累積導致土壤有效應力下降，使地層如流體般失去支撐力，進而引發地表沉陷、地下管線上浮以及噴砂等災害，其中地下管線上浮，使接頭變形導致管線破裂，對民眾生活機能造成重大影響，故地下管線因土壤液化導致上浮破壞之相關研究值得深入探討。液化期間地下管線與土壤的相互作用複雜，浮力與阻抗力之動態變化難以量測，致使過往相關研究多侷限於經驗性描述與簡化力平衡，缺乏可反映時變過程與細部力學機制之完整系統。為突破上述限制，本研究使用 1g 振動台模型試驗與非侵入式粒子影像測速法 (Particle Image Velocimetry, PIV)，觀測地下管線於液化條件下之動態上浮行為與周圍土體變形過程。透過攝影與影像處理，成功量測管線在不同震動時刻之運動歷程，並追蹤管線上方土壤剪裂帶之發展。本研究利用PIV 技術揭示剪裂帶主要自管線頂部向兩側發展，震動期間近楔型破壞面，說明土壤失去剪力強度後對結構物之抵抗力急遽下降，進一步導致管線迅速上浮。在理論分析方面，本研究建構一套土壤剪裂帶發展、黏滯阻力、孔隙水壓及覆土載重隨地下管線上浮變化之力學模式，並以牛頓第二運動定律為基礎推導出位移的歷時方程式，進一步簡化模型推導解析解，並與數值解法進行比較，結果顯示兩者在計算上吻合，但與實驗觀測結果相比，解析與數值模型皆出現明顯偏差。進一步分析發現，主要誤差來源在於模型初期假設黏滯阻力為常數，未能反映液化過程中土壤剪應變速率與孔隙水壓急遽變化所導致之黏滯特性演化。因此，本研究修正模式中之黏滯係數假設，改採時變黏滯係數表示方式，使預測結果更貼近實際試驗觀察，亦有助於反映液化土體力學行為之非線性與時變特性。

Soil liquefaction induced by earthquakes poses a significant hazard to underground infrastructure. In saturated loose sands, the buildup of excess pore water pressure reduces effective stress, causing the ground to lose shear strength and behave like a fluid. This can lead to ground settlement, sand boils, and particularly, uplift of buried pipelines. Uplift-induced deformation often results in joint failure and rupture of pipelines, compromising essential lifeline services. Despite its importance, the uplift behavior of pipelines during liquefaction remains poorly understood due to the complexity of soil–structure interaction and the difficulty of measuring dynamic forces during shaking. This study combines 1g shaking table experiments with non-intrusive Particle Image Velocimetry (PIV) to investigate the uplift response of pipelines buried in liquefiable soil. PIV analysis revealed the formation of shear bands initiating from the pipe crown and propagating outward in a wedge-shaped pattern, correlating with the loss of confinement and rapid uplift. A dynamic mechanical model was developed, incorporating shear band evolution, viscous resistance, excess pore pressure, and the reduction in overburden weight as uplift progresses. Based on Newton’s second law, a time-dependent displacement equation was derived and solved using both analytical and numerical approaches. While the two solutions agreed closely, discrepancies with experimental data were noted. Further investigation indicated that the assumption of a constant viscous coefficient led to underestimation of the uplift response under certain shaking conditions. By introducing a time-dependent viscous coefficient that accounts for evolving shear strain rates and pore pressure conditions, the modified model achieved improved agreement with the observed behavior, reflecting the nonlinear and transient nature of liquefied soils.