紅土礫石層剪力波速剖面與明挖隧道受振行為模擬;Shear wave velocity profile of lateritic gravel and seismic behavior simulation of open cut tunnel

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Title:	紅土礫石層剪力波速剖面與明挖隧道受振行為模擬;Shear wave velocity profile of lateritic gravel and seismic behavior simulation of open cut tunnel
Authors:	鮑暐文;Pao, Wei-Wen
Contributors:	土木工程學系
Keywords:	地工離心機;振動台;紅土礫石;剪力波速;隧道;Geotechnical centrifuge;Shaking table;Lateritic gravel;Shear wave velocity;Tunnel
Date:	2024-08-23
Issue Date:	2024-10-09 14:53:11 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究以離心振動台共進行5組離心模型振動台試驗，將30 cm高之自由場試體放置於 80 g的人造離心重力場，模擬24 m厚紅土礫石層之自由場受振反應，紀錄不同深度之加速度歷時、地表沉陷與土體側向位移量歷時，以探討土層的剪力波速、放大倍率、地表沉陷量及地層沿深度之側向變位，以及隧道受振期間引致的動態特性。試驗結果顯示，(1) 無連續壁僅埋置隧道的試驗情況下，輸入振動條件為1 Hz、15 cycle、PBA = 0.25 g，試驗量測土層最大剪應變於深度8.4 m ~ 14.8 m為同深層隧道最大剪應變之30倍，為經驗公式 γ=V_max/C_s 求得土層最大剪應變之2倍，故以公式推求隧道最大剪應變較為合理，安全係數為15，其中2 Hz與3 Hz輸入之基盤加速度較小，故只比較各試驗條件下1 Hz的振動事件；(2) 土層的放大倍率，以能量的觀點來看（累積絕對加速度，CAV），由深度24 m往上傳遞至深度16.7 m大約放大1.1倍；深度24 m傳遞至深度7.3 m大約放大2.3倍；深度24 m傳遞至深度2 m大約放大2.9倍；(3) 隧道頂部無覆土、隧道頂部有覆土及無連續壁僅埋置隧道的不同試驗情況下，都將會於隧道頂版及底版角落位置產生較大的應變量。無連續壁僅埋置隧道的試驗條件下產生最大的應變量約為埋置連續壁與隧道條件的3 ~ 5倍，連續壁的存在可減少隧道角落位置產生的應變量；(4) 受振後隧道產生的殘餘應變量約為受振期間最大應變量的十分之一，且殘餘應變會隨振動事件次數累加；(5) 土層剪應變量隨輸入PBA越大而有遞增的趨勢，趨勢並非為線性增長。 ;This study involves five sets of centrifuge shaking table tests, with a free-field model 30 cm in height placed within an 80g artificial gravity field to simulate the seismic response of a 24-meter-thick red clay gravel layer in a free field. The acceleration time histories at different depths, surface settlements, and lateral displacements of the soil were recorded to investigate shear wave velocity, amplification factors, surface settlements, and lateral displacements along the depth of the soil layer, as well as the dynamic characteristics induced by tunnel vibrations. The test results indicate the following: (1) Without continuous walls, the maximum shear strain in the soil was 30 times greater than that in the tunnel and double the amount calculated by the empirical formula. Using the formula provides a more reasonable estimate for the tunnel′s maximum shear strain, with a safety factor of 15. (2) The amplification factor of the soil layer increased with depth, with 1.1 times at 16.7 m, 2.3 times at 7.3 m, and 2.9 times at 2 m. (3) Significant strain occurred at the corners of the tunnel roof and floor, with the absence of continuous walls resulting in strains 3 to 5 times higher. Continuous walls help reduce this strain. (4) Residual strain after vibration was about one-tenth of the maximum strain and accumulated with repeated vibration events. (5) Shear strain in the soil layer increased with larger input PBA, though the increase was not linear.
Appears in Collections:	[Graduate Institute of Civil Engineering] Electronic Thesis & Dissertation

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