| 摘要: | 本研究使用中央大學地工離心機進行6組離心模型振動台試驗，探討不同型式建築物於可液化地盤之沉陷與受震行為，地盤條件為相對密度55%之土層，總地盤厚度為16.4 m，地下水位距離地表之深度為2 m。建築物基礎型式分為淺基礎與樁基礎，基礎尺寸依照建築物大小分為10 m (L) × 6.8 m (W) 及6.8 m (L) × 4.8 m (W)，建築物基礎與地盤間之接觸應力皆為71 kPa。此外，本研究利用圓錐貫入試驗 (Cone penetration test, CPT) 之錐尖阻抗值進行簡易液化評估，依據簡易評估流程建立液化引致之地表及建築物沉陷超越機率曲線。
當輸入基盤最大加速度為0.08 g (AI = 0.4 m/s)、0.17 g (AI = 1.7 m/s)及0.35g (AI = 7.4 m/s)時，可得以下結論: (1) 對淺基礎而言，大尺寸之淺基礎 (大1.5倍) 沉陷量可分別降低43% (0.033 m)、31% (0.030 m)及12% (0.020 m);(2) 對淺基礎而言，大尺寸之淺基礎 (大1.5倍) 建築物傾斜角分別增加50%、12%及5%;(3) 對樁基礎而言，大尺寸之基礎 (大1.5倍) 沉陷量可分別降低69% (0.051 m)、55% (0.050 m)及21% (0.034 m);(4) 對樁基礎而言，大尺寸之基礎 (大1.5倍) 建築物傾斜角可分別降低30%、14%及8%;(5) 對小型建築物而言，使用樁基礎形式之建築物沉陷量可分別降低5%、4%及3%。對大型建築物而言，使用樁基礎形式之建築物沉陷量可分別降低48%、38%及12%;(6) 當液化發生時，外加載重之應力增量(∆σz)受影響範圍深度等於基礎寬度(B)。根據試驗結果反算，可建立修正外加載重之垂直應力增量曲線，用以估計液化發生時土壤之有效覆土應力。意即當土壤液化發生時，土壤仍有殘餘強度其有效覆土應力不為零
;This study considers the building′s performance at liquefaction sites and when using the centrifuge at National Central University. Six experiments are tested wherein the uniform liquefiable sand with 55% of relative density. Two kinds of foundations (shallow and pile foundations) with different widths and lengths were placed with the same contact pressure of 71 kPa. The large foundation (Foundation L) was 10.0 meters length and 6.8 meters width (prototype). The small foundation (Foundation S) was 6.8 meters length and 4.8 meters width (prototype). Furthermore, this study employs a cone penetration test to assess liquefaction-induced settlements (CPT). A simplified process for establishing the probability of exceeding settlement curve.
The results showed that (1) For the shallow foundation, when the foundation dimensions are larger (1.5 times difference), settlement dramatically decreases to 43% (0.033 m), 31% (0.030 m) and 12% (0.020 m) under the base input motions of 0.08g (AI = 0.4 m/s), 0.17g (AI = 1.7 m/s), and 0.35g (AI = 7.4 m/s). (2) For the shallow foundation, when the foundation dimensions are larger (1.5 times difference), the tilting angle of structure increases by 50%, 12% and 5% under the base input motion of 0.08g (AI = 0.4 m/s), 0.17g (AI = 1.7 m/s), and 0.35g (AI = 7.4 m/s). (3) For the pile foundation, when the foundation dimensions are larger (1.5 times difference), the settlement decreases to 69% (0.051 m), 55% (0.050 m), and 21% (0.034 m) under the base input motion of 0.08g (AI = 0.4 m/s), 0.17g (AI = 1.7 m/s), and 0.35g (AI = 7.4 m/s). (4) For the pile foundation, when the foundation dimensions are larger (1.5 times difference), the tilting angle of structure increases by 30%, 14%, and 8% under the base input motion of 0.08g (AI = 0.4 m/s), 0.17g (AI = 1.7 m/s), and 0.35g (AI = 7.4 m/s). (5) For the small structure, using the pile foundation instead of the shallow foundation reduces settlement by only 5%, 4%, and 3% under the base input motion of 0.08g (AI = 0.4 m/s), 0.17g (AI = 1.7 m/s), and 0.35g (AI = 7.4 m/s). For the large structure, when the pile foundation is used instead of the shallow foundation, settlement reduces by 48%, 38%, and 12% under the base input motion of 0.08g (AI = 0.4 m/s), 0.17g (AI = 1.7 m/s), and 0.35g (AI = 7.4 m/s). (6) During soil liquefaction, the vertical stress increment due to surface loading (∆σ_z) only affected with a depth equal to the foundation width (B). From the back analysis. a modified vertical stress increment due to surface loading curve established, which can be used to estimate the effective overburden pressure in the liquefaction soil layer, meaning that the soil′s effective overburden stress is not zero during liquefaction and retains some residual strength. |
