Centrifuge Modelling on Dip-Slip Fault Rupture Propagation in Multiple Soil Strata

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题名:	Centrifuge Modelling on Dip-Slip Fault Rupture Propagation in Multiple Soil Strata
作者:	陳耀基;Soegianto, Dicky Pratama
贡献者:	土木工程學系
关键词:	地工離心機;正斷層;逆斷層;複合土層;Centrifuge modelling;normal fault;reverse fault;multiple soil strata
日期:	2020-06-12
上传时间:	2020-09-02 14:18:21 (UTC+8)
出版者:	國立中央大學
摘要:	活動斷層錯動會對近斷層的結構物與地下基礎造成永久變位，例如1999年台灣的集集地震、土耳其的Kocaeli地震和Duzce地震和2008年汶川大地震，都造成人民生活上嚴重的危害，也讓人們開始注意地盤中剪裂帶的發展，以及斷層破裂帶上鄰近結構物與地下基礎的影響。自然沉積的地盤非均勻且非均質，若表層是沉積土壤而底層是較堅硬的岩層，斷層錯動過程中，剪裂帶通過岩層與表土層也會引發一連串複雜的交互行為。本研究以離心模型模擬正斷層與逆斷層通過在地盤底部為軟岩層、地表砂土層時的剪裂帶與地表位移的發展，共進行八組試驗。軟岩層使用水泥拌合砂土混合而成的複合土層進行模擬，試驗前以無圍壓縮實驗與直剪試驗，評估養護七天後不同水泥比例下之土層強度。本研究使用砂土水泥混合比例為5% 之材料模擬軟岩層，單壓強度為0.975 MPa、摩擦角為43.5度、凝聚力為148 kPa；上覆土層為石英矽砂，摩擦角為37度、單位重15.6 kN/m3 。模型總高度為100毫米，於80 g之離心力場中模擬總厚度8公尺之土層。試驗結果顯示：(1)岩層與總土層厚度比，為引發正斷層與逆斷層錯動剪裂影響範圍的主要因素。正斷層錯動時，隨著岩層厚度的增加，影響區域也增加；在土層厚度比30% 時，斷層破裂帶影響範圍最大。(2)軟岩層與砂層的厚度比值會影響軟岩層裂隙發展。隨著砂層厚度減少，裂隙越往遠處發展。(3)正斷層與逆斷層之試驗結果皆顯示土層表面變形與底層土壤特性具有相關性。(4)岩石層底層由於裂隙傳遞範圍大而有較大變形；砂土層底層由於裂隙傳遞範圍小而有較小變形。 ;Permanent ground displacement due to the fault slip is a concern to infrastructures adjacent to the active fault. For instance, severe and serious damages happened during the big earthquake like Chi-Chi earthquake in Taiwan and Kocaeli and Duzce earthquake in Turkey at 1999. These 3 disasters are the turning point on put more concern on the behavior of the fault slip to either to the soil deposit itself or the building and infrastructure located in the fault affected zone. Furthermore, natural soil deposit is rarely found to be homogeneous and uniform, some part of the soil has higher strength layers, like soft rock stratum, at the bottom of the soil strata, causing some complex behavior while the fault rupture is propagating through both soft rock and soil strata. In this study, 8 centrifuge modelling test simulating both reverse fault and normal fault are conducted to observe mechanism of soft rock base layer affects the whole soil deposit surface. The soft rock layer is simulated by using a mixture of accelerated sand and cement. Both uniaxial compression tests and direct shear tests are conducted to evaluate the strength of the different proportion of cement. All the mixture is cured for 7 days before it tested. The 5% cement mixture is selected due to its uniaxial compression strength of 0.975 MPa, which can simulate soft rock and have a brittle mode as the post-failure behavior. The Mohr–Coulomb failure criterion is 43.5 degrees and 148 kPa of friction angle and the cohesion. The upper layer stratum is pluviated quartz sand with 37 degrees of friction angle at unit weight of 15.6 kN/m3. The model have different thickness ratio between soft rock layer and sandy layer with 100 mm total soil deposit thickness, which is corresponded to 8 meters in the prototype scale in 80 g centrifugal acceleration field. Based on the experiments results, it shows that: (1) The thickness ratio of the rock stratum plays a major role for the length of the affected zone in both reverse fault and normal fault simulation; although, the affected zone for the normal fault reach maximum length when the sandy soil ratio at 30%. (2) The thickness ratio between the soft rock layer and sandy soil layer affects the crack propagation in soft rock stratum, the crack propagates to wider area as thinner sandy soil thickness. (3) In both normal fault and reverse fault slip, the surface distortion is dependent on type of material at the bottom layer. (4) The deformation of the rock-based strata has the widest, due to its crack propagation and the sand based layer has the narrowest deformation zone, due to its narrow rupture propagation at based layer.
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