Abstract
摘要:根據近幾年來世界上幾個著名災害性地震之調查結果,顯示近斷層結構物受到地震破壞之原因。除了強地動外,另一主要因素為活動斷層之斷盤錯動所導致之近地表岩土層變形。以1999年集集地震為例,在斷層作用時之斷層帶附近,大多數結構物均遭受到嚴重損毀。然而少數結構物即使位於斷層帶,結構體本身卻僅有剛體位移或轉動而未受損。因此斷層作用時,近地表岩土層變形行為與此一變形對人工結構物之影響,實有進一步研究之需要。
了解位於地表下的斷層尖端擴展受上覆岩土層對斷層跡修飾的效應,以及探討斷層作用時,隨斷層尖端擴展主要變形區內土體內應力、應變的空間分布及其對結構物之影響,學理上對斷層帶退縮距離的決定相當重要。另外加強對斷層錯動-土壤-結構互制的了解,針對直接承受斷層錯動衝擊的結構物,如何強化結構設計,盡量減少衝擊的程度也是地震減災可行的方法。
目前對於活動斷層近地表變形特性的研究在研究方法大致上可以分為現地調查、物理模型試驗以及數值分析等三大類,本計畫之研究為突破單一方法學提出結果之侷限性,因此併用現地調查、物理模型實驗(離心機砂箱試驗、1g砂箱實驗)及數值分析之方法,分別進行基本行為觀察及定量分析。第一年將針對逆斷層,選擇車籠埔斷層為主要研究對象,探討斷層兩側岩層變形行為(包含剪切帶發育、遷移及影響參數等)、斷層錯移在近地表可能影響範圍;進行離心機砂箱實驗,探討逆斷層錯動時,上覆岩土層變形行為及對結構物之影響。並以砂箱實驗配置與實驗所得之材料參數進行數值分析,以測定邊界條件及輸入參數之合理性。再將已驗證之數值分析工具,以全尺度數值分析探討斷層作用時上覆土層變形行為,及其對人工結構物之影響,並提出較合理的安全性探討指標,作為判斷建築物或設施安全性的參考。
Abstract: According to the investigations of well-known disastrous earthquakes in recent years, distortion of ground induced by faulting is one distinct cause of damage to near-fault engineering structures in addition to strong ground motion. Taking the 1999 Chi-Chi earthquake as an example, most of the engineering structures within the earthquake-induced deformation zone were severely damaged. Conversely, a few buildings in the zone retained intact although those buildings had been displaced and rotated. Therefore, characteristics of fault-related deformation on the ground and near ground ,and its effect on engineering structures within are worthy of further study.
The determination of theoretical setback widths used to avoid the earthquake hazard due to distortion of ground induced by faulting is deemed as essential as the understanding on how propagation of fault-tip affects the width of deformation zone on the ground of the soil/rock mass, the spatial distribution of strain and stress within the zone, and the foundation response. In addition, modification of the design methods of the foundations by studying the interaction among the fault rupture, geomaterial and foundation is a useful means to mitigate an earthquake hazard associated with soil structure interaction inducing by faulting.
Currently the approaches to investigate the near ground deformation due to reactivation of active faults can be categorized as (1) field investigation (2) laboratory testing and (3) numerical modeling. In order to breakthrough the limitation of individual approach, field investigation, numerical modeling along with laboratory testing, including sand box experiments under both 1-g and centrifuge conditions, will be conducted for characterizing and quantitating deformation induced by faulting in this study. The first-year target is pined on the type of thrust faults. The Chelongpu fault, which is thrust-dominated, is chosen to investigate deformation behavior of the soil/rock mass straddled the fault trace (including initiation and development of the shear zone, and its affecting factors) and affected extent due to its reactivation.
Fault sandbox experiments under centrifuge conditions (hereinafter referred to as centrifuge testing) will be performed to gain insights on the deformation behavior of the soil/rock mass associated with faulting as well as the response of the foundation.
Boundary conditions and parameter values for numerical models will be verified based on the configurations of the centrifuge testing and its resultant parameter values. Thus, full-scale numerical modeling can be carried out for studying the deformation behavior of the soil/rock mass and its effect on engineering structures. In consequence, reasonable safety indices can be suggested as safety assessment of buildings and infrastructure.
Keyword(s)
活動斷層
近地表變形
離心機砂箱實驗
土壤結構互制
退縮距離
減災工法
active faults
near-ground deformation
centrifuge testing
soil structure interaction
setback width
hazard mitigation strategy