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不同排水速度/滑移速度條件下高嶺土 之摩擦特性探討;Relationship of frictional characteristics of kaolin clay in different slip rates and drainage conditions
http://ir.lib.ncu.edu.tw/handle/987654321/75069
title: 不同排水速度/滑移速度條件下高嶺土 之摩擦特性探討;Relationship of frictional characteristics of kaolin clay in different slip rates and drainage conditions abstract: 大規模山崩常造成生命財產之重大損失，而滑移面摩擦特性受滑移速度、圍岩排水條件和滑移距離等因素影響，因此，瞭解滑移面摩擦特性與上述因素之關聯性有助於山崩防災研究。本研究探討滑移速度和排水條件對高嶺土摩擦係數之影響，試驗試體浸泡於水中一天，使含水量趨近於飽和，以1 MPa之正向應力進行試體壓密，旋剪試驗全程處於浸水環境，於單、雙向與徑向排水條件下以滑移速度10-7~1 m/s，量測高嶺土之視摩擦係數。徑向排水條件結果顯示，當滑移速度10-6~10-2 m/s之試驗於200~10秒和滑移速度1 m/s之試驗於0.4 秒時，視摩擦係數先降至低谷值(0.03~0.22)再漸增，並且低於其他兩排水條件(相同滑移距離)之視摩擦係數(0.25~0.58)，故此現象應為激發超額孔隙壓力所引致。當滑移速度10-7~10-1 m/s時，三種排水條件試驗皆呈現位移強化行為；當滑移速度為1 m/s時則皆為位移弱化，且皆出現上述之低谷值。在從10-6到10-2 m/s下，所有實驗之穩態摩擦係數均隨滑移速度上升而上升。計算徑向排水和乾試體條件試驗過程中之溫度變化，於滑移速度1 m/s試驗，徑向排水試驗最終溫度72度，乾試體試驗最終溫度188度，於滑移速度10-1 m/s試驗，實驗最終溫度約56~65度，於滑移速度10-2 m/s試驗，實驗中溫度變化不超過8度。由上述結果與前人研究可以判斷超額孔隙壓力激發機制有：(1)孔隙體積壓縮而激發。(2)溫度上升使孔隙流體膨脹而激發。(3)水汽化而激發。因此，超額孔隙壓力之累積同時與不同排水條件和滑移速度有關，結果指出邊坡滑動面排水條件將影響滑移面是否加速，若邊坡滑動面排水良好，能快速將超額孔隙壓力排出，而滑移面強度將逐漸增強而使滑移趨緩；此外，若超額孔隙壓力生成速度快過消散速度，則可能促成緩慢滑移(潛移)邊坡加速而轉變成遠距快速滑移。;Large landslide usually causes loss of life and property. The slip rate, drainage condition and shear displacement control the frictional characteristics of slip zone. Moreover, the effective stress of slip zone decreases with increasing pore pressure. The strength of slip zone is controlled by the slip rate and pore pressure. To know the relation between the frictional characteristics and previous parameters contribute to research of landslide prevention. This study aims at exploring the influence of slip rates and drainage conditions on the strength of kaolin clay. A low to high velocity rotary shear apparatus was used to measure the apparent friction coefficient of wet kaolin clay under a normal stress of 1 MPa and slip rate ranged from 10-7 to 1 m/s. The drainage conditions are controlled by alloy holders including radial, single and double drainage conditions. The experimental results show: (a) the steady-state friction coefficients at radial drainage condition under slip rates from 10-7 to10-1 m/s (slip-strengthening behavior) ranged from 0.25 to 0.58 and under 1 m/s of slip rate (slip-weakening behavior) is 0.08 and; (b) the steady-state friction coefficients single drainage condition under slip rates from 10-6 to10-1 m/s (slip-strengthening behavior) ranged from 0.30 to 0.4 and under 1 m/s of slip rate (slip-weakening behavior) is 0.18; (c) the steady-state friction coefficients double drainage condition under slip rates from 10-6 to10-1 m/s (slip-strengthening behavior) ranged from 0.18 to 0.58. Besides, the friction coefficient at radial drainage condition under slip rates from 10-6 to10-2 m/s dropped rapidly (before slip displacements < 2 m) after first peak and increased again after the drop, which represents the excess pore pressure was induced and dissipated at the initial stage, especially. Calculate the temperature change during the course of the radial drainage and dry test conditions. At the slip rate of 1 m/s test, the test temperature of the radial drainage test specimen is up to 72 degrees; the test temperature of the dry test specimen is even up to 188 degrees. At the slip rate of 10-1 m/s test, the final temperature of the experiment range from 56 to 65 degrees. At slip rate of 10-2 m/s test, the temperature change in the experiment does not exceed 8 degrees. According to the above results and previous studies can determine the excess pore pressure generation mechanism: (1) Pore volume compression and pore pressure generation. (2) The rise in temperature leads to pore water generation. (3) Water vaporization leads to pore water generation. The results could be applied to the study of large landslide from creeping tuning into catastrophic failure. Therefore, the accumulation of excess pore pressure is related to different drainage conditions and slip rates. It is pointed out that the drainage condition of the sliding surface will affect the acceleration of the sliding surface. If the sliding surface is well drained, which can quickly dissipate excess pore pressure, then the strength of slip surface will increase and the slip will be slowed down. In addition, if the generated rate of excess pore pressure is faster than the dissipated rate of excess pore pressure, it may cause the creep slip to become a rapid slip.
<br>Fri, 27 Oct 2017 08:18:32 GMT結合TRIGRS與TOPMODEL模式連續推估地下水位於淺層山崩預測;Coupling of TRIGRS and TOPMODEL in estimation of groundwater level for shallow landslide prediction
http://ir.lib.ncu.edu.tw/handle/987654321/75067
title: 結合TRIGRS與TOPMODEL模式連續推估地下水位於淺層山崩預測;Coupling of TRIGRS and TOPMODEL in estimation of groundwater level for shallow landslide prediction abstract: 降雨入滲造成地下水位抬升，使邊坡土體重量增加且抗剪強度降低，常為邊坡破壞主因。USGS結合降雨入滲與無限邊坡模式之一維暫態模式TRIGRS假設每一網格的土體於該模式的環境下形同個別自由體，並未考慮土體內的地下水側向流補注，無法真實地反應地下水位。本研究改進李浩瑋(2011)結合TRIGRS與TOPMODEL之研究，將每單位小時由TRIGRS計算得之地下水位使用TOPMODEL修正，並將修正後地下水位當作下一小時的初始地下水位，在TRIGRS中繼續計算，直至降雨事件結束。
本研究以2004年艾利颱風之降雨事件，模擬大漢溪流域的匹亞溪集水區地下水位在淺層土壤中之變化，並且討論土壤飽和度分佈對誘發山崩之影響。結合TRIGRS與TOPMODEL連續推估的解釋山崩總體正確率為89.9%，成功率曲線下面積(AUC)為0.838。若僅使用TRIGRS模擬結果，其總體正確率為76.7%，成功率曲線下面積為0.793，使用TOPMODEL修正TRIGRS模式其總體正確率為85.5%，成功率曲線下面積為0.810。結果顯示結合TRIGRS與TOPMODEL連續推估模式更能有效解釋山崩分布。使用馬莎颱風降雨資料帶入新模式預測山崩之結果，總體正確率為95.1%，預測率曲線下面積為0.816；僅使用TRIGRS模擬結果，總體正確率為96.8%，預測率曲線下面積為0.763，亦為可接受之預估結果。;Rainfall infiltration is the main reason most of the shallow slope failure because the rise of the groundwater level will make the weight of the slope to increase and the shear strength to deteriorate. In the past, the USGS proposed TRIGRS model combining rainfall infiltration and slope stability which is the one-dimensional vertical infiltration transient model to analyze the groundwater level. The model assumed that soil body of each grid as an independent individual and didn’t consider of hydrological influence, so it can not reflect the groundwater level refined. In this study, we modify the method of Hao-Wei Lee (2011) which combined TRIGRS and TOPMODEL models to calculate the groundwater level. At first, using TOPMODEL model to correct the groundwater level for each hour which is obtained by TRIGRS model, and then, this revised groundwater level is treated as the initial groundwater level for the next hour, and the correction will continue to the end of the rainfall event.
We use AERE typhoon rainfall event in 2004 to simulate the change of groundwater level of shallow soil layer in Piyaxi watershed of Dahanxi basin and discusses the effect of soil saturation degree distribution on induced landslide. The results show that, if the overall correct rate is 89.9% when the TRIGRS and TOPMODEL continuous estimation model are combined, the area under the success rate curve (AUC) will be 0.838, and if the overall correct rate is 76.7% when only the TRIGRS is used, the AUC is 0.793. Then the overall correct rate is 85.5% when use the TOPMODEL to correct TRIGRS model is used, the AUC is 0.810. It means the combination of TRIGRS and TOPMODEL continuous estimation model can display the more effective interpretation of landslide distribution. Finally, the Matsa typhoon rainfall data is put into the present model to predict the results of landslides, the area under the curve is 0.816, and the overall correct rate is 95.1%. The area under the curve is 0.763, and the overall correct rate was 96.8% when using TRIGRS model only.
<br>Fri, 27 Oct 2017 08:18:27 GMT曾文水庫集水區事件型降雨誘發山崩潛感及山崩機率預測模式;Event-based Landslide Susceptibility and Rainfall-induced Landslide Probability Prediction Model in the Zengwen Reservoir Catchment
http://ir.lib.ncu.edu.tw/handle/987654321/75065
title: 曾文水庫集水區事件型降雨誘發山崩潛感及山崩機率預測模式;Event-based Landslide Susceptibility and Rainfall-induced Landslide Probability Prediction Model in the Zengwen Reservoir Catchment abstract: 事件型山崩潛感模型是利用事件誘發山崩目錄及地形、地質因子和促崩因子訓練建模。若建立模型的事件之前有超大豪雨或颱風或大地震發生過，事件誘發山崩的分布特性可能與未受到干擾的情況有所不同。本研究訂定時隔6個月以上第一場超過降雨門檻的雨量事件為獨立事件，在曾文水庫集水區挑選賀伯颱風、桃芝颱風、敏督利颱風、20050615豪雨、20060609豪雨、莫拉克颱風、20110718豪雨、20120610豪雨、20150523豪雨共九期獨立事件建立山崩潛感模型。將模型進行交叉驗證，發現以豪雨事件建立的模型彼此之間相互預測結果表現不錯。敏督利模型由於坡度因子及促崩因子表現良好，預測其他事件的AUC皆達到0.710以上，解釋莫拉克颱風誘發山崩的AUC達0.673，為最穩定的事件型山崩潛感模型。
比較歷年山崩目錄按傳統方法建立之不包括促崩因子的山崩潛感模型與各個事件基礎山崩潛感圖，可以觀察到九個事件個別建立的基礎山崩潛感圖與歷年山崩潛感圖會有相近的潛感分布趨勢，表示歷年山崩潛感圖即可代表一個區域的基礎潛感値分布。本研究選用歷年山崩潛感模型為基礎潛感模型，將各事件分為極端事件及一般事件，將不同潛感區間中相同雨量條件下的崩壞比取其平均值，分別建立山崩潛感‒崩壞比和最大時雨量/總雨量關係式，利用雨量因子間的相關係數將關係式合併以計算在不同雨量分布下各個潛感體質的崩壞比。各事件山崩機率圖的預估山崩面積與事件誘發山崩目錄比較結果顯示，本研究建立之關係式低估桃芝颱風誘發山崩；高估賀伯颱風、敏督利颱風及豪雨事件誘發山崩，預測莫拉克颱風誘發山崩與實際誘發山崩面積較為吻合。;An event-based landslide susceptibility model is constructed based upon an event landslide inventory, topographic factors, geological factors and triggering factors. If an extreme rainfall, typhoon, or a major earthquake happened before a modeling event, the characteristics of landslide distribution may be different with undisturbed conditions. In the present study, an independent event is defined as the event without a prior-event which exceeds the rainfall threshold of the region within 6 months or more. In the Zengwen reservoir catchment area, this study chooses nine independent events, including Herb typhoon, Toraji typhoon, Mindulle typhoon, 20050615 rainfall, 20060609 rainfall, Morakot typhoon, 20110718 rainfall, 20120610 rainfall, and 20150523 rainfall, to establish nine event-based landslide susceptibility models. These models are then cross-validated. The results are good between rainfall events. Due to good performance of slope factor and triggering factors, Mindulle model is the most stable event-based landslide susceptibility model for typhoon events. It shows that AUC of the prediction curve for landslide induced by Morakot typhoon is 0.673; AUCs of prediction curve for other events are more than 0.710.
Compare the landslide susceptibility model built by multi-temporal landslide inventories, via traditional approach without triggering factors, to the nine basic susceptibility maps built by each event, a similar trend of susceptibility distribution among them can be observed. This study chooses the multi-temporal landslide susceptibility map as representative basic susceptibility of the region. The events are divieded into extreme events and common events. In each susceptibility bin and each rainfall bin, the average of probability of landslide failure is calculated from every events landslide inventory of same type, and then a relationship among landslide susceptibility, probability of failure, and rainfall intensity or total rainfall is completed. Utilizing the correlation coefficient between two rainfall factors, this study combines the two relationships to calculate the probability of failure of different susceptibility values in rainfall event. Comparing the result of landslide area predicted by the relationship and each event inventory shows that the relationship underestimate landslide area of Toraji typhoon, and overestimate landslide area of Herb typhoon, Mindulle typhoom and rainfall events. Predicted landslide area of Morakot typhoon is approximate to actual landslide area.
<br>Fri, 27 Oct 2017 08:18:25 GMT裂隙網路迴流效應對流場及溶質傳輸之影響;The effect of local flow on flow and contaminant transport in discrete fracture networks
http://ir.lib.ncu.edu.tw/handle/987654321/75063
title: 裂隙網路迴流效應對流場及溶質傳輸之影響;The effect of local flow on flow and contaminant transport in discrete fracture networks abstract: 目前對於封閉裂隙(dead-end fracture)並無詳細的研究與解析，尤其在二維離散模式中，通常將封閉裂隙視為無導水能力的區域，而在模式生成離散裂隙網路階段時被去除、忽略；然而，在三維離散模式下卻顯示出重要的局部迴流效應(local flow effect)，發生迴流效應之封閉裂隙可稱為迴流單元(local flow cell)，此迴流效性亦直接影響污染團在裂隙網路的傳輸機制。為瞭解迴流效應對離散裂裂隙網路中流場與保守性污染物傳輸的機制，本研究以雙片裂隙，建構多種裂隙位態組合，以裂隙網路數值模式探討迴流效應對於流場以及溶質傳輸之影響。本研究首先使用商用模式HYDRUS 3D，模擬一組正交裂隙網路下的裂隙岩體，分析母岩與裂隙交互作用下的影響，探討在何種母岩孔隙率及水力傳導係數下可忽略母岩影響。依據分析成果，進一步使用離散裂隙模式模擬不同裂隙位態組合下，流場及傳輸行為受封閉裂隙的影響。模擬結果顯示，背景水力梯度方向與裂隙交線之間的夾角為非正交時，封閉裂隙可提供局部流場而引致迴流效應發生，背景水力梯度方向與裂隙交線之間的夾角越小時，封閉裂隙中的迴流效應越大。愈大的迴流效應，將使得污染團更容易流入封閉裂隙中，造成傳輸過程較明顯的遲滯現象，污染團也因封閉裂隙造成的迴流效應而產生較大的污染團團塊變形及空間分佈偏移。;The dead-end fractures in discrete fracture networks (DFNs) play an important role in the analysis of flow and contaminant transport. In two-dimensional DFN cases, the dead-end fractures have usually been considered as no-flow zones and have been removed at the stage of constructing a DFN. Such simplification is not valid for three-dimensional DFNs. The local flow effect induced by dead-end fractures can considerably influence the flow and transport mechanism in the three-dimensional fracture networks. The study developed a full three-dimensional DFN model to assess the effect of dead-end fracture on flow and conservative solute transport in relatively simple DFNs. The testing scenarios included different fracture orientations intersected by two fracture plates. This study also employed the HYDRUS model to quantify the influence of matrix porosity and hydraulic conductivity on flow and contaminant transport. The results from HYDRUS provided indications for neglecting the influence of rock matrix. The results from the developed DFN model showed that the dead-end fractures can lead to local flow when the angle between the background hydraulic gradient and the fracture intersection is non-orthogonal. The smaller the angle the stronger the local flow in the dead-end fractures. Additionally, the local flows in dead-end fractures can trap contaminant plume and enhance retardation behavior in the solute transport procedure.
<br>Fri, 27 Oct 2017 08:18:22 GMT