A Study on the Recognition of Fracture Network Pattern and Hydraulic Boundary around a Borehole

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基本資料

Project title

Code/計畫編號

MOST108-2116-M019-003

Translated Name/計畫中文名

鑽孔場址周圍裂隙網絡系統型態與水力邊界辨識之研究

Project Coordinator/計畫主持人

Shih-Meng Hsu

Funding Organization/主管機關

National Science and Technology Council

Department/Unit

Department of Harbor and River Engineering

Website

https://www.grb.gov.tw/search/planDetail?id=13117094

Year

2019

Start date/計畫起

01-08-2019

Expected Completion/計畫迄

31-07-2020

Bugetid/研究經費

858千元

ResearchField/研究領域

地球科學

目前臺灣山區工程探勘工作因經費考量多以點狀調查為主，就工程開發設計觀點，如能獲得含水層線與面尺度、甚至三維空間之水力結構參數資料，更具參考價值。爰此，在有限調查經費資源下，為達成提供更多未來山區岩盤工程開發所需關鍵資料之目的，有必要以低成本的資料探勘方式，對既有資料進行整合與分析，藉由揭露額外水文地質參數資訊，降低參數資料本身不確定性，並連帶提升與之連動地下水流分析模式之精度。本計畫進行兩個主要研究內容，第一項為蒐集既有臺灣中南段山區262組水力試驗資料及鑽孔岩芯資料，結合Baker的通用暫態徑向流模式與碎形流動維度的概念，重新分析既有水力試驗資料，藉此獲取各試驗區段水流之維度n值(geometry of groundwater flow)，再藉由n值解釋每個封塞式驗區段鄰近區域裂隙岩體網絡型態特徵，而此推估成果之合理性，則應用RQD、裂隙寬、裂隙頻率與水力傳導係數等水文地質指標完成驗證。此外，本研究也利用既有封塞水力試驗資料、室內母岩試驗透水係數成果，結合Barker (1988)廣義徑向地下水流模型(GRF)雙孔隙模式(Double-porosity)，獲取每一試驗區段岩層裂隙通路與岩石基盤的相對透水比值(Kf/Km)，完成另一種解釋鑽孔周圍隙網絡型態的方法，並將結果與n值結果進行關聯分析，成果顯示n值越大(裂隙網絡密度越高)，Kf/Km比值也越大(地下水流行為由裂隙主導能力越強烈)，並建立兩者之間的關係，此成果也同時暗示n值除了可以用來解釋裂隙網絡密度狀態，亦可用來詮釋是否裂隙岩體結構為裂隙主導地下水流之結構。第二項則利用既抽水試驗資料結合水位洩降微分取點理論與地下水流域診斷法，分析鑽井遠處可能之水力邊界狀況，依據64孔抽水試驗資料分析成果顯示，過去依據場址附近地形作為水文地質邊界判定條件之方法，未必能呈現真實邊界情況。此外，比較兩種水位資料分析方法，分析成果具一致性，但地下水流流域診斷分析方法可以再藉由分析不同時期的抽水試驗資料，補足洩降微分方法所未提及的抽水試驗早、中期資訊，對該場址之水文地質特性揭露更多的訊息。總結以上分析及驗證成果，應用水流維度n值資訊及Kf/Km比值分析揭露場址區域周遭之裂隙樣態，將較過往更有效率決定場址適合使用之分析模型；應用水位洩降微分取點理論與地下水流診斷法，判定鑽井遠處可能之水文地質邊界狀況，亦於整體分析模式建構與處理場址周遭區域水文地質提供額外幫助，為臺灣山區之開發工程提供更具實務性之參考。 Due to budget limits, current engineering investigation programs in mountainous areas mainly focus on collecting essential hydrogeologic data on a borehole scale. The objective of this study is to produce advanced hydrogeological data to reduce the uncertainty of model parameters by integrating existing data with data mining techniques and low costs. The first study item is to collect 262 sets of hydraulic test data and drilling core data in the mountainous area of the Central and Southern Taiwan. The collected data are combined with Barker’s generalized transient radial flow model and the concept of fractal flow dimension to reanalyze the existing hydraulic test data and obtain the nvalue (geometry of groundwater flow) of the groundwater flow in each test section. The n-value results explain the characteristics of the fractured bedrock network in the adjacent area of each double packer inspection section. The rationality of this interpretation was verified using hydrogeological indicators such as RQD, fracture width, fracture frequency, and hydraulic conductivity. Besides, this study used the existing double-packer hydraulic test data, the permeability test results of intact rock samples, and Barker’s Generalized Radial Flow Model - DoublePorosity model to obtain the permeability ratio for each test section, in which Kf is hydraulic conductivity for fracture; Km is hydraulic conductivity for matrix. This is another approach for interpreting the fracture network around a borehole. At the same time, the result of Kf/Km is correlated with the n-value result, and the relation between two variables was developed. The result shows that the larger the n value, the larger the Kf/Km ratio. The relationship between n-value and Kf/Km also implies that the n value can be used not only to explain the density of the fracture network, but also to interpret whether the fracture rock structure is a fracture-driven groundwater flow structure. The second item uses the existing pumping test data combined with derivative analysis of displacement measurements and the analysis of diagnostic flow plot to identify possible hydraulic boundary conditions at the remote area of a drilling borehole. According to the results of 64-borehole pumping test data analysis, the past method of relying on the topography in the vicinity of the site as a criterion for determining the hydrogeological boundary may not be able to present the actual boundary conditions. Besides, when comparing two methods mentioned above, the results are consistent, but the diagnostic flow plots method provides additional information about the hydrogeological characteristics of the site by analyzing pumping test data in the early and mid-term periods, which cannot be obtained in the derivative method. Summarizing the above analysis and validation results, the application of flow dimension n-value information and Kf/Km ratio analysis has revealed fracture network patterns around a borehole site. The application of derivative analysis of displacement measurements and the analysis of diagnostic flow plot assists in determining possible remote hydrogeological boundary conditions for a drilling site. All efforts in this study provide a more practical reference for the engineering development project in the mountainous area of Taiwan.

Keyword(s)

裂隙網絡
水流維度
水力邊界
水文地質場址描述模型
fracture network
flow dimension
hydraulic boundary
hydrogeological site descriptive model

DSpace CRIS

A Study on the Recognition of Fracture Network Pattern and Hydraulic Boundary around a Borehole

基本資料

Description