利用開挖面影像建置岩石隧道沿線地質模型及規設階段地質剖面變異比較

Abstract

工程地質模型整合大地工程工址調查之地質條件及其地質材料空間分佈，以作為地質師與工程師必要之溝通工具。隧道工程經常面對未知及複雜場址之地質條件，故工程地質模型之精度有必要隨工程作業及地質調查階段的推進而逐步提高。然而，既有隧道工程通常只採用傳統的地質測繪方法作地下空間之地質詮釋並未應用隧道開挖面之地質資訊建立地真模型。 本研究介紹地質模型於隧道工程之應用及其地質不確定性。在隧道施工階段，岩層界面直接顯露於開挖面上故可藉由隧道開挖面影像評估隧道輪進開挖至每段里程之地質資訊。其出露之岩性屬1:1場址比例並同時揭示地表面下水平隧道線性之岩層特性及其空間分佈。因此，本研究提出藉由開挖面影像建立隧道沿線之工程地質模型，又稱地真模型，以評估規劃設計階段隧道地質剖面的變異。 本研究旨在建立一個半自動化的隧道開挖面平台，將每一輪進之開挖面影像整合與三維視覺化展示岩層交線，並以點與線標示開挖剖面岩層交線從而建立向量關係式以進行其層面之數學回歸和統計變異分析。開挖面影像存在一定的誤差來源，進而降低其地質模型之準確性。因此，本研究建立一套誤差評估方法以量化隧道開挖面上回歸交線與真實交線之間的方向、角度和位置偏差。 通過隧道開挖之地質記錄，工程地質模型可以得到精進並降低其地質不確定性，故地層或岩段之交界帶可配合地真資料的詮釋作劃分與展示。本研究所建置之地真模型可供隧道施工作即時回饋與設計調整，並與規設階段之隧道地質模型作變異比較以指引地質調查作業。對比地質調查資料，斷層帶水平寬度及其與隧道交匯之位置推估存在顯著的差異。隧道開挖遭遇斷層帶將大幅提高其地質不確定性並增加隧道災變之風險。

Engineering geological model is initiated as an essential tool to demonstrate the accumulation of physical properties underground for subsequent geotechnical engineering analysis, both acknowledged by geologists and engineers. In tunnel engineering projects, distinct phases of geological investigation require specific models to be adapted, at varying scales, due to the uncertainties that come from inadequate and insufficient knowledge of geological settings. Unknowns of surficial geologic conditions are inversely proportional to the amount and integrity of site reconnaissance. However, geotechnical site investigations for underground excavation usually consist of traditional geologic field mapping methods yet do not contribute to further geologic interpretation for volumetric modelling and visualization in support of subsurface ground-truth data. A review of geological modelling for the purposes of engineering application has been highlighted in this research. Tunnel excavation face exposes directly to subsurface distribution of lithology under construction stages of tunnelling project. As rock contact disclosure by tunnel face images, these data reveal the lithological characteristics at a 1:1 site scale beneath the ground in which rock unit can be determined along the alignment of tunnel for geological interpretation. Hereby, a data-driven approach is proposed in this research based on the implementation of tunnel face image for the establishment of engineering geological model. In association with this approach, the augmented engineering geological model is also known as the ground-truth model. This research aims to construct a semi-automated tunnel excavation face platform for the 3D representation of boundary between two rock units and quantify the contacts for vector mathematical interpretation and statistical analysis. Image data is subject to various sources of error, leading to a reduction in geo-model accuracy. Thus, error assessment is conducted to outline the deviation in terms of direction, angle and position between the mean and true interface line of intersection on the tunnel face. It is followed by the development of ground-truth model and subsequently compared with reconnaissance geological data towards an evaluation of geological variation in space. Engineering geological models can be refined and augmented with underground excavation-based records to a certain level of accuracy. Stratigraphic transition zone between two geologic formations can be determined based on ground-truth interpretation. In comparison with several types of reconnaissance data, there exhibits a significant variation in estimation of the fault zone’s width and its location with respect to tunnel station. The existence of fault-related stratum leads to a rise in uncertainty and geohazard risk for tunnel excavation.