以雙凹鍵結模式模擬基質支持岩石之行為研究

Abstract

以往以數值模擬方式探討岩石材料之力學性質時，大多採用彈塑性理論等連體力學分析軟體進行研究，其主要原因是目前對於岩材之微觀組態、力學行為掌握度不高，然而，岩材中局部的微小破裂與微觀組態對於岩材之力學行為影響甚鉅。故從微觀角度檢視岩石材料之特性時，透過非連續體分析－個別元素法－探討岩體力學行為是有效的研究途徑與重要方法。

目前岩石力學領域最廣泛應用的個別元素分析軟體－PFC (Particle Flow Code)中，對於描述岩材顆粒膠結行為以平行鍵結模式 (Parallel bond model)代表，而其鍵結模式因力學基礎與幾何形狀皆過於簡化，無法完整且適當的呈現岩材之力學行為，降低其模擬之可信度。因此，邱家吉(2014)透過膠結之力學性質與幾何因素兩部分進行修正，發展出一新鍵結模式雙凹鍵結模式 (Biconcave bond model)，幾何部分，透過觀察岩石薄片的晶粒結構，假設岩材為不同尺寸顆粒聚合而成之材料，且顆粒間膠結為雙凹形狀，並可存在於分離顆粒間；力學基礎部分則是建立在 Dvorkin理論之彈性解，以上述兩因素發展能合理描述岩材微觀性質之鍵結模式。 因此，本研究以雙凹鍵結模式進行一系列之模擬與探討，同時與PFC內建之平行鍵結模式進行比對。首先，從雙顆粒模擬檢視微觀參數與微觀力學行為對應關係，並探討兩鍵結模式之特性與不同；接著透過鋁棒平面應變試驗之模擬，檢視兩鍵結參數設定之成果、優劣與合理性，同時探討兩鍵結模式之微觀參數對應巨觀力學行為之關係，並檢視雙凹鍵結模式微觀參數設定之方法與程序；最後以真實砂岩之模擬檢視雙凹鍵結模式模擬之適用性與參數設定之合理性，藉由巨微觀力學基礎與考慮幾何因素之雙凹鍵結模式進行不同微觀組態砂岩之模擬、預測，利用已知巨觀力學參數，探討雙凹鍵結模式之微觀參數與巨觀行為之關係，進行有效率且更具物理意義之岩石行為模擬。

Former researches of rock materials using numerical simulation are mostly based on elastoplastic theory, because of the microscopic structure and microscopic mechanisms are still under investigating. However, micro-cracks and microscopic structure in rock materials play an important role which affect the mechanisms of rocks extremely. In order to investigate the mechanical behaviors of rock materials from microscopic perspect, discontinuum analysis – distinct element method is an effective and appropriate way to reach it. Currently, PFC (particle flow code) is a software that widely-used in rock mechanics based on distinct element method. In this software, “parallel bond model” is designed to describe rock particle cementation. However, parallel bond model is too simplified and unreliable to represent the mechanical behaviors of rock materials appropriately. Thus, Chiu (2014) developed a new model to describe rock particle cementation – Bicocave bond model (BCB), which improve the rock material mechanical behavior by two factors – basis of mechanic and geometric factors. In the improvement of material mechanical behavior, follows the elastic solution of Dvorkin theory. In the improvement of geometric factor, assumes the rock materials are composed of particles with different sizes, the shape of cement between particles are biconcave which allowed to set up between separate particles. Thus, this study performe a series of analysis and investigation using biconcave bond model, and compare with parallel bond model simultaneously. First of all, this study investigate the effects bwtwen microscopic parameters and microscopic behavior through simple model test, and discuss the characteristic of these two maodels. Moreover, this study investigate the relationship bwtwen microscopic parameters and macroscopic behavior by simulating the plane strain test which published by Tsai(2015).Through the results of simulations, this study compares the pros and cons of these two bonding model. And establish a procedure to determine the microscopic parameters of biconcave bond model. Finally, this study simulate the sandstones which includes different kinds of microscopic structure and properties. Propose a standard to set up microscopic parameters through macroscopic behavior in biconcave bond model, which is able to simulate and predict rock mechanics more efficiently.