以FLA3D探討套鑽法量測現地應力之不確定性

Study on the uncertainty of in-situ stress by overcoring method using FLAC3D

林冠均(Kuan-Chun Lin)

指導教授 ： 楊長義

淡江大學/工學院/土木工程學系碩士班/碩士(2022年)

https://doi.org/10.6846/TKU.2022.00060

摘要

現地應力量測結果之合理性，需要考量其適用條件、施作技術、地質材料異向性之影響等，本研究擬利用FLAC3D來模擬探討USBM套鑽法量測現地應力之不確定性因素。
獲致主要結論如下: [1]在均質岩體中，楊氏模數(E)、柏松比(ν)以及鑽孔/套鑽孔大小的變化，對於水平主應力值量測結果影響不大。[2]在水平主應力比k_H=0.5與2(應力異向性)產生主應力量測誤差皆比k_H=1之下還高。[3]採用間格60°孔內位移計的其中一組監測點若配置在水平最大或最小主應力方向上，則該方向的主應力值量測結果會較準。若位移計監測點互相夾45°，則可將兩組監測點同時放在水平最大最小主應力方向上，則兩個主應力值都很準確，但會造成主應力方向上的偏差。[4]擺放孔內位移計的旋轉偏差會導致量測主應力方向誤差最大可達19°，但是此一現象在k_H=1時並不會發生。鑽孔角度的偏差最大會造成水平主應力值之50%誤差。[5]在固定k_H=0.5，水平主應力值的材料異向性(E_t/E_n)愈大對主應力量測之誤差愈大。弱面走向角α<30°與α>75°時，對現地主應力值較大者誤差較大。[6]當水平最大主應力越趨於垂直弱面走向時(α≤45°)，所量測水平最大與最小主應力誤差都比較大。反之，當水平最大主應力越趨平行於弱面走向時(α>45°) 則量測誤差較小。[7]對異向性地盤，彈性係數比(E_t 〖/E〗_n)代表材料的異向性程度，異向性程度越嚴重者，對於水平主應力量測結果之誤差越大。[8]綜合比較應力異向性〖(k〗_H)與材料異向性(E_t/E_n)對主應力量測之影響，可知材料異向性之影響大於應力異向性。

關鍵字

現地應力 ； 套鑽法 ； USBM ； FLAC ； 材料異向性

並列摘要

The rationality of the in-situ stress measurement results needs to consider its applicable conditions, construction technology, and the influence of the anisotropy of geological materials. This study intends to use FLAC3D to simulate and explore the uncertainty factors of in-situ stress measurement by the USBM overcoring method.
The main conclusions are as follows: [1] In homogeneous rock mass, changes in Young's modulus (E), Poisson's ratio (ν) and the size of boreholes/sleeves have little effect on the measurement results of horizontal principal stress values . [2] In the horizontal principal stress ratio k_H=0.5 and 2 (stress anisotropy), the measurement error of principal stress is higher than that under k_H=1. [3] If one of the monitoring points using the 60° in-hole displacement meter with a grid is arranged in the direction of the horizontal maximum or minimum principal stress, the measurement results of the principal stress value in this direction will be accurate. If the monitoring points of the displacement meter are clamped at 45° to each other, the two groups of monitoring points can be placed in the direction of the horizontal maximum and minimum principal stress at the same time, and the two principal stress values are very accurate, but will cause deviation in the principal stress direction. [4] The rotation deviation of the displacement gauge placed in the hole will lead to a maximum error of 19° in the direction of the measured principal stress, but this phenomenon doesn’t occur when k_H=1. The deviation of the drilling angle will cause a maximum error of 50% of the horizontal principal stress value. [5] At a fixed k_H=0.5, the greater the material anisotropy (E_t/E_n) of the horizontal principal stress value, the greater the error of the principal stress measurement. When the weak plane strike angle α<30° and α>75°, the error is larger for the larger value of the in-situ principal stress. [6] When the horizontal maximum principal stress tends to be more vertical to the weak plane (α≤45°), the errors of the measured horizontal maximum and minimum principal stress are relatively large. On the contrary, when the horizontal maximum principal stress tends to be more parallel to the weak plane (α>45°), the measurement error is smaller. [7] For anisotropic sites, the elastic coefficient ratio (E_t 〖/E〗_n) represents the degree of anisotropy of the material. The more serious the degree of anisotropy, the greater the error of the horizontal principal stress measurement results. [8] Comprehensively compare the influence of stress anisotropy (k_H) and material anisotropy (E_t 〖/E〗_n) on the principal stress measurement, it can be seen that the influence of material anisotropy is greater than that of stress anisotropy.

並列關鍵字

In-situ stress ； Overcoring method ； USBM ； FLAC ； Material anisotropy

參考文獻

參考文獻

1. 石作珉(1994)，利用套鑽法量測現地應力之研究，地工技術雜誌，第46期。

2. 施國欽(1994)，岩體現地試驗之簡介，地工技術雜誌，第46期。

3. 黃燦輝(1985)，數值分析在大地工程上之應用，地工技術雜誌，第11期。

4. 楊長義(2018)，低放射性廢棄物坑道處置結構穩定驗證評估技術之研究，行政院原子能委員會核能研究所。