| Abstract: | 節理面之剪力強度具有規模效應(scale effect)問題：意謂，節理面尺寸越小，其抗剪強度愈高；反之，大尺寸節理面則其抗剪強度較低(如Bandis, 1980；Yang& Chen, 1999; 楊長義等,2003)。實際原因，其實與節理面間僅有在局部區域之真實接觸之面積比例有關；因為在粗糙度相近之大小節理面，大的節理面之實際接觸面積之比例非常低，故在該接觸點之節瘤承受甚高之集中應力(如圖1.1示意：Barton,2008)，極易發生破壞，致使抗剪強度低於小節理面。
Yang et al.(2011)曾以粗糙度近似的10cm及20cm石膏節理面(稱self-affine profile; Yang et al.,2001)進行剪力試驗結果，如圖1.2，大或小試體之磨損面積比雖與正應力及剪位移多寡有關，但其值均極低(3%~ 15%)；且大試體之磨損面積與總面積之比例相對確實較小試體少，故抗剪之剪力強度確實比較低。
在節理剪力試驗研究上，一般是以外部施加的正向力(N)或剪力(T)，除以試體整體受剪面積(A)而計算得作用在節理面間的平均正向應力及平均剪應力。但實際上，因真正受力接觸面積僅發生在少數節瘤面上，故作用於節理面間真實的接觸正向應力及剪應力，可能大於其平均應力計算值。本文是嘗試以富士感壓紙薄膜為量測介質，借感壓紙在受不同壓力作用後，會顯示出不同顏色深淺印痕反應。試驗時，特將感壓紙放置於兩節理平面間，透由內部之應力量測值與外部應力衡盒量測得正向應力及剪應力之關係，期望了解比較剪動過程中，在不同剪動情況下，探討實際的接觸應力與平均應力計算值兩者的差異。
本文主要獲致結論如下：在只加壓正向力下(單鋸齒及複合鋸齒)： (1) 富士感壓紙之印痕，會受不同正向應力及剪動量，造成印痕顏色發生深淺變化及印痕接觸面積的改變。(2) 因分佈接觸應力值與感壓紙印痕深淺分佈有相關，進而可藉以分析接觸應力值的改變。
在45°鋸齒型節理：(1) 外加正向應力較高時，使鋸齒產生張力裂縫所需施加之剪應力較少，所需驅動剪動距離較短。(2) 上坡面出現張力裂縫的位置，不因外加正向應力高低而有所變化，均出現在上坡面受力區之下緣部位。(3)在高應力狀態下，會先在下緣出現張力破壞，而後出現剪力破壞，看其節瘤破壞面可發現有張力破壞造成較粗糙的表面以及由剪力破壞造成叫平滑的表面。(4)其接觸應力分佈型態，亦不因正向應力高低或錯開位移量不同而有所變化，均為梯型分佈型態，僅在應力最大值分佈位置有所差別。
在30°鋸齒型節理： (1) 上坡面出現剪力破壞的位置，不因外加正向應力高低而有所變化，均出現在上坡面受力區之上緣部位。(2)其接觸應力分佈型態，亦不因正向應力高低或錯開位移量不同而有所變化，均為梯型分佈型態，僅在應力最大值分佈位置有所差別。
在45°+45°鋸齒型節理：(1)不論外加正向應力高低，兩隻鋸齒皆同時破壞，都先出現張力裂縫而後張力破壞。(2)由力位移圖可以發現即使兩隻同角度的鋸齒，其破裂點只有一個，所以是同時破壞。(3)從感壓紙可以觀測到兩隻鋸齒所量測到的力量是相同的。
在30°+30°鋸齒型節理：(1)不論外加正向應力高低，兩隻鋸齒皆同時破壞，都出現剪力破壞將鋸齒上部直接削斷。(2)由力位移圖可以發現即使兩隻同角度的鋸齒，其破裂點只有一個，所以是同時破壞。(3)從感壓紙可以觀測到兩隻鋸齒所量測到的力量是相同的。
在30°+45°鋸齒型節理(45°+30°鋸齒型節理亦同)：(1)不論外加正向應力高低，皆由45°高角度先破壞，先出現張力裂縫而後張力破壞，45°破壞完才換30°角開始被剪壞。(2)由力位移圖可以發現兩隻不同角度的鋸齒，其破裂點有兩個。(3)從感壓紙可以觀測到兩隻鋸齒所量測到的力量是不同的。
In general joint shear tests, external normal forces (N) or shear forces (T) are divided by the overall area of a specimen under shear forces (A) to calculate the average normal stress and shear stress applied on joint surfaces. However, the actual contact area under force merely occurs on several asperities. Therefore, the actual contact normal stress and shear stress between joint surfaces may be higher than the calculated average stress values. In this study, Prescale films developed by Fujifilm were used as the measurement material, which displays imprint of varying color shades corresponding to different pressure levels applied.
The primary findings are as follows.In only normal stress(single sawtooth and compound sawtooth):(1) The prints of Fuji prescale film will be subject to different forward stress and shear volume, resulting in print color changes in depth and imprint Change in contact area.(2)Due to the distribution of contact stress value and the film prints are related to the depth distribution, and thus can be analyzed by changing the contact stress value.
In a 30° saw-tooth joint: (1)The location of the shear damage on the slope,not due to the addition of normal stress level changes,its appear in the upper slope edge of the force area. (2) Its contact stress distribution pattern, nor because of the stress level or the amount of displacement is different from the change,only the maximum distribution of stress position difference.
In a 45° saw-tooth joint:(1)When plus the higher normal stress,the tensile force required to produce tension cracks less shear stress required to shear a shorter distance. (2)The cracks on the lower slope, not due to the higher force or lower force.(3)In the high stress state,the first crack appear in the lower edge of the tension damage,and then the tension damage surface can be found it have a rough surface,caused by rough surface and caused by the shear damage caused by smooth surface. (4)Its contact stress distribution pattern, nor because of the positive stress level or the amount of displacement is different from the change,only the maximum distribution of stress position difference.
In a 30°+30° saw-teeth joint: (1)Regardless of the plus normal stress level, two teeth are cracked at the same time, have first tension cracks and then tension damage. (2)By the force displacement can be found even if the two angles of the teeth, the peak point is only one, so it is destroyed at the same time. (3)It is observed that the power measured by the two serrations is the same.
In a 45°+45° saw-teeth joint: (1)Regardless of the plus normal stress level, two teeth are cracked at the same time, have first tension cracks and then tension damage. (2)By the force displacement can be found even if the two angles of the teeth, the peak point is only one, so it is destroyed at the same time. (3)It is observed that the power measured by the two serrations is the same.
In a 30°+45° saw-teeth joint(same of 45°+30° saw-teeth joint): (1)Regardless of the plus normal stress level, all by 45 ° high angle first damage, the first tension cracks and then the tension crack, 45 ° crack after the end of 30 ° angle was started to be broken. (2)By force displacement diagram can be found in two different angles of the peak.(3)It is observed that the strength measured by the two sawteeth is different. |
