【摘要】：巖石的峰后力學(xué)特性對充分發(fā)揮巖體的承載力以維持地下工程的穩(wěn)定性、揭示巖體中塑性區(qū)的演化發(fā)展及巖體工程支護優(yōu)化設(shè)計起著關(guān)鍵作用。因此,研究加卸載圍壓條件下巖石峰后力學(xué)性質(zhì)對工程設(shè)計有著非常重要的意義。本文通過對巖樣在殘余強度階段的加卸載圍壓試驗,研究巖石峰后的力學(xué)特性,提出了峰后彈性滑移力學(xué)機理,并據(jù)此建立了數(shù)值分析模型,對隧道圍巖變形進行數(shù)值分析。主要研究內(nèi)容及結(jié)論如下:(1)常規(guī)三軸試驗中巖石殘余強度的大小受峰值強度和圍壓的影響,在低圍壓下表現(xiàn)更強的圍壓敏感性;這是由于低圍壓下破裂面間只有少量接觸,作用力較小,隨著圍壓的增大,接觸面逐漸變得規(guī)整且面積增大,接觸作用增強,應(yīng)力-應(yīng)變關(guān)系也由脆性跌落向塑性滑移轉(zhuǎn)變;頁巖峰值至殘余階段主要發(fā)生的是內(nèi)聚力的喪失過程,而內(nèi)摩擦角弱化量很小。(2)殘余階段加卸載圍壓試驗中,卸載圍壓對殘余階段力學(xué)特性的影響在多次卸載-多次加載圍壓、多次卸載-一次加載圍壓和循環(huán)加卸載圍壓這三種試驗方案中具有相同的規(guī)律,即在軸向應(yīng)力處于初始?xì)堄嚯A段限定軸向位移不變,當(dāng)圍壓以均勻的速度卸載時,軸向應(yīng)力也相應(yīng)地均勻降低;卸載圍壓至設(shè)定值后,軸向應(yīng)力在施加軸向位移荷載后保持基本穩(wěn)定,軸向應(yīng)力-應(yīng)變關(guān)系呈現(xiàn)塑性變形特征。(3)加載圍壓后,軸向應(yīng)力-應(yīng)變曲線可分為三個階段,第一是在限定軸向位移情況下加載圍壓時軸向應(yīng)力隨圍壓增加而增大的軸向應(yīng)力恢復(fù)階段,第二是穩(wěn)定圍壓后施加軸向位移荷載時軸向應(yīng)力-應(yīng)變具有與峰前相同的線彈性變形階段,第三是當(dāng)軸向應(yīng)力達到殘余應(yīng)力時產(chǎn)生的彈性滑移變形階段。(4)殘余階段的力學(xué)機理可以簡化為彈性巖石塊體沿破裂面的摩擦滑移變形。(5)基于巖石殘余階段的彈性滑移作用機理,提出了巖石峰后單結(jié)構(gòu)面的彈性滑移模型,并通過ANSYS的接觸單元模擬峰后破裂面間的摩擦滑移作用;模擬了不同圍壓下三軸壓縮試驗過程,結(jié)果表明模型與實際試驗具有較好的擬合性。(6)基于峰后彈性滑移模型,用ANSYS模擬的隧道圍巖變形能夠很好地反映隧道圍巖的變形特性。巖體峰后的沿弱面的滑移變形是隧道圍巖變形的主要原因。
[Abstract]:The post-peak mechanical properties of rock play a key role in giving full play to the bearing capacity of rock mass to maintain the stability of underground engineering and to reveal the evolution and development of plastic zone in rock mass and the optimum design of rock mass engineering support. Therefore, it is very important for engineering design to study the post-peak mechanical properties of rock under loading and unloading confining pressure. In this paper, through loading and unloading confining pressure test of rock samples at the stage of residual strength, the mechanical properties of rock after peak are studied, and the mechanism of elastic slip after peak is put forward. Based on this, a numerical analysis model is established to analyze the deformation of surrounding rock in tunnel. The main research contents and conclusions are as follows: (1) in conventional triaxial tests, the residual strength of rock is affected by peak strength and confining pressure, and it is more sensitive to confining pressure under low confining pressure, which is due to the fact that there is only a small amount of contact between fracture surfaces under low confining pressure. With the increase of confining pressure, the contact surface becomes regular and the area increases, the contact action increases, and the stress-strain relationship changes from brittle drop to plastic slip. The loss of cohesion occurs mainly in the peak to residual stage of shale, but the weakening of internal friction angle is very small. (2) in the loading and unloading confining pressure test of residual stage, the influence of unloading confining pressure on the mechanical properties of residual stage is from multiple unload to multiple loading confining pressure. There are the same laws in the three test schemes of multiple unloading-one loading confining pressure and cyclic loading and unloading confining pressure, that is, when the axial stress is at the initial residual stage, the axial displacement is limited to be invariable, and when the confining pressure is unloaded at a uniform speed, After unloading the confining pressure to the set value, the axial stress remained basically stable after the axial displacement load was applied, and the axial stress-strain relationship showed the plastic deformation characteristic. (3) after loading the confining pressure, the axial stress remained basically stable after the axial displacement load was applied. (3) after loading the confining pressure, the axial stress-strain relationship showed plastic deformation characteristics. The axial stress-strain curve can be divided into three stages. The first is the axial stress recovery stage in which the axial stress increases with the increase of the confining pressure when confining pressure is loaded under the condition of limited axial displacement. The second is that the axial stress-strain has the same linear elastic deformation stage as before the peak when the axial displacement load is applied after stabilizing the confining pressure. The third is the elastic slip deformation stage when the axial stress reaches the residual stress. (4) the mechanical mechanism of the residual stage can be simplified as the friction slip deformation of the elastic rock block along the fracture surface. (5) based on the elastic slip mechanism of the residual stage of the rock, The elastic slip model of the single structure plane behind the peak of rock is proposed, and the friction slip between the fracture surfaces after the peak is simulated by the contact element of ANSYS, and the triaxial compression test process under different confining pressures is simulated. The results show that the model fits well with the actual test. (6) based on the post-peak elastic slip model, the deformation of tunnel surrounding rock simulated by ANSYS can well reflect the deformation characteristics of tunnel surrounding rock. The slip deformation along the weak plane behind the rock peak is the main reason of the tunnel surrounding rock deformation.
【學(xué)位授予單位】：重慶大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TD315

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