爆炸应力波与含结构面岩体的相互作用及裂纹扩展研究
发布时间：2018-08-12 20:10
【摘要】：随着我国地下岩土工程建设的快速发展,人们对爆破施工破岩技术提出了更高的要求:一方面,尽可能使能量沿预爆破方向释放,提高有效爆炸破岩能量的利用率,另一方面,有效控制爆生裂纹的发展方向,减少爆破对保留岩体的损伤和破坏。基于这两个目的,人们提出了切槽炮孔爆破、聚能药卷爆破等定向断裂控制爆破技术。然而,由于天然岩体中广泛分布着大量的节理、裂隙、孔洞等结构面,对爆炸应力波的传播和爆生裂纹的扩展都有显著的影响,极大地影响了爆炸破岩的效果。尤其在节理发育的岩体中,往往很难形成较好的爆破轮廓。要解决这一问题,最基本地,就要首先弄清爆炸应力波与含结构面岩体的相互作用及爆生裂纹的扩展特性。本文针对爆炸应力波在含结构面岩体中的波形转换机制、诱生裂纹与岩体中结构面的相互作用及其动态断裂特性开展了理论分析、实验研究和数值模拟“三位一体”的研究,主要得到以下结论:基于应力波理论,对P波和S波分别沿不同方向入射到动态裂纹时产生的反射波的反射系数进行了理论求解。当爆炸P波的传播方向与动态裂纹的扩展方向垂直时,在裂纹面处产生的反射拉伸P波与入射P波相互叠加,使垂直于裂纹面方向的应力场表现为拉、压交替的动态演化,动态裂纹呈“波浪式”向前扩展的断裂形态。当P波倾斜入射到动态裂纹处时,裂纹附近的应力场由纯拉伸应力场转变为(拉剪/压剪)复合应力场,使裂纹朝向P波波源的方向扩展。当爆炸P波的传播方向与运动裂纹的扩展方向相反时,裂纹面处只产生反射P波,此时,P波对裂纹尖端应力场的影响等效于在裂纹尖端的应力场中施加一个平行于裂纹面方向的应力常量,对裂纹的扩展角度和材料的断裂韧性都有较大影响。爆炸P波和S波在结构面处的相互转换显著改变了岩体介质中的应力场分布特征,进而决定了岩体中动态裂纹产生的位置及其扩展的方向。数值模拟了爆炸P波和S波分别与0°、45°和90°三种不同角度裂纹相互作用的动态过程,直观显示了P波和S波在遇到不同角度裂纹时的波形转换过程,得到了裂纹尖端附近颗粒质点的振动规律、试件内部应力场的分布特征及其诱生裂纹的断裂模式。开展了含张开裂纹介质分别在切槽炮孔爆破和普通炮孔爆破中爆生裂纹断裂机理的实验室实验。爆生裂纹扩展到垂直张开裂纹时,张开裂纹阻碍了裂纹的扩展,并沿张开裂纹两端产生新的翼裂纹,其扩展方向与爆生裂纹的扩展方向近似同向。结合数值模拟结果可知,爆炸应力波在遇到张开裂纹后,张开裂纹阻隔了爆炸应力波的传播,并在张开裂纹端部发生衍射,产生应力集中,诱导翼裂纹沿张开裂纹端部起裂。张开裂纹背面的应力是爆炸应力波在张开裂纹端部产生的衍射波绕射到张开裂纹背面引起的。与普通炮孔爆破相比,采用切槽炮孔爆破时,切槽方向爆生裂纹的起裂时间较非切槽方向早10ms,促使爆炸能量沿切槽方向优先释放;切槽爆破中翼裂纹起裂以Ⅰ型拉伸破坏为主,而普通炮孔爆破时翼裂纹起裂以Ⅱ型剪切破坏为主;切槽爆破中爆生翼裂纹的扩展速度和裂纹尖端的应力强度因子K_Ⅰ~d的衰减速率下降,较普通炮孔爆破时翼裂纹的扩展时间和扩展长度分别增加了22.7%和17.8%。实验分析了Ⅰ型动态裂纹与张开孔洞相互作用过程中裂纹的动态断裂特性。当Ⅰ型动态裂纹朝向邻近孔洞扩展时,孔洞对动态裂纹的扩展速度和裂纹尖端的动态应力强度因子有抑制作用,且孔洞直径越大,抑制作用越强;当Ⅰ型动态裂纹与孔洞贯通后,孔洞的存在阻碍了动态裂纹的扩展,表现为裂纹尖端被“钝化”,裂纹的起裂韧度提高了9.58%~13.87%;裂纹由孔洞处再次起裂时的扩展速度和动态应力强度因子出现明显的跳跃。裂纹断裂面分析表明,裂纹与孔洞贯通前,断裂面较为光滑,扩展路径平直;裂纹从孔洞处起裂后,断裂面的粗糙程度显著增加,扩展路径也更为弯曲。存在临界孔洞直径dc,使动态裂纹与临界孔洞贯通后,孔洞吸收的弹性变形能最多,应力集中程度最大,“钝化效应”最显著。开展了闭合结构面与动态裂纹相互作用的实验研究。结果表明由于应力加载率和结构面倾角的不同,动态裂纹与闭合结构面相遇后,产生三种可能的扩展形态:(1)动态裂纹直接穿过弱面向基质扩展;(2)动态裂纹沿弱面扩展;(3)动态裂纹沿弱面扩展一段距离后再偏向基质扩展。在节理岩体爆破中,由于应力加载率和结构面倾角的变化,爆生裂纹遇到闭合结构面后的扩展形态在时间上的不断演化和在空间上的不断叠加共同构成了节理岩体中密集的爆破裂隙。结合霍普金森杆实验系统和数字图像相关法定量分析了动态应力波强度、结构面倾角及其强度对动态裂纹的影响;获得了动态裂纹与结构面相互作用过程中的位移场和应变场随时间的动态演化云图。随着应力加载率的提高,动态裂纹在闭合结构面中的扩展速度增大,偏移距离下降,穿过弱面扩展的裂纹数量不断增多。随着闭合结构面倾角的增加,裂纹沿闭合结构面扩展的偏移距离呈非线性下降的特点:当闭合结构面倾角在30°~60°之间时,动态裂纹的偏移距离基本保持不变,当闭合结构面倾角大于60°或小于30°时,动态裂纹的偏移距离随结构面倾角的增加呈线性下降的特点。当结构面的抗拉强度高于加载力沿结构面方向的拉应力时,裂纹沿结构面的偏移距离受沿裂纹面方向的能量释放率的控制;当结构面的抗拉强度不足以抵抗加载力沿结构面方向的拉应力时,裂纹沿结构面的偏移距离受结构面方向的拉应力的控制。研究了应力波作用下相向扩展两条裂纹的动态断裂特性及其相互作用机理。焦散线实验结果表明相向扩展两条裂纹在扩展过程中呈“同性(裂纹尖端与裂纹尖端)相斥,异性(裂纹尖端与裂纹面)相吸”的特点。结合动光弹性实验和数值模拟结果可知,相向扩展的两条裂纹在相互作用的过程中,平行于裂纹面方向的应力常数项(T应力)显著增大,改变了裂纹的扩展角度、扩展速度、材料的断裂韧度。当T应力为负时,裂纹的扩展角度减小,裂纹沿竖直方向的扩展距离减少;反之,正的T应力,对裂纹扩展角度有促进作用,增大裂纹扩展的竖向距离。在分析多裂纹相互作用时,应采用三参数(K_Ⅰ、K_Ⅱ和T应力)来确定裂纹的扩展角度、扩展距离等断裂参数。在实际工程中,通过改变爆破介质的受力,增加负的T应力,有助于控制裂纹的走向,实现精细爆破施工;相反,若增加正的T应力,则有利于增大爆破破岩的范围,提高松动爆破的效果。数值分析了主应力比值、裂纹竖向间距和材料力学特性对相向扩展裂纹断裂行为的影响。当两裂纹尖端相距较大时,随着远场主应力比值的增大,裂纹尖端的Tresca应力由对称的蝴蝶状向扁平状发展,扩大了多裂纹相互影响的作用区域。当两裂纹尖端水平间距较小时,主应力比值的改变对裂纹尖端的应力场参数(K_Ⅰ、K_Ⅱ和T应力)和裂纹扩展轨迹影响较小。裂纹偏离初始方向扩展的最大竖向距离随裂纹初始竖向间距的增加呈非线性下降的特点。存在临界初始竖向间距S_c,当两条裂纹的初始竖向距离S小于临界竖向间距S_c时,裂纹沿竖直方向的最大偏移距离W_(max)基本稳定。当S大于S_c时,W_(max)随S的增大呈线性降低的趋势。随着材料弹性模量的增大,泊松比的减小,材料的临界竖向间距S_c下降。对于大理岩、花岗岩和有机玻璃三种材料而言,在相同的初始竖向间距下,相向扩展裂纹的扩展轨迹相互影响的显著程度依次是:大理岩花岗岩有机玻璃。结合T应力理论,分析了爆炸应力波与爆生裂纹的相互作用机理。当爆生裂纹的扩展方向与爆炸P波的传播方向相反时,爆炸P波对爆生裂纹的作用等效于在裂纹尖端施加负的T应力,增大了材料的断裂韧度,阻碍了裂纹的扩展,使裂纹的扩展速度急剧下降。反之,当爆生裂纹的扩展方向与爆炸P波的传播方向同向时,材料的断裂韧度下降,扩展速度上升。从实验的角度看,S波与裂纹的相互作用可使裂纹的扩展速度下降,显著改变了裂纹的扩展方向。
[Abstract]:With the rapid development of underground geotechnical engineering construction in our country, people put forward higher requirements for rock breaking technology in blasting construction: on the one hand, as far as possible to release energy along the direction of pre-blasting, improve the utilization rate of effective blasting rock breaking energy, on the other hand, effectively control the development direction of blasting cracks, reduce blasting damage to retained rock mass and Destruction. For these two purposes, directional fracture controlled blasting techniques such as notched blasting and shaped charge blasting have been proposed. However, a large number of joints, cracks, holes and other structural planes are widely distributed in natural rock mass, which have a significant impact on the propagation of explosive stress waves and the propagation of explosive cracks, greatly affecting the explosion. It is difficult to form a good blasting profile, especially in jointed rock mass. To solve this problem, the interaction between explosive stress wave and rock mass with structural plane and the propagation characteristics of explosive cracks must be clarified firstly. The interaction between induced cracks and structural planes in rock mass and their dynamic fracture characteristics are analyzed theoretically. The experimental study and numerical simulation of "trinity" are carried out. The main conclusions are as follows: Based on the stress wave theory, the reflection coefficients of P wave and S wave incident to dynamic cracks in different directions are calculated. When the propagation direction of explosive P-wave is perpendicular to the propagation direction of dynamic crack, the reflected tensile P-wave and incident P-wave are superimposed on the crack surface, so that the stress field perpendicular to the crack surface exhibits the dynamic evolution of tension and compression alternately, and the dynamic crack exhibits the fracture pattern of "wave-like" propagation forward. The stress field near the crack changes from pure tensile stress field to (tension-shear/compression-shear) composite stress field, which makes the crack propagate toward P-wave source. When the propagation direction of explosive P-wave is opposite to the propagation direction of moving crack, only reflective P-wave is produced at the crack surface, and then the effect of P-wave on the stress field near the crack tip is also discussed. When a stress constant parallel to the crack plane is applied to the stress field at the crack tip, both the crack propagation angle and the fracture toughness of the material are greatly affected. The dynamic process of explosive P-wave and S-wave interacting with cracks at different angles of 0, 45 and 90 was simulated. The waveform transformation process of P-wave and S-wave when they encounter cracks at different angles was visualized. The vibration law of particle near the crack tip and the stress field in the specimen were obtained. The distribution characteristics and fracture mode of cracks induced by cracks are studied. Laboratory experiments are carried out on the fracture mechanism of explosive cracks in notched blasthole blasting and ordinary blasthole blasting respectively. The propagation direction of explosive stress wave is approximately the same as that of explosive crack. According to the numerical simulation results, the propagation of explosive stress wave is blocked by the tensile crack, and diffraction occurs at the end of the tensile crack, which results in stress concentration and induces the crack initiation along the end of the tensile crack. The diffraction wave produced by the explosive stress wave at the end of the tensile crack is diffracted to the back of the tensile crack. Compared with the ordinary blasting, the initiation time of the explosive crack in the notched direction is 10 ms earlier than that in the non-notched direction when the notched blasting is used, which makes the explosive energy release preferentially along the notched direction. Tensile failure is dominant, while type II shear failure is dominant for wing crack initiation in ordinary blasting. The propagation velocity of wing crack and the attenuation rate of stress intensity factor K_ I~d at crack tip in notched blasting decrease, and the propagation time and length of wing crack increase by 22.7% and 17.8% respectively. The dynamic fracture characteristics of crack in the interaction between mode I dynamic crack and open hole are analyzed. The crack initiation toughness increases by 9.58%~13.87%. The crack propagation velocity and dynamic stress intensity factor appear obvious jump when the crack starts again from the hole. The analysis of crack fracture surface shows that the crack tip is "passivated" and the crack initiation toughness increases by 9.58%~13.87%. It is smooth and the propagation path is straight; the roughness of fracture surface increases significantly and the propagation path is more curved after the crack initiation from the hole. There is a critical hole diameter dc, which makes the elastic deformation energy absorbed by the dynamic crack and the critical hole pass through, and the stress concentration is the greatest, and the "passivation effect" is the most significant. The results show that there are three possible propagation modes after the dynamic crack meets the closed structural plane due to the difference of stress loading rate and inclination angle of the structural plane: (1) the dynamic crack propagates directly through the weak face to the matrix; (2) the dynamic crack propagates along the weak face; (3) the dynamic crack propagates along the weak face. In the blasting of jointed rock mass, due to the change of stress loading rate and dip angle of structural plane, the continuous evolution of blasting crack propagation form after encountering closed structural plane in time and the continuous superposition in space constitute a dense blasting crack in jointed rock mass. The influence of dynamic stress wave intensity, dip angle and strength of structural plane on dynamic crack is analyzed quantitatively by system and digital image correlation method. With the increase of the inclination angle of the closed structure plane, the offset distance of the crack propagating along the closed structure plane decreases nonlinearly. When the inclination angle of the closed structure plane is between 30 and 60 degrees, the offset distance of the dynamic crack remains basically unchanged, while that of the closed structure is between 30 and 60 degrees. When the inclination angle is greater than 60 degrees or less than 30 degrees, the offset distance of dynamic crack decreases linearly with the increase of the inclination angle of structural plane. The displacement distance of cracks along the structural plane is controlled by the tensile stress along the structural plane when the degree of stress is not enough to resist the tensile stress along the structural plane. The results of dynamic photoelasticity experiment and numerical simulation show that the stress constant term (T stress) parallel to the direction of the crack surface increases remarkably during the interaction between the two cracks, and the crack propagation is changed. When the T stress is negative, the propagation angle of the crack decreases and the propagation distance along the vertical direction decreases; on the contrary, the positive T stress promotes the propagation angle of the crack and increases the vertical distance of the crack propagation. In practical engineering, by changing the force of blasting medium and increasing negative T stress, it is helpful to control the direction of crack and realize fine blasting construction; on the contrary, if the positive T stress is increased, it is helpful to enlarge the range of blasting rock breaking and improve the effect of loose blasting. The effects of principal stress ratio, crack vertical spacing and material mechanical properties on the fracture behavior of a phase-propagating crack are investigated. When the two crack tips are separated greatly, the Tresca stress at the crack tip develops from a symmetrical butterfly to a flat shape with the increase of the far-field principal stress ratio, and the interaction region of multiple cracks is enlarged. When the horizontal spacing between crack tips is small, the change of the ratio of principal stress has little effect on the stress field parameters (K_I, K_II and T stress) and crack propagation trajectory. When the initial vertical distance S is less than the critical vertical distance S_c, the maximum deviation W_ (max) along the vertical direction of the crack is basically stable. When S is greater than S_c, W_ (max) decreases linearly with the increase of S. With the increase of elastic modulus, the Poisson's ratio decreases and the critical vertical distance S_c decreases. With the same initial vertical spacing between rock and plexiglass, the significant degree of the interaction between the propagation trajectories of phase-propagating cracks is: marble granite plexiglass. Combining with T-stress theory, the interaction mechanism between explosive stress wave and explosive crack is analyzed. When the propagation direction of explosive P-wave is opposite, the effect of explosive P-wave on explosive crack is equivalent to applying negative T-stress at the crack tip, which increases the fracture toughness of material, hinders the propagation of crack, and makes the propagation speed of crack decrease sharply. From the experimental point of view, the interaction between S wave and crack can decrease the crack propagation velocity and change the crack propagation direction significantly.
【学位授予单位】：中国矿业大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TU45
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本文编号：2180226
[Abstract]:With the rapid development of underground geotechnical engineering construction in our country, people put forward higher requirements for rock breaking technology in blasting construction: on the one hand, as far as possible to release energy along the direction of pre-blasting, improve the utilization rate of effective blasting rock breaking energy, on the other hand, effectively control the development direction of blasting cracks, reduce blasting damage to retained rock mass and Destruction. For these two purposes, directional fracture controlled blasting techniques such as notched blasting and shaped charge blasting have been proposed. However, a large number of joints, cracks, holes and other structural planes are widely distributed in natural rock mass, which have a significant impact on the propagation of explosive stress waves and the propagation of explosive cracks, greatly affecting the explosion. It is difficult to form a good blasting profile, especially in jointed rock mass. To solve this problem, the interaction between explosive stress wave and rock mass with structural plane and the propagation characteristics of explosive cracks must be clarified firstly. The interaction between induced cracks and structural planes in rock mass and their dynamic fracture characteristics are analyzed theoretically. The experimental study and numerical simulation of "trinity" are carried out. The main conclusions are as follows: Based on the stress wave theory, the reflection coefficients of P wave and S wave incident to dynamic cracks in different directions are calculated. When the propagation direction of explosive P-wave is perpendicular to the propagation direction of dynamic crack, the reflected tensile P-wave and incident P-wave are superimposed on the crack surface, so that the stress field perpendicular to the crack surface exhibits the dynamic evolution of tension and compression alternately, and the dynamic crack exhibits the fracture pattern of "wave-like" propagation forward. The stress field near the crack changes from pure tensile stress field to (tension-shear/compression-shear) composite stress field, which makes the crack propagate toward P-wave source. When the propagation direction of explosive P-wave is opposite to the propagation direction of moving crack, only reflective P-wave is produced at the crack surface, and then the effect of P-wave on the stress field near the crack tip is also discussed. When a stress constant parallel to the crack plane is applied to the stress field at the crack tip, both the crack propagation angle and the fracture toughness of the material are greatly affected. The dynamic process of explosive P-wave and S-wave interacting with cracks at different angles of 0, 45 and 90 was simulated. The waveform transformation process of P-wave and S-wave when they encounter cracks at different angles was visualized. The vibration law of particle near the crack tip and the stress field in the specimen were obtained. The distribution characteristics and fracture mode of cracks induced by cracks are studied. Laboratory experiments are carried out on the fracture mechanism of explosive cracks in notched blasthole blasting and ordinary blasthole blasting respectively. The propagation direction of explosive stress wave is approximately the same as that of explosive crack. According to the numerical simulation results, the propagation of explosive stress wave is blocked by the tensile crack, and diffraction occurs at the end of the tensile crack, which results in stress concentration and induces the crack initiation along the end of the tensile crack. The diffraction wave produced by the explosive stress wave at the end of the tensile crack is diffracted to the back of the tensile crack. Compared with the ordinary blasting, the initiation time of the explosive crack in the notched direction is 10 ms earlier than that in the non-notched direction when the notched blasting is used, which makes the explosive energy release preferentially along the notched direction. Tensile failure is dominant, while type II shear failure is dominant for wing crack initiation in ordinary blasting. The propagation velocity of wing crack and the attenuation rate of stress intensity factor K_ I~d at crack tip in notched blasting decrease, and the propagation time and length of wing crack increase by 22.7% and 17.8% respectively. The dynamic fracture characteristics of crack in the interaction between mode I dynamic crack and open hole are analyzed. The crack initiation toughness increases by 9.58%~13.87%. The crack propagation velocity and dynamic stress intensity factor appear obvious jump when the crack starts again from the hole. The analysis of crack fracture surface shows that the crack tip is "passivated" and the crack initiation toughness increases by 9.58%~13.87%. It is smooth and the propagation path is straight; the roughness of fracture surface increases significantly and the propagation path is more curved after the crack initiation from the hole. There is a critical hole diameter dc, which makes the elastic deformation energy absorbed by the dynamic crack and the critical hole pass through, and the stress concentration is the greatest, and the "passivation effect" is the most significant. The results show that there are three possible propagation modes after the dynamic crack meets the closed structural plane due to the difference of stress loading rate and inclination angle of the structural plane: (1) the dynamic crack propagates directly through the weak face to the matrix; (2) the dynamic crack propagates along the weak face; (3) the dynamic crack propagates along the weak face. In the blasting of jointed rock mass, due to the change of stress loading rate and dip angle of structural plane, the continuous evolution of blasting crack propagation form after encountering closed structural plane in time and the continuous superposition in space constitute a dense blasting crack in jointed rock mass. The influence of dynamic stress wave intensity, dip angle and strength of structural plane on dynamic crack is analyzed quantitatively by system and digital image correlation method. With the increase of the inclination angle of the closed structure plane, the offset distance of the crack propagating along the closed structure plane decreases nonlinearly. When the inclination angle of the closed structure plane is between 30 and 60 degrees, the offset distance of the dynamic crack remains basically unchanged, while that of the closed structure is between 30 and 60 degrees. When the inclination angle is greater than 60 degrees or less than 30 degrees, the offset distance of dynamic crack decreases linearly with the increase of the inclination angle of structural plane. The displacement distance of cracks along the structural plane is controlled by the tensile stress along the structural plane when the degree of stress is not enough to resist the tensile stress along the structural plane. The results of dynamic photoelasticity experiment and numerical simulation show that the stress constant term (T stress) parallel to the direction of the crack surface increases remarkably during the interaction between the two cracks, and the crack propagation is changed. When the T stress is negative, the propagation angle of the crack decreases and the propagation distance along the vertical direction decreases; on the contrary, the positive T stress promotes the propagation angle of the crack and increases the vertical distance of the crack propagation. In practical engineering, by changing the force of blasting medium and increasing negative T stress, it is helpful to control the direction of crack and realize fine blasting construction; on the contrary, if the positive T stress is increased, it is helpful to enlarge the range of blasting rock breaking and improve the effect of loose blasting. The effects of principal stress ratio, crack vertical spacing and material mechanical properties on the fracture behavior of a phase-propagating crack are investigated. When the two crack tips are separated greatly, the Tresca stress at the crack tip develops from a symmetrical butterfly to a flat shape with the increase of the far-field principal stress ratio, and the interaction region of multiple cracks is enlarged. When the horizontal spacing between crack tips is small, the change of the ratio of principal stress has little effect on the stress field parameters (K_I, K_II and T stress) and crack propagation trajectory. When the initial vertical distance S is less than the critical vertical distance S_c, the maximum deviation W_ (max) along the vertical direction of the crack is basically stable. When S is greater than S_c, W_ (max) decreases linearly with the increase of S. With the increase of elastic modulus, the Poisson's ratio decreases and the critical vertical distance S_c decreases. With the same initial vertical spacing between rock and plexiglass, the significant degree of the interaction between the propagation trajectories of phase-propagating cracks is: marble granite plexiglass. Combining with T-stress theory, the interaction mechanism between explosive stress wave and explosive crack is analyzed. When the propagation direction of explosive P-wave is opposite, the effect of explosive P-wave on explosive crack is equivalent to applying negative T-stress at the crack tip, which increases the fracture toughness of material, hinders the propagation of crack, and makes the propagation speed of crack decrease sharply. From the experimental point of view, the interaction between S wave and crack can decrease the crack propagation velocity and change the crack propagation direction significantly.
【学位授予单位】：中国矿业大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TU45
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本文编号：2180226
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