ZONAL DISINTEGRATION MECHANISM OF DEEP CRACK-WEAKENED ROCK MASSES UNDER DYNAMIC UNLOADING

Size and quantity of fractured zone and non-fractured zone are controlled by cracks contained in deep rock masses. Zonal disintegration mechanism is strongly dependent on the interaction among cracks. The strong interaction among cracks is investigated using stress superposition principle and the Chebyshev polynomials expansion of the pseudo-traction. It is found from numerical results that crack nucleation, growth and coalescence lead to failure of deep crack- weakened rock masses. The stress redistribution around the surrounding rock mass induced by unloading excavation is studied. The effect of the excavation time on nucleation, growth, interaction and coalescence of cracks was analyzed. Moreover, the influence of the excavation time on the size and quantity of fractured zone and non-fractured zone was given. When the excavation time is short, zonal disintegration phenomenon may occur in deep rock masses. It is shown from numerical results that the size and quantity of fractured zone increase with decreasing excavation time, and the size and quantity of fractured zone increase with the increasing value of in-situ geostress.

Zonal disintegration phenomenon in enclosing rock mass surrounding deep tunnels——Elasto-plastic analysis of stress field of enclosing rock mass

The zonal disintegration phenomenon (ZDP) is a typical phenomenon in deep block rock masses. In order to investigate the mechanism of ZDP, an improved non-linear Hoek-Brown strength criterion and a bi-linear constitutive model of rock mass were used to analyze the elasto-plastic stress field of the enclosing rock mass around a deep round tunnel. The radius of the plastic region and stress of the enclosing rock mass were obtained by introducing dimensionless parameters of radial distance. The results show that tunneling in deep rock mass causes a maximum stress zone to appear in the vicinity of the boundary of the elastic and the plastic zone in the surrounding rock mass. Under the compression of a large tangential force and a small radial force, the rock mass in the maximum stress zone was in an approximate uniaxial loading state, which could lead to a split failure in the rock mass.

Zonal disintegration mechanism of isotropic rock masses around a deep spherical tunnel

In order to investigate zonal disintegration mechanism of isotropic rock masses around a deep spherical tunnel, a new mechanical model subjected to dynamic unloading under hydrostatic pressure condition is proposed. The total elastic stress-field distributions is determined using the elastodynamic equation. The effects of unloading rate and dynamic mechanical parameters of isotropic deep rock masses on the zonal disintegration phenomenon of the surrounding rock masses around a deep spherical tunnel as well as the total elastic stress field distributions are considered. The number and size of fractured and non-fractured zones are determined by using the Hoek-Brown criterion. Numerical computation is carried out. It is found from numerical results that the number of fractured zones increases with increasing the disturbance coefficient, in-situ stress, unloading time and unloading rate, and it decreases with increasing parameter geological strength index, the strength parameter and the uniaxial compressive strength of intact rock.

Zonal disintegration phenomenon in rock mass surrounding deep tunnels

Zonal disintegration is a typical static phenomenon of deep rock masses. It has been defined as alternating regions of fractured and relatively intact rock mass that appear around or in front of the working stope during excavation of a deep tunnel. Zonal disintegration phenomenon was successfully demonstrated in the laboratory with 3D tests on analogous gypsum models, two circular cracked zones were observed in the test. The linear Mohr-Coulomb yield criterion was used with a constitutive model that showed linear softening and ideal residual plastic to analyze the elasto-plastic field of the enclosing rock mass around a deep tunnel. The results show that tunneling causes a maximum stress zone to appear between an elastic and plastic zone in the surrounding rock. The zonal disintegration phenomenon is analyzed by considering the stress-strain state of the rock mass in the vicinity of the maximum stress zone. Creep instability failure of the rock due to the development of the plastic zone, and transfer of the maximum stress zone into the rock mass, are the cause of zonal disintegration. An analytical criterion for the critical depth at which zonal disintegration can occur is derived. This depth depends mainly on the character and stress concentration coefficient of the rock mass.

Effect of heterogeneity on occurrence of zonal disintegration around deep underground openings

By utilizing the two numerical codes RFPA3 D and FLAC3 D, the effect of heterogeneity on failure mode and failure mechanism of rock around deep underground excavations under tri-axial stress is analyzed. It is found that zonal disintegration is a large scale shear-slip failure developed in deep surrounding rock mass under tri-axial stress, which is accompanied by a large amount of tensile failure. The distance between fractures and the number of fractures have a close correlation with the rock mass heterogeneity. With an increase of the homogeneity index of the rock mass, the distances between fractures decrease and the number of fractures increases. For an intact hard rock mass with relative high homogeneity, only failure mode characterized as v-shaped notches can be formed due to the intersection of intensively developed shear bands. None of the zonal disintegration can be formed due to the fact that with increasing homogeneity, the failure mechanism of rock mass is gradually dominated by shear failure rather than tensile failure.

Mechanism of zonal disintegration in surrounding rock mass around deep rock engineering and its application

The mechanical behaviors of deep rock mass are different from those of shallow rock mass.Through cases of Jinping II Hydropower Station,the special phenomenon of zonal disintegration in the surrounding rock mass around the diversion tunnels,is analyzed.On the basis of fracture mechanics,a new strength criterion for deep rock mass is derived.The new nonlinear strength criterion that is relative to the rock mass rating classification can be applied to the study of the tensile failure of deep rock mass.Subsequently,zonal disintegration model is established,and the radius of fractured zone and none-fractured zone of deep surrounding rock mass around cylindrical tunnel are obtained,their exact positions and the evolution law of zonal disintegration of surrounding rock mass is determined.To validate the present model,comparison between calculation results and the experiment observation on facture and failure around underground openings is carried out.It is found that the numerical simulation result is in good agreement with the experimental one on failure modes around the hole.Through sensitivity analysis,the effects of stress condition,cohesion and the angle of internal friction on the phenomenon of zonal disintegration are determined.Finally,the present model is adopted in the analysis of the zonal disintegration in the surrounding rock mass around the diversion tunnels in Jinping II Hydropower Station.Meanwhile,the magnitude and distributions of fractured zones are determined by numerical simulation.

THE EFFECTS OF THREE-DIMENSIONAL PENNY-SHAPED CRACKS ON ZONAL DISINTEGRATION OF THE SURROUNDING ROCK MASSES AROUND A DEEP CIRCULAR TUNNEL

In this study, it was assumed that three-dimensional penny-shaped cracks existed in deep rock masses. A new non-Euclidean model was established, in which the effects of penny- shaped cracks and axial in-situ stress on zonal disintegration of deep rock masses were taken into account. Based on the non-Euclidean model, the stress intensity factors at tips of the penny- shaped cracks were determined. The strain energy density factor was applied to investigate the occurrence of fractured zones. It was observed from the numerical results that the magnitude and location of fractured zones were sensitive to micro- and macro-mechanical parameters, as well as the value of in-situ stress. The numerical results were in good agreement with the experimental data.

THE ZONAL DISINTEGRATION MECHANISM OF SURROUNDING ROCK AROUND DEEP SPHERICAL TUNNELS UNDER HYDROSTATIC PRESSURE CONDITION: A NON-EUCLIDEAN CONTINUUM DAMAGE MODEL

A new non-Euclidean continuum damage model is proposed to investigate the zonal disintegration phenomenon of the surrounding rocks around deep spherical tunnels under hydrostatic pressure condition as well as the total elastic stress field distributions.The elastic stress fields of the surrounding rocks around deep spherical tunnels under hydrostatic pressure condition axe obtained.If the elastic stresses of the surrounding rocks satisfy the strength criterion of the deep rock masses,the number,size and location of fractured and nonfractured zones are determined.The effect of physico-mechanical parameters of the surrounding rocks on the zonal disintegration phenomenon is studied and numerical computation is carried out.It is found from numerical results that the number,size and location of fractured and non-fractured zones are sensitive to the physico-mechanical parameters of the surrounding rocks.

深部不同断面巷道分区破裂形态与围岩结构控制

采用理论分析、现场实测、模拟分析的方法,研究了各向等压条件下等效开挖矩形、直墙半圆拱和圆形断面分区破裂形态及围岩稳定结构。结论:3个断面分区破裂形态不同,矩形断面分区破裂呈“■”状分布,直墙半圆拱断面分区破裂呈多层的“■”状分布,圆形断面分区破裂呈“花瓣”状分布;三个断面位移特征相似,位移等值线浅部呈正立的“鸡蛋壳”形,深部呈“碗”形;支承压力在主破裂面处降低,在最外层主破裂面头部集中,在破裂面之间完整岩层处升高,呈分区集中,“波谷—波峰—波谷”震荡增高的特征向外传播;理想正方形破裂面弦长有an+1=2(1/2)an(n=1,2,3,4)关系;浅部围岩分区破裂形成后,相当于深部围岩的伪开挖,3个断面均存在多层“■”形围岩承载结构。巷道稳定原理就是促进多层承载结构相互依存,共同承载。具体措施:加密、加粗、加长锚杆(索)支护结构,建立浅部与深部多层承载结构相互联系,在浅部形成稳定锚固体促进深部围岩稳定,主破裂面精准注浆修复围岩破裂面和限制主破裂面滑移。

深部巷道围岩分区破裂化现象现场监测研究

随着矿产资源的开发,深部巷道围岩中出现了破裂区和完整区相间的分区破裂化现象,这是一种新发现的特殊工程地质现象,引起了国内外岩石力学界的关注,但相关研究还不深入。为在现场监测深部巷道围岩的分区破裂化现象,在淮南矿区近千米深井半径不同的巷道选择了4个监测断面,每个断面布置了3～5个钻孔,采用矿井钻孔电视成像仪对巷道断面围岩不同钻孔内的破裂情况进行了监测,监测到了围岩内的分区破裂化现象,并给出了4个断面围岩的分区破裂分布图。通过分析巷道所在岩层、地质资料及钻孔内裂隙的形状,说明裂隙是由巷道开挖引起的。监测结果表明,3个大断面巷道围岩内的相同破裂分区的半径和厚度相差不大,小断面巷道围岩内的破裂分区与大断面相似,只是相同各破裂分区的半径和厚度相应减小,表明各破裂分区的半径是巷道半径r的关系式为(2)i-1r(i=1,2,3,4)。4个监测断面围岩内均产生了4个破裂分区,第1个破裂分区厚度与巷道半径相当,破裂程度最严重,第2个破裂分区其后各破裂分区厚度和破裂程度均依次减小。研究结果对于认识深部巷道围岩的破裂模式及其稳定性支护具有重要意义。

深部巷道围岩的分区破裂机制及“深部”界定探讨

通过分析巷道围岩的应力状态和变形破坏多阶段、多水平的性状,揭示巷道围岩最大支撑压力区的体积变形状态及其后果,得出深部围岩区域破裂现象的发生条件、岩体的初始压力和围岩全过程变形状态,尤其是围岩峰值后状态下材料的残留强度关系。根据分区破裂现象的出现条件,提出界定浅部及深部工程活动的标准:浅部工程——坑道最大支撑压力区不破坏的深度;深部工程——坑道最大支撑压力区发生破坏的深度。

不同洞形与加载方式对深部岩体分区破裂影响的模型试验研究

随着地下工程开挖深度的增加,深部洞室围岩将产生不同于浅部洞室的分区破裂现象。为研究分区破裂的破坏机制和形成机制,以淮南矿区丁集煤矿高地应力深部巷道为工程背景,采用模型相似材料和数控真三维加载模型试验系统,开展圆洞、城门洞和马蹄形洞在沿洞轴向和垂直洞轴向加载条件下的洞室开挖真三维地质力学模型试验。模型试验研究表明:(1)初始最大主应力平行于洞轴方向且其量值超过1.5倍围岩单轴抗压强度是深部岩体产生分区破裂的重要条件;(2)洞室分区破裂的范围与洞形和洞室尺寸有关,洞室尺寸越大,分区破裂范围越大。模型试验结果有效揭示分区破裂的形成条件和破坏规律,为深入研究高地应力深部岩体的非线性变形特征与破坏机制奠定了坚实的试验基础。

电阻率法在深部巷道分区破裂探测中的应用

淮南丁集煤矿西部采区南运输大巷埋深达955 m,已显现出深部开挖的特征。为研究深部巷道围岩破裂情况,在该巷道选取2个监测断面(宽5.0 m,高3.8 m),每个断面布置5个钻孔,测量围岩电阻率沿钻孔深度的变化。电阻率是岩石的重要电性参数,岩体的破碎程度对电阻率的影响较大,一般有裂纹的地方,电阻率产生突变。采用ResiTest–4000电阻率测试仪和研制的孔内探头,对钻孔内岩体电阻率进行测试。岩石破碎区电阻率基准值根据每一钻孔电阻率平均值(剔除特异点)确定,大于基准值的为破碎区。根据测试结果,绘制巷道围岩分区破裂图,与钻孔电视观测结果较吻合。结果表明,该巷道围岩有4个破裂分区;破裂分区带的半径与巷道半径基本呈线性关系;巷道周边破裂区宽度最大,平均达到3.12 m,依次分区破裂带的宽度有递减趋势。

深部岩体分区破裂化现象数值模拟

利用数值手段模拟深部岩体分区破裂现象的产生及演化过程。从岩石的细观结构层次出发,基于最大拉应力准则和应变能密度理论建立单元破坏准则,并应用弹性损伤力学方法来模拟岩石的破坏行为,数值模拟过程中,必须考虑地下洞室开挖释放的能量足够引起围岩产生动力现象,即将开挖过程视为一个动力过程。基于上述思想,通过FLAC3D中的FISH语言开发分区破裂化现象的计算程序,并应用该程序求解某深埋巷道围岩破裂形态,得到破裂区和非破裂区的宽度和数量,数值模拟结果与现场观测成果有很好的一致性。

深部围岩分区破裂化模型试验研究

为研究深部巷道围岩破裂机理,在"深部巷道围岩破裂机理与支护技术模拟试验装置"进行了模型试验,系统研究了深部巷道围岩在最大初始开洞荷载与洞室轴线平行作用下直墙拱顶试验的破坏形态和机理。模型试验表明:当最大主应力与洞室轴线平行,在较大轴向压力作用下产生较大的朝洞内的膨胀变形,使得在围岩内产生较大的径向拉应变,其产生的拉伸断裂是出现分层破坏现象的关键,分布特点是随着轴向应力的增加其拉应变值增加,随距洞壁距离的增大其拉应变值减小。拉伸断裂面形成后,相当于在原来的介质内又形成了一个新的半径增大的洞室,洞室在较大的轴向压应力持续作用下,拉伸破坏过程不断重复出现,就会形成交替的破裂区域和未破裂区域,即分层破裂现象。

深部巷道围岩分区破裂三维地质力学模型试验研究

为模拟分区破裂的产生条件和破裂机制,以淮南矿区丁集煤矿深部巷道为工程背景,通过相似材料三维地质力学模型试验再现深部巷道围岩分区破裂的形成过程,通过多种测试手段获得巷道围岩内部的应变和位移呈现波峰和波谷间隔分布的波浪形变化规律,从巷道围岩的破裂现象及其应变和位移的变化规律,有效揭示深部巷道围岩分区破裂的形成条件和破坏规律,为深入研究深部巷道围岩的非线性变形破坏机制奠定坚实的试验基础。

深埋隧道开挖过程动态及破裂形态分析

地下工程开挖过程中,在洞室围岩中会产生拉压交替变化区,当地应力过大时,会产生分区破裂化现象。为了解释洞室围岩拉压交替变化和分区破裂化现象,根据隧道开挖卸荷这一动力学特征,建立隧道开挖过程的动态分析力学模型和计算模式,由此导出由开挖卸荷引起的扰动应力、扰动应变和扰动位移满足的平衡方程、物理方程、几何方程和边界条件。根据实际的位移约束条件,假设位移试函数,利用Hamilton时域变分原理,考虑时域变分条件和约束变分条件导出围岩体的积分–变分方程组,建立该方程组的模态矩阵。在给定开挖卸荷路径和零初始条件下采用Duhamel积分,得到离散振动方程组的稳态响应。通过矩阵变换,得到隧道围岩体扰动应力、应变和位移的解答函数式。算例分析表明,所给出的理论和方法能正确地反应出隧道开挖引起围岩内的动态过程,并能有效地对开挖引起的围岩的破坏形态进行评价。

深部岩巷分区破裂围岩稳定性控制方法及应用

深部高地应力岩巷开挖后围岩内出现分区破裂现象,采用传统的原设计方案巷道稳定性差。根据巷道围岩变形破坏的现场监测结果,经过理论分析和支护试验,提出了"提高法向约束、锚杆增韧止裂、协调耦合支护、应力内部转移、分区充填注浆、增强围岩强度"的锚注一体化综合控制方法理念。并提出了相对应的综合支护技术,即首先采用高预紧力超强锚杆及时支护围岩,锚杆的长度和数量分别由监测结果和分区支护能量判据确定;其次采用高强锚索让压梁支护巷道顶板,实现锚杆、锚索的协调耦合支护和围岩应力内部转移;最后采用中空分段螺旋式注浆技术进行滞后加固。最后针对监测巷道采用锚注一体化综合控制方法和技术进行了支护优化设计并进行现场支护试验,监测结果表明,优化支护的巷道稳定性良好。

深部巷道围岩分区破裂化数值模拟

采用有限差分数值计算软件FLAC对巷道围岩分区破裂化进行研究,分析了分区破裂的产生及演化过程,即巷道开挖后,随着原岩应力的释放,多条破裂带从巷道表面或临近周边逐步向围岩深处延伸,在延伸过程中,单条破裂带可能会分叉成两条甚至多条破裂带,这些破裂带互相交叉,在巷道浅部围岩形成网状间隔破裂区,在深部围岩形成环带状间隔破裂区。岩体初始应力水平、侧压系数及巷道断面形状等对巷道围岩分区破裂化都有显著影响。数值模拟结果与前人的现场研究成果有很好的一致性。

深部层状节理岩体分区破裂模型试验研究

随着地下工程开挖深度的增加,深部洞室围岩将产生不同于浅部洞室的分区破裂现象。为深入研究深部岩体分区破裂现象的形成机制和影响因素,以淮南矿区丁集煤矿的深部巷道为工程背景,利用模型相似材料和高地应力真三维加载模型试验系统,首次开展了带有软弱夹层的层状节理岩体的真三维地质力学模型试验。结果表明:(1)在满足一定应力条件下,带有软弱夹层的层状节理试验模型出现明显的分区破裂现象;(2)软弱夹层是影响层状节理岩体分区破裂现象的重要因素,在相同的应力条件下,软弱夹层使得巷道围岩的径向位移和应变明显增加;并且软弱夹层的间距越小,洞周破裂区的层数越多,范围越大;(3)洞周破裂区的形状近似为圆形,与是否存在软弱夹层及软弱夹层间距均无关。模型试验结果有效揭示了分区破裂的影响因素,为深入研究高地应力深部岩体的非线性变形破坏特征奠定了坚实的试验基础。