Load-bearing characteristics and energy evolution of fractured rock masses after granite and sandstone grouting

Experiments on grouting-reinforced rock mass specimens with different particle sizes and features were carried out in this study to examine the effects of grouting reinforcement on the load-bearing characteristics of fractured rock mass.The strength and deformation features of grouting-reinforced rock mass were analyzed under different loading manners;the energy evolution mechanism of grouting-reinforced rock mass specimens with different particle sizes and features was investigated;the energy dissipation ratio and post-peak stress decreasing rate were employed to evaluate the bearing stability of grouting-reinforced rock mass.The results show that the strength and ductility of granite-reinforced rock mass(GRM)under biaxial loading are higher than that of sandstone-reinforced rock mass(SRM)under uniaxial loading.Besides,the energy evolution characteristics of grouting-reinforced rock mass under uniaxial and biaxial loading mainly could be divided into early,middle,and late stages.In the early stage,total,elastic,and dissipation energies were quite small with flatter curves;in the middle stage,elastic energy increased rapidly,whereas dissipation energy increased slowly;in the late stage,dissipation energy increased sharply.The energy dissipation ratio was used to represent the pre-peak plastic deformation.Under uniaxial loading,this ratio increased as the particle size increased and the pre-peak plastic deformation of grouting-reinforced rock mass became larger;under biaxial loading,it dropped as the particle size increased,and the pre-peak plastic deformation of grouting-reinforced rock mass became smaller.The post-peak stress decline rate A_(v) was used to assess the post-peak bearing performance of grouting-reinforced rock mass.Under uniaxial loading,parameter A_(v) exhibited reduction as the particle size kept increasing,and the ability of post-peak of grouting-reinforced rock mass to allow deformation development was greater,and the bearing capacity was greater;under biaxial loading,A_(v) increased with the particle size,and the ability of post-peak of grouting-reinforced rock mass to allow deformation development was low and the bearing capacity was reduced.The findings are considered instrumental in improving the stability of the roadway-surrounding rock by granite and sandstone grouting.

Strength and deformation characteristics of irregular columnar jointed rock mass: A combined experimental and theoretical study

The irregularity of jointed network poses a challenge to the determination of field mechanical param-eters of columnar jointed rock mass(CJRM),and a reasonable prediction of deformation and strength characteristics of CJRM is important for engineering construction.The Voronoi diagram and three-dimensional printing technology were used to make an irregular columnar jointed mold,and the irregular CJRM(ICJRM)specimens with different dip directions and dip angles were prepared.Uniaxial compression tests were performed,and the anisotropic strength and deformation characteristics of ICJRM were described.The failure modes and mechanisms were revealed in accordance with the final appearances of the ICJRM specimens.Based on the model test results,the empirical correlations for determining the field deformation and strength parameters of CJRM were derived using the dip angle and modified joint factor.The proposed empirical equations were used in the Baihetan Project,and the calculated mechanical parameters were compared with the field test results and those obtained from the tunneling quality index method.Results showed that the deformation parameters determined by the two proposed methods are all consistent with the field test results,and these two methods can also estimate the strength parameters effectively.

Failure mode and strength anisotropic characteristic of stratified rock mass under uniaxial compressive situation

A stratified rock mass model was founded by FLAC^3D. The failure mode and anisotropic characteristic of strength for stratified rock mass were analyzed. The analysis results show that the numerical simulation can visually reflect the failure modes of rock samples under different inclination angles β of structural plane. The stiffness of rock sample before peak strength changes in the compressive procedure. With the increase of β, the compressive strength σc of rock sample decreases firstly and then increases; when β is in the range of 20°-30° and 80°-90°, σc has the largest sensitivity to r; while β falls in the range of 30°-70°, σc varies little. When φj〈β〈90° （ φj is friction angle of structure plane）, the results obtained from numerical simulation and theoretical analysis are in almost the same values; while β〈 φj or β=90°, they are in great different values. The results obtained from theoretical analysis are obvious larger than those from numerical simulation; and the results from numerical simulation can reflect the difference of compressive strength of rock samples for the two situations of β≥φj and β=90°, which is in more accordance with the real situation.

Early warning of rock mass instability based on multi-field coupling analysis and microseismic monitoring

In order to overcome the limitation that rock mass instability warnings are caused by a lack of deep consideration of the inherent mechanism of disaster formation, early warning signs of rock mass instability were detected and multi-field coupling was analyzed. A multi-field coupling model of a damaged rock mass was established. The relationship between microseismic activity parameters and rock mass stability was analyzed, and a multi-parameter early warning index system was established and its solution program was compiled. Based on the D-S data fusion theory,an early warning model of rock mass instability combining multi-field coupling analysis and microseismic monitoring was constructed. Taking an underground mine stope as an object, the multi-field coupling model and its solution program were used to analyze mining response characteristics. The seismic field data were used to verify the accuracy of the multi-field coupling analysis. The early warning model was used to predict the instability of stope rock mass,and the early warning result is consistent with a real-world scenario.

Empirical equations between characteristic impedance and mechanical properties of rocks

Based on a great number of experimental data on various mechanical properties of rock in the literature,six empirical equations between the characteristic impedance(product of density and P-wave velocity)and mechanical properties of rock are proposed.These properties include uniaxial compressive strength,tensile strength,shear strength,mode I fracture toughness,Young’s modulus,and Poisson’s ratio.These empirical equations show that the values of the aforementioned properties increase with increase in characteristic impedance.It also implies that the characteristic impedance of rock may be considered as an index to represent the main properties of rock.In this sense,it is possible to consider using characteristic impedance to classify rock masses for studies in the future.

Seismic bearing capacity of strip footings on rock masses using the Hoeke Brown failure criterion

In this paper,the bearing capacity of strip footings on rock masses has been studied in the seismic case.The stress characteristics or slip line method was used for analysis.The problem was analyzed in the plane strain condition using the Hoeke Brown failure criterion.First,the equilibrium equations along the stress characteristics were obtained and the rock failure criterion was applied.Then,the equations were solved using the finite difference method.A computer code has been provided for analysis.Given the footing and rock parameters,the code can calculate the stress characteristics network and obtain the stress distribution under the footing.The seismic effects have been applied as the horizontal and vertical pseudo-static coefficients.The results of this paper are very close to those of the other studies.The seismic bearing capacity of weightless rock masses can be obtained using the proposed equations and graphs without calculating the whole stress characteristics network.

Mechanical properties and failure characteristics of fractured sandstone with grouting and anchorage

Based on uniaxial compression experimental results on fractured sandstone with grouting and anchorage, we studied the strength and deformation properties, the failure model, crack formation and evolution laws of fractured sandstone under different conditions of anchorage. The experimental results show that the strength and elastic modulus of fractured sandstone with different fracture angles are significantly lower than those of intact sandstone. Compared with the fractured samples without anchorage,the peak strength, residual strength, peak and ultimate axial strain of fractured sandstone under different anchorage increase by 64.5–320.0%, 62.8–493.0%, and 31.6–181.4%, respectively. The number of bolts and degree of pre-stress has certain effects on the peak strength and failure model of fractured sandstone. The peak strength of fractured sandstone under different anchorage increases to some extent, and the failure model of fractured sandstone also transforms from tensile failure to tensile–shear mixed failure with the number of bolts. The pre-stress can restrain the formation and evolution process of tensile cracks, delay the failure process of fractured sandstone under anchorage and impel the transformation of failure model from brittle failure to plastic failure.

An Anisotropic Geomechanical Model for Jointed Rock Masses at Taishan Nuclear Power Station, Southern China

An anisotropic geomechanical model for jointed rock mass is presented. Simultaneously with deriving the orthotropic anisotropy elastic parameters along the positive axis, the equivalent compliance matrix for the deflection axis orthotropic anisotropy was derived through a three- dimensional coordinate transformation. In addition, Singh＇s analysis of the stress concentration effects of intermittent joints was adopted, based on two groups of intermittent joints and a set of cross- cutting joints in the jointed rock mass. The stress concentration effects caused by intermittent joints and the coupling effect of cross-cutting joints along the deflection-axis are also considered. The proposed anisotropic mechanics parameters method is applied to determine the deformation parameters of jointed granite at the Taishan Nuclear Power Station. Combined with the deterministic mechanical parameters of rock blocks and joints, the deformation parameters and their variability in jointed rock masses are estimated quantitatively. The computed results show that jointed granite at the Taishan Nuclear Power Station exhibits typical anisotropic mechanical characteristics; the elastic moduli in the two horizontal directions were similar, but the elastic modulus in the vertical direction was much greater. Jointed rock elastic moduli in the two horizontal and vertical directions were respectively about 24% and 37% of the core of rock, showing weakly orthotropic anisotropy; the ratio of elastic moduli in the vertical and horizontal directions was 1.53, clearly indicating the transversely isotropic rock mass mechanical characteristics. The method can be popularized to solve other rock mechanics problems in nuclear power engineering.

A Petrological, Geochemical, and Geochronological Study of Shuikou Ultrabasic Rock Mass in Wuding County, Yunnan Province, China

Geotectonically, the Shuikou ultrabasic-basic rock mass is located on the western margin of the Yangtze Platform. As revealed by field geological surveys, the Shuikou rock mass intrudes into the quartz sandstones of the Sinian Chengjiang Formation (Zac). It is dominated by pyroxenites and can be roughly divided into four lithofacies zones, namely gabbros at the outermost periphery and fine-, medium-, and coarse-grained pyroxenites from margin to center. With the transition from pyroxenites to gabbros, the Shuikou rock mass features gradual enrichment in silica and alkali overall, an increase in ΣREE and (La/Yb)N ratio, and a decrease in δEu values and Eu/Sm ratio, indicating that the Shuikou rock mass was formed from the continuous differentiation and crystallization of consanguineous magma and that low-degree partial melting occurred meanwhile. According to the U-Pb baddeleyite geochronology, the crystallization age of the Shuikou rock mass is 210.7 ± 3 Ma (MSWD = 1.01). Based on this, as well as the analysis of geochemical characteristics, the Shuikou rock mass occurred in a continental intraplate tensional environment, this is closely related to the activities of the Emeishan mantle plume during the same period.

Experimental study on the mechanical and failure behaviors of deep rock subjected to true triaxial stress:A review

It has become an inevitable trend of human development to seek resources from the deep underground.However,rock encountered in deep underground engineering is usually in an anisotropic stress state(σ_(1)>σ>σ_(3))due to the influences of geological structures and engineering disturbances.It is therefore essential to study the mechanical,seepage,and dynamic disaster behaviors of deep rock under true triaxial stress to ensure the safe operation of deep rock engineering and the efficient exploitation of deep resources.In recent years,experimental techniques and research on true triaxial rock mechanics have achieved fruitful results that have promoted the rapid development of deep rock mechanics;thus,it is necessary to systematically review and summarize these developments.This work first introduced several typical true triaxial testing apparatus and then reviewed the corresponding research progress on rock deformation,strength,failure mode,brittleness,and energy as well as the 3D volumetric fracturing(dynamic disaster)properties of deep rocks under true triaxial stress.Then,several commonly used true triaxial rock strength criteria and their applicability,the permeability characteristics and mathematical models of deep reservoir rocks,and the disaster-causing processes and mechanisms of disturbed volumetric fracturing(rockburst,compound dynamic disasters)in deep rock engineering were described.This work may provide an essential reference for addressing the true triaxial rock mechanics issues involved in deep rock engineering,especially regarding the stability of surrounding rock at depth,disaster prevention and control,and oil and gas exploitation.

Numerical analysis of seepage flow characteristic of collapse column under the influence of mining

Based on the importance of fractured rock mass seepage research, in order to analyze seepage flow characteristics of collapse column under the influence of mining, a method by embedding fractured rock mass flow solid coupling relationship into FLAC3D internal flow models is presented according to fluid-solid coupling theory and strength criterion. A calculation model of numerical analysis was established, and the influences of mining pressure and plastic damage to pore water pressure and seepage vector change rule were studied. The results show that collapse column is the main channel of confined water seepage upward. The impact is not big when the workface is away from the collapse column. But when the workface is nearing a collapse column, there will be a seepage channel on a side near the workface, in which seepage vector and head are comparatively large. With workface pushing through collapse column, the seepage channel transfers to the other side of the column. In addition, when the plastic damage area within the collapse column breaks through, a "pipeline flow" will be formed within the column, and seepage field will change remarkably and the possibility of water bursting will be greater.

基于Rockfall数值模拟的危岩体运动规律分析

危岩体发育过程具有渐进性,失稳过程具有突变性和强致灾性,危岩崩塌灾害是山区公路工程建设及运营过程中普遍存在的突发性重大安全隐患,前期预测和分析危岩体落石运动特征可为危岩体治理提供参考。本文以兴义环高某特大桥桥台上方的危岩体为例,通过现场调查研究,分析危岩特征,采用Rockfall数值软件模拟危岩落石运动轨迹、落石终点水平位置,分析落石速度及其能量大小。结果表明:危岩体W5发生崩塌后,有大部分落石到达桥面,且在到达桥面时仍有较大动能和转动速度,会对桥面造成严重撞击和破坏,威胁和影响行车安全。建议对危岩体进行防护或加固,以保障公路建设运营安全。

山东龙郓煤业10·20冲击地压事故区域应力背景与防控研究

矿山巷道、交通隧道等地下硐室围岩稳定与岩体所处区域地应力环境息息相关。分析区域深部地应力与地下硐室走向、形状等因素的关系,有助于提前规避硐室开挖风险。文章以山东龙郓煤业10·20冲击地压事故为背景,通过地应力测量与监测工作,初步揭示了山东西部地壳浅表层现今地应力环境,结合龙郓煤业矿区附近现今地应力场特征,探讨此次冲击地压事故产生的区域应力背景,并从地应力角度提出相应的防控建议。研究结果表明:测量深度范围内主应力大小总体上与深度成正比线性关系,最大水平主应力值为3.48~20.76 MPa,随深度增加梯度为0.0182 MPa/m;最小水平主应力值为3.44~14.95 MPa,随深度增加梯度为0.0130 MPa/m;区内最大水平主应力方位为北东43°~89°,平均方位为北东75°;地壳浅表层构造作用以水平构造作用为主,但随着深度的增加,逐渐向垂直构造作用转变;龙郓煤业10·20冲击地压事故的诱发机制主要是垂向应力大于水平主应力,现今处于拉张应力环境,尤其是巷道走向平行于最大水平主应力方向;建议龙郓煤业巷道轴线与最大水平主应力方向的夹角为60°~90°,同时巷道顶板可以采用拱形顶板,确保巷道岩体稳定。

岩体中应力波传播衰减规律研究进展

为揭示地质构造变化或爆破等产生的应力波在不同影响因素条件的衰减机制,学者们借助位移不连续法和等效连续介质法等理论方法,针对完整传播过程的入射、传播和透射3个不同阶段,开展了应力波传播衰减规律影响的研究。研究结果表明波形、岩体性质和节理性质均会对其衰减特性产生显著影响。总结以上研究方法,讨论各方法之间的联系和异同点,在此基础上提出亟待解决的问题和研究方向,为充分了解应力波传播过程中的衰减变化规律、完善波动理论和提高实际工程安全性提供参考。

基于三维裂隙网络的岩体剪切特性尺寸效应分析

为研究复杂裂隙岩体剪切特性的尺寸效应,以西藏怒江松塔水电站PDC3平硐为例,在现场采集裂隙信息的基础上,基于颗粒流PFC3D软件通过统计学方法及蒙特卡洛原理生成三维裂隙网络,构建等效岩体,进行大尺度直剪模拟试验得到裂隙岩体的抗剪强度、内摩擦系数及内聚力,分别研究其尺寸效应并确定不同参数下的REV尺寸,继而对相关参数和试样尺寸分别进行非线性回归拟合,探究其函数关系。结果表明:抗剪强度、内聚力及内摩擦系数随着试样尺寸的变化而趋于稳定,且不同参数得到的REV大小不同;综合分析不同参数的REV尺寸,得出研究区裂隙岩体的剪切特性REV尺寸为11 m×11 m×11 m;通过函数关系拟合,抗剪强度、内聚力和内摩擦系数与试样尺寸之间均存在指数函数关系。该成果为研究复杂裂隙岩体的力学REV以及合理确定力学参数提供了依据。

小秦岭金矿田航磁异常特征及找矿潜力分析

小秦岭作为我国第二大金矿田,随着浅部资源的消耗殆尽,探矿工作进入攻深找盲阶段。虽然开采历史悠久,但中深部勘查工作程度仍较低。笔者基于2020年小秦岭地区开展的1∶2.5万高精度航磁测量工作,在对航磁测量资料分析处理、数据反演和调查验证的基础上,结合区域成矿地质条件,分析总结了(隐伏)岩体、构造的航磁异常特征,建立了航磁异常推断解译标志,并对构造、隐伏岩体进行推断解译,为该区成矿预测及深部矿产资源勘查提供了地球物理依据。

基于常时微动的单结构面危岩体损伤识别实验

危岩体的动力学参数能够表征危岩体与基岩之间结构面的损伤,实际工程中人工激励危岩体较为困难,因此,如何根据场地常时微动特征识别危岩体动力学参数仍是亟需解决的问题.本文将常时微动激励下的危岩体振动问题归为欠阻尼条件单自由度结构受迫振动问题,将危岩体频谱幅值与基岩频谱幅值之比作为相对幅值谱,通过相对幅值K>1的最大峰值点对应的频率得到危岩体的一阶固有频率.以宏观裂缝控制型危岩体(悬臂式和错断式危岩体)及微观裂隙控制型危岩体(滑移式危岩体)为研究对象,通过模型实验验证了常时微动条件下测量危岩体一阶固有频率的可行性,通过切割裂缝模拟悬臂式危岩体和错断式危岩体结构面损伤弱化,发现随着损伤程度加剧,一阶固有频率呈明显下降趋势;通过水溶胶冻结融化模拟滑移式危岩体结构面损伤弱化,随着损伤程度加剧,其一阶固有频率无明显变化,高频段的重心频率发生明显变化.实验结果表明对于宏观裂缝控制型危岩体结构面损伤可通过危岩体的一阶固有频率进行识别,对于微观裂隙控制型危岩体结构面损伤可通过危岩体高频段的重心频率变化进行识别,将两者综合起来对危岩体结构面损伤进行识别将更加有效.

岩体临空面块体振动响应规律研究

结构面是控制岩体工程局部稳定的关键因素之一,查明结构面赋存及组合状态是岩体稳定性分析的前提条件,目前常采用地质调察的方法,由于勘察手段的局限性,存在遗漏时常需要补充勘察,成本耗费高。通过开展室内试验,对结构面模型的表面振动响应规律进行了研究,研究表明:对于单结构面模型,结构面前方的质点振幅存在增幅效应,对于由两条结构面切割的块体模型,仅在远离动力输入侧的结构面前方存在振幅放大效应。在试验成果的基础上开展了数值模拟分析,分别对不同结构面倾角的岩体模型进行计算,结果表明:相对于萨道夫斯基经验公式得到的振动衰减规律,当结构面与爆源方向地面夹角θ值小于90°时,结构面前方的振动波入射区域质点振幅存在明显放大效应,结构面后方质点振动幅值则显著衰减。随着结构面与边界面夹角θ的减小,结构面前质点峰值振速增幅率逐渐增大,并在θ=20°时波幅放大2.8倍。通过合理布置爆破振动监测测点,这一规律为爆破工程中识别结构面及块体提供判据。

倾倒型危岩体空间振动特征及损伤识别

目前,基于动力学指标反映危岩体损伤的研究多集中于分析危岩体单方向振动特征,当无法判断结构面演化方向或演化方向为多方向时,难以准确识别危岩体损伤。为探究危岩体损伤演化过程的空间3维振动特征,得到可反映危岩体空间3维损伤演化过程的高敏感性指标,本文将危岩体视为3维实体,通过数值模拟分析了倾倒型危岩体振型特征,并基于弹簧-质子摆振模型推导了危岩体水平向摆振和竖向摆振的振幅和固有频率的计算公式。结果表明:危岩体不同振型对其损伤的敏感性与结构面演化方向有关。单向动力学指标敏感性由该方向主振型决定,因此指标敏感性受结构面演化方向控制。监测方向与结构面法向或结构面演化方向一致时,指标敏感性最高;监测方向为结构面演化方向垂向时,动力学指标敏感性最差。将粒子轨迹应用于危岩体损伤识别,以3维向量表示危岩体振动过程中的空间位置,定义了粒子轨迹时域动力学指标算法。通过设计崩塌相似模型试验,人工切割加深后缘裂隙模拟危岩体结构面损伤演化过程,分析了危岩体演化过程中单向时频动力学指标和粒子轨迹时域动力学指标的变化规律;试验发现:与结构面损伤演化有强相关性的单向动力学指标(振幅标准差、峭度、主频)对危岩体损伤敏感性具有方向差异,各指标不同方向敏感性最高相差2.50~23.79倍;粒子轨迹动力学指标对危岩体结构面不同方向演化时的损伤均具有较高敏感性。

基于多尺寸结构面的循环剪切力学特性及其抗剪强度研究

岩石结构面的抗剪强度具有强烈的尺寸依赖性,开展结构面多尺寸试验对于研究大尺寸结构面力学特性具有重要的理论价值和实践意义。针对过往研究较少的循环作用下结构面力学特性尺寸效应问题,首先基于立方体劈裂试验获得不同粗糙度的近天然岩石结构面,然后运用三维扫描技术获得结构面点云数据,进而采用三维打印技术制作不同尺寸结构面树脂模型,最后,通过倒模法制作试样并进行室内试验,研究不同法向应力下结构面尺寸效应的规律以及不同粗糙度和不同法向应力对结构面抗剪强度的影响。基于黏着摩擦理论-Barton经验公式,提出了一个可以考虑结构面尺寸效应的峰值抗剪强度公式。研究结果表明:岩石结构面的峰值抗剪强度具有明显的负尺寸效应,且峰值抗剪强度的改变对小尺寸大法向应力和大尺寸小法向应力下的结构面更为敏感;低法向应力下的残余剪切强度具有明显的负尺寸效应,而高法向应力下的残余剪切强度随着结构面尺寸的增大,从正尺寸效应变为负尺寸效应。