Determination of geological strength index of jointed rock mass based on image processing

The geological strength index(GSI) system,widely used for the design and practice of mining process,is a unique rock mass classification system related to the rock mass strength and deformation parameters based on the generalized Hoek-Brown and Mohr-Coulomb failure criteria.The GSI can be estimated using standard chart and field observations of rock mass blockiness and discontinuity surface conditions.The GSI value gives a numerical representation of the overall geotechnical quality of the rock mass.In this study,we propose a method to determine the GSI quantitatively using photographic images of in situ jointed rock mass with image processing technology,fractal theory and artificial neural network(ANN).We employ the GSI system to characterize the jointed rock mass around the working in a coal mine.The relative error between the proposed value and the given value in the GSI chart is less than 3.6%.

Estimating the properties of weathered bedrock and pile-rock interaction from the geological strength index

The effect of variable rock mass properties on pile-rock interaction poses a great challenge to the design of stabilizing piles and numerical analysis of pile-rock interaction. The paper presents a novel method to estimate the properties of weathered bedrock, which can be applied to routine design of landslide-stabilizing piles for collivial landslides. The Ercengyan landslide located in the Three Gorges Reservoir, China, is the area of interest for this study. A geological investigation and triaxial tests were conducted to estimate the basic parameters, including Geological Strength Index(GSI), uniaxial compressive strength σ_(ci) and Hoek-Brown constant m_i of intact bedrock in the study area. Hoek-Brown criterion was used to estimate mechanical properties of the weathered rock, including elastic modulus E_m, cohesion c, friction angle Φ, and normal ultimate lateral resistance p_(max). A parametric study was performed to evaluate the effect of parameterizations of GSI, σ_(ci) and m_i on the bedrock properties and p-y curves. The estimated rock mass properties were used with PLAXIS 2D software to simulate pile-rock interaction. Effect of GSI on stress at the pile-rock interface and in the rock, pile bending moment, pile shear force, and p-y curve were analysed.

Estimating Unconfined Compressive Strength of Sedimentary Rocks in United Arab Emirates from Point Load Strength Index

In this paper, three rock types including Sandstone, Mudstone, and Crystalline Gypsum were part of a laboratory study conducted to develop a dataset for predicting the unconfined compressive strength of UAE intact sedimentary rock specimens. Four hundred nineteen rock samples from various areas along the coastal region of the UAE were collected and tested for the development of this dataset and evaluation of models. From the statistical analysis of the data, regression equations were established among rock parameters and correlations were expressed and compared by the ones proposed in literature.

Selection of regression models for predicting strength and deformability properties of rocks using GA

Recently,many regression models have been presented for prediction of mechanical parameters of rocks regarding to rock index properties.Although statistical analysis is a common method for developing regression models,but still selection of suitable transformation of the independent variables in a regression model is diffcult.In this paper,a genetic algorithm(GA)has been employed as a heuristic search method for selection of best transformation of the independent variables(some index properties of rocks)in regression models for prediction of uniaxial compressive strength(UCS)and modulus of elasticity(E).Firstly,multiple linear regression(MLR)analysis was performed on a data set to establish predictive models.Then,two GA models were developed in which root mean squared error(RMSE)was defned as ftness function.Results have shown that GA models are more precise than MLR models and are able to explain the relation between the intrinsic strength/elasticity properties and index properties of rocks by simple formulation and accepted accuracy.

Strength of massive to moderately jointed hard rock masses

The Hoek-Brown (HB) failure criterion and the geological strength index (GSI) were developed for the estimation of rock mass strength in jointed and blocky ground where rock mass failure is dominated by sliding along open joints and rotation of rock blocks. In massive, veined and moderately jointed rock in which rock blocks cannot form without failure of intact rock, the approach to obtain HB parameters must be modified. Typical situations when these modifications are required include the design of pillars, excavation and cavern stability, strainburst potential assessment, and tunnel support in deep underground conditions (around σ1/σci > 0.15, where σ1 is the major principal compressive stress and σci is the unconfined compressive strength of the homogeneous rock) in hard brittle rocks with GSI ≥ 65. In this article, the strength of massive to moderately jointed hard rock masses is investigated, and an approach is presented to estimate the rock mass strength envelope using laboratory data from uniaxial and triaxial compressive strength tests without reliance on the HB-GSI equations. The data from tests on specimens obtained from massive to moderately jointed heterogeneous (veined) rock masses are used to obtain the rock and rock mass strengths at confining stress ranges that are relevant for deep tunnelling and mining;and a methodology is presented for this purpose from laboratory data alone. By directly obtaining the equivalent HB rock mass strength envelope for massive to moderately jointed rock from laboratory tests, the HB-GSI rock mass strength estimation approach is complemented for conditions where the GSIequations are not applicable. Guidance is also provided on how to apply the proposed approach when laboratory test data are not or not yet available.

矿山岩质边坡地层结构及岩体抗剪强度参数随钻智能识别方法

地层类别及岩体抗剪强度参数的准确识别对岩质边坡的稳定性评估至关重要。基于无量纲的可钻性指标建立了岩体抗剪强度参数随钻识别模型,使得随钻测试结果能够不经标定或换算,即可直接识别岩体抗剪强度参数。结合无监督学习和自主设计的决策模块,对深度序列随钻数据进行智能识别和自动平滑处理,实现对地层结构的智能感知,并定量描述各岩层的随钻参数及抗剪强度参数。采用自主研发的高精度现场随钻测试设备对云南鹤庆北衙露天矿灰岩体区和F6-1断层交界区域的爆破钻孔过程进行监测,并以两个典型钻孔的全过程监测结果为例,展示随钻智能识别方法的应用。总体而言,ZK1钻孔随钻智能识别方法与原始地质剖面一致程度为90.85%,ZK2钻孔随钻智能识别方法与原始地质剖面一致程度为84.47%,钻孔成像验证表明该方法识别的地层能更准确地反映边坡实际地层情况。值得注意的是,该方法能够在大尺度与地质剖面结果一致的前提下,精准地识别出地质剖面未曾表现的关键层位。这一特性为破碎软弱岩层及其强度参数的识别,以及地质模型的精准构建提供了有力保障。该方法在岩土工程领域具有广泛的应用前景,为岩层性质和抗剪强度参数的实时智能识别及地质模型的精准构建提供了可靠的解决方案。

基于量化GSI系统对地下岩体力学参数的估算

地下岩体力学参数的准确获取可以为破碎岩体支护设计、采矿方法优化提供一定数据支撑,对保护井下作业人员安全起着重要作用。为准确、便捷获得地下岩体力学参数,采用岩体结构等级SR、岩体结构面等级SCR以及岩体完整性系数Kv 3个指标,通过多指标交集定量化获取GSI值,并结合地质强度指标GSI与扰动参数D之间存在的数理关系,量化扰动参数D,并应用Hoek-Brown强度准则确定岩体力学参数。将实际地质调查结果与室内岩石力学试验相结合,估算某地下铁矿岩体力学性能指标,发现矿体力学性能明显弱于围岩约60%,表明需加强进路巷道以及矿岩边界处的支护强度,该估算方法对地下岩体稳定性优化设计具有重要的指导意义。

Tunnel behaviour and support associated with the weak rock masses of flysch

Flysch formations are generally characterised by evident heterogeneity in the presence of low strength and tectonically disturbed structures. The complexity of these geological materials demands a more specialized geoengineering characterisation. In this regard, the paper tries to discuss the standardization of the engineering geological characteristics, the assessment of the behaviour in underground excava- tions, and the instructions-guidelines for the primary support measures for flysch layer qualitatively. In order to investigate the properties of flysch rock mass, 12 tunnels of Egnatia Highway, constructed in Northern Greece, were examined considering the data obtained from the design and construction records. Flysch formations are classified thereafter in 11 rock mass types （I-XI）, according to the siltstone -sandstone proportion and their tectonic disturbance. A special geological strength index （GSI） chart for heterogeneous rock masses is used and a range of geotechnical parameters for every flysch type is presented. Standardization tunnel behaviour for every rock mass type of flysch is also presented, based on its site-specific geotechnical characteristics such as structure, intact rock strength, persistence and complexity of discontinuities. Flysch, depending on its types, can be stable even under noticeable overburden depth, and exhibit wedge sliding and wider chimney type failures or cause serious deformation even under thin cover. Squeezing can be observed under high overburden depth. The magnitude of squeezing and tunnel support requirements are also discussed for various flysch rock mass types under different overburdens. Detailed principles and guidelines for selecting immediate support mea- sures are proposed based on the principal tunnel behaviour mode and the experiences obtained from these 12 tunnels. Finally, the cost for tunnel support from these experiences is also presented.

Effects of confinement on rock mass modulus:A synthetic rock mass modelling(SRM) study

The main objective of this paper is to examine the influence of the applied confining stress on the rock mass modulus of moderately jointed rocks（well interlocked undisturbed rock mass with blocks formed by three or less intersecting joints）. A synthetic rock mass modelling（SRM） approach is employed to determine the mechanical properties of the rock mass. In this approach, the intact body of rock is represented by the discrete element method（DEM）-Voronoi grains with the ability of simulating the initiation and propagation of microcracks within the intact part of the model. The geometry of the preexisting joints is generated by employing discrete fracture network（DFN） modelling based on field joint data collected from the Brockville Tunnel using LiDAR scanning. The geometrical characteristics of the simulated joints at a representative sample size are first validated against the field data, and then used to measure the rock quality designation（RQD）, joint spacing, areal fracture intensity（P21）, and block volumes. These geometrical quantities are used to quantitatively determine a representative range of the geological strength index（GSI）. The results show that estimating the GSI using the RQD tends to make a closer estimate of the degree of blockiness that leads to GSI values corresponding to those obtained from direct visual observations of the rock mass conditions in the field. The use of joint spacing and block volume in order to quantify the GSI value range for the studied rock mass suggests a lower range compared to that evaluated in situ. Based on numerical modelling results and laboratory data of rock testing reported in the literature, a semi-empirical equation is proposed that relates the rock mass modulus to confinement as a function of the areal fracture intensity and joint stiffness.

Discussion on“Empirical methods for determining shaft bearing capacity of semi-deep foundations socketed in rocks”[J Rock Mech Geotech Eng 6(2017)1140-151]

A new comprehensive set of data（n = 178） is compiled by adding a data set（n = 72） collected by Arioglu et al.（2007） to the data set（n = 106） presented in Rezazadeh and Eslami（2017）. Then, the compiled data set is evaluated regardless of the variation in lithology/strength. The proposed empirical equation in this study comprises a wider range of uniaxial compressive strength（UCS）（0.15 MPa 〈 σ_（rc） 〈156 MPa） and various rock types. Rock mass cuttability index（RMCI） is correlated with shaft resistance（r_s） to predict the shaft resistance of rock-socketed piles. The prediction capacity of the RMCI versus r_s equation is also found to be in a fair good agreement with the presented data in Rezazadeh and Eslami（2017）. Since the RMCI is a promising parameter in the prediction of shaft resistance, the researchers in the rock-socketed pile design area should consider this parameter in the further investigations.

Revisiting rock classification to estimate rock mass properties

This paper presents the results of ongoing research carried out by the author exploring methods to provide a more robust estimate of rock mass properties specifically for use in tunnel design.Data from various large-scale rock mass failures are introduced,including coal pillars.The damage-initiation,spalling-limit approach is compared to the coal pillar database.New comparisons of estimating the geological strength index(GSI)and relationships to estimate the Hoek-Brown failure criterion parameters,mb,s and a,are presented.

深部矿山非规则矿岩点载荷强度指标分布特性

针对深部矿岩在高地应力下钻孔岩芯饼化现象频发、现场取完整芯样困难等问题,选取采场爆破后的岩石与矿块进行现场点载荷试验,通过测试获得不规则尺寸试样的点载荷强度指标.采用指数型和线性型两种修正系数(f_(1),f_(2))对点载荷强度指标进行修正,得到修正后的点载荷强度指标为I_(s50-1)和I_(s50-2),获得修正前后的点载荷强度指标的分布特性及规律:修正前后的点载荷强度指标的分布频率基本满足正态分布,修正前的点载荷强度指标呈偏态型分布,修正后的点载荷强度指标基本呈标准正态分布.采用线性型修正后点载荷强度指标的正态分布更加明显,其点载荷强度值整体上大于指数型修正后的点载荷强度值,且在等效直径为50 mm左右时点载荷强度基本相等.指数型修正方式所得结果受尺寸效应影响较大,强度值偏差较大;而线性型修正方式所得结果更具准确性.在95%的置信度下,岩样标准点载荷强度指标的置信区间为1.09~1.57 MPa,均值为1.33 MPa;矿样的置信区间为0.37~0.45 MPa,均值为0.39 MPa.由于试样受爆破损伤的影响,岩样与矿样基于单轴抗压强度的点载荷强度指标计算值约为本试验结果的1.62和3.67倍.

Reply to Discussion on “Empirical methods for determining shaft bearing capacity of semi-deep foundations socketed in rocks”

Semi-deep foundations socketed in rocks are considered to be a viable option for the foundations in the presence of heavy loads imposed by high-rise buildings and special structures, due to the low settlement and high bearing capacity. In this study, the unconfined compressive strength（UCS） and rock mass cuttability index（RMCI） have been applied to investigating the shaft bearing capacity. For this purpose, a comprehensive database of 178 full-scale load tests is compiled by adding a data set（n = 72）collected by Arioglu et al.（2007） to the data set（n = 106） presented in Rezazadeh and Eslami（2017）.Using the database, the applicability and accuracy of the existing empirical methods are evaluated and new relations are derived between the shaft bearing capacity and UCS/RMCI. Moreover, a general equation in case of unknown rock types is proposed and it is verified by another set of data（series 3 in Rezazadeh and Eslami（2017））. Since rock-socketed shafts are supported by rock mass（not intact rock）,a reduction factor for the compressive strength is suggested and verified in which the effect of discontinuities is considered using the modified UCS, based upon RMR and RQD to consider the effect of the rock mass properties.

基于岩石物理力学参数的岩层强度指数计算方法及分类标准

围岩稳定性分类是井工煤矿进行支护设计的关键依据,而岩石的物理力学参数是围岩强度分类分级的重要指标。为此,在研究神东矿区煤系地层岩石物理力学性质的基础上,通过理论分析与现场实测的方法研究了岩石的物理力学参数与岩层强度之间的关系,提出了一种基于岩石物理力学参数的岩层(岩体)强度指标计算公式及岩性序列分类方法,将岩层稳定性以岩层强度指数分为极软弱岩层、软弱岩层、中等坚硬岩层、坚硬岩层、极坚硬岩层五类;揭示了岩层强度与岩石力学性能之间的关系,建立了岩石物理力学性质与岩层(岩体)之间的联系,并根据岩层(岩体)强度指标计算公式计算了神东矿区大柳塔5-2煤层上覆岩层的强度指数,并对其强度指数进行了分类,得出5-2煤层直接顶岩层属于Ⅱ类坚硬岩层,基本顶属于Ⅰ类极坚硬岩层;探讨了5-2煤层上覆岩层的强度指数与矿压显现及岩层运动的关系,揭示了大柳塔煤矿初次来压步距大与地表下层速度快的内因。

基于GSI的深部节理化岩体工作面稳定性分析

针对节理岩体力学参数选取困难问题,基于地质强度指标GSI,结合损伤力学原理和广义Hoek-Brown准则构建考虑节理强度的节理岩体力学模型,对深部节理化岩体工作面进行了稳定性分析。结果表明:所给出的节理等效系数能较好地描述节理间距与GSI之间的关系,节理岩体的破碎程度对工作面的稳定性产生了影响,随着岩体破碎程度的提高,工作面易发生顶板冒落、煤壁片帮等现象;当岩体较为破碎时,顶板失稳主要由节理的发育、贯通引起;岩体的完整性较好时,顶板的稳定性受采空区悬臂段顶板的影响较大。

基于凿岩台车钻进速度的隧道围岩基本质量指标计算方法

为保证隧道施工中岩体识别的准确性,针对冲击-旋转耦合式破岩的凿岩机提出1种基于钻进速度的隧道围岩基本质量指标(BQ)计算方法,包括基于钻进速度的BQ拟合计算式和钻进速度分级模式。首先,从能量角度分析冲击-旋转式凿岩机的破岩机理,推导由钻进参数和BQ值表达的凿岩机破岩功能关系计算式;其次,依托郑万高铁湖北段隧道工程获得92组样本,通过现场试验和室内试验,采集样本的钻进速度和可用于计算BQ值的岩石坚硬程度和岩体完整程度数据;最后,采用数理统计方法建立钻进速度与BQ值之间的关系,并在此基础上提出钻进速度分级模式。结果表明:钻进速度和BQ值之间具有良好的响应关系,当钻进压力一定时,可直接用钻进速度表示围岩BQ值;基于钻进速度的BQ值计算方法,包括中值拟合计算式及可覆盖95%数据的上、下限值计算式;钻进速度分级模式及选择原则可直接用于现场围岩级别的快速判定。

大断面砂质板岩隧道围岩动态设计分析——以道吾山特长隧道为例

通过现场取样得到的试样组围岩单轴饱和抗压强度数据,进一步计算出该试样组数据平均值与标准差,采用试样组数据标准差除以平均值得到试样组数据变异系数。之后采用统计学公式,计算试样组数据围岩饱和抗压强度修正标准值,同时考虑地下水、主要软弱结构面产状及初始应力状态等修正因素的影响,针对岩体基本质量指标BQ值进行修正,得出岩体基本质量指标修正值[BQ],结合岩体的定性特征进行综合评判,确定围岩详细分级,从而建立起隧道围岩动态设计体系。

基于岩体波速的Hoek-Brown模型GSI指标确定方法

常规的Hoek-Brown模型中地质强度指标GSI采用野外判别方法确定,但该方法受工程师经验影响较大。本文利用岩体波速、GSI与模量的关系,提出了一种采用岩体波速确定Hoek-Brown模型中GSI指标的定量计算方法,并提出了综合施工扰动影响的广义GSI指标。通过与常规方法对比,以及对长沙某项目的岩基载荷试验预测,验证了本文方法的可行性,对Hoek-Brown模型在工程中的广泛应用具有重要意义。

基于强度折减法的地下洞室岩体破坏与预警指标研究

随着地下洞室的迅速发展,其围岩稳定性与预警指标受到关注。文章基于强度折减法,采用数值模拟研究了不同施工方法下地下洞室的拱顶变形规律,以及隧道洞室的破坏模式,提出了以开挖完成后拱顶沉降随掌子面距离的变化曲线为地下洞室开挖的施工预警指标。结果表明:完成开挖后的拱顶沉降临界破坏曲线随掌子面距离的变化曲线可作地下洞室开挖的施工预警指标,呈现三段不同的区域变化;采用分四层开挖时围岩安全系数略小于分三层开挖;随着强度折减系数的增大,地下洞室左右边墙围岩出现局部破坏,随后,地下洞室周围发生局部失稳破坏,最后,地下洞室发生整体失稳破坏。

基于岩芯分级的Hoek-Brown准则参数研究及应用

地质强度指标(GSI)是Hoek-Brown准则中重要的参数,由于缺乏可具体测量的典型参数,GSI的取值主观性很强。基于工程钻探勘察中对片麻岩岩芯的研究,用野外典型完整岩芯照片和节理面照片代替GSI图里岩体结构的素描图,提出完整岩芯长度指标(RCL)和节理条件(Jc)两参数辅助GSI量化研究;最终建立一个直观的基于岩芯分级的通用GSI图。该GSI图与E.Hoek的方法相比主观误差小,根据该图计算出来的地基极限承载力与地勘单位建议值相比差值很小、精度高,该表可在场地钻探初期岩体力学参数的估算中推广使用。