Determination and applications of rock quality designation(RQD)

Characterization of rock masses and evaluation of their mechanical properties are important and challenging tasks in rock mechanics and rock engineering. Since in many cases rock quality designation （RQD） is the only rock mass classification index available, this paper outlines the key aspects on determination of RQD and evaluates the empirical methods based on RQD for determining the deformation modulus and unconfined compressive strength of rock masses. First, various methods for determining RQD are presented and the effects of different factors on determination of RQD are highlighted. Then, the empirical methods based on RQD for determining the deformation modulus and unconfined compressive strength of rock masses are briefly reviewed. Finally, the empirical methods based on RQD are used to determine the deformation modulus and unconfined compressive strength of rock masses at five different sites including 13 cases, and the results are compared with those obtained by other empirical methods based on rock mass classification indices such as rock mass rating （RMR）, Q-system （Q） and geological strength index （GSI）. It is shown that the empirical methods based on RQD tend to give deformation modulus values close to the lower bound （conservative） and unconfined compressive strength values in the middle of the corresponding values from different empirical methods based on RMR, Q and GSI. The empirical methods based on RQD provide a convenient way for estimating the mechanical properties of rock masses but, whenever possible, they should be used together with other empirical methods based on RMR, Qand GSI.

Using multivariate adaptive regression splines to develop relationship between rock quality designation and permeability

The assessment of in situ permeability of rock mass is challenging for large-scale projects such as reservoirs created by dams,where water tightness issues are of prime importance.The in situ permeability is strongly related to the frequency and distribution of discontinuities in the rock mass and quantified by rock quality designation(RQD).This paper analyzes the data of hydraulic conductivity and discontinuities sampled at different depths during the borehole investigations in the limestone and sandstone formations for the construction of hydraulic structures in Oman.Cores recovered from boreholes provide RQD data,and in situ Lugeon tests elucidate the permeability.A modern technique of multivariate adaptive regression splines(MARS)assisted in correlating permeability and RQD along with the depth.In situ permeability shows a declining trend with increasing RQD,and the depth of investigation is within 50 m.This type of relationship can be developed based on detailed initial investigations at the site where the hydraulic conductivity of discontinuous rocks is required to be delineated.The relationship can approximate the permeability by only measuring the RQD in later investigations on the same site,thus saving the time and cost of the site investigations.The applicability of the relationship developed in this study to another location requires a lithological similarity of the rock mass that can be verified through preliminary investigation at the site.

A novel approach to structural anisotropy classification for jointed rock masses using theoretical rock quality designation formulation adjusted to joint spacing

Rock quality designation(RQD)has been considered as a one-dimensional jointing degree property since it should be determined by measuring the core lengths obtained from drilling.Anisotropy index of jointing degree(AI_(jd))was formulated by Zheng et al.(2018)by considering maximum and minimum values of RQD for a jointed rock medium in three-dimensional space.In accordance with spacing terminology by ISRM(1981),defining the jointing degree for the rock masses composed of extremely closely spaced joints as well as for the rock masses including widely to extremely widely spaced joints is practically impossible because of the use of 10 cm as a threshold value in the conventional form of RQD.To overcome this limitation,theoretical RQD(TRQD_(t))introduced by Priest and Hudson(1976)can be taken into consideration only when the statistical distribution of discontinuity spacing has a negative exponential distribution.Anisotropy index of the jointing degree was improved using TRQD_(t) which was adjusted to wider joint spacing by considering Priest(1993)’s recommendation on the use of variable threshold value(t)in TRQD_(t) formulation.After applications of the improved anisotropy index of a jointing degree(AI'_(jd))to hypothetical jointed rock mass cases,the effect of persistency of joints on structural anisotropy of rock mass was introduced to the improved AI'_(jd) formulation by considering the ratings of persistency of joints as proposed by Bieniawski(1989)’s rock mass rating(RMR)classification.Two real cases were assessed in the stratified marl and the columnar basalt using the weighted anisotropy index of jointing degree(W_AI'_(jd)).A structural anisotropy classification was developed using the RQD classification proposed by Deere(1963).The proposed methodology is capable of defining the structural anisotropy of a rock mass including joint pattern from extremely closely to extremely widely spaced joints.

Correlation between the rock mass properties and maximum horizontal stress:A case study of overcoring stress measurements

Understanding the mechanical properties of the lithologies is crucial to accurately determine the horizontal stress magnitude.To investigate the correlation between the rock mass properties and maximum horizontal stress,the three-dimensional(3D)stress tensors at 89 measuring points determined using an improved overcoring technique in nine mines in China were adopted,a newly defined characteristic parameter C_(ERP)was proposed as an indicator for evaluating the structural properties of rock masses,and a fuzzy relation matrix was established using the information distribution method.The results indicate that both the vertical stress and horizontal stress exhibit a good linear growth relationship with depth.There is no remarkable correlation between the elastic modulus,Poisson's ratio and depth,and the distribution of data points is scattered and messy.Moreover,there is no obvious relationship between the rock quality designation(RQD)and depth.The maximum horizontal stress σ_(H) is a function of rock properties,showing a certain linear relationship with the C_(ERP)at the same depth.In addition,the overall change trend of σ_(H) determined by the established fuzzy identification method is to increase with the increase of C_(ERP).The fuzzy identification method also demonstrates a relatively detailed local relationship betweenσ_H and C_(ERP),and the predicted curve rises in a fluctuating way,which is in accord well with the measured stress data.

Computing in-situ strength of rock masses based upon RQD and modified joint factor: Using pressure and damage sensitive constitutive relationship

In th is study, a n e w m odel w as p re se n te d for com p u tin g stre n g th o f rock m asses based u p o n in -situo bservations o f RQD p o pularly kno w n as rock quality d esignation. This m odel links u p th e rock m assp aram eters from in -situ investigations w ith th e stre n g th p a ram eters o f jo in ted rocks obtain ed fromlaboratory scale ex p erim en tal observations. Using th e co n stitu tiv e relation, th e a u th o r derived a p ressu reand d am age sensitive plastic p a ra m e te r to d ete rm in e stre n g th o f rock m asses for varied ex te n ts ofd isco n tin u ity an d p ressu re induced dam age. The te s t results show th a t plasticity characterized byhard en in g an d softening inclusive o f dam ag e invariably d e p en d s u p o n m ean p ressu re an d e x te n t ofdefo rm atio n s alread y experien ced by rock m asses. The p re se n t w ork explores th e te s t d a ta th a t revealth e d ep en d en c e o f in -situ stren g th on increm ental jo in t p ara m e te rs o b tain ed from th e jo in t num ber,jo in t orien tatio n , jo in t roughness, gouge p a ram eters an d w a te r pressure. S ubstituting th e relationshipb e tw e e n th e RQD and m odified jo in t factor w ith th a t b e tw e e n m odulus ratio an d stren g th ratio, th em odel show s successfully th a t using d am age inclusive plastic p a ra m e te r an d RQD provides a relationshipfor estim atin g th e stre n g th o f rock m asses. One o f th e m ain objectives o f this w ork is to illustrate th a t th ep re se n t m odel is sensitive to p la s tic ity a n d dam ag e to g e th e r in estim atin g in -situ stre n g th o f rock m assesin foundations, u n d e rg ro u n d excavation an d tunnels.

结构面三维网络模拟计算RQD及精度对比研究

以汶川映秀镇百花大桥边坡岩体为实例,运用结构面三维网络模拟法计算RQD值,具体步骤为:在概率统计结构面各项参数获取结构面模拟参数的基础上,利用Monte-Carlo法生成岩体节理三维网络,在边坡震时主滑平面、主滑横剖面、水平面上各方向布置测线模拟钻孔,获取54个钻孔岩石质量指标RQD值,以其期望值作为最终RQD。以结构面测量统计得到的等效钻探RQD为真值,对比体积RQD法和网络模拟法的相对误差(体积RQD法为24.6%;结构面三维网络模拟法仅为3.3%),证实结构面三维网络模拟法相对误差要小得多,精度显著提高。结构面三维网络模拟法是计算RQD的好方法,具有广泛的应用前景。

三维节理岩体分形维数与RQD相关性研究

应用三维随机不连续面网络模拟技术对岩体结构统计均质区内的不连续面进行计算机模拟,再现岩体结构,并应用分形理论计算三维节理岩体的分形维数。平行于三维节理岩体网络模型的x,y,z轴布置测线,计算不同阈值下三维岩体的岩石质量指标(RQD)。对获取的分形维数与RQD分析表明,三维岩体RQD随分形维数增大而减小,二者具有良好的线性关系。最后,推导三维节理岩体的分形维数与若干个阈值下RQD的关系式,并根据不同阈值下RQD与分形维数关系曲线的斜率确定合理阈值。

基于三维裂隙网络的RQD尺寸效应与空间效应的研究

岩石质量指标(RQD)是岩土工程与地质工程中的重要概念,在岩体性质分析中起到了重要作用,但RQD存在着明显的尺寸效应与空间效应,这在以后岩体工程设计计算中并没有引起充分的重视。为研究RQD的空间效应,采用三维裂隙网络模拟方法模拟现场真实岩体,并在模型中设立大量测线获取岩体中不同位置的RQD值。结果表明,岩体中不同位置的RQD值并不相同,存在明显的空间效应。为获取可整体代表岩体好坏程度的RQD值,需在大量RQD样本的基础上进行分析。另外,为更好地体现岩体的非均质性,研究不同阈值下的RQD范围,最终确定可充分反映待分析岩体的最佳阈值,为4 m。尺寸效应是RQD参数的重要性质,通过改变测线长度的方法探讨RQD在不同尺度下的变化情况。总结、提出RQD的计算模型与公式,即:A-A模型、T-T模型、A-A-S模型、Priest-Hudson公式与Senz-Kazi公式。分别研究与对比不同模型下RQD的尺寸效应,结果表明,采用A-A-S模型可充分减少尺寸效应带来的RQD的计算误差;当阈值较大时,Priest-Hudson公式与Senz-Kazi公式存在一定的误差,基于三维裂隙网络模拟的方法进行RQD的计算将会更为准确。

岩石质量指标（RQD）的各向异性分析

各向异性是工程岩体的重要工程特性，岩石质量指标ＲＱＤ具明显的各向异性。本文运用结构面网络模拟技术，通过结构面间距、倾角、相对夹角以及结构面组数的敏感性分析，探讨了ＲＱＤ的各向异性规律。结合实际工程应用，提出正确引用ＲＱＤ指标的建议。

补充RQD值的几类岩体质量评价图

针对ＲＱＤ值不能全面反映裂隙间距、块体大小以及随机表象的多重尺度等问题，介绍了三种岩体质量评价图，即基于裂隙岩体分数维结构之上的分维岩体质量图、考虑裂隙长度的累积长度图、建立在不同岩块频度基础上的岩块累积频度图。根据不同图解对岩体质量进行了评价，并对岩体完整性作了划分。三种图解能较全面地反映岩体质量的特点。

基于三维激光扫描技术的岩体RQD获取方法与程序

在西南地区岩质边坡高陡的特殊地形条件下,常规的地面地质调查方法难以开展。引入三维激光扫描技术获取边坡体出露的结构面各项几何参数(产状、间距、迹长),然后以这些地质资料为基础,结合结构面网络模拟技术生成不同走向网络图,通过在网络图上布置人工虚拟钻孔来计算得到岩体质量指标(RQD)。结果表明:提出的方法适用性较强,方便可靠,不仅解决了常规地质调查方法在高陡边坡地段难以开展的问题,而且还克服了以往钻孔岩芯获取岩体RQD指标数据少、误差大的缺点,获得岩体RQD指标经过修正后能满足工程实际需求。

基于分形的岩体质量评价及广义RQD阈值确定

基于三维结构面网络模拟技术,对采样区岩体优势结构面进行仿真模拟,在建立的模型中分别沿垂直于X,Y,Z轴方向切取剖面,得到各剖面的结构面二维网络图,运用分形理论分别计算其结构面分布的分形维数,进而对岩体质量进行评价。在上述网络剖面图中模拟钻孔,不断改变广义RQD的阈值,得到不同阈值下的RQD值。将各剖面的分形维数与广义RQD值对比分析,可以为准确选取广义RQD的最佳阈值提供依据。以某段公路边坡为例,当阈值在0.2~0.3时,广义RQD值与结构面分形维数吻合较好,故选取的RQD阈值应在0.2~0.3之间较为合理。

RQD研究的几个理论问题

岩石质量指标ＲＱＤ是岩体工程分类和稳定性评价中最常用的定量描述参数。３０多年来，ＲＱＤ的概念和理论研究有了重大进展。本文对源于工程应用的几个ＲＱＤ理论问题进行了评述，同时提出了一些新的研究思路。

静动载条件下深部破碎巷道支护设计及稳定性分析

深部破碎围岩稳定性控制是制约深部金属矿安全高效开采的难题之一。以金川二矿区深部某中段破碎围岩条件下的采准巷道稳定性控制为工程背景,应用Q、RMR、GSI进行岩体质量分级与岩体力学参数估算,分别应用经验法和工程类比法进行采准巷道支护设计,并依据收敛约束法确定合理的释能支护时机。在此基础上,应用UNWEDGE软件对释能支护设计进行安全性评价,并通过RS2数值方法分析支护效果。研究结果表明:对于深部破碎采准巷道一次支护采用锚网喷支护,二次支护采用混凝土衬砌,最佳衬砌支护时机应满足巷道帮位移小于38 mm且顶板位移小于15 mm;静动载下有无支护数值分析结果表明,锚网喷支护满足巷道安全要求,同时对采准巷道围岩结构控制型、应力控制型破坏以及动力失稳破坏等起到良好的控制效果。研究结果为金川二矿区深部破碎采准巷道围岩稳定性控制提供了理论依据与技术支撑。

超大断面破碎软岩硐室围岩稳定性及控制技术研究

针对超大断面硐室围岩失稳问题,以锦丰金矿地下搅拌站超大断面硐室为研究对象,利用矿山地质钻孔数据库建立矿区岩石质量指标模型,并基于该模型选择搅拌站建设最优位置为150 m中段。通过实验室试验、现场调查及地应力测量确定围岩参数及应力分布特征,利用Phase2岩石力学软件对硐室开挖后的稳定性进行数值模拟分析,根据分析结果并结合工程类比法,提出管缝锚杆+挂网+湿喷混凝土+树脂锚杆+长锚索+壁后注浆+防底鼓反拱混凝土联合支护方案对围岩进行支护。采用数值模拟及现场应用效果监测方法对加固效果进行评价,结果表明:加固后的硐室最大变形量为31 mm,最大主应力为25 MPa,锚杆(索)均未发生破坏,混凝土衬砌所有单元的安全系数均大于1.2,支护结构处于合理有效的受力状态。采用该联合支护方式加固后的硐室处于稳定状态,支护效果良好,相关研究成果对类似工程具有重要借鉴意义。

保山西邑铅锌矿采选工程RQD与RBI对比研究

用岩石质量指标和岩体块度指数的理论,对钻孔岩心实测资料进行分析和对比研究,对钻孔周围岩体进行分级。结果表明:岩体块度指数在岩石质量评价中能更准确地反映其优越性,具有更为显著的工程意义。

煤矿床工程地质勘查中岩石质量指标(RQD)存在问题的探讨

岩石质量指标(RQD)是评价岩体完整性及质量分级的一个重要指标。针对矿区工程地质勘查规范中推荐的岩体质量评价方法,详细分析了岩石质量指标(RQD)在用于岩体分类与评价中存在的岩心长度的计算、采取率、硬度和结构对其赋值大小的影响,以及对规范理解的差异,提出了解决这些问题的有效方法与途径,为岩石质量指标(RQD)的正确应用及煤矿床岩体质量合理评价做了有益的探讨。

Determination of blast-induced ground vibration equations for rocks using mechanical and geological properties

In the recent decades, effects of blast loads on natural and man-made structures have gained considerable attention due to increase in threat from various man-made activities. Site-specific empirical relationships for calculation of blast-induced vibration parameters like peak particle velocity （PPV） and peak particle displacement （PPD） are commonly used for estimation of blast loads in design. However, these relation- ships are not able to consider the variation in rock parameters and uncertainty of in situ conditions. In this paper, a total of 1089 published blast data of various researchers in different rock sites have been collected and used to propose generalized empirical model for PPV by considering the effects of rock parameters like unit weight, rock quality designation （ROD）, geological strength index （GSI）, and uniaxial compressive strength （UCS）. The proposed PPV model has a good correlation coefficient and hence it can be directly used in prediction of blast-induced vibrations in rocks. Standard errors and coefficient of correlations of the predicted blast-induced vibration parameters are obtained with respect to the observed field data. The proposed empirical model for PPV has also been compared with the empirical models available for blast vibrations predictions given by other researchers and found to be in good agreement with specific cases.

利用RQD对岩体完整质量评价的操作方法

岩石质量指标(RQD)是表示岩石完整性的一种指标。也是评价岩石质量的一个重要指标,利用RQD指标能达到客观准确的评价岩石质量的目的。

基于数字图像处理功能的RQD分级方法的应用

RQD分级被广泛地应用于评价岩体的完整性。传统的RQD分级方法采用手工测量进行作业,工人劳动强度大,工作效率低,针对该问题,本文以巨龙铜矿为工程背景,提出了一种基于Image J图像分析功能的RQD分级方法。该方法首先通过拍摄钻孔岩心图像获取钻孔岩芯信息,然后通过Image J软件对钻孔岩芯图像中不同长度岩芯进行编号,通过测量分析功能得出不同编号的岩芯长度,进而计算RQD值,即可快速完成钻孔岩芯编录工作。计算结果与传统RQD分级方法所得结果误差仅在0.5%~1.0%,一致性较好,准确性较高。该方法便捷高效,适用于实际工程应用,尤其在高原地区以及工作环境恶劣地区值得推广。