09 Rock_Mass[1]
Strength of Rock and Rock Mass
Strength of Rock and Rock MassDesigning with rocks and rock masses bears many similarities to techniques that have been developed for soils. There is however a number of major differences:(1)The scale effect is overwhelming in rocks. Rock strength varies widely with sample size. Atone end, we have the intact rock (homogenous, isotropic, solid, continuous with no obvious structural defects) which really exists only at the hand-specimen scale. At the other end is the rock mass that is heterogeneous and anisotropic carrying all the defects that is characteristic of the rock mass at the field scale. In the design of engineering structures in rock, the size of interest is determined by the size of the rock mass that carries the stresses that are imposed on it.(2)Rock has tensile strength. It may have substantial tensile strength at the intact rock scale, butmuch smaller at the scale of the rock mass. Even then only in exceptional circumstances can the rock mass be considered as a “tensionless” material. Intact ro ck fails in tension along planes that are perpendicular to maximum tension (or minimum compression) and not along shear planes as suggested by the Coulomb theory).(3)The effect of water on the rock mass is more complex.(a)Pore space in most intact rocks is very small and so is the permeability. The watercontained in the pore space is not necessarily free water. The truly free water existsonly in the rock mass, in fractures, where water may flow at high rates.(b)In contrast to soils, water is more compressible (by about one order of magnitude)than intact rock. The difference would be smaller when compared with thecompressibility of the rock mass (especially close to the free surface where loose rockcommonly found).Note that in the derivation of the effectivesmall. This is not so for rocksincreasing the grain-to grain contactsignificant degree. The assumption ofwater controls the way anstress (total stress) is distributedconditions, the effective stressconcept passes the whole externalin rock, because water is more include its effect separately as a “water force” rather than mix its effect with the rock response (as in the effective stress theory).(4)In compression, intact rock does not fail according to the Coulomb theory. It is true, that itsstrength increases with confining pressure, but at failure there is no evidence for theappearance of a shear fracture as predicted by the Coulomb theory. Furthermore the “envelope “ is usually nonlinear following a y 2=x type of parabolic law. Interestingly, shear fractures do form, but not at peak stress; they form as part of the collapse mechanism, usually quite late in the post-failure history.Strength of Intact RockIntact rock has both tensile and compressive strength, but the compressive to tensile strength ratio is quite high, about 20. In uniaxial tension, failure follows the maximum principal stress theory:σ3=T owhich would suggest that the other two principal stresses have no influence. At failure a fractureplane forms that is oriented perpendicular to the σ3(Figure 28) Note that the Coulomb theory would predict shear failure in uniaxial tension at 45-φ/2with σ3. There was a suggestion to combine theCoulomb theory with the maximum stress theory (the tension cutoff) which would predict the properorientation of the failure plane for both tension andcompression. Others would rather replace both witha y 2=x type of parabola (Figure 29). As discussedearlier, the shear fracture does not appear at point of failure, so that this aspect of the Coulomb theory is meaningless. In fact, there is little point in using theMohr’s diagram. In rock mechanics, failure conditions are more meaningfully presented in theσ3-σ1 space using a nonlinear function for strength. Although there are many variations of this function, the most popular one is due to Hoek and Brown (1980) which has the general form of σσσσσ1332f c c m s =++This is shown in Figure 30. H ere σc is the uniaxial compressive strength of the intact rock, m is aconstant (characteristic of the rock type) and s is arock mass parameter. s =1 for intact rock. Typicalvalues of the m parameter can be found in the first row of Table 1. The s parameter is significant only in extending the strength function to the strength ofthe rock mass. The same diagram is often used to define the safety factor for an existing state of stress (σ3,σ1):τσSafety Factor f =σσ11where both σ1 and σ1f are measured at the value of σ3Strength of the Rock MassThe strength of the rock mass is only a fraction of the strength of the intact strength. The reason for this is that failure in the rock mass is a combination of both intact rock strength and separation or sliding along discontinuities. The latter process usually dominate. Sliding ondiscontinuities occurs against the cohesional and/or frictional resistance along the discontinuity. The cohesional component is only a very small fraction of the cohesion of the intact rock.Table 1. Finding the parameters m and s from classification parameters.In designing with the rock mass, two different procedures are used. When a rock block is well defi ned, its stability is best evaluated through a standard “rigid -body” analysis technique. All the forces on the block are vector-summed and the resultant is resolved into tangential and normal components with respect to the sliding plane. The safety factor becomes the ratio of the available resistance to sliding to the tangential (driving) force. This is the technique used in slope stabilityanalysis. The second technique is stress rather than force-based. Here the stresses are evaluated (usually modeled through numerical procedures) and compared with available strength. The latter is expressed in terms of the Hoek and Brown rock mass strength function. This is where the s parameter becomes useful. s=1 for intact rock and s<1 for the rock mass. Essentially, what we are doing is simply to discount the intact rock strength. The difficult question is what value to assign to s? There is no test that will define this value. In theory, its is possible to do field tests of the rock mass, but it is expensive and not necessarily very reliable. Hoek and Brown however have compiled a list of s values depending on the rock type and the rock classification ratings.A simplified version of this is presented in Table 1. To make use of this Table, one needs only the rock type and one of the ratings from either the CSIR or the NGI classification. Ratings that are not listed will have to be interpolated. User’s of this Table are however warned that this approach is given here as a guide and its reliability is open to question. Nevertheless, the given s values are so small that they would tend to under rather than overestimate thestrength of the rock mass. Problems however could arise when failure occurs along a single weak discontinuity (slope stability), in which case the stress-based approach is obviously invalid.We are going to show how design engineering structures in rocks through two examples. One will use the rock mass design using the Hoek and Brown approximation for strength and the other the technique of applying the block theory to designing rock slopes.In earlier discussions, we have worked an examplewith rock mass classification. Now let us assumethat we are going to build a twin-tunnel roadsystem at some depth in the worked rock mass.The plan is two make two inverted-U shapedtunnels, each tunnel to be 3 m high and 4 m wide.The tunnels are to be separated by a pillar (rockleft in place), preferably no more than 4 m wide.The safety factor for the pillar should be 1.5 orbetter. The depth of siting for the roadway has notbeen established yet, but it could range anywherebetween 100 and 300 m, the deeper the better.Your job is to find the appropriate depth withinthis range. This is an example for pillar design.The loading condition is determined by assuming that the weight of the overlying rock mass, as shown in Figure 31, is distributed evenly across the width of the pillar at AA (this is not quite true, the stresses are usually higher at the tunnel perimeter than at the center, but the high safety factor should take care of this). You follow this procedure now:(1)Find the rock mass strength using your classification and the strength table give above.(2)Find the volume and the weight of the overlying rock using 100 m for depth (check if youhave a unit weight for the rock in the report).(3)Distribute the total weigh over the cross sectional area AA. This is the average vertical stresson the cross section(4)Formulate the safety factor asSfStrength Vertical Sress(5) Check the safety factor at 300 m(6) See if you can get an algebraic expression for the safety factor using h as a variable.(7) What is the story you are going to tell the boss?In the second example, we are going to examine the stability of a block of rock found on a slope. Although this is going to be a simple problem, it will still illustrate the procedure involved in analyzing rock slope stability. Pay particular attention how the effect of ground water is incorporated into the stability analysis. We use block analysis when we expect the block to slide on a single or a combination of discontinuities and we have pretty good control over the geometry. This means that we have good knowledge of the size and through this the weight of the block and the geometry of the slope. In the simple two-dimensional case, which we are to discuss, the geometry is simply the slope angle. The biggest problem is how to get a decent estimate of the resistance to slide. In this regard, conditions are similar to rock mass analysis, where we had to come up with an estimate of the rock mass strength. Again, we will have to use a lot of judgement. There are two ways to proceed. One is to accept the definition of shear resistance as in the Coulomb theory. This means that the discontinuity shear strength is made up of two components, a cohesion and a frictional resistance. The cohesion supposed to represent the strength of "solid rock bridges" that may exist at the base and will have to be sheared off to let the block move. This is the hardest part to estimate, because it may vary between zero and the strength of the solid rock (no bread at the base). Usually, it is a very small fraction of the solid strength. The frictional part is simply the normal force times the tangent of the friction angle. We use forces rather than stresses here and the resistance force according to the Coulomb specification becomes:Discontinuity shear strength Cohesive force N =+tan φThe Coulomb type of specification is useful only in the "back analysis" of slope failures. In theconsulting business, a common chore is toredesign slopes that have either failed orshowed signs of instability (tension crack at the back of the slope). In cases like this, thea good estimate of the frictionand find the value of theshear strength. Having this,force is practically impossible. discontinuity strengthby the same author who wasinvolved in constructing the NGIw a t e r w a t e r t h r u s tclassification (reference). The Coulomb theory proposes a linear law for discontinuity strength, the Barton specification advances a non-linear law:τσσφ=⎛⎝⎫⎭⎪+⎛⎝⎫⎭⎪nnbJRCJCStan log10Here stress rather than force units are used. σn and τ would refer to the average normal stress and the unit shear strength respectively. For comparison with the Coulomb specification, τ and σn are obtained by dividing the shear resistance force and the normal force by the area of contact. The Barton strength uses three material parameters: JRC (joint roughness coefficient), JCS (joint compressive strength) and φb (basic friction angle). JRC varies between 0 (very smooth, planar joint) and 20 (rough undulating surface). JCS is a fraction of the compressive strength of the rock. The compressive strength should be discounted depending on the condition of the rock walls on the two sides of the joint. Usually the surface is weathered and altered and may carry soft filling. In the latter case, the strength would be very small indeed. The basic friction angle is what we would normally call the friction angle determined on a flat surface rubbing against another flat surface of the same rock.Besides needing three parameters as opposed to Coulomb's two, the nonlinear strength is different from the Coulomb law that it has no strength at zero normal stress. Essentially, the Barton specification is defined in terms of a friction angle that is adjusted for joint roughness and the strength of rock.Being armed with some knowledge of discontinuity strength, we can now attempt to find the safety factor for the problem shown in Figure 32. We are looking at the stability of the dark-shaded mass of rock. There is the possibility of sliding down along joint plane sloping at angle α. First, we should establish the forces that act on this block of rock. Weight is an obvious one. The water forces are based on the assumption that water flows along the slide plane and perhaps along other joints or as in this case in a tension crack as well. If there was no tension crack, we would have an uplift force alone arising from the fact that water would normally flow in at the high-elevation end and flow out at the low elevation. The head of water at the intake and discharge points is zero. It would normally maximize between. Here we assume a triangular distribution, assuming that the maximum head occurs at midpoint and its value is one half of the elevation difference between intake and the discharge points. The uplift force itself is equal to the area of the pressure distribution diagram (light-shaded area) and acts perpendicular to the slide surface. With a tension crack, there could be a slope-parallel water thrust due to water accumulating in the tension crack. Its value would be calculated from the upper (small) light-shaded triangle. For this the maximum head would occur at the base, with the maximum head being equal to the elevation difference between the top and the bottom of the tension crack.With the loads now defined, we can go and get an estimate to the shear resistance that could develop along the sliding surface. Let us use the Coulomb specification. Furthermore, let us put in an extra little story here. Imagine that you are a consulting engineer who was called to this site, because the people below that rock block claim that the block almost came down on them during the last big rainfall. This story would justify the assumption that the safety factor is close to unity. So do this:(1)Assume that the elevation difference between the intake and discharge points is 20 m and theslope angle is 30︒. Find the weight of the block of rock (hint: turn it into a triangle to ease thepain of calculation) using a width of 1 m in the third direction. Assume 25 kN/m3 for the unit weight.(2)Compute the uplift force and the water thrust(3)Resolve all the forces into components, normal and parallel with the slide plane(4)Sum the parallel (tangential) forces to get the Driving Force(5)Sum the normal forces and get the total frictional resistance by multiplying it with tan φ (use30︒)(6)Define the cohesive force as unit cohesion times the total area of contact; the unit cohesionwill stay as a variable now(7)Add the cohesive force to the total frictional force(8)Formulate the safety factor, equate it with 1 and compute the friction angle.After this operation, you have all the strength parameters defined and are ready to redesign the slope. In practice, you would get rid of the water by drilling drainage holes to intersect and drain the slide plane. Assuming that the drainage works, do the last thing:(9) Find now the safety factor for the slope with the water effect gone! If it is greater than about 1.25, tell the people that the slope is safe as long as they have the drainage holes clean. Otherwise you would have to install and anchor system to increase the safety factor (changing the weight of the block by shaving it would result in a minor improvement only, you can try this analysis too.)。
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岩体质量分级在金属矿山深部巷道支护方案设计中的应用
文章编号 ：１００２－５０６５（２０２３）１２－００５７－３
Application of rock mass classification in deep roadway support scheme design of metal mine
SUN Xian-teng
（Ｓｈａｎｄｏｎｇ Ｇｏｌｄ Ｇｒｏｕｐ Ｃｏ．， ＬＴＤ．， Ｊｉ’ｎａｎ ２５０１００， Ｃｈｉｎａ）
3 岩体质量（Q）分类法 巴顿岩体质量（Q）分类法综合考虑岩体的完整性、结
构面的形态、填充物的特征以及地下水等其他因素对岩体质 量的影响，考虑因素全面，软、硬岩石均适用 。 [1-2]
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2023年 6月下 世界有色金属 57
M 采矿工程 ining engineering
树脂锚杆长度经验公式如下 ： L=N(1.3+B/10) 式 中 ：L—— 锚 杆 长 度，m ；N—— 岩 层 稳 定 性 系 数 ； B——巷道跨度，m。 该巷道跨度 B 为 4.0m ；围岩稳定性较差，稳定性系数 取 1.1，求得 L 的取值为 1.87m。按照锚杆长度适当取大原 则，树脂锚杆长度确定为 2.0m。 4.2 锚杆直径、锚杆间排距 查阅《锚杆基本支护形式与支护参数》、《锚杆支护方案 与参数详表》，围岩质量等级为Ⅲ类时，锚杆直径的取值为 18~22mm，锚杆间排距为 0.6~1m。根据工程实践经验，选 取锚杆直径为 20mm，锚杆间排距为 0.8×0.8m。 4.3 喷射混凝土参数 该 巷 道 围 岩 质 量 等 级 为 Ⅲ 类，喷 射 混 凝 土 主 要 作 为 辅 助 支 护，使 围 岩、金 属 支 护 材 料 与 空 气、水 汽 隔 绝，防 止 岩 体、金 属 支 护 材 料 被 腐 蚀 氧 化，喷 射 混 凝 土 厚 度 确 定 为 50mm。 综 上 所 述，该 巷 道 围 岩 支 护 采 用 Φ20×2000mm 的 树脂锚杆，其间排距为 0.8×0.8m。锚杆安装完毕后，从巷 道最高处往巷道两帮挂装金属网，沿巷道走向的方向安装
On the negative effective mass density in acoustic metamaterials
On the negative effective mass density in acoustic metamaterials
H.H. Huang a, C.T. Sun a,*,G.L. Huang b
a School of Aeronautics and Astronautics, Purdue University, W. Lafayette, IN 47907, USA b Department of Systems Engineering, University of Arkansas at Little Rock, Little Rock, AR, 72204, USA
* Corresponding author. Tel.: +1 765 494 5130; fax: +1 765 494 0307. E-mail address: sun@ (C.T. Sun).
2017年十大动感人心歌曲_世界十大摇滚歌曲
2017年十大动感人心歌曲_世界十大摇滚歌曲想知道有哪些是十大动感人心歌曲吗?唱到您感动流泪的歌曲。
以下是小编为您收集整理提供到的范文，欢迎阅读参考，希望对你有所帮助!2017年十大动感人心歌曲_世界十大摇滚歌曲十大动感人心歌曲1、the dawn《the dawn》这是一首网上广为流传的关于魔兽争霸3的亡灵族的MV，其中动画部分由WarCraft3里面的过场CG剪辑而成，背景音乐为芬兰Dreamtale乐队的曲子The Dawn，改编自美国大片《The Rock勇闯夺命岛》中的经典插曲，所以听起来有相似之处。
2、Hero's Theme《Heros Theme》这首乐曲出自次世代新主机XBOX360上面的一款作品：《Kameo卡美奥》，是由著名的英国RARE工作室开发的。
其配乐是由捷克的一个很出名的乐团做的。
3、the mass《the mass》主打曲目The Mass[弥撒曲]是十七世纪欧洲教会音乐，起源于德国，节奏强劲紧凑，用声音营造出了一种人所不能触及的壮大与压力，中间不失去优美圣洁的曲调搭配，但是后来似乎被纳粹选作精神洗礼的一种工具，不过从音乐角度来说，这样旋律实在不应该被战争的结果左右。
之后像Michael Jackson等众多艺术家把它改编成为气势磅礴的进行曲、开场乐。
4、She is my sin《she is my sin》对Cser们来说，《NightWish夜愿》的歌曲早已深入人心，众所皆知，世界不少顶级战队的宣传片都采用的是他们的歌曲，NightWish的歌曲大都是金属音乐，而这首She is My Sin 就是1.6版CS的主题曲，很多翻译版本的1.6进入界面就会响起这首歌，当你在游戏前更改各种按键设置的时候，这首歌仿佛预示着大战马上爆发。
在she is my sin出名后，因为其震撼的歌声，成为许多视频或集锦的音乐。
5、Rock House Jail《rock house jail》电影《勇闯夺命岛》中的音乐，承担本片配乐的是好莱坞三大配乐大师之一—汉斯季莫，本片的配乐非常优美，以至于在全球各媒体都借用，仅CCTV就在1、2、5、10等频道都出现过。
工程岩体分级标准GB502182 术语、符号
2术语、符号2.1 术语2.1.1 岩石工程rock engineeting以岩体为工程建筑物地基或环境，并对岩体进行开挖或加固的工程，包括地下工程和地面工程。
2.1.2 工程岩体engineering rock mass岩石工程影响范围内的岩体，包括地下工程岩体、工业与民用建筑地基、大坝基岩、边坡岩体等。
2.1.3 岩体基本质量rock mass basic quality岩体所固有的、影响工程岩体稳定性的最基本属性，岩体基本质量由岩石坚硬程度和岩体完整程度所决定。
2.1.4 结构面sructural plane(discontinuity)岩体内开裂的和易开裂的面，如层面、节理、断层、片理等，又称不连续面。
2.1.5 岩体完整性指数(Kv)(岩体速度指数)intactess index of rock mass(velocity index of rock mass)岩体弹性纵波速度与岩石弹性纵波速度之比的平方。
2.1.6 岩体体积节理数(Jv)volumetric joint count of rock mass单体岩体体积内的节理(结构面)数目。
2.1.7 点荷载强度指数(Is(50))pointloadstrengthindex直径50mm圆柱形试件径向加压时的点荷载强度。
2.1.8 地下工程岩体自稳能力(stand－up time of rock mass for underground excavation)在不支护条件下，地下工程岩体不产生任何形式破坏的能力。
2.1.9 初始应力场initial stress field在自然条件下，由于受自重和构造运动作用，在岩体中形成的应力场，也称天然应力场。
2.2 符号。
0625_w02_qp_3
FOR EXAMINER’S USE
1 2 3 4 5 6 7 8 9 10 TOTAL
This question paper consists of 14 printed pages and 2 blank pages.
SP (NF/KS) S23400/3 © CIE 2002
[Turn over
density of rock = .............................. [2]
0625/3/O/N/02
5 3 A thermocouple is used to measure the temperature of the inner wall of a pottery kiln. (a) In the space below, draw a labelled diagram of a thermocouple that could be used for this purpose. [2]
Centre Number Candidate Name
w w w
Candidate Number
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m
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International General Certificate of Secondary Education CAMBRIDGE INTERNATIONAL EXAMINATIONS
(b) Describe how the volume of the rock could be found. .......................................................................................................................................... .......................................................................................................................................... ......................................................................................................................................[2] (c) The mass of the rock is 88 g and its volume is 24 cm3. Calculate the density of the rock.
Practical estimates of rock mass strength
The criterion is purely empirical and hence there are no ‘correct’ ways to interpret the various relationships which can be derived. Under the circumstances, it is not surprising that there have been a few less than useful mutations and that some users have been confused by the alternative interpretations which have been published.
shear stresses. However, these relationships are
cumbersome and the original approach used by Hoek
and Brown [1] is more practical. In this approach,
equation (1) is used to generate a series of triaxial test
Dr Evert Hoek Evert Hoek Consulting Engineer Inc. 3034 Edgemont Boulevard P.O. Box 75516 North Vancouver, B.C. Canada V7R 4X1 Email: ehoek@
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Page ii
MassLynx NT Users Guide
Contents
MassLynx NT User’s Guide............................................................................
Rock mass classification
Rock mass classification3.1 IntroductionDuring the feasibility and preliminary design stages of a project, when very little detailedinformation on the rock mass and its stress and hydrologic characteristics is available, theuse of a rock mass classification scheme can be of considerable benefit.At its simplest,this may involve using the classification scheme as a check-list to ensure that all relevantinformation has been considered. At the other end of the spectrum, one or more rockmass classification schemes can be used to build up a picture of the composition andcharacteristics of a rock mass to provide initial estimates of support requirements, and toprovide estimates of the strength and deformation properties of the rock mass.It is important to understand that the use of a rock mass classification scheme does not(and cannot) replace some of the more elaborate design procedures. However, the use ofthese design procedures requires access to relatively detailed information on in situstresses, rock mass properties and planned excavation sequence, none of which may beavailable at an early stage in the project. As this information becomes available, the useof the rock mass classification schemes should be updated and used in conjunction withsite specific analyses.3.2 Engineering rock mass classificationRock mass classification schemes have been developing for over 100 years since Ritter(1879) attempted to formalise an empirical approach to tunnel design, in particular fordetermining support requirements. While the classification schemes are appropriate fortheir original application, especially if used within the bounds of the case histories fromwhich they were developed, considerable caution must be exercised in applying rockmass classifications to other rock engineering problems.Summaries of some important classification systems are presented in this chapter, andalthough every attempt has been made to present all of the pertinent data from theoriginal texts, there are numerous notes and comments which cannot be included. Theinterested reader should make every effort to read the cited references for a fullappreciation of the use, applicability and limitations of each system.Most of the multi-parameter classification schemes (Wickham et al (1972) Bieniawski(1973, 1989) and Barton et al (1974)) were developed from civil engineering casehistories in which all of the components of the engineering geological character of therock mass were included. In underground hard rock mining, however, especially at deeplevels, rock mass weathering and the influence of water usually are not significant andmay be ignored. Different classification systems place different emphases on the variousparameters, and it is recommended that at least two methods be used at any site duringthe early stages of a project.3.2.1 Terzaghi's rock mass classificationThe earliest reference to the use of rock mass classification for the design of tunnelsupport is in a paper by Terzaghi (1946) in which the rock loads, carried by steel sets, areestimated on the basis of a descriptive classification. While no useful purpose would beserved by including details of Terzaghi's classification in this discussion on the design ofsupport, it is interesting to examine the rock mass descriptions included in his originalpaper, because he draws attention to those characteristics that dominate rock massbehaviour, particularly in situations where gravity constitutes the dominant driving force.The clear and concise definitions and the practical comments included in thesedescriptions aregood examples of the type of engineering geology information, which ismost useful for engineering design.Terzaghi's descriptions (quoted directly from his paper) are:•Intact rock contains neither joints nor hair cracks. Hence, if it breaks, it breaks acrosssound rock. On account of the injury to the rock due to blasting, spalls may drop offthe roof several hours or days after blasting. This is known as a spalling condition.Hard, intact rock may also be encountered in the popping condition involving thespontaneous and violent detachment of rock slabs from the sides or roof.•Stratified rock consists of individual strata with little or no resistance againstseparation along the boundaries between the strata. The strata may or may not beweakened by transverse joints. In such rock the spalling condition is quite common.•Moderately jointed rock contains joints and hair cracks, but the blocks between jointsare locally grown together or so intimately interlocked that vertical walls do notrequire lateral support. In rocks of this type, both spalling and popping conditionsmay be encountered.•Blocky and seamy rock consists of chemically intact or almost intact rock fragmentswhich are entirely separated from each other and imperfectly interlocked. In suchrock, vertical walls may require lateral support.•Crushed but chemically intact rock has the character of crusher run. If most or all ofthe fragments are as small as fine sand grains and no recementation has taken place,crushed rock below the water table exhibits the properties of a water-bearing sand.•Squeezing rock slowly advances into the tunnel without perceptible volume increase.A prerequisite for squeeze is a high percentage of microscopic and sub-microscopicparticles of micaceous minerals or clay minerals with a low swelling capacity.•Swelling rock advances into the tunnel chiefly on account of expansion. The capacityto swell seems to be limited to those rocks that contain clay minerals such asmontmorillonite, with a high swelling capacity.3.2.2 Classifications involving stand-up timeLauffer (1958) proposed that the stand-up time for an unsupported span is related to thequality of the rock mass in which the span is excavated. In a tunnel, the unsupported spanis defined as the span of the tunnel or the distance between the face and the nearestsupport, if this is greater than the tunnel span. Lauffer's original classification has sincebeen modified by a number of authors, notably Pacher et al (1974), and now forms part ofthe general tunnelling approach known as the New Austrian Tunnelling Method.The significance of the stand-up time concept is that an increase in the span of thetunnel leads to a significant reduction in the time available for the installation of support.For example, a small pilot tunnel may be successfully constructed with minimal support,while a larger span tunnel in the same rock mass may not be stable without the immediateinstallation of substantial support. The New Austrian Tunnelling Method includes a number of techniques for safetunnelling in rock conditions in which the stand-up time is limited before failure occurs.These techniques include the use of smaller headings and benching or the use of multipledrifts to form a reinforced ring inside which the bulk of the tunnel can be excavated.These techniques are applicable in soft rocks such as shales, phyllites and mudstones inwhich the squeezing and swelling problems, described by Terzaghi (see previoussection), are likely to occur. The techniques are also applicablewhen tunnelling inexcessively broken rock, but great care should be taken in attempting to apply thesetechniques to excavations in hard rocks in which different failure mechanisms occur.In designing support for hard rock excavations it is prudent to assume that the stabilityof the rock mass surrounding the excavation is not time-dependent. Hence, if astructurally defined wedge is exposed in the roof of an excavation, it will fall as soon asthe rock supporting it is removed. This can occur at the time of the blast or during thesubsequent scaling operation. If it is required to keep such a wedge in place, or toenhance the margin of safety, it is essential that the support be installed as early aspossible, preferably before the rock supporting the full wedge is removed. On the otherhand, in a highly stressed rock, failure will generally be induced by some change in thestress field surrounding the excavation. The failure may occur gradually and manifestitself as spalling or slabbing or it may occur suddenly in the form of a rock burst. Ineither case, the support design must take into account the change in the stress field ratherthan the ‘stand-up’ time of the excavation.3.2.3 Rock quality designation index (RQD)The Rock Quality Designation index (RQD) was developed by Deere (Deere et al 1967)to provide a quantitative estimate of rock mass quality from drill core logs. RQD isdefined as the percentage of intact core pieces longer than 100 mm (4 inches) in the totallength of core. The core should be at least NW size (54.7 mm or 2.15 inches in diameter)and should be drilled with a double-tube core barrel. The correct procedures formeasurement of the length of core pieces and the calculation of RQD are summarised inFigure 5.1.Figure 5.1: Procedure for measurement and calculation of RQD (After Deere, 1989).Palmström (1982) suggested that, when no core is available but discontinuity tracesare visible in surface exposures or exploration adits, the RQD may be estimated from thenumber of discontinuities per unit volume. The suggested relationship for clay-free rockmasses is:RQD = 115 - 3.3 Jv (5.1)Where Jvis the sum of the number of joints per unit length for all joint (discontinuity)sets known as the volumetric joint count.RQD is a directionally dependent parameter and its value may change significantly,depending upon the borehole orientation. The use of the volumetric joint count can bequite useful in reducing this directional dependence.RQD is intended to represent the rock mass quality in situ. When using diamond drillcore, care must be taken to ensure that fractures, which have been caused by handling orthe drilling process, are identified and ignored when determining the value of RQD.When using Palmström's relationship for exposure mapping, blast induced fracturesshould not be included when estimating Jv.Deere's RQD has been widely used, particularly in North America, for the past 25years. Cording and Deere (1972), Merritt (1972) and Deere and Deere (1988) haveattempted to relate RQD to Terzaghi's rock load factors and to rockbolt requirements inL = 38 cmL = 17 cmL = 0no pieces > 10 cmL = 20 cmL = 35 cmDrilling breakL = 0no recoveryTotal length of core run = 200 cmsΣ Length of core pieces > 10 cm lengthx 100 = 55 %RQD =Total length of core runX 10038 + 17 + 20 + 35200RQD =44 Chapter 3: Rock mass classificationtunnels. In the context of this discussion, the most important use of RQD is as acomponent of the RMR and Q rock mass classifications covered later in this chapter.3.2.4 Rock Structure Rating (RSR)Wickham et al (1972) described a quantitative method for describing the quality of a rockmass and for selecting appropriate support on the basis of their Rock Structure Rating(RSR) classification. Most of the case histories, used in the development of this system,were for relatively small tunnels supported by means of steel sets, although historicallythis system was the first to make reference to shotcrete support. In spite of this limitation,it is worth examining the RSR system in some detail since it demonstrates the logicinvolved in developing a quasi-quantitative rock mass classification system.The significance of the RSR system, in the context of this discussion, is that itintroduced the concept of rating each of the components listed below to arrive at anumerical value of RSR = A + B + C .1. Parameter A, Geology: General appraisal of geological structure on the basis of:a. Rock type origin (igneous, metamorphic, sedimentary).b. Rock hardness (hard, medium, soft, decomposed).c. Geologic structure (massive, slightly faulted/folded, moderately faulted/folded,intensely faulted/folded).2. Parameter B, Geometry : Effect of discontinuity pattern with respect to the directionof the tunnel drive on the basis of:a. Joint spacing.b. Joint orientation (strike and dip).c. Direction of tunnel drive.3. Parameter C: Effect of groundwater inflow and joint condition on the basis of:a. Overall rock mass quality on the basis of A and B combined.b. Joint condition (good, fair, poor).c. Amount of water inflow (in gallons per minute per 1000 feet of tunnel).Note that the RSR classification used Imperial units andthat these units have been retained in this discussion.Three tables from Wickham et al's 1972 paper arereproduced in Tables 4.1, 4.2 and 4.3. Thesetables can beused to evaluate the rating of each of these parameters toarrive at the RSR value (maximum RSR = 100).For example, a hard metamorphic rock which is slightlyfolded or faulted has a rating of A = 22 (from Table 4.1). Therock mass is moderately jointed, with joints strikingperpendicular to the tunnel axis which is being driven east-west, and dipping at between 20° and 50°. Table 4.2 gives the rating for B = 24 for driving with dip (defined in themargin sketch).Drive with dipDrive against dipThe value of A + B = 46 and this means that, for joints of fair condition (slightlyweathered and altered) and a moderate water inflow of between 200 and 1,000 gallonsper minute, Table 4.3 gives the rating for C = 16. Hence, the final value of the rockstructure rating RSR = A + B + C = 62.A typical set of prediction curves for a 24 foot diameter tunnel are given in Figure 4.2which shows that, for the RSR value of 62 derived above, the predicted support would be2 inches of shotcrete and 1 inch diameter rockbolts spaced at 5 foot centres. As indicatedin the figure, steel sets would be spaced at more than 7 feet apart and would not beconsidered a practical solution for the support of this tunnel.For the same size tunnel in a rock mass with RSR = 30, the support could be providedby 8 WF 31 steel sets (8 inch deep wide flange I section weighing 31 lb per foot) spaced3 feet apart, or by 5 inches of shotcrete and 1 inch diameter rockbolts spaced at 2.5 feetcentres. In this case it is probable that the steel set solution would be cheaper and moreeffective than the use of rockbolts and shotcrete.Although the RSR classification system is not widely used today, Wickham et al'swork played a significant role in the development of the classification schemes discussedin the remaining sections of this chapter.Figure 4.2: RSR support estimates for a 24 ft. (7.3 m) diameter circular tunnel. Note that rockboltsand shotcrete are generally used together. (After Wickham et al 1972).。
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• PROJECT SPECIFIC SYSTEMS
Development of Rock Mass Rating System
Rock Mass Rating System
(After Beiniawski 1989)
Guidelines for excavation and support of 10m span rock tunnels in accordance with the RMR system
‘Q‟ Classification System
• consists of two stress parameters • SRF can be regarded as a total stress parameter measure of – loosening load as excavated through shear zones – rock stress in competent rock – squeezing loads in plastic incompetent rock • JW is a measure of water pressure
Rock Quality Designation Index (RQD) (Deere et al. 1967)
• Aim : to provide a quantitative estimate of rock mass
quality from drill logs
• Equal to the percentage of intact core pieces longer than 100mm in the total length of core
ROCK MASS CLASSIFICATION
Presented by:
Neil Benson
Rock Mass Classification
• Why? • How does this help us in tunnel design?
Rock Mass Classification
WHY?
Engineering Rock Mass Classification Schemes
• Developed for estimation of tunnel support • Used at project feasibility and preliminary design stages • Simple check lists or detailed schemes • Used to develop a picture of the rock mass and its variability • Used to provide initial empirical estimates of tunnel support requirements
Q Classification Scheme
Resolves to three parameters • Block size • Interblock shear strength • Active stress ( RQD / Jn ) ( Jr / Ja ) ( Jw / SRF )
‘Q‟ Classification System
(After Barton et al. 1974)
‘Q‟ Classification System
• represents the structure of the rockmass • crude measure of block or particle size
(After Beiniawski 1989)
Rock Tunnelling Quality Index Q
• Based on case histories in Scandinavia • Numerical values on a log scale • Range 0.001 to 1000
(After Wickham et al. 1972)
Geomechanics Classification or Rock Mass Rating System (RMR) (Bieniawski 1976)
Based upon • uniaxial compressive strength of rock material • rock quality designation (RQD) • spacing of discontinuities
Procedure for Measurement and Calculation of RQD
Weathering of Basalt with depth
Multi parameter Rock Mass Classification Schemes
• Rock Mass Structure Rating (RSR)
a numerical value
• Demonstrates the logic in a quasi-quantitative rock mass classification • Has limitations as based on small tunnels supported by steel sets only • RSR = A + B + C
• condition of discontinuities
• groundwater conditions • orientation of discontinuities
Rock Mass Rating System
• Rock mass divided into structural regions • Each region is classified separately • Boundaries can be rock type or structural, eg: fault • Can be sub divided based on significant changes, eg:
Classification of individual parameters used in the Tunnelling Quality Index Q (cont‟d)
Q Classification Scheme
Resolves to three parameters • Block size • Interblock shear strength • Active stress ( RQD / Jn ) ( Jr / Ja ) ( Jw / SRF )
Rock Structure Rating
Parameter A: General area geology
Considers
(a) rock type origin (b) rock „hardness‟ (c) geotechnical structure
Rock Structure Rating
discontinuity spacing
Rock Mass Rating System
Rock Mass Rating System
BUT: 1976 to 1989 Bienawski • System refined by greater data • Ratings for parameters changed • Adapted by other workers for different situations
Ground interaction
Summary of rock mass characteristics, testing methods and theoretical considerations
Hale Waihona Puke Types of failure which occur in rock masses under low and high in-situ stress levels
(After Barton et al. 1974)
‘Q‟ Classification System
• represents roughness and frictional characteristics of joint walls or infill material
(After Barton et al. 1974)
RQD
• Directionally dependant parameter
• Intended to indicate rock mass quality in-situ
• Adapted for surface exposures as „Jv‟ number of discontinuities per unit volume • Used as a component in the RMR and Q systems
RSR support estimates for a 7.3m diameter circular tunnel
Examples RSR = 62 2” shotcrete 1” rockbolts @ 5ft centres
RSR = 30 5” shotcrete 1” rockbolts @ 2.5ft centres OR 8WF31 steel sets @ 3ft centres
Parameter B: Geometry : Effect of discontinuity pattern
Considers
(a) joint spacing (b) joint orientation (strike and dip) (c) direction of tunnel drive
Terzaghi‟s Rock Mass Classification (1946)