Rock Mass Classification The Effect of Rock Discontinuities on Engineering Structures A Report Submitted to the Department of Geology College of Science – Mosul University In Partial Fulfillment of the requirement For the Course Study of PhD In Structural Geology by
Azealdeen Salih Al-Jawadi MSc Engineering Geology Supervisor
Dr. Thanoon Hamid Al-Dabagh
1430
2009
Abstract
Combination between the structural geology and engineering geology is useful to get a wide view to solve many problems in rock mechanics. Utility of study the discontinuities discontinuities and all other geological structures to understand the elastic theory of rock rock mater material ial as well well as mass. mass. This This rep report ort provid provides es and instru instructi ctions ons for performing and documenting field work. The applications of geology to solving engineering problems is emphasized, rather than academic or other aspects of geol geolog ogy. y. Th Thee repo report rt pr prov ovid ides es the the guid guidan ance ce for for geol geolog ogic ic clas classi sifi fica cati tion on and and description of rock and rock discontinuities. Applications of standard indexes, .descriptors, descriptors, terminology, terminology, sampling, testing and performing discontinuity survey
:Introduction .1 Structural breaks or discontinuities generally control the mechanical behavior of rock masses. In most rock masses the discontinuities form planes of weakness or surfaces of separation, including foli foliat atio ion n and and bedd beddin ing g join joints ts,, join joints ts,, frac fractu ture res, s, and zones zones of crus crushi hing ng or shear shearin ing. g. Thes Thesee
discontinuities usually control the strength, deformation, and permeability of rock masses. Most enginee engineerin ring g proble problems ms relate relate to discont discontinu inuiti ities es rather rather than than to rock rock type type or intact intact rock rock strengt strength. h. .(Discontinuities must be carefully and adequately described (Throner, 2001 Civil and mining engineers have been building structures on or in rock for centuries and the principles of engineering in rock have been understood for a long time. Rock mechanics is merely a formal expression of some of these principles and it is only during the past few decades that the theory and practice in this subject have come together in the discipline which we know today as rock mechanics. A particularly important event in the development of the subject was the merging of elastic theory, which dominated the English language literature on the subject, with the discontinues approach of the Europeans. The gradual recognition that rock could act both as an elastic material and a disc discon onti tinu nuous ous mass mass resu result lted ed in a much much more more matu mature re appro approac ach h to the the subj subjec ectt than than had had .( previously been the case (Hoek, 2007 Knowledge of the rock mass behavior in general, and the failure process and the strength in particular, is important for the design of foundations, slopes, quarrying and underground excavation. A better potential understanding of the failure process and a better rock mass strength prediction :(make it possible to (Edelbro, 2003 .Reduce stability problems by improving design of the underground excavations• Improve near surface tunneling and ore extraction to avoid or minimize the area over which• .subsidence occurs due to tunneling and mining .Reduce waste rock extraction• Stability in rock is controlled principally by discontinuities in the rock mass. The role of discontinuity data collection is primarily to aid identifying the possible modes of failure. Rock outcrop mapping is the best field way to obtain discontinuity data. The degree of rock exposure is .usually the controlling factor in determining the accuracy of the data collected (Yu, et. al, 2003) Jointed Jointed rock masses comprise interlocking interlocking angular angular particles particles or blocks of hard brittle material separated by discontinuity surfaces which may or may not be coated with weaker materials. The strength of such rock masses depends on the strength of the intact pieces and on their freedom of movement which, in turn, depends on the number, orientation, spacing and shear strength of the discontinuities (Hoek, 1983). :(There are four principal ways of determining the rock mass (Edelbro, 2003 Mathematical Mathematical modeling: modeling: the stren strength gth of rock rock masses masses is descri described bed theore theoretic ticall ally. y. The rock rock • substance and the properties of the discontinuities are both modeled. A mathematical model requir requires es determ determina inatio tion n of a large large number number of parame parameter terss and is often often based based on simpli simplifie fied d .assumptions Rock mass classification: is often used in the primary stage of the project to predict the rock • mass mass quality quality and the possible possible need for support support.. The result result is an estima estimate te of the stabili stability ty quantified in subjective terms such as bad, acceptable, good, very good rock conditions. During the excavation, more information about the rock mass is received and the classification can be continuously updated. The values obtained by some of the classification systems are used to .estimate or calculate the rock mass strength using a failure criterion Large scale testing: proved data on the true strength of the rock mass at the actual scale of the• construction, and, indirectly, a measure of the scale effect that most rocks exhibit. As large scale tests are often neither practical nor economically feasible, most researchers have studied the scale dependency of rock mass strength in a laboratory environment. The scale thereby very .limited Back analysis of failure: back analysis of previous failures is attractive, as it allows more• representative strength parameters to be determined. Obviously, failure must have occurred and
the failure mode must be reasonably well established. There are relatively few data available on .rock mass failure that can be used for back analysis and even fewer data for hard rock masses
:Aim of Study .2 This study is aimed to establishment the basement of rock mass classification, which can be use in Iraq. Iraq. Combin Combinati ation on betwee between n engine engineeri ering ng proper properti ties es of intact intact rocks rocks and discont discontinu inuit ities ies,, nowadays used for rock mass classification systems to utilize rock mechanics researches. Before eighte eighteent enth h many many engineer engineering ing geologi geologists sts were were used used the intact intact rock rock proper properti ties es for studyi studying ng the problems of foundations, underground opening and slope stability. The objective of the entire en tire project is to develop a methodology, for different geological structures and rock types in North Iraq, that can be used to estimate the suitability for engineering structures. Figure (1) shows the three paths of the fiel field d and and labo labora rato tory ry inve invest stig igat atio ions ns,, which which conj conjuga ugate te to prod produc ucee the the desig design n and and suppo support rt of .engineering structures
:Tectonics and Initial State of Stresses .3 Distinction between loading and stress. Loading is the history of applied forces, displacement and temperature changes that produce the history of stress fields experienced by a body. In contrast, stress is a property of a single point in a body and a single time. There are three especially important mechanisms of loading: :a) Gravitat Grav itational ional loading loadi ng Due to gravitational forces and possible tectonic influence, the rock is already stressed before the underground opening is excavated. Thus, one speaks of an initial or primary state of stress, which, of course, is different from location to location (Figure 2)(Kovari, 1979). The observed :vertical normal stress is very close to that predicted from the weight o f the overburden σz = ρgz
.(where ρ is the density of the overburden, g is gravity (9.8 m/s2) and z is the depth (Suppe, 1985 There are two ways in which the initial stresses may give rise to difficulties in tunneling. Firstly, the material in the vicinity of the opening often reacts to the changes in the stress field by failure and creep processes, which may lead either to the closure of the opening or, if it is hindered, to the development of rock pressure. Secondly, in hard rock at great depths the much feared phenomenon of rock burst may occur. This is characterized by the explosive-like separation of plateshaped pieces of rock often of considerable size, which may endanger the lives of the people working in the tunnel. The mechanism of rock burst has not, as yet, been adequately investigated. All that is known with certainty is that the orientation of the tunnel axis in the relation to the directions of the principal stresses of the initial state of stress plays an important role. The stress tensor tensor in the rock rock cannot cannot be determ determine ined d theore theoreti ticall cally y becaus becausee of the changin changing g topogr topographi aphical cal condit condition ions, s, the general generally ly comple complex x struct structure ure of the rock rock mass mass and its nonline nonlinear ar stress stress-st -strai rain n .(relationship, and the tectonic forces which may still active today (Kovari, 1979
Hydrogeolog Data Engineering Intact Structural Discontinuitie Groundwater Laboratory Field Rock Numerical Engineering En Statistic Samplin Surface Stress Collections gineering Blocks Rock mass of structure s tructure design and
Geomechanic Classifications classification geology Description distribution conditions modeling testing water yRock gs supporting 1- Rock Mass Rating (RMR) System Sy stem 2- Modified Rock Mass Rating (M-RMR) System 3- Rock Mass Quality (Q) System 4- Geological Geological Strength Index Ind ex (GSI) 5- New Austrian Tunneling Method (NATM) 6- Mining Rock Mass Rating (RMR) (RMR ) System 7- Unified Rock Classification System (URCS) 8- Rock Mass Strength (RMS) 9- Slope Mass Mass Rating (SMR) 10- Rock Rock Mass Number (N) and Rock Condition Rating (RCR) 1111- Rock Mass Index In dex (RMi)
.Figure ( 1): Flow chart of the study
.Figure ( 1): Flow chart of the study :b) Thermal loading If a homogeneous rock is slowly heated or o r cooled, it will homogeneously expand and contract. :The relationship between strain and temperature change is ε = α ∆T
where ε is the strain, α is the linear coefficient of thermal expansion and ∆T is the temperature .(change (Suppe, 1985 :c) Displacement loading A third major mechanism by which rocks are loaded in the earth is the forced displacement of .(there adjacent surroundings, which is of major importance in tectonic deformation (Suppe, 1985
.Figure (2): Initial state of stress in rocks
:Geological Data Collection .4 Outcro Outcrop p confid confidence ence is the relati relative ve measur measuree of the predic predictab tabil ility ity or homogen homogeneit eity y of the structural domain and the lithology of the rock unit from one exposure to another or to the proposed :(site of investigation. The three levels of outcrop confidence are defined as (Moore, 2002 Level 1: High : Rock units are massive massive and homogeneous, and are vertically and laterally extensive. .Site geology has a history of low tectonic activity
Level II: Intermediate Intermediate : Rock characteristics are generally predictable, but have expected lateral and vertic vertical al variab variabili ility. ty. Struct Structura urall featur features es produce produced d by tecton tectonic ic activi activity ty tend tend to be syste systemat matic ic in .orientation and spacing Leve Levell III: III: Low : Rock Rock condit condition ionss are extrem extremely ely variab variable le because because of comple complex x deposit deposition ional al or struct structura urall histor history, y, mass mass moveme movement, nt, or buried buried topogr topography aphy.. Signif Significa icant nt and frequen frequentt latera laterall and .vertical changes can be expected Once Once a rock rock unit unit has been establ establish ished, ed, it can be define defined d by classi classifi ficat cation ion elemen elements ts and analyz analyzed ed for perfor performan mance ce in relati relation on to select selected ed perfor performan mance ce object objective ives. s. From From a geolog geologica icall description of the rock mass, and from a comparison between the size of the structure being designed and the spacing of discontinuities in the rock mass, decide which type of material behavior model is most appropriate. Figure (3) shows the transition from an isotropic intact rock specimen, through a highly anisotropic rock mass in which failure is controlled by one or two discontinuities, to an isotropic heavily jointed rock mass (Hoek and Brown, 1997). A rock mass can be said to be continuous if the consists of either purely intact rock, or of individual rock pieces that are small in relation to the overall size of the construction element studied (figure 4). For jointed rock masses, the issue of whether the rock mass can be considered continuous or discontinuous is also related to the construction scale in relation to the joint geometry (figure 5) .((Edelbro, 2003
Figure (3) : Simplified representation of the influence of scale on the type of rock rock mass mass beha behavi vior or mode modell whic which h shou should ld be used used in desi design gnin ing g .underground excavations or rock slopes
Figure (4): Example of continuous and discontinuous rock masses. .The tunnel size is constant
:Field Rock Description 4.1 Each Each rock rock unit unit is charact characteri erized zed in terms terms of specif specific ic classi classifi ficati cation on elemen elements ts that that affect affect performance of the rock for its intended use. The investigator may include any additional elements .considered necessary for further clarification and refinement Rock material properties properties : Determined by examining and classifying hand specimens, core sections, .drill cuttings, outcroppings, and disturbed samples using conventional geologic terminology Rock mass properties: Determined by geologic mapping, fixed line survey, geophysical survey, .remote imagery interpretation, core sample analysis, and geomorphic analysis Geohydrologic Geohydrologic properties properties : Determined by pressure testing; review of logs/data from water wells, observation wells, drill holes, and piezometers; review of published and unpublished maps and .reports; interpretation of rock material and rock mass properties; and dye tests
.Figure (5): Different construction sizes in the same kind of rock mass
The illustr illustration ation in Figure Figure (6) shows the six the six binary binary interactions of in situ stress, rock structure .(and water flow (Hudson and Harrison, 1997 .Rock structure/ stress-stress field affected by discontinuities :1 .Rock structure/ water flow-water flow-water preferentially flows flows along discontinuities :2 .Stress/water flow-high normal stresses reduce discontinuities :3 Water flow/stress-water pressure in discontinuities reduces :4 Water flow/rock structure-water flow causes discontinuity :5 .Stress rock structure-high rock structure-high stress can alter the rock structure :6
The following discussions provide a brief summary of the engineering significance associated .(with the more important field rock description (Throner, 2001 a. Unit designation: Unit designation is usually an informal name assigned to a rock unit that does not necessa necessaril rily y have have a relati relations onship hip to strati stratigra graphi phicc rank rank (e.g. (e.g. Al-Fat Al-Fat'ha 'ha limes limeston tonee or Injana Injana .(sandstone b. Rock Rock type: type: Rock Rock type type refers refers to the general general geologi geologicc classi classific ficati ation on of the rock rock (e.g. (e.g. marl, marl, sandstone, limestone, etc.). Certain physical characteristics are ascribed to a particular rock type with a geological name given according to the rocks mode of origin. Although the rock type is used primarily for identification and correlation, the type is often an important preliminary indicator of .rock mass behavior c. Degree of weathering: The engineering properties of a rock can be, and often are, altered to varyi varying ng degrees degrees by weathe weatheri ring ng of the rock rock materi material. al. Weathe Weatheri ring, ng, which which is disint disintegr egrati ation on and decomposition of the in-situ rock, is generally depth controlled, that is, the degree of weathering .decreases with increasing depth below the surface d. Hardness: Hardness is a fundamental characteristic used for classification and correlation of .geologic units. Hardness is an indicator of intact rock strength and deformability e. Texture: The strength of an intact rock is frequently affected, in part, by the individual grains .comprising the rock
.Figure (6): Six of the main rock mechanics interactions
f. Structur Structure: e: Rock Rock struct structure ure descri descripti ptions ons descri describe be the freque frequency ncy of discon discontin tinuit uity y spacin spacing g and thickness of bedding. Rock mass strength and deformability are both influenced by the degree of .fracturing g. Condition of discontinuities: discontinuities: Failure of a rock mass seldom occurs through intact rock but rather along discontinuities. The shear strength along a joint is dependent upon the joint aperture presence or absence of filling materials, the type of the filling material and roughness of the joint surface .walls, and pore pressure conditions h. Color: The color of a rock type is used not only for identification and correlation, but also for an index of rock properties. Color may be indicative of the mineral constituents of the rock or of the .type and degree of weathering that the rock has undergone i. Alteration: Alteration: The rock may undergo alteration by geologic processes at depth, which is distinctively .different from the weathering type of alteration near the surface j. Primary porosity: porosity: Free draining or not, estimating porosity from pores size and grain distribution. Very low primary porosity; pores not interconnected or free draining. Moderately primary porosity; pores visible under l0x hand lens, slowly free draining. draining. Highly porosity; porosity; pores visible to to naked eye, .rapidly free draining
:Data Collection 4.2 Classi Classific ficati ation on elemen elements ts are object objective ive physic physical al proper propertie tiess of a rock rock unit unit that that define define its engineering characteristics. Engineering classification of a rock unit takes into consideration the material properties of the rock itself, the structural characteristics of the in situ rock mass, the .systems of discontinuities, the topography or geomorphology and the hydrogeology
:Intact Blocks of Rock 4.2.1 Rock material properties are related to the physical properties of the constituent minerals and the type of mineral bonding. The properties are determined from examination of hand specimens, core sections, drill cuttings, outcroppings, and disturbed samples using qualitative procedures and simple classification tests, or in the laboratory using standard test methods. The results are applicable to hand specimens and representative samples of intact rock material. They do not account for the :(influence of discontinuities or boundary conditions of the rock (Throner, 2001, USACE,2001 :a. Mine M ineral ralog ogy Estimate percentage of principle and accessory minerals, type of cement and presence of .alterable minerals :b. Lithology Macro Description of Mineral Components. Use standard adjectives such as shaly, sandy, silty, .and calcareous. Note inclusions, concretions, nodules, etc :c. Degree Degr ee of Weathe W eathering ring .Unweathered: No evidence of any chemical or mechanical alteration (1) Slightly weathered: Slight discoloration on surface, slight alteration along discontinuities, less (2) .than 10 percent of the rock volume altered Moderately weathered: Discoloring evident, surface pitted and altered with alteration penetrating (3) .well below rock surfaces, weathering “halos” evident, 10 to 50 percent of the rock altered Highly weathered: Entire mass discolored, altercation pervading nearly all of the rock with some (4) . pockets of slightly weathered rock noticeable, some minerals leached away Decomposed: Rock reduced to a soil with relict rock texture, generally molded and crumbled by (5) .hand
:d . Hardness .Very soft: Can be deformed by hand (1) .Soft: Can be scratched with a fingernail (2) .Moderately hard: Can be scratched easily with a knife (3) .Hard: Can be scratched with difficulty with a knife (4) .Very hard: Cannot be scratched with a knife (5) :e. Texture Sedimentary rocks: clastic sedimentary rocks can be classified texturally according to grain size (1) .((Table 1), while carbonate rocks as shown in table (2) (BS 5930, 1981 Textural Textural adjectives: adjectives: Use simple simple standard standard textural textural adjectives adjectives such as prophyriti prophyritic, c, vesicular vesicular,, (2) . pegmatitic, granular, and grains well developed
:Rock Structure 4.2.2 :a. Thickness of Bedding .Massive: >1m (1) .Thick bedded: beds from 30cm – 1m thick (2) .Medium bedded: beds from 10cm – 30cm thick (3) .Thin bedded: < 10cm (4) :( b. Degree of Fracturing (Jointing .Un fractured: fracture spacing – 2m or more (1) .Slightly fractured: fracture spacing 60cm to 2m (2) .Moderately fractured: fracture spacing 20cm. to 60cm (3) .Highly fractured: fracture spacing 5cm to 20cm (4) .Intensely fractured: fracture spacing 20cm or less (5)
.Table (1): Texture classification of clastic sedimentary rocks Texture
Grain Diameter
Particle Name
Rock Name
*
mm 80
Cobble
conglomerate
*
mm 80 - 5
gravel
Coarse grained
mm 5 - 2
Medium grained
mm 2 - 0.4
Fine grained
mm 0.4 - 0.1
Very fine grained
mm 0.1
sand
sandstone
clay, silt shale, claystone, siltstone .Use clay-sand texture to describe conglomerate matrix *
.Table (2): Texture classification of carbonate sedimentary rocks Rock name Calcirudite Calcarenite Calcisiltite Calcilutite
Description Shelly, coarse grain Oolitic, medium grain Micritic, fine grain Argillacious
(.Grain size (mm 2.00< 0.06-2.00 0.002-0.06 0.002>
:c. Dip of Bed or Fracture :For each family of joints the orientation data are
(i) Dip i) Dip (0 to 90°) Measured with clinometers Measuring error + 2° Normal data scatter + 5°
(ii) Dip ii) Dip direction or strike (0 to 360°) Measured with geological compass Measuring error + 2o Normal data scatter + 5o
:For bedding most researchers used the following classification for expressing .Flat: 0 to 20 degrees (1) .Dipping: 20 to 45 degrees (2) .Steeply dipping: 45 to 90 degrees (3)
:Discontinuities 4.2.3 The The in-s in-sit itu u rock rock,, or rock rock mass mass,, is comp compri rise sed d of inta intact ct bloc blocks ks of rock rock sepa separa rate ted d by discontinuities such as joints, bedding planes, folds, sheared zon es and faults. These rock blocks may .vary from fresh and unaltered rock to badly decomposed and disintegrated rock Intact rock refers to the un fractured blocks which occur between structural discontinuities in a typical rock mass. These pieces may range from a few millimeters to several meters in size and their behavior behavior is generally elastic elastic and isotropic isotropic.. Their failure failure can be classifie classified d as brittle which implies a sudden reduction in strength when a limiting stress level is exceeded. In general, viscoelastic or time-dependent behavior such as creep is not considered to be significant unless one is dealing with .evaporates such as salt or gypsum
Joints 4.2.3.1
:
Joints are a particular type of geological discontinuity but the term tends to be used generically in rock mechanics and it usually covers all types of structural weakness. Strength, in the context of .(these notes, refers to the maximum stress level which can be carried by a rock specimen (Figure 3
:Joint Condition 4.2.3.2 This This is a very very comple complex x parame parameter ter which which includ includes es severa severall sub parame parameter ters: s: (1) type; type; (2) weathe weatherin ring g of walls; walls; (3) separa separatio tion; n; (4) roughn roughness ess;; (5) fillin filling g materi material; al; (6) spacin spacing; g; and (7) persistence . :Type ( 1 ) Type of joint if it can be readily readily determined determined (i.e., (i.e., bedding, bedding, cleavage, foliation, foliation, schistosit schistosity, y, or .(extension : Degree of joint wall weathering ( 2 ) Table (3) summarizes the recommendations of ISRM (1978) for the classification of wall :weathering. Which can be detailed as i) Un weathered: No visible signs are noted of weathering; joint wall rock is fresh, crystal bright,) .(type (I a). If slight discoloration of walls, the class will be (I b ii) Slightly weathered joints: Discontinuities are stained or discolored and may contain a thin) coating of altered material. Discoloration may extend into the rock from the discontinuity surfaces to .a distance of up to 20 percent of the discontinuity spacing
iii) Moderately weathered joints: Slight discoloration extends from discontinuity planes for greater ) than 20 percent of the discontinuity spacing. Discontinuities may contain filling of altered material. .Partial opening of grain boundaries may be observed o bserved iv) Highly Highly weathe weathered red joints joints:: All rock rock is decomp decompose osed. d. Origin Original al struct structure ure remain remains, s, entir entiree mass mass) discolored, alteration pervading nearly all of the rock with some pockets of slightly weathered rock noticeable, some minerals leached away. v) Completely weathered joints: All rock is converted to soil. Original structure is destroyed, rock ) reduced to a soil with relict rock texture, generally molded and crumbled by hand. .(Table (3): Classification for wall weathering (ISRM, 1978
: Joint wall separations ( 3 ) Separation is the perpendicular distance between between the rock walls walls of an open joint. If the joint is filled by air or water the separation becomes the aperture of the joint. It the joint has ha s filling the Grade
Ia Ib II III
Term
Fresh Fresh Slightly weathered Moderately weathered
Decomposed (%) rock 10 >
10-50
Description
No visible weathering Slight discoloration of walls General discoloration Part of rock is decomposed. Fresh rock is a continuum General decomposition of rock. Some fresh rock appears
IV
Highly weathered
50-90
V
Completely weathered
90 <
All rock is decomposed. Original structure remains
VI
Residual soil
100
All rock is converted to soil. Original structure is destroyed
.(appropriate term is width (ISRM ,1978 .i) Close. Opening <0.1 mm, which is cannot be resolved by naked eye) .ii) Moderately open. Opening < 1 mm. Walls come into contact with a small shearing movement) .iii) Open. Opening 1-5 mm. Walls come into contact con tact after a shearing movement) iv) Very open. Opening > 5 mm. Walls can remain separated until a big shearing displacement has) .happened The separation of joints governs the displacement necessary to mobilize the joint shear stress. .Moreover, open or very open joints can show nondilatant behavior : Roughness ( 4 ) :Bieniawski (1979) has proposed a roughness scale which is very easy to check in the field rough. Near vertical steps and ridges occur on the joint surface) .i) Very rough. Near .ii) Rough. ii) Rough. Some ridges are visible. Asperities happen. Joint surface feels very abrasive) .iii) Slightly rough. Some asperities happen. Joint surface feels asperous) Smooth. No asperities. Smooth .iv) Smooth. No Smooth feeling of a joint surface surface) .v) Slickensided. Visual evidence of polishing exists) The most important consequence of joint roughness is the display of dilatants behavior when close, coupled joints are subject to shearing stresses. The natures of fillings govern the shearing .stress of open, uncoupled joints and are a related parameter to roughness : Spacing ( 5 )
Spacing of discontinuities is the distance between them, measured along a line perpendicular lo discontinuity planes. The ISRM (1978) suggest the use of minimum, modal and maximum values of spacing to characterize a set of joints. This procedure has been superseded in practice by the use of mean spacing. Bieniawski (1979) defines the spacing as the ‘mean distance’. Spacing is measured with a tape along the rock outcrop, counting the number n umber of joints in a fixed distance and a nd multiplying . by the corresponding cosines of angles between the normal to joints and the plane of rock outcrop In practice the relationship between the span of the opening and the average joint spacing is decisive, in many cases, for stability considerations (Figure 7). With increasing span D, or D/d respectively, the influence of the jointing becomes more marked and the probability of an .(unfavorable joint combination, which could give rise to a rock fall, increase (Kovari, 1979
.Figure (7): Influence of the span on the stability of jointed rocks
It is an easy task for set of joints with vertical dip and strike not parallel to the slope. But many times the dangerous set of discontinuities for slope stability happens to be co mposed of joints with strike parallel to slope. In these cases systematic tape measurements are seldom possible. It is suggested to assess visually the model value of spacing of dangerous joints and measure it carefully .afterwards The classification of discontinuity spacing proposed by the ISRM (1978) and presented in .Table (4). Bieniawski (1979) has added a description of rock mass conditions .(Table (4): Classification for Joints Spacing (ISRM, 1978 and Bieniawski, 1979 Description Very wide Wide Moderate Close Very close
(Spacing (m 2< 0.6-2 0.2-0.6 0.06-0.2 0.06 >
Rock mass condition Solid Massive Blocky/seamy Fractured Crushed/shattered
: Infilling ( 6 ) Source, type, and thickness of infilling; alterated rock, or by deposition; clay, silt, etc.; how thick is the filler. Anyway, for practical purposes it is necessary to distinguish between gouge and soft gouge: (i) ‘gouge’ is no filling or filling with a material of high friction (calcite, sand, crushed rock, etc.); and (ii) ‘soft gouge’ is filling with a material of low friction (clay, mica, platy minerals, etc.). : Persistence ( 7 ) .ISRM (1978) classifies the joints as follows
.i) Persistent. i) Persistent. Continuous) persistent. Not continuous but several joints can coalesce to form a continuous separation) ii) Sub persistent. Not .surface persistent. Not continuous) .iii) Not iii) Not persistent. Not
:Field Estimates of JRC 4.2.3.3 The joint roughness coefficient JRC is a number that can be estimated by comparing the appearance of a discontinuity surface with standard profiles published by Barton and Choubey .((1977) and is reproduced in Figure (8
Figure (8): Roughness profile and corresponding JRC .(values (Barton and Choubey, 1977
The appearance of the discontinuity surface is compared visually with the profiles shown and the JRC value corresponding to the profile which most closely matches that of the discontinuity surface is chosen. In the case of o f small scale laboratory specimens, the scale of the surface roughn ess will be approximately the same as that of the profiles illustrated. However, in the field the length of the surface of interest may be several meters or even tens of meters and the JRC value must be .estimated for the full scale surface
:Faults and Shear Zones 4.2.3.4
.Extent: Single plane or zone; how thick (1) .Character: Crushed rock, gouge, clay infilling, slickenside (2)
:Slope 4.2.4 o
The orientation data for the slope are difficult to measure. The normal error is ± 5 (or even more). Classification must be done with the estimated values for slope face dip and dip direction and .checked with the extreme values. Adjusting factors can be different
:Groundwater 4.2.5 Groundwater conditions can be estimated in classifications in three different ways: (i) inflow of water; (ii) pore pressure ratio; and (iii) general conditions. For slopes the general cond itions are usually sufficiently adequate. The ISRM (1978) have proposed a seepage classification which has .) been adapted to surfacing joints in order to estimate groundwater conditions (Table 5 .(Table (5): Groundwater Conditions (ISRM, 1978 Description
Comp. Dry Damp Wet Dripping Flowing
Unfilled joints Joint Dry Stained Damp Wet Wet
Filled joints
Flow No No No Occasional Continuous
Filling Dry Damp Wet Outwash Washed
Flow No No Some drips Dripping Continuous
:Engineering Properties of Rock Samples 4.3 :Bulk Density 4.3.1 .The bulk density of intact rock is the density of the overall bulk of the rock specimen Weight = Bulk density Volume
:Porosity 4.3.2 .Porosity is defined as the ratio of the pore volume to the bulk volume of a substance Pore Volume Porosity = x 100 Bulk Volume
:Permeability 4.3.3 Permeability is a measure of the ability of a porous material to transmit fluid. The un it of .measurement is the Darcy Permeability x area x pressure change Quantity
=
Length x viscosity
:Elastic Wave Velocities in Rocks 4.3.4 The velocity of elastic waves in solids is a function of the density and elastic properties of a .material
E
.
(1 - µ ρ
.
) (1 + µ
V p = )( 1 - 2µ )
E ρ
.
= Vs 2 (1 + µ )
Where Vp = Velocity of bulk compressional waves, Vs = Velocity Velocity of shear wave, ρ = Density, E .= Young’s Modulus and µ = Poisson’s Ratio
:Uniaxial Compressive Strength 4.3.5 Laboratory test is presented by applying load on a measured area of rock specimen until un til failure .occurs, the ratio of maximum load to area is uniaxial compressive strength Maximum load = UCS Area
:Geomechanics Classification Systems .5 The famous world world wide wide used used syste systems ms in rock rock mechan mechanics ics are listed listed in table table (6). (6). The most commonly used parameters for these systems are the intact rock strength, joint strength, joint distance distance and ground water condition condition summarized summarized in table table (7). The field field form for discontinui discontinuities ties survey are presented in figure (8). This form may be modify according to the site, the geological .structures and engineering structures of the future studies
:Numerical Modeling .6 RocLab is a software program for determining rock mass strength parameters, based on the latest version of the generalized Hoek-Brown failure criterion (Figure 9). RocLab provides a simple and intuitive implementation of the Hoek-Brown failure criterion, allowing users to easily obtain reliab reliable le estima estimates tes of rock rock mass mass proper properti ties es and to visual visualize ize the effect effectss of changin changing g rock rock mass mass parameters on the failure envelopes. The rock mass properties determined by RocLab can be used as input for numerical analysis programs such as Phase2 (Examine2D) (Examine2D) (finite (finite element element stress stress analysis analysis and support design for excavations) or Slide (limit equilibrium slope stability analysis). Examine2D is a 2-dimensional plane strain indirect boundary element program for the elastic stress analysis of underground excavations. The program (Figure 10) is interactive and easy to use, and is ideal for performing quick parametric analysis, preliminary design and as a teaching tool for numerical stress .analysis in a geotechnical context
.Figure (9): Roclab program
.Figure (10): Examine2D program
Case
.7 :Studies
Once of the studies achieved in North Iraq on the core hole SI-CH1 which drilled near Mahalabya town –west Mosul, in the core of the south eastern dome of Sheikh Ibrahim anticline. The study entitled “Engineering rock mass classification of carbonate rocks in Sheikh Ibrahim anticline, west Mosul” was done by Al-Jawadi and Al-Banna (2008). The core hole is penetrated different formations of (264) meters thick. Factors of engineering classification were detected to revise the rock mass for underground storage. Two systems were used in this study, rock mass quality (Q-System) and rock mass ratio (RMR). Point load test on axial and lateral directions
were done for intact cores. Permeability measurement were taken for rock mass under different pressures (1,3,5,3,1) bar. The suitable primary design for excavation and supporting .operations were resulted in this study Another study was done by Al-Jawadi and Adeeb “Geoengineering Properties for Rocks and Preliminary Design of Shiekh lbrahim Tunnel – South Jazira Irrigation Project”, which presents engineering geological investigations and the tunnel design for the South Jazira Irrigation the rock masses in Sheikh Ibrahim tunnel, which mainly consist of gypsum, marl, limestone, sandstone and claystone. Engineering geological investigations have been carried out, and in two stages as field and laboratory investigations. Thirteen boreholes with a total length of (1200) m. have been drilled to assess and verify geoengineering properties for rocks to preliminary design of tunnel. Stress analysis around the tunnel openning has been executed by the two dimensions finite element analysis .( program (phase2
.Table (6): Some rock mass classification systems and there applications Rock mass classification systems (Rock Quality Designation Index (RQD (Rock Structure Rating (RSR Rock Rock Mass Mass Rati Rating ng (RMR (RMR)) Sys Syste tem m Rock Ma Mass Quality (Q (Q) System Modified Rock Mass Rating (M-RMR) System (Rock Mass Strength (RMS (Modified Basic RMR (MBR (Slope Mass Rating (SMR (Ramamurthy and Arora Classification (RAC (Geological Strength Index (GSI (Rock Mass Number (N (Rock Mass Index (RMi
Country USA USA S. Afri Africa ca Norway
Sweden Spain India
Applications Core logging, tunneling Tunnels with steel support . Tunn Tunnel els, s, mine mines, s, foun founda dati tion onss etc etc Tunneling, la large ch chambers Mining .Tunnels, mines, foundations etc Mining Slopes For intact and jointed rocks Mines and tunnels
India Norway
Rock engineering
.Table (7): Parameters included in different numerical and functional classification systems Parameters
Classification systems
RQD Block size Block building joint orientation Number of joint set Joint length Joint spacing Joint strength Rock type State of stress Ground water condition Strength of intact rock Blast damage
RSR
RMR
Q
MRMR
RMS
MBR X
SMR
RAC
GSI
N
X
X
RMi X
X
X
X
X X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X X
X X
X
X
:References .8 Al-Jawadi, A.S. and Al-Banna, N.Y. (2008) “Engineering rock mass classification of .1 carbonate rocks in Sheikh Ibrahim anticline, west Mosul ” The 6th periodical scientific .conference for dams and water resource research center, University of Mosul Al-Ja Al-Jawad wadi, i, A.S. A.S. and Adeeb, Adeeb, H.G.M. H.G.M. “Geoe “Geoengi nginee neerin ring g Proper Propertie tiess for Rocks Rocks and.2 Preliminary Design of Shiekh Ibrahim Tunnel – South Jazira Irrigation Project” Iraqi .Journal of earth science, under review Barton, N.R. and Choubey (1977) “The shear strength of rock joints in theory and practice”.3 .Rock Mechanics, Vol. 10, No. (1-2), pp. 1-54 Barton, N.R. and Bandis, S.C. (1982) “Effects of block size on the shear behavior of jointed .4 .rock” 23rd U.S. Symposium on rock mechanics, Berkeley, 739p Bieniawski, Z.T. (1979) “The geomechanics classification in rock engineering applications”.5 .Proc. 4th congr., Int. Soc. Rock Mech., Montreux 2, 41-48 .Bieniawski, Z.T. (1989) “Engineering rock mass classification” Wiley, New York, 251 p.6 B.S. 5930 (1981) “British standard code of practice for site investigations” British Standard.7 .Institution, HMSO, London, UK Edelbro, C. (2003) “Rock mass strength” Lulea University of Technology, Department of .8 .Civil Engineering, Division of Rock Mechanics, LTU – TR – 03/16 – SE Hoek, E. (1983) “Strength of jointed rock masses” Geotechnique, Vol. 23, No. 3, pp. 187-.9 .223 Hoek, E. and Brown, E.T. (1997) “ Practical estimates of rock mass strength” International.10 .Journal of Rock Mechanics and Mining Science, Vol. 34, No. 8, pp. 1165-1186 Hoek, E. (2007) “Practical rock engineering” Applied Seismology Laboratory, Liverpool.11 . University Department of Earth Sciences 313p. www.rocscince.com Hudson, J.A. and Harrison, J. P. (1997) “Engineering rock mechanics an introduction to the.12 . principle” Elsevier Science Ltd., UK International Society for Rock Mechanics Commission on Standardisation of Laboratory and.13 Field Tests (1978) “Suggested methods for the quantitative description of discontinuities in .rock masses” Int. J. Rock Mech. Min. Sci. & Geomech. Abstr. Vol.15, pp. 319-368 Kovari Kovari,, K. (1979) (1979) “Decis “Decision ion making making and field field measur measureme ements nts in tunnel tunneling ing”” 25th OYO.14 .Anniversary Lecture Meeting, Tokyo, Japan Moore, J. S. (2002) “Rock Material Field Classification System” Chapter 12 in “National.15 .engineering handbook” part 631 Geology, NSDA and NRCS, 210-VI-NEH Suppe, J. (1985) “Principles of structural geology” Prentice – Hall, Inc., Englewood Cliffs,.16 . New Jersey 07632, 537p Throner, R. (2001) “ Engineering geology field manual” Vol. I and II, U.S. Department of .17 .the Interior, Bureau of Reclamination. Washington, DC 20402.0001, 745p US Army Corps of Engineers (2001) “Engineering and design- geotechnical investigations”.18 .EM1110-1-1804, Washington, DC 20314-1000 Yu, Y. F., Siu, C.K. and Pun, W.K. (2003) “Guidelines on the use of prescriptive measures.19 .for rock cut slopes” Special Project Report, Special Projects Projects Division, SPR 3/2003
