21284723 Rock Mass Classification

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

2009 1430

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 and all other geological structures to understand the elastic theory of rock material as well as mass. This report provides and instructions for performing and documenting field work. The applications of geology to solving engineering problems is emphasized, rather than academic or other aspects of geology. The report provides the guidance for geologic classification and description of rock and rock discontinuities. Applications of standard indexes,

descriptors, terminology, sampling, testing and performing discontinuity survey.

1. Introduction: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 foliation and bedding joints, joints, fractures, and zones of crushing or shearing. These

discontinuities usually control the strength, deformation, and permeability of rock masses. Most engineering problems relate to discontinuities rather than to rock type or intact rock strength.

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 discontinuous mass resulted in a much more mature approach to the subject than 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 rock masses comprise interlocking angular 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 modeling: the strength of rock masses is described theoretically. The rock substance and the properties of the discontinuities are both modeled. A mathematical model requires determination of a large number of parameters and is often based on simplified

assumptions.•Rock mass classification: is often used in the primary stage of the project to predict the rock

mass quality and the possible need for support. The result is an estimate of the stability 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.

2 .Aim of Study:

This study is aimed to establishment the basement of rock mass classification, which can be use in Iraq. Combination between engineering properties of intact rocks and discontinuities, nowadays used for rock mass classification systems to utilize rock mechanics researches. Before eighteenth many engineering geologists were used the intact rock properties for studying the problems of foundations, underground opening and slope stability. The objective of the entire 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 field and laboratory investigations, which conjugate to produce the design and support of

engineering structures .

3 .Tectonics and Initial State of Stresses: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) Gravitational loading :

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 of 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 plate-shaped 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 in the rock cannot be determined theoretically because of the changing topographical conditions, the generally complex structure of the rock mass and its nonlinear stress-strain

relationship, and the tectonic forces which may still active today (Kovari, 1979.(

Engineering structure design and supporting

Rock mass classificationGeomechanic Classifications

1- Rock Mass Rating (RMR) System2- Modified Rock Mass Rating (M-RMR) System

3- Rock Mass Quality (Q) System4- Geological Strength Index (GSI)

5- New Austrian Tunneling Method (NATM)6- Mining Rock Mass Rating (RMR) System

7- Unified Rock Classification System (URCS)8- Rock Mass Strength (RMS)

9- Slope Mass Rating (SMR)10- Rock Mass Number (N) and Rock Condition Rating

(RCR)11- Rock Mass Index (RMi)

Engineering geology

Structural geology

Hydrogeology

Numerical modeling

Discontinuities

Laboratory testing

Groundwater conditionsStatistic

sStress

distributionField Rock Description

Intact Blocks of Rock

Data Collections Description

Sampling

Surface water

Figure ( 1): Flow chart of the study.

b) Thermal loading : If a homogeneous rock is slowly heated or 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 .(

4 .Geological Data Collection:Outcrop confidence is the relative measure of the predictability or homogeneity 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 and homogeneous, and are vertically and laterally extensive.

Site geology has a history of low tectonic activity.

Figure (2): Initial state of stress in rocks.

Figure ( 1): Flow chart of the study.

Level II: Intermediate: Rock characteristics are generally predictable, but have expected lateral and vertical variability. Structural features produced by tectonic activity tend to be systematic in

orientation and spacing.Level III: Low: Rock conditions are extremely variable because of complex depositional or structural history, mass movement, or buried topography. Significant and frequent lateral and

vertical changes can be expected.Once a rock unit has been established, it can be defined by classification elements and analyzed for performance in relation to selected performance objectives. From a geological 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 mass behavior model which should be used in designing

underground excavations or rock slopes.

4.1 Field Rock Description:Each rock unit is characterized in terms of specific classification elements that 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: 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 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.

The illustration in Figure (6) shows the six binary interactions of in situ stress, rock structure and water flow (Hudson and Harrison, 1997(.

1 :Rock structure/ stress-stress field affected by discontinuities.2 :Rock structure/ water flow-water preferentially flows along discontinuities.3 :Stress/water flow-high normal stresses reduce discontinuities.4 :Water flow/stress-water pressure in discontinuities reduces5 :Water flow/rock structure-water flow causes discontinuity6 :Stress rock structure-high stress can alter the rock structure.

Figure (4): Example of continuous and discontinuous rock masses.

The tunnel size is constant.

Figure (5): Different construction sizes in the same kind of rock mass.

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 necessarily have a relationship to stratigraphic rank (e.g. Al-Fat'ha limestone or Injana

sandstone.(b. Rock type: Rock type refers to the general geologic classification of the rock (e.g. 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 varying degrees by weathering of the rock material. Weathering, which is disintegration 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. Structure: Rock structure descriptions describe the frequency of discontinuity spacing and thickness of bedding. Rock mass strength and deformability are both influenced by the degree of

fracturing.g. Condition of 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: 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: 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. Highly porosity; pores visible to naked eye,

rapidly free draining.

4.2 Data Collection:Classification elements are objective physical properties of a rock unit that 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.

4.2.1 Intact Blocks of Rock: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. Mineralog y :

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 of Weathering :

)1 (Unweathered: No evidence of any chemical or mechanical alteration.)2 (Slightly weathered: Slight discoloration on surface, slight alteration along discontinuities, less

than 10 percent of the rock volume altered.)3 (Moderately weathered: Discoloring evident, surface pitted and altered with alteration penetrating

well below rock surfaces, weathering “halos” evident, 10 to 50 percent of the rock altered.)4 (Highly weathered: Entire mass discolored, altercation pervading nearly all of the rock with some

pockets of slightly weathered rock noticeable, some minerals leached away.)5 (Decomposed: Rock reduced to a soil with relict rock texture, generally molded and crumbled by

hand.

d . Hardness : )1 (Very soft: Can be deformed by hand.)2 (Soft: Can be scratched with a fingernail.)3 (Moderately hard: Can be scratched easily with a knife.)4 (Hard: Can be scratched with difficulty with a knife.)5 (Very hard: Cannot be scratched with a knife.

e . Texture : )1 (Sedimentary rocks: clastic sedimentary rocks can be classified texturally according to grain size

(Table 1), while carbonate rocks as shown in table (2) (BS 5930, 1981.()2 (Textural adjectives: Use simple standard textural adjectives such as prophyritic, vesicular,

pegmatitic, granular, and grains well developed.

4.2.2 Rock Structure:a. Thickness of Bedding :

)1 (Massive: >1m.)2 (Thick bedded: beds from 30cm – 1m thick. )3 (Medium bedded: beds from 10cm – 30cm thick .)4 (Thin bedded: < 10cm .

b. Degree of Fracturing (Jointing :( )1 (Un fractured: fracture spacing – 2m or more.)2 (Slightly fractured: fracture spacing 60cm to 2m.)3 (Moderately fractured: fracture spacing 20cm. to 60cm.)4 (Highly fractured: fracture spacing 5cm to 20cm.)5 (Intensely fractured: fracture spacing 20cm or less.

Table (1): Texture classification of clastic sedimentary rocks.

Texture Grain Diameter Particle Name Rock Name* 80 mm Cobble conglomerate

* 5 - 80 mm gravel

Coarse grained 2 - 5 mm

Medium grained 0.4 - 2 mm sand sandstone

Fine grained 0.1 - 0.4 mm

Very fine grained 0.1 mm clay, silt shale, claystone,

s

siltstone *Use clay-sand texture to describe conglomerate matrix.

Table (2): Texture classification of carbonate sedimentary rocks.

Rock name Description Grain size (mm(.Calcirudite Shelly, coarse grain <2.00Calcarenite Oolitic, medium grain 0.06-2.00Calcisiltite Micritic, fine grain 0.002-0.06Calcilutite Argillacious >0.002

c. Dip of Bed or Fracture:For each family of joints the orientation data are:

For bedding most researchers used the following classification for expressing :)1 (Flat: 0 to 20 degrees.)2 (Dipping: 20 to 45 degrees.)3 (Steeply dipping: 45 to 90 degrees.

4.2.3 Discontinuities:The in-situ rock, or rock mass, is comprised of intact blocks of rock separated by discontinuities such as joints, bedding planes, folds, sheared zones 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 is generally elastic and isotropic. Their failure can be classified 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 .

4.2.3.1 Joints

J

: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.(

4.2.3.2 Joint Condition:This is a very complex parameter which includes several sub parameters: (1) type; (2) weathering of walls; (3) separation; (4) roughness; (5) filling material; (6) spacing; and (7)

persistence .) 1 ( Type :

Type of joint if it can be readily determined (i.e., bedding, cleavage, foliation, schistosity, or extension.(

) 2 ( Degree of joint wall weathering : 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.

)i) Dip (0 to 90°(Measured with clinometers

Measuring error + 2°Normal data scatter + 5°

)ii) Dip direction or strike (0 to 360°(Measured with geological compass

Measuring error + 2o

Normal data scatter + 5o

)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.)iv) Highly weathered joints: All rock is decomposed. Original structure remains, entire 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(.

) 3 ( Joint wall separations : Separation is the perpendicular distance between the rock 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 filling the

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 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. ) 4 ( Roughness :

Bieniawski (1979) has proposed a roughness scale which is very easy to check in the field:)i) Very rough. Near vertical steps and ridges occur on the joint surface.)ii) Rough. Some ridges are visible. Asperities happen. Joint surface feels very abrasive.)iii) Slightly rough. Some asperities happen. Joint surface feels asperous.)iv) Smooth. No asperities. Smooth feeling of a joint 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. ) 5 ( Spacing :

Grade TermDecomposed

rock(%) Description

I a Fresh - No visible weatheringI b Fresh - Slight discoloration of wallsII Slightly weathered >10 General discoloration

IIIModerately weathered

10-50Part of rock is decomposed. Fresh rock is a

continuum

IV Highly weathered 50-90General decomposition of rock. Some fresh rock

appears

VCompletely

weathered <90 All rock is decomposed. Original structure remains

VI Residual soil 100All rock is converted to soil. Original structure is

destroyed

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 of joints in a fixed distance and 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(.

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 composed 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 Spacing (m( Rock mass conditionVery wide <2 Solid

Wide 0.6-2 MassiveModerate 0.2-0.6 Blocky/seamy

Close 0.06-0.2 FracturedVery close > 0.06 Crushed/shattered

) 6 ( Infilling : 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.).) 7 ( Persistence :

ISRM (1978) classifies the joints as follows.

Figure (7): Influence of the span on the stability of jointed rocks.

)i) Persistent. Continuous.)ii) Sub persistent. Not continuous but several joints can coalesce to form a continuous separation

surface.)iii) Not persistent. Not continuous.

4.2.3.3 Field Estimates of JRC: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.(

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 small scale laboratory specimens, the scale of the surface roughness 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.

4.2.3.4 Faults and Shear Zones:

Figure (8): Roughness profile and corresponding JRC values (Barton and Choubey, 1977.(

)1 (Extent: Single plane or zone; how thick.)2 (Character: Crushed rock, gouge, clay infilling, slickenside.

4.2.4 Slope:The orientation data for the slope are difficult to measure. The normal error is ± 5o (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.

4.2.5 Groundwater: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 conditions 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

5

).

Table (5): Groundwater Conditions (ISRM, 1978(.

DescriptionUnfilled joints Filled joints

Joint Flow Filling FlowComp. Dry Dry No Dry No

Damp Stained No Damp NoWet Damp No Wet Some drips

Dripping Wet Occasional Outwash DrippingFlowing Wet Continuous Washed Continuous

4.3 Engineering Properties of Rock Samples:

4.3.1 Bulk Density:The bulk density of intact rock is the density of the overall bulk of the rock specimen.

WeightBulk density =

Volume 4.3.2 Porosity:

Porosity is defined as the ratio of the pore volume to the bulk volume of a substance. Pore Volume

Porosity = x 100 Bulk Volume

4.3.3 Permeability:Permeability is a measure of the ability of a porous material to transmit fluid. The unit of

measurement is the Darcy. Permeability x area x pressure change

Quantity = Length x viscosity

4.3.4 Elastic Wave Velocities in Rocks:The velocity of elastic waves in solids is a function of the density and elastic properties of a

material.

E . (1 - µ )Vp =

ρ . (1 + µ )(1 - 2µ )

E

Vs = ρ . 2 (1 + µ )

Where Vp = Velocity of bulk compressional waves, Vs = Velocity of shear wave, ρ = Density, E = Young’s Modulus and µ = Poisson’s Ratio.

4.3.5 Uniaxial Compressive Strength:Laboratory test is presented by applying load on a measured area of rock specimen until failure

occurs, the ratio of maximum load to area is uniaxial compressive strength. Maximum load

UCS= Area

5 .Geomechanics Classification Systems:The famous world wide used systems in rock mechanics are listed in table (6). The most commonly used parameters for these systems are the intact rock strength, joint strength, joint distance and ground water condition summarized in table (7). The field form for discontinuities 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.

6 .Numerical Modeling: 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 reliable estimates of rock mass properties and to visualize the effects of changing rock 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) (finite element stress 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.

7. Case Studies:

Figure (9): Roclab program.

Figure (10): Examine2D program.

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 Country ApplicationsRock Quality Designation Index (RQD( USA Core logging, tunneling

Rock Structure Rating (RSR( USA Tunnels with steel supportRock Mass Rating (RMR) System S. Africa Tunnels, mines, foundations etc.

Rock Mass Quality (Q) System Norway Tunneling, large chambersModified Rock Mass Rating (M-RMR) System Mining

Rock Mass Strength (RMS( Sweden Tunnels, mines, foundations etc.Modified Basic RMR (MBR( Mining

Slope Mass Rating (SMR( Spain SlopesRamamurthy and Arora Classification (RAC( India For intact and jointed rocks

Geological Strength Index (GSI( Mines and tunnelsRock Mass Number (N ( IndiaRock Mass Index (RMi ( Norway Rock engineering

Table (7): Parameters included in different numerical and functional classification systems.

Parameters Classification systems

RQD RSR RMR Q MRMR RMS MBR SMR RAC GSI N RMiBlock size X X

Block building

joint orientation

X X

Number of joint set

X X X X

Joint length

X

Joint spacing

X X X X X X X X X X X X

Joint strength

X X X X X X X X X X X

Rock type XState of stress

X X X

Ground water

conditionX X X X X X X X

Strength of intact rock

X X X X X X X X X X

Blast damage

X X

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