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ECG 403: ENGINEERING GEOLOGYECG 403: ENGINEERING GEOLOGY

Rock Classification SystemRock Classification Systemby ZBMby ZBM

Rock mass classification system was proposed inRock mass classification system was proposed in

order to formalize an empirical approach oforder to formalize an empirical approach ofclassification for geotechnical engineering works.classification for geotechnical engineering works.

The rock mass classifications were developed forThe rock mass classifications were developed forinvestigation procedures and the mostinvestigation procedures and the mostpredominant design approachpredominant design approach

The rock mass classification is also a system ofThe rock mass classification is also a system of

classification for a systematic planning andclassification for a systematic planning anddocumentation of the related ground information.documentation of the related ground information.

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The investigation procedures in the classificationThe investigation procedures in the classificationsystem will enable :system will enable :

i) Identification of significant parameters influencingi) Identification of significant parameters influencingbehaviourbehaviour of rock massof rock mass

ii) Groupings of similar rock mass quality andii) Groupings of similar rock mass quality and

behaviourbehaviouriii) Understanding of the characteristics of each rockiii) Understanding of the characteristics of each rock

mass classificationmass classification

iv) Derivation of quantitative data and guidelines foriv) Derivation of quantitative data and guidelines forengineering designengineering design

v) A common basis of communication betweenv) A common basis of communication between

engineers and geologistsengineers and geologists

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Types of Rock Mass Classification SystemsTypes of Rock Mass Classification Systems

Rock Quality DesignationRock Quality Designation

GeomechanicsGeomechanics Classification System (RMR System )Classification System (RMR System )

RockRock TunnelingTunneling Quality IndexQuality Index -- QQ

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1. Rock Quality Designation1. Rock Quality Designation The rock quality designation (RQD) is to quantitatively estimateThe rock quality designation (RQD) is to quantitatively estimate rock massrock mass

quality from drill core logs.quality from drill core logs. The RQD is evaluated by determining the percentage recovery ofThe RQD is evaluated by determining the percentage recovery of core incore in

lengths greater than twice its diameter or intact core pieces lolengths greater than twice its diameter or intact core pieces longer than 100nger than 100mm (4 inches) of the total length or core.mm (4 inches) of the total length or core.

RQD is intended to represent the rock mass quality in situ.RQD is intended to represent the rock mass quality in situ. The RQD values corresponding to the rock mass rating incrementsThe RQD values corresponding to the rock mass rating increments arearegiven;given;

Table 1: Rock Mass Rating Increments for Drill Core QualityTable 1: Rock Mass Rating Increments for Drill Core Quality

RQD (%)RQD (%) RatingRating

9090--100100

7575--9090

5050--7575

2525--5050

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Measurement and Calculation of RQDMeasurement and Calculation of RQD

Say Total length of core run = 200 cmSay Total length of core run = 200 cm

Length of core pieces > 10 cm lengthLength of core pieces > 10 cm length

RQD =RQD = ---------------------------------------------------------------------------------------------------- X 100X 100

Total length of core runTotal length of core run

38 + 17 + 20 + 3538 + 17 + 20 + 35

RQD =RQD = ------------------------------------------------ X 100 = 55%X 100 = 55%

200200

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2. Rock Mass Rating System2. Rock Mass Rating System

BieniawskiBieniawski (1976) published the details of a rock mass classification call(1976) published the details of a rock mass classification callededthethe GeomechanicsGeomechanics Classification or the Rock Mass Rating (RMR)Classification or the Rock Mass Rating (RMR)systemsystem..(Bieniawski(Bieniawski, 1989)., 1989).

The following six parameters are used to classify a rock mass usThe following six parameters are used to classify a rock mass using theing theRMR system:RMR system:..

i)i) UniaxialUniaxial compressive strength of rock material.compressive strength of rock material.

ii) Rock Quality designation (RQD).ii) Rock Quality designation (RQD).iii) Spacing of discontinuities.iii) Spacing of discontinuities.

iv) Condition of discontinuities.iv) Condition of discontinuities.

v) Groundwater conditions.v) Groundwater conditions.

vi) Orientation of discontinuities.vi) Orientation of discontinuities.

The Rock Mass Rating system is presented inThe Rock Mass Rating system is presented in TableTable , giving the ratings for, giving the ratings for

each of the six parameterseach of the six parameters These ratings are summed to give a value of RMRThese ratings are summed to give a value of RMR

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Rock Tunneling Quality Index, Q3.

The Norwegian Geotechnical Institute proposed a Tunneling Quality Index (Q) for thedetermination of rock mass characteristics and tunnel support requirements. Thenumerical value of the index Q varies on a logarithmic scale from 0.001 to a maximum of1,000 and is defined by:

Q = RQD x Jr x JwJn Ja SRF

where

RQD is the Rock Quality DesignationJn is the joint set numberJr is the joint roughness numberJa is the joint alteration numberJw is the joint water reduction factor

SRF is the stress reduction factorThe rock tunneling quality Q can be considered to be a function of only three parameters,i.e1. Block size (RQD/ Jn)

2. Inter-block shear strength (Jr / Ja)3. Active stress (Jw/SRF)