Tuesday, November 23, 2010

Core recovery parameters

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Core recovery parameters describe the quality of core recovered from a borehole.

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[edit] Total core recovery

Total core recovery (TCR) is the borehole core recovery percentage.
TCR is defined as the quotient:
TCR = \left(\frac{l_{\mathrm{sum~of~pieces}}}{l_\mathrm{tot~core~run}}\right)\times 100 %
l_\mathrm{sum~of~pieces} = Sum of length of core pieces
l_\mathrm{tot~core~run} = Total length of core run

[edit] Solid core recovery

Solid core recovery (SCR) is the borehole core recovery percentage of solid pieces in a borehole core.
SCR is defined as the quotient:
SCR = \left(\frac{l_{\mathrm{sum~of~solid~core~pieces}}}{l_{\mathrm{tot~core~run}}}\right)\times 100 %
l_{\mathrm{sum~of~solid~core~pieces}} = Sum of length of solid core pieces
l_{\mathrm{tot~core~run}} = Total length of core run

[edit] Rock quality designation

rock-quality designation (RQD) Rough measure of the degree of jointing or fracture in a rock mass, measured as a percentage of the drill core in lengths of 10 cm or more. High-quality rock has an RQD of more than 75%, low quality of less than 50%. Rock quality designation (RQD) has several definitions. The most widely used definition was developed in 1964 by D. U. Deere. It is the borehole core recovery percentage incorporating only pieces of solid core that are longer than 100 mm in length measured along the centerline of the core. In this respect pieces of core that are not hard and sound should not be counted though they are 100 mm in length. RQD was originally introduced for use with core diameters of 54.7 mm (NX-size core). RQD has considerable value in estimating support of rock tunnels. RQD forms a basic element in some of the most used rock mass classification systems: Rock Mass Rating system (RMR) and Q-system
RQD is defined as the quotient:
RQD = \left(\frac{l_{\mathrm{sum~of~100}}}{l_{\mathrm{tot~core~run}}}\right)\times 100  %
l_{\mathrm{sum~of~100}} = Sum of length of core sticks longer than 100 mm measured along the center line of the core
l_{\mathrm{tot~core~run}} = Total length of core run

[edit] Classification table

From the RQD index the rock mass can be classified as follows:
RQD Rock mass quality
<25% very poor
25-50% poor
50-75% fair
75-90% good
90-100% excellent

[edit] Rock mass rating system

The Rock Mass Rating (RMR) system is a geomechanical classification system for rocks, developed by Z. T. Bieniawski between 1972 and 1973.

[edit] Definition

The following six parameters are used to classify a rock mass using the RMR system
  1. Uniaxial compressive strength of rock material
  2. Rock Quality Designation (RQD)
  3. Spacing of discontinuities
  4. Condition of discontinuities
  5. Groundwater conditions
  6. Orientation of discontinuities
Each of the six parameters is assigned a value corresponding to the characteristics of the rock. These values are derived from field surveys. The sum of the six parameters is the "RMR value", which lies between 0 and 100.

[edit] Classification table

Below is the classification table for the RMR system.[1]
RMR Rock quality
0 - 20 Very poor
21 - 40 Poor
41 - 60 Fair
61 - 80 Good
81 - 100 Very good

[edit] Applications

Rock Mass Rating has found wide application in various types of engineering projects such as tunnels, slopes, foundations, and mines. It is also adaptable for knowledge-based expert systems.

[edit] Q-system

For the linguistics formalism, see Q-systems.
The Q-system of rock mass classification was developed in Norway in 1974 by Nick Barton, Lien, R., and Lunde, J at NGI (Norwegian Geotechnical Institute). The system was developed on the basis of an analysis of 212 tunnel case histories from Scandinavia. It is a quantitative classification system and is an engineering system facilitating the design of tunnel supports. The Q-system uses six different parameters to assess the rock mass quality. The parameters are:
  • Rock Quality Designation RQD
  • Joint set number Jn
  • Roughness of the most unfavorable joint or discontinuity Jr
  • Degree of alteration of filling along the weakest joint Ja
  • Water inflow Jw
  • Stress Reduction Factor SRF
The Q-factor can then be calculated as:
Q=\frac{RQD}{J_n}\frac{J_r}{J_a}\frac{J_w}{SRF}

[edit] References

  • Barton, N. Lien, R. & Lunde, J. 1974. "Engineering classification of rock masses for the design of tunnel support", Rock Mechanics. 6:4:189-236.
  • Barton, N. Lien, R. & Lunde, J. 1977. "Estimation of support requirements for underground excavations", Proc. of 16th Symp. on Design Methods in Rock Mechanics, Minnesota, 1975. pp. 163–177. ASCE, NY. Discussion pp. 234–241.
  • Barton, N. & Grimstad, E. 1994. "The Q-system following twenty years of application in NMT support selection", 43rd Geomechanic Colloquy, Salzburg. Felsbau, 6/94. pp. 428–436.
  • Barton, N. 2002. "Some new Q-value correlations to assist in site characterization and tunnel design", Int. J. Rock Mech. & Min. Sci. Vol. 39/2:185-216.
  • Barton, N. 2006. Rock Quality, Seismic Velocity, Attenuation and Anisotropy. Taylor & Francis, UK & Netherlands, 729 p.
  • Deere, D U (1964). "Technical description of rock cores", Rock Mechanics Engineering Geology, 1 (16-22).
  • Deere, D U, Hendron, A J, Patton, F D & Cording, E J (1967). "Design of surface and near surface constructions in rock", Proc. 8th U.S. Symp. Rock Mechanics, ed. Fairhurst, publ. AIME, New York, (237-302).
  • Deere, D U & Deere, D W (1988), "The RQD index in practice", Proc. Symp. Rock Class. Engineering Purposes, ASTM Special Technical Publications 984, Philadelphia, (91-101).
  • Deere, D U (1989). "Rock quality designation (RQD) after twenty years", U.S. Army Corps of Engineers Contract Report GL-89-1, Waterways Experiment Station, Vicksburg, MS (67).
  • Grimstad, E. & Barton, N. 1993. Updating the Q-system for NMT. Proc. of the International Symposium on Sprayed Concrete - Modern Use of Wet Mix Sprayed Concrete for Underground Support, Fagernes, 1993, (Eds. Kompen, Opsahl and Berg) Norwegian Concrete Association, Oslo.
  1. ^ "Table: 11". U.S. Department of Energy. http://www.ocrwm.doe.gov/documents/spg42gm3_a/tables/tab_11.htm. Retrieved 2006-11-27. 

[edit] Further reading

  • Bieniawski, Z.T. "Engineering Rock Mass Classifications", John Wiley and Sons, New York, 1989
  • Hack, H R G K (1998). Slope stability probability classification SSPC, 2nd edition, ITC publication no 43, Enschede, Netherlands, ISBN 90-6164-154-3 (258).
  • Pantelidis, L (2009). "Rock slope stability assessment through rock mass classification systems", International Journal of Rock Mechanics and Mining Sciences, 46(2), (315–325).
  • Price, D G (2009). Engineering geology : principles and practice, ed. by M.H. de Freitas, Berlin etc.: Springer, ISBN 978-3-540-29249-4 (450).
  • — "The Rock Mass Rating (RMR) System (Geomechanics Classification) in Engineering Practices." Rock Classification Systems for Engineering Purposes, 17-34. Philadelphia, Pennsylvania: American Society for Testing and Materials, 1988
  • Charts and information to calculate RMR: http://www.rocscience.com/hoek/pdf/3_Rock_mass_classification.pdf
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