ABSTRACTRock mass characterization is an integral part of rock engineering practice especially in analyzing rock mass failure conditions and their characteristics. This report was based on the rock mass characterization experiment conducted at the Lugoba quarries in Chalinze, Coast region by using geomechanics classification or rock mass rating (RMR) system.It was concluded that the part of the rock mass in the quarry (which I dealt with) described as very good rock which needs no major supports although there is potential of forming wedges as drawn in stereonet diagrams by the UNWEDGE software.It was also concluded that serious care during observations and field level risk assessment should be done at the site before conducting experiments as the rock mass was highly damaged by poor drilling and blasting practices, and sufficient equipments for conducting the experiment should be provided at the site.

Table of ContentsABSTRACTiLIST OF TABLESii1. INTRODUCTON12. LITERATURE REVIEW12.1 THEORETICAL PRINCIPLES23. EXPERIMENTAL PROCEDURES34. PRESENTATION OF RESULTS AND DISCUSSION44.1 RESULTS44.2 DISCUSSION OF RESULTS54.3 SOURCES OF ERRORS65. CONCLUSION66. RECOMMENDATION67. NOMENCLATURE78. REFERENCES8APPENDIX9

LIST OF TABLESTable 1: Results from rock mass mapping4Table 2: Classifying the discontinuity conditions4Table 3: Determination of RMR value5Table 4: Stereonet wedge diagrams drawn from UNWEDGE software5Table 5: Possible wages formed for section I of 20mW wall9Table 6: Possible wages formed for Section II of 20mW wall11Table 7: A. Classification parameters and their ratings14Table 8: B. Guidelines for Classification of Discontinuity Conditions15Table 9: C. Effect of Discontinuity Orientations in Tunneling15Table 10:D. Rating Adjustment for Discontinuity Orientations15Table 11: E. Rock Mass Classes Determined from Total Ratings15Table 12: F. Meaning of Rock Mass Classes15

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1. INTRODUCTONDuring the feasibility and preliminary design in early stages of a mining or related project, when very little detailed information on the rock mass and its stress and hydrologic characteristics is available, the use 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 relevant information has been considered. At the other end of the spectrum, one or more rock mass classification schemes can be used to build up a picture of the composition and characteristics of a rock mass to provide initial estimates of support requirements, and to provide estimates of the strength and deformation properties of the rock mass.The primary objective of classification systems is to quantify the intrinsic properties of the rock mass based on past experience. The other objective is to investigate how external loading conditions acting on a rock mass influence its behavior. Therefore its the purpose of this practical experiment to bring an understanding of these processes which can lead to the successful prediction of rock mass behavior for different conditions.The main objective of the experiment was to characterize rock mass by using geomechanics classification/Rock Mass Rating (RMR) System and describing the suitability of the rock for other designing structures and to determine whether there is a necessity of supporting the rock mass before failure. The experiment was both quantitative and qualitative where by different rock mass characteristics were observed and rated according to geomechanics classification scheme. This report contains literature review and theoretical principles about engineering rock mass classification, experimental procedures, presentation of results and discussion, conclusion and recommendation.

2. LITERATURE REVIEWRock mass classification schemes have been developing for over 100 years since Ritter (1879) attempted to formalize an empirical approach to tunnel design, in particular for determining support requirements and other purposes. Some of them are Terzaghis rock mass classification, Terzaghi 1946; Classifications involve stand-up time for unsupported span, Lauffer 1958; Rock Quality designation index, RQD developed by Deere et al 1967 and Rock Structure rating by Wickham et al 1972, Geomechanics classification or Rock Mass Rating (RMR) scheme developed by Bieniawski (1973, 1976) and the tunnelling quality index (Q) developed by Barton et al. (1974). Hoek and Brown (1980), Goodman (1993) and Brown (2003), among others, have reviewed the considerable number of rock mass classification schemes such as those mentioned in the previous paragraph. Two of these schemes, the tunnelling quality index (Q) and the CSIR geomechanics classification or Rock Mass Rating (RMR) scheme are currently widely used in civil engineering and in mining practice. Bieniawskis RMR scheme has been modified by Laubscher (1977, 1990), to Modified Rock Mass Rating (MRMR) to make the classification more relevant to mining application particularly for use in cave mining applications.2.1 THEORETICAL PRINCIPLESThe following six parameters are used to classify a rock mass using the RMR system:i. Uniaxial compressive strength of rock material.ii. Rock Quality Designation (RQD).iii. Spacing of discontinuities.iv. Condition of discontinuities.v. Groundwater conditions.vi. Orientation of discontinuities.Strength of the intact rock material- The uniaxial compressive strength of the intact rock may be measured on cores. Alternatively, for all but very low-strength rocks, the point load index may be used.Rock Quality Designation (RQD) is used to provide a quantitative estimate of rock mass quality from drill core logs. RQD is defined as the percentage of intact core pieces longer than 100 mm (4 inches) in the total length of core. The core should be at least 54.7 mm or 2.15 inches in diameter and should be drilled with a double-tube core barrel. Spacing of joints- In this context, the term joint is used to describe all discontinuities.Condition of joints- This parameter accounts for the separation or aperture of discontinuities, their continuity or persistence, their surface roughness, the wall condition (hard or soft) and the nature of any in-filling materials present.Groundwater conditions- An attempt was made to account for the influence of groundwater pressure or flow on the stability of underground excavations in terms of the observed rate of flow into the excavation, the ratio of joint water pressure to major principal stress, or by a general qualitative observation of groundwater conditions.The RMR can be obtained by adding together the first five parameters and then adjusting them by the sixth parameter. The rock condition can then be explained according to the rating and by using Bieniawski (1976) standard tables attached to the appendix.RMR = (classification parameters) + discontinuity orientation adjustmentRock mass classes are then determined from total ratings in table 11 in the appendix.

3. EXPERIMENTAL PROCEDURESIn applying this classification system, the rock mass in the selected area to be mapped was divided into a number of structural regions measured by a measuring tape (20 m each) and each region was classified separately. The boundaries of the structural regions usually coincide with a major structural feature such as a fault or with a change in rock type. Dip, dip direction and strike were measured by compass; joint sets, surface condition, and continuity of the joints were observed and recorded in a field notebook. In some cases, where significant changes in discontinuity spacing or characteristics, within the same rock type, the division of the rock mass into a number of small structural regions were necessary.

4. PRESENTATION OF RESULTS AND DISCUSSION4.1 RESULTSThe rock mass mapping was done in two sections each of 20m and the following information was obtained:Table 1: Results from rock mass mappingSection I (20 m)

Joint setJoint spacing (m)Dip.Dip directionJoint conditionAlterationContinuity

A0.3576326Dry, very roughTight1

B0.4048042Dry, roughSlightly tight1

C0.4261051Dry, smoothSlightly tight1

D0.6051016Dry, smoothTight1

E0.5246134Dry, roughTight1

Section II (20m)

10.4103009Dry, RoughTight1

20.5752332Dry,Very roughTight1

30.7048290Dry, Very roughSlightly tight1

40.6279358Dry,Very roughTight1

50.4776062Dry, RoughSlightly tight1

DETERMINATION OF RMRTable 2: Classifying the discontinuity conditionsParameterValue of descriptionRating

Discontinuity length (persistence)10-20m1

Separation (aperture)104-102-41-2For this low range, uniaxial compressive test is preferred

Uniaxial compressive strength (MPa)>250100-25050-10025-505-251-5