Rock Mass Classification - Lab 02

MNG 551 – Section 001

ASTM D6032 & 5878

Thales de Faria César

Lab completion: 09/17/14

Report submittal: 09/24/14

PURPOSE

The purpose of this lab report is to characterize and determine the rock properties in order to conduct

us to a more specific study with better equipment. The three tests perfomed in this report, RMR, RQD

and CMRR, combine rock features and structures to provide a number that we can quantify and make

decisions of what is better to do to provide safety and save money.

Equipment Used

Rock Quality Designation (RQD)

Drill Core

Tape Measure

FERM Classification Book

RMR

A rock mass to classify

Ability to perform laboratory and field testing

RMR classification charts and tables

CMRR

A drill core sample from roof

Ability to perform laboratory and field testing

CMRR Software provided by NIOSH

Ball-peen hammer

Chisel

PROCEDURE

Rock Quality Designation (RQD)

1) With a tape measure, measure the length of each core piece greater than 4 inches.

2) Sum the lengths of core pieces greater than 4 inches.

3) Measure the total length of the drill core

4) Use the equation Sum of the drill core pieces

𝑇𝑜𝑡𝑎𝑙 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡ℎ𝑒 𝑑𝑟𝑖𝑙𝑙 𝑐𝑜𝑟𝑒𝑥100 to calculate the RQD.

5) Record the approximate description using the table 1

6) Use the FERM classification booklet to classify the rock type of each core piece

Bieniawski’s Rock Mass Rating

1) From the descriptions provided in the problem statement, determine ratings for parameters 1

to 5 in table 6.9A

2) Use table 6.10 to determine the discontinuity strike and dip classification

3) Use the strike and dip classification to determine rating adjustment for joint orientations in

table 6.9B

4) Use table 6.9C to determine the rock description

5) Use table 6.9D to determine cohesion and friction angle of the rock mass

6) Use table 6.4 to determine average stand-up time of an unsupported excavation

7) Use the equations provided in section 2.4 to estimate the modulus of deformation of the rock

mass

Coal Mine Roof Rating

Part 1

1) Open the CMRR program in the NIOSH folder located in the start menu

2) Select File > New, and fill out the project description. Click next

3) Fill out the general information tab

4) Fill out the unit information tab

5) Fill out the specific information for each unit

6) Fill out the CMRR tab

7) The CMRR is shown at the top right of the dialogue box

8) Save the plot of the roof layers

9) Save the CMRR report

Part 2

1) Perform the chisel splitting test on the three different rock types to determine cohesion of the

joint.

2) Perform the moisture sensitivity test on each rock type to determine the moisture sensitivity.

3) Perform the ball-peen hammer test on each rock type to determine the strength index

4) Determine de FERM classification of each rock type

5) Fill out the forms on the CMRR program and determine the CMRR. Remember to include a

plot of the roof layers and CMRR report in your lab report.

RESULTS

Rock Quality Designation (RQD)

Following the procedures listed above we had the data do fill out the table 1.

RQD DATA SHEET

Project: Rock Mass Classification Date: 09/17/14

Core Box I.D. no.:

Recorders: Luis Felipe, Philipe,

Rachel and Thales

Total Length of Core Run, mm (in): 244.48 (96.25) Checkers:

Core Diameter, mm (in): Data Checked:

Run

Sketch or

Photographic

Length of Each Sound

Piece Remarks

Image of Core of Core > 100mm (4-

inch)

1

Photo is provided in

the next page

7''

335

5.75''

5.75''

5.5''

7''

7''

2 None 333

3 4'' 323

4

5''

332

6''

5.5''

5''

8.25''

7.75''

5 8''

328 8.75''

Lengths of Sound Piece of Core >

100mm (4-inch): 96.25"

RQD (%) = (96.25"/235.45")*100]

RQD (%)= 40.88 Rock Classification: Poor Rock

Table 1. RQD Data Sheet

Picture 1. Core Sample

Bieniawski’s Rock Mass Rating

Following the steps listed in procedures we were able to fill out the table 2 and come up with a RMR

value for the sample.

Rock Mass Rating (RMR)

(1) Strenght Rating 12

(2) RQD Rating 17

(3) Joint Spacing Rating 15

(4) Joint Condition Rating 20

(5) Groundwater Rating 7

(b) Joint Orientation Adjustment -5

Total Rating 66

Class No. II

Description Good Rock

Cohesion (kPa)

300 - 400

kPa

Friction Angle 35 - 45

Stand-up Time 3yr to 1mo

Modulus of Deformation (Gpa) 32

Table 2. Rock Mass Rating (RMR)

Coal Mine Roof Rating

Part 1

After follow the steps provided above we achieved the picture below. (CMRR report is

attached in the end of the paper)

Picture 2. CMRR Value

Part 2

Following the procedure listed above we were able to fill out the Table 3 and using the

program provided in class we obtained ground water CMRR value for the problem. (CMRR

report is attached in the end of the paper)

Unit A Unit B Unit C

Thickness (ft) 3 0.5 6.5

FERM class 994 994 994

Strength Index 2 2 2

No. of

Discontinuities 2 1 1

(1) Cohesion Weak Weak Weak

(1) Roughness Wavy – Planer Weak - Planer Jagged - Wavy

(1) Spacing 0.5 0.25 0.75

(1) Persistance 50 30 30

(2) Cohesion Weak - -

(2) Roughness Wavy - -

(2) Spacing 10 - -

(2) Persistance 20 - -

Contact Quality S S S

Water Sensitivity Slight Slight Slight

Water Movement Light Drip

Bolt 5

Table 3. CMRR Underground Data Sheet

Picture 3. CMRR Value

DISCUSSION

Rock Quality Designation (RQD) and FERM Classification

After measure the drill core we obtained a total length of drill core pieces of 96.25 in and a total

length of the drill core of 235.45 in. Through the equation provided on procedures we could calculate

the RQD, which is 40.87% and this number gives to the rock the classification of poor rock. This rock

is described as shattered, very blocky and seamy.

Because of this experiment relies on human evaluation to be complete, it is more likely to contain

errors.

Bieniawski’s Rock Mass Rating

In this test the information was provided on Lab Manual and we had to find out the rock

classification. The RMR value that was 66 and this number put the rock the into class number 2,

describing it as a good rock mass. Other characteristics from the rock were inferred, such as its

cohesion value that is between 300 and 400 kPa, its friction angle that ranges from 35 to 45 degrees

and the stand-up time from 1 month to 3 years depending on the size of span. By the equation on page

35 of Rock Mechanics Lab Manual, we were able to calculate the deformation modulus and it is 32

GPa.

Coal Mine Roof Rating (CMRR)

Part 1

By fill in the CMRR software with the data given, we were able to determine a final groundwater

adjusted CMRR value of 52.9, classifying this as a moderate roof, requiring a six feet long roof bolt to

support the rock mass.

Part 2

On this part of the lab we had to perform the chisel splitting test in order to determine cohesion of the

joint. Also, we had to perform the ball-peen hammer test to determine strength index. For the moisture

sensitivity we were provided with the information. These three tests combined give us a better

comprehension of the rock properties.

Once we’ve filled the information obtained from the tests on the CMRR software we got a final

groundwater adjusted CMRR value of 50.8, classifying this as a moderate roof, requiring a five feet

long roof bolt in order to support the rock mass.

A possible source of error in this test is sloppy perform of the test, because it depends on human

ability.

CONCLUSION

By completing these three experiments, RQR, RMR and CMRR we were able to transform

features and properties of the rock into numbers to quantify and better understand the rock

behavior and apply these numbers on engineering projects. RQD have provided a percentage

of 40.88, putting the core sample into a category of poor rock. The RMR test provided a final

value of 66, which classify the sample as a good rock mass. For the CMRR test, we have

obtained a moderate roof for both tests.

EXERCISES

1) Under RQD system, natural joints and fractures must be considered. Artificial discontinuities

should be ignored in the calculation.

2) It is useful to give a general idea of what we should expect from the rock. We shouldn’t

consider RQD system as a final evaluation of rocks.

3) Bieniawski’s geomechanics classification system combines the most significant geologic

parameters of influence to give a primary understanding of the rock behavior. It uses five

classifications parameters, listed below:

o Strength of Intact Rock Material.

o Discontinuity Spacing.

o Joint Condition.

o Rock Quality Designation (RQD).

o Groundwater Conditions.

4) It was developed to classify rock masses from coal mines roofs and evaluate them. It is

designed for bedded coal measure rocks and concentrates on the bolted horizon and

its ability to provide a stable mine structure.

5) Discontinuities and its conditions.

6) It can reduce rock strength, compromising the stability of the roof.

7) CMRR, RMR, Q-system and GSI