strength characteristics for limestone and dolomite rock matrix using tri-axial system

IJSTE - International Journal of Science Technology & Engineering | Volume 1 | Issue 11 | May 2015 ISSN (online): 2349-784X

All rights reserved by www.ijste.org

114

Strength Characteristics for Limestone and

Dolomite Rock Matrix using Tri-Axial System

Miteshkumar Bharatbhai Patel Dr. M. V. Shah

PG Student Assistant Professor

Department of Applied Mechanics Department of Applied Mechanics

L D College of Engineering L D College of Engineering

Abstract

Propagation of hair cracks, existing fissures into a rock mass is most common process associated in mining and tunneling

operation. The propagation of these features cracks or widening joints into a rock mass can be simulated into common approach

known as matrix formation into rock mass. This research study is an attempt to overcome this deficiency by postulating both

longitudinal and transverse cracks with wide range of degree of orientation, fissures into cylindrical rock specimen through

various specified geometrical rock matrix patterns. Limestone and Dolomite which comes under a category of soft to medium

hard strength where used for this study using microfine cement as a binder material to obtain strength characteristics and failure

mechanisms. Also it is intended to determine modulus of elasticity (secant modulus) for various rock matrix and its comparison

with intact rocks specimens. Series of triaxial test and compression test were carried out for both type of rock specimen using

automated triaxial conventional testing machine. The results indicate that there is a considerable effect of rock matrix and its

orientation both on shear parameters and failure mechanisms as compared to intact rock specimen.

Keywords: Rock Matrix, StressStrain Curves, Tri-Axial Test, Jointed Specimens, Microfine Cement ________________________________________________________________________________________________________

I. INTRODUCTION

For practical purposes, rock mechanics is mostly concerned with rock on the scale that appears in engineering and mining work,

and so it might be regarded as the study of the properties and behavior of accessible rock due to changes in stresses or other

conditions. Two distinct problems are always involved: (i) The study of the orientations and properties of the joints, and (ii) The

study of the properties and fabric of the rock between the joints. Joints are the most significant discontinuities in rocks. Joints are

breaks of geological origin along which there has been no visible relative displacement. A group of parallel or sub-parallel joints

is called a joint set, and joint sets intersect to form a joint system. The propagation of these features cracks or widening joints

into a rock mass can be simulated into common approach as, matrix formation in to rock mass. Sedimentary rocks often contain

two sets of joints approximately orthogonal to each other and to the bedding planes. These joints sometimes end at bedding

planes, but others, called master joints, may cross several bedding planes. Some research works are required in the area of rock

matrix. There is no general equation that exists, which adequately defines completely matrix properties of all types of rock. This

property varies from rock to rock and other factors also.Resist the thrust generated by the excavation. focuses has been made

towards rock matrixes, thats why efforts has been made to study the behavior of different rock matrix of different patterns which actually simulates crack and joints patterns when rock mass is under stress due any external disturbance. The different types of

matrixes are available on site such as (1) Polyhedral block (2) Equidimensional block (3) Prismatic block (4) Tabular block (5)

Rhombohedral block (6) Columnar block.

Fig. 1: Types of Matrix

In present investigation two types of rock viz. Millionite limestone and Dolomite are used for laboratory investigation to know

the shear and compression capacity of this rock samples with three simplest matrix pattern are used viz. (1) single vertical cut

(90), (2) one vertical and one horizontal cut at H/2, (3) one vertical and two horizontal cut at H/3 are adopted (Figure 3). The microfine cement is used as binding material to join this rock matrix for testing purpose.

Strength Characteristics for Limestone and Dolomite Rock Matrix using Tri-Axial System (IJSTE/ Volume 1 / Issue 11 / 020)


115

Fig. 2: Cylindrical Sample under Confining Pressure

Fig. 3: Matrix Pattern

II. MATERIALS AND EXPERIMENTAL SETUP

Rock Sample: A.

Source of the Millionite limestone and Dolomite was procured commercially from Saurashtra coastal area, and Chotta udaipur,

Baroda, Gujarat respectively.

Test Methodology: B.

The rock triaxial test is performed according to IS-13047-2010 and shear parameters are obtained for three different confining

pressures viz. 3, 5 & 7 N/mm2 for the intact and for different rock matrix pattern specimens of Millionite limestone & Dolomite

at the constant strain rate of 0.315 mm/min. The usual procedure for conducting a tri-axial compression test is first to apply the

confining pressure 3 all around the cylinder is held constant & then to apply axial load 1 (Figure 2). Through plunger vertical load is applied which causes failure in the sample.

III. LABORATORY TESTING

Index Properties: A.

Cylindrical samples having 54mm diameter and 108mm height was obtained in accordance with IS 13030-1991 as shown in

table 1, 2, 3, 4.

Index properties of Millionite limestone: 1) Before Jointing:

Fig. 4: Intact Rock Fig. 5: 1-Vertical Cut



116

Fig. 6: 1-Vertical and 1-Horizontal Cut at H/2 Fig. 7: 1-Vertical and 2-Horizontal Cut At H/2

2) After Jointing:

Fig. 8: 1-Vertical Cut Fig. 9: 1-Vertical and 1-Horizontal Cut at H/2 Fig. 10: 1-Vertical And 2-Horizontal Cut At H/2

Table - 1 Index Properties of Millionite Limestone with Binding Material

Type of matrix Sample no. Water content Void ratio Density

w = (Mw/Ms)*100 (%) e =Vv/Vs =M/V (kN/m3)

Intact rock

13 0.30 0.10 2115

14 0.20 0.11 2118

15 0.20 0.10 2141

1- vert. cut

4 2.09 0.12 1972

5 1.90 0.12 2094

6 2.05 0.13 2026

1-vert.

1-horiz. Cut

7 4.51 0.14 2051

8 4.39 0.14 2031

9 4.60 0.13 2023

1-vert.

2-horiz. Cut

10 5.77 0.16 2004

11 5.90 0.16 2006

12 5.70 0.15 2007

Index properties of Millionite limestone without binding material



1- vert. cut

1- vert. cut

16 2.10 0.13 2000

17 1.97 0.14 2135

18 2.12 0.14 2083

1-vert.

1-horiz. cut

19 4.28 0.10 2000

20 4.62 0.11 2090

21 4.50 0.11 2034

1-vert.

2-horiz. cut

22 5.75 0.14 2045

23 5.80 0.16 2063

24 5.98 0.20 2097

Index properties of Dolomite: 3) Before Jointing:



117

Fig. 11: Intact Rock Fig. 12: 1-Vertical Cut

Fig. 13: 1-Vertical and 1-Horizontal Cut at H/2 Fig. 14: 1-Vertical and 2-Horizontal Cut At H/2

4) After Jointing:

Fig. 8: 1-Vertical Cut Fig. 9: 1-Vertical and 1-Horizontal Cut at H/2 Fig. 10: 1-Vertical and 2-Horizontal Cut At H/2

Table - 2

Index Properties of Dolomite

Index properties of Dolomite using cement as a binding material



Intact rock

51 0.35 0.017 2492

52 0.35 0.017 2496

53 0.35 0.022 2471

1- vert. cut

54 0.50 0.020 2485

55 0.53 0.018 2476

56 0.54 0.023 2476

1-vert.

1-horiz. cut

57 0.60 0.023 2449

58 0.62 0.014 2454

59 0.65 0.021 2442

1-vert.

2-horiz. cut

60 0.70 0.024 2411

61 0.73 0.025 2435

62 0.68 0.025 2437

Index properties of Dolomite without using cement as a binding material



1- vert. cut 63 0.40 0.020 2475



118

64 0.35 0.021 2487

65 0.35 0.020 2473

1-vert.

1-horiz. cut

66 0.48 0.023 2452

67 0.50 0.021 2445

68 0.54 0.024 2447

1-vert.

2-horiz. cut

69 0.73 0.026 2439

70 0.72 0.025 2430

71 0.73 0.024 2441

Strength of Cubes: B.

The Unconfined compressive strength and Compressive strength of microfine cement + 3% sodium silicate slurry is obtained by

casting cylindrical cubes and 70*70mm square respectively in accordance with IS 9143:1979 and results are obtained which is

shown in table 5. For U.C.S and Compression test microfine cement + 3% sodium silicate slurry has high strength then without

sodium silicate as per table 5. Table - 3

Compressive Strength of U.C.S and Compression Test

Compressive strength of binder material (microfine cement) 7 day(N/mm2)

Sample no. U.C.S 70 X 70mm square cube

With 3% sodium silicate Without sodium silicate With 3% sodium silicate Without sodium silicate

1 0.245 0.204 1.09 0.94

2 0.245 0.163 1.17 0.87

3 0.286 0.163 0.95 0.86

IV. ANALYSIS OF RESULTS AND DISCUSSION

Mohrs Circles: A.

Fig. 4: Mohrs Circles for Millionite Limestone Using Binding Material

Fig. 5: Mohrs Circles for Millionite Limestone without Binding Material



119

Fig. 6: Mohrs Circles for Dolomite Using Microfine Cement as Binding Material

Fig. 7: Mohrs Circles for Dolomite without Binding Material

Table - 4

Cohesion (C) and Internal Friction Angle ()

Matrix

pattern

Intact

rock

1-vert.

cut

1-vert

1-horiz.

Cut

1-vert.

2-horiz.

Cut

Types

of rock

Millionite

limestone

With binding

material

c (N/mm2) 7.3 5.8 3.2 0.9

() 26 30 33 34

E (N/mm2) 1271.65 1195.48 696.82 632.80

Compressive strength

(N/mm2) 29.05 - - -

Without

binding

material

c (N/mm2) - 4.9 2.8 0.4

() - 13 15 23

E (N/mm2) - 757.52 747.76 421.53

Dolomite

With binding

material

c (N/mm2) 9 6 2.7 1.1

() 24 29 31 33

E (N/mm2) 1123.43 1064.61 837.21 738.96

Compressive strength

(N/mm2) 80.18 - - -

Without

binding

material

c (N/mm2) - 5.4 2 0.6

() - 21 24 28

E (N/mm2) - 840.06 631.52 610.06

From the above table it is observed that for the Millionite limestone if we use cement as a binding material then as the no. of

joints increasing viz. intact, 1-vertical, 1-vertical & 1-horizontal, 1-vertical & 2-horizonatal cut, the percentage decrement in

cohesion (c) is observed as 20.54%, 56.16%, 87.67% respectively, the percentage increment in internal friction angle () is observed as 15.38%, 26.92%, 30.76% respectively, the percentage decrement in Modulus of elasticity (E) is observed as

5.98%,45.20%, 50.23% respectively with respect to intact rock, & if we dont use cement as a binding material then the

percentage decrement in c is observed as 42.85%, 91.30% respectively, the percentage increment in internal friction angle () is observed as 15.38%, 76.92% respectively, the percentage decrement in Modulus of elasticity (E) is observed as 27.69%, 44.35%

respectively with respect to 1-vertical cut.

From the above table it is observed that for the Dolomite if we use cement as a binding material then as the no. of joints

increasing viz. intact, 1-vertical, 1-vertical & 1-horizontal, 1-vertical & 2-horizonatal cut, the percentage decrement in cohesion

(c) is observed as 33.33%, 70%, 87.67% respectively, the percentage increment in internal friction angle () is observed as 20.83%, 29.16%, 37.5% respectively, the percentage decrement in Modulus of elasticity (E) is observed as 5.23%, 25.47%,

34.22% respectively with respect to intact rock, if we dont use cement as a binding material then as the no. of joints increasing viz.1-vertical, 1-vertical & 1-horizontal, 1-vertical & 2-horizonatal cut, the percentage decrement in cohesion c is observed as

62.96%, 88.88% respectively & the percentage decrement in internal friction angle ()14.28%, 33.33%, respectively, the percentage decrement in Modulus of elasticity (E) is observed as 24.82%, 20.23% respectively with respect to 1-vertical cut.



120

Stress-Strain Curves: B.

Fig. 8: Comparison of Jointed Millionite Limestone Matrix Pattern at 3 N/Mm

From the above stress-strain curves it is observed that for the jointed Millionite limestone at 3 N/mm2 confining pressure, as

the no. of joints increasing 1-vertical, 1-vertical & 1-horizontal, 1-vertical & 2-horizonatal cut, the percentage decrement in

stress with respect to intact rock is observed as 13.64%, 51.13%, 66.77% respectively.


From the above stress-strain curves it is observed that for the jointed Millionite limestone at 5 N/mm2 confining pressure, as

the no. of joints increasing 1-vertical, 1-vertical & 1-horizontal, 1-vertical & 2-horizonatal cut, the percentage decrement in

stress with respect to intact rock is observed as 6.17%, 42.83%, 55.74% respectively.


From the above stress-strain curves it is observed that for the jointed Millionite limestone at 7 N/mm2 confining pressure, as the no. of joints

increasing 1-vertical, 1-vertical & 1-horizontal, 1-vertical & 2-horizonatal cut, the percentage decrement in stress with respect to intact rock is

observed as 2.06%, 38.04%, 46.74% respectively.



121

Fig. 11: Comparison of Not Jointed Millionite Limestone Matrix Pattern at 3 N/Mm

From the above stress-strain curves it is observed that for the not jointed Millionite limestone at 3 N/mm2 confining pressure, as the no. of

joints increasing 1-vertical, 1-vertical & 1-horizontal, 1-vertical & 2-horizonatal cut, the percentage decrement in stress with respect to 1-

vertical cut is observed as 14.63%, 72.56%, respectively.


From the above stress-strain curves it is observed that for the not jointed Millionite limestone at 5 N/mm2 confining pressure,

as the no. of joints increasing 1-vertical, 1-vertical & 1-horizontal, 1-vertical & 2-horizonatal cut, the percentage decrement in

stress with respect to 1-vertical cut is observed as 7.13%, 57.67%, respectively.







122

Fig. 14: Comparison of Jointed Dolomite Matrix Pattern at 3 N/Mm

From the above stress-strain curves it is observed that for the jointed Dolomite at 3 N/mm2 confining pressure, as the no. of

joints increasing 1-vertical, 1-vertical & 1-horizontal, 1-vertical & 2-horizonatal cut, the percentage decrement in stress with

respect to intact rock is observed as 17.58%, 51.57%, 68.39% respectively.


From the above stress-strain curves it is observed that for the jointed Dolomite at 5 N/mm2 confining pressure, as the no. of

joints increasing 1-vertical, 1-vertical & 1-horizontal, 1-vertical & 2-horizonatal cut, the percentage decrement in stress with

respect to intact rock is observed as 12.75%, 43.53%, 54.91% respectively.


From the above stress-strain curves it is observed that for the jointed Dolomite at 7 N/mm2 confining pressure, as the no. of joints increasing

1-vertical, 1-vertical & 1-horizontal, 1-vertical & 2-horizonatal cut, the percentage decrement in stress with respect to intact rock is observed as

11.70%, 33.68%, 47.10% respectively.



123

Fig. 17: Comparison of Not Jointed Dolomite Matrix Pattern at 3 N/Mm

From the above stress-strain curves it is observed that for the not jointed Dolomite at 3 N/mm2 confining pressure, as the no.

of joints increasing 1-vertical, 1-vertical & 1-horizontal, 1-vertical & 2-horizonatal cut, the percentage decrement in stress with

respect to 1-vertical cut is observed as 16.65%, 62.04%, respectively.











124

V. REASONS

The most noteworthy seen from stress-strain curve is the occurrence of the downward concave behavior in the early stages of

loading indicating the development of non-uniform normal stresses. The failure has been observed instantaneously because the

failure of intact rocks can be identified as brittle material.

VI. CONCLUSION

The above study reveals that value of cohesion (c) is observed to be decreasing while angle of internal frication angle () is increasing with increases in number of joints. The Normal stress is found to be decreasing as numbers of joints are increasing.

Strength of jointed rock is dependent on the direction of applied loading with respect to orientation of joints. In jointed rock

specimen the failure is observed in terms of hair cracks surrounding the jointed rock area where as in unjointed specimen the

failure is observed in terms of broken pieces of specimen. The strength of the rock specimen jointed by microfine cement is

higher than the unjointed specimen. The load carrying of vertical cut specimen is higher than the horizontal cut specimen and

also with increase in number of horizontal cut the load carrying capacity of specimen decreases. Observed that shear angle was

dependent on confining pressure and the spacing of joint in the specimen.

REFERENCES

[1] Arza J., Alejano L.R., & Walton G. (2014). Strength and dilation of jointed granite specimens in triaxial test. International Journal of Rock Mechanics & Mining Sciences, Science direct, vol. 69, 93104.

[2] Ghazvinian A., Hadei M.R., et al. (2013), Shear behavior of inherently anisotropic rocks, International Journal of Rock Mechanics & Mining Sciences, Science direct- Elsevier, vol. 61, 96110..

[3] He Manchao, Nie Wena, et al. (2011), Micro and macro-fractures of coarse granite under true-tri-axial unloading condition, Mining Science and Technology (China), Science direct-elsevier, vol. 21, 389394.

[4] Mikael Rinne (2010), Fracture mechanics and subcritical crack Growth approach in brittle rock, International Journal of Rock Mechanics & Mining Sciences, Science direct, vol. 20, 551 -706.

[5] Tetsuya Tokiwa, Makoto Matsubara, et al. (2013), Formation mechanism of extension fractures induced by excavation in soft sedimentary rock, Science direct, vol. 4,105-111.

[6] Zuo Jianping, Wang Zhaofeng, et al. (2013), Failure behavior of a rock-coal-rock combined body with a weak coal interlayer, International Journal of Rock Mechanics & Mining Sciences, Science direct-Elsevier, vol. 3,907-912.

[7] IS:-9143-1979:- Method for the determination of unconfined compressive strength of rock materials. [8] IS:-9179- 200:-, Method for preparation of rock specimen for laboratory testing. [9] IS:-9179- 200:-, Method for preparation of rock specimen for laboratory testing. [10] IS:-11315 (part 2)-1987:- Methods for quantitative description in discontinuous rock mass. [11] IS:-13030-1991, Method of test for laboratory determination of Water content, porosity, density and Related properties of rock material. [12] IS:-13047-2010, Method for determination of strength of rock materials in tri-axial compression.

strength characteristics for limestone and dolomite rock matrix using tri-axial system

Documents