IN BORD AND PILLAR MINE

Presented By

Anurag Kumar Jha& Satish Kumar

DESIGN OF SUPPORT SYSTEM

OUTLINES

IntroductionObjectiveBarton’s Q-system (NGI-Q system) Rock quality designation index (RQD) CMRI-RMR rock mass classification Calculation Conclusion

INTRODUCTIONCMRI-RMR system

NGI-Q system

Accidents of underground coal mine

OBJECTIVETo design of support system for development as

well as depillaring panel

In development gallery

In the working face

In slice

At the goaf edge

Support determination parametersDepth of workingHeight of extractionStrata behaviourGeological conditionSpan of areaMethod of extractionEquipment used in excavation

Barton’s Q-system (NGI-Q system) Rock quality index

Where, RQD=Rock quality designation Jr=Joint roughness number Jw=Joint water reduction

number Jn=joint set number Ja=joint alternation number SRF=stress reduction factor

Application of Q-systemMaximum unsupported span

ESR = excavation support ratioRock load

Where,F=1 if Jr >=9 orF= (0.5Jr)/3 if Jr <9

Estimation of rock typeQ- value Rock type

0.001-0.01 Exceptionally good

0.01-0.1 Extremely poor

0.1-1 Very poor

1-4 Poor

4-10 Fair

10-40 Good

40-100 Very good

100-400 Extremely good

400-1000 Exceptionally good

Rock quality designation index (RQD)

The percentage of intact core pieces longer than 100mm or 10cm or 4inch in the total length of core of bore hole sample.

Rock quality description by RQD

Sl. No. RQD (%) Rock quality

description

1 0-25 Very poor rock

2 25-50 Poor rock

3 50-75 Fair rock

4 75-90 Good rock

5 90-100 Very good rock

CMRI-RMR rock mass classificationParameters of CMRI-RMR

1. Layer thickness(cm) 2. Structural features 3. Rock weatherability 4. Strength of roof rock 5. Ground water seepage(ml/min)

The five parameters should be determined individually for all the rock type in the roof at least 2m height.

CMRI-RMR rock mass classification

Parameters of RMR with ratingSl. No. Parameter Max. Rating

1 Layer thickness 30

2 Structural features 25

3 Rock weatherability 20

4 Strength of roof rock 15

5 Ground water seepage 10

Combined RMR Combined RMR for more than one rock type

in the roof

Rock quality description by RMR Sl. No. Rock mass rating Rock quality

1 0-20 Very poor

2 20-40 Poor

3 40-60 Fair

4 60-80 Good

5 80-100 Very good

APPLICATION OF RMR

APPLICATION OF RMRCalculation of rock load in roadway

Where,RMR=Rock mass ratingB=Roadway width (m)D=Dry density(t/m3)

Estimation of rock load in slices by RMR

Estimation of rock load in goaf edges by RMR

RMR CALCULATION CHART

Parameter Ranges of values1 Strength of

intact rock material

Point-load strength index(MPa)

>10 4-10 2-4 1-2 For this low range uniaxial compressive

test is preferred

Uniaxial compressive strength(MPa)

>250 100-250 50-100 25-50 5-25

1-5 <1

Rating 15 12 7 4 2 1 02 Drill core quality(RQD) % 90-100 75-90 50-75 25-50 <25

Rating 20 17 13 8 33 Spacing of discontinuities >2m 0.8-2m 200-

800mm60-200mm <60mm

Rating 20 15 10 8 54 Condition of discontinuities very rough

surfacesnot

continuesno

separation un-

weathered wall rock

Slightly rough

surfacesSeparation

<1mm slightly

weathered

Slightly rough

surfacesSeparation

<1mmHighly

weathered

Slicken sided

surfaces or Gouge <5mm thick

Separation 1-5mm

continuous

Soft gouge>5mm

thick or separation

>5mmcontinuous

Rating 30 25 20 10 05 groundwater Inflow per 10m

tunnel length(l/min)

NONE <10 10-25 25-125 >125

Ratio of joint water pressure

and major compressive

stress

0 <0.1 0.1-0.2 0.2-0.5 >0.5

General conditions completely damp Wet dripping flowingRating 15 10 7 4 0

SAMPLE CALCULATION

SAMPLE CALCULATIONExperimental observation of RMR parameters

A. Strength of intact rock material (A) Uniaxial compressive strength= 137MPa According to previous table value of A=12

B. Drill core quality (RQD) in % =62% The value of B= 13 According to the value of RQD the rock is fair good

C. Spacing of discontinuities =1.2m The value of C=15

D. Condition of discontinuity Slicken sided surface or gauge <5mm thick separation 1-

5mm continuous. The value of D = 10

E. Ground water condition Inflow per 10m tunnel length (l/min)=12 l/min The value of E = 7

Value of RMR = A+B+C+D+E = 12+13+15+10+7=57

So according to value of RMR, we have seen that the rock is fair .

If,The gallery width (B) = 4.5m Density of rock (D) =2.25 t/m3

SUPPORT DESIGN IN GALLERY Rock load in roadway (t/m2)=2.44 t/m2 Factor of safety = 2

Required support resistance = 4.88 t/m2 or more Strength of one bolt = 6 t Required support resistance in gallery for 1m

length =4.88x4.5x1 =22 t/m2

The number of bolts required in a row=22/6 = 3.66 or 4

So,The roof bolt should be arrange in a fashion that the

first bolt from the pillar should be 0.6m from the pillar and the rest are 1.2m from each other and the distance between the two rows should be 1m

SUPPORT DESIGN AT THE JUNCTION

Area of expose roof = 4.5x4.5 =20.25m2 The total rock load coming = 20.25x2.44 =49.5t The required support resistance = 49.5x2=99t Total no. of roof bolt required = 99/6 =16.5 We know that, we have to increase the roof bolt

by 25% at the junction so Final no of bolts=16.5x1.25=20.625 or 21 So,

we will put the support at 1m grid at the junction as we know that roof bolt is permanent support so we will apply some temporary support just line chock and slipper at the place of junction.

SUPPORT DESIGN AT THE SLICES

According to previous equation in terms of RMRThe rock load in slices (t/m2) = 4.43 t/m2 Let the width of the slice is 4.5m We are assuming the factor of safety by 2 than Total load coming = 20t Required support resistance = 40t No of roof bolt required = 7

We will put the roof bolt in 0.8m grid and install more temporary support like chock support at 2.4m interval and triangular support at the face in slice.

SUPPORT DESIGN AT THE GOAF EDGES

According to previous equationRock load in goaf edges (t/m2)=5.28 t/m2 Rock load coming at goaf edges = 23.76 t Required support resistance =47.53 t No of roof bolt=8

We will install the roof bolt at the goaf edge in the interval of 0.5m and we will install skin to skin hydraulic prop in front of chock support to support the goaf edge and prevent the goaf roadway so no man can inter in this area and the roof fall effect of will also be reduced by this way.

CONCLUSION

RMR is sufficient for rock load calculation.

Mine has a heterogeneous rock type and in this case it is very tough to find the rock load at every place.

It is very economic, reliable and easier method