2a95 Tunnelling - Blast Design

CONTENTS PAGE

PREFACE 1

1 CROSS SECTION CONDITIONS 3

2 GEOLOGY 12

3 DRILLING 16

4 CHARGING 42

5 FIRING 52

6 EXAMPLES OF APPLICATION 58

APPENDICES 68

PREFACE

1

TUNNELLING - BLAST DESIGN PROJECT REPORT 2A-95

This project report is one out of four reports about conventional tunnelling. 2A-95 TUNNELLING Blast Design 2B-95 TUNNELLING Prognosis for Drill and Blast 2C-95 TUNNELLING Costs for Drill and Blast 2D-95 TUNNELLING Quality Assurance These reports are part of a larger project package about tunnelling and shaft excavation, see also Appendix D. A considerable amount of information on tunnelling has been systematized and brought up to date through these reports, to be used for

- economic dimensioning - choice of alternative - time planning - cost analysis, tender, budget and cost control - choice of excavation method and equipment.

The estimation part of some of these reports also exist as PC programmes for use on personal computers, see Appendix D. This report is partially based on data provided by the drilling pattern programme TUNNPLAN. TUNNPLAN is developed by the Departement of Building and Construction Engineering (IBA) and is a necessary tool when data controlled drilling is employed. See also Appendix C. The basis of the report is mainly work studies and statistics from tunnelling in Norway. The report includes the recent advances within data controlled drilling; longer rounds and increased drillhole diameter. The data are normalized and representative for well organized tunnelling.

PREFACE

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The report is a continuation and update of the blasting pattern part in the Project Report 2-88 TUNNELLING Prognosis for Drill and Blast. A overview of earlier versions of PR 2A-95 is given in Appendix B. This report is prepared by a project group at The Norwegian Institute of Technology. The members of the project group are the civil engineers Svein Eirik Aune, Krister Jacobsen, Jan Lima, Jrgen Moger, Pl-Egil Rnn and professor Odd Johannessen. The project group is solely responsible for all evaluations and conclusions presented in this report. Economic support has been granted by

- Statkraft Anlegg AS - Vegdirektoratet - Statsbygg - Atlas Copco Rock Drills AB - Scandinavian Rock Group.

By reference, registration and similar, we ask for the following formulation: NTNU-DEPARTMENT OF BUILDING AND CONSTRUCTION ENGINEERING (1995): PROJECT REPORT 2A-95 TUNNELLING Blast Design Reprint of the report has to be agreed by IBA. Trondheim, October 1995 Odd Johannessen professor

The report gives method and data for designing blasting patterns.

1. CROSS SECTION CONDITIONS Contents

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Page

1.0 INTRODUCTION 4

1.1 ROAD TUNNELS 51.11 Cross Section Design 51.12 Necessary Additional Area 8

1.2 RAILWAY TUNNELS 10

1.3 WATER TUNNELS 11

1. CROSS SECTION CONDITIONS 1.0 Introduction

4

1.0 INTRODUCTION

Tunnels are built for different purposes. This affects the choice of cross sectiondesign.

Geometrically, the main categories of cross sections are divided into

cross sections with circular contour- cut circle- cut circle with three circular arcs.

cross sections with vertical walls- circular crown- three circular arcs in the crown.

Most cross section types are symmetrical about a vertical axis and based on the twomain categories above.

Profiles normally used for road and railway tunnels will be introduced in thefollowing.

1. CROSS SECTION CONDITIONS 1.1 Road Tunnels

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1.1 ROAD TUNNELS

1.11 Cross Section Design

This chapter is based on "Handbok 021 Vegtunneler", Veglaboratoriet, StatensVegvesen 1992.

Based on the density of traffic and tunnel length, tunnels are divided into differentclasses. This is also the basis on which to decide the number of tunnel tubes, crosssection design, distance and design of turning niches, the need for emergency laybyand safety equipment.

The tunnel cross section must provide enough space to allow specified vehicles topass each other with sufficient clearance, and space for necessary road equipment andtechnical installations. The cross section has to be designed in accordance withstandards for roads in the open. Tunnels are classified as high cost terrain, and thewidth of the shoulder should therefore be reduced in the tunnel.

The specifications for road tunnels define 8 different tunnel cross sections for drilland blast tunnels, see Figure 1.1.

The tunnel profiles are specified with a T for tunnel and a number for the total width(tunnel width).

The dimensions of the different profiles according to the specifications for roadtunnels are shown in Figure 1.2 and Table 1.1.

The tunnel profiles T11 and T12 are designed as a split T9 profile, with a larger widthand a transition radius in the tunnel crown.

With a view to practical tunnelling, the road specifications semi-circular crosssection seems unfavourable without data controlled drilling. An alternative is to use across section with vertical walls and circular crown. Tunnel profiles T4 and T5 aredesigned in compliance with this principle.


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Figure 1.1 Design of road tunnels.


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Figure 1.2 Dimension parameters of road tunnel profiles T8 to T10.

TunnelProfile

TotalWidth

(m)

TrafficWidth

(m)

FreeHeight

(m)

CentreHeight

(m)

RadiusR

(m)

TheoreticalArea(m2)

T4 4.0 3.0 3.0 1.33 2.40 13.63T5 5.0 4.0 4.6 2.16 3.31 25.62T8 8.0 6.0 4.6 1.64 4.36 43.78

T8.5 8.5 6.5 4.6 1.62 4.55 46.90T9 9.0 7.0 4.6 1.53 4.79 50.45T10 10.0 7.0 4.6 1.05 5.13 52.03T11 11.0 9.0 4.6 1.53 4.79 63.78T12 12.0 10.0 4.6 1.53 4.79 70.73

Table 1.1 Dimensions of different tunnel profiles.


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1.12 Necessary Additional Area

Superstructure, contour and drainage require additional area. Rock protruding withinthe theoretical profile are not allowed for road tunnels. The conditions for calculationof additional area are

- superstructure : 0.6 tunnel width- drainage : 1.0 m2- contour : increased radius with 0.15 m in walls and crown to make

sure to get sufficiently large cross section.

Tunnel-Profile

TheoreticalArea

(m2)

AdditionSuperstructure

(m2)

AdditionContour

(m2)

AdditionDrainage

(m2)

Planned CrossSection

(m2)

T4 13.6 2.4 1.7 1.0 18.7

T5 25.6 3.0 2.3 1.0 31.9

T8 43.8 4.8 2.7 1.0 52.3

T8.5 46.9 5.1 2.7 1.0 55.7

T9 50.4 5.4 2.9 1.0 59.7

T10 52.0 6.0 2.9 1.0 61.9

T11 63.8 6.6 3.2 1.0 74.6

T12 70.7 7.2 3.3 1.0 82.2

Table 1.2 Blasting area from theoretical net area with addition for superstructure,contour and drainage.

In addition to superstructure, contour and drainage, there will be a necessaryadditional area as different rock support methods are employed.


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Planned Cross Section with Different Rock Support Methods

Tunnel

Profile

Theoretical Area

(m)

Planned Cross

Section without

Rock Support

(m2)

Shotcrete

R = R0 + 0.15

Plate Lining

R = R0 + 0.20

Concreted

Lining

R = R0 + 0.35

T4 13.6 18.7 20.5 21.1 23.0

T5 25.6 31.9 34.4 35.2 37.7

T8 43.8 52.3 55.1 56.1 59.0

T8.5 46.9 55.7 58.6 59.6 62.6

T9 50.4 59.7 62.7 63.7 66.8

T10 52.0 61.9 64.9 65.9 69.0

T11 63.8 74.6 77.8 79.0 82.3

T12 70.7 82.2 85.7 86.9 90.4

Table 1.3 Necessary blasted area, with and without rock support.

Figure 1.3 Relation between standard profile and blasted profile.

1. CROSS SECTION CONDITIONS 1.2 Railway Tunnels

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1.2 RAILWAY TUNNELS There has not yet been published updated standard cross sections by NSB (The Norwegian State Railway). The cross section will depend on

- single track or double track - diesel or electric traction - tunnel length - design speed.

Figure 1.4 shows examples of cross section with single track and double track respectively. For necessary additional area, see Section 1.12.

Figure 1.4 Standard profile for single track and double track tunnel. Design speed is 200 km/hr.

1. CROSS SECTION CONDITIONS 1.3 Water Tunnels

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1.3 WATER TUNNELS

For water tunnels, the transmission capacity are decisive of dimension and shape ofthe cross section. Because of this, one are more free as to adapt the cross section totunnelling method and rock stability conditions.

When rock is not allowed to protrude a planned cross section, there is normally noneed of additional area in the contour.

Additional area for rock support is normally not necessary.

2. GEOLOGY Contents

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Page

2.1 ROCK BLASTABILITY 13

2. GEOLOGY 2.1 Rock Blastability

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2.1 ROCK BLASTABILITY

The blastability index (SPR) describes the blastability of the rock mass. The rockmass blastability is given by

- rock type blastability- the rock mass fracturing- type of explosives.

The blastability of the rock type is influenced by

- anisotropy- density- sonic velocity- mineralogy and grain binding.- charging density of the explosive

A classification of blastability of different rocks is shown below.

Good blastabilitySPR = 0.38

Coarsegrained homogeneous granites, syenites andquartz diorites. For example "Swedish granite".

Medium blastabilitySPR = 0.47

For example gneiss.

Poor blastabilitySPR = 0.56

Metamorphic rocks with slated structure, oftenwith high content of mica and a low compressivestrength. For example mica schist in the Ranaregion in Norway.

In this report, the classification of rock blastability is simplified, distinguishingbetween good and poor blastability. For intermediate values, the curves may beinterpolated.

The formula for calculating the blastability index is shown in [2.1]. The index ismeant to aid the evaluation of blastability and assumes access to laboratory data froma representative sample of the particular rock. The index does not take intoconsideration the rock mass fracturing and orientation of fractures.


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SPR 0.736 I LTc

1000wc

a0.6 0.7

0.4 0.250.2

=

[2.1]

In = sonic velocity the normal to foliation (m/s)Ip = sonic velocity the parallel to foliation (m/s)Ia = Ip/Inc = (Ip+In)/2 = dry sonic velocity (m/s)w = detonation velocity of explosive (m/s) = density of rock (g/cm3)LT = charging density of explosives (kg of explosives per volume unit of drillhole)

Below is an example of calculation of blastability for a given tunnel where theexplosives were dynamite and ANFO with a dynamite part of 21 %.

Input data:

In = 3991 m/sIp = 4854 m/sIa = Ip/In = 4854/3991 = 1.2162c = (Ip + In)/2 = 4422.5 m/sw = 0.79 2200 + 0.21 3000 = 2368 m/s = 2.72 g/cm3 LT = ANFO %ANFO + dyn %dyn = 0.93 0.79 +1.45 0.21 = 1.0392

SPR 0.736 1.21624422.51000

23684422.5

2.720.45

0.6 0.7

0.4 0.250.2

=

=

10392. [2.2]

Calculated SPR indicates a blastability between medium and good. The rock in theexample is limestone.


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CONTROLLABLE VARIABLESDRILLING- Diameter drill hole- Drilled length- Drill pattern- Incorrect drilling

CHARGING- Type of explosives- Energy of explosives- Charging method- Design of charging- Charged length- Firing pattern

BLASTING- Firing system- Firing interval- Water (partly)

NON-CONTROLLABLE VARIABLESGEOLOGY- Rock parameters- Rock mass joint

OTHER- Incline/Decline- Water (partly)

t = 0 secondsCHARGED ROUND

Typical productionround firesin less than 7seconds

t < 7 secondsRESULT

- Fragmentation- Throw- Muck pile shape- Loadability- Vibrations- Advance per round- Contour- Flyrock- Non-detonating holes- Poor blast result

Figure 2.1 Controllable and non-controllable variables in the blasting process oftunnelling .

Front pageContentsPrefaceChapter 1 Cross section conditionsIntroductionRoad tunnelsRailway tunnelsWater tunnels

Chapter 2 GeologyRock blastability

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2a95 Tunnelling - Blast Design