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 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.
1
PREFACE
The report gives method and data for designing blasting patterns.
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, Jørgen Moger, Pål-Egil Rønn 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
2
1. CROSS SECTION CONDITIONS
Contents
Page 1.0
INTRODUCTION
4
1.1
ROAD TUNNELS 1.11 Cross Section Design 1.12 Necessary Additional Area
5 5 8
1.2
RAILWAY TUNNELS
10
1.3
WATER TUNNELS
11
3
1. CROSS SECTION CONDITIONS
1.0 Introduction
1.0 INTRODUCTION
Tunnels are built for different purposes. This affects the choice of cross section design. 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 two main categories above. Profiles normally used for road and railway tunnels will be introduced in the following.
4
1. CROSS SECTION CONDITIONS
1.1 Road Tunnels
1.1 ROAD TUNNELS 1.11 Cross Section Design
This chapter is based on "Handbok 021 Vegtunneler", Veglaboratoriet, Statens Vegvesen 1992. Based on the density of traffic and tunnel length, tunnels are divided into different classes. This is also the basis on which to decide the number of tunnel tubes, cross section design, distance and design of turning niches, the need for emergency layby and safety equipment. The tunnel cross section must provide enough space to allow specified vehicles to pass each other with sufficient clearance, and space for necessary road equipment and technical installations. The cross section has to be designed in accordance with standards for roads in the open. Tunnels are classified as high cost terrain, and the width of the shoulder should therefore be reduced in the tunnel. The specifications for road tunnels define 8 different tunnel cross sections for drill and 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 road tunnels 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 width and a transition radius in the tunnel crown. With a view to practical tunnelling, the road specifications´ semi-circular cross section seems unfavourable without data controlled drilling. An alternative is to use a cross section with vertical walls and circular crown. Tunnel profiles T4 and T5 are designed in compliance with this principle.
5
1. CROSS SECTION CONDITIONS
1.1 Road Tunnels
Figure 1.1 Design of road tunnels.
6
1. CROSS SECTION CONDITIONS
Figure 1.2
1.1 Road Tunnels
Dimension parameters of road tunnel profiles T8 to T10.
Tunnel Profile
Total Width (m)
Traffic Width (m)
Free Height (m)
Centre Height (m)
Radius R (m)
Theoretical Area (m2)
T4
4.0
3.0
3.0
1.33
2.40
13.63
T5
5.0
4.0
4.6
2.16
3.31
25.62
T8
8.0
6.0
4.6
1.64
4.36
43.78
T8.5
8.5
6.5
4.6
1.62
4.55
46.90
T9
9.0
7.0
4.6
1.53
4.79
50.45
T10
10.0
7.0
4.6
1.05
5.13
52.03
T11
11.0
9.0
4.6
1.53
4.79
63.78
T12
12.0
10.0
4.6
1.53
4.79
70.73
Table 1.1 Dimensions of different tunnel profiles.
7
1. CROSS SECTION CONDITIONS
1.1 Road Tunnels
1.12 Necessary Additional Area
Superstructure, contour and drainage require additional area. Rock protruding within the theoretical profile are not allowed for road tunnels. The conditions for calculation of additional area are - superstructure : - drainage : - contour :
TunnelProfile
0.6 · tunnel width 1.0 m2 increased radius with 0.15 m in walls and crown to make sure to get sufficiently large cross section.
Theoretical Area
Addition Superstructure
Addition Contour
Addition Drainage
Planned Cross Section
(m2)
(m2)
(m2)
(m2)
(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 necessary additional area as different rock support methods are employed.
8
1. CROSS SECTION CONDITIONS
1.1 Road Tunnels
Planned Cross Section with Different Rock Support Methods Tunnel
Theoretical Area
Planned Cross
Shotcrete
Plate Lining
Section without
Profile (m)
Concreted Lining
Rock Support (m2)
R = R 0 + 0.15
R = R 0 + 0.20
R = R 0 + 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.
9
1. CROSS SECTION CONDITIONS
1.2 Railway Tunnels
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.
10
1. CROSS SECTION CONDITIONS
1.3 Water Tunnels
1.3 WATER TUNNELS
For water tunnels, the transmission capacity are decisive of dimension and shape of the cross section. Because of this, one are more free as to adapt the cross section to tunnelling method and rock stability conditions. When rock is not allowed to protrude a planned cross section, there is normally no need of additional area in the contour. Additional area for rock support is normally not necessary.
11
2. GEOLOGY
Contents
Page 2.1
ROCK BLASTABILITY
13
12
2. GEOLOGY
2.1 Rock Blastability
2.1 ROCK BLASTABILITY
The blastability index (SPR) describes the blastability of the rock mass. The rock mass 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 blastability SPR = 0.38
Coarsegrained homogeneous granites, syenites and quartz diorites. For example "Swedish granite".
Medium blastability SPR = 0.47
For example gneiss.
Poor blastability SPR = 0.56
Metamorphic rocks with slated structure, often with high content of mica and a low compressive strength. For example mica schist in the Rana region in Norway.
In this report, the classification of rock blastability is simplified, distinguishing between good and poor blastability. For intermediate values, the curves may be interpolated. The formula for calculating the blastability index is shown in [2.1]. The index is meant to aid the evaluation of blastability and assumes access to laboratory data from a representative sample of the particular rock. The index does not take into consideration the rock mass fracturing and orientation of fractures. 13
2. GEOLOGY
SPR =
2.1 Rock Blastability
0.736 ⋅ I a c 1000
0.4
0.6
⋅ LT
w ⋅ c
0.7
[2.1]
0.25
⋅ρ
0.2
In I p Ia c w
= sonic velocity the normal to foliation (m/s) = sonic velocity the parallel to foliation (m/s) = I p/In = (I p+In)/2 = dry sonic velocity (m/s) = detonation velocity of explosive (m/s) ρ = density of rock (g/cm 3) 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 the explosives were dynamite and ANFO with a dynamite part of 21 %. Input data: In I p Ia c w
= 3991 m/s = 4854 m/s = I p/In = 4854/3991 = 1.2162 = (I p + In)/2 = 4422.5 m/s = 0.79 · 2200 + 0.21 · 3000 = 2368 m/s ρ = 2.72 g/cm3 LT = ρANFO · %ANFO + ρdyn · %dyn = 0.93 · 0.79 +1.45 · 0.21 = 1.0392
SPR
0.7 0.736 ⋅ 1.2162 0.6 ⋅ 10392 .
=
4422.5 1000
0.4
2368 4422.5
⋅
=
0.25
⋅ 2.72
0.45
[2.2]
0.2
Calculated SPR indicates a blastability between medium and good. The rock in the example is limestone. 14
2. GEOLOGY
DRILLING - Diameter drill hole - Drilled length - Drill pattern - Incorrect drilling
2.1 Rock Blastability
CONTROLLABLE VARIABLES CHARGING BLASTING - Type of explosives - Firing system - Energy of explosives - Firing interval - Charging method - Water (partly) - Design of charging - Charged length - Firing pattern NON-CONTROLLABLE VARIABLES GEOLOGY OTHER - Rock parameters - Incline/Decline - Rock mass joint - Water (partly) t = 0 seconds CHARGED ROUND Typical production round fires in less than 7 seconds
t < 7 seconds RESULT - 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 of tunnelling .
15
