community technical workshop...geotechnical considerations (miningone, ben roache) ... rock breakage...

TERRAMIN AUSTRALIA LIMITED

COMMUNITY

TECHNICAL WORKSHOP

Blasting and Geotechnical

8th Dec 2016

TERRAMIN AUSTRALIA LIMITED SLIDE No. 2

Overview

Introduction

Tunnel Construction Cycle (Joe Ranford, Terramin Australia)

Vibration and Blasting Impacts (SAROS Group, Tony Zoitas)

Geotechnical considerations (MiningOne, Ben Roache)

Seismicity

Subsidence

Question and Answer


Introduction

Community Technical Workshops

Ground Water Meeting

Blasting and Geotechnical

Visual amenity

Dust and Noise

Other topics of interest

Core concerns related to blasting/geotech:

Contamination inc. mixing aquifers

Impact to bore water quality

Clogging bore with silt

Clogging bore with cement


Development Cycle

Drill

Blast/Charge

Bog/Muck

Support

Map

Repeat


Cut and Fill Mining

Designed Lift 4


Drilling holes for explosives

Twin boom drills on articulated carrier – Jumbo

~60 holes per face

2.5m – 3.5m depth

45mm diameter

Potential Concerns

Vibration

Fracture propagation

Mitigation Strategies

Proximity

Clay cover – Natural dampening

Geotechnical modelling

Design


Blasting/Charging

Detonator

Sequential firing

Not all at once

Primer

Explosive (4kg/hole)

ANFO

– Ammonium Nitrate

– Diesel (~5%)

AN Emulsion

Perimeter holes

Decoupled

Limits impact on walls

Limits fracture propagation


Rock Breakage

Explosion crushes rock

<100mm

Shock wave cracks rock

𝑉 = 𝐾𝑅

𝑄

−𝐵

Expanding gasses spread

cracks

Area of influence <1m

<1m


Blasting/Charging Cont.

Perimeter holes

Decoupled

Limits impact on walls

Limits fracture propagation

Path of least resistance

Potential Impacts

Ground vibration

Excess damage to rock


Proximity

Blast designs

Monitoring and reporting

Design

Perimeter


Bogging/Mucking and Haulage

10 t/bucket

~200t per cut

Loaded directly into trucks

Stockpiled

Potential Concerns

Surface noise

Dust


Mostly underground

Equipment Selection/modification

Noise barriers (vegetation screens)

Dust suppression


Ground Support

Ground Support

Rock bolts (2.4m-3m)

Cable bolts (6m)

Surface Support

High Tensile Mesh

Fiber reinforced shotcrete

Potential Concerns

Instability/subsidence


Appropriate installation/regular audits

MiningOne

8th December 2016

Discussion of

Proposed Blasting

Activities – Bird in

Hand Project

T Zoitsas

Copyright © Saros (International) Pty Ltd

Introduction

Tony Zoitsas

• B App Sc (Hons) Geology

• Director of Saros (International) Pty Ltd

• Independent specialists in blasting and vibration

• 20 years experience in blasting and vibration consulting

and instrumentation systems

• Member of the AusIMM

• Member of the IQA

• Vice President of the International Society Explosive

Engineers Australian Chapter

15


Project Overview

16


Decline Development

17


Production Blasting

18


Production Blasting

19


Why Blast?

20

Blasting activities are required to facilitate the excavation

of rock in areas where this can not be achieved by

mechanical methods alone

The two phases of the mining operation which require the

utilisation of drill and blast practices include:

• Development of the Decline / Access Drives

• Production of the Ore Body

With the proposed cut and fill method of mining, the

blasting practices will be consistent across both phases of

the development and production activities


Explosive Reaction

Ammonium

Nitrate

3NH4NO3

21

Fuel

CH2

+

Nitrogen

3N2

Carbon

Dioxide

CO2

Water

7H2O

++


Detonation

Direction of burning

22

Detonation Front

Expanding gases

and vapour

Unconsumed

product

Shock waves

Typical VoD - ~4,500 to 6,000 m/s


Scales of Blasting

Blasting activities can be adjusted in

accordance with the specific site requirements

and constraints

23

From small scale

activities in highly

sensitive locations


Scales of Blasting

Blasting activities can be adjusted in

accordance with the specific site requirements

and constraints

24

To large scale mining

operations


Blasting Impacts

25

Ground Vibration

Controls

• Rock type

• Explosive quantity

• Explosive type

• Degree of Confinement

• Initiation timing

Air Overpressure

Controls

• Burden to free face

• Uncharged collar length

• Explosive quantity

• Explosive type

• Rock type

• Initiation timing

• Number of holes


Development Blasting

26



27



28

Design profile

Final profile


Compliance Requirements

With respect to blasting activities, the typical compliance

limits that the Bird in Hand Mine would be required to

comply with are as follows:

• Ground Vibration – Not to exceed 5mm/s for 95% of

occasions, with an upper limit of 10mm/s

• Air Overpressure – Not to exceed 115dBL for 95% of

occasions, with an upper limit of 120dBL

29


Compliance Requirements

• These limits are in line with the Australian Standards

and are adopted by most state regulatory authorities

• Australian blasting compliance limits are amongst the

most stringent in the world

• Both ground vibration and air overpressure limits are

based on human comfort criteria and are well below

damage thresholds

• The issue of air overpressure will only be relevant in the

early stages of the decline development

30


Vibration Impacts

31


Displacement

32

-5

-3

-1

1

3

5

0 0.5 1 1.5 2 2.5 3

Vibration

Vibration

-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.02

0 0.5 1 1.5 2 2.5 3

Displacement

Displacement

14 microns

4.16mm/s


Displacement

Blast induced displacement in perspective:

• Blast – 14 microns

• Thickness of a human hair – ~30 microns

• Sheet of Paper – 100 microns

• Thermal Effects on Residential Dwelling – up to 2000

microns

33


Air Overpressure

34

115dBL @ 20Hz

65dBA


Air Overpressure

35

Audible frequencies


Environmental Effects

Peak overpressure levels from wind

36

115dBL blast limit


Controlled Blasting

Pre-tensioned concrete

• 32,000,000 Lt

• 18 metres high

• 56 metres dia

• 20 metres away

37


Controlled Blasting

Concerns related to:

• Horizontal plane within walls

• Vertical wall joints

• Floor joints

38


Controlled Blasting

Floor joints were the

main concern

39

Joints were keyed in

and grouted

Hydrophyllic

Seal


Monitoring Systems

40


Monitoring Systems

41


Analysis and Interpretation

42


Questions

43

Copyright © Saros (International) Pty Ltd 44

e: [email protected]

www.saros.com.au

BRISBANE

t: +61 7 3367 3400

3/11 Parkview St

MILTON QLD 4064

Contact Saros for more information:

1300 327 347

Bird-in-Hand Mine

Geotechnical Engineering

Introduction

Ben Roache, BAppSci, BEng

Member Engineers Australia

Chartered Engineer, CPEng

Currently the Geotechnical Manager with Mining

One Consultants

About 20 years experience in the mining and civil

industries, covering underground

mining/tunneling, open pit mines and civil

projects

46

Geotechnical Engineering - Summary

1. Ground support design

2. Surface subsidence

3. Earthquakes

4. Mine induced seismicity

47

Key concepts

Mining method

Ground support

Underground void sizes

Filling of the mine

Subsidence types

Seismicity types

48

Ground Support Design

What is ground support?

49


What is ground support?

50


What do we need it to do?

Maintain a safe work place.

Maintain areas accessible for mining activities.

51


How do we design it?

Experience – lessons learnt over time.

Understanding the geology and the expected ground

conditions. Every mine location is different.

Empirical techniques. Another experience based

design tool.

Kinematic wedge assessments.

Numerical tools, such as stress assessment computer

programs that can help understand the how the

ground will react around our underground openings.

52

Surface Subsidence

There are many causes of ground surface

subsidence, but we will most often experience

change in ground surface level due to:

Excavating a hole and then filling it in, but not

compacting the material.

Seasonal fluctuations in groundwater level.

Sinkholes – always in the news, and usually

associated with geology where materials can wash

away over time with excess water.

Mining induced surface subsidence, such as shaft

collapses or large scale collapse.53

Old Workings in the Adelaide Hills

There is a significant amount of old mine

workings in the Adelaide Hills.

Old timers didn’t fill many of their mine workings.

Voids were commonly left open.

Shafts were often filled with rubbish or

unconsolidated fill. Often capped poorly with

wooden sleepers.

Can and do fall in naturally.

54

Subsidence Examples

55

Subsidence Examples

56

Subsidence Examples

57

Mine Related Subsidence – common types

58

Continuous

Mine Related Subsidence – common types

Discontinuous

59

Case Study – Waihi NZ

60

Case Study – Waihi NZ

Mining methods – filling as they mine. Corenso

orebody is using a cut and fill mining method,

and has been demonstrated to not cause failure

to surface.

Numerous technical reports available on the

internet on the technical assessment for this

mine.

Mining One acts as a reviewer for the Hauraki

District Council.

61

Subsidence - What about BIH?

Mining method is important

62

Subsidence - What about BIH?

Extent of void?

63

Underground Mining Related Surface

Subsidence at BIH

Key point – there will be only small voids opened

during mining, and left following mining. Fill is

placed as they mine.

The voids left underground with this mining

method will not be able to propagate to surface.

Failed “material bulks and chokes”.

Some of the decline near the surface, following

mining will be rock filled, to avoid the mistakes

made by historical miners. 64

Natural Earthquakes

We do not expect naturally occurring

earthquakes to impact on the mine, or cause

instability in the mine, or on the surface.

During a 5 year mine life, there is a 10% chance

of exceedance of a 0.0057g earthquake. This is

a minor amount of shaking and not associated

with any damage of structures.

We design the ground support to consider this,

and remain stable.

65

Mining Induced Seismicity

The mine is relatively shallow.

The dimensions of the mine are small.

The blast sizes will be small.

The natural energy in the ground around the

mine is not at an intensity for mine induced

seismicity to commence.

66


Question and Answers

Presentation on website

Questions to:

[email protected]

Hotline (08) 8536 8010

mailto:[email protected]

community technical workshop...geotechnical considerations (miningone, ben roache) ... rock breakage...

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