Record 1972/25

VIBRATION TESTS DURING BLASTING AT THE PRpPOSEDBELCONNEN 54-INCH TRUNK SEWER CONSTRUCTION SITE

A.C.T. 1972

by

9B.11. Dolan

COINIVIOAMEALTH OF AUSTRALIA

DEPARTMENT OFNMONA DEVE_OPMENEMAEZ--U CDF 9ULEiNLAHOeumnea eaDwau/a -up) elECDPHM_CO

The information contained in this report has been obtained by the Department of National Developmentas part of the policy of the Commonwealth Government to assist in the exploration and development ofmineral resources. It may not be published in any form or used in a company prospectus or statementwithout the permission in writing of the Director, Bureau of Mineral Resources, Geology & Geophysics.

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Record 1972/25 .

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VIBRATION TESTS DURING BLASTING AT THE PRproSED ELCONNEN 54~INCH TRUNK SEWER CONSTRUCTION SIT

A.C~T. 1972. "

,·by

The information ,contained in this report has been obtained by the Department of National Development as part of the ,policy of t!'te CommOnwealth GoVernment to assist in the exploration and development of minera'i resources. It ,may not be piJblished in any form or used in a company prospectus or statement without the permission in writing of the Director. Bureau of Mineral Resources. Geology & Geophysics.

I I I I I I I I I I I I I I I I I I I I

Record 1972/25

VIBRATION TESTS DURING BLASTING AT THE PROPOSED BELCONNEN 54-INCH TRUNK SEWER CONSTRUCTION SITE,

A.C.T. 1972

by

B.H. Dolan

I I I I I I I I I I I I I I I I I I I I

CONTENTS

SUMMARY

1. INTRODUCTION

2. GEOLOGY

3. METHODS AND EQUIPMENT -

4. RESULTS

5. CONCLUSIONS AND RECOMMENDATIONS

6. REFERENCES

ILLUSTRATIONS

Plate 1. Plan and cross-section.

Plate 2. Plots of ground motion versus distance.

Page

1

-1

- 1

3

4

4

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SUMMARY

Measurements of the vibration due to blasting at the si~e of the proposed sewer construction were taken to determine the effect on· a nearby electricity pylon. The predicted level of vibration due to blasting 40 feet from the tower is unlikely to cause damage according to the United States Bureau of Mines recommendations. Short delay periods may cause larger levels of vibrations.

I I I I I I I I ·1 I I I I I I I I I I I

1. INTRODUCTION

At the request of the Commonwealth Department of Works the Bureau of Mineral Resources, Geology & Geophysics has made vibration measurements on the conStruction site of the Belconnen 54-inch trunk Sewer. Excavation for the proposed pipeline trench comes to within 40 feet of the nearest leg of an electricity' tower . It was requested that measurements of the ground vibration due to blasting be measured at the tower and that determinations of the safe levels for blasting be made. At the time of writing, work has ceased and the Department of Works has requested that BMR make further measurements when the work continues.

2. GEOLOGY

. Bedrock in the test area consists of Upper Silurian to Devonian rhyolite tuff of the Deakin Volcanics. This is hard and well consolidated . . There is generally a good cover of weathered ' material, and few outcrops.

3~ METHODS AND EQUIPMENT

The equipment consisted of a Sprengnether Engineering . Seismograph Model VS-.1200, S.I.E. 24-channel seismograph, four Hall-Seers HS-1 3-D geophones and four Hall ... Sears HS-JLP 3-D geophones. .

The Sprengnether seismograph is a calibrated instrument with a special 3 ... component seismometer, and it was used to measure the ground motion at the base of the tower. The 3-D geophones were spaced between the tower and the blast in order to measure the rate of attenuation of the wave motion through the ground. One 3-D geophone was fixed t9 a leg of the tower five feet above ground. The velocity of the ground motion due to the shock wave was measured by the seismometer and the geophones. Two of the 3-D geophones were buried with the seismometer. This served to calibrate the geophones.

According to Nicholls, Johnson, & Duvall (1971) the peak velocity of each component of ground motion can be related to distance and charge weight per delay interval by an equation of the form: .

Where v =

Ii =

D =

W =

-2-

D B v = H(W~)

velocity of ground motion (in. sec -1)

intercept at ~ = 1.0

shot to gauge distance (ft)

charge weight (lb)

B = slope or decay exponent.

Hand B are constants that have to be determined for each site and possibly for each shooting procedure.

The test blast consisted of three holes each filled with 9 lb of ammonium nitrate and diesoleum (ANFO) denotated by half a plug of gelignite. Delays of 50 to 60 ms were used. The geophone spacing was 25 feet and the distance from the first shot-hole to the nearest leg of the tower was 153.7 feet.

Safe vibration levels

On the basis of a statistical study by the U.S. Bureau of Mines (Nicholls et al., 1971) and the recommendations of other investigators (Edwards & Northwood, 1960; Langefors, Kihlstrom, & Westerberg, 1958) damage to structures caused by ground vibration is more closely associated with velocity of the ground motion than with either displacement or acceleration. _The most widely accepted safe blasting level for buildings is 2.0 in. sec for anyone of the three components of ground motion. The average values that cause major and minor damage are shown below.

Peak Ground M<?,tjon Velocity (in sec )

5.4

7.6

Damage Level

Minor

Major

Description

Fine plaster cracks, opening of old cracks.

Fall of ~laster, serious cracking.

All of the major damage recorded by the U.S. Bureau of Mines and -1 94 percent of the minor damage occurred at levels greater than 2.0 in. sec .

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In the Standards Association of Australia (S.A.A.) Expiosives Code, section 10.7.4 deals with ground vibrations when blasting in built up areas. It is written that the maximum allowable resulta.!ll of the three components of ground vibration shall not exceed 0.75 in. sec . It notes that the recommended limit is a compromise between safety and comfort but is heavily biased towards comfort. The recommendation gives a factor of safety of about 6 for light damage.

4. RESULTS

The peak velocity of ground moti~r recorded from the test blast at the base of the tower was 0.15 in. sec (peak displacement for f = 100 Hz is 0.00002 in).

The peak velocity of ground motions recorded by each geophone is plotted against the shot-to-geophone distance for the first shot (Plate 2, fig. 1) on a log-log scale. This is the distance in a straight line to the shot, not a distance measured along the ground.

The average ground motion velocity is related to the distance and charge size by the equation.

D -1.5 %\ . -1 v = 4.6 (W~ m. sec

The constantsH and B were determined from the measurements of ground motion velocity. Plotted in Plate 2, fig. 2. D is measured in feet andW in pounds or"explosive (ammonium nitrate and diesoleum (ANFO».

The linear regress~£n line (the dark line) through the data points passes through 1.0 in. sec at 40 feet. The error involved, principally in mc~asuring the trace deflection and because of the variations in reponse between geophones, means ~qat the peak velocity of ground motion at 40 feet could reach 1.8 in. sec . ..

. It ~as ob~1rved also that a high. reading of peak.veloCityof ground motion (4 m. sec at 25 feet) was obtamed from the third shot of the 3-s~£tsequence. Interpolated to 40 feet this represents a reading of 2 in. sec . It is considered that this may be due to addition of vibrations from the preceding shots, a phenomenon that has been observed in previous investigations elsewhere (Davis, 1970) .

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5. CONCLUSIONS AND RECOMMENDATIONS

Using the present blasting procedure the ground vibration at 4~ feet from the shot will be unlikely to cause damage to a structure according U.S. Bureau of Mines recommendation, but short delay periods between shots may cause an additive effect that may be damaging. Therefore it is recommended that the delay period be increased to twice the present delay and that further measurements of the ground vibration be made.

6. REFERENCES

DAVIS, J. V., 1970 - Ground vibrations from turmel blasting. Tunnels and Tunnelling, May 1970. .

EDWARDS, A.T., & NORTHWOOD, T.D., 1960 - 'Experimental studies on the effect of blasting on structures. The Engineer., Vol. 210, Sept. 30, 1960.

LANGEFORS, V.L.F., KIHLSTROM, B., & WESTERBERG, H., 1958 -Ground vibrations in Blasting. Water · Power, · February 1958.

MITCHELL, C., GERDES, L., WALRAVEN, L., & HENDERSON, G., 1970 - Geology of Belconnen Sheet G4A. Bur. Miner. Resour. Aust. Drawing No. 155/ A16.

NICHOLLS, H.R., JOHNSON, C.F., & DUVALL, W.!., 1971 - Blasting vibrations and their effects on structures. Bull. U.S. Bur. Min. G56.

STANDARDS ASSOCIATION OF. AUSTRALIA, 1967 .:. Standard CA23-1967 Australian standard rules for the storage and handling of explosives (known as the S.A.A. Explosives Code). Sydney.

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I I I I I I I I I I I I I I I I

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PLATE

1 0 1 2 · 3 4 KILOMETRES ~1~1'~I~I~r~I--~II~

o I 2 3MILES

LOCALITY MAP

PLAN

SPRENG NETHER 0 L-~-. -? ~\6fJ

rRAN51t11SSION roweR

£/~~O f i on Con/ou,s,ff F"I

CROSS - SECTION

·rORTH LEG . F" TOWER

Elevation 1851 FEET . G8 G7G6 G5 G4 1849 FEET SHOT -.. HOLE I.- · Ir--.--....L.--_J...·: ___ .L.-__ -.L.-.,.-___ ..LI __ ~

14 _ -"G3 .;. SHOT X-.. ----------- 0 ".. ~~

SPRENGNETHER

10 0 10 20 METRES i~il~i~li~~il~I~I~1 +'-------.LI-rr-----~I--~I

40 0 . 40 SOFEET

BELCONNEN 54-INCH TRUNK SEWER CONSTRUCTION

LOCAtiON: - PLAN . AND · CROSS SECTION

7lJ occ~tTipony Record No. 1972 ·

I I I I I I I I I I I I I I I I I I I I

400 -III , IJ) ...

3-00 :r u ~

2 -00 I t 11

1-50 Q 2 a IE

1·00 u

0·80 ~ .. ~

0 -60 u 9

o·So ... :>

0 ·30

020

015

PLATE 2

PLOT OF PEAK GROUND MOTION VERSUS

DISTANCE FROM THE N~ I SHOT OF THE TEST BLAST

KE Y ,

• Data -from lSI SHeH

• Data from "d SHOT

I :i: DEVIATION

Fig. I

----_~.. DISTANC£ FRO.. Bl.ST IN FEET

0 '1 0 L--_---1---'---L--'---'-1-_...l.----1 __ .L-_~. -'---'--_.l--_---1_---1_-'------lo-1-""""----"' ....... ~__'___"____'__~_'___..Lf

10

400 --

300

200

I !IO

100

0-80

0 .60

0·50

0 -40

0 -30

0·20

015 _.

0 -10

1-0

'" , -III UJ X U

~ -z Q .... 0 ~

0

~ 0 Q: u

... 0

>-~ .., 0 J

'" :>

" .. ... CI.

•

1' 5 2 -0 . ' ·0 4{) 5 ·0 7 ·0 10 ·0 15·0 20·0 30·0 4O-o!lCH) 70·0 1000 I$()O 2OO{) 300'0

PLOT OF PEAK GROUND MOTION VELOCITY VERSUS - I '

SCALED DISTANCE· (D/WT)

Fig. 2

•

• I I -- --.... __ SCALED DISTANCE D/w2 (rr/LB~)

i ; , ~

· : : 1 I:

· i !

• i­

i

_~ __ ~ __ L-~_L __ ~ __ ~ __ ~ __ L_ __ ~~~~_~ __ ~~~I-· ~F--~~._q

1·5 20 3 ·0 4 -0 50 7-0 10{) 15 -0 20 -0 30-0 4O'O$()'0 70-0 100-0 150·0 200-0 300·0

To accompony Record No_ 1972/25 IS5/B5 - 132A