Measurement of underwater blast waves on Daniel Johnson Dam

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Measurement of underwater blast waves on Daniel Johnson Dam

Rainer, J. H.

NATIONAL RESEARCH COUNCIL OF CANADA

DIVISION OF BUILDING RESEARCH

DBR INTERNAL REPORT NO.

472

Measurement of Underwater Blast Waves

on Daniel Johnson

Dam

by

J.

H. Rainer

A N A L Y Z E D

Chockadby:

A.C.C.Warnock

~ p p m d b y :

L.W.Gold

Das:

April 1982

h J W d fa:

~ ~ d r o - ~ u g b e c

WEASlIRRMENl'

OF UNDERWATER

BLAST

WAVES

ON

DANIEL

JOHNSON

Dm

by J.H. R a i n e r

I. INTRODUCTION

The measurements d e s c r i b e d h e r e i n were performed i n November 1981 a s p a r t of a n i n v e s t i g a t i o n of t h e e f f e c t s o f f u t u r e b l a s t i n g work on t h e Daniel Johnson Dam on t h e Manicouagan R i v e r , Quebec i n c o n n e c t i o n w i t h t h e A d d i t i o n a l Power p r o j e c t ( " P u i s s a n c e a d d i t i o n n e l l e " ) a t Manicouagan 5. ( F i g u r e 1 shows a view of t h e dam.)

The work d e s c r i b e d was planned i n c o n s u l t a t i o n w i t h s t a f f of Hydro-Qu6bec and w i t h t h e Board of C o n s u l t a n t s f o r t h e A d d i t i o n a l Power p r o j e c t . The measurements were c a r r i e d o u t w i t h t h e a c t i v e

p a r t i c i p a t i o n of members of t h e s t a f f ?f Hydro-Qu6bec under t h e d i r e c t i o n of D r . P a u l LeComte, Chef d l E t u d e , MBcanique d e s Roches, GBologie & G6o technique.

The purposes of t h e tests were:

1 ) t o measure t h e b l a s t waves a r r i v i n g a t t h e dam from e x p l o s i o n s o u r c e s i n t h e v i c i n i t y of f u t u r e rock b l a s t s i n o r n e a r t h e r e s e r v o i r ; 2) t o i n v e s t i g a t e t h e shadowing e f f e c t a t t h e dam f o r b l a s t s o r i g i n a t i n g a t v a r i o u s l o c a t i o n s n e a r t h e f u t u r e w a t e r i n t a k e channel ; 3) t o d e t e r m i n e t h e s u i t a b i l i t y of measurement i n s t r u m e n t a t i o n f o r f u t u r e w a t e r and rock t e s t b l a s t s and t h e f i n a l e x c a v a t i o n b l a s t ;

4) t o measure t h e response of t h e dam t o v a r i o u s w a t e r b l a s t s and ground t r a n s m i t t e d b l a s t waves.

This r e p o r t i s concerned mainly w i t h t h e f i r s t t h r e e i t e m s ; a s p e c t s of t h e r e s p o n s e of t h e dam w i l l be d e a l t w i t h i n a n o t h e r , l a t e r , r e p o r t .

11. EXPERIMENTAL

Procedure

1. Hydrophones: Four hydrophones manufactured by K i s t l e r I n s t r u m e n t C o r p o r a t i o n of Amherst, N.Y., model #202A5/623M123, w i t h a maximum range of 400 p s i (2756 kPa), were employed. C a l i b r a t i o n c o n s t a n t s f o r each i n s t r u m e n t were s u p p l i e d by t h e m a n u f a c t u r e r , a s shown i n Table 1 (A and B). These were checked i n t h e l a b o r a t o r y by

s u b j e c t i n g t h e t r a n s d u c e r s t o a known a c o u s t i c a l n o i s e s o u r c e i n a n a n e c h o i c chamber. Values s o o b t a i n e d were w i t h i n 10% of t h e

m a n u f a c t u r e r ' s v a l u e s . A s t h i s r e p r e s e n t e d a p p r o x i m a t e l y t h e p r e c i s i o n of t h e a c o u s t i c a l measurements, t h e c a l i b r a t i o n c o n s t a n t s from t h e m a n u f a c t u r e r were t a k e n t o be c o r r e c t .

A t t h e dam s i t e , e a c h hydrophone was mounted on a s t e e l H-

s e c t i o n a s shown i n F i g . 2. The s e n s i t i v e e l e m e n t was 7.6 c m (3.0 i n . ) from t h e f a c e of t h e dam. The H-section was lowered i n t o t h e w a t e r by means of two r o p e s f o r m i n g a "V" and g u i d e d a l o n g t h e s l o p i n g f a c e of t h e a r c h t o t h e a p p r o p r i a t e w a t e r d e p t h . The s i g n a l c a b l e from e a c h hydrophone was b r o u g h t t o a m o b i l e l a b o r a t o r y parked a t t h e t o p of t h e dam and passed t h r o u g h t h e power s u p p l y t o a seven-channel "Racal" FM

t a p e r e c o r d e r . I n a d d i t i o n t o t h e f o u r hydrophones, t h e 50 Hz low-pass f i l t e r e d a c c e l e r a t i o n s i g n a l from s t a t i o n C7, e l e v a t i o n 1168 f t ( s e e F i g . 3 ) , and a 100 m s t i m i n g p u l s e t r i g g e r e d manually a t t h e end of t h e b l a s t count-down were r e c o r d e d ; one c h a n n e l was l e f t empty f o r n o i s e r e d u c t i o n on p l a y b a c k . Recording s p e e d of 15 i n . / s p r o v i d e d a f r e q u e n c y c u t - o f f of 5000 Hz. A l l r e c o r d e r g a i n s f o r t h e w a t e r b l a s t s were set a t 1 , w i t h t h e e x c e p t i o n of Event 4 d u r i n g which t h e y were a t 0.5 f o r t h e f o u r hydrophones. These c o n s t a n t s e t t i n g s w e r e a d o p t e d i n o r d e r t o minimize t h e p o s s i b i l i t y of o v e r l o a d i n g t h e r a n g e of t h e t a p e r e c o r d e r , even though t h i s meant a p o t e n t i a l l o s s of d e f i n i t i o n of some very low s i g n a l s

.

Two l a y o u t s of hydrophones were used a s i s shown i n Fig. 3. C o n f i g u r a t i o n A c o n s i s t s of hydrophones A1

,

A2, A3 and A4, c o r r e s p o n d i n g t o l o c a t i o n s V4-5, V6-7, V7-8 and V9-10, r e s p e c t i v e l y , a t 15.2 m (50 f t ) w a t e r depth. C o n f i g u r a t i o n B i s d e s i g n a t e d by B1, B2, B3 and B4 on a r c h V7-8. B1 a t 61 m (20 f t ) d e p t h and B3 (same as A3) a t 15.2 m (50 f t ) w a t e r d e p t h a t t h e c e n t e r of t h e a r c h , whereas B2 i s n e a r C7 and B4 i s n e a r C8, a l s o a t 15.2 m (50 f t ) d e p t h .

2. E x p l o s i v e Charges: The p o s i t i o n s of t h e c h a r g e s a r e shown i n F i g . 3 and a r e d e s i g n a t e d by L o c a t i o n s 1 t o 7 around t h e f u t u r e w a t e r i n t a k e c h a n n e l . L o c a t i o n s 1 t o 5 a r e a t 15.2 m (50 f t ) w a t e r d e p t h and

rest a g a i n s t t h e r o c k . L o c a t i o n - 6 i s a l s o a g a i n s t t h e r o c k a t 31.5 m (115 f t ) d e p t h i n l i n e w i t h t h e a x i s of t h e f u t u r e i n t a k e c h a n n e l . L o c a t i o n 7 r e p r e s e n t s t h e suspended c h a r g e d e t o n a t e d a t 15.2

m

(50 f t ) w a t e r d e p t h , l o c a t e d a few hundred metres from t h e o t h e r b l a s t

l o c a t i o n s , a p p r o x i m a t e l y p a r a l l e l t o t h e l o n g a ' x i s of t h e dam.

A l l b l a s t s c o n s i s t e d of a 2 kg (4.4 l b ) s t i c k of dynamite; t h e count-down of t h e b l a s t e r was t r a n s m i t t e d by p o r t a b l e r a d i o t o t h e b l a s t c o o r d i n a t o r n e a r t h e mobile l a b o r a t o r y . From t h e r e , t h e count- down was p a s s e d t o t h e o t h e r r e c o r d i n g s t a t i o n s t h r o u g h o u t t h e dam by e x i s t i n g t e l e p h o n e network. The s e q u e n c e of e v e n t s and t h e i r

c h a r a c t e r i s t i c s a r e summarized i n T a b l e 2.

111. ANALYSIS

The r e c o r d e r s i g n a l s were played back a t a speed r e d u c t i o n of 1 6 t i m e s and d i s p l a y e d o n a g a l v a n o m e t e r r e c o r d e r . Records of some

e v e n t s showing t h e f o u r hydrophones and t h e a c c e l e r o m e t e r a t C7, 1168 f t a r e shown i n F i g s . 4 t o 9. I n o r d e r t o d e f i n e t h e i n i t i a l p u l s e b e t t e r , m a g n i f i e d p l o t s were produced w i t h t h e a i d of t h e d i g i t a l d i s p l a y of a F a s t F o u r i e r Transform (FFT) a n a l y z e r . With a t a p e speed-up of f o u r

t i m e s and a n a n a l y z e r f r e q u e n c y r a n g e of 1600 Hz, t h i s r e s u l t e d i n a n e f f e c t i v e low-pass f i l t e r of 6400 Hz. The r e s u l t i n g t i m e h i s t o r i e s f o r s e l e c t e d e v e n t s a r e shown i n F i g s . 10 t o 14. Peak p o s i t i v e and n e g a t i v e a m p l i t u d e s were d e t e r m i n e d from t h e c u r s o r of t h e FFT a n a l y z e r d i s p l a y a n d a r e t a b u l a t e d i n T a b l e s 1 (A and B ) . The f o r m e r p r e s e n t s t h e r e s u l t s i n ST. u n i t s , t h e l a t t e r i n i m p e r i a l u n i t s .

I V . RESULTS

1. P o s i t i v e and N e g a t i v e Wave F r o n t : The t i m e v a r i a t i o n s of t h e b l a s t s i g n a l s a t t h e dam ( F i g s . 4 t o 14) show a n i n i t i a l p o s i t i v e p u l s e f o l l o w e d v e r y s h o r t l y t h e r e a f t e r by a n e g a t i v e p u l s e u s u a l l y of s i m i l a r s h a p e and magnitude. T h i s n e g a t i v e p u l s e r e s u l t s from a

r e f l e c t i o n of t h e o r i g i n a l p u l s e o f f t h e f r e e w a t e r s u r f a c e a s d e p i c t e d i n F i g . 15. The c o n s t r u c t i o n of t h i s r e f l e c t i o n i s a i d e d by t h e

d e f i n i t i o n of a v i r t u a l image of t h e s o u r c e p o i n t a s shown i n F i g . 15; a s t r a i g h t l i n e between t h e image p o i n t and t h e p o i n t of r e c e p t i o n d e f i n e s

t h e p o i n t of r e f l e c t i o n . The d i f f e r e n c e i n t r a v e l t i m e between t h e d i r e c t and r e f l e c t e d p a t h a c c o u n t s f o r t h e time d e l a y between t h e p o s i t i v e and n e g a t i v e p u l s e .

T a b l e 3 shows a comparison between t h e measured and c a l c u l a t e d d e l a y s f o r t h e two p u l s e s . The c a l c u l a t i o n employed d i s t a n c e s measured from s i t e p l a n s and a r e t h e r e f o r e somewhat a p p r o x i m a t e . E l e m e n t a r y geometry was used t o d e t e r m i n e t r a v e l p a t h d i f f e r e n c e s . A c o u s t i c wave v e l o c i t y i n w a t e r was t a k e n t o be 1435 m / s (4708 f t / s ) a t 9°C. The measured t i m e d i f f e r e n c e s a r e t h e times between t h e p o s i t i v e and t h e n e g a t i v e peaks a s i n d i c a t e d i n F i g s . 10 t o 14. For Event 12, t h e suspended c h a r g e , t h e t h e o r e t i c a l time d i f f e r e n c e i s n o t c a l c u l a t e d s i n c e t h e l o c a t i o n of t h e d e t o n a t i o n i s n o t a c c u r a t e l y known. T a b l e 3

shows t h a t t h e c a l c u l a t e d and measured d i f f e r e n c e s i n t r a v e l t i m e s a g r e e r e a s o n a b l y w e l l f o r E v e n t s 4 t o 8 , conf i r m i n g t h e r e f l e c t i o n model

d e s c r i b e d above. The agreement i s somewhat l e s s s a t i s f a c t o r y f o r E v e n t s 11 and 15.

2. Amplitudes of P o s i t i v e and N e g a t i v e Peaks: T a b l e 1 shows t h a t f o r E v e n t s 4 t o 7 ( L o c a t i o n s 1 and 2) r e a s o n a b l y c l o s e agreement e x i s t s i n a m p l i t u d e s of p o s i t i v e and n e g a t i v e p e a k s f o r a l l f o u r hydrophone l o c a t i o n s . A s n o s u b s t a n t i a l d i f f e r e n c e s a r e e v i d e n t among t h e s e f o u r e v e n t s , t h e i r peak p r e s s u r e v a l u e s have b e e n a v e r a g e d , d e s i g n a t e d a s "Average of 4 , 5 , 6 , 7" i n T a b l e 1. T h e s e r e s u l t s show t h a t t h e n e g a t i v e peaks a r e of s i m i l a r a m p l i t u d e t o t h e p o s i t i v e o n e s ; t h i s would b e e x p e c t e d from t h e r e f l e c t i o n model d e s c r i b e d above.

3. Comparison Between Charges A g a i n s t Rock and Suspended Charge: For p u l s e s h a p e s i n F i g s . 10 and 13 and a m p l i t u d e s of p o s i t i v e and n e g a t i v e p u l s e i n T a b l e 1, a c l o s e c o r r e s p o n d e n c e i s s e e n between c h a r g e s a g a i n s t t h e r o c k , E v e n t s 4 t o 7 , and t h e suspended one,

d i f f e r e n t d i s t a n c e s a r e i n v o l v e d , b u t i n e s s e n c e t h e y a r e comparable i n c h a r a c t e r .

For c h a r g e s d e t o n a t e d a g a i n s t t h e s h o r e , t h e p r e s s u r e s emanating from t h e c h a r g e a r e i n c r e a s e d d u e t o r e f l e c t i o n s from t h e rock. For a p e r f e c t r e f l e c t o r , d o u b l i n g of t h e p r e s s u r e would o c c u r a s compared t o a f r e e l y suspended charge. However, changes i n impedance from w a t e r w i t h rock change t h i s somewhat. For a n o r m 1 a n g l e of

i n c i d e n c e , t h e r a t i o of r e f l e c t e d t o t h e i n c i d e n t a m p l i t u d e s , &/A1 i s g i v e n by Kolsky (1963) : where: p = d e n s i t y ; c = bulk v e l o c i t y ; w = s u b s c r i p t f o r w a t e r ; r = s u b s c r i p t f o r rock.

The t r a n s m i t t e d wave r a t i o A ~ / A I i s g i v e n by:

3 3

For p r a 3000 kg/m

,

c r = 4000 m / s , pw = 1000 kg/m

,

= 1435 m / s , t h e

r e f l e c t e d wave r a t i o A2/A1= 0.80. I t i s p o s s i b l e t h a t n o n l i n e a r b e h a v i o u r of t h e rock immediately a d j a c e n t t o t h e d e t o n a t i o n would r e s u l t i n a f u r t h e r r e d u c t i o n of t h i s r e f l e c t i o n c o e f f i c i e n t . A d d i t i o n a l r e f l e c t i o n s from more d i s t a n t c o n t o u r f e a t u r e s of t h e r e s e r v o i r and i t s s h o r e l i n e c a n a l s o b e e x p e c t e d , b u t t h e s e w i l l n o t a f f e c t t h e wave f r o n t s i n c e t h e t r a v e l t i m e t o t h e dam i s l o n g e r . Some i d e n t i f i a b l e a r r i v a l s of r e f l e c t e d p u l s e s h a v i n g a c o n s t a n t t i m e d e l a y a t e a c h of t h e f o u r hydrophone s t a t i o n s f o r E v e n t s 4 , 12 and 1 5 a r e shown i n F i g s . 4 , 8 and 9 , r e s p e c t i v e l y , where some a r e i n d i c a t e d by arrows b e s i d e t h e t r a c e s . The peak a m p l i t u d e s of t h e s e p u l s e s is from 0.5 t o 0.2 t i m e s t h e i n i t i a l peak p r e s s u r e s ; u n f o r t u n a t e l y , i t was n o t p o s s i b l e t o t r a c e t h e t r a v e l p a t h s of t h e s e s e c o n d a r y p u l s e s . An e x a m i n a t i o n of t h e t i m e h i s t o r y of p r e s s u r e s , F i g s . 4 t o 9 , shows t h a t t h e i n i t i a l p o s i t i v e and n e g a t i v e i m p u l s e i s f o l l o w e d by a lower l e v e l d i s t u r b a n c e of random c h a r a c t e r , n o t u n l i k e t h a t of a n e a r t h q u a k e , l a s t i n g from 100 t o 150 m s . F o r t h e p a r t i a l l y s h i e l d e d c h a r g e s , E v e n t s 8 and 11, low f r e q u e n c y components of 20 Hz and l e s s can be d i s c e r n e d i n F i g s .

6

and 7 e s p e c i a l l y f o r Hydrophone A l . These low f r e q u e n c y components a r e , however, of small magnitude, l e s s t h a n 7 kPa ( 1 p s i ) peak t o peak. 4. S h i e l d i n g E f f e c t of T e r r a i n : S h i e l d i n g r e f e r s t o a r e d u c t i o n of p r e s s u r e s when a n o b s t r u c t i o n i s n e a r t o o r d i r e c t l y i n t e r s e c t s t h e s t r a i g h t l i n e j o i n i n g t h e s o u r c e and p o i n t o f o b s e r v a t i o n . Because t h e p r e c i s e d e t a i l s of t h e r o c k c o n t o u r s n e x t t o t h e b l a s t l o c a t i o n a r e not known, a q u a n t i t a t i v e p r e d i c t i o n of t h e

s h i e l d i n g e f f e c t i s n o t f e a s i b l e . However, q u a l i t a t i v e l y , t h e

phenomenon i s w e l l i l l u s t r a t e d by t h e r e s u l t s o b t a i n e d . A s e x p e c t e d , t h e peak p r e s s u r e s i n T a b l e 1 f o r E v e n t s 4 t o 7 a t L o c a t i o n s 1 and 2 ( s e e F i g . 3) show no e f f e c t of s h i e l d i n g . Event 8 a t L o c a t i o n 3 r e p r e s e n t s a p p r o x i m a t e l y a t a n g e n t i a l l i n e of s i g h t from t h e r o c k t o p o r t i o n s of t h e dam and c l e a r l y d i s p l a y s a d e c r e a s e i n peak p r e s s u r e of t h e c l o s e s t hydrophone, A l , from a b o u t 15 p s i ( 1 0 3 kPa) t o 1.8 p s i (12 k P a ) , and a lesser d e c r e a s e f o r t h e r e m a i n i n g t h r e e hydrophones. T h i s i s i l l u s t r a t e d by t h e f i g u r e s i n T a b l e 1 and t h e p l o t i n Fig. 16. The n a t u r e of t h e p r e s s u r e wave a l s o changes. The i n i t i a l peak p o s i t i v e and n e g a t i v e p r e s s u r e s a r e n o t t h e l a r g e s t anymore, b u t s u b s e q u e n t

p u l s e s exceed t h e f i r s t o n e s . T h i s i s a l s o t h e c a s e i n Event 11

a l t h o u g h , b e c a u s e of c h a n g i n g l o c a t i o n s , o t h e r v a r i a b l e s a r e i n t r o d u c e d which may a f f e c t t h e time h i s t o r y of t h e p r e s s u r e s . F i n a l l y , f o r

E v e n t s 9 and 10, which a r e l o c a t e d away from t h e d i r e c t l i n e of s i g h t of t h e hydrophones, t h e s h i e l d i n g i s a l m o s t t o t a l and less t h a n 1% of t h e p r e v i o u s d i r e c t p r e s s u r e s i s r e c o r d e d .

The s h i e l d i n g e f f e c t is i l l u s t r a t e d i n F i g . 16 which shows peak p r e s s u r e s a t t h e f o u r hydrophone l o c a t i o n s f o r t h e v a r i o u s e v e n t s . For Event 8 t h e l a r g e s t d e c r e a s e i n p r e s s u r e a s compared w i t h t h e a v e r a g e of E v e n t s 4 t o 7 i s s e e n t o o c c u r a t Hydrophone A1 n e a r e s t t h e b l a s t . The d e c r e a s e s become p r o g r e s s i v e l y l e s s f o r t h e o t h e r hydrophones i n t h e e a s t e r l y d i r e c t i o n of t h e dam. T h i s d e m o n s t r a t e s t h a t a t t h e l o c a t i o n s t e s t e d , s h i e l d i n g d o e s n o t produce a s h a r p d e m a r c a t i o n between d i r e c t b l a s t e f f e c t s and t h e s h i e l d e d r e g i o n s , b u t r e s u l t s i n a g r a d u a l r e d u c t i o n i n p r e s s u r e o v e r a wide t a r g e t a r e a . The peak p r e s s u r e s f o r Event 11 a t L o c a t i o n 6 a r e s e e n t o b e e v e n lower t h a n t h o s e coming from t h e s h a l l o w e r L o c a t i o n 3 , most p r o b a b l y b e c a u s e of g r e a t e r t o p o g r a p h i c a l s h i e l d i n g r a t h e r t h a n a s a d i r e c t r e s u l t of t h e d e e p e r w a t e r d e p t h . T h e o r e t i c a l p r e d i c t i o n of t h e e f f e c t of s h i e l d i n g f o r p r e s s u r e wave p r o p a g a t i o n i n w a t e r f o l l o w s t h e same p r i n c i p l e s a s t h o s e u s e d i n p r o p a g a t i o n of sound i n a i r . The q u a n t i t a t i v e e s t i m a t i o n of s h i e l d i n g d u e t o a b a r r i e r c a n be a c h i e v e d by means of t h e d i a g r a m i n Fig. 17 ( t a k e n from Delany, 1972). I t s h o u l d be n o t e d t h a t t h e h i g h e r f r e q u e n c y components a r e s u b j e c t t o g r e a t e r d i f f r a c t i o n l o s s e s a s governed by t h e p a r a m e t e r 2d/X, and t h a t f o r a g r a z i n g b a r r i e r a n g l e , i.e., 2d/X = 0 , t h e s i g n a l r e d u c t i o n amounts t o 5 dB, o r 0.56 t i m e s what t h e p r e s s u r e would have been w i t h o u t t h e b a r r i e r .

5. T h e o r e t i c a l C a l c u l a t i o n s of B l a s t P r e s s u r e : F o l l o w i n g t h e e m p i r i c a l r e l a t i o n s h i p p r e s e n t e d by Henrych (1979) and n e g l e c t i n g h i g h e r o r d e r t e r m s , t h e peak o v e r p r e s s u r e Ap of a suspended c h a r g e is:

where: R = R / w ' / ~ ( ~ n - k ~ l / ~ ) ; R = r a d i a l d i s t a n c e (m);

w

= t r i n i t r o t o l u e n e (TNT) e q u i v a l e n t c h a r g e mass ( k g ) ; kp = k i l o g r a m f o r c e .

C o l e (1948) p r e s e n t s a s l i g h t l y d i f f e r e n t r e l a t i o n s h i p :

where: W = w e i g h t , l b of TNT; R = d i s t a n c e , f t .

These r e l a t i o n s h i p s f o l l o w c l o s e l y t h e g r a p h s p r e s e n t e d by Langefors and K i h l s t r ' k (1963) which i n t u r n a r e a c o l l e c t i o n of d a t a m o s t l y by

Enhamre (1954). Applying t h e d i s t a n c e s from t h e s o u r c e t o t h e hydrophones g i v e n i n T a b l e 3 , and a c h a r g e mass of 2 kg, t h e peak

p r e s s u r e s a s c a l c u l a t e d by b o t h r e l a t i o n s h i p s a r e t a b u l a t e d i n Table

4.

Note t h a t i n a l l c a s e s t h e l i m i t of

R

<

50 i n Eq. ( 3 ) i s exceeded. No range l i m i t a t i o n s a r e g i v e n w i t h Eq. ( 4 ) . To a c c o u n t f o r t h e r e f l e c t i o n a t t h e dam s u r f a c e , Eqs. ( 1 ) and ( 2 ) can a l s o be u t i l i z e d . Taking f o r c o n c r e t e p, = 2500 kg/m3, and cc = 3000 m / s , t h e r e f l e c t i o n r a t i o of A2/A1 = 0.67 i . e . , 67% of t h e incoming wave i s r e f l e c t e d back, w h i l e

from Eq. ( 2 ) , 1

-

0.67 = 0.33, o r 33% i s t r a n s m i t t e d i n t o t h e c o n c r e t e of t h e dam.

The c a l c u l a t e d and e x p e r i m e n t a l peak p r e s s u r e s i n T a b l e

4

s h o u l d n o t be compared d i r e c t l y , s i n c e t h e former a r e free-f i e l d

p r e s s u r e s ' and need t o be a d j u s t e d f o r r e f l e c t i o n phenomena. T h i s w i l l b e d e a l t w i t h l a t e r .

DISCUSSION

1. P o s i t i v e and N e g a t i v e P u l s e s a t Wave F r o n t : The

r e f l e c t i o n model shown i n Fig. 15 e x p l a i n s t h e p r e s e n c e of t h e n e g a t i v e p u l s e i n t h e wave f r o n t and t h e t i m e d e l a y s measured. It c a n be

e x p e c t e d t h e n t h a t t h e p r e s s u r e f l u c t u a t i o n s behind t h e wave f r o n t a r e t h e r e s u l t of v a r i o u s r e f l e c t i o n s , b o t h from t h e w a t e r s u r f a c e and t h e r e s e r v o i r bottom. I n g e n e r a l t h e n , b o t h a p o s i t i v e and a n e g a t i v e p u l s e of e q u a l magnitude can be e x p e c t e d whenever t h e d i f f e r e n c e i n t r a v e l time between t h e d i r e c t p a t h and t h e s u r f a c e - r e f l e c t e d p a t h i s l o n g e r t h a n t h e p u l s e d u r a t i o n . T h i s r e p r e s e n t s a c o n d i t i o n d i f f e r e n t t o t h a t p r e s e n t e d i n L a n g e f o r s and Kihlstr-&n (1963) which d e s c r i b e s measurements a t c l o s e r a n g e , f o r which c a s e o n l y a p o s i t i v e wave f r o n t i s

o b t a i n e d .

2. E f f e c t of D i s t a n c e of Hydrophone from D a m S u r f a c e : The incoming p r e s s u r e waves a r e r e f l e c t e d a t t h e dam s u r f a c e . I f t h e hydrophone i s mounted a t some d i s t a n c e from t h i s s u r f a c e , a complex i n t e r a c t i o n of incoming and r e f l e c t e d waves w i l l be monitored. S i n c e p r a c t i c a l c o n s i d e r a t i o n s p r e c l u d e l o c a t i n g t h e s e n s i n g element of t h e hydrophone f l u s h w i t h t h e s u r f a c e , t h e p o t e n t i a l e r r o r i n t r o d u c e d by l o c a t i n g t h e hydrophone away from t h e s u r f a c e needs t o be c o n s i d e r e d .

The t r a v e l time f o r t w i c e t h e 7.6 c m ( 3 i n . ) d i s t a n c e from t h e dam s u r f a c e t o t h e hydrophone i s 0.10 ms. For a s h a r p l y r i s i n g

i n c i d e n t p u l s e , a r e f l e c t e d p u l s e of t h e same shape b u t 0.67 times i n a m p l i t u d e would t h e n a p p e a r a t 0.10 ms l a t e r , superimposed on t h e

i n c i d e n t one. T h i s would g i v e r i s e t o a s e c o n d a r y peak and a

l e n g t h e n i n g of t h e r e c o r d e d p u l s e by 0.10 m s as compared w i t h t h e p u l s e t h a t a c t u a l l y e x i s t s a t t h e s u r f a c e o f t h e dam. I f t h e i n c i d e n t wave h a s a v e r y s h a r p peak and w i t h i n 0.1 m s d r o p s t o 0.33 o r less of i t s peak a m p l i t u d e A1, t h e n t h e r e f l e c t e d p u l s e of . a m p l i t u d e 0.67 A1 w i l l n o t be r e g i s t e r e d by t h e h y d r o p h o n e s as b e i n g l a r g e r t h a n t h e peak i n c i d e n t wave. The measured peak a m p l i t u d e s would t h e n a c t u a l l y

r e p r e s e n t t h e f r e e - f i e l d p r e s s u r e s and n o t t h e r e f l e c t e d p r e s s u r e a t t h e dam s u r f a c e .

Every e f f o r t s h o u l d t h e r e f o r e be made t o r e d u c e t h e d i s t a n c e f r o m hydrophone t o t h e dam s u r f a c e and t o i n c r e a s e t h e f r e q u e n c y c o n t e n t of t h e r e c o r d i n g p r o c e s s i n f u t u r e tests.

3. Agreement Between C a l c u l a t e d and Measured P r e s s u r e s : The f r e e - f i e l d and t h e measured p r e s s u r e s n e e d t o b e a d j u s t e d b e f o r e a q u a n t i t a t i v e c o m p a r i s o n c a n be made. U n f o r t u n a t e l y , b e c a u s e of t h e f o l l o w i n g u n c e r t a i n t i e s , t h i s c a n o n l y b e d o n e i n a v e r y a p p r o x i m a t e manner.

a ) The measured p r e s s u r e s are p r o b a b l y t o o low d u e t o t h e 5000 Hz f r e q u e n c y l i m i t a t i o n o f t h e r e c o r d i n g p r o c e s s .

b) A s w a s p o i n t e d o u t a b o v e , t h e p o s i t i o n i n g of t h e hydrophones was s u c h t h a t p r e s s u r e s somewhere b e t w e e n t h e f r e e - f i e l d c o n d i t i o n and t h e r e f l e c t e d p r e s s u r e s a t t h e dam s u r f a c e were measured, a m o u n t i n g t o a maximum o f 1.67 t i m e s t h e i n c i d e n t wave

a m p l i t u d e .

c ) The c a l c u l a t e d p r e s s u r e s need t o be r a i s e d by a maximum of 8 0 % t o a c c o u n t f o r t h e r e f l e c t i o n a t t h e r o c k s u r f a c e .

The a d j u s t m e n t s b) and c ) r e s u l t i n a n u p p e r bound m u l t i p l i e r of (1.67) (1.80) = 3.0, t o b e a p p l i e d t o t h e c a l c u l a t e d r e s u l t s i n T a b l e 4.

T h i s t h e n p l a c e s t h e measured r e s u l t s w i t h i n 113 t o 112 o f a n u p p e r bound of t h e c a l c u l a t e d o n e s . The r a t i o o f measured t o c a l c u l a t e d v a l u e s i s a l s o s e e n t o i n c r e a s e w i t h d i s t a n c e ; however, no p l a u s i b l e e x p l a n a t i o n f o r t h i s t r e n d c o u l d b e found.

4. I m p l i c a t i o n s on D a m Response: , I n i t i a l c o m p a r i s o n s o f t h e a c c e l e r a t i o n r e s p o n s e o f E v e n t s 5 , 6 , 7 and E v e n t 11 show t h a t

comparable peak a c c e l e r a t i o n r e s p o n s e s are o b t a i n e d f o r g r e a t l y

d i f f e r e n t peak p r e s s u r e s . T h i s i n d i c a t e s t h a t t h e r e s p o n s e i s n o t w e l l c o r r e l a t e d w i t h t h e a m p l i t u d e of t h e p r e s s u r e wave f r o n t . By way of e x p l a n a t i o n , t h i s c a n b e r a t i o n a l i z e d by r e f e r e n c e t o a n o s c i l l a t o r s u b j e c t e d t o t h e p o s i t i v e and f o l l o w i n g n e g a t i v e p u l s e . F o r

o s c i l l a t o r s h a v i n g n a t u r a l p e r i o d s s u b s t a n t i a l l y g r e a t e r t h a n t h e t i m e

d e l a y between t h e p u l s e s , t h e r e s p o n s e from t h e p o s i t i v e i m p u l s e would b e s u b s t a n t i a l l y c a n c e l l e d o u t by t h e r e s p o n s e o f t h e s u c c e e d i n g

n e g a t i v e p u l s e . The p r e s s u r e f l u c t u a t i o n s b e h i n d t h e wave f r o n t t h u s become more i n f l u e n t i a l .

A d d i t i o n a l q u a n t i t a t i v e s t u d i e s on t h e dam r e s p o n s e w i l l be c a r r i e d o u t i n o r d e r t o a r r i v e a t more d e f i n i t i v e c o r r e l a t i o n s between t h e c h a r a c t e r i s t i c s of t h e b l a s t wave and t h e r e s p o n s e of t h e dam.

V I . PERFORMANCE OF INSTRUMENTATION

The hydrophones and a s s o c i a t e d c a b l e s and e l e c t r o n i c s performed w e l l u n d e r f i e l d c o n d i t i o n s . F u t u r e measurements, however, should c o n s i d e r t h e f o l l o w i n g changes o r improvements:

1) mounting t h e s e n s i n g element of t h e hydrophone c l o s e t o t h e dam s u r f a c e , from

7.6

cm (3.0 i n . ) t o p r e f e r a b l y 2 t o 3 cm ( a p p r o x i m a t e l y 1 i n . ) ; 2 ) i n c r e a s i n g t h e r e c o r d e r g a i n s f o r a s m a l l e x p e c t e d p r e s s u r e l e v e l s o a s t o improve t h e s i g n a l - t o - n o i s e r a t i o of t h e measurements. F u r t h e r a t t e m p t s s h o u l d a l s o be made t o r e d u c e t h e h i g h f r e q u e n c y n o i s e from t h e hydrophones t h a t c a n be s e e n i n Fig. 12 i n o r d e r t o improve t h e d e f i n i t i o n of low p r e s s u r e s i g n a l s ; 3 ) a n a u t o m a t i c t r i g g e r i n g d e v i c e s h o u l d be d e v i s e d t o produce a common t i m i n g p u l s e on a l l t a p e r e c o r d e r s t h a t a r e employed i n a common e x p e r i m e n t a l set-up. T h i s d e v i c e s h o u l d be a c t i v a t e d by t h e p l u n g e r of t h e b l a s t e r a t o r s l i g h t l y ahead of t h e t i m e of d e t o n a t i o n ;

4 ) one o r more a c c e l e r o m e t e r s i g n a l s d i r e c t l y o p p o s i t e a hydrophone s h o u l d be r e c o r d e d w i t h low p a s s f i l t e r s e t t i n g s s u b s t a n t i a l l y h i g h e r t h a n 50 Hz i n o r d e r t o d e t e c t any p o s s i b l e c o r r e l a t i o n between h i g h f r e q u e n c y a c c e l e r a t i o n s and t h e hydrophone

p r e s s u r e s .

5 ) The hydrophone s i g n a l s s h o u l d be r e c o r d e d a t a h i g h e r speed t o p r o v i d e a h i g h e r f r e q u e n c y r e s p o n s e , p r e f e r a b l y 10,000 Hz o r above.

V I I . CONCLUSIONS

These r e s u l t s p e r m i t t h e f o l l o w i n g c o n c l u s i o n s .

1) A wave f r o n t having a p o s i t i v e and n e g a t i v e p o r t i o n of

a p p r o x i m a t e l y e q u a l s h a p e and a m p l i t u d e h a s been measured. T h i s i s e x p l a i n e d by a w a t e r - s u r f a c e r e f l e c t i o n model. The d e l a y between t h e two p o r t i o n s of t h e p u l s e i s shown t o be a f u n c t i o n of t h e d i f f e r e n c e i n t r a v e l t i m e between t h e d i r e c t and t h e s u r f a c e - r e f l e c t e d p r o p a g a t i o n p a t h .

2 ) The s h i e l d i n g e f f e c t of t e r r a i n on t h e b l a s t wave i s w e l l

d e m o n s t r a t e d by t h e r e s u l t s , v a r y i n g from t h e d i r e c t b l a s t p r e s s u r e s t o a v i r t u a l a b s e n c e of o v e r - p r e s s u r e when t h e s o u r c e i s h i d d e n from t h e t a r g e t . The d e g r e e of s h i e l d i n g from d i r e c t

t o h i d d e n s o u r c e s i s g r a d u a l and i s n o t accompanied by sudden changes f n t h e p r e s s u r e d i s t r i b u t i o n on t h e t a r g e t .

3 ) The hydrophones and a s s o c i a t e d equipment performed w e l l d u r i n g t h e t e s t s . Some improvements i n n o i s e r e d u c t i o n , r e c o r d i n g t e c h n i q u e and placement of hydrophones a r e i n d i c a t e d f o r f u t u r e t e s t s , however.

4 ) P r e l i m i n a r y r e s u l t s show t h a t t h e maximum dam r e s p o n s e d o e s n o t depend d i r e c t l y o n t h e a m p l i t u d e of t h e b l a s t wave f r o n t , b u t i s

l i k e l y t o depend more on t h e random p r e s s u r e v a r i a t i o n s behind t h e f r o n t . T h i s w i l l b e f u r t h e r i n v e s t i g a t e d i n c o n n e c t i o n w i t h a d d i t i o n a l dam r e s p o n s e s t u d i e s .

5 ) The measured peak p r e s s u r e s a r e from 113 t o 1 / 2 of t h e u p p e r bound p r e s s u r e s a t t h e dam s u r f a c e a s p r e d i c t e d f r o m two

e m p i r i c a l r e l a t i o n s h i p s . The measured p r e s s u r e s i n c r e a s e w i t h d i s t a n c e r e l a t i v e t o t h e p r e d i c t e d ones. U n c e r t a i n t i e s i n

comparisons between measured and c a l c u l a t e d r e s u l t s i n c l u d e f r e q u e n c y r e s p o n s e l i m i t a t i o n s of t h e r e c o r d i n g s y s t e m ,

a s s e s s m e n t of t h e r e f l e c t i o n s o f f t h e r o c k and t h e dam s u r f a c e , and e x c e e d a n c e of t h e r a n g e of v a l i d i t y of t h e e m p i r i c a l

r e l a t i o n s h i p s .

ACKNOWLEDGEMENTS

The work d e s c r i b e d was c a r r i e d o u t i n c o l l a b o r a t i o n w i t h D r . P a u l Lecomte of Hydro Quebec. The c o o p e r a t i o n and a s s i s t a n c e of D r . Lecomte and of h i s co-workers i s g r e a t l y a p p r e c i a t e d . The Board of C o n s u l t a n t s f o r t h e A d d i t i o n a l Power p r o j e c t a t Manic 5 a r e D r . W. Chadwick of Los Angeles, C a l i f o r n i a , D r . R.W. Clough of B e r k e l e y , C a l i f o r n i a , D r . A.J. Hendron of Urbana, I l l i n o i s , and M r . B. Kihlstrijrn of Stockholm, Sweden. The a s s i s t a n c e of E. L u c t k a r and R. G l a z e r , t e c h n i c a l o f f i c e r s i n t h e D i v i s i o n of B u i l d i n g R e s e a r c h , i n p r e p a r i n g t h e i n s t r u m e n t a t i o n and i n c a r r y i n g o u t t h e measurements i s g r a t e f u l l y acknowledged. I X . REFERENCES 1 ) C o l e , R.H. (1948) Underwater E x p l o s i o n s , P r i n c e t o n U n i v e r s i t y P r e s s , P r i n c e t o n , N.J.

2 ) Delany,

M.E.

(1972) "A P r a c t i c a l Scheme f o r P r e d i c t i n g Noise L e v e l s (L10) A r i s i n g f r o m Road T r a f f i c , " NPL A c o u s t i c s R e p o r t AC 57,

N a t i o n a l P h y s i c a l L a b o r a t o r y , U n i t e d Kingdom.

3) Enhamre, E. (1954) " E f f e c t s of Underwater E x p l o s i o n on E l a s t i c S t r u c t u r e s i n Water," T r a n s . Royal I n s t i t . of Technology, B u l l . 42 of t h e I n s t i t u t i o n H y d r a u l i c s , Stockholm.

4 ) Henrych, J. (1979) The Dynamics of E x p l o s i o n s and i t s U s e ,

Developments i n C i v i l E n g i n e e r i n g , 1 ; E l s e v i e r S c i e n t i f i c P u b l i s h i n g Co., New York, N.Y.

NATIONAL RESEARCH COUNCIL CANADA DIVISION OF BUILDING RESEARCH

ERRATA

MEASUREMENT OF UNDERWATER BLAST WAVES ON DANIEL JOHNSON DAM

by

J.H.

R a i n e r

DBR I n t e r n a l Report 472, A p r i l 1982.

p.3: below middle of page, change "(20 i t ) " t o "(200 i t ) "

-p.5: Eq. (2) s h o u l d r e a d :

p.6: F o u r t h l i n e from bottom of page s h o u l d r e a d :

-

1 / 3 1 / 3

where: R = R/W (m-kg

)

;

p.7: l a s t p a r t of f i r s t p a r a g r a p h s h o u l d r e a d :

". . .

,

w h i l e from Eq. ( 2 ) , 1

+

0.67 = 1.67, o r 1.67 t i m e s t h e incoming wave i s t r a n s m i t t e d i n t o t h e c o n c r e t e of t h e dam."

5)

Kolsky,

H.

(1963) Stress Waves in Solids, Dover Publications,

New York, N.Y.,

213

p .

6) Langefors,

U.

and KihlstrGm, B.

(1963) The Modern Technique of Rock

Blasting, John Wiley

&

Sons, Inc.

,

New York, N.Y.

hl

.

0 4 CO rr) U h

.

9 rn \O

.

d U 0

.

h U h

= ;

_rr) u

.

6 ln rr, rr) U hl

.

ln 4 rr) ln 4 h h l O 0 4 6. 4 0 I lnh n m m 3 u D n CO v PO

8

1 UJ t.l PC Q) b rl U Q

3

m Q) b 9 m Q) b 04 d cb d U d c H

4

a 04 n W l n r r ) l d l n h 0 3 l n h V

2

h h I u h l - 4 - 3 0 W l n b

??'?'?'?

?

".

0

.

r r ) U \ O h l W hl h hl m l n l n u r r ) 4 \O 9 a

?02"2"0.'4

?'?

h u o o w r n h l u 0 \ O \ O b h U 4 CO b

*

m h l - ~ u m

. . . * .

? ?

rr)

.

r r ) h l n U h OI Cl hl 9 h h h h l h h d m h l ? O r h l * f n

. .

CO42rr) Q)

.

.

h 4 O C O l n d c \ O O U bCOOICOrr) cd h CO b J= 0 U

"24"."?".,

,024

"0.

COuuCOo * m \ O r r ) h h 0 m r r ) d Q ) CO CO d d

"."2"."0.=?

m

. .

ln hl

.

\O \O h h C O \ D h l m 9 C O l n d m h h U*

2

9 h

. .

e4

".4

m o r r ) e \ O rr) y.) 0 o o l n h l *

*

₂

rr) 4 d d d 4

4"0."0.".?

?=?

m h \ o u h l U h u O Q \ O O 4

*

OI 0 d d d * 4 C v h l h l h l h l h l h l d h l

. . .

hl l n m l n l n l n m m r r , l n

z

d d d d 4 d d C n 4 I

+

I

+

I + I

+

a U m a c c U . . O 0 h O b U

.;:

rr) P _d (d Q) u a b o h 03 I h U 3 m w a

w

u rn h CO I h 3 V rr) C9 a h CO I h U 3 V a J hl rn h a? I h V 4 a

..

g

d U lu hl 4 d d h l r r ) + l n \ O h rC) 4 a -M l n O a u l n \ o h a o m O d h l d d d

2

'8

\o"

a~ M

5 %

a s

8 Q ) U w 0

w

h ln H 4 I u U d l n rl a d u 0 a 0 b d d a b d haJ (d

x

rn U c)

3

aJ a 0

s

a 0 b a

z

PO 0 PC

2

d n

'8

_t.l 9 u c a 0 3 2 W V O . ln h

2

..

(d 04 A \

'e

a UJ

..

U

n n n n n n n n n

S S S S S S S S S

* e * * * * * e *

Table

3

Carparison of Measured and Calculated Differences

in

Arrival Tires

iktrrren Initial Positive

.ad

Begatire Pulses

1 2 3 4

Hyd rop hone

- - -- - - - - - - - -

D i s tance Calcu- Distance Calcu- Distance Calcu- Distance Ca 1 cu-

t o Gauge Measured l a t e d t o Gauge Measured lated t o Gauge Measured l a t e d t o Gauge Measured l a t e d

Event

m

~ 1 6 ms m

m s

m s m I~LS

ms

m

m

m6

Table 4

Measured and Calculated Peak P o s i t i v e P r e s s u r e s

Hydrophone S t a t i o n

1A a t

V4-5

2A

a t V6-7

3A

a t

V7-8

4A

a t

V9-10

Approximate D i s t a n c e From Charge t o Gauge,

m ( f

t )

315 (1033)

425 (1395)

525 (1722)

665 (2182)

Measured

Average of E v e n t s 4, 5, 6, 7

Peak P r e s s u r e :

kPa ( p s i )

104

(15.1)

77.2

(11.2)

84.7

(12.3)

71.7

(10.4)

- - - -- - pp --- - - -

C a l c u l a t e d

Eq. 3

-

Henrych (1979)

Peak

Ap, kPa ( p s i )

115

(16.7)

88.6

(12.9)

69.3

(10.1)

54.7

(7.9)

P r e s s u r e :

*

Eq.4

-

Cole (1948)

A P ,

kPa ( p s i )

102

(14.8)

73.0

(10.6)

57.3

(8.3)

43.9

(6.4)

*These p r e s s u r e s a r e f r e e - f i e l d p r e s s u r e s a s p r e d i c t e d by t h e e m p i r i c a l r e l a t i o n s h i p s and do n o t account

f o r t h e r e f l e c t e d waves a t t h e dam s u r f a c e o r

a t

t h e r o c k f a c e .

Fig. 1 Daniel Johnson Dam (Manic/

5)

on

Manicouagan River, Quebec.

CHARGE LOCATIONS 1

-

7 I T U R E T A K E A N N E L

--

-

D R A I N A G E A N D S E R V I C E G A L L E R I E S

\

b L O C A T I O N S O F H Y D R O P H O N E S R E S E R V O I R M A N I C O U A G A N 5 EL. 3 5 6 . 2 m f P L A N

-

E L E V A T I O N F I G U R E 3 L O C A T I O N O F C H A R G E S A N D H Y D R O P H O N E S T A T I O N S

IMAGE POINT OF SOURCE WATER SURFACE

REFLECTED PATHS BLAST

LOCAT l OP ? h l C C . . F I G U R E 1 5 S C H E M A T I C F O R P A T H S O F D I R E C T A N D R E F L E C T E D B L A S T F R O N T S CHARGE EVENT LOCAT l ON

-

CHARGE DEPTH SYMBOL

rn ft

- -

15.2 50 o 15.2 50 O---a 15.2 50 0- o 15.2 50 a- a 35.1 115 .-.-A A

...

15.2 50 A A

-

-

.0

...

-

A"-&.

.

.

..

_..

..

-0,-

;*:-.-**

**<--: A ...a -&a. l

-

-

8-

_-

0

N

o

.,.-.A A.,

,.,

.-.

.-.-.A

.-.-.

.-.&"-'-

8 a-.

-c i

$5

1

c 7

I

c 8 c 9

I

Clio

V4-5 V6-7 V7-8 V9-10 LOCATIONS ALONG D A M F I G U R E 1 6 M E A S U R E D P E A K I N I T I A L P R E S S U R E S A L O N G D A M

0.

I I

-

I SHADOW

-

_0.

PATH DIFFERENCE d

=

a

+

b

-

c

A

=

WAVELENGTH

-

_0.

-

_0.

1. F I G U R E 1 7 S H I E L D I N G O F A P U R E - T O I V E P O I N T S O U R C E B Y A B A R R I E R ( D E L A N Y , 1 9 7 2 )