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Study of Snow Problems on Expressways in Japan: Report Prepared
for Nihon Doro Kodan
NATIONAL RESEARCH COllNClL OF CANADA DIVISION OF BUILDING RESEARCH
DBR INTERNAL REPORT NO.
447
STUDY OF SNOW PROBLEMS ON EXPRESSWAYS IN JAPAN Report p r e p a r e d f o r Nihon Doro Kodan
b y P e t e r S c h a e r e r
Cheeked by: E
.
P.
Approved by: L.
W.
G.
Date: August 1978STUDY OF SNOW PROBLEMS ON EXPRESSWAYS IN JAPAN Report p r e p a r e d f o r Nihon Doro Kodan
by
P e t e r S c h a e r e r
TERMS OF REFERENCE
Nihon Doro Kodan ( J a p a n Highway P u b l i c C o r p o r a t i o n ) i n v i t e d e x p e r t s from Canada f o r a s t u d y v i s i t o f snow and i c e c o n t r o l problems on
n a t i o n a l expressways b u i l t and m a i n t a i n e d b y Nihon Doro Kodan. The v i s i t was made 20 February t o 3 March 1978 by P . J . C a r r o f t h e B r i t i s h Columbia Department o f Highways, J . Hode Keyser o f t h e Ecole P o l y t e c h - n i q u e d e Montreal, and P.A. S c h a e r e r o f t h e N a t i o n a l Research Council o f Canada.
During t h e v i s i t i n f o r m a t i o n c o n c e r n i n g snow and i c e c o n t r o l on expressways i n J a p a n was o b t a i n e d from meetings w i t h s t a f f o f Nihon Doro Kodan a t t h e i r h e a d q u a r t e r s i n Tokyo, a t c o n s t r u c t i o n o f f i c e s i n Sapporo, N i s h i n e , S e n d a i , and a t s e v e r a l maintenance o f f i c e s .
O b s e r v a t i o n s o n l o c a t i o n were made a t t h e Doo Expressway, t h e Tohoku Expressway between Kazuno and S e n d a i
,
t h e Kanetsu Expressway between Yuzawa and Nagaoka, and t h e Hokuriku Expressway between Fukui andT s u r u g a . A l l t h e m e e t i n g s were w e l l o r g a n i z e d , c h a i r e d , and documented. T h i s r e p o r t d e a l s w i t h t h e i m p r e s s i o n s c o n c e r n i n g a v a l a n c h e s and d r i f t i n g snow, two t o p i c s i n which t h e a u t h o r h a s s p e c i a l e x p e r t i s e . OBSERVATIONS OF SNOW AND AVALANCHES
I t was n o t e d t h a t Nihon Doro Kodan i s engaged i n a program o f c o l l e c t i n g d a t a c o n c e r n i n g s n o w f a l l , w e a t h e r , and a v a l a n c h e s a t p l a n n e d and c o n s t r u c t e d expressway s i t e s . The importance of t h e s e o b s e r v a t i o n s f o r making d e c i s i o n s c o n c e r n i n g t h e d e s i g n o f t h e highways and t h e maintenance f a c i l i t i e s must b e s t r e s s e d . Nihon Doro Kodan r e l a t e s c e r t a i n d e s i g n e l e m e n t s t o t h e 1 0 - y e a r maximum depth o f snow on t h e ground, and i t was a g r e e d t h a t snow d e p t h i s a b e t t e r c h o i c e f o r t h i s purpose t h a n annu a1 snow f a 11
.
I n f o r m a t i o n a b o u t a c t u a l a v a l a n c h e o c c u r r e n c e s i s v a l u a b l e f o r s t u d i e s c o n c e r n i n g a v a l a n c h e c o n t r o l . I t i s recommended t h a t
p o s s i b ground c r a f t ,
. e b e f o r e t h e expressways a r e b u i l t . O b s e r v a t i o n s from t h e u s u a l l y y i e l d b e t t e r r e s u l t s than o b s e r v a t i o n s made from a i r - t h e r e f o r e s u r v e y s from h e l i c o p t e r s o r a i r p l a n e s should b e l i m i t e d t o i n a c c e s s i b l e t e r r a i n . I n f o r m a t i o n a b o u t t h e type o f o b s e r v a t i o n s t h a t s h o u l d b e made a r e c o n t a i n e d i n t h e Canadian S t a n d a r d s f o r a v a l a n c h e o b s e r v a t i o n s . TYPES OF AVALANCHES The a v a l a n c h e s t h a t t h r e a t e n t h e expressways o c c u r on s t e e p n a t u r a l s l o p e s and on man-made s l o p e s i n deep c u t s . The n a t u r a l and man-made a v a l a n c h e p a t h s f r e q u e n t l y c a n n o t b e avoided because o f t h e wide c u r v e s and low h o r i z o n t a l g r a d e s r e q u i r e d by t h e g e o m e t r i c d e s i g n
s t a n d a r d s f o r expressways.
The n a t u r a l avalanche p a t h s t h a t could b e observed d u r i n g t h e s t u d y t o u r were r a t h e r s h o r t . The s t a r t i n g zones were n o t h i g h e r t h a n 300 m
above t h e v a l l e y and many o f them were covered w i t h a t h i n f o r e s t . T h i s would l e a d t o t h e c o n c l u s i o n t h a t t h e a v a l a n c h e s a r e u s u a l l y smal l e r t h a n t h o s e o b s e r v e d i n Canada.
I n f o r m a t i o n r e c e i v e d from t h e s t a f f o f Nihon Doro Kodan and t h e l i t e r a t u r e d e s c r i b i n g a v a l a n c h e s t u d i e s i n Japan i n d i c a t e t h a t t h e m a j o r i t y o f dangerous a v a l a n c h e s n e a r highways a r e f u l l - d e p t h o n e s t h a t run d u r i n g t h e snow melt s e a s o n i n March. The s u r f a c e - l a y e r a v a l a n c h e s t h a t o c c u r e a r l i e r i n t h e w i n t e r seem t o b e s m a l l . T h i s was confirmed d u r i n g t h e v i s i t when no l a r g e avalanche d e p o s i t s were d i s c o v e r e d n e a r t h e t r a v e l l e d r o u t e . The l a c k o f r e c e n t a v a l a n c h e s was e v i d e n t
p a r t i c u l a r l y i n t h e Kazuno-Nishine a r e a where, a c c o r d i n g t o e x p e r i e n c e i n Western Canada, t h e s n o w f a l l r e c o r d e d by Nihon Doro Kodan c o u l d produce, on t h e a v e r a g e f o u r p e r i o d s o f avalanche a c t i v i t y p e r w i n t e r .
I n t h e a r e a s v i s i t e d t h e c u t s l o p e s had a s t a n d a r d g r a d i e n t o f 1 : 1 and berms a t 7 m d i f f e r e n c e s of h e i g h t . Experience shows t h a t t h i s t y p e o f s l o p e would f a v o r t h e f o r m a t i o n o f a v a l a n c h e s , b e c a u s e i n
Canadian s t u d i e s most a v a l a n c h e s were o b s e r v e d t o s t a r t on s l o p e s w i t h i n c l i n e s o f 40 t o 45 d e g r e e s when no deep snow d r i f t s were p r e s e n t ; f u r t h e r m o r e , t e n s i l e s t r e s s e s t h a t c o u l d l e a d t o a f a i l u r e develop i n t h e snow a t t h e edge o f t h e berm.
RECOMMENDATIONS FOR AVALANCHE CONTROL
The high-speed and high-volume t r a f f i c on expressways demands t h a t a v a l a n c h e s b e c o n t r o l l e d . They must n o t b e allowed t o s l i d e o n t o t h e roadways under uncon t r o l l ed c o n d i t i o n s .
Avalanche c o n t r o l methods found p r a c t i c a l i n o t h e r c o u n t r i e s
i n c l u d e t h e m o d i f i c a t i o n o f t e r r a i n , s t r u c t u r e s , and a r t i f i c i a l r e l e a s e . A t expressways a r t i f i c i a l r e l e a s e through e x p l o s i o n s o r o t h e r methods should b e c o n s i d e r e d f o r n a t u r a l a v a l a n c h e p a t h s w i t h i n f r e q u e n t a v a l a n c h e s o n l y , b e c a u s e t h e method r e q u i r e s e x t e n s i v e c o n t r o l o f
t r a f f i c and c l o s u r e o f t h e highway. The a r t i f i c i a l r e l e a s e must n o t b e a p p l i e d a t c u t s l o p e s because t h e a v a l a n c h i n g snow would b e d e p o s i t e d o n t h e highway and would have t o b e h a u l e d away. Furthermore, t h e time
r e q u i r e d f o r t h e r e l e a s e o f t h e a v a l a n c h e s and snow removal would b e i n t o l e r a b l y l o n g .
J a p a n h a s a h i g h s t a n d a r d o f a v a l a n c h e c o n t r o l on t h e i r N a t i o n a l Highways and N a t i o n a l Expressways
.
R e t a i n i n g b a r r i e r s a n d snow s h e d s were e v i d e n t a t numerous a v a l a n c h e s i t e s , even on highways w i t h low t r a f f i c volumes. I n Canada, a v a l a n c h e s would n o t b e c o n t r o l l e d on highways w i t h s i m i l a r a v a l a n c h e and t r a f f i c c o n d i t i o n s .Because a v a l a n c h e s a r e c a u s e d by a combination of s e v e r a l f a c t o r s such a s s n o w f a l l , t e m p e r a t u r e , wind, shape and i n c l i n e o f t e r r a i n , and v e g e t a t i o n , and b e c a u s e t h e r e l a t i v e s i g n i f i c a n c e o f them v a r i e s w i t h
t h e a r e a , c a u t i o n must b e u s e d i n a p p l y i n g c o n t r o l measures. A t y p e o f c o n t r o l p r o v e n i n one a v a l a n c h e a r e a may n o t n e c e s s a r i l y b e t h e most advantageous i n a n o t h e r . For t h i s r e a s o n it i s recommended t h a t avalanche c o n t r o l b e s t u d i e d f o r e a c h a r e a i n d i v i d u a l l y .
AVALANCHE CONTROL ON CUT SLOPES
S e v e r a l a1 t e r n a t i v e s t h a t may b e i n v e s t i g a t e d f o r a v a l a n c h e c o n t r o l o n c u t s l o p e s f o l l o w . I n a l l a l t e r n a t i v e s a t t e m p t s s h o u l d b e made t o p l a n t t r e e s on t h e c u t s l o p e s .
a ) Reduction o f t h e s l o p e g r a d i e n t - E x p e r i e n c e i n Western Canada shows t h a t c u t s l o p e s w i t h a g r a d i e n t 1 : 2 do n o t produce a v a l a n c h e s .
S l o p e s w i t h a g r a d i e n t 1 : 1 . 5 do n o t u s u a l 1 y produce a v a l a n c h e s o r o n l y s m a l l o n e s when:
- t h e r e i s no accumulation o f d r i f t i n g snow
- t h e snow d e p t h does n o t exceed 2
m
-
t h e r e a r e no i r r e g u l a r i t i e s such a s r o c k o u t c r o p s I t i s n o t known w h e t h e r o r n o t t h e s e c o n c l u s i o n s a r e a p p l i c a b l e t o a v a l a n c h e c o n d i t i o n s i n J a p a n , and i t i s recommended t h a t s t u d i e s b e made c o n c e r n i n g t h e i n f l u e n c e of t h e s l o p e i n c l i n e on t h e forma- t i o n o f a v a l a n c h e s . O b s e r v a t i o n s o f t e s t s l o p e s would b e a d v a n t a g e o u s . A lower i n c l i n e i s u s u a l l y needed t o m a i n t a i n t h e motion o f t h e a v a l a n c h e r a t h e r t h a n t o i n i t i a t e i t , t h e r e f o r e s t u d i e s must d i s t i n g u i s h between t h e s l o p e g r a d i e n t a t t h e p o i n t o f f r a c t u r e and t h a t i n t h e a v a l a n c h e t r a c e . A r e d u c t i o n o f t h e s l o p e g r a d i e n t i n c u t s l o p e s may n o t o n l y i n h i b i t t h e f o r m a t i o n o f a v a l a n c h e s b u t h a s t h e a d d i t i o n a l b e n e f i t s o f r e d u c i n g e r o s i o n , g i v i n g b e t t e r c o n d i t i o n s f o r t h e growth o f v e g e t a t i o n , t h u s b e i n g a e s t h e t i c a l l y more p l e a s i n g .b ) R e t a i n i n g b a r r i e r s
-
B a r r i e r s when b u i l t h i g h enough and spaced d e n s e l y enough a r e t h e m s t e f f e c t i v e a v a l a n c h e c o n t r o l , b u t a r e p r o b a b l y a l s o t h e most e x p e n s i v e . The h e i g h t o f t h e b a r r i e r s mustt a k e i n t o c o n s i d e r a t i o n t h e d e p t h o f snow from snow f a l l and d r i f t i n g a s w e l l a s snow d e p o s i t e d on t h e s l o p e by snow b l o w e r s . c) Wide d i t c h
-
A d i t c h 4 m wide and 1 m deep a t t h e t o e o f t h e c u ts l o p e would c a t c h t h e a v a l a n c h e snow on s h o r t s l o p e s .
The method c o u l d b e a p p l i e d a t s l o p e s n o t h i g h e r t h a n 1 5 m and a t l o c a t i o n s where i t would b e easy t o o b t a i n t h e a d d i t i o n a l width o f c r o s s s e c t i o n . d) High b a r r i e r a t t h e t o e o f t h e s l o p e
-
A b a r r i e r o r c o n c r e t e w a l l a t t h e t o e o f t h e c u t s l o p e w i l l c a t c h t h e a v a l a n c h e snow. R O A D W A Y / /f'
" " ' / ' / f l The s p a c e b e h i n d t h e b a r r i e r , h e i g h t H , must b e s u f f i c i e n t t o s t o r e t h e e x p e c t e d volume o f a v a l a n c h e snow and snow d e p o s i t e d by snow b l o w e r s .The volume o f a v a l a n c h e snow A i s :
A = C r - C d - L 0 D where
L = l e n g t h o f t h e s l o p e
D = maximum depth o f snow
C r = c o e f f i c i e n t of t h e roughness o f t h e ground; on smooth, even ground C r = 1
on ground w i t h berms, r o c k , s h r u b s , C r = 0 . 5
Cd = c o e f f i c i e n t t a k i n g i n t o a c c o u n t t h e i n c r e a s e o f d e n s i t y o f t h e s l i d i n g snow, d r y snow Cd = 0 . 7 5
wet snow Cd = 0 . 5
Berms - In Canada berms a c r o s s s l o p e s were found t o have l i m i t e d
e )
-
s u c c e s s i n i n h i b i t i n g a v a l a n c h e s , b u t e x p e r i m e n t s i n J a p a n
appeared t o b e f a v o u r a b l e . Berms a r e p r o b a b l y more s u c c e s s f u l i n a r e a s w i t h wet snow which deforms p l a s t i c a l l y and r e l i e v e s s t r e s s e s more r e a d i l y t h a n d r y snow. T h i s would l e a d t o t h e c o n c l u s i o n t h a t berms c o u l d b e a p p l i e d i n Honshu, b u t n o t i n Hokkaido.
AVALANCHE CONTROL ON NATURAL SLO PES
The a l t e r n a t i v e s o f c o n t r o l l i s t e d f o r c u t s l o p e s may a l s o b e a p p l i e d a t n a t u r a l a v a l a n c h e s l o p e s . I n a d d i t i o n t o t h e methods d i s c u s s e d , d e f l e c t o r s and r e f o r e s t a t i o n s h o u l d b e c o n s i d e r e d .
D e f l e c t o r s o f e a r t h o r c o n c r e t e can u s u a l l y b e b u i l t a t r e l a t i v e l y low c o s t , b u t t h e y r e q u i r e s p a c e f o r t h e s t r u c t u r e and room f o r t h e a v a l a n c h e s t o r u n o u t h a r m l e s s l y .
A dense f o r e s t i n t h e s t a r t i n g zone o f t h e a v a l a n c h e s i s a n e f f e c t i v e c o n t r o l , b u t many y e a r s a r e r e q u i r e d b e f o r e t h e t r e e s w i l l
grow l a r g e enough. R e t a i n i n g b a r r i e r s might have t o b e a p p l i e d i n t h e meantime.
DR I FTI NG SNOW
'Ihe p r i n c i p a l problems w i t h d r i f t i n g snow a t t h e expressways o f Nihon Doro Kodan a p p e a r t o a r i s e from t h e l o c a t i o n o f snow f e n c e s , t h e f o r m a t i o n o f d r i f t s b e h i n d guard r a i l s , and t h e r e s t r i c t e d v i s i b i l i t y b e c a u s e o f blowing snow. Snow d r i f t problems a r e b e i n g g i v e n much a t t e n t i o n . A s t u d y o f f e n c e s i s b e i n g c a r r i e d o u t a t t h e Tohoku Expressway S o u t h o f hlorioka and s h o u l d y i e l d v a l u a b l e i n f o r m a t i o n . S k e t c h e s o f t h e snow f e n c e s l a y - o u t a t t h e Sasson Expressway, d i s c u s s e d a t t h e meeting o n March 23rd a t Sapporo, show t h a t snow d r i f t problems a r e b e i n g s t u d i e d c o n s c i e n t i o u s l y and t h e snow f e n c e s p l a n n e d
a) Fence l o c a t i o n - A b a s i c r u l e r e q u i r e s f e n c e s t o b e p l a c e d a t a b o u t a 90° a n g l e t o t h e d i r e c t i o n o f t h e wind, b u t t h e d i f f i c u l t i e s a r e t o e s t i m a t e t h e d i r e c t i o n o f t h e wind which would produce snow d r i f t i n g and t o a c c o u n t f o r v a r i a b l e wind d i r e c t i o n s . Experience has shown t h a t t h e b e s t f e n c e l o c a t i o n i s found by t r i a l and e r r o r on t h e s i t e . About t h r e e w i n t e r s o f experimenting a r e u s u a l l y n e c e s s a r y , and f o r t h i s r e a s o n p o r t a b l e , removable f e n c e s s h o u l d b e used i n i t i a l l y .
I n complex t e r r a i n , such a s c u t and f i l l s e c t i o n s over s h o r t
d i s t a n c e s , i n t e r c h a n g e s , t u n n e l e n t r a n c e s , and i r r e g u l a r b o u n d a r i e s o f f o r e s t s , t h e wind i s o f t e n d e f l e c t e d and forms d r i f t s a t
unexpected l o c a t i o n s . I n such c a s e s t h e l o c a t i o n o f d r i f t s and countermeasures can b e s t u d i e d i n a model t e s t . Model s t u d i e s i n a waterflume, developed by F . H . Theakston a t t h e U n i v e r s i t y o f Guelph, O n t a r i o , Canada, have been found rnos t s u c c e s s f u l
.
b) D r i f t s a t guard r a i l s - T h i s problem e x i s t s i n Canada t o a lesser
d e g r e e because t h e r e i s l i t t l e need f o r embankments h i g h e r t h a n 1 . 5 m i n open t e r r a i n , and t h e medians a r e wide and r e q u i r e no b a r r i e r s . There does n o t a p p e a r t o b e any ready s o l u t i o n f o r t h e p r e v e n t i o n o f d r i f t s a t guard r a i l s . One method of m i t i g a t i n g t h e problem would b e t o b u i l d t h e highway f i l l s e c t i o n s a b o u t a s h i g h a s t h e maximum snow d e p t h and s l o p i n g them w i t h a g r a d i e n t 1:4 o r l e s s . The f l a t s l o p e s would e l i m i n a t e b o t h t h e need f o r guard r a i l s and t h e f o r m a t i o n o f d r i f t s a t t h e s h o u l d e r , b u t d r i f t s would s t i l l form a t t h e b a r r i e r i n t h e median.
c ) R e s t r i c t e d v i s i b i l i t y - T h i s problem i s encountered f r e q u e n t l y i n Canada, p a r t i c u l a r l y on t h e P r a i r i e s , and t h e o n l y s o l u t i o n known i s
t o warn r o a d u s e r s and t o c l o s e t h e highways when n e c e s s a r y . CONCLUDING REMARKS
The s t u d y v i s i t showed t h a t Nihon Doro Kodan i s making a s t r o n g e f f o r t t o f i n d s o l u t i o n s t o snow problems on t h e N a t i o n a l Expressways.
Thanks a r e due t o M r . Mitsuyoshi Maeda, P r e s i d e n t o f Nihon Doro Kodan f o r making t h i s v i s i t p o s s i b l e .
