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Technical Note (National Research Council of Canada. Division of Building Research), 1960-08-01
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Avalanche Defence on the Trans-Canada Highway Between Mt. Revelstoke National Park and Glacier National Park
Schaerer, P. A.
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NOT FOR PUBLICATION
DIVISION OF BUILDING RESEARCH
USE
No.
316ｾＮｎａｌ
NOTlE
'f
EClHI N][ CAlL
••
PREPARED BY P. Schaerer CHECKED BY APPROVED BY R.F.L.
August 1960
PREPARED FOR D.J. Gormley 1 Regional Construction Engineer 1
Department of ｈｩｧｨｷ｡ｹｳｾ Kamloops1 B.C.
SUBJECT -AVALANCHE DEFENCE ON THE ｔｒａｎｓｾｃａｎａｄａ HIGHWAY BETWEEN MT. REVELSTOKE NATIONAL PARK AND GLACIER NATIONAL PARK
In discussions with Mr. D.J. Gormley during the summer 1959
and in a letter dated 23 October 19599 it was arranged that the author
of this note would review the avalanche defences on the Rogers Bass
route during the summer of 19600 The observations made during the
winter 195971960 would then be available and a better picture of the
action of the planned defences could be gained. The author reviewed
the avalanche defences during a visit to Glacier in May and June 1960.
The following comments cover the avalanches between Mt. Revelstoke National Park and Glacier National Park.
Highway Section between Mt. Revelstoke National Bark and Albert Canyon Frequent avalanches occur in the Silver Creek Cut between
Station 20 and Station 80. The snow slides on the bare steep rock.
Avalanches can be expected at this site after heavy ｳｮｯｷｦ｡ｬｬｳｾ after
ｲ｡ｩｮｾ and during the snow melting period.
It appears that supporting structures would be the best
defence. These structures would retain the snow on the slope above the
highway and would prevent the snow from sliding. The structures
-could be strong fences of timberp steel or aluminum or nets of steel
cables or nylon. There would be no problem with the foundation as
the fences could be anchored into the rock. The structures and the
arrangement of the structures could be designed according to the Swiss standards 1 issued by the Forest Service of the Swiss Federal Department of the Interior.
2
-- The following must be known before any supporting structures can be designed:
(I) the location where the avalanches usually start to slide.
(2) the maximum snow depth in the area where the avalanches
start.to slide. Observations on the maximum snow
depth on anundisturbed area near the highway would be sufficient.
These observations should be made during the winter 1960/ 1961.
Highway Section between Albert Canyon and Illecillewaet
Experience during the past two winters has shown that in tliis section dangerous avalanches do not occur very frequently. The highway should be closed at times when avalanches are likely to reach the highway.
Slides between Station 262 (Mile ＴＹＹＮＷｾ and Station 273 (Mile 499.9)
No large and effective earth structures which would stop
or divert the avalanches can be built on the ｳｴ･･ｰｾ wet side hill.
It may be possible to widen the highway cut in the slide path thus creating more catching space for the avalanche snow between the
mountain and the highwayo This would reduce ｳｬｩｧｨｴｾ the amount
of snow deposited on the highwayo Slide at Station 281 (Mile 50001)
A bench might be built in the avalanche path if the
stability of the mountain slope above the highway will permit it.
The bench should have a width of 80 feet9 and an access road from
the highway to the bench with a grade of not more than 25 per cent o The bench would retain some avalanche snow and reduce snow clearing work on the highway.
Slide at Station 307 (Mile 500.5)
A diverting dam could be built to divert the avalanches to the east side into an area where there is enough storage space between the highway and the mountain for most of the avalanche snow. This dam could divert not more than two avalanches each winter.
After two avalanches had occurred9 the dam would be backfilled with
snow and would be no longer effective. The dam would also control
the creek which crosses the highway at this location. The creek
could be diverted to the side where a culvert could be SUitably located.
A project for the diverting dam is shown in Figo 10
The estimated earth quantity to be moved 1s ＸｾＰＰＰ cubic yards o
The-work could be done by bulldozer onlyo It is suggested that
this
dam be built only if the work can be included in the gradingcontract for the highway or at the time when a channel is ｣ｯｮｾ
structed for the creeko It would be useful to observe how this
avalanche affects the highway before any defence is constructed o Highway Section between Illecillewaet and Glacier National Park
The avalanches in this section were observed and surveyed
by the avalanche survey crew from the Dept0 of ｾ｢ｬｩ｣ Works during
the winter 1959/600 A copy of a pIan showing the· avalanches that
occurred was forwarded in June 19600
Jack MacDonald Avalanche
A Shed is planned for the protection of the highway in
"this avalanche patho The location of the shed as designed by
Choukaloss> Woodburn!> Hooley
&
McKenzies> Consulting Engineerss> isfrom Siiation 499 + 44 to Siiation 504 + 550 This is an ample length
and no avalanches should affect the highwayo
!Ille design loads for the shed are ｾ
Deposit ｬｯ｡､ｾ 600 Ib per sqo fto
Moving ｬｯ｡､ｾ 500 u It It It
Lateral loadg 250 tt Ii ｾ Ii
It is considered that these loads are adequateo Avalanches may
be,!!eflected on the ｬｾｧｬ slope on the backfills> jump into the
airs> 'and land on the shedo The impact force created by such
avalanches!> however!> does not exceed the design loads o The back=
fill behind the shed should not be wider than 65 feet on the tapo
If consideration is given to a further increase of this Widths> then
the fill should have a slope of 2g1 or less on the uphill stdeo
In the winter of 1959/1960 only one avalanche crossed the
highway!> this being an March 190 The avalanche activity was
generally high at Rogers Pass on this day1I and the highway would
have been closed o A shed!> therefore!> would not have been necessary during this particular winter o
ｾ･ｲ Slide
This avalanche slides in a shallow gully through heavy
timber and crosses the highway between Station 510 + 50 and Station
512
+ 000 The avalanche was not noticeable before the timber wascleared for the highway and no protection was planned o
4
-The accumulation area of this avalanche is in an open area on the heavy timbered mountain side, approximately 1,500
feet above the valley. Avalanches here are usually caused by
rain and by warm weather. -It is expected that the highway would be closed when this avalanche occurs, but snow could be deposited
on the highway toa considerable depth. In winter 1959/1960
avalanches occurred on 29 January and 18 Marcho On both dates
there was a high avalanche hazard on Rogers Pass and it was assumed that the highway would have been closed.
The possibilities of defence were studied during a
field inspection on 13 May 1960 and the following was ｦｯｵｮ､ｾ
(1) Supporting structures in the accumulation area would
prevent any avalanches from starting to slide, but construction costs for such structures are likely to be high.
(2) The steep mountain side with slopes between 32 and 45
degrees ､ｯｾｳ not permit an effective defence in the
avalanche path.
(3) A wider cut with wider ditch on the side of the highway
would retain some avalanche snow, but it would not prevent the highway from being blocked with snow. The following is suggested for the avalanche defenoe. The behaviour of this avalanche should be observed during the
next few winters. A light shed might have to be constructed later
if the avalanche occurs too frequently and too much snow is deposited
on the highway. If additional earth material is required for the
highway grading, it might usefUlly be obtained from this site so that the highway will he wider where it crosses the avalanche patho Twins Avalanche
A shed is planned for the protection of the highway between
Station 527 + 40 and Station 533 + 300 The shed appears to be at
the right location.
The follOWing design loads for the shed were recommended in 1959: Deposit ｬｯ｡､ｾ Moving loadg Lateral loa dg 600 Ib 500 II 250 " It It " " It "
The aeposit load appears to be adequate. The moving load is
probably high and may occur in extreme cases only (once in 20
years). The shed could be designed for a normal maximum moving
load of 400 lb per sq. ft. and a lateral load of 200 lb per sq.
ft.
Avalanches crossed this highway location four times
during the winter 1959/60. On January 29 a major avalanche
crossed the Illecillewaet river, derailed a freight train and deposited 10 feet of snow·on the railway tracks for a lengthrof 150 feet. From the distance whi:: h this avalanche travelled and from the effect on the train pit could be computed that the avalanche had a speed of 65 miles per hour when it reached the Illecillewaet river.
All the avalanches were confined to the two gullies and only windblast with snow dust affected the highway location
outside the gully. Lanark Avalanohe
A shed is planned for the proteotion of the highway
between Station 550 + 25 and Station 560 + 50. The shed appears
to be looated correctly.
The following design loads for the shed were reoommended
in 1959'
Station 550 + 25 to Station 555 + 50g
Deposit loadg 800 Ib per sq. ft.
Moving ｬｯ｡､ｾ 600 n ft
"
ftLateral loadg 300 "
"
ft flStation 555 + 50 to Station 560 + 5Dg
Deposit 10ad2 400 lb per sq. ft.
Moving loa d g 400 ｾ II tt ft
I
Lateral load: 200 "
"
"
Itｾ･ｳ･ loads were reviewed and it was found that they are adequateo
Snow depth and snow density measurements proved that the major avalanche on 30 January 1960 would have caused a moving load on the future shed whioh was between 500 and 600 lb per sq. ft.
ｾ･ snow deposit on the planned shed would not have reaohed the
...
Five avalanches reached the highway during the winter
1959/19609 about the number of avalanches which can be expected
during an average wintero The avalanches followed the-deep creek
channel in the long fano The artifio1al dam on the west side
was not touched by any avalanche. The dam on the east side was
affected by an avalanche of light snowg which was higher than
the dam. The damv however9 protected the highway from the main
effect of the avalanche and only few snowballs and snowdust came
over the dam0
On 24 November and 30 Januaryy avalanches of wet and
heavy snow were deflected on avalanche snow,previously deposited on the highway fill and they continued sliding along the partly completed grade\!:Ifor a length of 180 feet .and 235 feet respectivelyo It is expected that this phenomenon will not be observed when
the shed is constructed as the avalanches would slide downward on the 5gl slope of the shed.
Care must be taken to ensure that no bench is created above the shed when earth is excavated for the backfill behind
the shedso A, bench could cause jumping of an avalanche0 There
is already a small bench 240 feet from the highway centreline but
it is not dangerouso This bench must not be widened or deepenedo
The lanark shed is not expected to be completed in
19600 It would be an advantage if the western part of the shed
with the section crossing the creek channel could be completed
first0 Observations during the winter 1960/1961 could prove how
the avalanches act on this shed
and
on the backfill o Thisexperience would be useful for the design of the similar structure
for the Jack MacDonald avalanche0 Avalanches at the Lanark site
must be expected after the first heavy snowfalls in the valleyv
usually after
15
November oOn 10 June 19609 Mro Bo Pennerv Res1.dent Englneerv had
discussions w1th the author of this note on the pressure that an
avalanche would exert on the head wall at the culvert in the
Lanark Avalanche. The highest pressure occurs when a fast moving
avalanche of dry snow hits the wallo The 'e'vslanche may have a
speed of 100 feet per second9 a depth of 25 ｦ･ｾｴ and a snow density
of 0.20 or 13 lb per CUo fto It must be assumed that the avalanche
oomes to a full stop at the wall and the snow is compaoted there o
The pressure is ｲｯｕｧｨｬｪｲｾ
ｄ･ｮｾｩｴｹ x ｾ･ｾ､Ｒ = 13 x 1002 = 4000 lb per sqo fto
with 9
per sqo ft o for every 10 fto height o During the past three winters
when observations were made in this slidepath9 smaller9 wet snow
avalanches had always filled the gully first before one maximum dry avalanche occurred as described above o
Boundary Slide
This small avalanche between Station 571 + 00 and Station
574 + 00 occurs after rain and during snow melting periods o
It could cover one lane of the highwayo An additional wide cut
on the mountainside of the highwaY,could reduce the hazard of
this slide to the highway0 The ｣ｕｾ should only be made however
if the excavated material is required for the highway gradingo A final report on the avalanche defence on Rogers Pass
is being prepared o Each avalanche and the method of defence will·
be described there and recommendations for future observations
and later adjustments will be giveno The avalanches in the section
between Mto Revelstoke National Park and Glacier National Bark will be included in this reporto
SUGGESTED DIVERTING DAM AT MILE 500·5 SLIDE PATH
:!
I I CUTLINE - - _ U) V N + 10 ｾ U W CENTRELINE HIGHWAY o co + U) o It) CROSS-SECTION OF DAM o 10 + it)NOTE: THIS PROJECT IS BASED ON LOCATION PLAN NO. 326-8. IT IS A PRELIMINARY PROJECT. CHANGES MAY BE REQUIRED AFTER
I I ' •
ACCURATE SURVEY. SCALE I =200
FIGURE I
AVALANCHE DEFENCE, TRANS -CANADA HIGHWAY, BRITISH COLUMBIA
