Publisher’s version / Version de l'éditeur:
Technical Note (National Research Council of Canada. Division of Building Research), 1961-08-01
READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.
https://nrc-publications.canada.ca/eng/copyright
Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.
Questions? Contact the NRC Publications Archive team at
PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.
NRC Publications Archive
Archives des publications du CNRC
For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous.
https://doi.org/10.4224/20338512
Access and use of this website and the material on it are subject to the Terms and Conditions set forth at
Observations on Hostel at Fort McPherson N.W.T.
Johnston, G. H.
https://publications-cnrc.canada.ca/fra/droits
L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.
NRC Publications Record / Notice d'Archives des publications de CNRC:
https://nrc-publications.canada.ca/eng/view/object/?id=f41f48f2-45ec-411f-82d8-a76e952480f0 https://publications-cnrc.canada.ca/fra/voir/objet/?id=f41f48f2-45ec-411f-82d8-a76e952480f0
DIVISION OF BUILDING RESEARCH
NATIONAL RESEARCH COUNCIL OF CANADA
'If
E
C
JHI
N II
C
AIL
NOT FOR PUBLICATION
NOTE
No.
341
FOR INTERNAL USE
PREPARED BY G. H. Johnston CHECKED BY H. B. Dickens APPROyED By N.B.H.
PREPARED FOR
Record Purposes
August 1961
SUBJECT Observations On Hostel At Fort McPherson N.W.T.
During the course or a visit to Fort McPherson on August 23rd to 26th, 1960, ror the purpose or establishing precise ground control points ror aerial photographic surveys of northern settlements being conducted by the Department of Northern Arrairs and National Resources, the author made a brier inspection of the roundations for the large hostel
completed in 1958 and reported to have experienced significant movements in the winter of 1959-60. The following notes record the information obtained during the visit.
Hostel Construction History
The hostel roundation consists or concrete piers cast in place in holes excavated to shale encountered at depths
ranging rrom
8
to 14 feet (average 12 rt.). Although all piers were to be founded on the shale, there is a possibility that a few were only carried down to the loosely consolidatedmaterial above the shale, which in some cases contains a great deal or ice. The excavations were very close together and some,
;
I
which were excavated in
1957
filled with water and wore left over the winter before the piers were placed. Under the boilerhouse section of the hostel the whole area was excavated down to shale, the piers placed and the area then backfilled.Immediately following the concrete placement for the piers the excavations were backfilledo 'l'he presence of
water around the piers together with the general cold regime of the surrounding ground may have had some detrimental
effect on the concrete during the curing period. There is some doubt as to whether all the piers were tied into the footings and how they were tied in.
Large continuous concrete beams were then placed on top of the piers.
Building ｐ･ｲｦｯｲｭ｡ｾ
During the winter of
1959-60,.
a great deal of movement was reported in the superstructure which caused large (1")cracks to open between partitions, stairways and walls--windows would not open and in some instances, breaks in water and steam lines occurred in the buildings.
ｾＮｾＮ H. McNab, Structural Engineer for the DPW, Edmonton office, visited HcPherson on Naroh Ｒｌｾ and
25, 1960
and invest-igated the trouble occurring at the hostel. lfust of the trouble, according to his report, was apparently caused by poor or under-design of the concrete beams which showed considerable cracking at points of stress (e.g. where insufficient reinforcing steel had been placed). Hovement of the foundations and shrinkage of the wood used in the construction were considered to have been contributing factors.Observations - August,
1960
No remedial measures had been carried out by DPW up
to the time of this visit. Most of the cracks which had opened up in the superstructure in the winter of
1959-60
had closedagain in the interior of the bUilding. The cracks in the concrete beams and piers however, were quite evident and par-ticularly severe at the S.W. corner of the building.
.'
The general area around the hostel slopes from south to north and all water from the area south of the hostel drains across the hostel lot Lmder the building. The yard around the hos tel bas been baclcfilled with shale and graded so that a large depression rernains w1der the building forming a natural lake bed into which considerable rLm-off can drain. 'fhere are also depressions around individual piers caused by settlement of the backfilled material.
A great deal of water had ponded under the building probably during the spring run-off, as evidenced by water marks on the concrete piers--being as much as 3 ft. above ground level in some cases. At the time of this visit considerable water remained under the building, but was kept under control by intermittent pumpinr; each day.
It was impossible to determine whether any heaving or settlement of the piers had occurred. However, to follow future movements, if any,
19
elevation reference points were established on concrete piers along the west wing and the south-west corner of the building by drilling holes in the concrete piers with a star drill at set elevations. Two groups of reference points were established--nine being at one elevation and ten at anotherelevation. The centre of the 3/13" hole drilled in the concrete is to be taken as the reference point--these should be accurate
to :!:Lll
4 •
During the construction period in
1957,
five thermo-couple strings were fabricated at the Northern Research Station, Norman Wells and given to ｽｾＮ R. G. Harding (DPW ResidentEngineer) to install in the pier excavations imnlediately adjacent to the pier. Three of the strings were located--one of which was on the hostel; on the N.Y. pier of the boilerhouse wing. The other two were found attached to concrete piers under the 8chool--1e. west of the hostel. Temperature readings were taken using a portable precision potentiometer with ice bath reference junction.
,
Ground ｔ･ｭｰ･ｲ｡ｴｾ (,He corded on August
24,
1960)A School #1
:/12
Depth (ft.)=
2'.5.'
11' Temp. (OF.) =34.3°
29.0°
ＲｌｾＮＶﾰ Depth (ft.)=
+1' 2'8'
Temp. (OF. )=
44.2°(Air)36.9°
28.0°
B Hostel #1 (N.IV. corner of Depth (ft.) = Temp. (OF.) = boilerhouse wing)
3'
6' 12'37.1°
30.3°
27.1°
It was virtually impossible to probe through the shale backfill under the building to determine the depth of thaw. Two or three excavations were made beside piers under the west wing but had to be abandoned at from 12ii_18il below the grade
level because of water entering the hole and because of the very sticky clay material encountered. The whole area under the
building was saturated with water. Comments and Recommendations
It is very difficult to say whether or to what extent movement of the piers had caused the troubles experienced.
Certainly, the construction tecIDliques and the drainage conditions, in particular, which have existed at the site are reason to
suggest that some movement (heaving, settlement or both) may have occurred. The one thermocouple string under the hostel showed that, for that particular pier, the ground was frozen from at least the 6' depth. However, some of the piers may not be frozen in at that depth and if they did not have sufficient anchorage {and tie-in to their footings) could be subject to frost action forces which could be quite severe due to the large quantity of water available for ice lens growth. Thus these piers could be subject to frost heave during the winter months followed by settlement during the swarner thaw season.
,
5
It is also possible that water could percolate
alongside the pier down ｢･ｬｯｴｾ the footing, against which the backfill is loosely placed, and freeze there thus subjecting the footing and pier to upward movement. .
However, it appears, as reported by ＱｾＮ McNab, that underdesign of the main concrete beams and subsequent failure of some of these members has contributed to the troubles
experiencedo Other factors such as insufficient strength
(nailing) in superstructure members, shrinkage of wood materials upon drying and also, in some cases, poor concrete work may have had an effect.
Certainly the drainage conditions existing on the site are critical and if not rectified will cause further thawing of the underlying permafrost.
Drainage measures had been proposed for the site as shown on DPW drawing 8-6 but as yet had not been carried out. These consisted of a drainage interceptor ditch along the south boundary of the property connecting to a main ditch running
north along the east boundaryo In addition, a ditch was proposed under the centre of the hostel connecting with the ditch on the east side of the propertyo The south side interceptor ditch is required to prevent more water from collecting under the building. Local water from the area immediately adjacent to the hostel can be collected in the ditch joining the main ditch. Care should be taken to see that water from other sources (such as from the
boilerhouse or laundry or septic tanks) is not allowed to collect under the bUilding.
Proper use should be made of the shutters provided, to control the air flow under the buildingo These should be closed
in the summertime (they were wide open during this visit) and opened in the wintertime to promote freezing and thus counteract summer thaw.
It would be useful to deternline if any movement of the concrete piers does occur. This could be done by making periodic checks on elevation reference points during critical times of the year, such as spring and fall. The large water tank in the
boilerhouse could be used as a level gauge--this large tank is placed on a concrete slab and periodic examination of the water
level in the tank would show whether differential movement is occurring.
Water which ponded under the building left well defined marks on many of the concrete piers which, if they remain well defined, could serve as reference points.
