Soil Temperature Installation at Prince George, B.C.

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Publisher’s version / Version de l'éditeur:

Technical Note (National Research Council of Canada. Division of Building Research), 1958-06-01

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Eden, W. J.

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r1.t1

NATIONAL RESEARCH COUNCIL OF CANADA

ｾﾣＬＮＭ

DIVISION OF BUILDING RESEARCH

'fE

C

1HIN ][ CAlL

NOT FOR PUBLICATION

NOTJE

No.

252

FOR INTERNAL USE

PREPARED BY VI.J. Eden CHECKED BY CBC APPROVED BY NBH

PREPARED FOR Mza. C.P. Harford, City Englneer,

Prinoe George, B.C. June

1958

SUBJECT Soil Tempezaature Installation at Prinoe George, B.C.

SUN:rf.t.ARY_•

This report desoribes the instrumentntion supplied to the City of Prince George to measure solI temperatures around water mains. The

installation was made in November

1957

under the direotion or ｲｾＮ C.P. lrnrford, City Engineer. Instzauctions are given for carrying out and reoording the observations.

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SOIL T8?tPD:HA'1'fTHE ｉＮｎｾｾｔＮＡ｜ｌｌＧ｜ｔｉｏｎ AT PRINCE GEORGE, B.e.

by

"N.J. Eden

To ｮｓＬＧｊＺｴｾｴ in the study of problems w:i.th frozen water

nervlce in Prince George, B.C., ｾ･ Division of Building

Rosearch agreed to supply the neoessary ｩｮｳｴｲｵｷｾｮｴ｡ｴｩｯｮ to

ﾷｾ｡ｳｵｲ･ soil temperatures In Prince George. This roport

describes sn installation @sde in the fall of

1957

under

the direction of

7r.

C.P. Barford, City ｅｮｾｩｮ･･ｲＮ Instruotions

ar Biven for making end recording the observations.

For the City of Prince George. the reoorda \ul1 be

used to determine the thermal recime of the soil surrounding

｢ｬｾｩ･､ water servioes. For the Division, records will be

obtained for t 1e ｾ･ｮ･ｲ｡ｬ study of soil temperatures as

reI ted to ｯｬｬｲｾｴｩ｣ oonditions.

The thermooouple oircuit was prefabricated in the

Division's laboratories in Ottawa and shipped to Prince George

for installation in Hovembezt 1957. A potentiometer beoame

available 1n January

1958

and was shipped to Prince George so

that tomperatuI'o records began at that date. The Installation

The site chosen for the installation was one of ｴＬｾ

ｳｾｲＮｧ･ｳｴ･､ by the City of Prinoe George. It is lenown as the

"Central Station" located on ｈ｡ｲｰ･ｾ Street on Lot

8, BLK55,

nC937.

The installation consisted of tl1rea strines of

thermo-couples, on over the water main, one at tho cnntre of a

Anow-cleared streot and the third in ,round were a normal

snow fall ｾＳｓ allowed to sect nulate. T e soil oonditions were

unlforl:1, oonsisting of sandy gravel, grading from 2 in. SiZ8

to flne sand. Figure 1 is a site plan of the installation

prep red from informs'l;ion received 'rom the city.

Strine No.1 was lonated 12 ft from the 11strmTIent hut

provided by too city undor a snow-covered surface. It oonsisted

of

6

thermooouples pIa oed at depths of 1, 2.

3, 5.

7 and ｾｏ ft.

'11 e second s·tring t"/SS s1 tua ted under the centre of J,Jarper

streov. The ｳｴｉＧｾｮｧ had 10 thermocouples at the follOWing depths:

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2

-over the water main, had 10 thermooouplos at 2, .3,

h,

5, 6,

7, 8,

9

and 10 ft plus 1 thermooouple used to measure the

tornpero ture near the wator ma in. rl!he thermooouples were

tapod to a 2- by 2-in. wooden post to maintain the correot spaoing.

The instrument hut was an

8-

by 8-ft wooden ｳｨ･ｬｴ･ｾ

and provision was made for heating the hut when readings

V:Tero belng taken.

lJ.'he Clrouit

Figure 2 is a cirouit ､ｩ｡ｴｾ｡ｭ for the Prince George

installation Which consisted of several elemonts. There

were three thernooouple strings aaoh terminating in a

jlJnotion box sealed \'7i th a bi tu:minous sealing oompound. From

the junction box a oopper lead wire from each thermocouple

ｴｯｲｾｩｮ｡ｴ･､ in the rotary switoh. One constantan load, ｣ｯｾｭｮ

to all the thermooouples in the string, ｴ･ｲｙｾＮｮ｡ｴ｡､ in tho

reference junction. The copper member of the referenoe junction

was lod through the switch to the potentiometer.

The ｴｨ･ｾｮｯ｣ｯｵｰｬ･ｳ were made of 20-gauGe

copper-oonstantan duplex wire; each member was covered by polyvinyl

chloride, and the two leads were enoased in cotton impregnated

with asphalt. Ｑｾ･ thermocouple points were proteoted by

plastic tubing and were dipped in glyptol enamel. The duplex

TIire terminated in a metal junotion box in whioh the .oopper membors were connected to 20-gauge pvo-covered copper lead

wire. The constantan members met at a cornmon po5.nt and viera

led to the referenoe junction by a single 20-gauge constantan oonduotor.

The refer'enoe junction consisted of a therm.ocouple

immersed In a thermos flask filled with crushed ice and VIa ter to m."l:Lntain a temperature of .32°F.

'J.'he switch \'laS a 28-point rotary type )·iian.ufactnred by

Lewis Engineering Corporation. It is the ｾＡｰ･ often used by

tho Division in thermocouple circuits. Table I lists the

owi toh point numbers corresponding to the various ther:'l1oooupleo.

Before being shipped.f. the oj.rouit assem'bly was c}10clwd

and found to be accurato to "loP. The potentiometer ｷｾｳ a

Rubicon portable model reading in mill! vol ts; ins't;ructions for

its ｬｊｧＬｾ r{ere inoluded when the instrument was delivered. One

prccautlon should be taken wlth tLls instrument - it must NOll'

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- 3

-TABLE I

ｾｶｬｩ tah point Thermooouple string Depth below Remarks

No. No. surfaoe

li't. 1 1 1 2 1 2

ｾ

1 ₃ Under snow 1

₅

cover

ｾ

1

7

1 10

7

2 1 8 2 2 9 2

a

Under oentre 10 2 line of 11 2

l

street 12 2

il

2

₇

2 8

ｩｾ

2

9

2 10

17

3

2 18

₃

a

19

:3 20

₃

ｾ

Over water 21

₃

main 22

₃

₇

ｾ｡

;;

8

:3

9

ｾＶ

,

10

3

On

6

in water main at

7-ft

depth

ffhe oircuit diagram in Fig. 2 indicates the oorrAot

v!iring for obtaining temperatures above

32°F.

['or readings below the freezing point it is necessary to interchanGe the

Ie ads to the potentiometer. Reading the Potentiometer_, i_I

To obtain readings, the potentiometer should bo placed

on a solId level base. It: should be switohed on at loast

5

minutos be foro any readings are taken. When ｡､ＮＱｵｳｴｩｮ｛ｾ the

:i.nstrumcnt tho f:irst step is to centre the galvanmnetor. Course adjustment is made by turn:1.nc; the galvanometer knob.r:.tne

ad,ju.stment is made by slid:I.ng the etohed glass plate nntil the

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-4-The next step is to balance the instrument. against the standard cell. This is dono by turning the resistanoe knobs Rl and R2 as direoted in the manufaoturer's instructions. The balance of the instrwnent ahould be checked frequently while the

readings are being made.

The emf's of the th armoo ouple9 are de termlned by

pressing on the emf button. This button Should not be depressed oontinuously otherwise Q slight error is introduoed.

The millivolt readings obtained are converted to temperatures by using thq conversion table appended to this

report. .

Troatment of Records

It has been found that seasonal variations in soil temperatures extend to e depth of about 20 ft. Daily

variations extend to a depth of about 2 1/2 ft. To assess the magnitude of seasonal wave, temperatures need only be takon at intervals of 2 weeks or 1 month. The daily wave, it it is to be studied in detail, requires frequent readings. To overoome the daily variations it is suggested that readings be taken at the same time of day at eaoh interval.

Prom ｴｾＢｬｩｳ installation. the Division requires sufficient reoords to draw up a graph showing the monthly variations of

temperature vl1th depth. An example of this type of graph 18 ｳｨｯｾｾ in Fig. 6 of "Ground Temperature Illvestigations in Canada" by d.B. Crawford and R.F. Legget .. Engineering ｊｯｾｮ｡ｬＬ Vol. ｬｾｯ

No.3,

Naroh

1957

ｾ (Research Paper No.

33

of the Division of

Building Re3aarohJ. To onllect infor@Stlon on the goneral problem of frozen water mains, additional records suoh as the water ｴ･ｭｰ･ｲ｡ｴｴｾ･ｳＬ rates of flow and the depth of frost

enoountered in winter exoavation would be helpful. It is believed that the meteorologioal records obtained from Prince George Airport by the ｄ･ｾ｡ｲｴｭ･ｮｴ of Transport will be adequate for c orrela tion purposes. The fOI'"'AJ' supplied by Mr. G.W. Jonea

of the Engineering Dapartment, City of Prinoe George, if oompleted, will supply very acceptable infornmtion for the Division's records.

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APPEnDIX 101

• - il11111"01

t Conver 1 TenD. of ｾＧＢｶ Temp .. of r.cv _ r . . . _ｾ

-

_ｾ

10 -.4tR

ｾｧ

ＫＮＰＶｾＮ

11 _-.L!.

!

+.

o

r,c:

< ｃＩｾ

12

_{ＭＮｾＲＳ}

₃₇

+.107

iR

- .1..\.02

-.3

81

38

+.129

ｾＶ

+.15°

11 -.360

+.172

1)

_-.340

₄₁

_+.193

17 -.319

₄₂

+.21[)

18 -.298

tta

+.2i

8

19 ••27

6 +.200

20 -.25

J'g

+.2a1

21

_ＭＮＲｾ

ｾ

_+.3°3

22 _-.2

ｾ

ｦｲｾ

+.32

5 ｾｾ

-.193

ＫＮＳｾＭＷ

-.171

49 +.3 9

ｾｾ

-.15°

50 +·ili

O

-.128

51

....

2

27

....107

52

ＫＮｾＭＳｱＮ

28

•• 08ft

§a

+.11.57

29 -.06

ｾ

+.479

30

-.043

_ｾｧ

+.5°0

)1 -.021

+.r)23

3

2

-.000

57 _{ＫＮＵｾＵ}

ｾｾ

+.022

58 +.5

7 +.043

g6

+.589

+.612

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GROUND SURFACE

ｾＯｾＬ

SWITCH-#17 2' 3' ,..

-19 4' 20 5' SWITCH #26 21 6'

_ /

22 7 23' 8' _,,/ｾ 24 9' 6" WATER 25 10" MAIN STRING NO. 3

--

3' t 4' L E A D - I Y 10 II s' CABLE 12 6' /3 7' 14 S' 15 9' 16 10' STR I NG NO. 2 6 10' STRING NO. I 4 5' 5 7' DEPTH OF THERMOCOUPLE

ｾｾ

ｊＱ＿Ｏ｜ＧＭｾｾｾｾ

SWITCH#, I' SWITCH#7 I' 2 2' 2' 3

PROFILES OF THERMOCOUPLE STRINGS

HARPER

ST LEAD IN CABLE 6" ASBESTOS CEMENT WATER MAIN N

-t-66' I f-o. - - - - ＭＭＭＭＮＮＺＮＮＮＮＮＮＺＮＮＮＮＭＭＭＭＭＭｾＮｉ I II

I

I I ST RING NO. 3

J

Ii W I ｾｬ STRING N O . 2 : : , .J

ｉｈｾｔｦＭＭＭＺＭＭＭＭＭＭＢ［Ｍｾ｣ｲＭＭｾＺＺ

_ｾＭＭ _{-- __} _ＭＭｾ _II

ｾＺ

_a:: APPROX.

/:1

0..1

TRAVELLED II

I

PORTION. II I GRAVEL SURFACE I

I

I I

6 I

ST R I NG NO. I Iw ｉｾ _...J

I .

ll. o a:: Q.

SITE PLAN

SCALE /": 20'-0" (CITY OWNED) 'LOT 8 BLK 55 OL 937

FIGURE

SOIL TEMPERATURE

MEASUREMENT AT

CENTRAL STATION

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e

j 1 0 - 1 POTENT I.DMETER , 1 0 + I

e

ｾ STRING NO. I

LJ

SELECTOR SWI TCH