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Equipment and methods for soil frost action studies
NATIONAL RESEARCH COUNCIL OF CANADA DIVISION OF BUILDING RESEARCH
DBR INTERNAL REPORT NO. 503
EQUIPMENT AND METHODS FOR SOIL FROST ACTION STUDIES
by E . Penner and D . Eldred
Checked by: Approved by:
Prepared for: Record Purposes
ABSTRACT
ANALYZED
Date: August 1985
This paper d e s c r i b e s methods developed by t h e authors f o r s t u d i e s o f f r o s t a c t i o n i n s o i l s , and t h e DBR f a c i l i t i e s f o r t h e s e
EQUIPMENT AND METHODS FOR SOIL FROST ACTION STUDIES
E. Penner and D. E l d r e d
T h i s r e p o r t i s a r e c o r d of t h e c u r r e n t methods and f a c i l i t i e s f o r s o i l f r o s t a c t i o n s t u d i e s a t DBR d e v e l o p e d by t h e a u t h o r s .
The c u r r e n t phase of t h e f r o s t a c t i o n s t u d i e s commenced when a f r o s t c e l l d e s i g n e d and d e v e l o p e d by W.A. S l u s a r c h u k of N o r t h e r n E n g i n e e r i n g S e r v i c e s (NES) was a c q u i r e d . The c e l l was m o d i f i e d , p a r t i c u l a r l y w i t h r e s p e c t t o t h e method of a p p l y i n g t h e o v e r b u r d e n p r e s s u r e and t h e s u p p l y of w a t e r t o t h e s o i l sample, b u t t h e f e a t u r e t h a t was u n i q u e , and r e t a i n e d , i s t h e upside-down d i r e c t i o n of f r e e z i n g of t h e sample. I n a d d i t i o n , i n t h e NES c e l l t h e sample i s a l l o w e d t o a d f r e e z e t o t h e w a l l s of t h e sample h o l d e r . Heaving d i s p l a c e m e n t due t o l e n s i n g and e x p a n s i o n r e s u l t i n g from t h e w a t e r l i c e phase change of p o r e w a t e r i s accommodated by t h e s l i d i n g of t h e u n f r o z e n p o r t i o n i n s i d e t h e c e l l . T h i s d o e s n o t e r a d i c a t e a l l
f r i c t i o n a l r e s i s t a n c e t o h e a v i n g , b u t c a l i b r a t i o n of t h e f r i c t i o n i s
p o s s i b l e and, of c o u r s e , no d i f f i c u l t i e s a r e e n c o u n t e r e d when no o v e r b u r d e n p r e s s u r e i s a p p l i e d .
The l a b o r a t o r y f r e e z i n g t e c h n i q u e a d o p t e d is t h e ramped f r e e z i n g method i n i t i a t e d by t h e North-West A l a s k a (NWA) f r o s t heave program. T h i s
t e c h n i q u e i n v o l v e s t h e s y s t e m a t i c l o w e r i n g of t h e t e m p e r a t u r e a t b o t h e n d s of t h e sample a f t e r i n d u c i n g c r y s t a l l i z a t i o n . The most i m p o r t a n t a d v a n t a g e of t h e ramping method i s t h a t r a t e s of f r o s t p e n e t r a t i o n s i m i l a r t o t h o s e below a c h i l l e d g a s p i p e l i n e can be s i m u l a t e d i n t h e l a b o r a t o r y .
The ramp t e m p e r a t u r e g e n e r a t i o n and t e m p e r a t u r e c o n t r o l of t h e sample was improved a t DBR by c o m p u t e r i z a t i o n , which h a s l e d t o g r e a t e r c o n t r o l o f t h e o v e r a l l f r e e z i n g p r o c e s s .
METHODS AND MATERIALS F r o s t c e l l
F i g u r e 1 shows t h e c u r r e n t v e r s i o n of t h e f r o s t c e l l , which c o n t a i n s t h e m o d i f i c a t i o n s made t o t h e NES c e l l d e s i g n . I t s h o u l d be n o t e d t h a t f r e e z i n g i s from t h e bottom up
-
a major i n n o v a t i o n t o l a b o r a t o r y f r e e z i n g of s o i l s i n t h e o r i g i n a l NES c e l l . The p l a t e a t t h e t o p of t h e specimen i s t h e s o - c a l l e d warm end. T h i s p l a t e h a s p r o v i s i o n f o r c i r c u l a t i n gt e m p e r a t u r e - c o n t r o l l e d l i q u i d and t h e s u p p l y of w a t e r t o t h e sample t h r o u g h a porous p l a t e . The warm p l a t e r e s p o n d s t o t h e movement i n d u c e d by i c e s e g r e g a t i o n and p r o v i d e s a c o n v e n i e n t l o c a t i o n t o measure heave w i t h time. S i n c e X-rays a r e u s e d t o l o c a t e i c e growth, m e t a l o b j e c t s must n o t o b s t r u c t t h e X-ray beam i n t h e r e g i o n between t h e X-ray g e n e r a t o r and t h e f i l m .
A t h i n t e f l o n f i l m s h e e t i s g l u e d t o t h e i n s i d e of t h e c e l l t o r e d u c e f r i c t i o n between t h e c e l l w a l l and t h e u n f r o z e n s o i l . The t h e r m i s t o r l e a d s and t h e t h e r m i s t o r s l i e i n a s h a l l o w g r o o v e immediately b e h i n d t h e t e f l o n s h e e t . The g r o o v e s c i r c l e t h e c e l l w a l l a t r i g h t a n g l e s t o t h e d i r e c t i o n of
h e a t flow. Thus, t h e t h e r m i s t o r l e a d s l y i n g i n a n i s o t h e r m a l p l a n e i n t h e c e l l r e d u c e t e m p e r a t u r e e r r o r s r e s u l t i n g from t h e r m a l c o n d u c t i o n . Tenney C o n t r o l l e d E n v i r o m e n t a l Chamber A commercial c o n s t a n t - t e m p e r a t u r e a i r chamber i s u s e d t o h o u s e t h e f r o s t c e l l d u r i n g t h e f r e e z i n g p r o c e s s . The t e m p e r a t u r e i n t h e Tenney Chamber i s c o n t r o l l e d a t a b o u t +O.l°C. A c o n s t a n t t e m p e r a t u r e e n v i r o n m e n t around t h e c e l l r e d u c e s v a r i a b l e h e a t l o s s e s from t h e sample d u r i n g t h e f r e e z i n g p r o c e s s . There i s , however, a m a t t e r of o v e r a l l h e a t l o s s e s t h r o u g h t h e s i d e s of t h e c e l l . Chamber t e m p e r a t u r e s a r e k e p t a t a b o u t t h e a v e r a g e of t h e sample-end t e m p e r a t u r e s . T h i s r e d u c e s t h e unwanted h e a t l o s s e s from t h e sample t o manageable v a l u e s . The f l a t n e s s of t h e i c e l e n s e s a t t e s t s t o i t s s u c c e s s .
P h i l i p s X-Ray Equipment
A p o r t a b l e 200 KV X-ray g e n e r a t o r i s u s e d t o p i n p o i n t t h e l o c a t i o n of t h e growing i c e l e n s w h i l e h e a v i n g i s i n p r o g r e s s . T h i s e n a b l e s t h e i c e l e n s t e m p e r a t u r e s t o be a s c e r t a i n e d and i s f u n d a m e n t a l t o t h e problems u n d e r i n v e s t i g a t i o n . The Tenney Chamber h a s a s t e e l a c c e s s door which must remain open w h i l e e x p o s i n g t h e sample t o X-rays. An i n n e r d o o r c o n s t r u c t e d of p l a s t i c i s u s e d t o k e e p X-ray f i l m e x p o s u r e t i m e low and s t i l l m a i n t a i n a c o n s t a n t t h e r m a l environment i n s i d e t h e chamber. By t r i a l and e r r o r i t was e s t a b l i s h e d t h a t t h r o u g h t h e p l a s t i c door an e i g h t minute e x p o s u r e t i m e a t f u l l power i s s u f f i c i e n t t o p r o v i d e t h e r e q u i r e d p h o t o g r a p h i c d e t a i l . An I n d u s t r i x AA f i l m i s sandwiched between one s e t of f l u o r o m e t a l l i c (Kyoyko
SMP 1 0 8 ) and one s e t of 0.010 i n c h (0.254 mm) l e a d i n t e n s i f y i n g s c r e e n s .
During e x p o s u r e t h e f i l m h o l d e r i s mounted b e h i n d t h e c e l l i n s i d e t h e chamber. The X-ray beam was c o l l i m a t e d s o t h a t t h e image would c o v e r t h e
8+ x 11 i n c h f i l m . Because of t h e l o c a t i o n of t h e f i l m r e l a t i v e t o t h e c e l l
t h i s g i v e s a s l i g h t l y l a r g e r image t h a n t h e a c t u a l s i z e of t h e f r o z e n
sample. A d i s t a n c e of a b o u t 2 metres s e p a r a t e s t h e X-ray g e n e r a t o r and t h e X-ray f i l m .
Modified IIotpack R e f r i g e r a t e d L i q u i d Bath C i r c u l a t o r
Hotpack b a t h s a r e u s e d t o s u p p l y t e m p e r a t u r e - c o n t r o l l e d l i q u i d f o r t h e f r o s t c e l l - e n d h e a t e x c h a n g e r s . C i r c u l a t i n g f l u i d s u s e d f o r t h e two sample-end t e m p e r a t u r e s a r e computer c o n t r o l l e d . A t h i r d b a t h p r o v i d e s a r e a d y s o u r c e of c h i l l e d l i q u i d t o i n d u c e c r y s t a l l i z a t i o n a t t h e s t a r t of e a c h h e a v i n g e x p e r i m e n t . To p r o v i d e computer c o n t r o l of t h e l i q u i d b a t h t e m p e r a t u r e s , a n
e l e c t r i c a l r e s i s t o r was added t o one l e g of t h e w i r e l e a d between t h e b a t h t e m p e r a t u r e s e n s o r and one l e g of t h e Wheatstone b r i d g e of t h e h o t p a c k c o n t r o l l e r . With a s p e c i a l multiprogramrner ( c u r r e n t d i g i t a l t o a n a l o g c o n v e r t e r ) a c o m p u t e r - c o n t r o l l e d c u r r e n t s u p p l y of up t o f20.00 ma was p r o v i d e d a c r o s s t h e i n s t a l l e d r e s i s t o r of t h e t e m p e r a t u r e b a t h . The
s m a l l e s t o u t p u t s t e p w i t h t h e HP multiprogrammer i s 0.01 ma, which w i t h t h e h o t p a c k t e m p e r a t u r e b a t h s , g a v e a t e m p e r a t u r e change of 0.0015°C.
The m o d i f i c a t i o n t o t h e t e m p e r a t u r e c o n t r o l of t h e Hotpack l i q u i d b a t h c i r c u l a t o r i s shown i n F i g u r e 2. With t h i s a p p a r a t u s v a r i o u s t e m p e r a t u r e -
controlled freezing sequences can be programmed. They are used most
frequently to reduce the end temperatures uniformly with time, e.g.,
0.02OC
per day. When this is done at both ends of the sample, a controlled frost
line penetration into the sample is achieved.
The program for controlling the end temperatures has most of the
elements of a proportional controller. The system's digital voltmeter reads
the temperature of the sample's end. The programmed temperature sampling
and adjustment frequency depends on the magnitude of the error signal.
If
the end temperature is different from the required set temperature (error
signal), the multiprogrammer signals a current change to the bath resistor
and the bath temperature changes accordingly. When the computer is
programmed to ramp the end temperature at a rate of 0.02OC/day with a 10 ohm
signal resistor, it does it in steps of 0.0015°C.
Hence, the set
temperature is changed approximately every 108 minutes. Greater frequency
is possible if the daily rate of temperature change is larger.
Guildline Temperature Bath for Calibrating Thermistors
The temperature of the calibration bath is measured with a Model 9535
Guildline thermometer having a resolution of O.OOl°C and a claimed accuracy
of O.Ol°C over a 24 hr. period. The Guildline thermometer is calibrated
monthly with a standard platinum resistance thermometer to
4O.OOl°C to
assure continued accuracy.
The glass-encased thermistors to be installed in the frost cell are
calibrated using the HP temperature measuring system also used for actual
frost heaving experiments. Prior to calibration the thermistors are given
the usual stabilizing thermal shock treatment of 10-20 alternate exposures
to ice bath and boiling water temperatures.
Computer System
The new HP 1000, Series A600, Model 6 computer replaced the HP 9835,
and
isrunning under the RTE-A operating system. It is now fully
operational. A 2623/2671 graphics terminal, a 7910 twelve megabyte disc
drive, a 7908 16.5 megabyte disc and a 2631 printer are on one HPIB. A
3455A voltmeter, a 3495A scanner and a 6942A multiprogrammer are on a second
HPIB, and a 72456 plotter is on a third HPIB. With this arrangement,
plotting and printer operations do not interfere with the temperature
control of the frost cell or the temperature ramping program. A photograph
of the frost heave facilities is shown in Figure 3.
A list of the frost
action software programs appears below.
Data Acquisiton Programs
(1) Data acquisiton start-up and initialization.
(2) Scan channels, measure, compute, post data to extended
memory area and disc, file and print results.
(3) Water reset.
(4)
Change scan period.
Temperature Control Programs
(1) Cold side control start-up and initialization.
(2) Cold side control with ramp function.
(3) Cold side control status output to terminal.
(4)
Manual change of cold side control parameters.
(5) Warm side control startup and initialization.
(6) Warm side control with ramp function.
(7) Warm side control status output to terminal.
(8)
Manual change of cold side control parameters.
(9) Manual setting of cold side temp.
(10) Manual setting of warm side temp.
(11) Cold side control status to printer.
(12) Warm side control status to printer.
Graphics Programs
(1) Frost action plot to terminal
(isotherm, water heave, total heave and segregation ratio).
(2) Frost action plot to 72458 plotter.
(3) Cold side and warm side temperature plot to terminal.
(4)
Cold side and warm side temperature plot to 72458 plotter.
(5) Single record (1 scan) temperature profile vs depth with
digitizing function to terminal.
(6) Single record (1 scan) temperature profile vs depth with
digitizing function to 72458 plotter.
Utilities Programs
1)
Cold side temperature (Cell 1) manual read.
2)
Warm side temperature (Cell
1) manual read.
3) Cold side temperature (Cell 2) manual read.
(4)
Warm side temperature (Cell 2) manual read.
(5)
Disc data file initialization.
(6)
Disc data file read to extended memory area.
(7) Function keys definition
1.
(8)
Function keys definition 2.
Preparation of Soil Specimen and Placement
The frost cell (Figure 1) may be used for both undisturbed and
remoulded soils. However, the cell is designed and so best suited for
remoulded samples. Details on specimen preparation will be confined to
remoulded soils.
Sample homogeneity and reproducible specimen preparation are basic to
carrying out reproducible experiments. Ice lens growth and heaving are
generally extremely sensitive to variations.
Preparation of specimens may begin either with air-dried soils or with
soils at their field moisture content. Air-dried soils are usually ground,
sieved and mixed thoroughly as a pretreatment to wetting.
Water i s added g r a d u a l l y d u r i n g mixing w i t h a handheld e l e c t r i c b l e n d e r t o b r i n g t h e s o i l t o 1 o r 2% above t h e l i q u i d l i m i t . The w e t s o i l i s t h e n s t o r e d f o r s e v e r a l d a y s i n s e a l e d c o n t a i n e r s .
P r e p a r a t i o n of t h e specimen i s done d i r e c t l y i n t h e f r o s t c e l l . A f t e r mixing t h e w e t s o i l a g a i n , i t i s poured i n t o t h e c e l l s l o w l y t o a v o i d l a r g e bubble entrapment. The u p p e r p a r t of t h e c e l l i s t h e n p l a c e d o v e r t h e lower s e c t i o n and t h e c o n s o l i d a t i o n p r o c e s s c a n begin.
The c o n s o l i d a t i o n program depends on t h e t y p e of f r e e z i n g e x p e r i m e n t t o b e c a r r i e d o u t . R e p r o d u c i b i l i t y of f r e e z i n g r u n s , however, do depend t o a l a r g e e x t e n t on r e p r o d u c i b l e d e n s i t i e s . The sample may be c o n s o l i d a t e d t o e q u i l i b r i u m a t t h e o v e r b u r d e n p r e s s u r e r e q u i r e d f o r t h e f r e e z t n g p r o c e s s , o r specimens may be c o n s o l i d a t e d t o a common p r e s s u r e f o r c o m p a r a t i v e f r e e z i n g e x p e r i m e n t s .
The f r o s t c e l l i s p l a c e d i n s i d e t h e c o n s t a n t t e m p e r a t u r e chamber a f t e r c o n s o l i d a t i o n . The w a t e r s u p p l y system i s u s u a l l y f l u s h e d w i t h d e a i r e d w a t e r t o p u r g e any
a i r
b u b b l e s c a u g h t i n t h e system. The sample i s t h e nallowed t o e q u i l i b r a t e t h e r m a l l y , w i t h t h e w a t e r i n t h e s u p p l y system, and u n d e r t h e s t a r t i n g o v e r b u r d e n p r e s s u r e . C i r c u l a t i o n of c o n t r o l l e d t e m p e r a t u r e l i q u i d s may be s t a r t e d a t t h i s s t a g e t h r o u g h t h e end h e a t e x c h a n g e r s . The u s u a l p r o c e d u r e i s t o have t h e c o n t r o l l e d - t e m p e r a t u r e l i q u i d s c i r c u l a t i n g t h r o u g h t h e warm-end h e a t exchanger a t t h e s t a r t i n g t e m p e r a t u r e and t h e cold-end l i q u i d s c i r c u l a t i n g a t t h e s t a r t i n g t e m p e r a t u r e b e f o r e f r e e z i n g u n t i l t h e r m a l e q u i l i b r i u m i s a t t a i n e d . It i s t o be n o t e d t h a t most s a t u r a t e d s o i l s w i l l n o t c r y s t a l l i z e s p o n t a n e o u s l y i n t h e c e l l above -1 O C . I n i t i a t i n g I c e C r y s t a l l i z a t i o n i n t h e Sample I n i t i a l i z a t i o n of f r e e z i n g i s c a r r i e d o u t by c i r c u l a t i n g c h i l l e d l i q u i d t h r o u g h t h e sample c o l d - s i d e h e a t exchanger from a s e p a r a t e h o t p a c k c o n s t a n t t e m p e r a t u r e t a n k u n t i l c r y s t a l l i z a t i o n t a k e s p l a c e . B e f o r e t h i s o p e r a t i o n i s s t a r t e d , t h e sample i s a t t h e r n a l e q u i l i b r i u m w i t h warm and c o l d - s i d e l i q u i d c i r c u l a t i n g b a t h s . The c o l d - s i d e l i q u i d f l o w t h r o u g h t h e h e a t
exchanger i s s t o p p e d and l i q u i d from a t a n k a t about -lO°C i s c i r c u l a t e d f o r a s h o r t p e r i o d . A t t h e same t i m e t h e computer s c r e e n i s programmed t o show t h e t e m p e r a t u r e of t h e s o i l o n t h e c o l d - s i d e a t a p p r o x i m a t e l y one second i n t e r v a l s . When t h e -10°C l i q u i d i s c i r c u l a t e d , t h e t e m p e r a t u r e on t h e c o l d s i d e s l o w l y d e c r e a s e s . A t c r y s t a l l i z a t i o n t h e c o l d - s i d e t e m p e r a t u r e rises s u d d e n l y b e c a u s e of l a t e n t h e a t r e l e a s e . A t t h i s p o i n t t h e -lO°C c t r c u l a t i n g f l u i d i s c u t o f f and t h e c o l d - s i d e c o n t r o l t a n k l i q u i d i s a g a i n c i r c u l a t e d t h r o u g h t h e c o l d - s i d e h e a t exchanger. The t e m p e r a t u r e of t h e sample r e v e r t s t o t l ~ e p r e f r e e z i n g t e l n p e r a t u r e s . The o n l y d i f f e r e n c e i s t h a t f r e e z i n g i s now t a k i n g p l a c e : w a t e r movement e i t h e r i n t o o r o u t of t h e sample o c c u r s (depending on s o i l t y p e and thermal c o n d i t i o n s ) and h e a v i n g i s e v i d e n t .
C o n t r o l l e d F r e e z i n g R a t e and Data R e c o r d i n g
A f t e r c r y s t a l l i z a t i o n t h e t e m p e r a t u r e p a t t e r n t o be f o l l o w e d a t h o t h e n d s of t h e sample i s e x e c u t e d by t h e computer. T h i s may he a t e m p e r a t u r e ramping p a t t e r n a t b o t h e n d s a t any d e s i r e d r a t e , e g g . 0.02OC d e c r e a s e p e r day, c o n s t a n t t e m p e r a t u r e s a t h o t h e n d s , o r c o n s t a n t t e m p e r a t u r e a t t h e warm
end and ramped t e m p e r a t l l r e a t t h e c o l d end. Other t h e r m a l modes c a n a l s o b e e x e c u t e d .
Another program i n i t i a t e d a t t h i s t i m e i s t h e a u t o m a t i c r e c o r d i n g of t h e d a t a w i t h a n o n - l i n e p r i n t e r t h a t g i v e s t h e sample t e m p e r a t u r e s a t s e l e c t e d t i m e s , t h e sample l e n g t h change ( h e a v e ) and t h e w a t e r volume i n t a k e . The s t a t u s of t h e t e m p e r a t u r e c o n t r o l a t b o t h ends i s a l s o r e c o r d e d . The d a t a a r e s t o r e d on d i s c and i n t h e form of h a r d copy. P r i n t o u t s c a n b e r e q u e s t e d of a l l t h e d a t a a s r e q u i r e d . Graphs c a n a l s o b e r e q u e s t e d a t any t i m e of f r o s t p e n e t r a t i o n , w a t e r i n t a k e , t o t a l heave v a l u e s anrl i c e s e g r e g a t i o n r a t i o s v s t i m e ; i n a d d i t i o n , t h e p a t t e r n of t e m p e r a t u r e c o n t r o l a t b o t h e n d s a s a f u n c t i o n of t i m e i s a l s o a v a i l a b l e i n g r a p h form. When t h e s c r e e n i s n o t u s e d f o r o t h e r p u r p o s e s , t h e c o n t r o l s t a t u s of t h e end t e m p e r a t u r e c a n be d i s p l a y e d . The computer u p d a t e s t h i s i n f o r m a t i o n a t l e a s t e v e r y t h i r t y seconds.
T o t a l Heave and Water I n t a k e Heave Measurements
The i n s t r u m e n t a t i o n f o r b o t h heave and w a t e r measurements a r e s e r v i c e d
by t h e same power s u p p l y . The i n p u t v o l t a g e i s monitored a u t o m a t i c a l l y and a l a r m s a r e t r i g g e r e d i f t h e v a r i a t i o n e x c e e d s t h e r e q u i r e d a c c u r a c y l i m i t s . The d i f f e r e n c e between t h e two v a l u e s of t o t a l h e a v e and w a t e r i n t a k e heave i s a r e c o r d of i n s i t u pore w a t e r heave.
A v i n t a g e g l a s s - c a s e d a n a l y t i c a l b a l a n c e h a s been automated t o p r o v i d e a c c u r a t e measurements of w a t e r i n t a k e by t h e heaving sample. A f o r c e
t r a n s d u c e r was i n s t a l l e d between one end of t h e h o r i z o n t a l b a l a n c e beam and t h e b a s e of t h e b a l a n c e e n c l o s u r e . A v e n t e d w a t e r c o n t a i n e r was hung from t h e o t h e r end of t h e b a l a n c e beam w i t h a v o l u m e t r i c c a p a c i t y of a b o u t 50 cc. A t u b i n g arrangement s u p p l i e s w a t e r from t h e b a l a n c e t o t h e f r o s t c e l l t h r o u g h a p o r o u s p l a t e . V o l t a g e o u t p u t from t h e f o r c e gauge was c a l i b r a t e d i n terms of w a t e r s u p p l y . An a c c u r a c y of
+
0.01 mm of heave was a c h i e v e d which i s e q u i v a l e n t t o 2 0.31 c c i n t a k e of w a t e r f o r t h i s s i z e of sample. The e x t e r n a l w a t e r s u p p l y l e v e l was a d j u s t e d t o s t a y w i t h i n 0 and +2 cm of t h e p o r o u s p l a t e a t t h e end of t h e sample.Measurements of specimen heave a r e made o v e r t h e e n t i r e f r e e z i n g p e r i o d u s i n g a DCDT mounted between t h e t o p of t h e f r o s t c e l l and t h e heave
t r a n s f e r p i p e ( F i g u r e 1). Measurements a r e a c c u r a t e t o '0.002 mm.
EXPERIMENTAL WSULTS
-
EXAMPLESWith t h e a p p a r a t u s and e x p e r i m e n t a l methods d e s c r i b e d above, t h e measurements of w a t e r i n t a k e and h e a v i n g a r e much more p r e c i s e t h a n was p r e v i o u s l y p o s s i b l e . I c e l e n s growth r a t e changes can b e o b s e r v e d d u r i n g f o r m a t i o n . With t h e X-ray c a p a b i l i t y g i v i n g e x a c t l e n s p o s i t i o n and t h e sample p r o f i l e t e m p e r a t u r e measurements t a k e n a t t h e same t i m e , i t i s
p o s s i b l e t o d e t e r m i n e t h e t e m p e r a t u r e of t h e a c t i v e l y growing f a c e of t h e i c e l e n s .
An i n t e r e s t i n g p a t t e r n of growth t e m p e r a t u r e d u r i n g r h y t h m i c i c e l e n s i n g emerges from e x p e r i m e n t s . T h i s l e d t o a s s e s s m e n t s of i c e l e n s growth b e h a v i o u r n o t p o s s i b l e p r e v i o u s l y . Some r e s u l t s a r e g i v e n below.
A r e c o r d of c o m p u t e r - c o n t r o l l e d sample end t e m p e r a t u r e s i s g i v e n i n F i g u r e 4 ( a ) . In t h i s e x p e r i m e n t , t h e t e m p e r a t u r e s were d e c r e a s e d i n i n c r e m e n t s of 0.0015°C t o g i v e a t o t a l d r o p of 0.02OC p e r 24 h o u r p e r i o d . F i g u r e 4 ( b ) g i v e s t h e O°C i s o t h e r m p e n e t r a t i o n d u r i n g t h e p e r i o d of ramped t e m p e r a t u r e c o n t r o l shown i n F i g u r e 4 ( a ) . F i g u r e 4 ( c ) g i v e s t h e r e c o r d of t h e t o t a l h e a v e ( i n s i t u w a t e r a n d w a t e r i n t a k e ) measured a s a f u n c t i o n of t i m e , a s w e l l a s t h e h e a v e due t o w a t e r i n t a k e o n l y . The f o u r i c e l e n s e s were formed o v e r t h e t i m e p e r i o d s marked on t h e c u r v e . I n d i c a t e d a l s o a r e t i m e s a t which X-rays were t a k e n .
It may be s e e n t h a t t h e r a t e of t o t a l h e a v e and w a t e r i n t a k e heave go t h r o u g h a r a t e change d u r i n g t h e f o r m a t i o n of t h e i c e l e n s .
I n a d d i t i o n t o a measured heave r a t e c h a n g e , t h e t e m p e r a t u r e a l s o changes. From t h e X-ray which shows t h e l e n s l o c a t i o n a t t h e t i m e of t h e measured t e m p e r a t u r e g r a d i e n t c u r v e ( F i g u r e 4 ( d ) ) , t h e t e m p e r a t u r e a t t h e f a c e of t h e growing i c e l e n s c a n be c a l c u l a t e d . The d a t a i n T a b l e 1 g i v e s s u c h t e m p e r a t u r e c a l c u l a t i o n s f o r l e n s e s 3 and 4. A t t h e t i m e of l e n s i n i t i a t i o n t h e AT below O°C i s less t h a n a t s u b s e q u e n t t i m e s . On t h e o t h e r
hand b o t h t h e t o t a l and i n t a k e w a t e r h e a v e o v e r t h e l e n s f o r m a t i o n p e r i o d i n c r e a s e s t o a maximum t h e n r e d u c e s . T h i s p a t t e r n i s always t h e same and many e x p e r i m e n t s have been c a r r i e d o u t showing h e a v e and l e n s t e m p e r a t u r e w i t h s i m i l a r c h a r a c t e r i s t i c s . A p o s i t i v e p r i n t of t h e X-ray t a k e n when t h e t e m p e r a t u r e g r a d i e n t i n F i g u r e 4 ( d ) was e s t a b l i s h e d i s g i v e n i n F i g u r e 4 ( e ) , X-ray
5.
I n t h i s f i g u r e , a l l t h e p o s i t i v e p r i n t s of X-rays t a k e n d u r i n g t h e f u n c t i o n of l e n s e s 3 and 4 a r e shown. The g r a i n s i z e c h a r a c t e r i s t i c s are g i v e n f o r t h i s s o i l i n Appendix l ( a ) .TABLE 1. ICE LENS DATA. SOIL M I X NO. 2.
RAMP
RATE -0.02/24 HR. PERIOD.X r a y No. Lens No.
Lens/O°C
Lens Temp. s e p a r a t i o n Time
O C mm min
.
1 S t a r t of 3-
0.240 26.08 7,115 2 Midway t h r o u g h 3-
0.258 27.84 8 , 6 19 3 Near end of 3-
0.270 29.72 10,009 4 S t a r t of 4-
0.238 26.55 11,382 5 Middle of 4-
0.250 27.92 12,816 The h e a v e r e c o r d of a n o t h e r e x p e r i m e n t i s shown i n F i g u r e 5. T h i s i s a d i f f e r e n t s o i l mix, Appendix l ( b ) , from s i m i l a r s o i l m a t e r i a l s . Again t h e t i m e of t h e X-rays are marked on t h e heave t i m e curve. The change i n heaver a t e may be n o t e d a g a i n a s t h e l e n s growth p r o g r e s s e s . Table 2 g i v e s t h e t e m p e r a t u r e d a t a . The p a t t e r n of t e m p e r a t u r e changes i s s i m i l a r t o t h a t i n Table 1. The growth t e m p e r a t u r e s a t t h e i c e l e n s c o n t i n u o u s l y r e d u c e s and when a new l e n s i s i n i t i a t e d t h e t e m p e r a t u r e i n c r e a s e s t o g i v e a warmer t e m p e r a t u r e d u r i n g t h e e a r l y s t a g e of growth.
SUMMARY
The p r e c i s i o n of t e m p e r a t u r e measurements and c o n t r o l d u r i n g heaving experiments h a s improved t o t h e p o i n t t h a t changes i n growth r a t e of
ice
d u r i n g rhythmic i c e l e n s f o r m a t i o n c a n be observed. It i s now a l s o p o s s i b l e t o l o c a t e t h e
ice
l e n s e s p r e c i s e l y u s i n g X-rays. Hence, t h e t e m p e r a t u r e of t h e a c t i v e l y growing i c e phase can be determined.TABLE 2. I C E LENS DATA. SOIL M I X NO. 1.
RAMP
RATE -0.01°C/24 HR. PERIODLens O°C
Lens Temp. s e p a r a t i o n Time
OC mm min
.
X r a y No. Lens No.
S t a r t of 1 Toward end of 1 Middle of 2 S t a r t of 3 Toward end of 3 S t a r t of 4 Toward end of 4 End of 4 S t a r t of
5
Toward end of 5 S t a r t of 6 Middle of 6 S t a r t of 7WATER SUPPLY T O SAMPLE HEAVE TRANSFER P I P E
-I
A I R PRESSURE INLET W A R M S I D E TYGON TUBING COOLING L I Q U I D TOP A L U M I N U M COPPER WATER SUPPLY TUBE 57 rnm ( 2 114") URETHANE INSULA Z IG-ZAG WATERSUPPLY GROOVE POROUS PLATE
- - - - - - . . - - - . - - - THERMISTOR LEADS . . - - - SAMPLE HOLDER I \ I C \ S P I R A L COOLING GROOVE T I O N COOLING L I Q U I D F I G U R E 1 S C H E M A T I C O F F R O S T C E L L MK I1
L I Q U I D TEMPERATURE BATH NO. 1 ELECTRICAL BATH D I G l T A L VOLTMETER COMPUTER TO BATH NO. 2 OUTPUT S I G N A L f 20 MA F I G U R E 2 S C H E M A T I C O F M O D I F I C A T I O N T O T E M P E R A T U R E C O N T R O L L E R O F H O T P A C K L l Q U I D B A T H C l R C U L A T O R
1 . H P 1000. MODEL 6 COMPUTER 10. TENNEY CONTROLLED ENV I RONMENTAL CHAMBER 2 . H P 9835 COMPUTER 11. CHAMBER GLASS SECTION FOR OBSERVATION 3 . HP 3455A VOLTMETER AND 3495A SCANNER OF CELL
4 . H P 6942A MULTIPROGRAMMER 12. PH l L l PS X-RAY GENERATOR 5 . VOLTAGE SUPPLY FOR DCDT 13. HOTPACK FOR W A R M S I D E 6 . H P 7245A PLOTTER 14. H O l P A C K FOR COLD SIDE
7 . H P GRAPHICS PRINTER 15. HOTPACK FOR CRYSTALLIZATION I N I T I A T I O N 8. HP 2631 PRINTER 16. H P FLOPPY D I S C DRIVE
9. WATER SUPPLY BALANCE 17. HP FLOPPY SLAVE D I S C
F I G U R E 3
-1.0 0 2 0 0 0 4 0 0 0 6 0 0 0 8 0 0 0 1 0 0 0 0 1 2 0 0 0 1 4 0 0 0 1 6 0 0 0 T I M E , m i n F I G U R E 4 ( a l R A M P F R E E Z I N G M E T H O D . R E C O R D O F R A M P E D S A M P L E E N D T E M P E R A T U R E S A T - 0 . O Z " C 1 2 4 h P E R I O D . E X P E R I M E N T A L P E R I O D 16 0 0 0 M I N U T E S , S O I L M I X N O . 1 T I M E , m i n 6 0 5 0 4 0 E E 3 0 2 0 1 0 F I G U R E 4 1 b l R E C O R D O F O ' C I S O T H E R M P E N E T R A T I O N 7 0 . 1 , 1 1 1 1 1 1 1 1 1 I I I ... DEPTH OF 0 C I S O T H E R M ...
-
... WATER HEAVE I ...----
TOTAL HEAVE OF X - R A Y ... ...-
- ... ... 3 ... ... ._.. ... 1 X - ~ ~ Y No. - ... - : & - --
-
0 2 0 0 0 4 0 0 0 6 0 0 0 8 0 0 0 1 0 0 0 0 1 2 0 0 0 1 4 0 0 0 1 6 0 0 0F I G U R E 4 ( c l
OF THERMISTOR
-
-
-
-
-
0 1 T E M P E R A T U R E . ' C F I G U R E 4 ( d ) E X A M P L E OF T E M P E R A T U R E G R A D l E N l IN S A M P L E ( X - R A Y NO. 5 1X - R A Y , NO. 5 4 3 2 1 TIME, min 12 816 11 382 10 009 8 619 7 115 F I G U R E 4 ( e l P O S I T I V E P R I N T S O F A L L X - R A Y S T A K E N D U R I N G A C T I V E F R O S T H E A V I N G I 1 I I -
-
W A T E R H E A V E- - - -
-
T O T A L H E A V E - - - --
- --
- - I I I I I I I I I T I M E , i n i n F I G U R E 5 R E C O R D O F T O T A L A N D W A T E R - I N T A K E H E A V E S O I L M I X N O . 2 . R A M P R A T E - 0 . Ol'C124 h P E R I O D1 I 1 l l l l l - - - - - - - - - - - - - - - I 1 1 1 1 1 1 1 l I 1 1 1 1 1 1 1 1 I 1 I l l l l L , 0 0 1 0 . 0 1 0 1 1 . 0 G R A I N S I Z E , m m A P P E N D I X A H Y D R O M E T E R A N A L Y S I S O F S O I L M I X N O . 1 I I I I I I I ~