1 1 1 . 4 . FROST THRUST MEASUREMENTS ON PILES

R . E . Reed

Upward t h r u s t on founda t ion p i l i n g due t o f r o s t a c t i o n has been a problem i n t h e d e s i g n , c o n s t r u c t i o n , and maintenance of s t r u c t u r e s throughout a r c t i c , s u b a r c t i c , and t empera t e r e g i o n s . Seasona l f r e e z i n g and thawing o f t h e upper l a y e r s of ground cause d i f f e r e n t i a l movements which can be d e t r i m e n t a l t o a founda t ion . I n p i l e founda- t i o n s , t h e heaving of t h e ground d u r i n g t h e f r e e z i n g season i m p a r t s an upward t h r u s t t o t h e p i l e by ad f r eeze and t h e s t a b i l i t y of a p i l e founda t ion i s dependent upon t h e p rope r e v a l u a t i o n of t h i s f o r c e wi th t h e o t h e r f o r c e s on t h e founda t ion .

During t h e p a s t 15 y e a r s , cons ide rab l e r e s e a r c h has been conducted t o e s t a b l i s h des ign c r i t e r i a f o r e s t i m a t i n g t h e l oad c a p a c i t y of p i l e s i n permafros t (References 1, 2 , 3, 4 , 5 and 6 ) . The problem o f f r o s t t h r u s t on p i l i n g has long been recognized and s e v e r a l methods have been used t o cope wi th i t . A r u l e o f thumb f o r embedment of p i l e s t o a dep th i n permafros t e q u a l t o tw ice t h e expec ted dep th o f t h e a c t i v e l a y e r has been used t o c o u n t e r a c t t h e heave t h r u s t (Reference 7 ) . I n v e s t i g a - t i o n s a t Fa i rbanks , Alaska have i n d i c a t e d t h a t a minimum embedment o f 10 f t i n permafros t i s r e q u i r e d t o c o u n t e r a c t heave t h r u s t i n t h e a r e a (Reference 5 ) . Oil-wax f i l l e d c a s i n g s o r s l e e v e s , g r ea se c o a t i n g s , t a r paper wraps , and t r e a t e d b a c k f i l l m a t e r i a l s have a l s o been used t o reduce o r e l i m i n a t e p i l e heave t h r u s t (Reference 8 ) .

Although s e v e r a l measures have been i n v e s t i g a t e d and used a s ant i -heave dev i ce s on founda t ion p i l i n g , very l i t t l e i n fo rma t ion has been o b t a i n e d on t h e a c t u a l magni- t ude o f t h e f r o s t t h r u s t which c r e a t e s t h i s heave problem. This pape r p r e s e n t s t h e r e s u l t s o f a f i e l d t e s t t o measure t h e f r o s t t h r u s t on c r eoso t ed t imbe r , and 8 i n . s t e e l p i p e , p i l e s . The t e s t i s one of a s e r i e s of t e s t s conducted by t h e U.S. Army Cold Regions Research and Engineer ing Labora tory (USA CRREL). A comprehensive r e p o r t on t h e s e r i e s i s i n p r e p a r a t i o n (Reference 9 ) . The f i e l d d a t a was o b t a i n e d from a t e s t i n s t a l l a t i o n a t t h e Alaska F i e l d S t a t i o n (AFS) o f CRREL a t Fa i rbanks , Alaska.

TEST INSTALLATION

S i t e Condi t ions

The Alaska F i e l d S t a t i o n i s l o c a t e d about 2 .5 m i l e s n o r t h e a s t of t h e c i t y of Fa i rbanks , Alaska. Fa i rbanks h a s a c o n t i n e n t a l c l i m a t e , s h e l t e r e d from marit ime i n f l u e n c e s by v a r i o u s Alaskan mountain r anges . The mean annua l t empera tu re i s 25.E°Fwith extremes of 93' t o -66OF. The mean f r e e z i n g and thawing i n d i c e s a r e about 5300 and 3200 deg ree days , r e s p e c t i v e l y . Average annual p r e c i p i t a t i o n i s about 12 i n . of wate r and wate r equ iva l en t i n c l u d i n g a mean annua l s n o w f a l l of about 40 i n .

The heave f o r c e measurements i n s t a l l a t i o n was i n s t a l l e d i n P i l e S i t e B a t AFS (F igu re 1) . This p i l e s i t e , approx imate ly 100 x 200 f t i n s i z e , was o r i g i n a l l y c l e a r e d o f a l l t r e e s , b rush , and s u r f a c e o rgan ic m a t e r i a l i n t h e s p r i n g of 1950. I n t h e summer of 1952, 32 t e s t p i l e s were i n s t a l l e d i n t h e a r e a and l a t e r t e s t e d i n e x t r a c t i o n and i n l o a d - s e t t l e m e n t (Reference 1) .

S o i l c o n d i t i o n s a t t h e f i e l d s t a t i o n , i n g e n e r a l , c o n s i s t of o r g a n i c and i n o r g a n i c s i l t s wi th p e a t l a y e r s t o dep ths of 75 t o 125 f t , wi th sands and g r a v e l s encounte red below t h e s i l t and ex t end ing t o s c h i s t bedrock a t about 250 f t . F igu re 2 shows t h e b o r i n g l o g s , wa te r c o n t e n t , and d ry u n i t weight o f t h e m a t e r i a l i n t h e s ea sona l thaw zone a t two l o c a t i o n s a t t h e t e s t s i t e of t h e t e s t i n s t a l l a t i o n . S o i l d e s c r i p t i o n s a r e i n accordance wi th t h e method o f d e s c r i b i n g and c l a s s i f y i n g f r o z e n s o i l s developed by CRREL and t h e N a t i o n a l Research Counci l of Canada (References 10 , 11 and 1 2 ) .

Heave Force Measurement Devices

I n t h e summer of 1962, two heave f o r c e t e s t p i l e s were i n s t a l l e d i n P i l e S i t e B a t AFS. The i n s t a l l a t i o n i n c l u d e d r e s t r a i n e d heave t e s t p i l e s of c r eoso t ed t i m b e r and 8 i n . d i a m e t e r s t e e l p i p e and a l s o of i d e n t i c a l l y i n s t a l - l e d b u t u n r e s t r a i n e d ( o r dummy) p i l e s , t h a t were a l lowed t o move upward w i t h t h e heav ing ground (F igu re 3 ) . The heave f o r c e t e s t d e v i c e s c o n s i s t e d of t h e t e s t p i l e s o f c r e o s o t e d t i m b e r and s t e e l p i p e and 25 f t anchor p i l e s . The anchor p i l e s were made from s e c t i o n s of 6WF25 s t e e l s e c t i o n s and 8 i n . s t e e l p i p e f o r t h e t imbe r and p i p e t e s t p i l e s r e - s p e c t i v e l y . The t e s t p i l e s extended t o a dep th of 6 .5 f t , which a t t h e t ime of i n s t a l l a t i o n was t h e assumed dep th of

t h e s e a s o n a l thaw l a y e r , and t h e anchor p i l e s e x t e n d e d 25 f t i n t o p e r m a f r o s t d i r e c t l y below t h e t e s t p i l e s ( F i g u r e 3 ) .

Four 1 i n . s t e e l r o d s e x t e n d e d t h r o u g h t h e f u l l l e n g t h o f t h e t e s t p i l e s t o t r a n s f e r t h e heave t h r u s t t o t h e a n c h o r p i l e s . I n t h e t i m b e r p i l e i n s t a l l a t i o n , t h e r o d s were welded t o t h e a n c h o r p i l e . I n t h e p i p e p i l e i n s t a l l a t i o n , t h e r o d s were h e l d by n u t s b e a r i n g on a 1 1 / 2 i n . p l a t e welded t o t h e i n s i d e o f t h e a n c h o r p i l e . P r o v i n g r i n g s were p l a c e d a t t h e t o p s o f t h e a s s e m b l i e s be tween two 1 1/2 i n . t h i c k p l a t e s , and t h e t o p p l a t e s were r e s t r a i n e d by n u t s on t h e 1 i n . d i a m e t e r r o d s . The j o i n t between t h e 8 i n . t e s t p i p e and a n c h o r p i l e s was s e a l e d w i t h a r u b b e r g a s k e t t o p r e v e n t t h e e n t r a n c e o f ground w a t e r o r s l u r r y . Each assembly was pre-assembled and i n s t a l l e d a s a u n i t i n t o 1 8 i n . d i a m e t e r d r y a u g e r e d h o l e s and b a c k f i l l e d w i t h s i l t s l u r r y .

I n s t r u m e n t a t i o n

To r e c o r d ground t e m p e r a t u r e and t h e advance o f f r e e z e and thaw t h r o u g h t h e s e a s o n a l thaw zone , thermo- c o u p l e a s s e m b l i e s were a t t a c h e d t o e a c h t e s t and dummy p i l e ; t h e the rmocoup les were s p a c e d a t 6 i n . i n t e r v a l s f rom t h e ground s u r f a c e t o a d e p t h o f 6 . 0 f t . A d d i t i o n a l a s s e m b l i e s were f a s t e n e d t o , and i n s t a l l e d w i t h , t h e a n c h o r p i l e s , w i t h the rmocoup les l o c a t e d a t 6 . 0 , 8 . 0 , 1 0 . 0 , 1 5 . 0 , 2 0 . 0 , 25 .0 and 31 .0 f t d e p t h s .

V e r t i c a l movements of e a c h t e s t and dummy p i l e were m o n i t o r e d by t h r e e e x t e n s o m e t e r - t y p e d i a l gauges mounted on i n s t r u m e n t a t i o n beams ( F i g u r e 3 ) and p o s i t i o n e d 120 d e g r e e s a p a r t a round t h e p i l e . The i n s t r u m e n t a t i o n beams were s u p p o r t e d by 4 . 5 i n . d i a m e t e r p i p e p i l e s d r i v e n t o a p p r o x i m a t e l y 11 f t below t h e ground s u r f a c e w i t h 7 i n . , d i a m e t e r p i p e u s e d a s c a s i n g t h r o u g h t h e a c t i v e l a y e r . The a n n u l a r s p a c e be tween t h e c a s i n g and p i l e s was f i l l e d w i t h o i l t o p r e v e n t h e a v i n g o f t h e i n s t r u m e n t a t i o n s u p p o r t s .

P r o v i n g r i n g s were i n s t a l l e d above e a c h t e s t p i l e t o r e c o r d t h e heave t h r u s t d u r i n g t h e f r e e z i n g s e a s o n . A 60 ,000 l b c a p a c i t y p r o v i n g r i n g was u s e d i n t h e p i p e p i l e i n s t a l l a t i o n and a 50,000 l b c a p a c i t y r i n g i n t h e t i m b e r p i l e i n s t a l l a t i o n . Both p r o v i n g r i n g s were p r o t e c t e d by a n i n s u l a t e d e n c l o s u r e , h e a t e d w i t h two t h e r m o s t a t i c a l l y c o n t r o l l e d 100 watt e l e c t r i c l i g h t b u l b s t o m a i n t a i n t h e t e m p e r a t u r e a t 65OF ( F i g u r e 4 ) .

s h e The e n t i r e t e s t a r e a was

l t e r t o f a c i l i t a t e maximum f r o s by a wood f r ame

t- p e n e t r a t i o n by p r e v e n t - i n g t h e a c c u m u l a t i o n of snow and t o s h i e l d t h e i n s t r u m e n t a - t i o n f rom s u n l i g h t and s n o w f a l l which c o u l d c a u s e d e f l e c t i o n s o f t h e i n s t r u m e n t a t i o n beams.

TEST PROCEDURE AND RESULTS

Ground and A i r Tempera tu res

A l l thermocouple a s s e m b l i e s were obse rved two o r t h r e e t i m e s weekly from t h e l a s t week o f Oc tobe r 1962 t h r o u g h J u n e 1963. Tempera tu res were r e c o r d e d w i t h a p o r t - a b l e p r e c i s i o n m i l l i v o l t p o t e n t i o m e t e r h a v i n g a n i c e b a t h r e f e r e n c e j u n c t i o n . The ground t e m p e r a t u r e i s o t h e r m s f o r e a c h heave t e s t p i l e , based on t e m p e r a t u r e o b s e r v a t i o n s f rom t h e t e s t p i l e a s s e m b l i e s , a r e p l o t t e d on F i g u r e s 5 and 6 , which a r e c o m p o s i t e p l o t s o f t h e r e s u l t s o f t h e two t e s t i n s t a l l a t i o n s . The d e p t h t o p e r m a f r o s t was assumed t o be a p p r o x i m a t e l y 6 . 5 f t . The 32OF i s o t h e r m d i d n o t p e n e t r a t e t o t h a t d e p t h u n t i l mid-February a t t h e p i p e p i l e and l a t e F e b r u a r y a t t h e t i m b e r p i l e . The s l i g h t d i f f e r e n c e i n . p e n e t r a t i o n c o u l d be because s t e e l i s a b e t t e r c o n d u c t o r o f h e a t t h a n t i m b e r and c o l d a i r would n a t u r a l l y f low t o t h e b o t t o m o f t h e p i p e p i l e .

D a i l y a i r t e m p e r a t u r e o b s e r v a t i o n s were made a t t h e t e s t s i t e and t h e mean a i r t e m p e r a t u r e s a r e p l o t t e d on F i @ r e s 5 a n d 6 . The mean a i r t e m p e r a t u r e dropped below 32'F i n mid O c t o b e r and remained below 32OF u n t i l mid A p r i l . The t e m p e r a t u r e f l u c t u a t e d g r e a t l y d u r i n g t h e w i n t e r and t h e l o w e s t t e m p e r a t u r e s were o b s e r v e d i n e a r l y J a n u a r y . The a v e r a g e a i r t e m p e r a t u r e s i n J a n u a r y were t h e warmest i n 26 y e a r s .

V e r t i c a l Movements

V e r t i c a l movement o b s e r v a t i o n s were made on b o t h t e s t p i l e s t w i c e d a i l y t h r o u g h o u t t h e f r e e z i n g s e a s o n . Con t inuous p l o t s o f t h e v e r t i c a l movement o f e a c h p i l e a r e shown on F i g u r e s 5 and 6 . V e r t i c a l movement o f t h e dummy p i l e s i n c r e a s e d d u r i n g t h e f r e e z e b a c k o f t h e s e a s o n a l thaw zone and t h e n c o n t i n u e d s l i g h t l y a f t e r comple te f r e e z e b a c k . T o t a l h e a v e amounted t o 4.10 i n . and 4 .15 i n . f o r t h e s t e e l a n d t i m b e r dummy p i l e s , r e s p e c t i v e l y . V e r t i c a l move- ment o f t h e t e s t p i l e s , r e s t r a i n e d by t h e p r o v i n g r i n g s and r e a c t i o n d e v i c e s , was a maximum o f 0 . 7 i n c h e s f o r t h e s t e e l p i l e and 0 . 3 i n c h e s f o r t h e t i m b e r p i l e .

Heave F o r c e Measurements

P r o v i n g r i n g r e a d i n g s were made t w i c e d a l l y a t a p p r o x i m a t e l y t h e same t i m e e a c h morning and a f t e r n o o n from t h e s t a r t o f t h e f r e e z i n g s e a s o n u n t i l J u n e 1963. The a v e r g e s o f t h e d a i l y heave f o r c e measurements a r e p l o t t e d on F i g u r e s 5 and 6 . The m e a s u r a b l e heave f o r c e s t a r t e d a f t e r t h e 32OF i s o t h e r m had p e n e t r a t e d a p p r o x i m a t e l y 1 2 i n . The maximum heave f o r c e o c c u r r e d when t h e 32OF i s o t h e r m had p e n e t r a t e d between 90 and 100% o f t h e s e a s o n a l thaw zone and t h e n f l u c t u a t e d t h r o u g h o u t t h e r e m a i n d e r o f t h e w i n t e r i n r e s p o n s e t o t h e f l u c t u a t i o n o f a i r ( g r o u n d ) t e m p e r a t u r e s .

DISCUSSION OF RESULTS

The r e s u l t s i n d i c a t e a s l i g h t l a g between t h e p e n e t r a t i o n o f t h e 32OF i s o t h e r m and t h e s ta r t of m e a s u r a b l e p i l e heave f o r c e . F a c t o r s c a u s i n g t h i s s l i g h t l a g c o u l d be t h e weakness o f t h e a d f r e e z e bond d u r i n g t h e i n i t i a l f r e e z e b a c k o f t h e ground s u r f a c e , t h e f r i c t i o n a l r e s i s t a n c e of t h e u n f r o z e n s o i l b e n e a t h t h e f r o s t , and t h e f r e e z i n g p o i n t d e p r e s s i o n . Because o f t h i s f r e e z i n g p o i n t d e p r e s - s i o n and t h e e r r o r f a c t o r i n the rmocoup le o b s e r v a t i o n s , t h e a c t u a l f r o s t l i n e p e n e t r a t i o n p r o b a b l y l a g s beh ind t h e p e n e t r a t i o n o f t h e 32OF i s o t h e r m .

Heave o f t h e dummy p i l e s and t h e heave f o r c e i n c r e a s e d c o n s i d e r a b l y d u r i n g t h e f r e e z e b a c k o f t h e s e a s o n a l thaw l a y e r . G r a d u a l heave o f t h e dummy p i l e s c o n t i n u e d t h r o u g h o u t t h e w i n t e r u n t i l s u r f a c e t h a w i n g s t a r t e d i n t h e s p r i n g . The a r e a s u r r o u n d i n g t h e t e s t s i t e had a n u n d i s t u r b e d snow c o v e r i n c o n t r a s t t o t h e s h e l t e r e d a r e a a t t h e t e s t p i l e s and would have a s h a l l o w f r o s t p e n e t r a t i o n . T h i s g r a d u a l h e a v i n g t h r o u g h o u t t h e w i n t e r I s a t t r i b u t e d t o i c e l e n s e s formed by t h e m i g r a t i o n o f w a t e r f rom t h e su r round- i n g s o i l . Heaving t h r o u g h o u t t h e w i n t e r , a t a d i m i n i s h i n g r a t e , would a l s o o c c u r i n non-pe rmaf ros t a r e a s o r a r e a s h a v i n g a deep a c t i v e l a y e r where comple t e f r e e z e b a c k d o e s n o t o c c u r e a c h y e a r .

Maximum heave f o r c e s o f 55,800 l b f o r t h e s t e e l p i p e and 35,600 l b f o r t h e c r e o s o t e d t i m b e r p i l e o c c u r r e d when f r e e z e b a c k o f t h e a c t i v e l a y e r was between 90 and 100% c o m p l e t e . Dur ing t h e r e m a i n d e r o f t h e w i n t e r s e a s o n , d i s t i n c t f l u c t u a t i o n s i n heave f o r c e were o b s e r v e d . The peaks o r maximum p o i n t s o f t h e s e f l u c t u a t T o n s o c c u r r e d s h o r t l y a f t e r a d e c r e a s e i n a i r and ground t e m p e r a t u r e .

The low p o i n t s a p p e a r e d j u s t a f t e r warming t r e n d s i n t h e a i r t e m p e r a t u r e and had a d i s t i n c t t i m e l a g w i t h d e p t h , a s o b s e r v e d d u r i n g t h e c o o l i n g p e r i o d s . S i m i l a r f l u c t u a t i o n s have b e e n o b s e r v e d by J a p a n e s e i n v e s t i g a t o r s ( R e f e r e n c e 1 3 ) and t h e d e c r e a s e i n heave f o r c e was i n f e r r e d t o be a r e l a x a t i o n phenomenon. The r a t e o f advance o f t h e f r e e z i n g f r o n t would b e l o w e r d u r i n g t h e warmer p e r i o d s and heave f o r c e d e c r e a s e s when s o i l heave d e c r e a s e s . Dur ing p e r i o d s o f h i g h e r s u r f a c e t e m p e r a t u r e s , t h e r e l a x a t i o n r a t e o f t h e s o i l i m m e d i a t e l y s u r r o u n d i n g t h e p i l e might exceed t h e heave r a t e and t h e f r o s t t h r u s t c o u l d be r e d u c e d .

Creep o f t h e a n c h o r p i l e s i s a f a c t o r i n t h e d e c r e a s e i n heave f o r c e . P e r m a f r o s t t e m p e r a t u r e s a l o n g t h e e n t i r e l e n g t h o f t h e a n c h o r p i l e s were r e l a t i v e l y h i g h and m a r g i n a l (31 .0 - 31.5OF). A t t h e s e h i g h t e m p e r a t u r e s , i t i s c o n s i d e r e d p o s s i b l e f o r p r o g r e s s i v e movement o f t h e a n c h o r p i l e s t o o c c u r e s p e c i a l l y u n d e r t h e h i g h l o a d s i n d i c a t e d on t h e p r o v i n g r i n g s . A l o a d o f 55,000 l b s on t h e 8 i n . p i p e p i l e i n s t a l l a t i o n r e p r e s e n t s a n a v e r a g e u n i t s t r e s s of a p p r o x i m a t e l y 7 p s i on t h e 25 f t a n c h o r p i l e . P i l e i n v e s t i g a t i o n s conduc ted i n p e r m a f r o s t i n d i c a t e move- ments c o u l d o c c u r u n d e r s u c h t e m p e r a t u r e and l o a d c o n d i t i o n s ( R e f e r e n c e 5 ) . Movement o f t h e a n c h o r p i l e s i s i n d i c a t e d by t h e f a c t t h a t t h e r e was permanent movement o f b o t h t e s t p i l e s a t t h e end o f t h e t e s t . Had no c r e e p o f t h e a n c h o r p i l e s o c c u r r e d , a l l o f t h e v e r t i c a l movement s h o u l d have b e e n p roduced s o l e l y by t h e d e f l e c t i o n of t h e p r o v i n g r i n g s and t h e e l a s t i c e l o n g a t i o n o f t h e s t e e l r o d s and p i l e s , i . e . , 0 . 0 4 i n . f o r a 10 ,000 l b l o a d . The f a c t t h a t a p p r o x i - m a t e l y 0 . 5 i n . o f permanent movement o f t h e s t e e l p i p e p i l e and 0 . 2 i n . movement o f t h e t i m b e r p i l e remained a t t h e end of t h e t e s t i n d i c a t e d t h a t some movement o f t h e a n c h o r p i l e s h a d o c c u r r e d d u r i n g t h e t e s t s .

CONCLUSIONS

Tne r e s u l t s o f t h i s f i e l d i n v e s t i g a t i o n i n d i c a t e t h a t h e a v i n g f o r c e s g e n e r a t e d on p i l i n g o f t h e s i z e s and t y p e s t e s t e d d u r i n g t h e s e a s o n a l f r e e z i n g o f t h e f r o s t s u s c e p t i b l e s o i l s may r e a c h o r e v e n s u r p a s s 50,000 l b f o r t h e s e movements. Under normal f i e l d c o n d i t i o n s , s u c h up- l i f t f o r c e s c o u l d exceed t h e sum o f t h e u l t i m a t e a n c h o r i n g c a p a c i t y o f t h e p e r m a f r o s t embedment and t h e imposed p i l e l o a d , r e s u l t i n g i n a n upward a n n u a l d i s p l a c e m e n t . Maximum r a t e o f heave o c c u r s d u r i n g t h e e a r l y w i n t e r months, a t r e l a t i v e l y s h a l l o w d e p t h s , and t h e maximum heave f o r c e on

p i l i n g o c c u r s d u r i n g p e r i o d s o f a c t i v e f r o s t p e n e t r a t i o n w i t h v e r y c o l d n e a r - s u r f a c e ground t e m p e r a t u r e s . Maximum o r n e a r maximum heave f o r c e s c a n be produced a t r e l a t i v e l y s h a l l o w d e p t h s ( 3 f t ) o r a t g r e a t e r d e p t h s (more t h a n 6 f t ) u n d e r t h e s e c o n d i t i o n s .

Although t h i s i n v e s t i g a t i o n was conduc ted i n a p e r m a f r o s t a r e a , i t may be assumed t h a t heave f o r c e s i n t h e same o r d e r o f magni tude can be p roduced i n t e m p e r a t e r e g i o n s b e c a u s e o f f r o s t a c t i o n u n d e r s i m i l a r s o i l and m o i s t u r e c o n d i t i o n s n e a r t h e ground s u r f a c e . Based on t h e l a r g e r heave f o r c e r e g i s t e r e d on t h e p i p e p i l e s , i t i s con- c l u d e d t h a t t h e e f f e c t i v e u n i t a d f r e e z e bond o f t h e a c t i v e l a y e r i s dependen t on s u r f a c e c o n d i t i o n s a s w e l l as on s u r f a c e a r e a . Maximum a v e r a g e u n i t a d f r e e z e ( t a n g e n t i a l ) s t r e s s d e v e l o p e d on t h e s t e e l p i p e p i l e ( F i g u r e 7 ) was a p p r o x i m a t e l y 4 1 p s i as opposed t o 1 2 p s i on t h e c r e o s o t e d t i m b e r p i l e . S i m i l a r c o n c l u s i o n s have been r e a c h e d i n p i l e l o a d s e t t l e m e n t tests conduc ted i n p e r m a f r o s t ( R e f e r e n c e 5 ) .

Based on t h e r e s u l t s o f t h i s f i e l d i n v e s t i g a t i o n and p r e l i m i n a r y l a b o r a t o r y s t u d i e s conduc ted i n t h e c o l d rooms, a n i n v e s t i g a t i o n i s now b e i n g made u s i n g similar f i e l d i n s t a l l a t i o n s t o i n v e s t i g a t e t h e e f f e c t i v e n e s s o f v a r i o u s p i l e s u r f a c e and b a c k f i l l t r e a t m e n t s i n r e d u c i n g t h e heave t h r u s t on p i l e s and powerpo les . P r e l i m i n a r y r e s u l t s i n d i c a t e t h a t i t may be p o s s i b l e t o r e d u c e t h e heave t h r u s t t o t o l e r a b l e magn i tudes w i t h o u t c o m p l e t e l y i n s u l a t i n g t h e t o p 4 t o 6 f t o f t h e p i l e w i t h c a s i n g s o r s l e e v e s , a p r o c e d u r e t h a t r e d u c e s t h e l a t e r a l s t a b i l i t y o f t h e p i l e .

ACKNOWLEDGMENTS

T h i s i n v e s t i g a t i o n i s p a r t o f a s t u d y b e i n g conduc ted a t USA CRREL f o r t h e O f f i c e , Ch ie f o f E n g i n e e r s , D i r e c t o r a t e o f M i l i t a r y C o n s t r u c t i o n . S u b s t a n t i a l s u p p o r t was f u r n i s h e d by p e r s o n n e l o f t h e Alaska F i e l d S t a t i o n , USA CRREL, u n d e r t h e d i r e c t i o n o f M r . F .F . K i t z e .

REFERENCES

1. U.S. Army Corps of Engineers, "Pile Extraction Tests, Fairbanks Research Area", ACFEL TR-59, Status Report No. 1 and 2, June 1955.

2. Linell, K.A., "Interim Report, on Load Tests of Piles in Permafrost", ACFEL Technical Report 58, June 1955

3. U.S. Army Corps of Engineers, "Freezeback Control and Pile Testing, Kotzebue Air Force Station, Alaska", Technical Report 66 (Draft) ACFEL, New England Division, Corps of Engineers, May 1957.

4. "Freezeback Control and Pile Testing, Bethel Air Force Station, Alaska", USA CRREL Technical Report 143 (In preparation).

5. Crory, F.E., "Installation and Testing of Piles in Permafrost Pile Site C", USA CRREL Technical Report 140 (In preparation).

6. U.S. Army Corps of Engineers, "Arctic and Subarctic Construction, Building Foundations", Engineering Manual for Military Construction (Manual Corps of Engineers EM 1110-395-374 ) .

7. MJller, S.W., "Permafrost or Permanently Frozen Ground and Related Engineering Problems": 1st Ed., U.S. Geol. Survey Spec. Report Strategic Eng. Study 62, 1943; 2nd Ed., U.S. Army Military Intelligence Div., Office Chief Engineer, 1945.

8. Pewe, T.L. and R.A. Paige, "Frost Heaving of Piles with an Example from Fairbanks, Alaska", Geological Survey Bulletin, 111-1, Washington, 1963.

9. Crory, F.E. and R.E. Reed, "Measurement of Frost Heaving Forces on Piles", USA CRREL Technical Report 145 (In preparation).

10. Linell, K.A. and C.W. Xaplar, "Description and Classi- fication of Frozen Soils", Proceedings of International Conference on Permafrost, Purdue University, Nov. 1963.

11. U.S. Army Corps of Engineers, "Engineering and Design, Arctic and Subarctic Construction, Site Selection and Development" (Manual Corps of Engineers EM 1110-345-371).

P i h l a i n e n , J . A . and G . H . J o h n s t o n , "Guide t o a F i e l d D e s c r i p t i o n o f P e r m a f r o s t f o r E n g i n e e r i n g Purposes" , Tech . Mem. 79 , N a t i o n a l Resea rch C o u n c i l , NRC 7576, O c t . 1963.

K i n o s h i t a , S . and T . Ono, "Heave F o r c e o f F r o z e n S o i l " , Low Tempera tu re S c i e n c e , S e r . A , Vol . 21, p . 117-139, 1 9 6 3 (Text i n J a p a n e s e ) .

D i s c u s s i o n

J . A . Ellwood a s k e d how t h e p i l e s a r e i s o l a t e d f rom t h e s o i l t o r e d u c e movements. The a u t h o r r e p l i e d t h a t CRREL i s e x p e r i m e n t i n g w i t h s u r f a c e t r e a t m e n t s and b a c k f i l l i n g w i t h t r e a t e d m a t e r i a l s . C o a t i n g s , a p p l i e d by b r u s h o r s p r a y i n g , which i n c l u d e epoxy and enamel p a i n t , have r educed t h e a d f r e e z i n g bond by a s much a s 20 p e r c e n t .

C . A . Noble a s k e d f o r i n f o r m a t i o n on t h e magni tude o f movement i n t h e a n c h o r p i l e s y s t e m . Reed r e p l i e d t h a t t h e t o t a l movement u n d e r 55 ,000 l b s . o f l o a d was a b o u t 2/10 i n c h . Because o f c r e e p a c t i o n o f t h e a n c h o r p i l e s y s t e m , t h i s might n o t be t h e maximum movement. I n e a r l i e r t e s t s t h e maximum f o r c e s were 25,000 l b s - h a l f o f t h e p r e s e n t t e s t .

WATER CONTENT DRY UNIT WEIGHT PERCENT OF WV WElOHT PCP

0. SOILS EXPLORATION MIDWAY BETWEEN 8"PIPE TEST AND DUMMY PILES

BORING LOG 23 MAy'61

EL.472.7

Thowd organic SlLT

Dark Worn SlLT 3 1.0 ThW.4

Oh. brown, orgonle SILT ' 3 k - ~ b l Fmmn

WATER CONTENT DRY UNIT WEIGH1 PERCENT OF ORY WEIQHT PCF

%mWd by driving lf Shllby Tub* -/Jock Hommw.

b. SOILS EXPLORATION MIDWAY BETWEEN TIMBER TEST AND DUMMY PILES

F I G U R E 2 B O R I N G L O G S A N D S O I L D A T A

8a 94J I - / 6

F I G U R E 3

P L A N A N D E L E V A T I O N V I E W O F T E S T I N S T A L L A T I O N

F I G U R E 4

V I E W O F I N S U L A P R O V I N G R I N G

T E D E N C L O S U R E A R O U N D

a# 3459 -2 o

F I G U R E 5

0 0 z z Of 3 yg g;

2 P

6 0

T E S T O B S E R V A T I O N S - 8" S T E E L P I P E P I L E

OR 3 C f V - Z l

- 2-

- 4 -

- - ASSUMED R i7 TABLE (JULY 1962)

F I G U R E 6

a 0

2 a . o= 36 S 2 k!& 3

X V )

k 0

T E S T O B S E R V A T I O N S - C R E O S O T E D T I M B E R P I L E

mi 3 4 - 5 9 - 2 2

- 2-

- 4 -

- - ASSUMED RE TABLE /JULY I9621

F I G U R E 7

A V E R A G E A D F R E E Z E B O N D S T R E S S V S TIME