Lunar and Martian soil mechanics - soil shear strength and penetration resistance under high vacuum, and composition of desorbed gases from heated soil sample

Nelson, J. D.

Vey, E.

English

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. 
Third Quarterly Progress Report 
IITRI Project No. M272, Phase I11 
STUDIES OF LUNAR AND MARTIAN 
SOIL MECHANICS 
by 
E. Vey and J. D. Nelson 
September 30, 1965 
IIT RESEARCH INSTITUTE 
Technology Center 
Chicago, Illinois 60616 
Third Quarterly Progress Report 
IITRI Project No. M272, Phase I11 
Contract No. NASr-65(02) 
STUDIES OF LUNAR AND MARTIAN 
SOIL MECHANICS 
E. Vey and J. D. Nelson 
for 
National Aeronautics and Space Administration 
Structures and Operations Problem Group 
Space Vehicles Division 
Washington, D. C. 
September 30, 1965 
TABLE OF CONTENTS 
Section Page 
I. INTRODUCTION. . . . . . . . . . . . . . . . .  1 
TI. DETERMINATION OF SHEAR STRENGTH PARAMETERS. . 2 
111. PENETRATION RESISTANCE UNDER DYNAMIC 
L O A D I N G . .  . . . . . . . . . . . . . . .  5 
IV . COMPOSITION OF ADSORBED GAS LAYERS. . . . . .  8 
V .  PLANNED RESEARCH FOR THE NEXT QUARTER . . . .  12 
V I .  CONTRIBUTING PERSONNEL. . . . . . . . . . . .  13 
STUDIES OF LUNAR AND MARTIAN 
SOIL MECHANICS 
I. INTRODUCTION 
This is the third quarterly report on Phase I11 of 
Project NASr-65(02) , "Studies of Lunar and Martian Soil 
Mechanics". Phase I11 was initiated on December 15, 1964 and 
this report covers the period from June 15, 1965 to September 15, 
1965. 
The work to date has closely followed the outline of work 
set forth in IITRI Proposal No. 65-183M, entitled "Studies of 
Lunar and Martian Soil Mechanics". Efforts during the three 
month period covered in this report have been devoted to the 
determination of shear strength parameters under vacuum, the 
resistance of soil to dynamic penetration, and the determination 
of the composition of desorbed gases. 
11. DETERMINATION OF SHEAR STRENGTH PARAMETERS 
In the final report on Phase II,L'*it was pointed out that 
because of scatter in the data it would be necessary to obtain 
additional data points before the apparent trends could be firmly 
established. In this reporting period additional direct shear 
tests were performed on quartz powder. 
In agreement with previous results a marked increase in 
stiffness of the soil was observed under ultra-high vacuum. At 
low values of normal stress, the shear stress reached a peak 
at very small displacements (approximately 0.005 in.) after which 
the shear stress deereased and then increased to a maximum at 
approximately 0.150 to 0.200 in. Figure 1 shows the maximum 
- I/ 
Vey, E. and J. D. Nelson, "Studies of Lunar Soil Mechanics", 
Final Report, IIT Research Institute Proposal No. M272-11, 
Contract NASr-65(02), February 1965. 
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F i g .  1 EFFECT OF VACIIIIM ON MAXIM1TE.l SHEAR STRESS IN QUARTZ POWDER 
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shear  s t r e s s  as a function of the vacuum leve l  a t  which the 
experiment w a s  performed. 
s t r e s s e s  were observed the second maximum point  i s  the  one shown 
i n  t h i s  f igure .  
In those cases where t w o  peak shear 
The shear s t r e s s  w a s  p lo t ted  as a funct ion of normal s t r e s s  
i n  Fig.  2 t o  obtain the rupture diagram f o r  the s o i l .  Although 
there  i s  a considerable amount of s c a t t e r  i n  the data  i t  can be 
seen t h a t  i f  l i n e s  a r e  drawn bounding the points  f o r  atmospheric 
condi t ions and ul t ra-high vacuum an increase i n  shear s t rength  
under vacuum i s  indicated qui te  c l e a r l y .  From F ig .  1 it  appears 
t h a t  the shear s t rength  decreased somewhat a t  rough vacuum 
l e v e l s  (approximately t o r r ) .  While the data  ind ica t ing  t h i s  
a r e  scarce i t  would be reasonable t o  expect because of the 
removal of hygroscopic moisture and, hence, surface tension i n  
the  s o i l .  Consequently, the increase i n  shear s t rength  due t o  
the  removal of adsorbed gas from the p a r t i c l e  surfaces  should be 
a t  least  equal t o  o r  g rea t e r  than the difference indicated i n  
Fig.  2 .  
While the s c a t t e r  makes i t  d i f f i c u l t  t o  separate  the 
increase  i n  shear s t rength  into cohesive and f r i c t i o n a l  components 
the s lopes of the boundary l i nes  do not  change appreciably and, 
hence, an increase i n  the apparent cohesion i s  indicated.  
I f  the  s t rength  increase i s  caused by the development of 
i n t e r p a r t i c l e  forces  and/or an. increase i n  f r i c t i o n  as the  r e s u l t  
of t he  removal of adsorbed gas then the shear s t rength  would be a 
funct ion of the amount of gas removed r a the r  than the vacuum 
level a t  which the t e s t  w a s  performed. The amount of gas 
removed depends not  only on the ul t imate  a t t a inab le  vacuum l e v e l  
bu t  a l s o  the length of time under vacuum, the amount of bakeout 
of t he  system and s o i l  and the degree and type of contamination of 
t h e  e n t i r e  system p r i o r  t o  pumpdown. Consequently, the s c a t t e r  
of t he  data  i n  Fig. 1 and 2 may be a t t r i b u t e d ,  a t  l e a s t  i n  p a r t ,  
t o  va r i a t ions  i n  the pumpdown h i s to ry  of d i f f e r e n t  experiments. 
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Thus, while a quant i ta t ive measure of the change i n  shear  
s t rength i s  not  possible  an increase under ul t ra-high vacuum i s  
d e f i n i t e l y  indicated,  It i s  believed t h a t  t h i s  increase i s  
derived from increases  i n  both apparent cohesion and in t e rna l  
f r i c t i o n .  
111. PENETRATION RESISTANCE ITDER DYNAMIC LOADING 
Dynamic penetrat ion experiments were a l s o  performed t o  
supplement the data  obtained i n  Phase I1 of t h i s  program. 
r e s u l t s  of these experiments are  shown i n  F ig .  3 and 4 along 
with those obtained previously i n  the form of the penetrat ion 
caused by 0.3 in . - lb  work as  a funct ion 06 the  porosi ty .  
The 
In  -Fig. 3 which shows the r e s u l t s  i n  quartz powder i t  can 
be seen t h a t  the curves have the same shape as w a s  indicated 
before .  An increase i n  penetrat ion res i s tance  under rough vacuum 
i s  indicated and t h i s  w a s  due t o  the removal of pore a i r  e f f e c t s .  
A fu r the r  increase i n  res is tance i s  indicated a t  high and u l t r a -  
high vacuum l e v e l s ,  
From Fig. 4 i t  can be seen t h a t  the r e s u l t s  f o r  o l iv ine  
powder a lso agree c lose ly  with the previous r e s u l t s .  
da ta  an increase i n  penetrat ion res i s tance  under rough vacuum 
l e v e l s  and a fur ther  increase under u l t ra -h igh  vacuum i s  evident 
as w a s  the case f o r  quartz .  However, the r e s u l t s  f o r  high 
vacuum (approximately loo6 t o r r )  a r e  c lose r  t o  those f o r  rough 
vacuum whereas i n  the quartz they were c lose r  t o  those f o r  u l t r a -  
high vacuum. Thus, although the removal of adsorbed gas from 
the  p a r t i c l e  surfaces  produces an increase i n  the shear s t rength  
(and, hence, the penetrat ion res i s tance)  i n  both s o i l s ,  the  
vacuum l e v e l  a t  which t h i s  e f f e c t  becomes appreciable  i s  con- 
s iderably  higher f o r  the o l iv ine  than the quartz ,  Possible  
reasons f o r  t h i s  a r e  1) the gas adsorbed on the o l iv ine  has a 
higher  adsorption energy than t h a t  adsorbed on the quar tz ,  
2) a g rea t e r  amount of gas i s  adsorbed on the o l iv ine  than the 
In these 
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and/or contact  area a t  a s p e r i t i e s  because of d i f f e r e n t  grain 
shape and s i z e  i s  l e s s  for the  o l iv ine  than the quartz .  
It may be noted t h a t  these r e s u l t s  are cons is ten t  with 
those of the d i r e c t  shear t e s t s  and porosi ty  a t t a ined  by s o i l  
deposited i n  vacuum. 
I V .  COMPOSITION OF ADSORBED GAS LAYERS 
Experiments a r e  present ly  being performed t o  determine 
the components of the gas layers  adsorbed on the s o i l  p a r t i c l e s .  
The equipment being used i n  these experiments w a s  described i n  
the previous quar te r ly  r epor t . l /  
fabr ica ted  from th in  tantalum sheet  i n t o  which the s o i l  i s  placed 
and through which low vol tage a l t e rna t ing  current  i s  passed t o  
heat  the s o i l .  The maximum temperature t h a t  can be obtained i n  
t h i s  way i s  approximately 900°C. 
c losed except fo r  a s m a l l  hole facing the i n l e t  po r t  of an u l t r a -  
high vacuum, mass spectrometer typeJ residual  gas analyzer.  Thus, 
the desorbed gas issues  from the hole i n  a molecular beam which 
i s  then analyzed with the mass spectrometer. 
It cons is t s  of a s m a l l  container  
The container  i s  completely 
Preliminary experiments have been performed on quartz  
c rys ta l s ,  quartz  powder and ol ivine c r y s t a l s .  The pure quartz  
and o l iv ine  c r y s t a l s  were prepared by f i r s t  coat ing a la rge  
quar tz  c r y s t a l  o r  piece of o l iv ine  with machinists bluing.  It 
w a s  then wrapped i n  aluminum f o i l  and crushed between two s t e e l  
p l a t e s .  In  t h i s  way smaller pieces  having a l l  f r e sh  surfaces  
could be obtained. The powder w a s  the  same as t h a t  used i n  a l l  
previous experiments. 
The r e l a t i v e  peak heights of the ma jo r  peaks t h a t  were 
observed a r e  shown i n  F i g .  5 ,  6 and 7 .  While these r e s u l t s  a r e  
L' Vey, E .  and J .  D. Nelson, "Studies of Lunar and Martian S o i l  
Mechanics", Second Quarterly Progress Report, I I T  Research 
I n s t i t u t e  Project  M272-111, June 30, 1965. 
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only preliminary it appears that the major peaks of the desorbed 
gas for all three materials are at M/e values of 2 and 18. The 
existence of the relatively high 18 peak suggests that both the 
2 and 18 peaks are due to desorbed H20 from the crystals. 
also appears that a greater amount of gas is desorbed from the 
olivine than the quartz but the data is not conclusive. 
It 
V. PLANNED RESEARCH FOR THE NEXT QUARTER 
The work to be carried out  in the remaining quarters will 
closely follow that outlined in IITRI Proposal No. 65-183M, 
"Studies of Lunar and Martian Soil Mechanics". The schedule for 
the next 
1. 
2. 
3 .  
4 .  
5 .  
quarter is as follows: 
Direct shear tests on enstatite and obsidian 
powders in vacuum at temperatures from +270"F 
to the lowest obtainable. 
Dynamic penetration tests on enstatite and 
obsidian powders at varying vacuum levels and 
porosities a 
Determination of the composition of  adsorbed 
gas. 
Generation of clean particle surfaces. 
Mart-ian soil experiments. 
VI. CONTRIBUTING PERSONNEL 
The following personnel contributed to the work described 
in the present program. 
E. Vey was project engineer. 
J. D. Nelson was responsible for the experimental work 
and analysis of the data, 
t t T  R E S E A R C H  I N S T I T U T E  
1 2  
R .  A .  Wetzel a s s i s t e d  i n  the performance of the experi- 
ments and data ana lys i s .  
W .  E .  Jamison was i n  charge of the vacuum f a c i l i t i e s  and 
designed the equipment fo r  the determination of the composition 
of adsorbed gases. 
I I T  R E S E A R C H  I N S T I T U T E  
1 3  


Studies of lunar and Martian soil mechanics Third quarterly progress report, Jun. - Sep. 15, 1965

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