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Technical Note N-1438



DOSIST II - AN INVESTIGATION OF THE IN-PLACE
STRENGTH BEHAVIOR OF MARINE SEDIMENTS



By

H. J. Lee



June 1976




Sponsored by

NAVAL FACILITIES ENGINEERING COMMAND



Approved for public release; distribution unlimited.



CIVIL ENGINEERING LABORATORY

Naval Construction Battalion Center

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4. TITLE (and Subtitle)

DOSIST II - AN INVESTIGATION OF THE IN-PLACE
STRENGTH BEHAVIOR OF MARINE SEDIMENTS



5. TYPE OF REPORT & PERIOD COVERED



Not final; Jul 1974 -Jul 1975



6 PERFORMING ORG. REPORT NUMBER



7. AUTHORfs



H. J. Lee



CONTRACT OR GF



9. PERFORMING (



•ID ADDRESS



CIVIL ENGINEERING LABORATORY
Naval Construction Battalion Center
Port Hueneme, California 93043



62759N;

YF52. 556.999.01. 101



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Naval Facilities Engineering Command
Alexandria, Virginia 22332



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June 1976



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SUPPLEMEN



<EY WORDS (Co.



Soil testing, corers, sediment cores, deep-ocean sediments, vane shear tests, soil strength
profiles.



ABSTRACT (Continue on reverse side It necessary end identity by block number)

DOSIST II (Deep Ocean Sampling and In-Situ Testing) was a cruise in the Western
North Atlantic Ocean conducted to evaluate the in-place engineering behavior of several
typical deep ocean sediments. In-place vane shear tests were performed, and sediment
cores (gravity, piston, and box) were taken. Laboratory tests were conducted on the cored
samples to classify the sediments and to determine which testing procedure best reproduces
the measured in-place strength. This was found to be consolidated-undrained triaxial



DD | JAN 73 1473 EDITION OF 1 NOV 65 IS OBSOLETE



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20. Continued

testing. The sediments tested in-place were a foraminifera-dominated calcareous ooze and
a proximal turbidite. Both of these sediments are nearly cohesionless and retain little of
their in-place strength when sampled. A deep sea pelagic clay was cored and subjected to
laboratory testing, but was not tested in-place. Estimated in-place strength profiles were
derived for each of these sediments to subbottom depths in excess of 50 feet (15 m).



Library card
I



Civil Engineering Laboratory
DOSIST II - AN INVESTIGATION OF THE IN-PLACE
STRENGTH BEHAVIOR OF MARINE SEDIMENTS, by
H. J. Lee

TN-1438 16 p. illus. June 1976 Unclassified

1. Soil testing 2. Sediment cores I. YF52. 556.999 .01. 101

DOSIST II (Deep Ocean Sampling and In-Situ Testing) was a cruise in the Western North
Atlantic Ocean conducted to evaluate the in-place engineering behavior of several typical deep ocean
sediments. In-place vane shear tests were performed, and sediment cores (gravity, piston, and box)
were taken. Laboratory tests were conducted on the cored samples to classify the sediments and to
determine which testing procedure best reproduces the measured in-place strength. This was found
to be consolidated-undrained triaxial testing. The sediments tested in-place were a foraminifera-
dominated calcareous ooze and a proximal turbidite. Both of these sediments are nearly cohesionless
and retain little of their in-place strength when sampled. A deep sea pelagic clay was cored and
subjected to laboratory testing, but was not tested in-place. Estimated in-place strength profiles
were derived for each of these sediments to subbottom depths in excess of 50 feet (15 m).



Unclassified

ASSITICATION OF THIS P AGEfWhe



CONTENTS

Page

INTRODUCTION 1

OBJECTIVE 1

FIELD OPERATIONS 2

Vessel 2

Equipment 2

Sites Visited 3

IN-PLACE TEST RESULTS 4

LABORATORY TESTS 6

ANALYSIS AND DISCUSSION 7

Site I (pelagic clay) 11

Site III (globigerina ooze) 11

Site IV (turbidites) 12

SUMMARY AND CONCLUSIONS 13

ACKNOWLEDGMENTS 13

REFERENCES 14

LIST OF ILLUSTRATIONS

Figure 1 . In-place vane shear strength profile for Site III . . 5

Figure 2. In-place vane shear strength profile for Site IV. . . 5

Figure 3. Triaxial test stress path diagram for Site I - core

D0S1D 9

Figure 4. Triaxial test stress path diagram for Site III - core

D0S3C 9

Figure 5. Triaxial test stress path diagram for silts from

Site IV - cores D0S4B and 4D 10

Figure 6. Triaxial test stress path diagram for sands from

Site IV - cores D0S4B and 4D 10



Figure 7.
Figure 8.
Figure 9.



Table 1 .
Table 2.

Table 3.
Table 4.
Table 5.



List of Illustrations (continued)

Page

Strength profiles for Site I (pelagic clay) 12

Strength profiles for Site III (globigerina ooze) . . 12

Strength profiles for Site IV (turbidite) 12

LIST OF TABLES

Summary of Test Sites Investigated 4

Identification of Cores Taken and Vane Tests

Performed 6

Index Properties of Site I Cores 7

Index Properties of Site III Cores 8

Index Properties of Site IV Cores 8



INTRODUCTION

The DOSIST (Deep Ocean Sampling and In Situ-Testing) cruises are
part of a continuing effort at CEL to investigate the engineering proper-
ties of marine sediments. The cruises consist of in-place vane shear
testing and sediment coring leading to laboratory engineering property
testing. The overall objective of the work is to develop laboratory
testing and coring procedures that can be used to obtain good estimates
of in-place engineering behavior of sediments. Coring and laboratory
testing is emphasized because it is more economical, more parameters

(including long-term drained properties) can be measured, and a greater
range of subbottom depths can be investigated. In-place testing is
conducted during the DOSIST cruises to provide a basis for evaluating
the properties measured in the laboratory. That is, the properties
measured in the laboratory are compared with the in-place properties,
and techniques are developed for estimating the latter given only the
former. The difference between the results obtained from the two types
of measurements is termed sampling disturbance. The procedures used for
obtaining in-place properties using results of laboratory tests are
termed sample disturbance correction techniques.

One sample disturbance correction technique was presented by Lee

(1973a). It involved measuring the residual negative pore water pressure
retained by cored samples and using the relative magnitude of this
pressure as an indicator of the property changes that occurred during
coring and handling. Good correlations between degree of disturbance
and the residual pore water pressure were found for cohesive marine
sediments. Other sample disturbance correction techniques have also
been proposed (Ladd and Lambe, 1963).



OBJECTIVE

The objective of this interim report is to present and analyze the
results of in-place and laboratory tests conducted on typical ocean
sediments from the Western North Atlantic Ocean. A final report to be
prepared in about one year will recommend procedures for coring, testing,
and estimating the in-place behavior of most of the typical deep ocean
sediment types.

A secondary objective of DOSIST II was to obtain the strength
properties of three sites where the CEL 20K anchor is to be field-tested.
The results presented in this report can be used to predict the holding
capacities of the anchors prior to the field tests.



Another objective of DOSIST II was to obtain box core samples for
dynamic property testing. These have been transported to the University
of California, Berkeley, where they are currently being tested.



FIELD OPERATIONS

Vessel

The USNS LYNCH (T-AGOR-7) was used as a support vessel during
DOSIST II. The ship is typical of the Navy's oceanographic vessels and
is adequately equipped with winches and U-frames for deploying conven-
tional oceanographic corers and other gear.

Equipment

In-place vane shear strength measurements were made with the ONR
vane tower developed by Dr. Adrian Richards of Lehigh University (Richards
et al. , 1972). The device is capable of inserting standard vanes (2x4
inches to 4 x 8 inches) (50 x 100 mm to 100 x 200 mm) to about 8 feet (2 m)
into the seafloor. The vane is rotated at about every foot (third of a
meter) of penetration, and the peak torque is used to calculate the in-
place undisturbed strength of the sediments. The sediment is remolded
by rapidly returning the vane to its original position. A second strength
measurement is made on the remolded sediment, and a sensitivity is
calculated (undisturbed strength divided by remolded strength) . The
vane is rotated at 90 deg/min (1.6 rad/min) , a relatively rapid rate.
This rate was chosen for operational convenience to reduce the time the
device needs to remain on the seafloor.

The ONR device was used rather than CEL's DOTIPOS (Demars and
Taylor, 1971) because of its lighter weight and greater water depth
capabilities (15,000 feet versus 6,000 feet) (4,600 m versus 1,800 m) .
One of the major problems with the ONR device is that it is tall and can
be easily tipped over on the seafloor. The support vessel must remain
close to the tower, or large lateral forces will be exerted by the
tether line. Single-point deep sea anchoring was used to maintain the
ship's position during testing.

Coring was conducted with a typical long piston corer and a spade-
type box corer. Cores were also taken with free-fall boomerang corers
and a NAVOCEANO hydroplastic corer.

The long piston corer used is a Benthos Model 2450, a 2.6-inch-ID
(66— mm) triggered corer, weighing 2,700 pounds (1.2 Mg) . The piston is
self -deactivating. During corer penetration, the piston is held at the
sediment surface, and greater core recovery is produced. As the corer
is being withdrawn, the piston splits, with one section locking into
place at the top of the sediment and the other section being pulled to a
stop at the top of the corer. By allowing the piston to split in this
manner, additional material (''flow-in'') is not sucked into the bottom
of the corer during withdrawal.



The corer was not designed to obtain engineering quality samples as
defined by Hvorslev (1949). However, it is typical of the intermediate-
size piston corers currently in use by the oceanographic community
(Clausner and Lee, 1975). The corer has obtained samples up to 40 feet
(12m) in length in very soft sediments. The longest sample CEL has
obtained is 28 feet (8.5 m) (on an earlier cruise).

The spade-type box corer obtains samples that are only 2 feet (0.6 m)
in length. However, the cross-sectional area of the sample is so
large (12x8 inches) (300 x 200 mm) that almost completely undisturbed
samples are guaranteed. These samples were taken to determine the
maximum quality of sample that could be achieved and to use them in
triaxial testing to simulate strength profiles to greater subbottom
depths (as explained later). Also, high quality samples were needed for
CEL's soil dynamics program.

Free-fall boomerang cores were taken to determine the general
sediment type of a site prior to deploying the vane tower or long-piston
corer. A NAV0CEAN0 hydroplastic corer was used at one of the sites
after the CEL piston corer was lost.

Sites Visited

Table 1 lists the sites that were investigated along with their
geographic coordinates. Site I is located north of the Puerto Rico
trench in deep water (18,000 feet) (5,500 m) . It was selected as a site
with a low calcium carbonate content that would probably contain a
pelagic clay deposit. This was found to be the case. Site III is
located north of Grand Bahama Island on the Blake Plateau in about 4,000
feet (1,200 m) of water. This site was selected as a location with a
high calcium carbonate content (calcareous ooze). Site IV is located a
few miles (several kilometers) southeast of Puerto Rico in a 6,000-foot-
deep (1 ,800 m) enclosed basin. The sediment at this site is a calcium
carbonate-rich proximal turbidite (alternating silt and sand layers).
Site II was to be located in a deep channel north of Nassau. This site
was not visited because of highly irregular bottom topography.

The cruise was conducted between 23 November and 13 December 1974.
During this time the LYNCH sailed from Charleston, South Carolina, to
San Juan, Puerto Rico. Some ship time was lost as a result of adverse
weather conditions, especially in the vicinity of the Bahamas Islands.

The in-place vane shear tests, which were conducted from a moored
ship, had locations that were within 300 feet (90 m) of each other
at each general test site. The cores, taken while the ship was in a
drifting mode, are much more widely scattered. The distance between
cores at a general site is as much as 3 miles (5 km) . Since the test
sites were selected partly for their flatness and areally uniform sediment
conditions, it is assumed that variations among properties over the area
of a general test site are negleeible.



Table 1. Summary of Test Sites Investigated



Site


Approximate
Longitude


Approximate
Latitude


Water
Depth


Sediment
Type


In-
Place
Vane
Tests


Box

Cores


Piston
Cores


Other


General Comments


Feet


Meters


I

III

IV


66°15'W
77°12'W
65°54'W


21°N
28°N

17°53'N


17,900
3,700
6,500


5,460
1,100
2,000


pelagic clay
foram ooze
turbidites


3

2


1
1
1


1
2


1 hydro-
plastic
core

1 boomer-
ang


Numerous manganese
nodules; typical
"red clay"

Sediment is highly sen-
sitive with laboratory
strength less than 1/10
field strength

Alternating sand-silt
clay layers; relatively
dense and competent



IN-PLACE TEST RESULTS



In-place vane shear tests were conducted at Sites III and IV. Site
I was too deep for the ONR vane tower.

The results of these tests are given in Figures 1 and 2 in the form
of original vane strength and sensitivity versus subbottom depth. At
several points (usually in sand layers) insufficient torque was available
to rotate the vane. At these points an arrow is drawn indicating the
maximum shearing resistance developed. The actual strength would be
higher.

In the sand layers at Site IV, some drainage must have occurred
during vane rotation. The strength given, therefore, is not a true
undrained shearing strength, but rather a strength index property. The
strengths in the Site III oozes and the Site IV silts are probably true
undrained shearing strengths.

Table 1 lists the number of cores that were obtained at each site.
Table 2 gives the CEL identification for each core and its exact geo-
graphic coordinates.

The CEL piston corer was lost during lowering at Site I. It evi-
dently pre-triggered 5,000 feet (1,500 m) below the ship and fell to the
end of the coring cable, causing the cable to part. Apparently, reso-
nance in the coring cable was set up by a series of consistent, large
swells passing through the area. The resulting large motions of the
corer could easily have caused pre- triggering. Future coring operations
will be conducted with a pressure-activated triggering device, thereby
reducing problems with pre-triggering.

To conduct the coring operations at Site IV, a similar Benthos
corer was borrowed from NAVFAC (FP0-1) in Washington.



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Table 2. Identification of Cores Taken and In-Place Vane Tests Performed



Site
Number


Core or

Vane Test

Number


Corer
Type


Core
Length


Latitude


Longitude


Ft-in.


Meters


I


DOS- IB


box


2-0


0.61


20°57'41"N


66°15'12"W




DOS- ID


hydroplastic


4-1


1.24


20°56'17"N


66°15'24"W


III


DOS-3A


boomerang


3-6


1.07


27°59'30"N


77°10'32"W




DOS-3B


box


2-0


0.61


28°02'00"N


77°12'00"W




DOS-3C


piston


18-0


5.49


28°01'52"N


77°12'43"W




Vane Test
3V-1








28°00'10"N


77°11'39"W




Vane Test
3V-2








28°00'11"N


77°11'36"W




Vane Test
3V-3








28°00'17"N


77°11'36"W


IV


DOS-4A


box


2-0


0.61


17°52'36"N


65°55'11"W




DOS-4B


piston


8-7


2.62


17°52'00"N


65°55'08"W




DOS-4D


piston


8-8


2.64


17°53'13"N


65°S3'13"W




Vane Test

4V-1








17°53'00"N


65°53'48"W




Vane Test

4V-2








17°53'00"N


65°53'48"W




LABORATORY TESTS



The core samples were subjected to standard index property tests
(water content, sieve analysis, hydrometer, Atterberg limits, grain
density, and carbonate content), miniature vane shear tests,
consolidated-undrained triaxial tests with pore pressure measurements,
and residual pore water pressure tests. Standard CEL procedures were
followed as described in earlier reports (Lee, 1973a and 1973b). Some
difficulties were encountered, however, because the sediments from Sites
III and IV were nearly or completely cohesionless. Atterberg limits
tests could not be performed; the samples retained no negative residual
pore water pressures, and most of the specimens could not be trimmed for
triaxial testing in the usual manner. The samples that could not be
trimmed were remolded and placed in a triaxial specimen former. An
attempt was made to place the sediment at its original density.



The index properties and vane shear strengths of the cores taken at
the three sites are given in Tables 3, 4, and 5. Triaxial test results
are presented in the form of stress paths (Figures 3 through 6) . A
stress path is a plot of the principal stress difference versus the sum
of the major and minor principal effective stresses (o-> and 03). The
stress path diagram defines the drained strength parameters, Jj| and c,
and provides considerable additional data about the sediment's behavior
(as discussed by Lee, 1973b).



ANALYSIS AND DISCUSSION

As discussed above, no residual pore water pressures were retained
by samples from the two sites where in-place vane tests were performed.
This is because these samples contained relatively coarse-grained material
(50% or more sand-sized). The pore sizes are large, so the pore water
menisci at the sample surface have large radii. The residual pore water
pressures attainable vary inversely with the radii of the pore water
menisci.



Table 3. Index Properties of Site I Cores



Core

No.


Subbottom
Depth


Water

Content

(%)


Sand
(%)


Silt
(%)


Clay
(%)


Color

(Munsell)


Original

Vane
Strength


Remolded

Vane
Strength


Liquid
Limit
(%)


Plastic
Limit

(%)


Inches


cm






psi


kPa


psi


kPa


ID


1.0


2.5


96.3






















IB


1.5


3.8


97.7










0.38


2.6


0.11


0.8


73.1


34.7


ID


3.5


8.9


103.5


2


13


85


10YR4/3
brown/dk br


0.32


2.2


0.13


0.9


78.4


34.9


IB


4.0


10.2


111.8






















IB


4.5


11.4


98.9






















ID


6.5


16.5


99.5






















IB


12.0


30.5


94.0






















IB


14.0


35.6


97.5










0.47


3.2


0.18


1.2


78.1


37.3


IB


20.0


50.8


99.0






















ID


21.0


53.3


94.5






















ID


22.5


57.2


97.8





7


93


10YR4/3


0.63


4.3


0.27


1.9


85.1


40.1


ID


25.0
36.0


63.5
91.4


94.0
100.0






















ID


47.0


119.4


96.3





7


93


10YR4/3


0.64


4.4


0.25


1.7


110.5


47.9



Table 4. Index Properties of Site III Cores



Core
No.


Subbottom
Depth


Water

Content

(%)


Grain
Density
(g/cc)


Sand
(%)


Silt
(%)


Clay
(%)


Color
(Munsell)


Carbonate

Content

(%)


Original

Vane Shear

Strength


Remolded

Vane Shear

Strength


Inches


cm






psi


kPa


psi


kPa


3B


3.3


8.4






63


37














3B


10.0


25.4


54.0




49


51














3B


16.8


42.7






46


54














3C


22.0


55.9


67.8


2.72








86










3C


23.0


58.4


63.1










80










3A


25.5


64.8


70.6


2.71


59


41






0.057


0.4


-0.0


-0.0


3C


30.5


77.5


63.8


2.68


62


38


10YR8/3
v pale br












3C


33.5


85.1


63.8


2.68


59


41














3C


36.5


92.7


55.6


2.69


53


47


10YR7/3
v pale br


83


0.26


1.8


0.01


0.1


3A


38.5


97.8


50.9


2.71


37


63














3C


66.5


168.9


48.2


2.68


54


46














3C


69.5


176.5


49.5




54


46














3C


71.0


180.3


54.7




















3C


72.0


182.8


52.3










80










3C


119.0


302.3


57.7










80










3C


120.0


304.8


53.7










82










3C


163.5


415.3


52.8




















3C


168.0


426.7


54.7










77










3C


202.5


514.4


50.5


2.67


35


29 36


10YR8/3












3C


205.5


522.0


49.4


2.67








86


0.35


2.4


0.009


0.1



Table 5. Index Properties of Site IV Cores



Core
No.


Subbottom
Depth


Water
Content

<%)


Grain
Density
(g/cc)


Sand
(%)


Silt
(%)


Clay
(%)


Color
(Munsell)


Carbonate
Content

(%)


Original

Vane Shear

Strength


Remolded

Vane Shear

Strength


Comments


Inches


cm






psi


kPa


psi


kPa


4A


2.0


5.1


79.0






















Clayey silt


4A


5.6


14.2


70.0






















Clayey silt


4D


13.5


34.3


34.7


2.71




















Coarse
sand


4D


16.5


41.9


32.1


2.71


91








54










Coarse
sand


4B


43.0


109.2


57.0


2.71


10


52


38














Silt


4B


47.0


119.4


58.8


2.72










78










Silt


4B


50.0


127.0


52.0




11


59


30


5Y7/2
It gray




1.43


9.96


0.37


2.6


Silt


4B


53.5


135.9


51.5










5Y7/2
5Y7/3




0.70


4.83


0.12


0.8


Fine sand


4B


89.5


227.3


44.8










pale
yellow




0.25


1.72


-0.0


-0.0


Fine sand


4D


98.0


248.9




2.88


16


50


34




56










Very fine
sandy silt


4B


cc














5Y7/3












Silty sand



(ctj + ct 3 )/2 (kPa)



Paths are labeled as to the
samples' subbottom depths




4 6

(oj + o 3 )/2 (psi)

Figure 3. Triaxial test stress path diagram for
Site I - core D0S1D.



(a x + a 3 )/2 (kPa)



80 100 120 140 160 180 200



Paths are labeled as to the
samples' subbottom depths




0_= 32 deg (0.56 rad)
psi (0 kPa)



10 15 20

(oj + a 3 )/2 (psi)



- 120

- 100

a.
80 5
60 '_,

40

20



Figure 4. Triaxial test stress path diagram for
Site III - core D0S3C.



(aj + ct 3 )/2 (kPa)
30 40 50



Paths are labeled as to the
samples' subbottom depths.



= 42 deg(0.73 rad)
7= Opsi (OkPa)




(ct 1 + ct 3 )/2 (psi)

Figure 5. Triaxial test stress path diagram
for silt from Site IV - cores
D0S4B and 4D.



(ffj + o 3 )/2 (kPa)
80 100 120 140



Paths are labeled as to the
samples' subbottom depth



40.5 deg (0.707 rad).
c = 0.5 psi (3.4 kPa)




60 3.



15 20

(oj + o 3 )/2 (psi)

Figure 6. Triaxial test stress path diagram for sands from
Site IV - cores D0S4B and 4D.



10



Since there were no residual pore pressures, the sample disturbance
correction procedures of Lee (1973a) could not be applied. Instead the
procedures of Lee (1973b), which are based on Ladd and Lambe (1963),
were used. These procedures involve the application of relatively large
consolidation stresses (i.e., well above the in-place overburden pres-
sures) in the triaxial cell. Basic stress path parameters (Skempton's
parameter, A, and c and <j)) are obtained. The strength of the sample
under the correct in-place overburden pressure is calculated (using an
equation given by Lee, 1973b). Most of the effects of sample disturbance
are corrected for in this manner. This procedure can also be used to
obtain estimated strength profiles for the sediment below the level of
sampling. To do this, it must be assumed that the type of sediment does
not change greatly below the level of sampling.


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