pling has been accomplished in shallow waters by 
scuba divers and in deeper water by submersibles. 
Submersibles permit direct observation of the 
sampling process and can acquire samples with 
thin wall devices in the upper six feet of sediment. 
Laboratory experiments on seafloor sediments 
have been conducted using samples recovered by 
coring devices, submersibles, or other means. 
Meaningful engineering measurements can be made 
in the laboratory and related to in situ measure- 
ments. Selective sampling of large areas should 
yield reconnaissance information of wide applica- 
bility such as in preliminary site studies. 
b. Future Needs Prediction of foundation stabil- 
ity should be facilitated by determining such 
sediment properties as permeability and dynamics 
of water movement, depth-dependent strength 
gradients, compressibility characteristics, and elas- 
tic and plastic equilibrium to predict foundation 
stability. Mass sediment stability characteristics 
include bearing capacity, settlement, slope stabil- 
ity, penetrability, and breakout forces. 
These properties are important to such applica- 
tions as operation of mining machinery on the 
ocean floor, reflection and refraction of sound 
energy striking the ocean floor, geophysical explo- 
ration, and foundation site selection and prepara- 
tion. 
To determine slope stability and layer thick- 
nesses, sediment properties must be known to 
considerable depths. Properties cannot be deter- 
mined now below the uppermost few feet. Also, 
there is a need to determine the probability of 
occurrence, the properties, and possible effects of 
turbidity currents on installations. Instrumenta- 
tion systems able to remain submerged for long 
periods must be developed. 
Chemical additives or mechanical conditioning 
may be able to increase sediment strength or 
prevent stirring fine particles which reduce visibil- 
ity. However, in some places the need for artifi- 
cially improving visibility is eliminated since strong 
currents carry suspended sediments away. 
Comparative analytical studies of all common 
sediment types are needed to relieve the need for 
detailed in situ sampling. Instrumentation systems 
lowered to the ocean floor could transmit or 
record data on density, sound velocity, shear 
strength, and sediment bearing capacity to quickly 
characterize an area. 
V1-64 
Research and development needed to advance 
undersea soil mechanics capabilities include: 
—Samplers for use by divers, submersibles, and 
surface ships. 
—Instruments for on-site measurements like vane 
shear at several depths within a sediment body. 
—Equipment to take long borings in deep water, 
including techniques to re-enter bore holes. 
—Instrument packages for narrow beam echo 
sounding and high resolution profiling devices to 
be towed at cruising speeds. 
—Instruments to record properties of turbidity 
currents. 
Foundation engineering criteria must be estab- 
lished and transformed into pertinent seafloor data 
requirements. Because underwater foundations 
will be constructed on the basis of information 
acquired under adverse conditions, methods are 
needed to inspect them and surrounding soil and 
to effect repairs. : 
Interaction between underwater foundations 
and bottom soil can result in the creation of 
complex moments and forces. Techniques are 
needed whereby lateral, uplift, twisting, and over- 
turning forces and moments can be applied and 
measured singly and in combination. Sensors to 
detect changes in pressures, deflections, or dis- 
placements would be useful in surveying the ocean 
floor locally prior to and following construction. 
3. Physical and Chemical Properties of Seawater 
a. Current Situation The three properties that 
most affect underwater design are pressure, temp- 
erature, and salinity. They influence the basic 
physical properties of seawater—density, specific 
volume, electrical conductivity, compressibility, 
sound velocity, viscosity, and surface tension. 
Osmotic pressure, freezing point, and boiling point 
are determined by salinity only. 
(1.) Density On the average one cubic foot of 
seawater weighs 64 pounds; one cubic foot of ice 
weighs 56 pounds, and one cubic meter (35 cubic 
feet) of seawater weighs one long ton or 2,240 
pounds. However, these values vary with tempera- 
