The sediment at Site III is a typical foraminif era- dominated calcar- 

 eous ooze. The strength of the sampled material (vane tests on cores, 

 Figure 8) is nearly zero. However, the measured in-place strengths are 

 quite high [2 to 4 psi (10 to 30 kPa) , Figure 1]. This is clearly a 

 ''problem material'' for geotechnical investigations. The method of 

 residual pore water pressures cannot be used to correct for disturbance 

 since the residual pressures are negligible. 



Strength profiles constructed using the results of triaxial tests 

 (Figure 8) are about 70% of the measured in-place values. This is a 

 relatively good correlation considering the overall difficulty involved 

 in working with this material. The differences may be a result of the 

 strain level at which strength is measured. In the triaxial tests the 

 strength was taken at the 20% strain level. In the field vane test the 

 actual strain is undefined but is certainly very high along the plane of 

 failure, well in excess of 20%. Since the ooze appears to mobilize its 

 strength at high strain levels, the difference in the type of test 

 performed could account for the difference between field vane and triaxial 

 test results. Also, partial drainage during field testing could cause 

 the difference. In any case, strength profiles constructed using triaxial 

 tests and the methods of Lee (1973b) appear to reproduce, at least 

 relatively closely, strengths measured in the field. These procedures 

 are recommended for dealing with very difficult materials like globigerina 

 oozes. 



The measured in-place sensitivities (5 to 10) of this ooze are very 

 high. A facility that applies repeated loads to the material could 

 easily cause it to liquefy. Dynamic testing of cores from this site, 

 currently underway at the University of California, Berkeley, will 

 provide additional information on this problem. 



Site IV (turbidites) 



The sediment at Site IV consists of alternating layers of silt and 

 sand, characteristic of turbidity current deposition. Since the deposit 

 is near land [about 10 miles (16 km) off the coast of Puerto Rico] and 

 the sands are coarse, the sediments are termed proximal turbidites. 



The in-place strength profile of Figure 2 illustrates how the 

 properties vary as one progresses through the layers of silt and sand. 

 The ''strength'' in the sand is not a true undrained shearing strength, 

 since partial drainage is certain to occur. However, it is an index of 

 how strong and dense the material is. The strengths of the silts are 

 probably valid as undrained shearing strengths. 



The comparative strength profile of Figure 9 once again demonstrates 

 how poorly the laboratory vane test duplicates field behavior when 

 dealing with coarser grained material (i.e., material that cannot retain 

 a residual pore pressure) . The strength profile developed through 

 triaxial testing of the silt samples reproduces the measured field 

 strengths very well. This procedure is recommended for compensating for 

 disturbance when dealing with the silt layers of proximal turbidites. 



13 



