SUMMARY 



1. The critical sample disturbance mechanisms were determined, and an 

 experimental test program was developed to investigate the importance 

 of several of the mechanisms. As a result of this program, a general 

 framework for analyzing the extent of disturbance in seafloor soil 

 samples was developed. This framework is based on the work of Ladd and 

 Lambe (1963) and is summarized by the curve in Figure 5. This curve is 

 a plot of the ratio of field to laboratory vane strength versus the 

 ratio of laboratory residual pore water pressure to a reference residual 

 pore pressure. By measuring the laboratory vane strength and pore water 

 pressure and estimating the reference pore pressure, it is possible to 

 obtain a good estimate of the in-situ shear strength. The reference 

 pore pressure may be estimated from Equation 1 if the parameter K Q is 

 known. This parameter may be obtained from Figure 4 and an estimate of 

 the overconsolidation ratio. This estimate may often be made intuitively, 

 although usually a consolidation test is required. 



The remaining items related to the influence of the specific dis- 

 turbance mechanisms. 



2. Mechanical disturbance. Sampling and handling cause changes in 

 engineering properties. Two samplers investigated (NCEL fixed-piston 

 and Lehigh gravity) recovered high quality samples of moderately plastic 

 soils (plasticity index greater than 20 percent) and more disturbed 

 samples of less plastic soils. A standard handling procedure, involving 

 storage under refrigeration and 100 percent humidity and testing soon 

 after sampling, appeared to yield a minimum amount of disturbance. 

 Samples vibrated at high and low frequency were more disturbed (addi- 

 tional 25 percent strength reduction), but the disturbance can be com- 

 pensated for by using the residual pore pressure framework of Figure 5. 



3. Porewater expansion was investigated analytically. It was deter- 

 mined that strength reductions on the order of 40 percent might occur 

 when sampling soils from the deeper portions of the oceans. However, 

 the extent of this disturbance is compensatible using the residual pore 

 pressure framework. A few problem soils which have rigid interparticle 

 bonding require additional investigation. 



4. Significant gas expansion was determined to cause an intolerable 

 amount of disturbance that could not be evaluated using residual pore 

 pressures. Based on the experience of the author, however, most sea- 

 floor soils do not contain enough gas to cause extreme disturbance. 



5. Temperature effects were not investigated directly. However, 

 existing research (Mitchell, 1969) indicates that non-time-dependent 

 properties are not strongly affected if testing is performed at the 

 highest temperature the sample has ever experienced. This procedure 

 was followed in the tests summarized in this report. 



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