transported, stored, trimmed, and tested. A number of researchers 

 (Noorany and Seed, 1965; Ladd and Lambe, 1963; Skempton and Sowa, 1963; 

 and Beard, 1972) have investigated the hypothetical process in which no 

 sample disturbance occurs other than that involved in the release of the 

 in-situ shear stresses. The term "perfect sampling" has been used by 

 these investigators in the past to describe this process. This term is 

 actually incorrect since some disturbance does occur during the process. 

 In this report the term, "in-situ shear stress removal," will be used 

 in place of "perfact sampling." The researchers above have determined 

 that strength reductions on the order of five percent may result from 

 in-situ shear stress removal when sampling clayey soils. Somewhat 

 greater reductions may result with silty soils. 



Mechanical Disturbance 



One of the most common forms of disturbance is that resulting from 

 routine handling, possible mishandling, and cutting of samples. These 

 activities result in a certain amount of soil particle reorientation 

 and interparticle bond breaking. The shear strength is usually de- 

 creased, and the compressibility increased. 



Probably the greatest amount of mechanical disturbance occurs when 

 the sample is taken from the ground. Suggestions as to how this dis- 

 turbance may be reduced through good sampler design are given by 

 Hvorslev (1949), Jakobson (1954), and Kallstenius (1958). Most of the 

 common seafloor sediment samplers fall considerably short of satisfying 

 the criteria of these researchers. 



Pore Water Expansion 



Water is a slightly compressible medium to the extent that for 

 every 10,000 feet of water depth increase the water is compressed by 

 about 1.5 percent. When a sample is taken, therefore, the pore water 

 expands by the same amount. Several writers (Monney, 1967; Richards 

 and Parker, 1967; and Crisp, 1968) have expressed concern that water 

 expansion may alter soil engineering properties , but an indication of 

 the possible extent has not been provided. 



Gas Expansion 



Some sediments contain large quantities of dissolved gas, usually 

 methane. When these sediments are sampled and brought to the surface, 

 most of the gas comes out of solution. This is a much more serious 

 problem than water expansion because gas is considerably more compres- 

 sible and forms bubbles when it comes out of solution. Therefore, the 

 disturbance is concentrated at localized points where the integrity of 

 the interparticle bonding can be totally destroyed. 



