Experiments show that the compressive strength characteristic of cobalt crust and substrate is random and their frequency distribution exhibits positive skew characteristics. Utilizing the theory zof compressive strength of rocks, the P(III) curve is proposed to be used as a density function of frequency distribution for parameters of substrate and rock mechanics. Through sample experiment parameters, the theoretical distribution curve for compressive strength of the substrate is inferred. From this, the calculation result show that the probability of rock σ c ≥ 68.1MPa is less than 0.1%, and the probability of rock σ c ≥ 19.3MPa is less than 0.1%.
Rich cobalt-crust with a high exploitation value generally is 4∼6cm in depth, and attaches on rock surface of seamount in large areas. In general, substrate is alkalescency basalt or metamorphosis basalt. Cobalt-crust attaches on the surface of substrate directly, and the coverage rate of crust generally is between 20% and 60% (Manheim,1986; Yang,2002)of the total area of seamount. For the time being, researchers who are studying mining instruments are apt to choose mining carts as their first choice, which can walk directly in deep-sea regions and use the method of mechanical desquamation of crust (Halkyard,1985). Therefore, mechanics attribute parameters of substrate underneath cobalt-crust is one of the key features in mining instrument design. However, China still has its vacancy in the research of mechanics attribute parameters for substrate underneath cobalt-crust in the middle Pacific Ocean investigation area. Previously, only one sampling investigation of cobalt-crust was made, and that was in the voyage of DY95–8(.Ocean Institute of National Bureau of Ocean). Many studies show (Ronold and Bierager, 1992; Quest, Chow and Phoon, 1992; Brazkala and Pula, 1996; Harr, 1997; Jian, 2000; Pine,1992) that the distribution of macro mechanics attributes parameters of rocks is random.
