A NEW MODEL OF MARINE SEDIMENT COMPACTION

Void ratio (or, equivalently, porosity) is a major controlling parameter in models of seafloor density, sound speed, thermal conductivity, electrical resistivity and many other properties. We present a simple but practical empirical model of marine sediment compaction and physical characteristics based on expressing the void ratio of sediment as a fraction of the difference between the depositional void ratio, e_o and the minimum possible residual void ratio, e_r, without crushing or melting the grains. We assume the values of e_o and e_r are inherent characteristics of the sediment type.

Previous workers have related void ratio to the base 10 logarithm of vertical effective stress. The compression index, C_i, is the slope of the compaction curve in e-log₁₀(σ) space, and is either assumed to be constant or allowed to vary as a linear function of void ratio (e.g., Long et al., 2011). Our model defines C_i to be the square root of the proportional void ratio (C_i(e) = (e_p)^1/2 = [(e-e_x)/(e_o-e_x)] ^½). This formulation: 1) establishes a direct relation between void ratio and effective stress: e=(e₀-e_r)^-1[log₁₀(σ₀/σ)+2(e₀-e_r)]²/4 +e_r ; 2) applies over all possible void ratios and stresses; 3) can never result in negative void ratio, or any other non-physically realizable occurrence; 4) better fits data from compression tests on sediments, as we demonstrate with data from the Gulf of Mexico and Nankai Trough.