One-dimensional normal compression laws for resedimented mudrocks

Four different empirical models used to describe the one-dimensional normal compression behavior of mudrocks have been evaluated by investigating the behavior of 15 different resedimented mudrocks. These mudrocks originate from a wide variety of geologic origins and were tested in the laboratory over an effective stress range of 0.1-100 MPa. The normal compression of silt-rich, low liquid limit mudrocks is best described by assuming a log-linear relationship between vertical effective stress, sigma(v)' and void ratio. For smectite-rich, higher liquid limit mudrocks their behavior is better described by assuming a log-linear relationship between sigma(v)', and porosity. The assumption of a log-log relationship between (1 + void ratio) and sigma(v)' is not the most appropriate for any particular mudrock type, but gives a reasonably good description of compression behavior for all mudrocks, and is therefore ideal for situations in which the general composition of a sediment is unknown. For all mudrocks, the assumption of an exponential relationship between porosity and sigma(v) gives a very poor fit to the experimental data. As mudrocks undergo compression to high effective stresses, high liquid limit mudrocks display a much greater compressibility and a corresponding larger loss in porosity compared to more silt-rich mudrocks. The porosities of all materials tend to converge into a much narrower range above about 10 MPa, where all mudrocks display a similar compression behavior and a constant value of compression index of 0.21 regardless of their composition. At low effective stresses though, their compression behavior is strongly controlled by composition.