Prediction of the geotechnical properties of late quaternary Mississippi delta deposits

Abstract

Mississippi delta sediments sampled from 141 boreholes drilled offshore of southeastern Louisiana were investigated in order to develop a method of predicting their geotechnical properties. Regression analysis and correlation analysis were used to establish the form and strength of predictive relationships. Many geotechnical properties appear to be related to depth of burial, but other factors such as grain size, degree of consolidation, age, rate of accumulation, and environment of deposition are also important. Samples from selected areas were grouped on the basis of grain size, as inferred from sediment descriptions, and on the basis of degree of consolidation, as inferred from shear strength profiles. A separate set of predictive equations was developed for the geotechnical properties of each group of samples. In nearly all cases, the correlation of each property with depth of burial and with selected other properties is much stronger for these smaller groups of samples than for all Mississippi delta samples as a group. The predictive relationships developed for groups of modern delta clays are similar but quite distinct from those developed for the older clays of the St. Bernard and Plaquemines deltas and for the clays deposited very slowly along the margins of developing deltas. This same pattern holds for the relationships developed to predict the geotechnical properties of the coarser-grained sediments. The Lambda method was used to determine the maximum load that sediments can withstand at selected sites within the study area. It was assumed that loads were transferred to the sediments by open-ended pipe piles driven to various depths. The results obtained using borehole profiles of geotechnical properties were compared with those obtained using predictive equations. For piles embedded to depths as great as 100 m, the error ranged from 4 to 15%.