Permanent deformation behavior of naturally occurring bituminous sands

Abstract

Oil sand, or tar sand, is a generic name given to bituminous sand deposits that are rich in bitumen or asphalt content to the extent that oil can be extracted from these deposits. The typical 8% to 15% presence of bitumen in the soil composition makes these naturally occurring sands low load-bearing materials. In this study, repeated load triaxial tests were conducted on three types of oil sand materials with natural bitumen contents of 8.5%, 13.3%, and 14.5% by weight. The oil sand specimens were compacted close to field densities and then tested for permanent deformation at two temperatures using a newly proposed test procedure. The procedure applied stress states and ratios determined from field-loading characteristics of haul trucks and mining equipment at two different load pulse durations or loading frequencies (related to field-trafficking speeds). Both the test data and axial permanent strain models developed in the form of power functions of the number of repeated load applications indicated a strong dependency of oil sand permanent strain development on the applied vertical to horizontal (or major to minor principal) stress ratio. Using the test data, permanent strain and deformation models were developed with high correlation coefficients to account for the applied stress states and ratios, test temperature, and bitumen content. These models generalized for oil sand deformation behavior may be used as practical predictive equations to estimate the amount of rutting in oil sand materials and to alleviate potential sinkage problems faced by off-road haul trucks, shovels, and other mining equipment in the field.