The geotechnical behaviour of hydraulically placed fills

In industry, particulate waste materials may be disposed of by mixing with water and then pumping to a void where the particles will sediment out and the excess water will be decanted. This waste disposal method can result in very large volumes of material which are described as being 'hydraulically placed fills'. The waste material often consists of very fine particles, which can have a wide variety of composition, shape and size. The final sediments may have a very high moisture content and be difficult materials for sampling and testing and for construction purposes. The hydraulically placed fills covered in this study, pulverized fuel ash (PFA) and I ' fluorspar tailings, consist mainly of particulate material in the fine' sand to silt range. The study focuses on the compressibility and shear strength characteristics of these materials and was based on laboratory testing of reconstituted specimens. A water pluviation technique was used for specimen preparation which simulates in-situ conditions. This resulted in very loose samples (e-I.60) for one dimensional (I-D) consolidation and triaxial tests. The original materiafs and mixes of varying fines content were tested. The compressibility ofPFA alJd fluorspar mine'tailings was found to be similar to that of sands, with a unique first loading stage depen~ant on initial conditions, an elastic rebound on unloading and a normal compression line (NCL) at high stresses. Secondary compression was found to be linear with respect to the logarithm of time and significant for these types of deposits. The use of a fractal crushing compressibility equation was found to be suitable for estimating the coefficient ofcompressibility ofthe materials. Undrained and drained triaxial shear tests were performed on both materials. In the undrained tests, the specimens showed variable degrees of instability, defined as loss of shear strength after a peak value is reached. An initial state parameter (vo), based on the I-D NCL, is proposed as a practical and simple method for classifying the undrained behaviour of the materials. The critical state line, peak stress ratio and the stress ratio defining phase transformation (also known as quasi-steady state) were found to be parallel to NCL in e:log p' space The amount of fines affected these gradients with shallower slopes corresponding to smaller fines contents. No instability was observed on the drained tests. The use of Bolton's relative dilatancy index ~djusted for values of Q consistent with the crushing strength of the particles, gave a good correlation with the observed drained behaviour.EThOS - Electronic Theses Online ServiceGBUnited Kingdo