Characterisation of Ballina clay

Abstract

This paper describes a comprehensive characterisation study carried out on clay from the National Soft Soil Testing Facility located at Ballina in northern New South Wales (NSW, Australia). Ballina clay represents the estuarine soft clays of high to extremely high plasticity from the Richmond river valley in NSW. They are structured and lightly overconsolidated with an average organic content around 3%. Index properties as well as mechanical parameters were estimated from laboratory tests performed on tube specimens retrieved using a fixed-piston sampler. Index characterisation tests were combined with constant rate of strain tests, incremental loading tests and stress-path triaxial testing to evaluate compressibility, stiffness, permeability and strength parameters. These deposits display very high compressibility and a low undrained shear strength which is larger in triaxial compression. Ballina clay shows a non-linear stress-strain response either in one-dimensional compression or undrained shearing. The consolidation coefficient, and consequently the water permeability, reduces dramatically with the stress level in the overconsolidated zone, mainly due to soil destructuration. A brittle response has been observed during shearing that reduces the undrained shear strength by around 50% after peak. Geotechnical profiles describing the variation of index and mechanical properties with depth are provided and compared against in situ test results. It is shown that the use of the fixed-piston sampler, in combination with non-destructive methods, to assess and select samples for laboratory testing provided good quality and reliable test results which are in agreement with data interpreted from in situ tests.

Analytical solution and numerical simulation of vacuum consolidation by vertical drains beneath circular embankments

“…Results of a series of more recent site investigations at the Ballina Site, as reported in Li et al (2014), Kelly et al, 2014Kelly et al, (2014, and Pineda et al (2014Pineda et al ( , 2016, are also taken into account in current study.…”

Getting high-quality samples in ‘sensitive’ soils for advanced laboratory tests

“…The main mineral components are kaolinite, illite, quartz, illite/ smectite, and amorphous minerals. Detailed [55] characterization of the natural Ballina clay is given by Pineda et al [58]. Figure 23a shows the profiles of natural water content, Atterberg limits, particle size distributions, and electrical conductivity estimated for specimens obtained from boreholes Inclo 2 and Mex 9, 50 m away from each other.…”

“…The cylindrical shape was convenient to avoid sharp edges. The block specimen was covered with several layers [58]. b, c CPTu profiles from the estuarine deposits at Ballina site [34] of plastic wrap and foil seal to avoid moisture losses.…”

“…Both have shown good correlation with sample quality descriptors e v and De/e 0 for a wide variety of soils. Figure 36 shows V s estimates for three natural soils: low-plasticity Boston Blue clay (USA) [38], low-plasticity silty deposits from Castelló d'Empuries [3] as well as high-plasticity Ballina clay [58]. Block (Sherbrooke) specimens as well as tube samples (fixed piston, Shelby tube, and SPT samplers) are included in this figure.…”

“…Attention was focused on evaluating differences in soil microstructure, in terms of the pore size [58] and silty deposits [3]. b Boston Blue Clay [38] distribution estimated from MIP tests, for specimens located at different levels along the centreline and the perimeter within the tube.…”