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.

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This paper presents results of a series of experiments modelling uplift and lateral drag of a rigid pipe buried in dry sand. The main aim of these tests is to document the gradual transition from shallow to a deep sand failure mechanism as the pipe embedment depth increases, identify which parameters affect this transition, and determine experimentally the critical embedment depth, beyond which the normalized reaction acting on the pipe remains constant with increasing pipe embedment. Measurements of the reaction as a function of the relative sand–pipe movement and analysis of images captured during the tests with the particle image velocimetry method suggest that the critical embedment depth depends on sand density, but not on the direction of pipe movement. Outcomes of this study contribute to identifying the limits of applicability of simplified methods used to determine the peak reaction on pipes subjected to ground movements and the estimation of rational parameters for the analysis of deeply buried pipes with beam-on-nonlinear Winkler foundation models.

A soft soil field testing facility has been recently established near Ballina, New SouthWales, on the east coast of Australia, which is aimed at improving design and construction methods for transport infrastructure. Several sampling, laboratory and in situ testing campaigns have been performed to characterise the material properties of the soil. High-quality laboratory testing has been performed at one location through the soil profile and a range of geophysics, cone penetrometer, seismic dilatometer, shear vane and permeability tests have been carried out at other locations. The in situ tests have demonstrated that the stratigraphy and test data are reasonably uniform across the site. Seasonal groundwater variations cause the in situ stress state to vary with time. In situ test data have been compared with laboratory tests in order to estimate soil material properties at the locations of the in situ tests. The accuracy of published correlations was variable and site-specific correlations were found to provide a better outcome. The coefficient of consolidation and the water permeability obtained from small-scale laboratory tests shows good agreement with in situ estimations based on piezocone penetration test (CPTu) dissipation tests and BAT tests, respectively. The correlation between laboratory and in situ data is used to develop a robust geotechnical model for the Ballina site.

This paper presents an air pluviation system, developed to facilitate 1-g physical model tests in granular soils. The deposition process is fully automated and requires minimal input from the operator, thereby significantly reducing the time required to deposit large volume of granular material, improving the uniformity of the prepared specimens, and the reliability of test results. The components comprising the pluviation system have been calibrated to produce loose-to-very dense sand beds, of relative density that ranges between Dr=7% and Dr>100% of the maximum density achieved with the procedures described in the pertinent standards. The testing chamber where sand is deposited is instrumented with an array of pressure sensors, and the rig is equipped with a miniature Cone Penetration Testing (mini-CPT) device. Measurements from the earth pressure sensors and cone tip resistance profiles are used to evaluate how friction at the sand-chamber interfaces affects the distribution of geostatic stresses inside the chamber, the uniformity of sand beds, and boundary effects during deposition and during mini-CPT testing. The air pluviation system allows preparing layered sand profiles by adjusting the deposition parameters on the fly, and this feature is demonstrated via the analysis of mini-CPT tests performed in layered sand beds.

This paper presents results of scaled physical model tests performed to measure the reaction developing on a rigid pipe buried in dry sand, when the pipe is subjected to vertical downwards movement relative to its surrounding soil. The aim of this experimental study is to evaluate the efficacy of methods used to determine the properties of vertical bearing springs, an integral part of beam-on-nonlinear Winkler spring models used for the analysis of buried pipelines subjected to permanent ground displacements. We show that bearing capacity formulas used in practice to estimate the ultimate reaction developing on buried pipes may provide reasonably accurate estimates, provided that they are used together with sand friction angle values that account for the fact that granular materials do not obey an associative flow rule, and with bearing capacity factors compatible with the mode of sand failure observed in the tests. We also provide evidence suggesting that laying pipes in loose sand backfills does not have a beneficial effect on the reaction developing on the pipe, compared to medium dense sand, and we recommend against using loose sand material properties for the estimation of the properties of vertical bearing springs.