Discrete element modelling of a flexible membrane for triaxial testing of granular material at high pressures

The discrete element method (DEM) has been used to simulate triaxial tests on a bonded material at high pressures. A key feature of the model is the use of a flexible membrane that allows the correct volumetric deformation and the true failure mode to develop while applying constant confining pressure to the triaxial sample. The correct pattern of behaviour has been observed across a wide range of confining pressures, with both shear planes and barrelling failure being observed. The radial pressure applied by the membrane remains constant after large strains and deformation

Sample Preparation Technique for Fiber Reinforced Cemented Soils

Soil stabilization refers to the process of changing soil properties to improve strength and durability and the load carrying capacity of the soil. The analysis of reinforced soil for complete understanding of its mechanical behavior requires the preparation of the representative composite specimens. However, obtaining a homogenous and consistent composite specimen is a tedious task. In this paper, the sample preparation of artificially cemented and geosynthetic reinforced cemented soils with controlled initial relative density, void ratio and varying percent of fiber and cement content is described, and example results are presented for a range of soils. 100 mm height and 50 mm diameter samples were prepared for high pressure triaxial testing to determine the mechanical behaviour of artificially cemented and fiber reinforced cemented sands. Several difficulties in the preparation and testing of samples were identified and discussed

Dynamic characteristics and failure mechanism of vegetated revetment under cyclic loading

This research is focused on the dynamic behavior and failure mechanisms of an ecologically vegetated bituminous mixture applied in a riverbank revetment model. The dynamic bearing capacity of the vegetated riparian slope was evaluated. The dynamic soil pressure distribution and deformation were analyzed, followed by 3D elastic-plastic finite element modeling. Experimental results showed that the cumulative vertical settlement increased rapidly with the loading time. Vegetation added into bituminous mixtures was found to be effective in inhibiting the development of the vertical displacement of sand. The research described in this paper provides a theoretical basis and guidelines for the protection of riverbank slopes

Shakedown solutions for pavements with materials following associated and non-associated plastic flow rules

Existing lower-bound shakedown solutions for pavement problems are generally obtained by assuming that materials obey an associated flow rule, whereas plasticity of real materials is more inclined to a non-associated flow. In this paper, a numerical step-by-step approach is developed to estimate shakedown limits of pavements with Mohr–Coulomb materials. In particular, influences of a non-associated flow rule on the shakedown limits are examined by varying material dilation angle in the numerical calculations. It is found that the decrease of dilation angle will lead to accelerated reduction of pavement shakedown limits, and the reduction is most significant when the material friction angle is high. Furthermore, existing lower-bound shakedown solutions for pavements are extended, in an approximate manner, to account for the change of material dilation angle and the shakedown results obtained in this way agree well with those obtained through the numerical step-by-step approach. An example of pavement design using shakedown theory is also presented

Strain softening and instability of sand under plane-strain conditions

A comprehensive experimental study on the strain softening and instability behaviour of granular soil under plane-strain conditions is presented in this thesis. A new plane-strain apparatus was developed and used in this study. The study was carried out by conducting specialised plane-strain tests on a marine dredged sand. Based on several series of drained and undrained tests, the drained and undrained characteristics of the sand under plane-strain conditions were determined. It was shown that the critical state line under the plane-strain condition is different from that under the triaxial condition. The strain softening behaviour of sand was investigated using strain path testing method. Two types of strain softening, material softening and banding softening were identified.Doctor of Philosophy (CEE

Lime stabilisation of organic clay and the effects of humic acid content

The effectiveness of lime as a chemical additive for the stabilisation of organic clay is considered uncertain, especially in the long term. The presence of humic acid is believed to be the main detrimental constituent of organic matter that renders lime stabilisation inefficient. In this paper, the amount of humic acid that may render lime stabilisation inefficient was carefully investigated. Artificial organic clay, prepared by mixing commercial kaolin and various amounts of humic acid (0.5%, 1.5% and 3.0%) was treated with hydrated lime. The strength properties of lime-treated organic clays were examined by unconfined compressive strength (UCS) and drained and undrained triaxial compression tests. Curing periods of 7, 28 and 90 days were chosen as key points to monitor the evolution and the effect of the stabilisation process on lime-treated specimens. Overall, the development of physical and engineering properties of lime-treated organic clay was most affected when the humic acid content in clay exceeded 1.5%

Liquid limit of selected postglacial soils from west-central Poland

The aim of this paper is to establish a correlation between the liquid limit value obtained in the Casagrande apparatus (wL/cup) and in the cone penetrometer (wL/cone) for typical glacial sediments from west-central Poland and compare them with the correlation equations published in the literature. The following correlation was formulated: wL/cone = 0.91wL/cup+ 1.98. The analysis presented in this paper proves that deriving a generalized and universal relationship wL/cup/wL/cone for all cohesive soils, regardless of their origin, is very challenging and may not be reliable for use in the engineering practice. It is verified that, in the range of low values of liquid limit, the cone penetrometer gives higher values of wL than those obtained from the Casagrande apparatus. However, for the Polish postglacial soils analysed in this paper, the cone penetrometer underestimates the results in relation to the Casagrande apparatus above wL = 22%. For the purpose of this study, wL = 22% was defined as “the point of equivalent results” (wL/cone = wL/cup)

The influence of chloride salts on compressibility behaviour of lime-treated organic clay

Previous studies have shown that the compressibility behaviour of lime-treated organic clay with varying humic acid contents were not effective as time prolonged. Therefore, chloride salts in the amounts of 0.5%, 2.0% and 5.0% were introduced in conjunction with lime-treated organic containing 1.5% humic acid content to assess the influence of salts on the improvement of compressibility behaviour of lime-treated organic clay. The compressibility behaviour of lime-treated organic clay with varying amounts of chloride salts was studied at different curing periods. The influence of the chloride salts on the lime-clay reactions was analysed in terms of changes in void ratio (e), volumetric strain (e1), compression index (Cc), and coefficient of consolidation (cv) which defines a soil's compressibility. The addition of chloride salts to the lime-treated organic clay shows less compressible behaviour in the long term as evidenced by the oedometer tests. The results confirm the effectiveness of salt in lime-treated organic clay. The influence of chloride salts on compressibility behaviour of lime-treated organic clay

Investigations on Properties of Recycled Aggregate Concrete Made from Different Construction Debris Sources

The urbanization movement in developing countries including China has resulted in tremendous construction wastes from building and infrastructure demolition. Construction debris in the form of old concrete, bricks, tiles, and other wastes are currently being handled in multiple ways, such as being sent to landfill, backfilled as road base, or recycled as new aggregate for concrete production. One uncertainty with recycling and reusing the construction debris in the new concrete mixing is the effects of unknown waste sources on concrete properties. This research started from collecting construction debris from several locations (e.g., suburban infrastructure site, urban demolished reinforced concrete buildings, and the newly damaged laboratory concrete specimens). These different debris types were crushed into particles and went through the sieve analysis for the collection of appropriate sizes of coarse aggregate. The properties of recycled aggregates in terms of density, water absorption, and Los Angeles abrasion were tested. The recycled coarse aggregate was used to replace 30% of the natural aggregate by weight as concrete materials. Through the experimental studies following ASTM standards, concrete properties in terms of slump, ultrasonic pulse velocity, and compressive strength were tested and compared among the batches using recycled aggregates from different waste sources. Similar slump and ultrasonic pulse velocity values were found among these batches. The compressive strength of recycled aggregate concrete turned lower in the early age, while the 28-day strength values were more comparable. The research provided insights of how recycled aggregates from various construction waste sources would affect concrete properties based on raw aggregate properties