The purpose of hydraulic barriers, such as geosynthetic clay liners (GCLs), is to isolate waste liquids from the environment. Bentonite clay is widely used in GCLs because of its elevated sealing capacity in the presence of water and its ability to restrict the migration of solutes (chemico-osmotic efficiency or semi-permeable membrane behaviour). However, exposure to high concentrations of inorganic solutions can change the clay fabric increasing its hydraulic conductivity and degrading its membrane behaviour, with a consequent harm to the environment. The aim of this research was to study the hydraulic and chemico-osmotic performance of amended clays. For this purpose, an engineered clay (HYPER clay) was developed through treatment of a natural bentonite with an anionic polymer and the results were compared with two amended clay materials (multi-swellable bentonite (MSB) and a dense prehydrated GCL (DPH GCL)). To demonstrate the potential benefits of polymer treatment, material characterisation through X-ray diffraction analysis, density of solid particles, Atterberg limits, and swelling tests was performed on treated and untreated samples. Subsequently, hydraulic conductivity and chemico-osmotic tests were performed with CaCl₂ solutions on treated and untreated clays, to evaluate the modified clays resistance to chemical attack. The results of this research showed that the present amendment technology has a great potential for future GCL applications. X-ray diffraction analysis demonstrated the intercalation of the polymer in the interlayer region of the clay inducing a dispersed clay structure. The swell index and the liquid limit of the clay increased with increasing polymer dosage suggesting a potential benefit of the polymer on preserving the hydraulic performance of the clay. Unlike the untreated clay, HYPER clay treatment maintained low hydraulic conductivity of the clay to CaCl₂ even in the long term and protected the clay against the destructive role of diffusion, maintaining the initial osmotic efficiency in the long term. Test results were also compared with other amended clays MSB and DPH GCL. These two amended clay materials displayed a chemico-osmotic behaviour at the steady state similar to that observed on untreated clay. On the other hand, the preservation of the chemico-osmotic efficiency of the HYPER clay with time suggests that the carboxymethyl cellulose was not flushed out during the long period of permeation with deionised water.

Experiments on bentonite slurry infiltration into saturated sand have been carried out in a modified laboratory set-up that provides a hydraulic gradient comparable to real tunnels. Test series 1 investigated the characteristics of mud spurt and filter cake formation during water–bentonite slurry infiltration, before and after removing the external filter cake formed on the original boundary between the slurry and the sand. Test series 2 examined the conditions of filter cake formation during water–bentonite–sand slurry infiltration. The experimental results of series 1 indicate that, in the second infiltration, a new external filter cake will be formed for low concentrations of slurries (40 and 50 g/l), whereas hardly any new external filter cake formed for high concentration of slurry (60 g/l) owing to the formation of an internal filter cake in the sand during the first infiltration. The formation of this internal filter cake meant that the infiltration distance was much smaller for the second infiltration than that in the first for 60 g/l slurry. The experimental results of series 2 with a water–bentonite–sand slurry showed no external filter cake formation, but depth filtration was observed for high-density slurry (1300 and 1500 kg/m³). For low-density slurries (1050 and 1100 kg/m³), a thicker external filter cake, but with a higher permeability, than that in series 1 was observed on the sand surface, because the cake consisted to a large extent of sand particles. Mechanisms of mud spurt and filter cake formation are discussed, with a new solution for mud spurt and the theory of depth filtration.

Infiltration of pressurised bentonite slurry into saturated sand has been investigated in two laboratory set-ups. The first set-up is comparable to set-ups described in the literature for slurry infiltration tests. The second one results in a hydraulic gradient in the soil comparable to what can be expected in front of a tunnel-boring machine. The different characteristics of mud spurt and filter cake formation were clearly identified in the experimental results. The transition from mud spurt to filter cake formation depends on the infiltration velocity according to the literature. However, this was not found in these tests.

The purpose of this paper is to present long-term measurements in a full-scale study on a basal reinforced piled embankment that make it possible to validate calculations used for the design of the geosynthetic reinforcement (GR). These calculations are normally carried out in two steps. To validate steps 1 and 2 together, it is necessary to measure GR strains. To validate calculation steps 1 and 2 separately, arching A needs to be measured, which is the pressure on the pile cap above the GR. An extensive monitoring project was conducted over a period of four years, in a basal reinforced piled embankment on 17 m of soft clay and peat. This study presents the measured GR strains and load distribution including arching, accompanied by measured groundwater levels and deformations. The subsoil support of the geosynthetic reinforcement disappeared quickly, arching developed over the first three months, and an annual cycle in the load distribution became apparent. Arching effects increase during the summer when conditions are relatively dry, resulting in a larger load on the piles and a reduction in the load on the GR. Additionally, the measured changes after an extremely rainy week are presented.

This paper presents two modifications to the traditional formulation of the load-transfer method; a distinct unloading path is defined for the load-transfer functions, and the displacement variable is modified to consider the effects of passive soil displacements. The discrete formulation can account for different properties along the pile depth, as in the case of soil layering. Modeling distinct unloading functions enables loading cycles to be simulated as well as the analysis of residual loads. An instrumented pile load test is used to calibrate the method. Example computations are presented and discussed, highlighting the main features of the model.

The performance of earth pressure balanced tunnel boring machines (EPB-TBM) is dependent of a variety of parameters. Moreover, these parameters interact in a rather challenging way, making it difficult to adequately model their behaviour. Artificial neural networks have the aptitude to model complex problems and have been used in a variety of construction engineering problems. They can learn from existing data and then be used to predict the results, which makes them adequate for modelling problems where large amount of data is generated. In this work, a multilayer feedforward artificial neural network has been used to predict the torque at the cutter head of an EPB-TBM. A time series neural network has been used, where torque was predicted as a function of the measured torque and the volume of the injected foam on previous time steps. Results indicate that feedforward artificial neural network can be used to predict the torque at the cutter head in a EPB-TBM