The construction of railway embankments on loose foundations using reinforcing elements results in improvement of the embankments' slope stability, which significantly reduces the amount of earthworks. In addition, reinforcement of foundation and embankment is essential to increase bearing capacity and minimise settlements. In this study, a preliminary numerical analysis was performed to design and set up a series of experimental tests for investigating the efficiency of micro piles in reinforcing the high railway embankments on loose foundation. To this end, two experimental models of embankment were explored: one without reinforcement and another reinforced with micro piles to stabilise the embankment slope. The minimised arrangement of micro piles to reinforce the experimental model was obtained according to the results of the preliminary numerical simulation using Plaxis-2D finite-element code. The experimental data included bearing capacity of the embankment, displacement of foundation and embankment and axial strain of the micro piles. Finally, the efficiency of micro piles in reinforcing high embankments on loose subgrades was assessed by comparing the experimental data of non-reinforced and reinforced embankments.

The stress–strain–time behaviour was investigated for sand that was treated by a new biologically inspired silicification process. This ground treatment method offers the potential to achieve similar performance as existing soil treatment methods using lower concentrations of environmentally benign component materials. This experimental study evaluated the influence of a polyelectrolyte pretreatment and test procedure on the fundamental strength of medium dense Ottawa 20/30 sand silicified with 20% sodium silicate. Samples were subjected to unconfined single-increment, unconfined incremental, and confined incremental creep tests. The results show that the creep behaviour of silicified samples is similar to the behaviour of traditionally treated sand. Fundamental strengths were approximately 50 kPa when unconfined, and ranged from 117 kPa to greater than 340 kPa when confined at 69 and 138 kPa, respectively. The data also show that incremental creep tests may be a more rapid means of determining parameters for creep modelling than the existing standardised single-increment test method. Parameters for modelling long-term deformation behaviour are consistent with published parameters for existing soil treatment methods even though compositional differences exist between the samples used in studies.

The methods for modelling the effect of a prefabricated vertical drain (PVD) in plane strain finite-element analysis have been reviewed. The methods are classified into four groups of using: (1) solid element; (2) macro-element; (3) one-dimensional (1D) drainage element; and (4) equivalent vertical hydraulic conductivity (k _ve) to model the effect of the PVD, respectively. With the k _ve method, a PVD improved subsoil can be analysed the same as for an unimproved one. For all the methods, the average degree of consolidation in a plane strain analysis is matched with that under an axisymmetric condition by modifying the hydraulic conductivity of subsoil, and/or the spacing or the discharge capacity of plane strain drains. Finally, the effectiveness of the k _ve method has been demonstrated by modelling a large-scale model test of PVD consolidation. The numerical results indicate that the k _ve method performs as well as that of explicitly modelling the PVD consolidation under axisymmetric condition.

The performance of a soil-nailed slope is significantly influenced by the slope geometry, nail parameters and facing material types. The objective of the present study was to examine the influence of nail inclination and facing material types on the stability and deformation behaviour of soil-nailed slopes subjected to seepage flow at 30 g . A series of centrifuge model tests were carried out on 5V:1H slopes with and without soil nails. Bored and grouted soil nails including nail heads were modelled using thin aluminium tubes coated with a thin layer of sand-smeared adhesive. Two different nail inclinations of 10 and 25° with the horizontal were adopted with two different material facing types. All the models were thoroughly instrumented with displacement transducers for measuring surface settlements of the slope and pore pressure transducers to capture the development of the phreatic surface within the slope during the centrifuge test. In addition, the centre column of soil nails were instrumented at their mid-length to measure nail forces at the onset of seepage flow during the centrifuge test. A digital image analysis technique was employed to arrive at displacement vectors placed on the front elevation of the slope and markers attached to the facing to monitor face movements. Stability analysis of soil-nailed slopes with nail inclinations ranging from 0° to 30° in increments of 5° with the horizontal was carried out to ascertain optimum nail inclination for a 5V:1H slope with facing. The results indicate that stabilising the earth slope subjected to seepage using soil nails has a significant effect on the stability and deformation behaviour of the slope and is strongly influenced by nail inclination and the facing material type. For an identical type of facing and nail layout, a 5V:1H slope stabilised with soil nails inclined at 10° was observed to perform better than a slope stabilised with soil nails inclined at 25°. The measured nail forces were found to be on the higher side for a slope stabilised with soil nails inclined at 10° than at 25°. The observed centrifuge model tests were found to corroborate well with results of the slope stability analysis.

The soil profile in many coastal areas often consists of very loose sandy soil extending to a depth of 3 to 4 m from ground level underlain by clayey soils of medium consistency. The very low shearing resistance of the foundation bed causes local as well as punching shear failure of soil. Structures built on these soils, may also suffer from excessive settlements. This paper discusses grouting as one of the possible solutions to the foundation problems by improving the properties of loose sandy soil at shallow depths.

The interaction behaviour between a floating column and the surrounding soil, with or without a surface cement stabilised slab, has been investigated by laboratory model tests as well as finite-element analysis (FEA) using an axisymmetric unit cell model. Based on the test and the FEA results, a method for calculating the consolidation settlement–time curve of floating-column-improved soft clayey subsoil has been developed. This method has been modified from the earlier method of Chai and Pongsivasathit by treating a part of the column improved layer with a thickness of H _c as an unimproved layer in settlement calculation to consider the effect of possible penetration of the column into the soft soil layer below the column. An explicit equation for calculating the value of H _c has been proposed as a function of area improvement ratio ( α ), depth improvement ratio ( β ), load intensity (p) and the undrained shear strength (s _u) of the soft clayey soil. The validity of the method has been checked using the laboratory model test results as well as four field case histories in Japan.

Ground improvement techniques can be adopted to prevent existing buildings built on liquefiable soils sustaining damage in future earthquakes. Impermeable geomembrane containment walls may be an economic and successful technique but their design and performance are currently not well defined or well understood for this application. This paper describes centrifuge testing carried out to investigate the performance of such containment walls as a liquefaction remediation method for a single degree of freedom frame structure. The results were compared with those from similar centrifuge testing carried out with the same structure founded on unimproved sand, to assess the effectiveness of the remediation method. It was found that the geomembrane containment walls tested were effective at reducing structural settlement and did not significantly increase the accelerations transmitted to the structure. Structural settlements were reduced primarily by mobilising hoop stress and preventing lateral soil movement. By preventing surface drainage, a decrease in the volume change of the foundation sand was also observed. In addition, the impermeability of the walls may be important as this prevented rapid migration of pore water from the free field to the foundation region.