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Ballast plays a vital role in transmitting and distributing the train wheel loads to the underlying track substructure. The load-bearing capacity, safe train speed, and the levels of noise and vibration, as well as passenger comfort depend on the behaviour of ballast through particle interlocking and the corresponding deformation of this granular assembly. Attrition and breakage of ballast occur progressively under heavy and continual cyclic loading, causing track deterioration and rail misalignment affecting safety, while exacerbating the intensity of track maintenance. In the absence of realistic computational models, the track substructure is traditionally designed using mostly empirical approaches. In this book, the authors present the detailed information on the strength, deformation, and degradation aspects of fresh and recycled ballast under monotonic, cyclic, and impact loading using innovative geotechnical testing devices. A constitutive model for ballast incorporating particle breakage is presented representing a more realistic stress-strain response. The mathematical formulations and numerical models are validated using controlled experimental simulations and fully instrumented field trials. Revised ballast gradation is described to provide greater track resiliency and extended longevity. The book also provides a detailed description of geosynthetics for substructure improvement considering track deterioration caused by particle degradation, fouling, and impeded drainage. New to this second edition are extensive discussions on subgrade soil stabilisation, causes and mechanisms of soil fluidisation (mud pumping) under cyclic loading, and preventive and remedial measures to alleviate undue instability of ballast tracks. This book should prove most beneficial for final-year civil engineering students and for postgraduate teaching and learning. It is an ideal supplement for practising railway engineers and researchers engaged in the challenging tasks of futur

Attributed to environmental preservation in urban infrastructure development, the recycling of waste materials produced in the coal and steel industry as well as the reusing of waste tires is a high priority in Australia. In this article, the practical applications of (i) coal wash (CW) and steel furnace slag mixtures, (ii) CW and fly ash mixtures, and (iii) rubber elements derived from recycled tires are discussed. In this regard, some examples of real-life applications are elucidated in relation to coastal reclamation as well as road and rail construction (e.g., Port Kembla, Kangaroo Valley highway, and Chullora Rail Precinct). The article outlines various aspects of site investigation, construction techniques, and the installation of instrumentation to evaluate the field performance of these waste materials in contrast to traditional (natural) quarried materials. The results from these case studies demonstrate that properly engineered granular waste mixtures can exhibit promising characteristics even to exceed the current technical standards, implying reduced intensity of maintenance. The research outcomes strongly support sustainable solutions to be embraced in the future development of transportation infrastructure, capable of withstanding increased freight loading and enhanced longevity.

Rail track transitions are the discontinuities along the railway lines where conventional track adjoins the tunnels and bridges and are responsible for a sudden change in track structural properties. Frequent movement of fast passenger trains and heavy freights cause enhanced impact loads and differential settlements at these transitions that further lead to accelerated track degradation and increased maintenance costs. This paper presents a brief introduction to track transitions, the associated problems, and their causes and explains the occurrence of differential settlement at track transitions through analytical and numerical (2D FEM) modelling approaches. The stiffness effect on track settlement response under train loading is investigated, considering an Euler-Bernoulli beam on elastic foundation (BOEF). Vertical displacements of the track are calculated for various track stiffness values under train wheel loading (P = 10 tonnes). The results proved that the stiffer tracks undergo lesser settlements than the softer tracks. The effect of sudden stiffness variation is investigated by considering a one-step track transition where the stiffness suddenly changes from 80 MN/m (slab track) to 5 MN/m (ballast track). The results show that the settlement on ballasted track is almost 12 times greater than those on the slab track resulting in a large differential settlement at track transition.

The abundance of granular waste materials coupled with their successful reuse in construction fills has provided sustainable alternatives to a rather expensive quarried natural rock aggregate. This study focuses on the application of coal wash (CW) as an admixture to mitigate the undesirable shrink and swell characteristics of expansive black soils under unconfined compression loading. CW is a by-product of the coal industry that requires an enormous area of landfill for storage. These landfills pose a serious environmental problem because coal is still being produced in many parts of the world. A series of unconfined compression tests were conducted on CW-soil mixtures with and without wet and dry cycles; these wet and dry cycles mimic the shrink and swell characteristics of expansive soil observed in the field. Our findings show that cracking and shrinking impact the fabric of CW-soil over time, which reduces their shear strength. The incorporation of CW into black soil reduces its susceptibility to shrinkage and swelling during wet and dry cycles. The relationship between the shear strength reduction after repeated wetting and drying are proposed for consideration in the design. The study shows that the addition of CW can improve the geotechnical properties of expansive soils under unconfined compression and curtail the degradation of the areas used to store the CW.

This paper presents a novel approach to smoothen the abrupt stiffness variation along railway transitions and provides a step-by-step design of a multistep transition zone comprising adjoining segments with changing stiffness values. The influence of stiffness on track dynamic response applied to transition zones is investigated analytically, considering a beam on an elastic foundation. Vertical track displacements for varying stiffness values under different combinations of axle loads and speeds are calculated analytically and numerically, and they are found to be in good agreement. The results indicate that stiffer tracks undergo less settlement compared to those having a smaller stiffness. The effect of abrupt stiffness variation at transition sections is analyzed under four-carriage loading that causes considerable differential settlement, which is further exacerbated by increased train speeds. A mathematical process is introduced to determine the optimum stiffness of each segment to ensure a gradual change in stiffness while minimizing the corresponding differential settlement. The proposed methodology is further validated through the finite element modelling approach and worked-out examples epitomizing the effects of stiffness variation along the number of transition steps. From a practical perspective, this study provides a significant extension for design rejuvenation of transition zones by minimizing the differential settlement at any two consecutive transition segments.

Microscale contacts are inherent in most geotechnical failures such as soil liquefaction, landslides and internal instability, thus study of these failures based on microscale concepts can significantly enhance our intrinsic understanding as well as the quality of prediction and designs. Despite rapidly increasing investigation on micro-mechanisms of soil failures, especially based on Discrete Element Method (DEM), cohesive behaviours of particles are usually ignored and simplified, resulting in incomplete and/or inaccurate understanding. My study aims to overcome this imperative limitation and improve our modelling capability by investigating the influence of microscale cohesive contacts on fundamental soil behaviours such as the formation of angle of repose and direct shear. Different degrees of cohesion between particles are incorporated into DEM models and the results are validated against experimental data. The results show cohesive contacts can significantly affect soil behaviour and the predicted outcomes if they are not considered properly. The prediction capability of this DEM model can be further applied to study the cohesive behaviour of geomaterials in various geotechnical problems such as soil clogging and debris flow.

Railways are often subjected to periodic cyclic loading and intermittent rest periods. Excessive consolidation settlements can affect the performance of railway tracks built on the soft subgrade. The consolidation behaviour under railway loading conditions with rest periods has not been evaluated thoroughly. In this study, laboratory testing was conducted to investigate the influence of periodic cyclic loading and rest periods on the consolidation of Holocene soft clay from Ballina NSW. The specimens were subjected to a loading frequency of 1 Hz for 54 h with multiple rest periods. The recorded settlements and excess pore-water pressures (EPWP) during cyclic consolidation were employed to determine the corresponding hydraulic gradient, void ratio, resilient (dynamic) modulus and damping ratio. The settlement and accumulated EPWP can be observed during cyclic loading. In contrast, settlements do not occur within a rest period, despite the rapidly dissipating EPWP at the start of a given rest period. The maximum EPWP and settlements decrease as the number of resting period increases. An analytical model capturing the effect of cyclic loading and rest period is proposed where the unique relationships between the hydraulic gradient and the flow rate are established.

Transportation networks on the eastern coast of Australia are often built on or traverse coastal flood plains and marine clays with unfavourable soil conditions. In the past two decades, a significant number of laboratory investigations were carried out in soft soil improvement using Prefabricated Vertical Drains (PVDs) combined with vacuum-assisted surcharge preloading. In addition, significant research efforts were made to reduce the maintenance costs of railway tracks and increase their longevity by using synthetic inclusions such as geocomposites, geogrids and shock mats. These research outcomes were implemented and validated in practice through several field investigations along the eastern coast of Australia. This paper demonstrates the significance of instrumentation and data interpretation in geotechnical field investigations through 6 case histories. Field trials including Port of Brisbane Land Reclamation, Ballina Bypass Upgrade and Sandgate Rail Separation Projects were presented highlighting innovative ways of monitoring the performance of PVDs with vacuum and non-vacuum surcharge preloading. Also, railway track design improvements using geosynthetic and shock mats were discussed through Bulli and Singleton trial track case studies. Further, the heavy haul track testing facility at Russell Vale, New South Wales, was discussed as an alternative for expensive and time-consuming field trials.

This study presents the use of rubber grids (RGs) fabricated from end-of-life conveyor belts (i.e. discarded from the mining industry) to improve the performance of ballast tracks. The square apertures of these recycled rubber sheets were cast using a waterjet cutting process. A series of large-scale impact tests were performed on ballast specimens stabilised with three different grids of varied effective area ratios (KA.eff) to evaluate their effectiveness in mitigating the applied impact forces, in relation to both displacement and breakage of the ballast aggregates. Smart Ballast particles with motion-sensing capabilities were adopted to monitor the interaction between the grid and ballast assembly. The impact test results indicate that the inclusion of a RG decreases the deformation and breakage of ballast as well as reduces its vibrations. This study demonstrates that these recycled RGs with optimum effective area ratios can be more effective than conventional polymer geogrids, apart from the obvious environmental benefits.

The rapidly increasing demand for rail infrastructure to transport passengers and freight has inevitably led to a need for more robust and sustainable track foundations. However, heavy haul rail tracks often run across unfavourable soil conditions (e.g., saturated soft estuarine soils), resulting in frequent track failures accompanied with high maintenance cost. Recent site investigations along the South Coast rail line (NSW, Australia) showed considerable track degradation induced by subgrade mud pumping, requiring urgent attention and studies. This paper thus presents extensive laboratory and numerical investigations on the mechanism and possible solutions for mud pumping. While the effects of mud pumping on track performance are investigated through large-scale permeability and shear tests using the collected fouled ballast, the subgrade soil is subjected to cyclic triaxial and large-scale cyclic testing to understand the soil fluidization and fine particle migration. Transducers are installed at different layers to observe the depth-dependent response of soil foundation under various conditions. The results show that when specimens are subjected to unfavourable cyclic stresses, the fine particles migrate from the lower toward the upper soil layers along with the redistribution of pore water. When the water content of the upper soil layer reaches the liquid limit, the top of the specimen transforms into a slurry. Micro-analysis based on CFD-DEM coupling indicates a serious degradation in soil fabric and strength, thus the formation of mud under rising excess pore water pressure (EPWP). The study indicates that adding reasonable mass of cohesive fines can enhance the resistance of subgrade soils to fluidization, while geotextiles and geocomposites can also be used to mitigate mud pumping. Prefabricated vertical drains (PVDs) can continually reduce the buildup of EPWPs over the time due to the substantial reduction in drainage path, suggesting the efficiency of usi

Demand for the development of transportation infrastructure built on soft clays soils has increased in the past decades because of the rapid surge in population density along the coastal belts of many countries. Acceptable ground conditions are also becoming limited. Due to these reasons, ground improvement is pertinent and required as an essential part of infrastructure development. The application of prefabricated vertical drains with vacuum and surcharge preloading can be one of the economical techniques for transportation infrastructure projects. Consoldiation of soft soil by applying a surcharge alone can become lengthy. The application of prefabricated vertical drains (PVDs) with vacuum can reduce the waiting period significantly by decreasing the drainage path length in the radial direction. In this paper, factors affected the performance of the system including (a) drain spacing and partially penetrating drains, (b) smear zone, (c) vacuum systems, (d) application of numerical analysis for multi-drain system, (e) the optimum time for switching off vaccum pump, are discussed with their advantages and limitations.

Cohesion and rolling friction play key roles in governing the behavior of soil; however, only a limited number of studies have been able to assess the simultaneous contributions of these two microparameters on the macroproperties of soil. In this respect, the innovation of the current study includes an attempt to examine the interplay of these two primary parameters on the angle of repose (AoR) based on the discrete-element method (DEM). Lifting cylinder tests on cohesive wet sand have been carried out in DEM, while the cohesion and rolling friction are captured through proposed computational models. In this paper, macroparameters, such as the geometry and developmental stages of sand piles obtained in DEM simulation, are compared with experimental data, while their microevolution is quantified in detail. The results show that a large AoR can only be obtained when the cohesive and rotational frictional forces work in tandem. Increasing the cohesion and rolling friction results in smaller contact numbers, with increasing chain-like connections between particles and larger pore spaces to account for a larger AoR. For the first time, this study distinctly identifies three major stages that contribute to the AoR, based on the development of contact numbers and the transformation of energy. Accordingly, the linkage between macroscale AoR and the microstructural coordination number is formulated with varying levels of cohesion and rolling friction. The DEM results prove that the more cohesive the particles are, the greater the delay in the dissipation of kinetic energy.

Coupling discrete element method (DEM) with computational fluid dynamics including Navier-Stokes theories (CFD-DEM) and Lattice Botlzmann method (LBM-DEM) has been used widely to model the response of soil foundation under increasing seepage flows; however, a comparison of these methods in predicting soil and fluid behaviours during fluidization has not been carried out in a rigorous way. The current paper will hence provide an evaluation on their performance by applying them to model a laboratory test where a sandy soil is subjected to fluidization process under increasing hydraulic gradient. A brief discussion about the differences in their theories and numerical algorithm is made before the DEM is used to simulate a representative soil element while NS-based CFD and LBM are used separately to model upward fluid flows. The mutual interactions between fluid and solid phases are carried out and update to each other through third-party platforms. The results show relatively similar hydraulic conductivity predicted by the two methods, which agrees well with the experimental data; however, the critical hydraulic gradient estimated by LBM-DEM coupling is found closer to the experimental value. The CFD-DEM coupling provides more stable computation through its averaged fluid variables, whereas LBM-DEM coupling can provide more detailed interactions between fluid and soil particles at micro-scale due to its high resolution. The study then suggests several conditions which can optimize the efficiency of using these methods in practical applications.

Stone columns have been increasingly adopted as an environmentally friendly and cost-effective method for stabilizing and reinforcing soft ground embankments. This paper presents a coupled modelling using the discrete element method and continuum modeling approach to study the load-deformation responses of stone columns. In the coupled discrete-continuum model, a soft soil domain under an embankment is simulated by the continuum method (i.e., finite difference method-FDM), while a stone column is simulated by the discrete element method (DEM). A series of interface elements are introduced to facilitate the force-displacement transmission of both domains. The DEM transfers moment and contact forces to the FDM, and then the FDM moves displacements back to the DEM. The model is calibrated and further validated by experimental data. Contact force distributions and shear stress contours developed in the stone column and surrounding clay are captured to provide a better understanding of the load-deformation responses of the stone column from a micromechanical perspective.

Recent laboratory investigations indicate that low-to-medium plasticity subgrade is vulnerable to subgrade fluidisation due to excessive local hydraulic gradients that develop under cyclic loading. This study primarily investigates the role of geosynthetics to dissipate accumulated excess pore water pressure (EPWP), and minimise particle migration and subgrade fluidisation in typical railway track environments using the dynamic filtration apparatus (DFA). The experiments indicate there is an upward migration of moisture and fine particles towards the ballast-subgrade interface which cause the soil specimen to soften (slurry) under undrained cyclic tests. The combined prefabricated vertical drains (PVDs) and geocomposite system can dissipate the rapid accumulation of EPWPs due to the reduction in drainage path lengths and additional confinement at the ballast and subgrade interface. The excess pore pressure gradients (EPPG) that developed at different depths of the soil specimens were measured to assess the potential for the upward migration of fine particles.

This paper presents novel solutions for increasing the stability and resiliency of track structures by developing a synthetic energy-absorbing layer (SEAL) using recycled rubber products based on large-scale laboratory tests (i.e., drop-hammer impact tests and cubic triaxial tests). This includes (1) installing recycled rubber mats under ballast, and (2) using SEAL composed of a mixture of rubber crumbs, steel furnace slag, and coal wash with changing amounts of rubber: 0%, 10%, 20%, 30%, and 40% (by weight) to replace traditional rockfill as subballast. The test results confirm that the inclusion of a recycled rubber mat underneath the ballast layer actively reduces ballast deformation and the propagation of impact loading within the depth of the substructure. Also, the SEAL mixture with 10% rubber reduces the track lateral dilation, reduces ballast breakage and load distribution, and also maintains an acceptable settlement.

This paper presents a study on the interface behavior of geogrids and sub-ballast (capping) using a series of large-scale direct shear tests and discrete element modelling (DEM). Direct shear tests were carried out on sub-ballast with and without geogrid inclusions. The laboratory test data show that the interface shear strength is governed by normal stress and types of geogrid. The three-dimensional DEM was used to study the interface shear behavior of the sub-ballast subjected to direct shearing loads. Irregular-shaped particles of capping aggregates were modelled by clumping of many balls together in appropriate sizes and positions. Different types of geogrids were modelled by bonding small spheres together to form the desired grid geometry and apertures. The DEM model was then used to investigate the evolutions of contact force distributions and fabric anisotropy during the shear tests and the role of geogrid in micro-mechanical perspective.

Large cyclic and impact loads exerted by heavy haul trains can cause significant deformation and degradation of ballast, leading to poor track geometry and track instability. The application of recycled rubber elements in track substructure to increase confinement of both sub-ballast and shoulder ballast is an innovative solution. In Australia, there is a lack of adequate recycling that leads to large stockpiles of waste tyres. In addition, the reusability of giant off-the-road tyres discarded from mining industry is seriously limited due to their size and weight (over 3.0 m in diameter weighing about 3 tonnes). This study presents a real-size prototype test using the Australia's first and only National Facility for Cyclic Testing of High-speed Rail to investigate the performance of a hybrid track where tyre-infilled granular waste materials were placed below the ballast layer to replace the traditional capping layer, and arc segments cut from the giant off-the-road tyres were used to confine shoulder ballast. The performance of this hybrid track is compared with an unreinforced track conducted earlier at the same loading conditions. Test results demonstrate that the use of this hybrid system with recycled rubber elements significantly decreases vertical and lateral displacements of ballast and effectively controls the distribution of vertical stress with depth, while reducing vibration and ballast breakage. The outcomes of this study provide a unique solution in a circular economy perspective to strengthen railways to cater for heavier and faster freight trains.

This paper investigates soil fluidisation at the microscale using the discrete element method (DEM) in combination with the lattice Boltzmann method (LBM). Numerical simulations were carried out at varying hydraulic gradients across the granular assembly of soil. The development of local hydraulic gradients, the contact distribution, and the associated fabric changes were investigated. Microscale findings suggest that a critical hydromechanical state inducing fluid-like instability of a granular assembly can be defined by a substantial increase in grain slip associated with a rapid reduction in interparticle contacts. Based on these results, a new micromechanical criterion is proposed to characterise the transformation of granular soil from a hydromechanically stable to an unstable state. The constraint ratio (ratio of the number of constraints to the number of degrees of freedom) is introduced to portray the relative slippage between particles and the loss of interparticle contacts within the granular fabric. Its magnitude of unity corresponds to the condition of zero effective stress, representing the critical hydromechanical state. In practical terms, the results of this study reflect the phenomenon of subgrade mud pumping that occurs in railways when heavy-haul trains pass through at certain axle loads and speeds.

Vegetated ground is strengthened by the suction generated during evapotranspiration as well as physically and mechanically by the reinforcement effect induced by tree roots. When suction suddenly decreases during flooding or intense rainfall, the shear strength of the soil-plant system relies mainly on the physical root reinforcement. In this paper, the pull-out behaviour of simulated roots embedded in a compacted soil is investigated to assess how the soil-plant system is mechanically strengthened. An analytical framework is developed to estimate the pull-out force and it is validated using a series of pull-out tests. The tests are carried out on simulated roots embedded in a box of compacted soil having different water contents and equivalent dry unit weights. The results show that the pull-out capacity of this root system is mainly influenced by the initial (as-compacted) suction, and the length and diameter of the roots. The model predictions agree reasonably well with the experimental observations.

Rapid globalisation and the rise in population have substantially increased the demand for rail infrastructure which have been critical in transporting passengers and freight across landmasses for over a century. The surge in demand often leads to the construction of railway lines along with unfavourable soil conditions which result in different forms of substructure challenges such as uneven track deformations, ballast degradation, and subgrade mud pumping. A widespread site investigation along the eastern coast of New South Wales, Australia, indicated the prevalence of mud holes or bog holes along the tracks. The field studies suggest that low-to-medium plasticity soils are highly susceptible to mud pump when subjected to heavy axle loads under impeding drainage conditions. Subsequent laboratory investigations conducted on the remoulded soil samples collected from the sites indicated the sharp rise in cyclic axial strains and excess pore pressures along with the internal redistribution of moisture content as the governing mechanism for mud pumping. Numerical simulations performed using discrete element method coupled with computational fluid dynamics show that at a high hydraulic gradient, there is a substantial loss of soil contact network which leads to the upward migration of soil particles. The role of plastic fines and the inclusion of geosynthetic layer between the ballast and subgrade are also discussed in this paper. It was observed that the addition of 10% of cohesive fines increased the resistance of subgrade soils to mud pumping. On the other hand, geosynthetic inclusions not only assist in dissipating high cyclic excess pore pressures but also inhibit the upward migration of fine particles.

Understanding and quantifying the long-term deformation behaviour of granular materials under repeated loads is imperative for ensuring the longevity of railway tracks. One of the most relevant characteristics of granular materials under repeated cycles of loading and unloading is their ability to achieve a relatively stable state (shakedown) after being subjected to initial compression. The shakedown response of blended rubber-granular waste mixtures under triaxial test conditions has been studied by past studies highlighting the influence of the rubber content, confining stress, and cyclic loading amplitude. However, a clear methodology for estimating shakedown yield limits of these granular mixtures has not been discussed in detail. The current study highlights the influence of peak shear strength of these mixtures under static loading on their shakedown response in cyclic loading conditions. It is observed that the variation of static shear strength with rubber contents and confining stresses is found to affect the shakedown response. A unified method of estimating the shakedown limit is proposed by analysing permanent axial strains with normalised cyclic stress ratio at different loading cycles. The proposed method is validated through two independent sets of drained cyclic triaxial test data on coal wash-rubber crumb mixtures and rail ballast.

The reuse of waste materials in engineering projects is a sustainable concept that is being increasingly adopted in civil projects including the transportation infrastructure sector. A mixture of coal wash (CW), a waste produced by the coal mining industry, and rubber crumbs (RC), produced by shredding waste rubber tyres, is a possible alternative to natural quarried rock aggregates that are traditionally used in sublayers of transportation corridors. These materials have different properties than traditional aggregates and their geotechnical behaviour must be investigated before they can be confidently used in transportation infrastructure projects. This study particularly addresses the compaction characteristics of four CWRC mixtures (i.e. 0, 5, 10 and 15% rubber content) with a focus on the energy absorbing nature of rubber. The compaction energy must be increased to compensate for the energy absorbed by rubber and produce a compact packing of particles whilst keeping the breakage levels to a minimum. The strength and deformation properties of the mixture are also addressed through static triaxial tests under three confining pressures to simulate field conditions (i.e. 25, 50 and 75 kPa). The preliminary results showed that the mixture has sufficient strength for transportation sublayers that are not the main load bearing layers such as the subbase layer in roads and the capping/subballast layer in railways. Despite the compressibility of rubber which induces higher settlements, for the loads applied in practice at the level of a subbase or a capping layer, the expected settlements are within the allowable limits.

Instability of subgrade soil sometimes associated with soil fluidisation can lead to uncontrollable deformation and failure at a critical number of loading cycles for a given cyclic deviator stress and frequency. Although numerous laboratory experiments on the performance of Prefabricated Vertical Drains (PVDs) and geocomposites have already been carried out in the past, how effectively this combination can mitigate the potential for subgrade fluidisation under repeated (cyclic) loading is still not properly understood. The primary objective of this paper is to evaluate the integrated role of PVDs and geocomposite in preventing subgrade fluidisation using Dynamic Filtration Apparatus (DFA). Laboratory experiments show that the continuous dissipation of EPWP and the substantial reduction in drainage path lengths by PVDs can prevent subgrade fluidisation at shallow depths, while geocomposite can provide adequate surficial drainage and effective confinement at the ballast/subgrade interface. By measuring the Excess Pore Pressure Gradients (EPPGs) during cyclic loading, the test results convincingly reveal the promising performance of PVD-geocomposite combination under different loading conditions.

This study presents a microscale approach for evaluating the internal instability of natural granular soils using the discrete element method. The coordination number and the stress reduction factor are combined to assess the internal instability of soil. Distinct boundaries are identified between various soils that are internally stable and unstable. The microscale investigations are then compared with constriction and particle size-based criteria. The findings reveal that the constriction-based criterion predicts internal instability with significantly better accuracy. The relationship between microscale parameters and the constriction-based retention ratio is also examined for practical purposes.

Because of their distinct features such as biodegradability and favourable engineering properties, naturally occurring materials including jute and coconut fibres have been used increasingly in numerous geoengineering applications in recent years. However, these materials can sometimes decompose rapidly when subjected to adverse environmental conditions, resulting in severe degradation of their engineering characteristics and consequently causing damage to the design target. This paper presents a numerical approach where the finite-element method (FEM) is used to estimate the influence that the degradation of natural fibre drains can have on soil consolidation. A subroutine which can describe the reduction in drain discharge capacity over time is incorporated into the FEM model. Different cases including those varying the rate and time-dependent form of biodegradation are examined in this paper. The results of this investigation indicate that the dissipation of excess pore pressure can be hampered significantly if drains decay too early and speedily, particularly when the discharge capacity falls below 0·03 m3/d. Different rates of decay can impose different consolidation responses in the surrounding soft soil. Application of the proposed FEM to compare with laboratory data indicates an acceptable agreement between the predictions and the measurements.