Effect of Flexible Membrane in Triaxial Test on the Mechanical Behaviour of Rockfill Material using Discrete Element Method

The investigation of rockfill materials poses challenges due to their large particle size, associated high cost, and long laboratory testing duration. As a result, empirical correlations based on historical experimental studies are commonly used to design and analyse rockfill structures. However, the extensive use of rockfill in a wide range of applications and limited understanding of its mechanical behaviour emphasize the need for further research. These make it necessary to develop a robust technique capable of capturing key parameters such as particle shape and breakage, allowing for the simulation and study of large-scale assemblies with realistic boundary conditions. Given that the behaviour of rockfill is highly scale-dependent, primarily due to particle breakage, the simplified laboratory tests on the scaled-down assemblies can be misleading. Particle breakage is a fundamental phenomenon in the mechanical behaviour of rockfill and significantly affects shear strength, deformability, and porosity under different stress levels. The particle breakage is influenced by factors such as the rockfill’s maximum particle size, mineralogy, particle shape, gradation, and confining stresses. This study adopts a computationally efficient breakage method called the Modified Particle Replacement Method (MPRM) based on the Discrete Element Method. A Tile-Based Flexible Membrane (TBFM) for triaxial test modelling has been developed by employing segmental rectangular walls to create a deformable membrane. The effects of critical parameters, including particle shape, confining stress, membrane resolution, degree of flexibility, and the characteristic strength of the particles, are examined. The findings of the combined MPRM-TBFM approach demonstrate the significant influence of membrane flexibility on volumetric-related behaviour

Effect of Flexible Membrane in Triaxial Test on the Mechanical Behaviour of Rockfill Material using Discrete Element Method

The investigation of rockfill materials poses challenges due to their large particle size, associated high cost, and long laboratory testing duration. As a result, empirical correlations based on historical experimental studies are commonly used to design and analyse rockfill structures. However, the extensive use of rockfill in a wide range of applications and limited understanding of its mechanical behaviour emphasize the need for further research. These make it necessary to develop a robust technique capable of capturing key parameters such as particle shape and breakage, allowing for the simulation and study of large-scale assemblies with realistic boundary conditions. Given that the behaviour of rockfill is highly scale-dependent, primarily due to particle breakage, the simplified laboratory tests on the scaled-down assemblies can be misleading. Particle breakage is a fundamental phenomenon in the mechanical behaviour of rockfill and significantly affects shear strength, deformability, and porosity under different stress levels. The particle breakage is influenced by factors such as the rockfill’s maximum particle size, mineralogy, particle shape, gradation, and confining stresses. This study adopts a computationally efficient breakage method called the Modified Particle Replacement Method (MPRM) based on the Discrete Element Method. A Tile-Based Flexible Membrane (TBFM) for triaxial test modelling has been developed by employing segmental rectangular walls to create a deformable membrane. The effects of critical parameters, including particle shape, confining stress, membrane resolution, degree of flexibility, and the characteristic strength of the particles, are examined. The findings of the combined MPRM-TBFM approach demonstrate the significant influence of membrane flexibility on volumetric-related behaviour

Swell-shrink Cycles of Lime Stabilized Expansive Subgrade

AbstractSubgrades of expansive nature are one of the main causes of damage to road network in Australia. Consequently, lime stabilization has been widely used to reduce the swell- shrink potential of these types of soils and thus reduce the associated damage. After stabilization and compaction, the subgrade will naturally be exposed to cycles of full swell and or partial shrinkage due to climatic cycles. This paper investigates this behaviour for lime stabilized compacted expansive soil from weathered Quaternary Volcanic geological deposits located in Western Victoria; Australia. These soils were stabilized with varying percentages of hydrated lime (2, 3, 4, 6 and 8 percent) and the swell-shrink paths of both untreated and treated soils were studied. Test specimens were compacted at optimum moisture content and maximum dry density. The samples were subjected to full swell-shrink cycles under a surcharge of 25kPa to reach structural stabilization and to simulate the impact of climatic wetting and drying cycles. Vertical deformation and swell-shrink cycle relationships for untreated and treated samples were obtained and analyzed. The results of lime stabilization indicate that equilibrium is reached after three cycles for both untreated and treated samples. In addition, results suggest that maximum deformation occurs in the second swelling cycle. Vertical deformation of untreated sample was reduced to a third after adding 2 percent lime and reduced to a sixth after adding 3 percent lime. The gradient of swelling and shrinkage path reduced to about a sixth and third when it is treated with 2 and 3 percent, respectively. The treated samples reached maximum swelling at a higher degree of saturation than the untreated sample

Recycled-glass blends in pavement base/subbase applications: laboratory and field evaluation

This paper presents the findings of a field and laboratory evaluation on the use of recycled glass blends as unbound pavement base/subbase materials. The parent recycled aggregates studied in this research were Fine Recycled Glass (FRG), Recycled Concrete Aggregate (RCA) and Waste Rock (WR). The geotechnical performance of the recycled aggregate blends of particular interest in this research were FRG blended with RCA (FRG/RCA) and FRG blended with WR (FRG/WR) in pavement base applications. The geotechnical performance of a trial road pavement was assessed by means of initial laboratory tests and subsequently field tests. The initial laboratory experimental programme included specialized geotechnical tests including Repeated Load Triaxial and triaxial tests to characterize the recycled materials. The subsequent trial road pavement constructed comprised of 7 different sections of FRG blends in the pavement base varying from 10 to 30% recycled glass content as well as 2 control sections with RCA and WR. Field tests were undertaken with nuclear density gauges and Clegg Impact Hammers to assess the performance of the various trial pavement sections. The recycled glass blend with 20% glass content was found to be the optimum level, where the blended material was workable, and also had sufficiently high strength. The field testing results indicated that FRG blends are suitable in pavement subbase applications and is a viable additive when used in limited proportions with other recycled aggregates in pavement subbases. FRG blends may however not fully meet specified requirements as a pavement base material

Impact of Compaction Methods on Resilient Response of Unsaturated Granular Pavement Material

Compaction of aggregates is an important part of the design, construction and research of pavement geotechnics projects. An important application of compaction is sample preparation for pavement design studies. Conventionally, the impact method of compaction is used for studies on pavement materials. However, recently, some researchers have been using other methods of compaction, such as static compaction, specifically for studying the unsaturated behavior of pavement materials. The objective of this study is to investigate the effect of compaction techniques on resilient behavior of compacted laboratory specimens. Studies show that the resilient behavior of unsaturated compacted road pavement materials is influenced by suction. In this regard, two types of recycled Construction and Demolition (C&D) material were selected and static and impact compaction methods were utilized for sample preparation. Further, accuracy of four predictive resilient modulus models with or without incorporation of suction was investigated. Test results show the impact of compaction method on particle breakage, matric suction and accordingly resilient behavior of C&D granular material

Physical properties and shear strength responses of recycled construction and demolition materials in unbound pavement base/subbase applications

Construction and Demolition (C&D) materials are increasingly used as construction materials in engineering applications. Their usage currently includes applications such as pavements, ground improvement, engineered fills, pipe bedding, backfill and aggregates in concrete. A comprehensive laboratory evaluation of physical and shear strength characteristics of recycled C&D materials was undertaken using gradation, Los Angeles Abrasion, unconfined compression, California Bearing Ratio (CBR), direct shear and consolidated drained triaxial tests. The recycled C&D materials evaluated were recycled concrete aggregate (RCA), crushed brick (CB), reclaimed asphalt pavement (RAP), waste excavation rock (WR), fine recycled glass (FRG) and medium recycled glass (MRG). All the recycled C&D materials are classified as well-graded materials and their compaction curves are controlled by water absorption and surface characteristics. RAP, FRG and MRG exhibit flat compaction curves while RCA, WR and CB exhibit bell-shaped compaction curves. The shear responses of the recycled C&D materials are classified into two groups: dilatancy induced peak strength and dilatancy associated strain-hardening behaviors. RCA, WR and CB are dilatancy induced peak strength materials in that their peak strength is clearly observed after the maximum dilatancy ratio occurs. Higher dilatancy ratios in these materials are associated with higher peak friction angles. RAP, FRG and MRG on the other hand are dilatancy associated strain-hardening materials, which exhibit strain-hardening behavior even with a relatively high magnitude of dilatancy. Based on the evaluation of the shear strength characteristics, it is ascertained that the compacted C&D materials have the potential to be used in pavement base/subbase applications as they have the required minimum effective friction angles. RCA, CB and WR in particular are found to also meet the physical and shear strength requirements for aggregates in pavement base/subbase applications

Flexural beam fatigue strength evaluation of crushed brick as a supplementary material in cement stabilized recycled concrete aggregates

In recent years, efforts have been made by various researchers to explore the sustainable use of Construction and Demolition (C&D) materials as a construction material in civil engineering applications. Recycled crushed brick is a commonly found material from demolition activities and works to date on this material in pavement applications have been limited to its usage in unbound pavement layers. This research was undertaken to evaluate the performance of crushed brick as a supplementary material in cement stabilized recycled concrete aggregates. An extensive suite of tests were undertaken on the crushed brick and recycled concrete aggregate blends stabilized with 3% cement. The laboratory evaluation comprised pH, plasticity index, foreign materials content, particle size distribution, linear shrinkage, California Bearing Ratio, modified Proctor compaction, Repeated Load Triaxial test, Unconfined Compressive Strength Test and Flexural Beam Tests. The cement stabilized blends with up to 50% crushed brick content and 3% cement were found to have physical properties, which comply with the local state road authority requirements. The results of Repeated Load Triaxial tests indicated the Recycled Crushed Aggregate/Crushed Brick (RCA/CB) blends performed well with 50% Crushed Brick (CB) content just on the border line for bound pavement material. Unconfined Compression Strengths met the minimum requirement for 7 days of curing for all blends, while the 28 day strength of the blends also improved significantly. The results of the flexural beam tests were noted to be consistent with past works with cement stabilized quarry produced crushed rock products. The modulus of rupture and flexural modulus for all the cement-stabilized blends were found to be consistent with the previous works, which indicate that these blends are suitable for applications such as cement-stabilized pavement subbases. The fatigue life was also within the range that has been previously reported for quarry materials. The cement-stabilized blends with crushed brick as a supplementary material with up to 50% brick content and 3% cement were found to have physical and strength properties, which would comply with road authority requirements

Calcium carbide residue: Alkaline activator for clay-fly ash geopolymer

Calcium Carbide Residue (CCR) and Fly Ash (FA) are waste by-products from acetylene gas and power plant production, respectively. The liquid alkaline activator studied in this research is a mixture of sodium silicate solution (Na2SiO3), water and CCR. The primary aim of this research is to investigate the viability of using CCR, a cementitious waste material, as an alkaline activator and FA as a precursor to improve the engineering properties of a problematic silty clay to facilitate its usage as stabilized subgrade material. The influential factors studied are Na2SiO3/water ratio, FA replacement ratio, curing time, curing temperature and soaking condition for a fixed CCR content of 7%. Strength development is investigated via the unconfined compression test. Scanning Electron Microscopy (SEM) observation is used to explain the role and contribution of influential factors on strength development. CCR dissolves the silicon and aluminum in amorphous phase of FA and the Na2SiO3 acts as a binder. The maximum soaked strength of the clay-FA geopolymer is found at Na2SiO3/water ratio of 0.6 and FA replacement ratio of 15%. The optimal Na2SiO3/water ratio is approximated from index test, which is a very practical approach. The clay-FA geopolymers with 40 C curing exhibit higher strength than those with room temperature curing, indicating the possibility of using clay-FA geopolymer for pavement subgrade applications. The 7-day soaked strength at the optimal ingredient meets the strength requirement for subgrade materials specified by the local national road authority. CCR is found to be a sustainable alkaline activator for geopolymer stabilized subgrade materials, which will result in the diversion of significant quantities of this by-product from landfills

Geotechnical characteristics of stabilised aged biosolids

Stockpiles of air-dried sludge from wastewater treatment plants, known as biosolids, are constantly increasing worldwide. This subsequently adds to the urgency of stabilising biosolids in an effort to convert them into a suitable construction material for use in engineered fills. This paper reports the result of a laboratory testing programme on biosolids stabilised with two types of waste materials, namely, bauxsol and fly ash. The biosolids collected from the Western Treatment Plant in Melbourne were stabilised in different ratios and tested to determine their compaction, strength, permeability and deformation characteristics. Both static and dynamic compaction methods were used in the preparation of the test specimens. Results suggest that the hydraulic conductivity values of biosolids consistently decrease with increasing amounts of additives, which is an indication of decreasing void ratio of material. In addition, increasing the amount of additives was found to lead to a subsequent decline in the compressibility of the stabilised biosolids. The strength of the biosolids samples increased with the addition of bauxsol and fly ash, with the highest shear strength found to be achieved with around 10% fly ash mixture. The application of stabilised biosolids in road embankments is discussed as a sustainable solution in geotechnical engineering applications