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Construction activities are generating substantial amounts of construction waste due to the rapid increase in economic growth and infrastructure developments. A series of laboratory model tests were conducted to investigate the feasibility of using recycled aggregate as backfills to construct the rammed stone columns. Recycled aggregates and gravel aggregates with the same particle size distributions were used to construct the rammed stone columns. The direct shear test results showed that the recycled aggregate exhibits similar behavior of initial compression but more significant expansion compared to those of the gravel aggregate. The critical bearing capacity of the rammed stone column using recycled aggregate as backfills was 6.2%–6.5% lower than that using the gravel aggregate as backfill, but was 36.1% higher than that of the traditional stone column. The rammed stone column was failed in bulging failure mode with the maximum bulging position of approximately 2d from the column head. The critical bearing capacity of the rammed stone columns could be estimated according to that of the traditional stone column by considering the effects of the tamping energy. [ABSTRACT FROM AUTHOR]

Preloading using either vacuum or fill surcharge is an effective method for the treatment of very soft saturated clay. The preloading will reduce the water content and increase the shear strength of soil. However, when the soil to be treated is very soft, it is difficult to take soil samples for laboratory tests or carry out in situ tests to determine the soil properties including shear strength. Therefore, there is a need to develop an analytical method to estimate the shear strength during preloading. In this paper, a simple correlation among settlement, water content and undrained shear strength using critical state theory is proposed for saturated soil under one-dimensional loading condition to allow the undrained shear strength variation of the soil to be estimated during preloading without testing. Laboratory model test and field monitoring data are used to verify the validity of this method and the proposed correlation is effective to be used as rough estimations on the undrained shear strength of soft clay. [ABSTRACT FROM AUTHOR]

When using jet grouting for soil stabilisation, effects of the installation process need to be evaluated. This could be particularly important for applications in challenging ground conditions and low initial ground stability. This study investigates such effects in soft marine clays using numerical finite-element (FE) simulations for both flat and sloping terrains. Additionally, an analytical solution using the modified Hagen–Poiseuille equation was developed to (a) assess the pressure induced by the grout at any installed depth and (b) illustrate the importance of maintaining a proper amount of return flow to avoid build-up of excessive pressures in the ground during the jet-grouting process. Combining the analytical and the FE simulations, jet-grouting induced soil displacements, were determined. For flat terrain, the area affected by jet grouting was approximately three to four times the column radius. By contrast, for the studied slope (inclination of 1 : 3), the influenced area increased to about ten times the column radius. The obtained displacement magnitude was also considerably larger for sloping terrain than for flat terrain. The reported findings relate to jet grouting in marine clays (which is not the normal application of this technology) and cannot be extrapolated to other soils. [ABSTRACT FROM AUTHOR]

The soil arching effect is the key mechanism for load transfer in pile-supported reinforced road (runway) foundations. To investigate the formation and evolution process of soil arching effect in the whole process of embankment filling and soft soil foundation consolidation, a three-dimensional hydro-mechanical coupled numerical model of pre-fabricated high-strength concrete (PHC) pile-reinforced soft soil runway foundation was established based on the foundation treatment project in Pudong Airport. The laws of variation of soil settlement, pore water pressure and pile soil stress were analysed, and the influence of pile spacing was considered. These data from both numerical simulation and field test indicate the soil arching effect in the foundation reinforced by PHC piles and preliminarily reveal the evolution of soil arching in the process of embankment filling and soft soil foundation consolidation. The preliminary results encourage the authors to continue this research to investigate the evolution of soil arching under aircraft dynamic loads through adding a more suitable constitutive model or subroutine in this numerical model. [ABSTRACT FROM AUTHOR]

AbstractThis study improved the vibratory probe compaction (VPC) technique by combining it with well-point dewatering to address the challenges of treating newly dredged silt ground. Specific methods were presented to determine the operating frequency based on multi-channel analysis of surface waves (MASW) results, as well as the spacing between compaction points derived from vertical vibration velocity measurements. The effects of well-point dewatering were analyzed through field monitoring of groundwater level, pore water pressure, and ground settlement. A comparative evaluation of the reinforcement of the improved and conventional VPC techniques was conducted through in-situ tests. The results indicate that continuous dewatering suppresses the excessive rise of excess pore water pressure during compaction, effectively eliminating equipment tilting and settlement due to sandblasting water, and enhancing construction efficiency by over 40%. The average standard penetration blow count (N63.5) increases from 4.3 to 11.4, the ground bearing capacity reaches 140.8 kPa and the average ground settlement is 42.5 cm. The cone resistance and sleeve resistance also exhibit higher values, and the risk of soil liquefaction is effectively eliminated. The experiments and practices provide some successful experiences for the wider application of this technique in similar newly reclamation grounds. [ABSTRACT FROM AUTHOR]

In our recent paper, we reported the development and application of the aerosol injection technique to accelerate the consolidation in soft soils. Aerosol injection technique is a process that involves injecting air under high pressure into soft soil to create a network of fractures, which gives rise to enhanced permeability. In this paper, we present an experimental study on the permeability of soft soil specimens with pre-made fractures in a triaxial device. Some emphasis is given to the variation of permeability with time. Some major influence factors are considered, e.g. the fracture roughness, confining pressure, pre-consolidation pressure, soil structure and mineral composition. The decrease in permeability with time is mainly due to the self-healing mechanism in soft soils, which is dictated by the soil deformation and migration of fines driven by the confining pressure and hydraulic gradient. [ABSTRACT FROM AUTHOR]

A full-scale experimental geosynthetic-reinforced piled embankment (GRPE) and its numerical back analysis are presented in this article. The site is in Virvée (France) and is part of the new South Europe Atlantic high-speed line project. A GRPE system using geosynthetics with high tensile stiffness (≥10,000 kN/m) was proposed as an optimized solution to replace a classical pile-supported embankment (PE). Based on full-scale tests, three-dimensional finite-element models are considered to simulate both GRPE and PE solutions. The numerical results obtained are presented in comparison with in situ measurements. Settlements, pile stresses, and the geosynthetic strains are investigated. Then, a parametric study was conducted for the GRPE system to evaluate the influences of pile net spacing, geogrid tensile stiffness, and different numbers of high to relatively low tensile stiffness geosynthetic layers on the load transfer performance. The results show that the geosynthetic number of layers has less impact for the high tensile stiffness cases on the system settlement and load transfer efficiency. The use of a double-layer geosynthetic reinforcement with high tensile stiffness enhances the overall performance of the geosynthetic-reinforced piled embankment. [ABSTRACT FROM AUTHOR]

In this research, experimental studies and numerical analyses were carried out to investigate how the usage of geotextile and geopolymer coated geotextile as a hybrid method changes the uplift behavior of the screw piles in cohesionless soil. In this context, traditional pile behavior, the effect of different number of helixes and embedment depths on screw piles, the mechanism of geotextile and the effects of geopolymer coating process were investigated. In addition, experimental studies were modeled by using Plaxis 3D and parametric studies were carried out after verification between the results of experimental study and numerical analysis. In the numerical analysis, a segmented helix model consisting of four 90-degree slices was developed instead of the planar helixes commonly used in the literature. For further investigation of the effectiveness of hybrid method, parameters such as improvement ratios and breakout factors were calculated. When the results obtained within the scope of the study were evaluated, the geopolymer coating process increased the bearing capacity of the geotextile by 24 % at 27 % less elongation. It was also seen that uncoated and geopolymer coated geotextile increased the screw pile performance in terms of improvement ratios by 294 % and 364 %, respectively. [Display omitted] [ABSTRACT FROM AUTHOR]

A tank test was performed simulating two-dimensional planar flow conditions at a meter scale to evaluate the effectiveness of microbial-induced desaturation and precipitation (MIDP) in stratified soil conditions. The tank setup (116.5 cm tall, 122 cm wide, and 5.25 cm thick) was filled with two layers of fine sand (a target layer of 40 cm and nontarget layer of 21 cm above) that were confined by silt layers above (6 cm), between (9 cm) and below (9 cm) the sand layers. Multiple flushes of substrate solution, containing calcium, nitrate, and acetate, were injected into the lower sand layer to stimulate indigenous nitrate-reducing bacteria to produce biogenic gas, biominerals, and biomass. Embedded sensors were used to measure the changes in electrical conductivity, volumetric water content, and pore pressure in both the target and nontarget sand layers during and between treatment cycles. Time-lapse camera images were used to determine flow velocity distributions in the target layer and identify modes of gas migration. At the end of the test, hydraulic conductivity, calcium carbonate content, and soil–water characteristic curves (SWCCs) were measured on intact samples of the treated material. The results showed that most of the reaction products were formed in the targeted sand layer. During the first treatment cycle, the degree of saturation in the target sand layer decreased to 75% within 5–12 days, at which point it started to migrate upwards until it got trapped and formed a lens underneath the silt layer above. During the second and subsequent treatment cycles, seepage velocity increased due to the entrapment of biogenic gas, the reaction rate increased due to the accumulation of biomass, and the gas formed channels through the silt and migrated further upwards into and through the upper sand and silt layers by irregular venting events. After 4–5 cycles, an equilibrium condition was reached at which the degree of saturation fluctuated from 65 to 80% when gas was being produced and vented to 80–90% when substrates were depleted. The CaCO3 content after 10 cycles over 12 weeks ranged from 1.6% close to the inlet to 0.5% close to the outlet, with an average of 0.68%. The formation of biomass and CaCO3 had a relatively large impact on the saturated hydraulic conductivity but a very limited impact on the SWCC. [ABSTRACT FROM AUTHOR]

The paper focuses on the identification of the 3D failure envelope of a shallow foundation on soft soil reinforced by rigid inclusions. A nonlinear 3D finite element model is first validated against literature results and novel centrifuge experimental data. The failure envelope, defined in the vertical force (V), bending moment (M) and horizontal force (H) space, is then constructed using numerical swipe tests. Analytical formulas are introduced to describe the 3D failure envelope shape and inclination, considering the influence of the coverage area, the thickness, and the friction angle of the load transfer platform. Finally, the efficiency of a rigid inclusion foundation is highlighted by comparing its failure envelope to that of the same foundation without rigid inclusions. The proposed analytical failure envelope can be used by engineers to quantify the bearing capacity of rigid inclusion foundations and by researchers to develop novel macroelements submitted to complex coupled loads. [ABSTRACT FROM AUTHOR]

Enzyme induced carbonate precipitation (EICP) is a new bio-cementation technique that utilizes plant-sourced urease to catalyze urea degradation and reaction with calcium iron, resulting in the formation of calcium carbonate (CaCO3) for soil improvement. EICP has considerable promise for novel and sustainable engineering applications such as soil strengthening, pollutant remediation, and other in situ field applications. In this study, the effect of EICP on the geotechnical characteristics of expansive soil is examined. A series of laboratory tests have been performed with an optimal concentration ratio of 0.75 mol/L. The outcomes of the compaction experiment indicated a slight increment in the dry density of the expansive soil from 15.78 to 16.71 kN/m3.Further, it diminished the optimal moisture content of the soil, decreasing it from 22.3 to 18.5%. The utilization of EICP improves the soil mechanical characteristics, reducing swelling pressure by 80% and increasing the UCS, cohesion, friction angle, unsoaked and soaked CBR by 66%, 44%, 49%, 441%, and 430%, approximately. Additionally, it leads to a significant decrease in soil permeability, approximately 63%. Moreover, SEM and XRD analysis confirmed the presence of CaCO3 content in the treated soil. The experimental findings indicated that the EICP method holds promise in enhancing expansive soil within engineering projects. [ABSTRACT FROM AUTHOR]

The feasibility of Carrillo's method is confirmed for consolidation problems of unsaturated soils under instantaneous loading in this study. In the plane strain and axial symmetry consolidation models, the coupled governing equations expressed by the excess pore-air and pore-water pressures are transformed into the equivalent uncoupled equations expressed by two functions of excess pore pressure using a decoupled method. Then, two rigorous theorems are used to prove that Carrillo's method is suitable for unsaturated soil consolidation under the plane strain and axial symmetry conditions. Finally, the mathematical formulas by Carrillo's method for unsaturated soil consolidation under plane strain and axisymmetric conditions are presented, and are verified against those of the existing analytical solutions. It turns out that the combinations of existing solutions to the conditions of a single direction flow by the proposed formulas can directly furnish the solutions to unsaturated soil consolidation with both horizontal and vertical flows. [ABSTRACT FROM AUTHOR]

Shallow geothermal energy systems (SGES) are a promising technology for contributing to the decarbonization of the energy sector. Soil thermal conductivity (λ) governs the heat transfer process in ground under a steady state; thereby, it is a key parameter for SGES performance. Soil mixing technology has been successful in enhancing the shear strength of soils, but is adopted in this paper for the first time to improve soils as a geothermal energy conductive medium for SGES applications. First, the thermal conductivity of six types of soils was systematically investigated and the key parameters analyzed. Next, graphite-based conductive cement grout was developed and mixed with the six soils in a controlled laboratory setting to demonstrate the significant increase in soil thermal conductivity. For example, the thermal conductivity of a very silty dry sand increased from 0.19 to 2.62 W/m·K (a remarkable 14-fold increase) when mixed with the conductive grout at a soil-to-grout ratio of 6∶1. In addition, the mechanical properties of the cement grouts and cement-mixed soils were examined along with the microstructural analysis, revealing the mechanism behind the thermal conductivity improvement. [ABSTRACT FROM AUTHOR]

Stone columns have garnered significant interest in geotechnical engineering as an effective ground improvement technique for enhancing the load-bearing capacity and mitigating settlement issues in soft soils. This study presents a comprehensive bibliometric analysis of scholarly literature on stone columns, utilizing data from the Web of Science database spanning from 1975 to 2023. The analysis aims to provide insights into publication trends, influential journals, key research institutions and authors, geographical distributions, and emerging themes in this domain. Through a systematic data curation process, 505 relevant publications were analyzed using Excel and VOSviewer software. The findings reveal a notable emphasis on geosynthetic encasements, load-settlement behavior, and soft soil reinforcement, with China being a major contributor. Over the past 48 years, the research has evolved from static loading to dynamic loading, sustainable structures, and artificial intelligence applications, as evidenced by the highly cited publications. This study maps the development, current state, and potential future directions of stone column research, serving as a valuable resource for researchers and practitioners in geotechnical engineering.

In this research, experimental studies and numerical analyses were carried out to investigate how the usage of geotextile and geopolymer coated geotextile as a hybrid method changes the uplift behavior of the screw piles in cohesionless soil. In this context, traditional pile behavior, the effect of different number of helixes and embedment depths on screw piles, the mechanism of geotextile and the effects of geopolymer coating process were investigated. In addition, experimental studies were modeled by using Plaxis 3D and parametric studies were carried out after verification between the results of experimental study and numerical analysis. In the numerical analysis, a segmented helix model consisting of four 90-degree slices was developed instead of the planar helixes commonly used in the literature. For further investigation of the effectiveness of hybrid method, parameters such as improvement ratios and breakout factors were calculated. When the results obtained within the scope of the study were evaluated, the geopolymer coating process increased the bearing capacity of the geotextile by 24 % at 27 % less elongation. It was also seen that uncoated and geopolymer coated geotextile increased the screw pile performance in terms of improvement ratios by 294 % and 364 %, respectively.

Microbially induced carbonate precipitation (MICP) has been shown to improve geotechnical properties of soil in many laboratory-scale tests. Field deployment of this technology requires large volumes of suspended bacterial inoculum media, and geotechnical engineers are still seeking a low-cost and quick method for upscaling applications. In this paper, we propose a four-step inoculation method to culture Sporoscarcina pasteurii for implementation of MICP in a prototypical dune in the Large Wave Flume at the O.H. Hinsdale Wave Research Laboratory of Oregon State University. The four-step inoculation method nonsterilely cultured the bacteria to 42 L in a common microbiology lab and scaled it up to 73 L in the field. The values of optical density at a wavelength of 600 nm (OD600) were obtained to determine the specific growth rate. Two different types of agar plates were evaluated for contamination and cell counting of the bacterial solutions. Shear-wave velocity of the treated dune was continuously measured by pairs of bender elements to monitor the treatment process. The average specific growth rates of the 42- and 73-L bacterial solutions were 5.11×10−3 and 1.27×10−3 min−1 , which were quite high compared with previous studies. The plate results indicated that the four-step inoculation method provided 108 cells/mL of bacterial solution with unobserved contamination. The increase in shear-wave velocity suggested the development of biocementation within sand particle contacts of the dune, demonstrating the effectiveness of the inoculation method. The results suggest that the four-step inoculation process discussed in this paper provides a large amount of bacterial solution for field-scale application of MICP. [ABSTRACT FROM AUTHOR]

Abstract The surging demand for sustainable and efficacious approaches of enhancing the ground has resulted in the investigation of novel waste materials. This study investigates the utilization of Polyoxymethylene (POM) as a granular column to ameliorate the ability of soft clay soil to resist horizontal loads. The study introduces a new implementation of polyoxymethylene columns as ground improvement approach to tackle the complexities related to soft clay soils. The capability of polyoxymethylene columns was analyzed through a sequence of laboratory experiments, containing engineering characteristic tests, unconfined compressive strength (UCS) tests, and consolidated isotropic undrained (CIU) triaxial tests. The effects of the number of columns, column diameter, column depth, substitute area ratio, depth penetration ratio, column aspect ratio, volume infusion ratio, and confining pressures, were evaluated to analyze the behavior of individual and clustered encapsulated polyoxymethylene columns. The findings verified a notable development in the ability of soft clay soil, when strengthened with polyoxymethylene columns, to oppose the lateral loads and maintain overall stability. Additionally, a regression analysis was implemented to establish a prediction model that estimates the increase in shear strength of POM columns based on different column dimensions. This model is a practical tool for evaluating the performance of reinforced soft clay soils in large-scale projects. This study not only accentuates the mechanical benefits of polyoxymethylene but also accentuates its environmental benefits, prescribing for the implementation of recyclable materials in ground renovation.

Excessive ballasted track deformations may occur during the railway operations due to poor load bearing capacity of the embankment (placed soil or natural ground) or the manifest accumulation of subsidence caused by the soil consolidation and the passage of trains. The principles of pressure grouting (or jet-grouting) technologies, used to create reinforcement elements for the rail trackbed stabilization, are presented, with reference to the specific construction condition on an existing and in-service railway track. A single-track railway, including the superstructure and substructure components, was modeled using the finite element method (FEM). Some soil stabilization options, based on the installation of grouted micropiles according to different layout configurations, were considered. The results of the numerical analyses, in the form of stress and strain behavior of the whole track structure, demonstrated that the use of jet-grouted micropiles is a rational and less expensive option, which can be installed on or close to the track, having positive effects on limiting the vertical deformations of the embankment without affecting the expected distribution of stress states in the embankment middle.

Abstract Marl soil is highly prone to erosion when exposed to water flow, posing a potential threat to structural stability. The common practice of stabilizing soil involves the addition of cement and lime. However, persistent reports of severe ruptures in many stabilized soils, even after extended periods, have raised concerns. In stabilized marls, unexpected ruptures primarily result from the formation of ettringite, which gradually damages the soil structure. This article aims to assess the impact of nanosilica on the formation of ettringite and the nanostructure of calcium silicate hydrate (C-S-H) during the marl soil stabilization process with lime. To achieve this, marl soil was stabilized with varying percentages of lime and nanosilica. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images were collected to observe changes in mineralogy and microstructural properties. Various geotechnical parameters, including granularity, Atterberg limits, compressive strength, and pH, were measured. The results indicate that the uniform distribution of nanosilica in marl-lime soils enhances pozzolanic activities, calcium aluminate hydrate growth (C-A-H), and the nanostructure of calcium silicate hydrate (C-S-H). According to XRD and SEM experiments, the presence of nanosilica reduces the formation of ettringite. Moreover, the compressive strength of modified samples exhibited an upward trend. In the experimental sample manipulated with 1% nanosilica combined with 6% lime, the compressive strength increased by 1.84 MPa during the initial 7 days, representing an approximately 18-fold improvement compared to the control sample.

The utilization of stone columns has emerged as a popular ground improvement strategy, whereas the drainage performance can be adversely hampered by clogging effect. Despite the ample progress of calculation methods for the consolidation of stone column-improved ground, theoretical investigations into the clogging effect have not been thoroughly explored. Furthermore, it is imperative to involve the column consolidation deformation to mitigate computational error on the consolidation of composite ground with high replacement ratios. In this context, an analytical model accounting for the initial clogging and coupled time and depth-dependent clogging of stone columns is established. Then, the resulting governing equations and analytical solutions are obtained under a new flow continuity relationship to incorporate column consolidation deformation. The accuracy and reliability of the proposed model are illustrated by degradation analysis and case studies with good agreements. Subsequently, the computed results of the current study are juxtaposed against the existing models, and an in-depth assessment of the impacts of several crucial parameters on the consolidation behavior is conducted. The results reveal that ignoring column consolidation deformation leads to an overestimate of the consolidation rate, with maximum error reaching up to 16% as the replacement ratio increases. Furthermore, the initial clogging also has a significant influence on the consolidation performance. Additionally, the increment of depth and time-clogging factors a and b will induce a noticeable retardation of the consolidation process, particularly in the later stage.

The methods for modeling rigid inclusion ground improvements are well documented in the literature, yet their application to large-scale geotechnical simulations remains underanalyzed. Due to the large number of discretization elements/nodes used in such simulation, certain simplifications are necessary. This paper presents methods for modeling rigid inclusion ground improvements in large-scale geotechnical simulations. The methodologies involve modeling the inclusions using continuum elements, beam elements or replacing them with an equivalent medium through homogenization techniques. The advantages and drawbacks of each method are discussed, particularly regarding their applicability to analyses covering significant areas. In the second part of the paper, a case study of the foundation of the conduit pipe in the dam of Szalejów Górny dry antiflood reservoir in Poland is simulated using two of the considered methods. The obtained results are compared and discussed.

The surging demand for sustainable and efficacious approaches of enhancing the ground has resulted in the investigation of novel waste materials. This study investigates the utilization of Polyoxymethylene (POM) as a granular column to ameliorate the ability of soft clay soil to resist horizontal loads. The study introduces a new implementation of polyoxymethylene columns as ground improvement approach to tackle the complexities related to soft clay soils. The capability of polyoxymethylene columns was analyzed through a sequence of laboratory experiments, containing engineering characteristic tests, unconfined compressive strength (UCS) tests, and consolidated isotropic undrained (CIU) triaxial tests. The effects of the number of columns, column diameter, column depth, substitute area ratio, depth penetration ratio, column aspect ratio, volume infusion ratio, and confining pressures, were evaluated to analyze the behavior of individual and clustered encapsulated polyoxymethylene columns. The findings verified a notable development in the ability of soft clay soil, when strengthened with polyoxymethylene columns, to oppose the lateral loads and maintain overall stability. Additionally, a regression analysis was implemented to establish a prediction model that estimates the increase in shear strength of POM columns based on different column dimensions. This model is a practical tool for evaluating the performance of reinforced soft clay soils in large-scale projects. This study not only accentuates the mechanical benefits of polyoxymethylene but also accentuates its environmental benefits, prescribing for the implementation of recyclable materials in ground renovation. [ABSTRACT FROM AUTHOR]

Vertical drains installed in soft clay deposits enhance the rate of consolidation in preloading projects. Using a mandrel to install the prefabricated vertical drains, its insertion and withdrawal will result in the remoulding of the soil zone surrounding it, called the smear zone. The extent of the smear zone is an important parameter that characterises the smearing effect. This paper describes this effect in terms of smear ratio (i.e. the ratio of the diameter of smear zone ds to the diameter of drain, dw) on the consolidation characteristics of soil with radial drainage. A series of radial consolidation tests with a predetermined smear zone in a model unit cell was conducted by varying the diameter of the smear zone. The experimental results show that beyond a smear ratio of 4, the soil behaves as if it is in a fully remoulded condition. The results were compared with some of the theoretical approaches reported in the literature. The analytical solution that predicts the time–settlement curve in a better way is identified. Also, it is observed that the gain in undrained shear strength due to the consolidation of soft clay decreases with the increase in the diameter of the smear. [ABSTRACT FROM AUTHOR]

In the Kashmir region of Pakistan, the presence of Siwalik clays engenders serviceability issues to the infrastructure causing substantial loss of property. In this study, an attempt has been made to address these issues using polypropylene fibres (PPFs) as a sustainable modifier. These fibres were used in five different proportions, namely 0.25, 0.5, 0.75, 1 and 1.25% as partial replacement of base soil to analyse their impact on the engineering behaviour of matrices. Classification, compaction, indirect tensile, unconfined and triaxial compression, swell potential, consolidation and California bearing ratio (CBR) tests were conducted on controlled as well as reinforced-clay samples for comparative analyses. The maximum improvements were observed in unconfined compressive strength (109%), tensile strength (300%), cohesion (13%), friction angle (110%), soaked CBR (800%) and un-soaked CBR (550%). Besides, the reduction in swelling strain by 92% was also recorded corresponding to 1 kPa effective vertical stress. The capital cost analyses showed that PPFs reduced the costs of backfill behind the retaining wall and foundation soil beneath isolated footing by 21 and 44.5%, respectively. Moreover, the modifier had no adverse effect on the aqueous media. Conclusively, PPFs can be used as sustainable modifiers leading to a potential solution for serviceability issues. [ABSTRACT FROM AUTHOR]

This paper describes California bearing ratio (CBR) tests carried out to investigate the suitability of waste polyethylene terephthalate (PET) bottles for ground improvement. For the studies, quarry dust is used as an infill, and it is prepared at a relative density of 57.6% within the CBR mould with a diameter of 150 mm. Experiments are carried out by embedding cut PET bottles with a diameter of 5.6 cm within the infill to provide cellular confinement in three different configurations, i.e. three-bottle, four-bottle and five-bottle configurations. The effect of bottle height on the performance of the systems is investigated by considering three cell (bottle) heights, viz., 6.6 cm, 9.3 cm and 11.6 cm. To analyse the performance of the cellular confinement, vertical stress distribution below the applied load is determined. It is observed that the performance of the PET bottle embedded system is better when it is placed within the isobar (σz/q) of 0.3. Based on the CBR values and improvement factor, it is observed that a four-bottle configuration with a height of 6.6 cm is effective in sustaining higher loads. The proposed study provides guidelines for using these bottles for stabilising blocked pavements. [ABSTRACT FROM AUTHOR]

Excessive ballasted track deformations may occur during the railway operations due to poor load bearing capacity of the embankment (placed soil or natural ground) or the manifest accumulation of subsidence caused by the soil consolidation and the passage of trains. The principles of pressure grouting (or jet-grouting) technologies, used to create reinforcement elements for the rail trackbed stabilization, are presented, with reference to the specific construction condition on an existing and in-service railway track. A single-track railway, including the superstructure and substructure components, was modeled using the finite element method (FEM). Some soil stabilization options, based on the installation of grouted micropiles according to different layout configurations, were considered. The results of the numerical analyses, in the form of stress and strain behavior of the whole track structure, demonstrated that the use of jet-grouted micropiles is a rational and less expensive option, which can be installed on or close to the track, having positive effects on limiting the vertical deformations of the embankment without affecting the expected distribution of stress states in the embankment middle. [ABSTRACT FROM AUTHOR]

Marl soil is highly prone to erosion when exposed to water flow, posing a potential threat to structural stability. The common practice of stabilizing soil involves the addition of cement and lime. However, persistent reports of severe ruptures in many stabilized soils, even after extended periods, have raised concerns. In stabilized marls, unexpected ruptures primarily result from the formation of ettringite, which gradually damages the soil structure. This article aims to assess the impact of nanosilica on the formation of ettringite and the nanostructure of calcium silicate hydrate (C-S-H) during the marl soil stabilization process with lime. To achieve this, marl soil was stabilized with varying percentages of lime and nanosilica. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images were collected to observe changes in mineralogy and microstructural properties. Various geotechnical parameters, including granularity, Atterberg limits, compressive strength, and pH, were measured. The results indicate that the uniform distribution of nanosilica in marl-lime soils enhances pozzolanic activities, calcium aluminate hydrate growth (C-A-H), and the nanostructure of calcium silicate hydrate (C-S-H). According to XRD and SEM experiments, the presence of nanosilica reduces the formation of ettringite. Moreover, the compressive strength of modified samples exhibited an upward trend. In the experimental sample manipulated with 1% nanosilica combined with 6% lime, the compressive strength increased by 1.84 MPa during the initial 7 days, representing an approximately 18-fold improvement compared to the control sample. [ABSTRACT FROM AUTHOR]

AbstractTraditional vacuum combined with surcharge preloading (TVSP) is commonly used for treating soft ground. However, the extensive use of sand as a horizontal drainage system poses a challenge due to its high demand for infrastructure construction and land reclamation. The straight-line vacuum combined with surcharge preloading (SVSP) is a technical improvement and innovation of the TVSP. It eliminates the sand cushion with the PVDs being directly connected to the vacuum pump through the main and branch pipes. This case presents the initial application of the SVSP for expressway ground treatment. The results indicate that the vacuum pressure in SVSP is 11 kPa greater than in TVSP. The SVSP induces a higher consolidation degree and higher settlement of soil ground. The higher vacuum pressure in the ground treated by SVSP also leads to a faster dissipation rate and a lower value of porewater pressure. Removing the sand cushion alters the boundary conditions for ground consolidation, leading to a lower consolidation degree for shallow ground than TVSP, and a higher consolidation degree for deep ground. The improvement depth progressively increases over time from the surface towards deeper layers. Additionally, the SVSP offers a cost saving of 20.1% compared to TVSP. [ABSTRACT FROM AUTHOR]

Micropiles are often implemented through drilling, steel pipe installation, reinforcement and grouting. However, in some parts of the world, especially in areas with fine-grained soils, these shafts are implemented by steel pile driving, followed by reinforcement, and grouting has been expanded considerably. In this study, micropile shafts were installed at the site by both driving and drilling methods. Reinforcement and grouting were carried out by two-step grouting and applying different grouting pressures in the micropiles. Some boreholes (at a distance of 0.3 m from the micropile axis) and test pits were drilled to investigate the penetration radius of the grout at different grouting pressures. Results showed that the bearing capacity of driven micropiles is about 4 to 14% more than that of drilled micropiles due to the soil compaction impacts. The average uniaxial compressive strength of the soil samples after micropiles grouting was dependent on the applied grouting pressure and increased from 25 to 56%. In addition, the direct shear test results showed an increase of 15% in the soil cohesion and an increase of 4° in the internal friction angle for the soil after grouting of the micropiles. [ABSTRACT FROM AUTHOR]