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Showing papers in "Transportation geotechnics in 2019"


Journal ArticleDOI
J. Pooni1, Filippo Giustozzi1, Dilan Robert1, Sujeeva Setunge1, B O'Donnell 
TL;DR: In this paper, the authors examined the durability performance of the enzymatic stabilization of expansive soils in road pavements subjected to moisture fluctuation and found that the strength of stabilized soils was considerably increased with the addition of enzyme based stabilizer, revealing its ability to maintain the material stiffness over moisture fluctuations.
Abstract: Expansive soils are problematic and susceptible to ground movements, causing significant damage to overlying structures and reduction of bearing capacity Geotechnical engineering has long recognized that the moisture variation triggers the expansive nature of soils resulting in its swell and shrinkage Numerous stabilizing additives have been used to treat expansive soils such as lime, cement and fly ash However, the use of bio-enzymes as a soil stabilizing agent is not currently fully understood This study examines the durability performance of the enzymatic stabilization of expansive soils in road pavements subjected to moisture fluctuation Number of experiments was performed under controlled conditions to investigate the mechanical and hydraulic response of stabilized soils subjected to cyclic moisture degradation at various initial moisture contents covering practical moisture ranges in applicable with road pavements Results showed that strength of stabilized soils was considerably increased with the addition of enzyme based stabilizer, revealing its ability to maintain the material stiffness over moisture fluctuation While wetting and drying tests had damaging effects on the UCS, enzyme based stabilization served to preserve soil strength effectively throughout the loading cycles Results obtained from the mechanical/hydraulics tests were further elaborated using imaging analysis which provides an insight into the mechanism of enzyme based stabilization and the influence of moisture when using this novel stabilization approach This research will substantially benefit geotechnical applications including cost-effective and sustainable road constructions

50 citations


Journal ArticleDOI
TL;DR: In this article, the performance and deformation of ballast bed are significantly influenced by the particle morphology (size and shape), the rheology (translation and rotation), and the degradation (breakage and abrasion).
Abstract: The performance and deformation of ballast bed are significantly influenced by the particle morphology (size and shape), the rheology (translation and rotation), and the degradation (breakage and abrasion). Regarding the ballast particle morphology, the ballast particle size is generally measured by sieving and described with the Particle Size Distribution (PSD), while the particle shape is normally classified as three characteristics, the form, angularity, and surface texture. Quantifying particle morphology with current manual methods is difficult to obtain accurate results (often subjective). Concerning the ballast particle rheology, almost all the related studies are based on numerical simulations, e.g. the Discrete Element Method (DEM). A limited number of studies were performed to record the translation and rotation with the electronic devices embedded in ballast layer. However, the numerical simulations can only precisely reflect the ballast particle rheology in quasi-static tests (e.g. direct shear test), and the electronic devices can only record the ballast particle rheology in the limited areas, where they were placed. The ballast breakage could be evaluated by the change of the PSD, but the determination of PSD involves significant errors. Additionally, the manual methods could not fully quantify the ballast abrasion. As a result, more accurate evaluation methods need to be developed and utilised for the validation and confirmation of the degradation-related studies.Towards these limitations, the studies on two-dimensional (2D) and three-dimensional (3D) image analysis methods for granular materials are reviewed, discussing their existing and potential utilisation in railway ballast applications. This paper can be of interest to the researchers, who are dealing with the performance and deformation of ballast bed. Additionally, a special attention can be paid to utilising the image analysis for accurate particle morphology quantification, particle rheology investigation and ballast degradation evaluation.

47 citations


Journal ArticleDOI
TL;DR: In this article, the freeze-thaw performance of loess with stabilizations was investigated, and fly ash and cement stabilization was used to improve the performance of frozen loess.
Abstract: Loess soil, widely distributed in cold regions, is detrimental for pavement foundation. To minimize the effects of seasonal freeze-thaw cycles, there is a need to investigate freeze-thaw performance of loess with stabilizations. In this study, loess classified as silt was first stabilized with fly ash and cement, and freeze-thaw durability tests, frost-heave and thaw-weakening tests, and unconfined compression strength tests then were performed to determine improvements with respect to the laboratory freeze-thaw performance. Based on achieved results, saturated specimens exhibited only half of the compression strength of unsaturated specimens, and there were indications that fly ash slightly improved loess freeze-thaw durability and frost susceptibility, while addition of cement to loess was effective to maintain zero mass loss and negligible frost susceptibility. Infiltration paths for water supply in soil specimens were also effectively cut by using cement.

46 citations


Journal ArticleDOI
TL;DR: In this paper, a series of large-scale laboratory tests using the track process simulation testing apparatus (TPSA) is carried out to assess the performance of under sleeper pads (USP) to reduce ballast degradation and to decrease permanent deformation.
Abstract: The degradation and deformation of ballast critically affect the track geometry, safety, and passenger comfort. The increase in axle loads and train speed increases the stress applied on the ballast and exacerbates the rate of ballast degradation. This situation is more critical when tracks are built on stiff subgrades (e.g. bridges, tunnels and crossings), hence the use of energy absorbing (damping) layers in track substructure is a countermeasure to minimize track damage. In this study, a series of large-scale laboratory tests using the track process simulation testing apparatus (TPSA) is carried out to assess the performance of under sleeper pads (USP) to reduce ballast degradation and to decrease permanent deformation. When placed beneath the sleeper, the energy absorbing nature of USP reduces the energy transferred to the ballast and other substructure components. Subsequently, the ballast layer experiences less deformation and degradation. Innovative tactile surface sensors (matrix-based) are used to measure the pressure and contact area between sleeper and ballast. The measured data show that an increase in contact area between sleeper and ballast decreases the stress applied on ballast, and thus a reduction in ballast breakage and corresponding reduced ballast deformation can be achieved. Furthermore, the influence of the USP stiffness is examined and the measured data offer an insightful understanding of the role of USP for given track and loading conditions in terms of energy dissipation and reduced ballast deformation.

46 citations


Journal ArticleDOI
TL;DR: In this paper, the collapse pressure on flexible pavements over rectangular trapdoors in homogeneous clay is investigated by a three-dimensional lower bound finite element limit analysis using semidefinite programming.
Abstract: A hole in a flexible pavement is commonly formed due to several environmental impacts. With a continued overload traffic action, a collapse of the hole over the flexible pavement can potentially occur resulting in a pothole on a road surface. Solutions of trapdoor problems are useful for predicting the failure of the hole taking place below the flexible pavement subjected to the overload traffic. In this paper, the collapse pressure on flexible pavements over rectangular trapdoors in homogeneous clay is investigated by a three-dimensional lower bound finite element limit analysis using semidefinite programming. Results of the present study are verified against the existing solutions for the cases of plane strain trapdoors. New lower bound solutions of the problem are numerically derived as functions of cover-depth ratios and aspect ratios of rectangular trapdoors while associated failure mechanisms are discussed and compared. Approximate algebraic equations for stability numbers of rectangular trapdoors are also presented.

46 citations


Journal ArticleDOI
TL;DR: In this article, three types of fine-grained soils were treated at three lime contents (lower, equal and higher than the lime fixation point) at four curing periods (7, 28, 90 and 365 days).
Abstract: Lime treatment is a widely-used technique for the stabilization and improvement of fine-grained soils in earthworks for transportation. In cold regions, lime treatment can be considered as an appropriate method to improve freeze-thaw resistance of fine-grained soils. The effectiveness of treatment can depend on soil nature, lime dosage and curing time. In the present work, three soils (silt of low plasticity, clay of low plasticity, and silt of high plasticity) were treated at three lime contents (lower, equal and higher than the lime fixation point) at four curing periods (7, 28, 90 and 365 days). The mechanical strength was determined from unconfined compression test performed on specimens having a diameter of 100 mm and a height of 100 mm. Freeze-thaw cycles were applied by varying the specimen temperature between −20 °C and 20 °C, the specimens being beforehand saturated. The mechanical strength of specimen subjected to ten freeze-thaw cycles was compared to those maintained in laboratory temperature (20 °C). Results showed that freeze-thaw cycles significantly decrease the mechanical strength of sample. This decrease can be explained by damage induced by ice lenses formation/thawing during freeze-thaw cycles, as illustrated by the observation at X-ray computed tomography. Interestingly, lime treatment mitigates this damage and increase the soil freeze-thaw resistance. The treatment appears more efficient for lower plasticity soil, a higher lime content, and a longer curing time. This conclusion seems depend on the specimen preparation procedure.

46 citations


Journal ArticleDOI
TL;DR: In this article, an experimental investigation was carried out to evaluate the performance of the subgrade soil by placing a single layer and double layers of geosynthetic reinforcements (Glasgrid, Tenax 3D grid and Tenax multimat) horizontally at varying depths from the top surface of sub grade soil.
Abstract: Geosynthetic reinforcement layers are often used to improve the performance of pavement structures. The performance of an unpaved road is routinely measured in terms of the California bearing ratio (CBR), which is an index of strength of subgrade soil of unpaved road. In the present study, an experimental investigation was carried out to evaluate the performance of the subgrade soil by placing a single layer and double layers of geosynthetic reinforcements (Glasgrid, Tenax 3D grid and Tenax multimat) horizontally at varying depths from the top surface of subgrade soil. Through a series of CBR tests in the laboratory, an attempt was made to determine the optimum depth of the reinforcement layer. The single layer of reinforcement has been placed at the middle, one-third and one-fourth of the height of the CBR specimen from the top surface of the soil in the CBR mould. The double layers of reinforcement were placed at one-fourth of the specimen height from the top surface and the bottom surface. The results show the significant contribution in terms of increased CBR value of the soil, resulting in reduced design thickness of the pavement layers above the subgrade soil. It has been observed that for a single layer reinforcement the Tenax 3D grid performs better than other geosynthetics used in this study while the Tenax multimat performs best for double layers. The results indicate that for the maximum benefit, the Tenax 3D grid reinforcement should be placed in between 0.3H and 0.36H where H is the height of the soil specimen. For Glasgrid and Tenax multimat reinforcements, the maximum effect of reinforcement is obtained when they are placed between 0.41H and 0.62H.

37 citations


Journal ArticleDOI
TL;DR: In this paper, a 3D FEM model considering the contacts between different layers was established to simulate different settlement scenarios, and the numerical results were first validated by the comparisons of rail deflections with a full-scale physical model testing.
Abstract: Rail irregularities caused by subgrade differential settlement will accelerate track degradation and lower ride comfort and safety. Since the track substructure is normally inaccessible, these problems are hard to be detected early. To study the mapping characteristics of deflection profiles in the ballastless track-subgrade system, a 3D FEM model considering the contacts between different layers was established to simulate different settlement scenarios. The numerical results were first validated by the comparisons of rail deflections with a full-scale physical model testing. Then the influences of subgrade differential settlement on the CRTS II type ballastless track were analyzed, including the deflection profiles, additional tensile stresses and contact stresses. The settlement transfer characteristics from the subgrade surface to the rail were revealed, which were largely dependent on the track equivalent flexibility. A unified formula in terms of the settlement amplitude and track equivalent flexibility was proposed to describe the geometry mapping relationship. The scenario of hanging track structure occurred at the subgrade differential settlement with wavelengths shorter than 15 m, or wave-length between 15 m and 20 m and amplitude larger than 15 mm. The thresholds of unacceptable settlement wavelengths for the additional stresses were 10–20 m for the concrete base and 10–15 m for the subgrade with the settlement amplitudes smaller than 15 mm. Differential settlement with shorter wavelengths was more vulnerable, and the critical scenarios of soil yielding at subgrade surface happened earlier than the concrete cracking in the track structure. Subgrade maintenance works, such as settlement restoration and soil improvement, were suggested to be implemented before the wavelength reached 10 m to avoid further development of settlement and potential threats to the track structure.

35 citations


Journal ArticleDOI
TL;DR: In this paper, a detailed case study of a subway cross passage including the temperature variations in brine and selected monitoring points around the passage based on the field testing results during freezing and frozen wall maintenance is presented.
Abstract: Artificial ground freezing (AGF) has been extensively used in the construction of subway cross passages in soft ground to ensure the safety of excavation. The temperature characteristics during freezing are of great interests, as it can be used to determine whether the frozen wall satisfies the design requirements in terms of dimension and strength. This paper presents a detailed case study of a cross passage including the temperature variations in brine and selected monitoring points around the passage based on the field testing results during freezing and frozen wall maintenance. In particular, temperature data was collected at various depths along settlement observation holes installed on top of the frozen wall. It was found that the frozen wall development rate toward the cross passage is 1.43 times faster than that away from the passage in the silt. A three-dimensional numerical model was used to analyse the temperature distribution and was able to accurately reflect the temperature distribution within the entire frozen zone with uneven distribution of the freezing pipes during freezing. This paper provides a valuable case study of the temperature characteristics of a cross passage with uneven freezing pipe distribution and a thermal model with complete thermal properties at both frozen and unfrozen status, which can be useful for thermal model calibration and/or temperature field prediction in artificial freezing engineering.

33 citations


Journal ArticleDOI
TL;DR: In this article, a series of novel experimental tests were conducted to determine the potential of geogrids to confine granular layers within ballasted railway lines operating at speeds close to critical velocity.
Abstract: This work describes a series of novel experimental tests to determine the potential of geogrids to confine granular layers within ballasted railway lines operating at speeds close to critical velocity. This is important because at low train speeds, vertical stresses are dominant, but when approaching critical velocity conditions, dynamic horizontal stress levels are magnified. Therefore the majority of previous geogrid investigations have been performed assuming constant horizontal stress levels, thus making them more relevant for lower speed lines. To investigate settlement under high relative train speeds, ballasted railway track samples were subject to combined vertical-horizontal cyclic loading. Three areas were explored: (1) the performance benefit from placing geogrid at the ballast-subballast interface, (2) the performance benefit from placing geogrid at the subballast-subgrade interface, (3) the effect of subgrade stiffness on geogrid performance at the subballast-subgrade interface. Testing was performed using a unique large-scale true triaxial apparatus which had the ability to vary stress levels in three Cartesian directions. Compared to the control conditions, the geogrid offered a settlement improvement of approximately 35% when placed at the ballast-subballast interface, and 10–15% when placed at the subballast-subgrade interface. Regarding subgrade CBR, it was found that the geogrid offered the greatest performance benefits when the subgrade was soft. Therefore it was concluded that for the ballasted rail structures under test, when subject to elevated levels of horizontal stress, geogrids reduced settlements compared to non-geogrid solutions.

32 citations


Journal ArticleDOI
TL;DR: In this article, a critical review of various problems associated with transition zones and the measures adopted to mitigate them is presented, which also includes critical reviews of research work carried out using large-scale laboratory testing, mathematical and computational modelling and field measurements on track transition zones.
Abstract: Track transitions such as bridge approaches, road crossings and shifts from slab track to ballasted track are common locations where track degradation accelerates due to dynamic and high impact forces; as a consequence there is higher differential settlement. These types of discontinuities cause an abrupt change in the structural response of the track due mainly to variations in stiffness and track damping. Track transition zones are prone to an accelerated deterioration of track material and geometry that leads to increased maintenance costs. Track deterioration also leads to vehicle degradation due to enhanced acceleration, low frequency oscillation, and high frequency vibrations. While ballast deterioration is a major factor affecting the stability and longevity of rail tracks, the cost of tackling transition related problems that detract from passenger comfort is also high. A good transition zone lessens the impact of dynamic load of moving trains by minimising the abrupt variations in track stiffness and ensuring a smooth and gradual change from a less stiff (ballasted track) to a stiff (slab track) structure. This paper presents a critical review of various problems associated with transition zones and the measures adopted to mitigate them; it also includes critical review of research work carried out using large-scale laboratory testing, mathematical and computational modelling and field measurements on track transition zones.

Journal ArticleDOI
TL;DR: In this paper, a laboratory testing plan is performed to assess the geotechnical properties of the mixtures with 0, 7, 10% and 13% FA content and it includes compaction tests, unconfined compressive strength tests, California Bearing Ratio (CBR) tests, collapse potential tests and permeability tests.
Abstract: The reuse of waste materials in engineering projects has become the subject of many research efforts worldwide as it provides economical as well as environmental benefits. Coal wash (CW) and fly ash (FA) are example waste materials that can be used as alternative aggregates in transportation infrastructure projects, specifically as base and subbase materials in roads. Class C FA has been extensively used as a stabilizing material due to its hardening potential. However, Class F fly ash, a non-pozzolanic material when used alone, has not been considered in past research projects. In this study, Class F fly ash is mixed with coal wash as a void filler to enhance its compaction efficiency and produce a compact and well interlocked structure. A laboratory testing plan is performed to assess the geotechnical properties of the mixtures with 0%, 7%, 10% and 13% FA content and it includes compaction tests, unconfined compressive strength tests, California Bearing Ratio (CBR) tests, collapse potential tests and permeability tests. The mixture with 7% FA is selected as the optimum mixture and its potential for tensile cracking under service loads is further investigated using four-point bending tests. Also, the resilient modulus and permanent deformations of the mixture are evaluated under different dry-back conditions using multistage repeated load triaxial tests.

Journal ArticleDOI
TL;DR: In this article, a dynamic analysis model comprising track, embankment and ground is presented based on the two-and-half-dimensional (2.5D) finite element method to predict the vibrations generated by train moving loads.
Abstract: As train speeds are increased, the issue of the critical speed must be faced, especially when tracks run across soft ground. This is the phenomenon describes the amplification of the track deflections due to coincidence of the train speed with the wavespeeds of the underlying ground. Modern high-speed lines are often constructed on ballastless track which has different dynamic behaviour to conventional ballasted track. Therefore, further research is needed to investigate the critical speed of ballastless track. In this paper, a dynamic analysis model comprising track, embankment and ground is presented based on the two-and-half-dimensional (2.5D) finite element method to predict the vibrations generated by train moving loads. The rails and track slab are modeled as Euler-Bernoulli beams resting on the embankment. The concrete base, embankment and ground are modeled by the 2.5D finite elements. The results show that the critical speed of ballastless track is higher than the Rayleigh wave velocity of the underlying soil and quite close to the Rayleigh wave velocity of the subgrade. The existence of the subgrade can highly improve the critical speed of the ballastless track even with a shallow subgrade of 1.25 m depth. The underlying soil stiffness is the conclusive factor in determining the track vibration amplitude. It is also found that the embankment plays an essential role in reducing the inhomogeneity of the lateral stress distribution and the amplitude of vertical stress in ballastless track.

Journal ArticleDOI
TL;DR: In this paper, the results of a series of large-scale direct shear tests on compaction characteristics and shear strength properties of kenaf fiber reinforced soil were presented.
Abstract: The reinforcement of structural elements and construction materials using natural fibers has gained popularity among researchers and industries due to environmental concerns and financial problems of synthetic fibers. The contribution of natural fibers as soil reinforcement elements enhances the shear strength properties as the stresses in the soil mobilize tensile resistance in the fibers. Despite the specific limitations of direct shear test, it is considered as one of the most commonly used techniques that gives the design engineers a quick measure of soil strength properties when a certain fine content exists in the soil mixture. Therefore, this study is intended to present the results of a series of large-scale direct shear tests on compaction characteristics and shear strength properties of kenaf fiber reinforced soil. A total number of 128 tests have been carried out to determine the compaction and shear strength characteristics of unreinforced and reinforced sand-clay mixtures. Subsequently, the influence of kenaf fiber reinforcement on the stress-displacement relationship, volume change, ductility and failure state of reinforced soil was evaluated. Based on the results, the addition of a certain amount of kenaf fiber to the sand-clay mixture enhances the mixture ductility, improves the shear strength parameters, and ultimately makes it an appropriate candidate to be used in construction projects such as pavement layers, slope protection, embankment, and building foundation.

Journal ArticleDOI
TL;DR: In this paper, a detailed examination of the core mineralogy, microfabric, grain size and suction response of expansive clays during moisture ingress can be explained by an examination of their core mineralogical properties.
Abstract: The complex swelling mechanism in expansive clays during moisture ingress can be succinctly explained by an examination of their core mineralogy, microfabric, grain size and suction response. This note has attempted to investigate these influential factors on five different expansive clay samples to enable further understanding of swell behaviour. Laser diffractometry tests were performed on the expansive clays to determine the clay-sized particle structure (

Journal ArticleDOI
TL;DR: In this paper, the influence of groundwater flow in a sandy layer on the temperature field during artificial freezing is studied, and the effect of seepage on the development of the frozen wall is considered.
Abstract: The influence of seepage on the development of the frozen wall must be considered when artificial ground freezing (AGF) is applied to the coarse-grained soil layers. In this paper, the influence of groundwater flow in a sandy layer on the temperature field during artificial freezing is studied. Model tests were carried out with different seepage velocity, and the temperature field changes of upstream and downstream as well as the development of the frozen wall were obtained. The experiment was numerically simulated using a finite element platform, COMSOL Multiphysics. The test showed that the frozen wall was symmetrical when there was no seepage, which was approximately elliptical. Under the seepage condition, the upstream and downstream frozen walls were asymmetrical, approximately heart-shaped. The asymmetry increased with the increase of seepage velocity and pipe spacing. When the seepage velocity increased, the closure time of frozen wall increased. The numerical simulation results and the experimental results were basically consistent. The asymmetry of the frozen wall under the seepage condition was quantitatively analyzed based on numerical simulations.

Journal ArticleDOI
TL;DR: A numerical-intelligent model for prediction of maximum surface settlement (Smax) of Tehran subway line 7 was modeled using the finite difference method (FDM) and the derived mathematical equation was prepared using the visual basic in the form of predictor software.
Abstract: Ground settlement due to excavation of shallow tunnels is a common phenomenon. To control the settlement, one should be able to predict it, and based on it he may consider required preventions and protections. There are different methods for predicting settlement, each having some strengths and weaknesses. The main weakness of these methods is that they do not consider enough effective parameters on the settlement. The numerical methods, contrary to the empirical and analytical methods, take into account the effects of a larger number of parameters. However, ideal selection of many parameters is associated with ambiguity and difficulty and is time-consuming. To overcome these issues, the intelligent methods are incorporated which are appropriate tools. The aim of this paper is to present a numerical-intelligent model for prediction of maximum surface settlement (Smax). At first, a section of Tehran subway line 7 was modeled using the finite difference method (FDM). Then a dataset including 100 Smax values were prepared for creating the intelligent model. Among the intelligent methods, the gene expression programming (GEP) method was selected to represent the mathematical equation and the built numerical-intelligent model explained a proper performance. The determination coefficient, R2, for both the training and testing phases was 0.976 and 0.931, respectively. At the end, the derived mathematical equation from the GEP model was prepared using the visual basic (VB) in the form of predictor software. According to accuracy of the prediction results, the presented equation and software are reliable and suitable as an alternative for the numerical modelling.

Journal ArticleDOI
TL;DR: In this paper, the authors report on physical model tests simulating erosion and sinkhole development due to cyclic leakages through defective sewers for five selected grading curves compatible with the Sewerage Code of Australia.
Abstract: Internal erosion through leaking sewers causes sinkholes in the non-karstic ground. As erosion resistance depends on particle-size distribution, improved erosion resistance of pipe embedment by modifying its gradation is worth study. This paper reports on physical model tests simulating erosion and sinkhole development due to cyclic leakages through defective sewers for five selected grading curves compatible with the Sewerage Code of Australia. Eroded soil mass, eroded soil properties, cavity initiation and evolution up to sinkhole failure were studied due to cyclic leakages through pipe cracks. Ground settlement during this process was also monitored using particle image velocimetry. Also, any potential to use existing geometric criteria which are proposed to assess internal stability in embankments to predict the risk of erosion through openings were also studied. Results indicate that poorly-graded sand with Dmax of 4.75 mm was highly susceptible to erosion through 10 mm wide cracks regardless of the fines percentage and the gradation. Remarkably, selected well-graded crushed rock with Dmax of 9.5 mm was highly resistive even through 30 mm wide openings. Modification of the existing standards for embedment materials in the current standard is recommended and as fine soil can create sinkholes even due to small pipe defects, the use of well-graded coarse sand or fine-gravel with about 15–20% medium-sized gravel particles is recommended.

Journal ArticleDOI
TL;DR: In this article, a series of dynamic triaxial tests were conducted on samples with multi-stage dynamic loading process under different confining pressures of 0.3, MPa, 0.4 and MPa.
Abstract: In order to explore the behavior of clay reinforced by polypropylene (PP) fiber, a series of dynamic triaxial tests were conducted on samples with multi-stage dynamic loading process under different confining pressures of 0.3 MPa, 0.4 MPa and 0.5 MPa. The soil physical properties were significantly affected by the seasonal freezing of the active layer. To simulate this effect, all samples were subjected to the freeze-thaw process of up to 15 cycles. Samples reinforced with 0.75% PP fiber showed the greatest dynamic strength, and a similar regularity was found for samples after 15 freeze-thaw cycles. The dynamic shear modulus decreased with the increase of confining pressure, but decreases with the increasing strain and number of freeze-thaw cycle. The dynamic shear modulus of samples with PP fiber is relatively larger than that of unreinforced samples. After 15 freeze-thaw cycles, the dynamic shear muduli of samples with 0.25%, 0.5% and 0.75% fiber increased by 27.3%, 50.1% and 63.6%, respectively, compared with the one of unreinforced samples at γ = 0.3% and σc = 0.3 MPa. The dynamic shear moduli of unreinforced sample and samples with 0.25%, 0.5% and 0.75% fiber content after 15 freeze-thaw cycles decreased by 7.9%, 7.6%, 5.4% and 6.3%, respectively, compared with the one before freeze-thaw cycle at γ = 0.05%. The damping ratio shows an increasing tendency with the increases of shear strain and fiber content. The damping ratio of samples reinforced with 0.25%, 0.5% and 0.75% fiber increased by 11.11%, 8.89% and 15.56%, respectively, compared with the one of unreinforced sample at γ = 0.005%. The Davidenkov model was adopted to describe the dynamic behavior of reinforced soil after freeze-thaw cycles at various confining pressures. The dependences of the normalized shear modulus on the shear strain amplitude are described. The behavior of the fiber after exposure to freeze-thaw cycles was analyzed by using Scanning Electron Microscope (SEM) method.

Journal ArticleDOI
TL;DR: In this paper, a series of large-scale drop hammer impact tests was carried out to investigate how effectively the rubber energy absorbing drainage sheets (READS) could attenuate impact loads and help mitigate ballast deformation and degradation.
Abstract: Ballasted tracks at transition locations such as approaches to bridges and road crossings experience increasing degradation and deformation due to dynamic and high impact forces, a key factor that decreases the stability and longevity of railroads. One solution to minimise ballast degradation at the transition zones is using rubber energy absorbing drainage sheets (READS) manufactured from recycled tyres. When placed beneath the ballast layer, READS distributes the load over wider area and attenuate of the load over a longer duration thus decreasing maximum stress, apart from reducing the energy transferred to the ballast and other substructure components. Subsequently, the track substructure experiences less plastic deformation and degradation. These mats also provide an environmentally friendly and cost-effective alternative. In this study, a series of large-scale drop hammer impact tests was carried out to investigate how effectively the READS could attenuate impact loads and help mitigate ballast deformation and degradation. Soft and stiff subgrade were used to investigate the load-deformation response of ballast (with and without READS), subjected to impact loads from a hammer dropped from various heights (hd = 100–250 mm). Laboratory test results show that the inclusion of READS helps to reduce the dynamic impact load transferred to the ballast layer resulting in significantly less permanent deformation and degradation of ballast, apart from significant attenuation of load magnitude and vibration to the underlying subgrade layers.

Journal ArticleDOI
TL;DR: In this paper, a compacted marl was treated with a new hydraulic binder composed of Crushed Granulated Blast Furnace Slag (CGBS) active by calcined eggshell waste (CES).
Abstract: Marls are considered difficult soils in the construction of road infrastructure. They are generally associated with high compressibility, high plasticity, and evolutionary behavior, resulting in many structural failures in the road embankment. The objective of this research is to study the mechanical behavior of a compacted marl treated with a new hydraulic binder composed of Crushed Granulated Blast Furnace Slag (CGBS) active by Calcined Eggshell Waste (CES). To conduct this research, unconfined compressive strength tests (UCS), soaked California Bearing Ratio (CBR) tests, and triaxial shear tests are performed for different cure periods. The specimens were prepared with a binder content, which varies between 0 and 15% by dry weight. The results indicate that the mechanical properties of the treated marl improved significantly. The addition of 15% of this new binder is capable of increasing the CBR index 22 times its initial value. Furthermore, an appreciable improvement in cohesion and internal friction angle is observed due to treatment, especially at later ages. The new hydrates produced by the pozzolanic reaction (C-S-H) were identified after treatment by Scanning Electron Microscopy (SEM). Overall, it appears that calcined eggshell activated blast furnace slag can be used as an effective binder for the stabilization of clay soils.

Journal ArticleDOI
TL;DR: In this article, the authors presented a numerical investigation on the interaction between buried rigid pipes and soils under downward relative movements, based on which a novel mathematical representation of the bearing force-displacement curve was derived.
Abstract: The downward resistance between pipes and soils dominates the serviceability and structural integrity of buried rigid pipelines when geohazard conditions such as ground subsidence and normal faults are encountered. This study first presented a numerical investigation on the interaction between buried rigid pipes and soils under downward relative movements, based on which a novel mathematical representation of the bearing force-displacement curve was derived. Sand backfills in the numerical model were characterized using plane-strain shear strength parameters, and the increment of elastic modulus with depth was accounted. Simulated results showed that the bearing resistance kept increasing with the relative displacement and the failure resistance was analogous to the local shear, rather than the general shear bearing capacity. The proposed force-displacement relationship consisted of a nonlinear region before the mobilization of failure resistance and a linear post-failure region. The rationality of proposed method was evaluated against experimental measurements reported in published studies and calculations from the commonly used method, which can provide a basis for assessing performance of buried rigid pipes under downward relative movement conditions.

Journal ArticleDOI
TL;DR: In this paper, a comparison between aggregates of steel slag and granite by means of monotonic and cyclic triaxial tests carried out on scaled down ballast specimens is presented.
Abstract: The ballast mechanical behavior is one of most important aspects governing the performance and safety conditions of railway track lines. Usually comprised of natural crushed rock, the research for alternative ballast materials becomes interesting both environmentally and economically. This paper presents a comparison between aggregates of steel slag and granite by means of monotonic and cyclic triaxial tests carried out on scaled down ballast specimens. The monotonic triaxial tests were conducted at three different confining pressures to failure and to critical state. The long-term cyclic tests (at least 106 cycles) were conducted in two stress paths compatible with heavy haul loadings. The results showed that the steel slag aggregate has higher values of strength parameters compared to the granite aggregate and better long-term deformability behavior, expressed by lower degradation and particle breakage and a faster tendency for stabilization the permanent deformation.

Journal ArticleDOI
TL;DR: In this paper, the authors evaluate the su of marine clay from Lianyungang in Jiangsu Province of China and determine the relationship between su and seismic piezocone test (SCPTU) parameters at the Liangyungang site.
Abstract: Undrained shear strength, s u is an important geotechnical parameter of soft clay. The seismic piezocone test (SCPTU) can provide valuable information regarding in-situ soil behavior and stratigraphy in geotechnical site investigation. Therefore, the relationships of s u with the data obtainable in SCPTU testing have long been a topic of research interest. The objective of this paper is to evaluate the su of marine clay from Lianyungang in Jiangsu Province of China. First, existing methods for obtaining the su values of clay soils from basic SCPTU penetrometer readings are reviewed. The relationships between su and SCPTU parameters at the Lianyungang site are then determined. su values derived from field vane testing and CPTU results are also discussed. The relationship between su and the pore pressure cone factor is proposed and the pore pressure cone factor is shown to be approximately about 8.03, providing a means to estimate su. A previously developed method of using maximum excess pore pressure is also utilized here for the overconsolidated clays within the stratigraphic sequence. Additionally, a relationship between su and shear wave velocity is proposed, linking stiffness with strength in a stiffness-strength correlation. The derived correlations are in accordance with those previously reported in the literature, and the results also showed that SCPTU tests can be used comprehensively to estimate the su of Jiangsu marine clay.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the mechanical properties of lean clay under the freeze-thaw (F-T) and thermostatic-curing (T-C) cycles.
Abstract: Using undrained triaxial shear tests, this study investigates the mechanical properties of lean clay under the freeze-thaw (F-T) and thermostatic-curing (T-C) cycles. The shear strength and Duncan-Chang model parameters, considering both the number of cycles and the freezing temperatures, were calculated from the hardening strain-stress curves. Compared to the shear strength in the T-C group, the F-T effect causes irreversible attenuation of shear strength in specimens with water content of 17.6%. Except for the damage ratio, the other four model parameters in the T-C group are all greater than those in the F-T group at the same cycle. Different fitting functions simply and directly reveal the trend of the model parameters with the cycles. The freezing rate due to freezing temperature induces a significant difference in water redistribution and dry density from the core to the surface layer of the specimen, which is why the model parameter and its fitting parameters don’t monotonically decrease with stepwise-reduced freezing temperatures. The gray correlation degree shows that the freezing temperature cannot be ignored when considering the F-T effect. The generalized Hooke's Law in principal-stress form demonstrates the applicability of the Duncan-Chang model while considering the F-T effect and the T-C effect.

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TL;DR: In this paper, a comparative analysis between the two track types is presented in terms of ground vibration with emphasis given to the influence of the stiffness and inertial parameters of the two tracks forms.
Abstract: With the development of non-ballasted track forms (often referred to as slab tracks) over the few last decades, it is important to understand their behaviour with respect to ground-borne vibration compared with the traditional ballasted tracks. This is important in deciding between the use of the two track forms. The present work aims to quantify the differences between slab tracks and ballasted tracks numerically by using the MOTIV model. This is a general and fully coupled three-dimensional model that works in the wavenumber-frequency domain. It can predict the vibration levels of the track and the ground due to the gravitational loading of a passing train and the wheel and rail unevenness. A comparative analysis between the two track types is presented in terms of ground vibration with emphasis given to the influence of the stiffness and inertial parameters of the two track forms. It is shown that, for the same fastener stiffness there are only small differences in ground vibration behaviour, with the mass of the track slab leading to reductions of 1–3 dB at frequencies above 16 Hz. However, if softer rail fasteners are used in the slab track, as is usual, this leads to further reductions above 63 Hz. The critical velocity on soft soil is also considered. Although there is little difference between the different tracks for a homogeneous ground, for grounds with a soft surface layer the critical velocity is increased by the slab bending stiffness. The maximum rail displacement is also smaller for a slab track than the equivalent ballasted track.

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TL;DR: In this paper, the authors used multiple linear regression (MLR), nonlinear regression and backpropagation artificial neural network algorithms to predict the resilient modulus of fine-grained materials based on 3709 soil samples collected from the Long-Term Pavement Performance (LTPP) website.
Abstract: For the realistic prediction of pavement performance, it is very important to accurately characterize the mechanical behavior of unbound material layers and subgrade soils. In pavement analysis using the elastic layered theory, material properties in terms of dynamic elastic modulus and Poisson’s ratio are the major input parameters. The dynamic elastic modulus of pavement materials or resilient modulus (MR) is measured by conducting repeated load triaxial compression tests typically not available to highway authorities due to the high costs involved in acquiring such high-performance equipment and/or lack of knowledge on how to operate this specialized equipment. Therefore, pavement engineers are obligated to use pavement design methodologies based on empirical tests. The main objective of this study is to use multiple linear regression (MLR), nonlinear regression and backpropagation artificial neural network algorithms to develop models to predict the resilient modulus of fine-grained materials based on 3709 soil samples collected from the Long-Term Pavement Performance (LTPP) website. The key input parameters selected for this study are: the confining pressure ( σ 3 ), nominal maximum axial stress ( σ 1 ), percent of silt (S), Liquid Limit (LL), Plasticity Index (PI), percent passing number 200 sieve (P#200), maximum dry density (ρmax-dry), percent of clay (C), optimum moisture content (wopt), and laboratory-determined resilient modulus. Results revealed that the change of wopt has a higher effect on MR compared with the change in density, the percent fines, percent of silt, percent of clay, confining pressure, PI and LL but less than the effect of changing axial stress. In addition, the best modeling technique to predict the resilient modulus of fine-grained soil was found to be the Artificial Neural Network (ANN) followed by the nonlinear regression and finally the MLR.

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TL;DR: In this paper, a 3D finite element model of the behavior of reinforced concrete tunnel linings is developed using the new PLAXIS concrete model, which accounts for increased soil stiffness at small strains.
Abstract: Earth pressure balance (EPB) shield-driven tunnelling involves a complex soil-structure interaction problem, where performance is heavily influenced by stress history and its development during construction. Numerical modelling must therefore focus on selecting appropriate constitutive models for soils and structures, simulating construction procedures and sequences, and modelling the soil/structure interface. Reliable numerical models to predict expected settlements, lining pressures and other design parameters are essential for safe tunnel design. This paper discusses these factors in detail by utilizing a well-documented case study of twin tunnels in Shanghai. A 3D finite element model of the behaviour of reinforced concrete tunnel linings is developed using the new PLAXIS concrete model. Predictions of four different advanced soil constitutive models are compared with measured field results to assess the model effectiveness and suitability. The undrained behaviour of the saturated soft silty clay soil at the tunnelling site is studied during and after advancement of the shield tunnelling machine. The comparison matrix includes surface settlement troughs along transverse sections, and changes developing in earth and pore water pressures around the tunnel. The HSSmall soil model, which accounts for increased soil stiffness at small strains, was found to be the most suitable for addressing these problems.

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TL;DR: In this article, the authors evaluated the performance of the Geosynthetic Reinforced Soil-Integrated Bridge System (GRS-IBS) in terms of lateral facing deformation, strain distribution along geosynthetics, and the location of potential failure zone (locus of maximum strain) subjected to service loading.
Abstract: This paper presents the evaluation of the performance of the Geosynthetic Reinforced Soil-Integrated Bridge System (GRS-IBS) in terms of lateral facing deformation, strain distribution along geosynthetics, and the location of potential failure zone (locus of maximum strain) subjected to service loading. Simulations were conducted using two-dimensional (2D) PLAXIS 2016 Finite Element (FE) program. The hardening soil model proposed by Schanz et al. (1999) was used to simulate the behavior of the backfill material; the interface between the backfill materials and the reinforcement was simulated using the Mohr-Coulomb frictional model, and the reinforcement and facing block were simulated using the linear elastic model. The numerical model was first verified using results of a field case study conducted at the GRS-IBS of Maree Michel Bridge, Louisiana. A parametric study was then carried out to investigate the effects of abutment height, span length, reinforcement spacing, and reinforcement stiffness on the performance of the GRS-IBS. The results of the FE analyses indicate that the abutment height and span length have significant impact on the maximum strain distribution along the geosynthetic, and the lateral facing displacement. It was noted that the reinforcement stiffness has a significant impact on the GRS-IBS behavior up to a certain point, beyond which the effect tends to decrease contradictory to the reinforcement spacing that has a consistent relationship between the GRS-IBS behavior and the reinforcement spacing. The results also indicate that the reinforcement spacing has greater influence on the lateral facing displacement than the reinforcement stiffness for the same reinforcement strength to spacing ratio (Tf/Sv), mainly due to the composite behavior resulting from closely reinforced soil.

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TL;DR: In this paper, the effect of freeze-thaw cycles on the resilient modulus and permanent deformation of reclaimed asphalt pavement (RAP)/natural aggregate mixtures for the construction of unbound base layers was evaluated.
Abstract: This paper presents an experimental study to evaluate the effect of freeze-thaw cycles on the resilient modulus and permanent deformation of reclaimed asphalt pavement (RAP)/natural aggregate mixtures for the construction of unbound base layers. A repeated load triaxial test was carried out on RAP and crushed limestone mixtures with varying RAP content (0%, 20%, 35%, and 50% of dry mass), on both standard samples and samples exposed to fourteen freeze-thaw cycles. Freeze-thaw conditioning resulted in a decrease of resilient modulus values and an increase of permanent deformation. This trend was most pronounced on the mixture with 0% RAP. Mixtures with 35% RAP exhibited stable resilient behavior and lowest change in accumulation of permanent deformation after freeze-thaw conditioning. With an increase in RAP content, the sensitivity of the mixtures to freeze-thaw cycling in regards to resilient and permanent deformation behavior is reduced, but only up to a certain RAP content.