The Experts below are selected from a list of 15297 Experts worldwide ranked by ideXlab platform
J. T. Shahu - One of the best experts on this subject based on the ideXlab platform.
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Reinforcement and mud-pumping benefits of geosynthetics in railway tracks: Numerical analysis
Geotextiles and Geomembranes, 2016Co-Authors: Sowmiya Chawla, J. T. ShahuAbstract:Abstract Laboratory tests were conducted on track materials to evaluate constitutive parameters for three different sets of constitutive relationships, namely, non-linear analysis, straight analysis and coupled analysis. The model test results of finite element analyses using various constitutive relationships are compared. The coupled analysis provided a better prediction of the measured results compared to the non-linear and straight analyses. A detailed parametric study of a prototype track was then performed using the coupled analysis to evaluate the effects of geosynthetics on track reinforcement and mud-pumping reduction. Geogrid reinforcement was found to significantly reduce tie displacement only at low Subgrade modulus values and effective Subgrade shear strength parameters. Geogrid reinforcement was equally effective at reducing tie displacement within the subballast thickness range of 450–1000 mm. High excess pore water pressure coupled with low effective cohesion gives rise to mud-pumping problems in silty soil Subgrades. The provision of geotextiles at the Subgrade surface facilitates quick in-plane drainage and dissipation of pore water pressure. Thus, excess pore water pressure was observed to be lower in a geotextile-stabilized track compared to that in an unreinforced track, indicating reduction in mud-pumping potential in the former.
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reinforcement and mud pumping benefits of geosynthetics in railway tracks model tests
Geotextiles and Geomembranes, 2016Co-Authors: Sowmiya Chawla, J. T. ShahuAbstract:Abstract The railroad track is one of the few geosynthetic applications in which a geosynthetic is used for multiple functions, namely, reinforcement, separation, filtration and drainage. In the present study, static and cyclic tests were performed on full-panel railway track models laid on compacted soil Subgrades. Tests were performed on model tracks with two different thicknesses of subballast layers and laid on two different Subgrade soils, namely, Dhanaury clay and Delhi silt. Model tracks were adequately instrumented to record induced stresses and displacements in the track. Model tracks were reinforced with a geogrid or a geotextile or both at suitable interfaces. Track conditions after heavy rainfall were simulated. The model tracks reinforced with a geogrid at the ballast–subballast interface were more effective in reducing the tie displacements, ballast and subballast strains and Subgrade displacements compared to the model tracks reinforced with a geotextile at the subballast–Subgrade interface when Dhanaury clay was used as the Subgrade soil. Conversely, the model tracks reinforced with a geotextile performed better with respect to reduced tie displacement, Subgrade displacement and subballast strain compared to the model tracks reinforced with a geogrid when Delhi silt was used as the Subgrade soil.
Navneet Garg - One of the best experts on this subject based on the ideXlab platform.
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time dependent drucker prager cap model coupled with panda pavement analysis using nonlinear damage approach to predict rutting performance of flexible pavements
Construction and Building Materials, 2020Co-Authors: Masoud K Darabi, Rashmi Kola, Dallas N Little, Navneet GargAbstract:Abstract An extended Drucker-Prager-Cap-Creep (D-P-Cap-Creep) constitutive relationship is coupled with the PANDA (Pavement Analysis using Nonlinear Damage Approach) model to predict rutting in granular and asphalt layers of flexible airfield pavements, respectively. The presented model treats the pavement structure as a system and predicts rutting performance as the summation of permanent deformation in the Subgrade, subbase, base, and asphalt layers. In addition to capturing the effects of densification and shear on permanent deformation with the D-P-Cap model, a creep law is defined to capture time- and rate-dependent behavior of granular layers and the Subgrade. Simulation results of D-P-Cap-Creep constitutive relationship in conjunction with PANDA are validated against test sections of Construction Cycle 3 (CC-3) at the National Airport Pavement Test Facility (NAPTF). Presented results demonstrate that incorporation of time hardening Creep law to D-P-Cap model resulted in reduction in deviation between field measurements and model predictions. It is argued that the D-P-Cap-Creep constitutive relationship may have a more pronounce effect on rutting evolution of flexible pavements with moist Subgrades with high clay contents.
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performance of flexible pavements over two Subgrades with similar cbr but different soil types silty clay and clay at the faa s national airport pavement test facility
Airfield and Highway Pavements. The 2008 Airfield and Highway Pavements ConferenceAmerican Society of Civil Engineers, 2008Co-Authors: Navneet Garg, Gordon F HayhoeAbstract:The National Airport Pavement Test Facility (NAPTF) is located at the FAA William J. Hughes Technical Center, Atlantic City International Airport, New Jersey. It is used to generate full-scale pavement response and performance data for development and verification of airport pavement design criteria. During the Construction Cycle 5 — Test Strip, four flexible pavement test items were subjected to accelerated traffic tests using representative aircraft landing gear configurations. Pavements were constructed over two Subgrades with similar california bearing ratio (CBR) (approximately 3) but different soil types (silty clay and clay). Two test items (LFC1-N and LFC1-S) were designed to fail in approximately 100 passes (4-wheel gear and 55,000 lbs wheel load) and the pavement structure consisted of 2.5-inch P401 HMA surface, 8-inch P209 crushed stone base, and 16-inch P154 subbase. The other two test items (LFC2-N and LFC2-S) were designed to fail in approximately 2000 passes and the pavement structure consisted of 2.5-inch P401 HMA surface, 8-inch P209 crushed stone base, and 24-inch P154 subbase. The test items exhibited permanent deformations at the surface (evidenced by rut depths) of over 4 inches and upheaval at the sides of the ruts in excess of 1 inch. This paper presents the results from Heavy Weight Deflectometer (HWD) tests, trafficking tests (rut depth measurements) and posttraffic tests (trenching study). The trenching involved removal of the P-401 AC layer, the P-209 base, and the P-154 subbase layer to reveal the Subgrade interface and subsequent Subgrade layers below. Tests conducted on the pavement component layers included CBRs, in situ densities and moisture contents. Layer interface profile measurements from trench walls clearly show shear flow in the Subgrade, with vertical movement of the Subgrade material in the upheaval areas. This information will be used for developing thickness design procedures and load evaluation of airport pavements.
Olivier Buzzi - One of the best experts on this subject based on the ideXlab platform.
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Full-scale model testing on the dynamic behaviour of weathered red mudstone Subgrade under railway cyclic loading
Soils and Foundations, 2019Co-Authors: Chonglei Zhang, Guanlu Jiang, Olivier BuzziAbstract:Abstract Although weathered red mudstone (WRM) is widely distributed in the southwest of China, its suitability as a fill material for the Subgrade bed of a high-speed railway (HSR) has not been comprehensively investigated. This paper presents the results of a field full-scale model testing of the cyclic loading and response of a railway track-Subgrade system for the Dazhou-Chengdu Railway, where some WRM has been used in a newly designed Subgrade structure. A control section of the HSR was also built using a traditional Subgrade bed (Group A&B material) to compare the performances of the different sections. To better understand the dynamic characteristics and cumulative deformation of the two types of Subgrade, the dynamic actions of different axle loads and different train speeds were simulated using specifically designed track-cyclic-loading equipment. The transverse and vertical distributions of the dynamic stress, dynamic displacement and acceleration of the track-Subgrade system were measured and evaluated. The influence of the wheel axle load on the growth factor of the dynamic parameters, the vertical attenuation coefficient of the dynamic stress, and the effect of using WRM in the Subgrade on the post-construction settlements were investigated. The tests enabled the development of cumulative settlement laws with railway loading for the two types of Subgrade. Although the dynamic parameters and cumulative settlement of the WRM Subgrade are always greater than those of better-quality material (Group A&B Subgrade), they comply with HSR regulations. In conclusion, the results demonstrated that weathered red mudstone can be used as a filling material in the newly designed Subgrade structure for HSRs.
Junhui Peng - One of the best experts on this subject based on the ideXlab platform.
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recycled aggregates from construction and demolition wastes as alternative filling materials for highway Subgrades in china
Journal of Cleaner Production, 2020Co-Authors: Junhui Zhang, Le Ding, Feng Li, Junhui PengAbstract:Abstract With the rapid advancement of urbanization in China, a huge amount of construction and demolition wastes (CDW) are generated. Recycling CDW into Subgrade materials is a promising way to process these wastes, with significant environmental and economic benefits. But very little work has been done in this field. Therefore, based on a CDW Subgrade construction case in Beijing, the physical and chemical properties of the CDW materials were analyzed. Then the construction procedures of the CDW Subgrade were presented, and a series of tests (compaction degree test, settlement observation, Portable Falling Weight Deflectometer test) were carried out. At the same time, the effects of different loose paving thicknesses, cycles of strong vibration on the Subgrade performances were assayed. Subsequently, grading analysis of the CDW particles, plate load test and Beckman beam deflection test were performed to evaluate the construction quality. According to the test results, the construction technologies of the CDW Subgrade, such as the optimum loose paving thicknesses and cycles of strong vibration, were determined. And then, the post-construction settlement monitor and radar survey were conducted for Subgrades filled with CDW and soil to further analyze the applicability of CDW. The results show that recycled CDW aggregates with proper grading and strict construction technologies perform well. The Subgrade filled with recycled CDW has a smaller deformation than that of the soil Subgrade. Finally, the life cycle assessments (LCA) of two treating schemes of CDW were conducted to analyze the environmental benifits: recycling utilization as Subgrade materials and directly landfilling. If the Subgrade is filled with the recycled CDW aggregates, CDW will be consumed in large quantities and the environmental impactions of eutrophication and ecotoxicity can be reduced obviously.
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modeling humidity and stress dependent Subgrade soils in flexible pavements
Computers and Geotechnics, 2020Co-Authors: Junhui Peng, Junhui Zhang, Yongsheng Yao, Anshun ZhangAbstract:Abstract This study aimed to develop a finite element model to simulate the flexible pavement structure by considering the nonlinear characteristics of Subgrade soils which are related to humidity and stress. First, an analytical model was proposed and proven to quantify the effect of the humidity and stress on the resilient modulus of Subgrade soils. Second, a UMAT was programmed to characterize nonlinear moisture and stress-sensitive relationship of Subgrade soils. Then, the humidity field values of Subgrade were calculated by GEOSTUDIO and verified by field measurement. Meanwhile, the humidity field values were imported into ABAQUS through MATLAB. Finally, the UMAT was implemented in the finite element model of flexible pavement structures. The finite element simulation indicated that the distribution of moisture content of Subgrade significantly affects the resilient modulus distribution of Subgrade and critical response of pavement structures. Resilient modulus of Subgrade soils in the vicinity of load area are significantly larger than those far away the load area. The surface deflection, the tensile stress at the bottom of inorganic binder base, and the compressive strains on the top of Subgrade increase greatly with the initial humidity field condition to the equilibrium humidity field condition.
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numerical method of flexible pavement considering moisture and stress sensitivity of Subgrade soils
Advances in Civil Engineering, 2019Co-Authors: Jianlong Zheng, Junhui Zhang, Yongsheng Yao, Junhui PengAbstract:Weaknesses of the Subgrade structure induce the asphalt surface diseases and shorten the service life of flexible pavement. However, the resilient modulus (Mr) of Subgrade soils is difficult to be evaluated directly since the Subgrade is hidden and covered by the granular or asphalt layer. This study aimed to establish a numerical approach to predict the dynamic behavior of flexible pavements considering the stress sensitivity and moisture variation of Subgrade soils. Firstly, 2D FEM simulations of flexible pavements were performed with half-sine loadings. A constitutive model of Subgrade soils was proposed to incorporate soil suction and octahedral shear stress. It was validated using the laboratory triaxial test data of 3 selected soils. Then, the developed model was programmed by the user-defined material subroutine (UMAT) in the software ABAQUS. Subsequently, the validity of FEM model was verified by the laboratory tank model. Finally, the effect of moisture contents on the dynamic response of pavement structures was studied by tensile stress and vertical compressive strain. Results show that the surface deflection of the FEM model is similar to that of the actual pavement structure with the R2 of 98.44%. The developed UMAT program is reliable since the distribution of Mr in the FEM model is influenced by the stress and moisture condition of Subgrade soils. When the moisture content is increased by 63%, the average Mr of Subgrade soils is decreased by 18.7%. Meanwhile, the stiffness softening of Subgrade soils increases vertical compressive strain at the top of the Subgrade and the tensile stress at the bottom of the surface layer. It is interesting that the developed model can be applied to analyze the fatigue cracking of both Subgrade and surface layers in the future.
Wei Wang - One of the best experts on this subject based on the ideXlab platform.
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Behavior and Control of the Ballastless Track-Subgrade Vibration Induced by High-Speed Trains Moving on the Subgrade Bed with Mud Pumping
Shock and Vibration, 2019Co-Authors: Junjie Huang, Qian Su, Wei WangAbstract:This paper investigates behavior and control of the ballastless track-Subgrade vibration induced by high-speed trains under mud pumping occurring in the Subgrade bed. The characteristics of mud pumping occurring in the Subgrade bed under the ballastless track structure are analyzed by visual observation and nondestructive testing. Then, based on the injection of the low-viscosity epoxy resin (LVER), the repair procedures for the mud pumping are proposed. A variety of on-site tests are performed on the ballastless track-Subgrade with and without mud pumping and also after mud pumping reinforcement to analyze the vibration of the ballastless track-Subgrade under the high-speed trains. The test results show that mud pumping can significantly increase the vertical vibration acceleration and displacement of the ballastless track structure and slightly decrease the vibration of Subgrade surface. After mud pumping reinforcement, the abnormal vibration of the ballastless track-Subgrade can be effectively controlled to make the vibration close to normal. In addition, the vibration ratio of the Subgrade surface to the concrete base is proposed as a way to evaluate the effectiveness of the reinforcement of the mud pumping using the LVER, based on the vibration attenuation feature of the ballastless track-Subgrade.
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influence of differential settlement on pavement structure of widened roads based on large scale model test
Journal of rock mechanics and geotechnical engineering, 2011Co-Authors: Xiaolin Weng, Wei WangAbstract:Abstract This study introduced at first the background of numerous highway widening projects that have been developed in recent years in China. Using a large ground settlement simulator and a fiber Bragg grating (FBG) strain sensor network system, a large-scale model test, with a similarity ratio of 1:2, was performed to analyze the influence of differential settlement between new and old Subgrades on pavement structure under loading condition. The result shows that excessive differential settlement can cause considerable tensile strain in the pavement structure of a widened road, for which a maximum value (S) of 6 cm is recommended. Under the repetitive load, the top layers of pavement structure are subjected to the alternate action of tensile and compressive strains, which would eventually lead to a fatigue failure of the pavement. However, application of geogrid to the splice between the new and the old roads can reduce differential settlement to a limited extent. The new Subgrade of a widened road is vulnerable to the influence of dynamic load transferred from the above pavement structures. While for the old Subgrade, due to its comparatively high stiffness, it can well spread the load on the pavement statically or dynamically. The test also shows that application of geogrid can effectively prevent or defer the failure of pavement structure. With geogrid, the modulus of resilience of the Subgrade is increased and inhomogeneous deformation can be reduced; therefore, the stress/strain distribution in pavement structure under loading condition becomes uniform. The results obtained in this context are expected to provide a helpful reference for structural design and maintenance strategy for future highway widening projects.
