Quantization effects and convergence properties of rigid formation control systems with quantized distance measurements

In this paper, we discuss quantization effects in rigid formation control systems when target formations are described by inter-agent distances. Because of practical sensing and measurement constraints, we consider in this paper distance measurements in their quantized forms. We show that under gradient-based formation control, in the case of uniform quantization, the distance errors converge locally to a bounded set whose size depends on the quantization error, while in the case of logarithmic quantization, all distance errors converge locally to zero. A special quantizer involving the signum function is then considered with which all agents can only measure coarse distances in terms of binary information. In this case, the formation converges locally to a target formation within a finite time. Lastly, we discuss the effect of asymmetric uniform quantization on rigid formation control.Comment: 29 pages, International Journal of Robust and Nonlinear Control 201

Field Measurements of Spontaneous Potential (SP) for Smart Well Monitoring and Control. A Field Test in the UK Chalk Aquifer

Imperial Users onl

Application of Shock Mats in Rail Track Foundation Subjected to Dynamic Loads

© 2016 The Authors. Published by Elsevier B.V. Rail track substructure (ballast, subballast and subgrade) is the most essential component of the railway system in view of track stability. The ballast is the largest component of the track substructure and it is the key load-bearing stratum packed with rock aggregates underneath and around the sleepers, thereby providing structural support against dynamic stresses caused by moving trains. However under large dynamic stresses exerted by heavy haul and high speed trains, the degradation of track substructure including ballast becomes significant. This in turn affects the track stability and creates frequent maintenance, thus increasing the life cycle cost of the rail network. Therefore, mitigating degradation of the ballast layer is vital in view of track longevity. In recent years, the use of resilient soft pads (shock mats) above the ballast (i.e. Under Sleeper Pad, USP) and below the ballast (i.e. Under Ballast Mat, UBM) has become a common practice. Many countries, including Australia have adopted the use of resilient pads in the rail track foundation. Currently, the studies on resilient mats are mostly limited to the reduction of vibration and noise. There is a lack of proper assessment of the geotechnical behavior of ballast when used along with shock mats. This paper provides an assessment of the triaxial behavior of the track substructure with and without shock mats under dynamic loading condition. A numerical model was developed based on the modified stress-dilatancy approach to capture the stress-strain and volume change behavior of ballast during impact loading. Model predictions are compared with laboratory results. It was found that the shock mats provide significant advantages in terms of reduced particle breakage and enhanced track stability

A full-scale laboratory investigation into railway track substructure performance and ballast reinforcement

To reduce railway track maintenance costs and meet the growing demand for rail travel the railway industry needs to significantly increase the performance of old existing tracks and design any new tracks accordingly. In this thesis, a new full-scale laboratory Geopavement & Railway Accelerated Fatigue Testing (GRAFT) facility at Heriot-Watt University is developed to study the performance of both unreinforced and reinforced railway track substructure systems. The new GRAFT facility enables accelerated testing of full-scale railway tracks and innovative railway products under realistic railway loading conditions. The unreinforced track systems represent typical railway tracks in the UK while the reinforced track systems represent sections of track implemented with various geosynthetic products. GRAFT consists of a track constructed within a steel tank. The track comprises a 750mm clay subgrade layer overlain by a clay formation layer overlain by a 300mm ballast layer. The track includes three hardwood sleeper sections overlain by an I-section steel beam which has similar stiffness properties to a BS 113 A rail section. Cyclic loading is applied to the track from a hydraulic testing machine with the centre sleeper directly under the loading actuator. The loading mechanism replicates a repeated quasi static single wheel load on the central sleeper of one half of a 3m long section of railway track. Based on the results found from the testing programme in GRAFT empirical relationships are developed between the unreinforced track performance in terms of track settlement and stiffness and the subgrade modulus, applied load and number of applied cycles. These relationships fit the GRAFT data presented in this thesis well and it is thought that they could be used (tentatively) to estimate track settlement on track after tamping/ballast renewal/new track. These relationships are shown to be consistent with other well known track settlement models and they indicate that subgrade stiffness and applied vertical load are two of the most significant parameters that influence track substructure deterioration. The results found from the reinforced track tests quantify the improvement in track performance available with each product under various track conditions. Two ballast ii reinforcement products have been tested; XiTRACK reinforcement and geocell reinforcement, along with a reinforced geocomposite used primarily for separation at the ballast/subgrade interface. In addition, a geocomposite product designed to replace a traditional sand blanket, used on the tracks where severe subgrade erosion conditions prevail, has been tested in GRAFT under flooding conditions. The most significant results show that XiTRACK reinforcement can considerably improve the performance of railway tracks while the performance of the track implemented with the sand blanket replacement product indicates that currently a traditional sand blanket with a geotextile separator is the recommended option for tracks with subgrade wet spots. From all the data recorded empirical settlement models are proposed for each of the geosynthetics compared for reinforcement purposes. These models form the basis for reinforced track design graphs that could potentially be used to form part of an initial cost-benefit analysis of different track reinforcement techniques considered for improving track performance and reducing maintenance. In order to use the track settlement design graphs developed within this thesis (in the field) a reliable measure of subgrade stiffness needs to be made on track. A reliable insitu measuring device could enhance railway site investigations. Several in-situ measuring devices that could potentially be used to measures subgrade stiffness and strength in the field have been tested within GRAFT. The devices studied include the Dynamic Cone Penetrometer (DCP), Light Falling Weight Deflectometer (LFWD), Pocket Penetrometer and Proving Ring Penetrometer. The accuracy of these devices is compared to Plate Load Tests (PLT) and unconfined compression strength tests and suggestions towards the use of such devices on track made. The results indicate that the DCP has the potential to be a quick and accurate in-situ measuring device for railway track site investigations. The GRAFT facility and the results found in GRAFT have been validated using a basic static 3D FE computer model termed SART3D (Static Analysis of Railway Track 3D). The program has been calibrated to GRAFT by modifying the FE mesh for the dimensions of GRAFT and inputting the GRAFT track properties. The validated results from this thesis have direct practical implications to the railway industry in terms of iii design recommendations on how best to investigate and improve key geotechnical parameters that influence railway track performance and hence reduce maintenance costs and extend asset life. A review of current design procedures used in the railway industry is given and a new design procedure is suggested to reduce track maintenance and offer an optimised design and maintenance strategy

Eleventh International Conference on the Bearing Capacity of Roads, Railways and Airfields

Innovations in Road, Railway and Airfield Bearing Capacity – Volume 2 comprises the second part of contributions to the 11th International Conference on Bearing Capacity of Roads, Railways and Airfields (2022). In anticipation of the event, it unveils state-of-the-art information and research on the latest policies, traffic loading measurements, in-situ measurements and condition surveys, functional testing, deflection measurement evaluation, structural performance prediction for pavements and tracks, new construction and rehabilitation design systems, frost affected areas, drainage and environmental effects, reinforcement, traditional and recycled materials, full scale testing and on case histories of road, railways and airfields. This edited work is intended for a global audience of road, railway and airfield engineers, researchers and consultants, as well as building and maintenance companies looking to further upgrade their practices in the field

The geomechanical behaviour of peat foundations below rail-track structures

This thesis presents the results of research conducted to define the response of peat foundations underlying railway embankments to heavy axle loads. Three field sites were investigated, two in Northern Alberta on Canadian National Railway’s Edson and Lac-La-Biche subdivisions, and one on the Lévis subdivision in southern Quebec. The scope of this thesis is fourfold: the development and installation of instrumentation; the laboratory testing of peat specimens retrieved from each site; the development of a conceptual model for the behaviour of peat beneath an embankment subjected to heavy axle loads; and finally, the modelling of the strength of the peat foundations relative to the applied loads. The first component of this research included the development and installation of instrumentation to measure in situ the distribution and magnitude of strain and pore pressure generation. The development included the assembly of instrumentation systems to measure all of the required parameters, and the development of the ShapeAccelArrayTM (SAA) from Measurand Inc. to measure horizontal cyclic motion under train loading. It was found the SAA, as provided by the manufacturer, was not able to provide accurate measurements of displacement. A method for determining the magnitude of cyclic displacement from the output of the MEMS accelerometers was developed from the laboratory testing data done as part of this study. This resulted in the ability to obtain a profile of cyclic displacement with depth. The second component of the research was the laboratory testing of peat specimens retrieved from the sites. Consolidated undrained triaxial tests and direct shear tests were conducted on remoulded peat, remoulded peat fibre and Shelby specimens of peat to investigate the fundamental mechanisms which control the strength of peat. The results were analyzed within the frameworks of elastic behaviour of cross-anisotropic materials and shear strength of fibre-reinforced soil. The test results from samples collected at all three sites were compared and the influence of peat fibres on the undrained strength was explored. The third component was the development of conceptual models for the undrained behaviour of peat, and peat foundations subjected to moving axle loads. A model for peat was developed from the cross-anisotropic response observed during the laboratory testing and correlations to fibre reinforced soil literature. This material model was then applied to the spatial distribution of stresses and orientation of principal stresses below embankments. The final component of the project was an analysis of the field data collected from all three sites to provide the magnitude and distribution of strain and pore pressure generation developed within the peat foundations. Further analysis of the measured response was conducted with both with calculations of effective stress paths and finite element modelling to determine the distribution of stress, the locations of potential yielding within the foundations and to determine how close to yielding the peat is under the maximum applied stresses. The results of this thesis provide new tools for the railway industry to evaluate the response and stability of railway embankments over peat foundations. The development of the SAA allows for the in situ measurement of the magnitude and distribution of displacement, and from this the strain, within soft soils under heavy axle loading. The conceptual models developed and applied to the undrained response of peat foundations provide a framework to evaluate the stability of railway embankments over soft foundations. The results of the application of this framework to the study sites included in this thesis provide context for further investigations