Analysis of permanent deformations of railway embankments under repeated vehicle loadings in permafrost regions

By large-scale dynamic tests carried out on a traditional sand-gravel embankment at the Beilu River section along the Qinghai-Tibet Railroad, we collected the acceleration waveforms close to the railway tracks when trains passed. The dynamic train loading was converted into an equivalent creep stress, using an equivalent static force method. Also, the creep equation of frozen soil was introduced according to the results of frozen soil rheological triaxial tests. A coupled creep model based on a time-hardening power function rule and the Druker-Prager yield and failure criterion was estab- lished to analyze the creep effects of a plain fill embankment under repeated train loads. The temperature field of the embankment in the permafrost area was set at the current geothermal conditions. As a result, the permanent deformation of the embankment under train loading was obtained, and the permanent deformation under the train loads to the total embankment deformation was also analyzed.

Use of Unconventional Aggregates in Hot Mix Asphalt Concrete

The study investigates use of dolomite sand waste as filler or/and sand material plus BOF steel slag as fine and coarse aggregate for design of high performance asphalt concrete.Both environmental and economic factors contribute to the growing need for the use of these materials in asphalt concrete pavements.This is particularly important for Latvia,where local crushed dolomite and sandstone does not fulfill the requirements for mineral aggregate in high and medium intensity asphalt pavements roads.Annually 100 to 200 thousand tons of steel slag aggregates are produced in Latvia.However,it has not been used extensively in asphalt pavement despite its high performance characteristics.Dolomite sand waste,which is byproduct of crushed dolomite production,is another widely available polydisperse by-product in Latvia.Its quantity has reached a million of tons and is rapidly increasing.This huge quantity of technological waste needs to be recycled with maximum efficiency.Various combinations of steel slag,dolomite sand waste and conventional aggregates were used to develop AC 11 asphalt concrete mixtures.The mix properties tests include resistance to permanent deformations(wheel tracking test,dynamic creep test)and fatigue resistance.Laboratory test results showed that asphalt concrete mixtures containing steel slag and local limestone in coarse portion and dolomite sand waste in sand and filler portions had high resistance to plastic deformations and good resistance to fatigue failure.

New approach for calculating permanent deformation in asphalt pavement

A new approach using the Fiber Bragg Grating(FBG)sensor and viscoelastic model to monitor and analyze the internal strain and temperature of asphalt pavement is proposed.Some parameters including peak strain,temperature and loading time were calculated with the application of multi-dimensional sensors group.These parameters were incorporated with viscoelastic model of five units to evaluate the permanent deformation of pavement.An application example was conducted,and the results show that it is feasible to analyze and calculate the permanent deformation of pavement structures with FBG sensors.

A Mechanical Model for Three-phase Permanent Deformation of Asphalt Mixture under Repeated Load

On basis of the Burgers model, a new model consisting of modified dashpot and Van Der Poel model was derived from rheological and viscoelastic theory. Subsequently, triaxial repeated load permanent deformation tests of AC16 asphalt mixtures were conducted to validate this new developed model. Parameters of new developed model were obtained by a nonlinear regression analysis of test data, and then permanent strains and flow number of each mixture were calculated. The experimental results prove that the new developed model can well describe three phases permanent deformation of asphalt mixture under repeated load and it can be used for pavement mechanical analysis and rutting prediction.

Dynamic Risk Analysis of Permanent Deformation of Sea Embankment

For evaluation of the permanent deformation of a sea embankment under stochastic earthquake excitation, a robust dynamic risk analytical method is presented based on conventional permanent deformation analysis and stochastic seismic response analysis. This method can predict not only the mean value of maximum permanent deformation but also the reliability corresponding to different deformation control standards. The earthquake motion is modelled as a stationary Gaussian filtered white noise random process. The predicted average maximum horizontal permanent displacement is in agreement with the conventional result, Further studied are the reliability of permanent deformation due to stochastic wave details at one seismic motion level and the risk of permanent deformation due to stochastic seismic strength, i. e., the maximum acceleration in a long period. Therefore, it is possible to make the optimal design in terms of safety and economy according to the importance of a sea embankment. It is suggested that the improved stochastic seismic model that can catch the behavior of the non-stationary random process For sea embankments should be further studied in future.

Centrifuge modeling of buried continuous pipelines subjected to normal faulting

Seismic ground faulting is the greatest hazard for continuous buried pipelines.Over the years,researchers have attempted to understand pipeline behavior mostly via numerical modeling such as the finite element method.The lack of well-documented field case histories of pipeline failure from seismic ground faulting and the cost and complicated facilities needed for full-scale experimental simulation mean that a centrifuge-based method to determine the behavior of pipelines subjected to faulting is best to verify numerical approaches.This paper presents results from three centrifuge tests designed to investigate continuous buried steel pipeline behavior subjected to normal faulting.The experimental setup and procedure are described and the recorded axial and bending strains induced in a pipeline are presented and compared to those obtained via analytical methods.The influence of factors such as faulting offset,burial depth and pipe diameter on the axial and bending strains of pipes and on ground soil failure and pipeline deformation patterns are also investigated.Finally,the tensile rupture of a pipeline due to normal faulting is investigated.

Centrifuge modeling of PGD response of buried pipe

A new centrifuge based method for determining the response of continuous buried pipe to PGD is presented. The physical characteristics of the RPI's 100 g-ton geotechnical centrifuge and the current lifeline experiment split-box are described: The split-box contains the model pipeline and surrounding soil and is manufactured such that half can be offset, in flight, simulating PGD. In addition, governing similitude relations which allow one to determine the physical characteristics, (diameter, wall thickness and material modulus of elasticity) of the model pipeline are presented. Finally, recorded strains induced in two buried pipes with prototype diameters of 0.63 m and 0.95 m (24 and 36 inch) subject to 0.6 and 2.0 meters (2 and 6 feet) of full scale fault offsets and presented and compared to corresponding FE results.

A geomechanics classification for the rating of railroad subgrade performance

The type of subgrade of a railroad foundation is vital to the overall performance of the track structure.With the train speed and tonnage increase,as well as environmental changes,the evaluation and influence of subgrade are even more paramount in the railroad track structure performance.A geomechanics classification for subgrade is proposed coupling the stiffness(resilient modulus)and permanent deformation behaviour evaluated by means of repeated triaxial loading tests.This classification covers from fine-to coarse-grained soils,grouped by UIC and ASTM.For this achievement,we first summarize the main models for estimating resilient modulus and permanent deformation,including the evaluation of their robustness and their sensitivity to mechanical and environmental parameters.This is followed by the procedure required to arrive at the geomechanical classification and rating,as well as a discussion of the influence of environmental factors.This work is the first attempt to obtain a new geomechanical classification that can be a useful tool in the evaluation and modelling of the foundation of railway structures.

Addressing the permanent deformation behavior of hot mix asphalt by triaxial cyclic compression testing with cyclic confining pressure

Rutting or permanent deformation is one of the major distress modes of hot mix asphalt in the field. Triaxial cycle compression testing （TCCT） is a standardized and scientifically accepted test method to address this distress mode in the lab and to characterize the resistance to permanent deformation. In most labs and according to EN 12697-25, standard TGCTs are carried out with cyclic axial loading and a constant confining pressure. In road pavements on the other hand, dynamic traffic loading due to passing wheels leads to cyclic confining pressure. In order to bring the TCCT closer to reality, the radial reaction and its phase lag to axial loading in standard TCCTs are analyzed and an enhanced TCCT with cyclic confining pressure is introduced. The cyclic confining pressure takes into account the viscoelastic material response by the radial phase lag to axial phase loading. In a subsequent test program, TCCTs with different confining pressure amplitudes were carried out on two hot mix asphalts. Results from standard and enhanced TCCTs were analyzed, compared and discussed. It is shown that the resistance to permanent deformation in- creases significantly when the viscoelastic material response is taken into account in the TCCT by introducing cyclic confining pressure.

Rutting prediction models for flexible pavement structures: A review of historical and recent developments

Rutting is the major distress mode in flexible pavements occurring due to the repeated movement of traffic loading. Deformation in the pavements comprise of both recoverable(elastic) and irrecoverable(plastic) part. Overall deformation occurring in the flexible pavement system due to continuous vehicular movement is contributed from all the components of pavement. A number of empirical models have been proposed by several researchers for analysis and prediction of accumulated rutting in different components of pavement. The accumulated permanent strain has been expressed as the function of the number of load applications and deviator stress applications in most of the models proposed;however, factors such as stress state, moisture content, material type and environmental conditions also impose a significant influence on the permanent deformation characteristics of pavement materials under cyclic loading. In this article, a comprehensive review has been carried out covering every aspect of deformation related to distress occurring in pavements. Important rut models, modeling approaches and modern concepts in the rutting analysis of pavement structures have been presented. In addition to review, fallacy existing in the current design practices related to adaptation of stiffness parameters and negligence of shear strength aspect of subgrade soil has been also presented with the support of literatures.

Refinement and estimation of asphalt flow number using partial load history

The effect of tertiary flow length on asphalt concrete(AC) flow number(FN) has been studied in this paper. The standard FN test(AASHTO T378) designated by American Association of State Highway and Transportation Officials(AASHTO) is currently among the widely adopted test for assessing the rutting performance of AC mixtures. The standard adopts the Fracken model(FM) for fitting the permanent deformation curve(PDC), prior to FN estimation. The FN was observed to vary as tertiary flow progresses. The FM, along with other PDC models(MFM-1 and MFM-2) obtained by modifying the FM, was utilized to analyze and minimized this variation. Variation of FN resulted because of mathematization of the PDC data. Instead of representing the actual initiating point of permanent shear deformation of the strain data, estimated values of FN were observed to indicate the inflection points of the fitted parent curve. As per standard FN range suggested by AASHTO T378, the observed variation in FN leads to the situation, where a single asphalt mix specimen can be regarded as appropriate for two different traffic levels, depending on the tertiary flow point at which the test is terminated. Supplementary steps in the FN estimation methods were proposed for refinement of FN values. For the refinement and further standardization of FN value and FN test respectively, FN:T(flow number to test duration ratio) has been recognized as the key and most simple solution. Two potential options for employing FN:T in the estimation of FN have also been highlighted. Several important correlations have been reported herein as well. Comparatively, MFM-1 was found to be more robust in FN:T curve utilization than MFM-2 and FM.

Experimental investigation of asphalt mixture containing Linz-Donawitz steel slag

Standard asphalt mixtures for road infrastructures consist of natural aggregate and bitumen. A number of research efforts have successfully investigated the possibility of replacing the conventional aggregate skeleton with industrial by-products such as slag originating from steel production process. However, little is known on the effect of steel slag on the mixtures performance properties such as resistance to low-temperature cracking and to permanent deformation, stiffness and fatigue. This paper presents a comprehensive investigation on the fundamental performance properties of different types of asphalt mixtures prepared with 100% LD slag aggregate and a conventional asphalt mixture containing natural Gabbro aggregate. Sophisticated testing methods were used to evaluate the key performance parameters for the set of asphalt mixtures investigated. In this study, low temperature cracking was addressed through thermal stress restrained specimen tests. Penetration tests and cyclic compression tests were used to evaluate the response of asphalt binder and asphalt mixture to permanent deformation due repeated loading, respectively. The cyclic indirect tensile test was selected for investigating both stiffness properties and fatigue resistance. For this purpose the complex stiffness modulus was measured to quantify material stiffness under different temperature and loading conditions providing information on the visco-elasto-plastic material behavior. Fatigue tests were used to determine the progressive and localized material damage caused by cyclic loading. The experimental results indicate that asphalt mixtures prepared with LD slag are suitable for asphalt pavement construction and that in most cases they perform better than conventional asphalt mixtures prepared with Gabbro aggregate.