Dynamic Compaction (DC) is a common deep compaction method that is usually used for densification of coarse-grained soils. Although traditional continuum-based models such as the Finite Element Method can be successfully applied for assessment of stress distributions or deformations induced by DC, they are typically not adequate for capturing the grain scale mechanisms of soil behavior under impact. In contrast, numerical models such as Discrete Element Method (DEM) in which the interaction of constituting distinct elements is explicitly simulated are promising for simulation of DC process. In this study, dynamic compaction in a dry rockfill was simulated through a two-dimensional DEM model. Based on the developed model, a series of analyses with various tamper weights and drop heights were conducted to investigate the effects of important factors such as energy and momentum per drop on DC results. Comparison of the obtained results with experimental observations reveal the capability of DEM for simulation of DC. The numerical simulations also confirm the positive effect of using conical-based tampers in DC process.

The present study analyzes and measures the vertical stiffness of ballasted railway track based on the beam on the elastic foundation method by focusing on the effects of dynamic stabilizer machine. Investigating the effects of this machine on the vertical stiffness of ballasted tracks can help the railway engineers in track maintenance planning and cost reduction. One of the methods for maintaining ballasted railway tracks is using the mechanized track maintenance trains to adjust longitudinal leveling, track alignment, and stabilize the railway. While the TAMPING machine has advantages for quickly correcting the track geometry, it also has disadvantages such as a reduction in the lateral resistance and stiffness. These disadvantages result from the penetration of TAMPING tines into the ballast layer, and lack of coherence in the ballast grading. The dynamic stabilizer machine, based on available technical literature, can reduce some of the deficiencies caused by the TAMPING machine. To examine these effects, a field experiment was conducted in Line No. 1 at Karaj Railway Station. Results of the tests performed in three steps including before TAMPING, after TAMPING, and after using the stabilizer machine indicate that, due to the absence of TAMPING for five years, the vertical stiffness was at its maximum level before TAMPING. After employing the TAMPING machine, the vertical stiffness decreased by approximately 69%, mainly due to the penetration of TAMPING tines into the ballast layer, which reduced the compaction and the contact surface between ballast particles. Following the passage of the dynamic stabilizer machine and application of horizontal vibrations and static vertical loads, which enhanced the compaction and proper interlocking of ballast particles, the vertical stiffness increased by approximately 47% compared to the step after TAMPING operation.

Subsequent to rails, sleepers are the most important elements of the railway superstructures, for which its role is to keep the geometry of the line, resist against vertical and lateral loads and transfer them to the layer of ballast. Contact point between sleeper and ballast play an important role in defecting of the railway tracks. For this reason; method of analysis, design and built of sleepers and also how they have been implemented in superstructures are of an important issue in the railway engineering researches. This paper presents investigation of contact stress distribution in lower surface of sleepers through some experiments on railway tracks. In this experiment one sleeper equipped with several load cells was installed on a railway track situated in Bahram station. After TAMPING, some load was passed over the sleeper and the exerted forces were measured and consequently were analyzed as an output. It should be stressed that passing trains with an identified axial load were passed over the installed sleeper before and after the stabilization. Results show the real contact stress distribution in lower surface of the sleeper in different status i.e. (after TAMPING, before and after stabilizing) and the effect and importance of required ballast compaction under the sleepers. With due consideration to the results achieved, it could be said that; right amount of ballast, sufficient compaction under the sleeper and performance of railway track's repair and maintenance machineries are of utmost importance and reduces non-uniformity of load distribution.

of initial texture and plastic fine content has been investigated. In order to model the different deposition condition four different specimen preparation methods are used. The tests are conducted on sands and its combination with to 25 fine percent using static and cyclic method. Four different specimen preparation methods are used consisting of Dry Funnel Deposition (DFD), Water Sedimentation (WS), Moist TAMPING (MT) and Air Pluviation (AP). Each method may be useful to model the behavior of some special deposited soils. For example, DFD is the best method to model the natural deposition of silty sands, while the WS method is suitable for simulating the sands natural deposition in the rivers. MT method is the best method to simulate the behavior of compacted embankments while SD method is suitable to prevent the segregation of particles with respect to other methods like Water Pluviation. Effect of sample preparation methods on the sands and silty sands behavior is investigated to some extent, while the clayey sands are rarely considered. The results show that water sedimentation method, Air pluviation method and Dry funnel deposition method tends to create dilative textures with continuous dilative behavior even in high clay fine content. In contrast, the wet TAMPING method shows the dilative behavior only for clean sands specimens and increasing fines will results in instability and complete strain softening behavior. In cyclic loading the difference between different methods are less with respect to static loading. It seems that the results of different methods tends to be identical with increasing in fine content. In general, increasing fine content up to 20 percent results in more instability. After that a threshold value can be estimated bout 2 percent, after that the instability becomes less with continuous increase in fines content. The valuable result is that the threshold value is not dependent on the specimen preparation method or initial texture of specimens.

Dynamic compaction (DC) technique with TAMPING is one of the soil improvement methods. Nowadays, there is a considerable interest in DC due to its advantages among the methods of soil improvement. In the present study, fuzzy logic and Sugeno inference system have been used to evaluate the influence of parameters involved in dynamic compaction over the depth of improvement. Input variables are used for loose granular soils and include tamper weight, height of TAMPING, tamper radius, print spacing, number of drops and soil layer geotechnical properties and four improvement depth of relative degree as output variables. Input and output data are extracted from the reliable scientific literature. Following development of the fuzzy model, the results of this study has been validated with the results of valid Dynamic Compaction operation in the world. Then as a case study with using the prepared model, Dynamic Compaction Operation in Shahid Rajaee Port in Iran has been analyzed. The results indicate that the effect of tamper weight is greater than the height of TAMPING and print spacing is in third importance grade. The interaction between tamper weight and dropping height plays the greatest role in the design procedures. Studies show that the optimal tamper radius for most compaction patterns with medium to high applied energies is equal 1.5 to 2 meters, the optimal dropping numbers are equal 25 and optimal print spacing is equal 6 to 7 meters so using this pattern leads to obtain maximum improvement depth.

In this paper, stress analyses in concrete sleeper has investigated by using results of the tests which have been done in main line of railway track. In these tests, special concrete sleeper (B70) installed in railway track. Five load cells fixed inside of the sleeper during constructing of that. After replacing this special sleeper with ordinary sleeper, and TAMPING in railway track, a train with certain axle load passed through that point of track. Forces on sleeper are analyzed (output of measurement). The results show that B70 concrete sleepers are designed well for tamped and no tamped cases. In the both cases, the stresses in sleeper cross sections are in allowed range. Also, the results show that the track without DTS operation (after replacing of the sleeper) decreases share of sleeper bearing and increases forces on adjacent sleepers. These forces together with dynamic effect of rail-sleeper interaction will accelerate sleeper's deterioration. This means that after replacing failured sleepers, the sufficient length of track must be operated by DTS and TAMPING machines.

Vertical stiffness of ballast railway is an effective parameter on track quality level and maintenance cost. As track dynamic surcharges could have great impact on the majority of stiffness, this parameter need to categorize as static or dynamic. Plate load test (PLT) and light weight deflectometer test (LWD) are two widespread used tests in railway construction processes to measure static and dynamic stiffness’s respectively. PLT is a time consuming test and its implementation is usually accompanied with temporary block of track but LWD have the opportunity to perform faster. On the other hand, static stiffness measured from PLT is the parameter which railway standards and guidelines used to define their criteria about the quality of different track pavement layers. So this paper is concerned to extract a mathematical relation between the results of these two tests. Linear regression method used for this purpose. Static and dynamic stiffness ratios are derived for both situations, before and after TAMPING process. Finally a finite element numerical model used to calculate vertical stiffness of ballast layer.

Although the current analysis and design of railway track systems are based on the assumption of continuous and linear behavior of the rail support system, repair and maintenance plans have considerable influences on the structural behavior of the track support system, particularly after accumulative loading or track TAMPING. Recent experimental investigation indicated the behavior of the track support system is time and stress dependent. The amount of traffic passed and the quality and quantity of maintenance activities can considerably influence the track response functions. Although some experimental investigations have been carried out to study the time and stress dependent characteristics of the ballast and subgrade materials, the effects of the consideration of these characteristics on the track analysis and design, need further evaluations. Furthermore, the recent extensive increases in axle loads, speed and traffic volumes in rail transport systems, require more precise analytical and mechanistic approaches for railway track system. This research is a response to this need. In this paper, the current practices in the analysis and design of railway track system are discussed. A mode of track support system with consideration of discrete supports is developed. By comparison of the analyses results obtained from track models with continuous and discrete support systems, the accuracy of the assumption made in the Winkler model, used in the current design approach, are evaluated. The nonlinear behaviors of the track support system were studied and the influences made by the consideration of the non-linearity of the track support system on the rail design criteria were investigated. Rail bending moments and rail deflections as the main rail design criteria are obtained form track with a linear support and nonlinear behaviors. Obtaining large discrepancies between the results obtained from linear and non-linear analyses, the importance of the track regular and systematic repairs, in particular TAMPING and stabilizing the ballast, are proved. It is shown that the consideration of regular repairs of the track support system improves the long term reliability and accuracy of the current track design approach. Recommendations are made on the track maintenance and repairs in order to keep the track support system in the linear conditions.

Dynamic Compaction (DC) is employed as a simple and economical method to improve weak soils in the last few decades. DC is usually applied for granular soils by falling a heavyweight (up to 40 tons) from a height (up to 40 m) at regularly spaced intervals. Significant issues in DC are the weight and height of the tamper, compaction pattern and the distance between TAMPING locations. Incorporated innovation in this paper is to introduce an analytical approach to optimize the compaction pattern and DC variables regarding regular constraints. The required energy for compaction is evaluated for square and diamond patterns. DC optimization is a non-linear and non-convex problem due to nonlinear equations in soil compaction behavior. Thus, a metaheuristic approach (Genetic Algorithm) is employed to find global optimum. The optimum answer presents the minimum compaction energy in each pattern. Results indicated that the maximum allowed values of tamper mass and the number of tamper drops were required to minimize compaction energy. The ratio of compaction energy at diamond pattern to square one was also found to be about 0.75 to 0.90 for the same compaction conditions.

Threshold shear strain is one of the basic parameters of soil during cyclic loading condition. The threshold shear strain should be determined for evaluating pore water pressure generation due to earthquake, vibrating machine and all the cyclic loading which apply permanently or temporary on the soil. According to many scientific researches, the threshold shear strain is the strain, which there is no pore water pressure generation at the saturated soils and no volume changes at the dry conditions during cyclic loading. By increasing the shear strain more than threshold shear strain (gt), pore pressure increase is noticeable at the saturated soil and the soil microstructure starts to change. In this study, the effects of plastic and non-plastic fines on the threshold shear strain of saturated sands were evaluated by performing a number of cyclic triaxial tests with strain control method at small shear strain. All the specimens contained 0%, 10%, 20% and 30% plastic and non-plastic fines prepared by wet TAMPING undercompaction method. As a result, by increasing plastic fines more than 20%, threshold shear strain increased significantly. Moreover, by increasing non-plastic fines, threshold shear strain fluctuated. It first increased and then decreased.