THE BASING OF STABILIZATION PARAMETERS OF A FORTIFIED RAILWAY BED

Dep. «Tunnels, Bases and Foundations», Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipropetrovsk, Ukraine, 49010, tel. +38 (050) 708 50 69, e-mail petrenko1937@mail.ru, ORCID 0000-0002-5902-6155 Dep. «Tunnels, Bases and Foundations», Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipropetrovsk, Ukraine, 49010, tel. +38 (066) 290 45 18, e-mail tutkin@mail.ru, ORCID 0000-0003-4921-4758 Dep. «Tunnels, Bases and Foundations», Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipropetrovsk, Ukraine, 49010, tel. +38 (096) 992 15 81, e-mail murzilka891@mail.ru, ORCID 0000-0002-6077-1689 Dep. «Tunnels, Bases and Foundations», Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipropetrovsk, Ukraine, 49010, tel. +38 (066) 290 45 18, e-mail a.alkhduor@inbox.ru, ORCID 0000-0001-5845-2710


Introduction
At the present time the railway transport in the unit transport system of Ukraine plays the leading role by guarantee the requirements of freight and passenger traffic.In modern conditions the railway operations concentrates on ensuring the necessary level of the track reliability, including the roadbed as the basis of the road embankment to a large extent determines the normal operation of the railway as the whole under the influence of the rolling stock.As it is known, the main cause of the traffic accident on the railways is the state of the track (50%), the state of the rolling stock (43%) and a human factor.Thus, it is necessary to develop new investigations with the using of subgrade reinforcement elements with different materials and determine the parameters of their efficiency, especially at higher train speeds.To achieve this goal of determining the basic parameters of the stress-strain state to stabilize the soil subgrade embankment reinforced with special materials it is required to solve next research tasks: 1) carry out the analysis of previous studies in the field of strengthening of subgrade by reinforcing materials; 2) investigate the effect of influence by reinforcing layer by geomaterials on deformation properties of subgrade strengthening in various designs; 3) determine the distribution of stresses in the subgrade, reinforced geomatherials under static load; 4) carry out the complex of experimental researches to explore the nature of the model subgrade deformation at different voltage level [2][3][4].

Purpose
Analyzing every works about the reinforcing of subgrade embankment, it should be noted that results of previous studies indicate to the using of traditional methods of strengthening subgrade railways are not always effective and it is necessary to develop new methods [1,[5][6][7][8]12].

Methodology
For research inclusions of the reinforcing geomatherials on the soil subgrade method were outlined and as a result of the study its materials loaded up to the level of adequate modern rolling stock.
The results of previous studies [5][6][7][11][12][13][14][15][16] indicate that the using of traditional methods of strengthening subgrade railways are not always effective and leads to the higher costs and time to conduct it.The modern ways of strengthening of railway subgrade have the several disadvantages, technological or economic nature, and therefore do not solve the issue in many causes reducing the deformability of the roadbed.Theoretical and experimental studies carried out in different countries, as well as monitoring of the test sites revealed that geotextile placed on main subgrade surface, comes into work with a ballast layer of soil and is the main site, with the stress-strain state of subgrade changing.
Thus, currently there is the problem of assessment the quality reinforcement, especially geosyn-thetic materials, railway roadbed [6,7,10,12].In this case, it is complicated by the fact that there is no single concept of subgrade strengthening the body over its depth, especially in combined versions [6].Therefore in the task of developing the method need to strengthen and evaluate of its stress-strain state.
The tests were conducted in a closed system i.e. at constant soil moisture.According to test result were constructed plots of the "stress -the relative strain".Base on the results of sample tests on the compression was verify the effectiveness of placing a geotextile to reduce the deformation of the sample at the laboratory studies were performed stabilization reinforced roadbed.Dimensions of the model in plane were accepted 680×120 mm.Front wall of the tray was made of a transparent Plexiglas for observations the development of deformities.Loading of models were carried out on the linkage system with shoulder leverage of 1:10.The load transmitted to the stamp area 155.3 cm 2 .In the process of model loading controlled the level of absolute displacements vertical load on the stamp was from 10 to 50 N with the stresses under the stamp changed from 0.0644 MPa to 0.332 MPa (as we know the normative power of the railways in the strengthening of 0.16 MPa).The settlement of stamp measured three dial gangs with a scale of 0.01 mm.Indicators on the stamp mounted symmetrically.Move the stamp recorded after each stage of the application load after and removed on indicators of the deformed samples and photography model.Moving of subgrade recorded of rules set on the side faces of the tray and strain model with a grid printed on its face.To substantiate methods prevent of substantially reduce the strains of subgrade for different types of reinforcement were conducted experimental researches in the tray with the geometric scale of modelling 1:20.There have been conducted several series of model tests with the specification of their deformation characteristics in depending on the nature of reinforcement (Fig. 1).
At the analysis of the parameters of the experimental studies reinforced by geotextile of subgrade found that the nature of the manifestation of deformation unreinforced model -variant 0 (Fig. 1,  a) is manifested by the appearance of the stamp core compression, which was clear from the distortion mesh 2×2 cm.towards the front of the model.Option 1 (Fig. 1, b) during the compression of the soil matrix with geotextile fabric has significantly changed its shape, detached from the main site and out of shape as a result of the critical strain, indicating that non-rationality of the option for placing reinforcing element.At the analysis of the option 2 (Fig. 1, c) states that the considerable effort in the geotextile separation zone formed matrix and reinforcement.In options 3 and 4 (Fig. 1, d, e) there is a homogeneous deformation, since the critical strain as bundle and pulling the valve were found.Therefore the reinforcement models of subgrade with the inline options are optimal to stabilize the railway subgrade.Having considered the option 5 (Fig. 1, f) at significant stresses detected deformation of soil matrix at the edges of stamp and the ballast layer consequently, the presence of cracks in surge -on the edge of stamp and the ballast layer, consequently, presence of cracks in surge -on the edge of the ballast and under the edge of the stamp is a negative effect.
Stabilization parameters that are accepted in the work for gutter tests also showed that the combined version 5 is the most effective measure of stabilization parameters.The additional geometric constructions, which simplify comparison, are shown in Fig. 2 and 3.So at the regulatory maximum stresses on the main site subgrade, which is equal to 0.08 MPa, the relative deformation of options to strengthen from the geotextiles are equal respectively: Option 0 -0.0078,Option 1 -0.0066,Option 2 -0.0065,Option 3a -0.0053, option 3b -0.0067, Option 4 -0.0046,Option 5 -0.0044, that is, the introduction of the geotextile reduces deformations at 1.2…1.8times (maximum decrease of strains in option 5).Modulus of elasticity, as one of the stabilization parameters, varied in the followed ranges; Option 0 -2.78 MPa, option 1 -12.5 MPa, option 2 -5 MPa, option 3a -25 MPa, option 3b -3.57MPa, option 4 -12.5 MPa, option 5 -25 MPa, that is, in options 3a and 5, with the introduction of geotextile modulus of elasticity increase in 9 times, respectively, the deformation characteristics of subgrade, in the conducted tests, were improved.
In the series of experimental and conducted research were carried out tests on the strengthening models by small-deformable layer of Rubble-Soils Mixe, which is located at a different depth from the main site of subgrade (Fig. 2).

Findings
When analyzing the results of experimental studies of the stress-strain state of subgrade reinforced, the small deformable layer of crushed stone-ground mixture, established the following.In option 1 (Fig. 2, a) slightly improved picture of deformation, however, is not essential.But stillcompared to unreinforced option 0 (Fig. 1, a), the damping stress is significant.By increasing the thickness of small deformed layer to 2 cm (0.4 m in nature) revealed its positive impact on the reduction of vertical deformations, and the impact of its location on these values.So in options 2, 3, 4 (Fig. 2, b, c, d) the influence of the position of the layer to change vertical displacements were recorded.In the version 5 (Fig. 2, e) was recognized sheared strain as a bundle and pulling out of the matrix and reinforcement (small deformed layer at a depth of 2 cm (0.4 m in nature) from the main site.When analyzing 6 options (Fig. 2, f) small deformed layer located at a depth 4 cm (0.8 m in nature) from the main site.It is established that uncritical deformation in the form deformation and loosening of fitting is not detected, so this option is effective to stabilize subgrade.As a result, were accepted parameters stabilization in the case of roadbed strengthening by small deformable layer and combined strengthening with relative deformation at the normative maximum stress to strengthen for variants equal respectively: Option 0 -0.0078,Option 1 -0.0062,Option 2 -0.0034,Option 3 -0.0034,Option 4 -0.034,Option 5 -0.0015,Option 6 -0.0034.We can say that: using of combination options, as the most effective, reduces strain in 5.2 times (The rest variants amplification -only at 1.3…2.

Originality and Practical value
On the base of analysis of the results of performed experiments were done the following conclusions.
The analysis of the carried out studies in the field of strengthening subgrade reinforcing materials allowed establishing a lack of development and ways to strengthen of subgrade railways.
In conducting experimental studies determined the distribution of stresses in the subgrade, reinforced geomaterial under static load as a model in the tray.On the base of the experimental studies results established the parameters of the stressstrain state to reinforce the roadbed small deformable layer is made of Rubble-Soil Mixes when the relative deformations equal from 0.008 to 0.017.
As established experimentally, the reinforcing roadbed as separate horizontal panels and strength by geotextile matrixes 1.5…1.6, the emergency of separation zones at the ends of the cloth show irrationally of these options, regardless of their location in height of the matrix.
In addition, it was found that the reinforcement of a closed shell also can not be a rational choice, even with the increasing the strength in 1.6 times, since the deformation of subgrade at this version of the reinforcement due to significant cracking.

Conclusions
The complex of experimental studies was conducted to explore the nature of the deformation model subgrade of various degrees of stress.Based on experimental studies, a way strengthen roadbed reinforcement Ruble-Soil Mixes wrapped in geotextile with bends and justified its position at a distance of 0.4 m from the main site, which will increase the strength of the roadbed in 1.8-2.0times and stability to improve the speed of the trains.