ESTIMATION OF SUBGRADE STRENGTHENING INFLUENCE USING SOILCEMENT ELEMENTS

Dep. «Bridges and Tunnels», Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipro, Ukraine, 49010, tel. +38 (056) 373 15 79, e-mail petrenko1937@mail.ru, ORCID 0000-0002-5902-6155 Dep. «Bridges and Tunnels», Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipro, Ukraine, 49010, tel. +38 (056) 373 15 79, e-mail tutkin@mail.ru, ORCID 0000-0003-4921-4758 Dep. «Bridges and Tunnels», Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St. 2, Dnipro, Ukraine, 49010, tel. +38 (056) 373 15 79, e-mail i-svjatko@yandex.ua, ORCID 0000-0002-7099-2637


Introduction
The main priority of rail transport is to provide of goods and passengers safety.
All facilities should be designed so as to correspond to its purpose, to be stable and reliable.Design of bases is a complex task that takes into account engineering and geological conditions as well as the design and performance properties of the structure.
Under the influence of the load from rolling stock and own weight of permanent way the soils deformed, and its deformation is greater than the greater tension in the soil.Deformation of soils bring to setting of structure.The tensions should not exceed the limits in order to be secured conditions of stability and safety of permanent way [1,4,10].
Breach of the foundation stability displace in the form of displacement of natural soil mass, bringing to injuries or disturbance of the roadbed, such as soil slips, dips and more.
Experience of designing and performance of track structure showed that over time should take some measures to improve the characteristics of the soil mass to be able to the follow normal performance of the roadbed.[5,3,13] Soilcement elements that are widely used abroad, as well as construction of industrial and civil objects for its purpose, can be used for the strengthening of transport facilities, in particular at strengthening the roadbed as well as weak bases.

Purpose
The aim of this work is to identify dependencies and parameters of subgrade strengthening and weak base using soilcement piles.Analyses of using of SCAD software system came for assessing of impact choose variant of strengthening for structure of roadbed spatial models.

Methodology
The most of appropriate and promising method for assessment of roadbed stress-strain state is modeling the spatial models using finite element method.In this paper considers the method of calculation of soil mass by software complex SCAD, which is a universal calculation system of finiteelement analysis of structures and orientate on solution the tasks of designing buildings and constructions rather complex structure.The method of finite elements it goes to the most modern and effective methods for the calculation of structures for various purposes.During the simulation we get a complete picture of the stress-strain state of the study area and the limit value loading, sedimentation, etc.
The spatial model based on volumetric finite elements to better take into account the real charac-teristics of the soil mass meets all the geometric characteristics and natural size of subgrade and permanent way, which was adopted in Ukraine.
Deformation characteristics, those taken in the model correspond to the values which have been obtained in the study of subgrade soil [6,7,14].
At the time modeling applied so restrictions (boundary conditions): − on the model bottom impose a ban on movements in the direction of the three axis -X, Y, Z; − lateral facets of base have a ban on movements over the axis X and Y; − diametrical sides of model -a ban of movements over axis Y (plane deformations condition).[8,9,12] Top of model and also embankment slopes have no restrictions -free from boundary conditions.
The thickness of the computational model (on the axis Y) adopted 1.15 m, which corresponds to the width of two standard sleepers and two distances between sleepers with its epures 1740 pieces/km.The model is symmetrical on thickness relatively of axis X. Inclination of the railway slope make 1: 1.5.General view of the roadbed plan is shown in Figure 1.All calculations performed by the multifrontal method of expansion of rigidity matrix with automatic optimization of the tape width, as this method is the most progressive when working with matrixes, which used to program complex SCAD [2,11,12,15].
After the complete linear calculation values of deformations relatively axis Z and axis X were obtained.Precision of matrix expansion is 1x1012.
General view of model in program complex SCAD shown in Figure 2.
In this paper have considered the following variants of strengthening: placement of soilcement piles with a diameter of 0.5 m only in the base of roadbed and in base and through the body of roadbed.Adopted by number of piles are two, three and five, respectively, for each variant.
In all cases soilcement piles were disposed symmetrically about the axis of the track.
During the calculations of strengthening variations the length of piles at the base is 3 m long and the length of piles in the base and in the body of embankment -9 meters.The distance from the lower end of the pile to the bottom of the calculation model is 1.0 m.

Findings
After carry out of the control calculation unfortified subgrade have been received the maximum deformations along the axis Z (Figure 3), that form 14.21 mm, and along the axis X (Figure 4) -2.45 mm.At the level of the transition from the body of the embankment to the base subgrade is a slight curvature in view of change point with characteristic modification of direction deformation behavior.
It should also be noted that in the area of crossing from base to embankment remain about 50% of total deformations, which is 7 mm.
According to the results obtained with the strengthening by two soilcement piles only in the base, the overall deformation on the axis Z in the level of rail head formed 13.4 mm (Figure 5.), that is 5.7% less than the control calculation.Deformations of model in which additional piles were in the body of the embankment totaled 12.20 mm, that is 14,1% less deformations of unfortified models.
By the level of foot sleeper the deformations on the axis Z have been reduced in the case of strengthening of base on 4.0% and in the case of strengthening the base with the body of the embankment -on 14.0%.In addition, the model the characteristic changes of izofields deformations on the places of piles existing.It should be noted that in the area of crossing between weak base and embankment total deformation decreased on average by 16%.
In strengthening of roadbed by three soilcement piles, so be observed decrease of deformation on the axis Z. Thus the effect of the pile using only in base and in the base and body of embankment significantly different.In the first case, reducing of deformations by the level of rail head happened on 8.2%, while in the second case -almost three times more -20.6%.
However, in the plane of crossing between the base and the body of embankment exist several another situation.On the contrary, the strengthening only base reduce the deformations was about 27.3%, whereas the strengthening through the body of embankments exists of decrease by only 23.0%.
The calculation results in the strengthening by five soilcement piles testify about the following.The maximum deformation in the level of rail head totaled 12.62 mm and 10.57mm at strengthening only bases and base with body of embankment respectively, representing a decrease of 11.2% and 25.6%.However, on the boundary of crossing from the base to the body of the embankments the effect from strengthening is the same reaching 29.1 … 29.5% with comparison the control calculation.Also on the present boundary become more pronounced the change of isolines (Figure 6).

Originality and practical value
The algorithm of forming design scheme for calculating of the embankment on the weak base by the finite element method has been determined.The selection of soil strength characteristics and the calculation parameters for use in numerical modeling has been done.The modeling of loading system process by rolling stock has been grounded.
Analysis of stress-strain state of the system «weak base -roadbed» permit to see the basic regularities of soil work and use of embankment cross-section profile strengthening by soilcement elements.
The method of subgrade on weak base modeling that reflects with their work under loading by own weight and rolling stock has been proposed.

Conclusions
The most effective variant at the arrangement of soilcement piles at the base and in the body of embankment is strengthening its by five piles.Thus there is a uniform soil mass in the level 25 … 30% on the all depth.Reducing of deformations is linear and describe by the equation y = 11.906-0,4867h,where h is the depth of plane base from top plane of railbed.However, even with the strengthening only two piles in the base effect from strengthening is 14.1%.

Fig. 1 .Fig. 2 .
Fig. 1.General view of the roadbed plan with permanent way

Fig. 3 .
Fig. 3.The calculation without strengthening by soilcement piles.Deformation on the axis Z

Fig. 6 .
Fig. 6.Deformation on the axis Z.The calculation the five piles at the base and body of embankments