**1. Introduction**

The traditional ballasted tracks have been used widely in railway transportation infrastructure. These tracks have been investigated in two views in terms of civil engineering, layers underneath the ballast layer (subgrade) and the ballast layer (pavement). Facing clayey soils in the subgrade of railway tracks reduces the bearing capacity, increases water absorption, and as a result, creates horizontal and vertical deformations that are transmitted through the ballast layer to the railway pavement. Construction of ballasted tracks on the clayey soft subgrade causes high settlement and low bearing capacity. In addition, significant maintenance costs and

time-consuming operations have been encountered due to the presence of clay. Despite the ballast layer advantages in low construction cost and time, proper drainage, simple technology, and proper damping, it has some disadvantages such as vertical and horizontal displacement, low vertical stiffness, need for time-consuming and expensive maintenance operation, low lateral resistance, slippage, pumping, dirty ballast, ballast breakage and flying ballast in high-speed railways. In this regard, many researches have been done to manage these drawbacks.

It will be a caught-in-crossfire situation when structures fail due to the presence of clayey soils and the need for their microstructural, mechanical, and strengthening properties to be improved before construction.

A huge amount of suitable material and enormous costs is needed in transportation projects. Thus different stabilizing methods have been considered by scientists [1].

Clayey soft soil can damage the transportation infrastructure due to its disadvantages such as low strength and huge volumetric changes that generate expensive maintenance costs [2, 3].

The subgrade of railway track is an important part that cans cause increased maintenance costs [4].

Facing soft subgrade causes a challenge in railway track design. The long-term behavior of soft subgrade under repeated load is important in track design [5].

Extensive costs and structural damages generate in clayey soil due to volumetric change arising from wet-dry conditions [6].

Cement and lime-stabilized subgrade soils are considered environmentally unfriendly. So, as a solution Sodium Alginate Biopolymer have used in pavement construction. The results show an increase in resilient modulus, stiffness and strength depending on the material type and concentration and curing time [7].

Lime-Microsilica has been used as a silty soil stabilizer in the railway subgrade to improve California Bearing Ratio (CBR). The results show an increase due to the use of additives [8].

The railway subgrade has been stabilized with Fly-ash. Results show a significant increase in shear strength, CBR, and cohesiveness [9].

Different methods such as preparing suitable material, using mechanical techniques, and using additives are common in subgrade enhancement. Application of chemical additives has been proposed using reliable research in soft subgrade, some of which are listed below:

Advanced techniques enhanced subgrade bearing capacity instead of the lime treatment method [10].

Application of cement and lime lonely had disadvantages such as insufficient specified properties and environmental impacts. So the combination of them in suitable dosage had an important influence. The optimum proportion was investigated using a compressive strength test, and results show the highest amount [11].

Due to rolling stock movement, forces are applied to the track and cause movement in horizontal and vertical planes. Horizontal forces have resisted by longitudinal and lateral resistance of the track. Using the different materials and procedures, resistance against forces has increased. Longitudinal resistance has improved using continuous welded rails (CWR) technology. However, it is impossible to join the rails in tight curves due to higher lateral forces. The material, size, geometry, and dimension of track components affect lateral resistance. Researchers have carried out several studies to enhance lateral resistance. In this regard, changing sleeper shape is a common method. Lateral resistance has influenced by various factors such as environment conditions, applied loads, track components, track geometry, and maintenance

## *Developing a Novel Superstructure System for the Ballasted Railways Using RRP235special... DOI: http://dx.doi.org/10.5772/intechopen.111470*

procedure. The lateral resistance between ballast and sleeper usually is conducted using the tests with single or multiple sleepers in full-scale or scaled model in laboratory or in situ [12]. The ballast layer geometry and interaction between the ballast and the sleeper is the main factor of lateral resistance [13]. With the introduction of CWR, buckling may occur due to thermal expansion. So, lateral resistance is an important factor in track stability. In this regard, a series of laboratory tests were carried out using STPT and track panel pullout test (TPPT) on different types of concrete sleepers. Results revealed the importance of the shape, the spacing, and the number of sleepers [14]. Determination of participation of each part on total lateral resistance has important to choose a sleeper and designing the components in railway. Lateral resistance of the sleeper achieves from sum of base, crib, and shoulder area. According to the experimental laboratory research on STPT test and corresponding to the material of sleeper, base area resistance of concrete, steel, and wood are 62%, 56%, and 51%, crib area are 28%, 27%, and 18% and shoulder area are 9%, 22%, and 26%, respectively [15].

The sleeper's shape significantly affects ballasted track's lateral resistance [16]. Changing the shape and material of the sleeper is recommended by scientists. In this regard, the frictional sleeper is an effective solution. The measurement has been conducted on conventional and frictional B70 sleepers by panel displacement method. Results show an increase in lateral resistance [17]. Based on the experimental test, the lateral resistance of three different frictional sleepers has been evaluated using the STPT test. Results indicated increases in lateral resistance due to frictional sleeperenhanced interaction between ballast particles and sleeper [18]. A numerical model in finite element software has developed and investigated the effect of shoulder extend, base friction, and ballast layer thickness. Compared with the conventional sleeper, the frictional sleeper led to increased lateral resistance. A decrease in the ballast layer causes an increase in lateral resistance. Increasing in ballast shoulder, results increase in lateral resistance [19]. Y-shape steel sleeper in ballasted track has been investigated based on experimental methods using STPT and lateral track panel test (LTPT). The longitudinal resistance force (LRF) in STPT and LTPT [20]. The lateral resistance of HA110, winged and middle-winged sleeper achieved from STPT test, compared to the conventional B70, increased [21].

Track maintenance is one of the factors that influence lateral resistance. The lateral resistance was reduced significantly due to surfacing and increased by mechanical stabilization following the surfacing [22, 23]. The influence of ballast material type on the interaction between ballast and sleeper has been investigated. So the ballast consisting of crushed and angular particles has more lateral resistance than rounded and crushed angular types [24]. The lateral resistance of polyurethane-mixed ballasted track has been investigated using a discreet element model. Results show increases in lateral resistance due to an increase in the bonding depth of the shoulder ballast [25]. Lateral support is a new method to enhance lateral resistance in ballasted tracks. Field investigation by using STPT and Multi Tie Push Test (MTPT) tests and numerical modeling illustrated that lateral supports significantly increase lateral resistance [26]. Ballast bonding is a way to enhance track performance. Lateral resistance increases in curves due to bonding stabilization technology [27]. Waste tiers have been used in ballasted track foundations, rendering higher lateral resistance [28]. The use of geogrid causes a decrease in lateral deformation [29]. A field and laboratory sample has been made by geogrid stabilized ballast layer. The STPT and track panel displacement tests have been conducted. The results show an increase in lab and field, respectively [30].

The comprehensive method that increase majority of ballasted track disadvantages considering economic impact rarely proposed. A method is needed that, while improving the desired properties in terms of mechanical, physical, durability, environment impact, construction time, maintenance operation and dynamic, is also economic and constructive. Slab-track is the method that developed recently due to its advantages compared to ballasted track. But the economic issues and complicated construction technology are the challenges to prevent comprehensive extension. So the middle method is containing majority advantages of both of methods is needed.
