Whenever any civil engineering project is undertaken existing soil and rock conditions are assessed then a design is developed that is compatible with these conditions. For example If the project involves designing a structural foundation and soil conditions are poor, it is necessary to use deep foundations. However, on some projects the soil conditions are so poor that it becomes very expensive to accommodate the design. When this happens, various methods of soil improvement are often considered. These methods are intended to improve the quality of soil. Although soil improvement is generally expensive and in some cases proposed construction cannot be practical unless the soil is first improved.

Some soil improvement methods are proprietary (i.e. they are protected by patent) and many of the methods require special equipments. Often proprietary methods are implemented by the design and build firms that do both the engineering design and the construction. However, other methods can be implemented by any qualified persons with ordinary equipments.

Presently used methods for ground improvement are removal and replacement of unsuitable soils, precompression, preloading or surcharging the soil before construction, drilling of vertical drains for removal of water, insitu-densification, vibrocompaction, dynamic compaction, blast densification, in-situ replacement of the soil, stabilization using admixtures, in-situ deep mixing, concrete- soil reinforcement and the use of geosynthetics (Rao and Kaushish, 2001), such as geotextiles, geogrids, geomembranes, geocomposites, geonets and other products such as geomats, geomeshes, geowebs, etc. But these methods are expensive, time consuming and some of them may cause damage to the existing structure or cause landslides by inducing excessive vibrations during compaction.

The use of recycled plastics in highway construction is vide and varied and as an additive to asphaltic concrete is not new, however, the influence of waste plastic reinforcement in soils has not been investigated so far. During the last two decades a large amount of research has been carried out on recycled material. Even though the research carried on the use of waste plastics is vast and extreme, but the dissemination of information is often limited. The problem is compounded by lack of a single resource containing relevant engineering and environmental characteristics of each material (Alaa et al., 2006). The majority of early studies dealt with new material identification and laboratory testing to determine material properties (Collins and Ciesielski, 1994; Edil and Benson, 1998). More recent research has included large-scale field tests, predominantly environmental studies, and processing technique characterization (O'Shaughnessy and Garga, 1999; Liu et al., 2000; Consoli et al., 2002).

This is a rapidly developing topic that is being driven by economic pressure to build on sites with marginal soils, the need to rebuild ageing infrastructure in urban areas, increased recognition of seismic hazards and various geoenvironmental problems (Conduito, 2002). Many new techniques have been developed and redefined during the last quarter of the twentieth century and contractors equipped to implement them have become much more common (Schaefer, 1997). This serious problem experienced by civil engineers is driving civil engineering to look for new techniques at a frequent rate. Methods that were only recently considered to be experimental are now proved and widely accepted (Conduito, 2002). Here in, we introduce the use of waste plastic material as a material for soil improvement which reduces permeability; increases shear strength and can also act as a separator between different layers, reinforcement, fluid barrier and protection of geosynthetics. By using this as a material for soil improvement, we can also save our environment as disposal of plastic is itself an environmental hazard. This technique is simple, economical and does not require any special equipment for use.

Due to heavy rainfall during winters in February 2005, a major slide (Figure 1) developed over Tunnel No. 1 -North Portal of J&K railway project, India. The maximum width of slide zone is above 90m. Besides acute cracks mostly develop at many places between toe of the slide and portal faces, about 19m long false portal and 35m long tunnel have been badly damaged. The tunnel is located at the foot of Vaishno Devi hill along the Reasi thrust zone or within the thrust. The Reasi thrust (M.B.F) separates the underlying younger rocks i.e. Siwalik Group of rocks from overlying older Pre-Cambrian Sirbon dolomite. This site consists of crushed dolomite and overburden derived from crushed rocks. Some outcrops of sandstone and claystone of Murree Formation were also recorded within the thrust zone. These outcrops are caught up pieces during the thrusting of the area.

Figure 1. Tunnel-1, Portal-2 of J&K Railway Project, India where major slump slide has taken place.

During monsoon rains, a crater of 8m dia. and 5m deep (well shaped) formed above the tunnel. This development indicated that ribs around this change got collapsed due to water pressure developed in the crushed material above the tunnel resulting in subsidence of slope area in the well formed. Due to this slide, time delay of 2 years has taken place.

Remedial measures (Figure 2) taken to tackle this problem

• Micropiling has been done to stabilize hill slope in the loose material.
• In addition to this reinforced earth walls are under construction which are made of 0.6m layers, each consisting of fill material, geogrid for reinforcement and geomembrane for drainage. Welded wire meshes with anchors are used as the outer case for R.E walls.
• In Sangaldhan region of J&K railway project, most of the tunnels are being excavated through Murree strata, which include alternate bands of sandstone/siltstone/claystone with three sets of jointing.

• Swelling of clay which leads to excessive pressure on the steel frame of tunnel.
• Excessive settlement has taken place in the region (Figure 3).
• Accumulation of too much of wet and cohesive muck created problem for workers and machinery operating which further lead to delay in regular speed of progress (Figure 4).

It has been observed that most of the problems occur when water comes in contact with such strata; so we require a fluid barrier to reduce the problems.

Figure 2. Remedial measures being taken to tackle the major slump slide.

Figure 3. Excessive Settlement that occurred in Sangaldhan region of J&K Railway Project, India.

Figure 4. Accumulation of too much of wet and cohesive muck.

• Installation of forepoles, during the heading process along the circumference of the arch and installation of Swellex bolts to avoid damage due to swelling and squeezing pressure.
• Installation of self drilling anchors at various points to remove water and cement grouting has been done to fill up voids in the strata (Figure 7).
• Reinforced concrete slabs of 30 cm thickness have been layer in nallahs nearby the tunnel site to prevent seepage of water (Figure 6).
• Protection work for slopes has been done (Figure 5).

Figure 5. Protection work for slopes.

Figure 6. RCC slabs of 30 cm thickness laid in nallahs near by tunnel site

Figure 7. Installation of self drilling anchors at various points to remove water

Plastic as a soil improvement material can perform five primary functions:-

• Separation between Different Layers: Waste plastic bags or sheets can be used as separators to prevent fine grained sub grade soils from being pumped into permeable granular road bases and to prevent road base material from penetrating into the underlying soft sub-grade. Separators maintain the design thickness and roadway integrity (Figure 8).
• Reinforcement for soil: Plastic bottles (Figure 9) when cut from both ends form a cylinder with faces open can be inserted into the soil or embankment as reinforcement (Figure 10). These can also be used for stabilising slopes (Figure 11).
• Fluid Barrier: Waste plastic bags or sheets joined with each other by the process of heating can act as a fluid barrier (Figure 12) to repel the flow of a liquid or gas from one location to another. This has application in asphalt pavement overlay, encapsulation of swelling soils and waste containments.
• Protection of Geosynthetics: A cushion of plastic bags can prevent puncture of geomembrane (by reducing point stress) from the stones in the adjacent soils or drainage aggregate during installation and while in service.
• Erosion Control: Thin layers of plastics added in filled pits or trenches can prevent soil erosion due to surface water runoff or by wind forces and also add to its stability.

Figure 8. Waste plastic as a separator.

Figure 9. Plastic bottles cut from both ends to form a cylinder.

Figure 10. Waste plastic as reinforcement for oil

Figure 11. Waste Plastic for Stabilising a Slope

Figure12. Waste Plastic Material as a Fluid Barrier.

Good specifications (Holtz, 2001) are essential for the success of any civil engineering project, especially when ground improvement is being done. Specifications should be based on the specific properties requirement for design, installation and long term performance.

All specifications include:-

• General Requirements: General requirements include the type of material and comments related to the stability of the material. Other items to be specified are protection from various sources that affect the performance of the material.
• Specific properties: Specific properties including physical index and performance properties as per requirement of the design must be listed. There average properties values must exceed the minimum (or be less than maximum) values specified for that property based on particular test.
• Placement procedure: Placement procedure should be specified in detail and on the construction drawing. These producers include grading and ground clearing requirements, aggregate specification, aggregate lift thickness and equipment requirement. Detailed placement procedures are given by Holtz et.al. (1997).
• Repair Procedure: Repair procedure for damaged section of the material should be detailed in the specifications.
• Acceptance and Rejection Criteria: Acceptance and rejection criteria should be clearly and concisely started in the specifications. All installation should be observed by a competent inspector who is having knowledge about placement procedure and design requirements. Sample and testing should be specified.

Figure 13. Waste Plastics for Erosion Control

Figure 14. UCS Test being performed in Laboratory.

Figure 15. Stress v/s Displacement for Sample 1

Figure 16. Sample at Failure.

Figure17. Stress v/s Displacement graph for Sample 2.

Figure 18. Sample at Failure.

Figure 19. Stress v/s Displacement graph for Sample 3.

Figure 20. Triaxial Test being performed in the laboratory.

Figure 21. Sample at Failure.

Figure 22. Stress v/s Displacement for normal sand sample.

Figure 23. Mohr Circle for normal sand sample.

Figure 24. Stress v/s Displacement for sand having plastic confinement around it.

Figure 25. Mohr Circle for sand sample having plastic Confinement around it.

Figure 26. Permeability tests being performed done in the laboratory.

Figure 27. Slope with Plastic Reinforcement.

Figure 28. Slope with-out plastic.

Figure 29. Effect of showering water on slope with without plastic reinforcement

Figure 30. Effect of showering water on slope plastic reinforcement.

• Environmental Considerations: For most soils; reinforcement materials should have a high resistance to chemical and biological attack, it is therefore, important to assure that the underlying soil is strong enough to support the structure without reinforcement.
• Construction (Survivability) Requirement: In addition to design strength, to survive construction, if it is ripped, punctured, torn or otherwise damaged during construction, its strength will be reduced and failure can result. For all critical applications, high to very high survivability materials are recommended.
• Softness and Workability: For extremely soft working conditions, geosynthetic stiffness or workability may be important consideration. The workability of the material is its ability to support work person during initial placement. Workability is generally related to stiffness, however stiffness evaluation technique and correlation with field workability are very poor (Tan, 1990).
• Experimental Program: A four phase experimental program was launched to establish the performance of proposed techniques as shown in Table 1:

Table 1. Four Phase Experimental Program

On the basis of this investigation, it has been observed that the engineering properties of soils are considerably altered and usage of waste plastics can be recommended as an effective agent for improvement of soils. This study has shown that the treatment of soils using waste plastics can be effectively used in the stabilization of problematic soils. More importantly it offers an interesting potential for making use of an industrial waste, which otherwise adversely affects the environment. This material can be used for fine grained soils in bulk to stabilize the unstable slopes.

In this paper, an attempt has been made to make use of waste plastics which proves to be an effective admixture for improving the quality of weak soils. Waste plastic materials such as scrap plastics, plastic bags provide a viable alternative both for their relatively lower cost and desirable engineering properties.

Based on the results obtained from experimental programme, the following can be concluded:

• It has been observed in clay samples that addition of plastic to clay sample increased its strength by a factor of 2 approximate when tested for UCS and in case of sand sample, there was signification improve in Shear Strength parameter, c and phi; when tested for Triaxial strength. Based on these observations; we can state that addition of plastic confinement layer in soil increases its shear strength of soil and also, adds to its stability. This property can prove useful in highways and building foundations.
• As observed in the experimental work, addition of a plastic layer in between soil sample reduced its permeability to zero. Based on the above observation, we can state that addition of plastic layer also reduces the permeability of soil. This property can prove useful as fluid barrier in case of protection of clay slope and also for reducing infiltration of water at tunnel sites.
• As observed during experimental work, plastic reinforcement in a model of slope reduced the rate of erosion. Based on the observation the authors state that addition of plastic cylinder in top layer of soil improve the stability of the slope by reducing the rate of erosion in soil to a considerable amount.
• Plastic can be used as a separator layer in highway and it can prove good as it is chemically inert, durable and does not deteriorate even for years.
• Waste plastic use in construction is economical as well as safe disposal of plastic whose disposal is otherwise an environmental hazard.
• Hence, using waste plastic material as resource has a two fold advantage. First, to avoid the tremendous environmental problems and second, to reduce the cost of stabilization of soils.