A reinforced soil foundation consists of one or more layers of a geosynthtics reinforcement and controlled fill placed below a footing to create a composite material with improved performance. Soils are good in compression and poor in tension. Geogrid reinforcement is good in tension and poor in compression. A composite of these materials offers the benefits of both geogrid reinforcement used in conjunction with the soil that enables the soil to perform better than it would in its unreinforced state, accommodating greater loads or standing at steeper angles. This saves on the export and import of materials from site, embracing sustainability and reducing polluting truck movements. Use of coal ash, which is a waste material left after burning of coal in thermal power plants, is a better & cost-effective solution to construct a stable slope.
Use of geosynthtics increases bond in the soil system due to the interlocking of soil particles with the reinforcement aperture as well as enhancing the bearing resistance of the transverse members of the reinforcement. Reinforced soil foundations may be used to construct shallow foundations on loose granular soils, soft fine grained soils or soft organic soils. The use of geosynthtics to improve the bearing capacity and settlement performance of shallow foundations has proven to be a cost effective foundation system.
It is shown that the load-settlement behaviour and ultimate bearing capacity of the footing can be considerably improved by the inclusion of a reinforcing layer at the appropriate location in the fill slope.
1.2 Soil Stabilisation
According to the soil stabilisation specifications the best compositions for soil cement are 75% sand, 25% silt and 10% clay. If this composition mixed with cement then it will exhibit good structural characteristics. But with these exact properties it will be not possible that be found. So that we must done one of two things i.e. (i) either can add higher percentage of cement is used for the satisfactory results. (ii) Or can lab tested on the soil and then added the required parts for make the soil idea.
Soil stabilisation defined as mechanical, chemical & physical process of the soil properties which alters with sufficiently to meet the soils specified requirements. Soil stabilisation can be stabilisation with such as plant juices, straw, natural oils, jutes, coir fibers, animals dung & different types of geogrids, fibers etc. Now-a-days soil stabilisation is widely used on the different types of soil and it is also cheap for the engineering properties. Cement, lime, bitumen and fiber reinforcement are the materials widely used as the soil stabilisation. Good soil stabilisation generally depends upon a availability of material variable, understanding of the mixing process, control of the material parameters cheap stabilisers and availability.
1.3 Methods to improve the properties of the soil
Soil improvement defined as a broadest sense of a property of which alters to improve its engineering performance. This may be either a permanent or temporary process which improve & measure the performance of construction facility. The various techniques are used for the soil improvement like surface compaction, vibration methods, dynamic compaction, grouting, chemical stabilisation, thermal methods, and precompression soil reinforcement applications of geomembrances & geogrids etc. From this technique the result of an application may be increased strength, to reduced permeability & compressibility and also improving ground & tail water conditions.
Before application of soil improvement techniques many factors must be considered for the selection of suitable technique like,
‘ Types of soil-sand, clay & organic etc.
‘ Types of structure
‘ Properties of soil like strength, compressibility, permeability etc.
‘ Load distribution of the structures
‘ Permissible settlements ( both total & differential)
‘ Availability of materials & equipments (stone, sand, water, admixture etc.)
‘ Environmental consideration & local experience and preferences
‘ Economic conditions.
1.4 Types of Soil Stabilisation
In soil improvement technique stabilisation of the soil is most commonly method used. There are many different methods used for soil stabilisation i.e. cement, lime and fly ash. Sometimes it can be used combinations of all three. The addition of fly ash is the most versatile and plentiful additive for using stabilisation. Basically it is industry by products and easily availability material. Also define as it is a solid waste product which is created by combustion of coal. It is used directly in the soil stabilisation for the self cementing properties. There is different type of fly ash but class C fly ash most commonly used in the stabilisation due to its self cementing properties.
After that we also stabilised with addition of lime to improving engineering properties of soil. Lime is basically use for construction purpose from very long periods in the history. Lime was first agent which is used for soil stabilisation in the modern construction practise. In the soil stabilisation when the lime is mixed with clayey soil it gives immediate effects on the properties of the soil because of its altering density & electrical charge around the clayey soil particles which leads to attracted them closer to each other. The primarily process is depends upon the modification of the engineering properties of the clayey soil when it is treated with lime. When lime is added with clay then all minerals react with lime and gives significant effect.
1.5 Cement Stabilisation
In this research cement stabilisation method is used so that it will be looked into the more detail. The advantage of cement stabilisation is effect on almost all types of soil. Soil stabilisation with cement has high compressive strength but low ductility. Cement is mixture of lime and clay which is heated to about 1500??C. Generally cement stabilisation reduces the permeability, compressibility & increase the durability, the volume stability for expansive clays. There are four factors that must be carefully controlled when cement stabilisation is used i.e. quantity of cement, compaction of treated soil, mixing of cement with the soil, and curing of treated soil.
1.6 Use of Polypropylene Fiber in Soil Stabilisation
Now-a-days there are many different types of fibers are used in soil stabilisation. It may be used in natural & manmade fibers. These include sisal fiber, jute, shredded tyre, metal, polymer, geosynthtics, polypropylene fiber etc. Above all these fibers have different advantage and disadvantage in the stabilisation. From the previous studies there have carried out that the use of polypropylene fibers in soil stabilisation according tho study polypropylene fiber have increase in tensile strength and fracture toughness, which can prevent the further development of cracks. The addition of polypropylene fibers may result the loss of water content in soils and can increase in shrinkage potential of cement stabilisation soil. The use of polypropylene fiber can reduces the swelling potential of soil but in cannot be decrease the shrinkage potential of soils. In the cement stabilisation the addition of polypropylene fiber can improve the plasticity and also gives a result that causes the variation of failure from brittle to ductile failure.
1.7 Objectives of Research
The various primary objectives of this study were as follows:-
‘ Examine the physical and mechanical properties of clayey soil
‘ Examine the effects of cement when used as a stabilisation method on clay
‘ Examine the effects of polypropylene fiber when added to cement stabilisation with different portions.
‘ To get optimum value of additives required
‘ To evaluate the CBR value and shear strength parameters with different proportion of fiber and cement
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