Note for Ground Improvement Techniques - GIT By ANNA SUPERKINGS
- Ground Improvement Techniques - GIT
- Note
- ANNA UNIVERISTY - HITECH
- Civil Engineering
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Fatima Michael College of Engineering & Technology GROUND IMPROVEMENT TECHNIQUE 1.1 Introduction Ground improvement has been both a science and art, with significant developments observed through ancient history. From the use of straw as blended infill with soils for additional strength during the ancient Roman civilizations, and the use of elephants for compaction of earth dams during the early Asian civilizations, the concepts of reinforced earth with geosynthetics, use of electrokinetics and thermal modifications of soils have come a long way. The use of large and stiff stone columns and subsequent sand drains in the past has now been replaced by quicker to install and more effective prefabricated vertical drains, which have also eliminated the need for more expensive soil improvement methods. The early selection and application of the most appropriate ground improvement techniques can improve considerably not only the design and performance of foundations and earth structures, including embankments, cut slopes, roads, railways and tailings dams, but also result in their cost-effectiveness. Ground improvement works have become increasingly challenging when more and more problematic soils and marginal land have to be utilized for infrastructure development. 1.2 Need for Ground Improvement Techniques As more engineering structures are built, it becomes increasingly difficult to find a site with suitable soil properties. The properties at many sites must be improved by the use of some form of soil improvement methods, such as: static or dynamic compaction, reinforcement, drainage or by the use of admixtures. Thus, it is important for the soil engineers to know the different soil improvement methods; the degree to which soil properties may be improved; and the costs and benefits involved. In this way, the soil engineer can gain knowledge in order to design ground improvement projects as well as to advise the client regarding value engineering to save cost and obtain maximum benefits for the specific project. The following are some of the methods used as ground improvement techniques: Surface Compaction, Deep Compaction, Preloading, Vertical Drains, Stone Columns, Vacuum Drainage, Mechanically Stabilized Earth (Reinforced Earth), Granular Piles, Micropiles, Lime Stabilization, Cement Stabilization, Chemical Stabilization, Grouting, Geotextiles, Lightweight Embankment Materials. 1.3 Current status and the scope in the profession Fatima Michael College of Engineering & Technology
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Fatima Michael College of Engineering & Technology Ground improvement has been both a science and art, with significant developments observed through ancient history. From the use of straw as blended infill with soils for additional strength during the ancient Roman civilizations, and the use of elephants for compaction of earth dams during the early Asian civilizations, the concepts of reinforced earth with geosynthetics, use of electrokinetics and thermal modifications of soils have come a long way. The use of large and stiff stone columns and subsequent sand drains in the past has now been replaced by quicker to install and more effective prefabricated vertical drains, which have also eliminated the need for more expensive soil improvement methods. The early selection and application of the most appropriate ground improvement techniques can improve considerably not only the design and performance of foundations and earth structures, including embankments, cut slopes, roads, railways and tailings dams, but also result in their cost-effectiveness. Ground improvement works have become increasingly challenging when more and more problematic soils and marginal land have to be utilized for infrastructure development. Rapid urban and industrial growth demands more land for further development. In order to meet this demand land reclamation and utilization of unsuitable and environmentally affected lands have been taken up. These, hitherto useless lands for construction have been converted to be useful ones by adopting one or more ground improvement techniques. Navi Mumbai is one such example. The field of ground improvement techniques has been recognized as an important and rapidly expanding one. 1.4 Some Techniques - an overview The ground can be improved by adapting certain ground improvement techniques. Vibrocompaction increases the density of the soil by using powerful depth vibrators. Vacuum consolidation is used for improving soft soils by using a vacuum pump. Preloading method is used to remove pore water over time. Heating is used to form a crystalline or glass product by electric current. Ground freezing converts pore water to ice to increase their combined strength and make them impervious. Vibro replacement stone columns improve the bearing capacity of soil whereas Vibro displacement method displaces the soil. Electro osmosis makes water flow through fine grained soils. Electro kinetic stabilization is the application of electro osmosis. Reinforced soil steel is used for retaining structures, sloping walls, dams etc…. seismic loading is suited for construction in seismically active regions. Mechanically stabilized earth structures create a reinforced soil mass. The geo methods like Geosynthetics, Geogrid etc. are discussed. Soil nailing increases the shear strength of the in-situ soil and restrains its displacement. Micro pile gives the structural support and used for repair/replacement of existing foundations. Grouting is injection of pumpable materials to increase its rigidity. Fatima Michael College of Engineering & Technology
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Fatima Michael College of Engineering & Technology The jet grouting is quite advanced in speed as well as techniques when compared with the general grouting. COMPACTION 2.1 Introduction Many types of earth construction, such as dams, retaining walls, highways, and airport, require man-placed soil, or fill. To compact a soil is to place it in a dense state. The dense state is achieved through the reduction of the air voids in the soil, with little or no reduction in the water content. 2.2 Objectives - Decrease future settlements - Increase shear strength - Decrease permeability 2.3 General Compaction Methods Coarse-grained soils Laboratory Field Vibrating hammer Hand-operated vibration plates Motorized vibratory rollers Rubber-tired equipment Free-falling weight; dynamic compaction (low frequency vibration, 4~10 Hz) Fine-grained soils Falling weight and hammers Kneading compactors Static loading and press Hand-operated tampers Sheepsfoot rollers Rubber-tired rollers 2.4 Laboratory Compaction The purpose of a laboratory compaction test is to determine the proper amount of mixing water to use when compacting the soil in the field and the resulting degree of denseness which can be expected from compaction at this optimum water. The proctor test is an impact compaction. A hammer is dropped several times on a soil sample in a mold. The mass of the hammer, height of drop, number of drops, number of layers of soil, and the volume of the mold are specified. Fatima Michael College of Engineering & Technology
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Fatima Michael College of Engineering & Technology Standard Proctor Test Weight of hammer = Height of fall = No. of Impacts = No. of layers = 2.6 kg 310 mm 25 3 Modified Proctor Test Weight of hammer = Height of fall = No. of Impacts = No. of layers = 4.9 kg 450 mm 25 3 2.4.1 Procedure - Several samples of the same soil, but at different water contents, are compacted according to the compaction test specifications. - The total or wet density and the actual water content of each compacted sample are Mt measured. , d Vt 1 w - Plot the dry densities d versus water contents w for each compacted sample. The curve is called as a compaction curve. 2.5 Field Compaction Equipment Smooth-wheel roller (drum) - 100% coverage under the wheel - Contact pressure up to 380 kPa - Can be used on all soil types except for rocky soils. - Compactive effort: static weight - The most common use of large smooth wheel rollers is for proof-rolling subgrades and compacting asphalt pavement. Pneumatic (or rubber-tired) roller - 80% coverage under the wheel - Contact pressure up to 700 kPa - Can be used for both granular and fine-grained soils. - Compactive effort: static weight and kneading. - Can be used for highway fills or earth dam construction. Sheepsfoot rollers - Has many round or rectangular shaped protrusions or “feet” attached to a steel drum - 8% ~ 12 % coverage - Contact pressure is from 1400 to 7000 kPa Fatima Michael College of Engineering & Technology
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