International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 04 Issue: 12 | Dec-2017 www.irjet.net p-ISSN: 2395-0072 © 2017, IRJET | Impact Factor value: 6.171 | ISO 9001:2008 Certified Journal | Page 1830 A Discussion of Liquefaction Mitigation Methods Maithili K L 1 1 Assistant Professor, Department of Civil Engineering, AMC EC, Bangalore, India ---------------------------------------------------------------------***--------------------------------------------------------------------- Abstract - Loose sandy deposits sometimes change to liquid state during rapid vibrations. This is called LIQUEFACTION and poses a serious problem. When the sandy soils liquefy, structures built on them are seriously affected; for example, heavy structures settle and light buried structures heave. Reliable remediation with respect to liquefaction is necessary in geotechnical engineering practice. The various methodologies for the assessment of liquefaction potential and remedial measures to mitigate liquefaction are based on continuous research and decades of experience in design and construction of structures. This paper reviews the different methods available for soil improvement and aspects of liquefaction resistant structures. Key Words: Liquefaction, Mitigation, Sandy soils, Soil Improvement, Grouting 1. INTRODUCTION When subjected to strong vibrations, saturated sandy soils may suddenly change into muddy water and start flowing. This phenomenon is called Dzliquefactiondz. )t is a process where the strength and stiffness of soil are reduced, which changes the soil to liquid state due to rapid loading like an earthquake shaking, blasting etc. When liquefaction occurs the strength of the soil reduces and the ability of the soil deposit to support foundations for structures like buildings and bridges decreases. Liquefied soil also applies higher pressure on retaining walls that cause them to tilt or slide. This movement can cause damage to structures on the ground surface. During liquefaction the water pressure in the soil increases and this may cause landslides and also collapse of dams. 2. LIQUEFACTION PHENOMENON It is important to understand the conditions that exist in a soil deposit before the application of rapid loading to understand liquefaction phenomenon. A soil deposit comprises of an assembly of individual soil particles, each particle being in contact with the neighboring particles. The overlying soil weight causes contact forces between the particles. Thus, the weight of the overlying soils is transmitted through these contacts. These contact forces hold the individual particles in place and allow the shear resistance of soil to support a structure on the ground surface. The strong vibrations produced during rapid loading like those produced during an earthquake, blasting etc. cause shear stresses, and the soil structure deforms resulting in decrease of contacts between the particles. As the soil arrangement changes, the loosely packed soil particles try to move into a denser configuration. But, during this rapid loading, there is not sufficient time for the water in the pores to be squeezed out. )nstead, the water is Dztrappeddz and inhibits the soil particles from moving closer together. Thus, the pore water pressure rises, contact forces between the individual soil particles decreases. Then the weight of the overlying structures which was originally supported in a vertical direction through the contact points is instead transmitted through pore water. The decrease of contact between the soil particles results in reduction of shear resistance of the soil, thereby softening and weakening the soil deposit. If the pore water pressure becomes too high, the soil particles lose connection with each other. The soil will then have very little strength, and will behave similar to a liquid with the unit weight of the saturated soil – hence the name Dzliquefactiondz. 3. LIQUEFACTION OF SANDS Taking the cohesion intercept as zero, the shear strength of sandy soils as given by Mohr – Coulomb equation is, S =  tan’ ȋͳȌ Where, S = shear strength  = effective stress ’ = Angle of shearing resistance in terms of effective stress. Consider a sand deposit at a depth z from the ground surface with the water table at the ground surface, the effective stress is given as  = satx z- wx z = ’x z Where, sat = saturated unit weight of the sand deposit w = unit weight of water ’= submerged unit weight of the sand deposit Thus (1) becomes, S = ’x z x tan’ If the sand deposit is shaken due to an earthquake or other oscillatory loads, extra pore water pressure ȋu’Ȍ builds up and the shear strength equation becomes S = (’x z – u’Ȍ x tan’ As the excess pore water pressure increases, the shear strength decreases. In extreme case, when the pore water pressure increases so high that the soil looses all its shear strength, then