25-08-2017, 09:32 PM
EFFECT OF GROUND GRANULATED BLAST FURNACE SLAG ON STABILIZED EMBANKMENT SOILS UNDER DYNAMIC LOADING
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ABSTRACT: The main objective of the present study is to improve various engineering properties of the soil by using waste material Ground Granulated Blast Furnace Slag (GGBS) as an alternative to lime or cement. In this study, usage of GGBS with different proportions in subgrade was analysed under static and dynamic loads. The Index and Engineering properties of soil with and without GGBS was determined for different combinations of GGBS with soil and an optimum content of usage of GGBS was found out.. It is observed that the strength improvement depends on the amount of GGBS. The work is further extended to know the variation in strength of soil with and without GGBS under dynamic loads by conducting cyclic triaxial tests. Results are presented for strain controlled unconfined cyclic triaxial tests carried out as per ASTM D3999 for determination of dynamic soil properties (i.e., shear modulus and damping ratio). The effect of GGBS inclusion is evaluated as a function of shearing-strain amplitude, confining stress, cycle number and GGBS content. It was found that the effect of GGBS content is significant on both shear modulus and damping ratio particularly at high shear strain amplitude. Thus effect of GGBS in the improvement of dynamic properties of pond sand is investigated and feasibility of GGBS for ground improvement is explored
Keywords
Pond Sand, Ground Granulated Blast Furnace Slag, CBR, Standard Proctor; Unconfined compression test, Cyclic triaxial test.
1. INTRODUCTION
Soil is generally considered as a three-phase system causing significant changes in the system characteristics due to interaction of these phases under applied static and dynamic loads. Static loads remain unchanged over space and time, while dynamic load represents loading conditions which vary both in their direction and magnitude. Damage due to dynamic loading (e.g. earthquake strong motions) is substantially influenced by the response of soil deposits which is governed by the dynamic soil properties.
Dynamic soil properties namely shear wave velocity, variation of stiffness or modulus reduction and material damping with strain levels, and liquefaction susceptible parameters are the primary input parameters for various dynamic studies and investigations. In general, soil properties depends on different state parameters such as the state of stress, void ratio, confining stress and water content, stress history, strain levels, and drainage conditions. Apart from the influence of the above-mentioned parameters, dynamic soil properties are significantly influenced by the dynamic amplitude and frequency of the applied load. Hence determination of the dynamic soil properties requires the consideration of all the above-mentioned influencing parameters.
For the measurements of strain dependent dynamic properties, several laboratory and field techniques are being used. At low strain levels, resonant column test, ultrasonic pulse test and the piezoelectric bender element tests are being used. However, at large strain levels, the cyclic triaxial test, cyclic direct simple shear test and cyclic torsional shear test devices are used. The recent developments in the numerical analysis for non-linear dynamic responses of grounds due to strong earthquake motions have increased the demand for the dynamic soil properties corresponding not only at small strain levels but also at large strain levels. The shear modulus and the damping of soils estimated at large strains would serve as a key factor for the assessment of ground response and geotechnical engineering related structures due to strong earthquake motions.
Laxmikant Yadu et al. (2013) studied the effect of granulated blast furnace slag in the engineering behavior of stabilized soil. The performance of GGBS stabilized soils was evaluated using physical and strength performance tests namely, plasticity index, specific gravity, free swell index, compaction, swelling pressure, California bearing ratio (CBR) and unconfined compressive strength (UCS) at different amounts of GGBS i.e., 3, 6, 9 and 12%. Based on strength performance tests, optimum amount of GGBS was determined as 9%. Moreover, results indicate that inclusion of GGBS increases the strength of soft soils. Similarly, significant improvement has been observed for unsoaked and soaked CBR value of soils.
B.K.Maheshwari & R.S. Jakka (2012) studied dynamic Properties of Solani Sand Reinforced with Coir Fiber. In this paper cyclic tri-axial tests are conducted on cylindrical reinforced and unreinforced sand samples (collected from solani river, Roorkee, India). Remolded samples were prepared with different percentages of fiber content and tested. Results shows that fiber content causes significant changes in both shear modulus and damping ratio at high shear strain amplitude. For example at 1.125% shear strain, shear modulus increases by a margin of 60% for 0.75% coir fiber contents. At 0.25% fiber content normalized shear modulus increases significantly with the increase in confining pressure and also damping ratio decreases with increase in confining pressure.
Kong Ling-Wei (2011) studied dynamic characteristics of soft clay under traffic load. In this paper a series of undrained dynamic triaxial tests were conducted at different cyclic stress level, confining pressure to investigate soft clayey soil dynamic characteristics. The results shows that as confining pressure increases, the shear modulus increases and damping ratio decreases. At higher confining pressure, the number of loading cycles required for liquefaction increases. And also results shows that as dynamic strain increases, shear modulus decreases and damping ratio increases.
This paper presents work in utilising industrial by-products as suitable admixture to enhance the geotechnical properties of soft soils. Hence laboratory tests were performed to study the effect of GGBS on the strength characteristics of soils under static and dynamic loads. Firstly tests were performed to determine optimum content of GGBS. Secondly Unconfined Cyclic triaxial tests were conducted to determine the effect of optimum content of GGBS on dynamic properties of soil.
2. MATERIALS
Soil sample was collected from Pond (Poorly graded sand) in NIT Tiruchirappalli, Tamil Nadu, India.
Ground Granulated Blast Furnace Slag was collected from Salem Steel Plant, Salem, Tamil Nadu.
The slag produced at blast furnace during pig iron manufacturing is called blast furnace slag. Depending upon the cooling process, three types of slags are generated; namely, air-cooled slag, granulated slag and expanded slag. Granulated slag is produced by quenching the molten slag by means of high-pressure water jets. This slag is crushed, pulverised and screened for use in various applications. Blast furnace slag has a glassy, disordered, crystalline structure which can be seen by microscopic examination which is responsible for producing a cementing effect. The GGBS used in this study was collected from Salem Steel Plant in Tamil Nadu, India.
5.0 UNCONFINED CYCLIC TRIAXIAL TEST RESULTS
5.1 Sample preparation and tests conducted
Cyclic triaxial tests were conducted on cylindrical samples prepared soil with 0%, 8%, 16% and 24% GGBS contents at three different shear strain levels i.e.07.85%, 12.25%, 16.80% at loading frequency of 1Hz and calculations were carried out as per ASTM D3999 (2011). Reinforced and un-reinforced Cylindrical samples of dimensions 38 mm diameter and 76 mm height were used. A total of 12 samples were tested.
5.2. Formulation used
The shear modulus is evaluated as the slope of a secant line that connects the extreme points on a hysteresis loop at a given shear strain, as shown in Fig. 5.1. As the cyclic strain amplitude increases, the shear modulus decreases.