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1g model tests on Buildings founded on sand-rubber tire shreds mixture
Abstract
The alarming rate at which the scrap rubber tires are generated, its uncontrolled disposal in the environment causing severe pollution are some of the major issues to be addressed. The disaster inflicted by the earthquakes on the low-rise buildings and the unavailability of an affordable low-cost isolation system demand immediate engineering attention. The past laboratory investigations show the potential for use of sand-rubber tire shred mixtures in various geotechnical applications. However, there is a lack of studies particularly on the use of these mixtures for the seismic isolation of buildings. In the present study 1-g laboratory model studies are carried out on the scaled typical low-rise buildings (consisting up to Ground+2 floor levels). Different base conditions such as fixed base and the one resting on sand-rubber tire shred mixture layer in a circular tank of 1.5m diameter and 0.85m height filled with sand are considered. A series of impact hammer tests were conducted on these scaled physical models instrumented with PCB Piezotronics make accelerometers. An HBM make digital carrier frequency amplifier with the data acquisition system is used to measure the impact force and the time histories of accelerations of the structure. The measured peak horizontal accelerations at the different levels of the structure show that the sand-rubber tire shred mixture possesses the adequate potential for their application as seismic isolation materials for low-rise buildings.
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Recycled waste tires when mixed with soil can play an important role as lightweight materials in retaining walls and embankments, machine foundations and railroad track beds in seismic zones. Having high damping characteristic, rubbers can be used as either soil alternative or mixed with soil to reduce vibration when seismic loads are of great concern. Therefore, the objective of this work was to evaluate the dynamic properties of such mixtures prior to practical applications. To this reason, torsional resonant column and dynamic triaxial experiments were carried out and the effect of the important parameters like rubber content and ratio of mean grain size of rubber solids versus soil solids (D
50,r/D
50,s) on dynamic response of mixtures in a range of low to high shearing strain amplitude from about 4×10-4% to 2.7% were investigated. Considering engineering applications, specimens were prepared almost at the maximum dry density and optimum moisture content to model a mixture layer above the ground water table and in low precipitation region. The results show that tire inclusion significantly reduces the shear modulus and increases the damping ratio of the mixtures. Also decrease in D
50,r/D
50,s causes the mixture to exhibit more rubber-like behavior. Finally, normalized shear modulus versus shearing strain amplitude curve was proposed for engineering practice.
This paper examines the strain-dependent dynamic properties (G/G o-logγ-DT curves) of dry and saturated sand-recycled rubber mixtures in a range of shearing strain amplitudes from (5 × 10 -4) % to (6 × 10-1) % using a fixed-free torsional resonant column device. The effect of the rubber content on the pore water pressure buildup and volumetric threshold strain γtv of saturated mixtures, as well as the effect of specimens' geometry on the experimental data, are also presented and discussed. Based on a comprehensive set of experimental results, a modified hyperbolic model, frequently used in practice, has been proposed. An increase in the rubber content leads to a more linear shape of the G/Go-logγ and DT-logγ curves and a reduction in the pore water pressure buildup. Damping is expressed in terms of DT-DTo, which eliminates the effect of the rubber content and the mean confining pressure. The final aim is to propose appropriate design G/G o-logγ-DT curves for sand-rubber mixtures currently used in practice.
This paper presents results of a series of element testing and model testing in which tire derived geosynthetics such as tire chips are utilized as liquefaction preventive backfill material. Undrained cyclic shear tests were conducted on tire chips and sand mixed tire chips for various percentages of mixtures, and the liquefaction potentials of the mixtures were evaluated. The best mixing percentage of tire chips was found to be close to 50% by the total volume of sand. Also, a model shaking table test on a caisson type quay wall was conducted on liquefaction prevention measures for backfill sand reinforced with tire chips. The test results have demonstrated that, despite the fact that the tire chips reinforced composite backfill has a very low relative density, there was no liquefaction in the backfill. Also, the earth pressure on the wall and its residual displacement could be substantially reduced, implying a good performance of the soil-structure system during earthquake loading.
Processed waste tires mixed with soils are applicable in lightweight fills for slopes, retaining walls, and embankments that may be subjected to seismic loads. Rubber's high damping capacity permits consideration of granulated rubber/soil mixtures as part of a damping system to reduce vibration. The dynamic properties of granulated rubber/soil mixtures are essential for the design of such systems. This research investigates the shear modulus and damping ratio of granulated rubber/sand mixtures using a torsional resonant column. Specimens were constructed using different percentages of granulated tire rubber and Ottawa sand at several different percentages. The maximum shear modulus and minimum damping ratio are presented with the percentage of granulated rubber. It is shown that reference strain can be used to normalize the shear modulus into a less scattered band for granulated rubber/sand mixtures. The normalized shear modulus reduction for 50% granulated rubber (by volume) is close to a typical saturated cohesive soil. Empirical estimation of maximum shear modulus of soil/rubber mixtures can be achieved by treating the volume of rubber as voids.
This paper presents the results of experimental investigations on sand–rubber tire shred mixtures. The sand and rubber tire shreds considered were of uniform fine size (<2 mm). Static and dynamic characterization was carried out for pure sand, pure rubber, and sand–rubber tire shred mixtures with rubber content varying 10, 30, and 50% by weight. First, strain-controlled consolidated undrained triaxial tests were carried out to determine static shear strength. Strain-controlled cyclic triaxial tests were then conducted to evaluate shear moduli and damping ratios in the medium to large strain range. Undrained moduli obtained from both experiments were compared. It was found that the mixture with 10% rubber content had the satisfactory static and dynamic properties required for seismic isolation of low-rise buildings.
This paper presents experimental results on the shear modulus of sand–tyre chip (STCh) mixtures. A series of bender element tests was carried out on specimens of sand mixed with varying proportions of tyre chips (TCh). Tests were carried out on STCh mixtures at a constant initial relative density of 50% for different initial effective confining pressures. The bender element test results indicate that the maximum shear modulus of the STCh mixtures increases with effective confining pressure and decreases with the gravimetric proportion of TCh, which ranged from 23 to 138 kPa and 0 to 40%, respectively. However, the strain-controlled cyclic triaxial test results show that the shear modulus at large shear strains decreases with increasing single-amplitude shear strain as a function of the proportion of TCh in the mixture. The lower the proportion of TCh, the larger the degradation observed. The modified Hardin and Drnevich mathematical formulation adequately captures the variation in shear modulus of the STCh mixtures for a wide range of shear strain amplitudes.
This paper presented the results of the investigations on the liquefaction potential and the dynamic properties of sand-tyre chip (STCh) mixtures. A series of strain controlled consolidated undrained cyclic triaxial tests were carried out on specimens of sand mixed with varying proportions of tyre chips (TCh). The specimens of STCh mixture were prepared at a constant initial relative density and tested at an effective confining pressure of 69 kPa. The results show that TCh significantly reduces the liquefaction potential of sand with the addition of gravimetric proportion of TCh between 20 and 40 % to sand. The maximum shear modulus (Gmax) of the STCh mixture was determined by bender element tests for different gravimetric proportions of TCh and effective confining pressures. The initial shear modulus has been found to be influenced by the proportion of TCh and confining pressure. The shear modulus degradation and damping ratio curves were developed for dynamic analysis of sand-scrap tyre mixtures. The increase of scrap tyre in sand-scrap tyre mixtures reduced the shear modulus degradation and increased the damping ratio.
A similitude is derived for the shaking table tests on saturated soil-structure-fluid model in 1 g gravitational field. The main tool used for deriving the similitude is the basic equations which govern the equilibrium and the mass balance of soil skeleton, pore water, pile and sheet pile structures, and external waters such as sea. In addition to the basic equations, an assumption is made upon the constitutive law of soil; i. e. the stress-strain relation is determined irrespective of the confining pressures if appropriate scaling factors are introduced for the stress and the strain for taking the effect of the confining pressures into account.
Applicability of this assumption is examined by using the presently available data under the confining pressures ranging from 0.05 to 1 kgf/cm² (from 5 to 98 kN/m²) and 0.05 to 4 kgf/cm² (from 5 to 392 kN/m²). The results indicate that the assumption is applicable within the intermediate strain levels; i. e. the strain levels which are lower than the strains at failure. In consequence, the similitude derived in the present study is applicable to the model tests in which the major concern is directed toward the deformation, rather than the ultimate state of stability, of the soil-structure-fluid system.
Increasing traffic in developing countries creates extra waste tires and may cause various environmental problems. Due to the lightweight and high capacity of rubber in damping energy, it can be used for seismic forces reduction and absorption of earthquake vibration. Many researchers have carried out many studies on static and dynamic properties of soils mixed with waste rubber. However, large-scale dynamic experimental tests which can be valuable and largely applied in civil engineering are very rare. In this study, dynamic properties of granular soils mixed with different percentages of granulated tire rubber are studied using a series of large-scale consolidated undrained cyclic triaxial tests. The samples diameters and heights were 15 and 30 cm, respectively. The results showed that, for all confining pressures, with an increase in rubber percentage, shear modulus decreases while for any percentage of rubber inclusion, shear modulus increased as the confining pressure increased. It was observed that, with an increase in rubber percentage, damping ratio decreased for the confining pressures of 50 and 100 kPa while this contribution was the reverse for the confining pressures of 200 and 300 kPa. It was also observed that, with a decrease in confining pressure, damping ratio increased for the soil without rubber inclusion and it was the reverse for the soil with rubber inclusion. Finally, new relations were introduced to define maximum shear modulus (Gmax) and normalized shear modulus (G/Gmax) as functions of confining pressure (σ3) and granulated rubber percentage (R).
This study examines the small-strain dynamic properties of mixtures composed of sandy and gravelly soils with granulated tire rubber in terms of shear modulus (GO), and damping ratio in shear (Dmin). Torsional resonant column tests are performed on dry, dense specimens of soil-rubber mixtures in a range of soil to rubber particles size 5:1–1:10 and rubber content from 0 to 35% by mixture weight. The experimental results indicate that the response of the mixtures is significantly affected by the content of rubber and the relative size of rubber to soil particles. Concering the small-strain shear modulus, an equivalent void ratio is introduced that considers the volume of rubber particles as part of the total volume of voids. Based on a comprehensive set of test results a series of equations were developed that can be used to evaluate the shear modulus and damping ratio at small shear strain levels if the confining pressure, the content of rubber by mixture weight, the grain size of soil and rubber particles, and the dynamic and physical properties of the intact soil are known.