Sand-rubber Mixtures Research Articles

Numerical Simulation of Geotechnical Isolation of Building Subjected to Earthquake Using Rubber Sand Mixtures

The use of recycled rubber in various civil engineering applications has seen a considerable rise in recent years. The rubber-soil mixture can exhibit a higher energy absorption capacity than soil alone, which would reduce the energy applied to structures, the stresses, and shocks they undergo. Base isolation is the process of isolating the base of a structure to limit the effects of earthquakes, so that the seismic forces applied to the base of the bedrock cannot move with the same intensity towards the super structure.In this work, the beneficial effects of rubber mixtures (RSM) in mitigating earthquakes when these mixtures are inserted as layers in the soil profile are highlighted; the approach is based on a method of using worn tires for seismic protection applications for infrastructures subjected to seismic loads. It involves mixing particles from used tires with soil materials and placing the mixtures under the foundation of the building as geotechnical insulation systems for vibration absorption.The foundation of a four-storey building is implanted in a soil profile in which a layer of rubber-sand mixture (RSM) has been inserted; to perform the role of seismic isolation when subjected to seismic excitation.The investigation is focused on the variation in the thickness of the layer on the one hand (between 1m and 4m), and on the other hand on the position of this layer in the soil mass (top, middle and bottom of the profile).The peaks of horizontal accelerations recorded at the base and top of the structure show that the sand-rubber mixture has adequate and promising potential for their application as seismic isolation materials for low-rise buildings. Moreover, the thickness of the layer and its location are two very determining parameters in the improvement of the performances of these RSM mixtures, especially in terms of reduction of the acceleration peak recorded.

The micro-mechanical behaviour of sand–rubber mixtures under shear: A numerical study based on X-ray micro-tomography

A CT image-based discrete element model (DEM) incorporating the realistic particle morphology of sand grains was developed to investigate the micro-mechanical behaviours of sand–rubber mixtures (SRMs) under triaxial compression. The model was validated by comparing the numerically simulated macro- and microscale mechanical behaviour of SRMs with the experimental results acquired in triaxial testing with in-situ μCT scanning. SRMs with irregularly shaped grains have a higher degree of heterogeneous distribution of contact force chains than those with spherical grains. Moreover, rubber content and particle shape have a significant influence on the ‘most active phase’, namely, the time-period during which the maximum number of contacts emerged to participate in the stress-transmission, of different types of contacts. The ‘most active phase’ of sand–sand contacts appeared earlier than that of sand–rubber contacts. SRMs with a lower rubber content were more likely to have an earlier ‘most active phase’ for each type of contact. The sequence of the ‘most active phase’ for the sand–rubber contacts and rubber–rubber contacts appeared during shear was affected by the particle shape of the SRM specimens. The results highlight the important role of rubber content and particle shape in the stress-transmission behaviour of SRMs.

Shaking table study on rubber-sand mixture cored composite block as low-cost isolation bearing for rural houses

Historical and recent earthquakes have caused severe damage to rural houses worldwide, which are often characterized by low story heights, high stiffness, and limited budgets. In this regard, low-cost seismic isolation strategies hold great potential for protecting low- and medium-rise buildings. This paper proposes a novel rubber sand mixture cored composite block (RSMCB) as a low-cost alternative to conventional expensive isolation bearings. The construction of the RSMCB involves filling the hollow of a plain concrete block with a lightweight material made of granulated rubber and natural sand and then covering the surface with a square brick slightly smaller than the hollow's size. To evaluate the effectiveness of the RSMCB, a series of shaking table tests were conducted, covering factors of rubber content, cover plate size, upper block mass, and paving mode. The results indicate that the utilization of the RSMCB layer effectively mitigates large displacement in the superstructure during the cyclic loading, thereby functioning as an energy dissipation and seismic reduction measure. Moreover, the isolation effect of the RSMCB layer increases with the seismic intensity attributed to the nonlinear variation of dynamic parameters of the mixed granular material with shear strain. These findings suggest that the proposed isolation strategy improves the strength and vertical stiffness of the original sand-rubber layer, making it a desirable and sustainable solution for seismic design applications in rural housing.

Theoretical calculation model for the thermal conductivity of scrap tire rubber–sand mixtures based on soil components

Theoretical calculation model for the thermal conductivity of scrap tire rubber–sand mixtures based on soil components

Internal Friction Angle of Cohesionless Binary Mixture Sand–Granular Rubber Using Experimental Study and Machine Learning

This study aimed to examine the shear strength characteristics of sand–granular rubber mixtures in direct shear tests. Two different sizes of rubber and one of sand were used in the experiment, with the sand being mixed with various percentages of rubber (0%, 10%, 20%, 30%, and 50%). The mixtures were prepared at three different densities (loose, slightly dense, and dense), and shear stress was tested at four normal stresses (30, 55, 105, and 200 kPa). The results of 80 direct shear tests were used to calculate the peak and residual internal friction angles of the mixtures, and it was found that the normal stress had a significant effect on the internal friction angle, with an increase in normal stress leading to a decrease in the internal friction angle. These results indicated that the Mohr–Coulomb theory, which applies to rigid particles only, is not applicable in sand–rubber mixtures, where stiff particles (sand) and soft particles (rubber) are mixed. The shear strength of the mixtures was also influenced by multiple factors, including particle morphology (size ratio, shape, and gradation), mixture density, and normal stress. For the first time in the literature, genetic programming, classification and regression random forests, and multiple linear regression were used to predict the peak and residual internal friction angles. The genetic programming resulted in the creation of two new equations based on mixture unit weight, normal stress, and rubber content. Both artificial intelligence models were found to be capable of accurately predicting the peak and residual internal friction angles of sand–rubber mixtures.

Synthesis and Evaluation of Engineering Properties of Polymer-Coated Glass Beads.

Modern construction projects are often challenging, which has increased the demand for innovative materials that ensure improved safety, durability, and functionality. To explore the potential of enhancing soil material functionality, this study synthesized polyurethane on the surface of glass beads and evaluated their mechanical properties. The synthesis of polymer proceeded according to a predetermined procedure, where the polymerization was confirmed through analysis of chemical structure by Fourier transform infrared spectroscopy (FT-IR) and microstructure observation by a scanning electron microscope (SEM) after complete synthesis. The constrained modulus (M) and the maximum shear modulus (Gmax) of mixtures with synthesized materials were examined by using an oedometer cell equipped with bender elements under a zero lateral strain condition. Both M and Gmax decreased with an increase in the contents of polymerized particles due to a decrease in the number of interparticle contacts and contact stiffness induced by the surface modification. The adhesion property of the polymer induced a stress-dependent change in M but was observed to have little effect on Gmax. Compared to the behavior of the rubber-sand mixtures, polymerized particles show the advantage of a smaller reduction of M.

A numerical study on the seismic design of buildings seated over an RSM layer

In recent years, there has been a significant effort to create innovative and affordable seismic protection systems that can be widely used in developing regions. Traditional isolators are often heavy and expensive, which restricts their application in residential buildings. To address this challenge, low-cost and low-tech approaches are being explored, such as the incorporation of rubber into the soil beneath a building’s foundation. This approach aims to dampen part of the seismic energy before it reaches the superstructure. This paper investigates the use of rubber-sand mixture (RSM) as a foundation layer to improve the seismic performance of structures. The effects of varying RSM dimensions on the footing acceleration response, structural weight, and base shear forces of a prototype five-story building are analyzed by numerical simulations. Results show that increasing the depth of the RSM layer and RSM content can significantly reduce the acceleration response, particularly for low-rise buildings with natural periods less than 0.3 s. Thicker RSM layers are found to be more effective in reducing input acceleration than wider layers, although such effect declines as the depth ratio exceeds 0.25. Furthermore, incorporating RSM as a base isolator can lead to a considerable reduction in both the maximum base shear force and structural weight, with up to 30% reduction achieved with RSM 35%. This study suggests that RSM has potential as a cost-effective and efficient solution for improving the seismic performance of low-to-mid-rise structures, and the effect of the depth of RSM layer and RSM content should be carefully considered for optimal design.

Dynamic Response of Tunnels with a Rubber-Sand Isolation Layer under Normal Fault Creep-Slip and Subsequent Seismic Shaking: Shaking Table Testing and Numerical Simulation

Tunnels may suffer severe damage when passing through an active fault in high-intensity earthquake zones. The present study aims to investigate the performance of an isolation layer composed of a rubber-sand mixture, an emerging trend in low-cost seismic mitigation studies. Based on the Ngong tunnel in the Nairobi-Malaba Railroad in Kenya, Africa, the effect of the rubber-sand isolation layer on the acceleration and strain of the tunnel lining was investigated through a shaking table test under small normal fault creep-slip and subsequent seismic shaking. The influences of the length of the isolation layer and the rubber content in the mixture were analyzed by numerical simulation. The results indicate that the isolation layer slightly reduces the acceleration response of the tunnel lining within the fault and obviously reduces the permanent strain of the invert and crown within the fault under small normal fault creep-slip and subsequent seismic excitation. The mitigation effect of the isolation layer is related to the length of the isolation layer and the rubber content in the mixture. In the case of this study, the length of the isolation layer is triple the fault width (influence range of the fault) and the appropriate enhancement of the rubber content of the isolation layer offers favorable conditions for mitigation effect, respectively.

Stress–strain–strength behavior of geosynthetic reinforced rubber–sand mixtures

Stress–strain–strength behavior of geosynthetic reinforced rubber–sand mixtures

A micromechanical investigation of sand–rubber mixtures using the discrete element method

Mixing soil or sand with tire rubber fibers or buffings is a practical and promising solution to the problem of global scrap tire pollution. However, sand–rubber mixtures exhibit unsatisfactory and complex mechanical properties in engineering applications due to the large deformation of rubber fibers. In this study, a detailed numerical approach to modeling mixtures of sand and rubber fibers via the discrete element method (DEM) was proposed, and the effect of rubber content on the macroscopic and microscopic mechanical behaviors of sand–rubber mixtures was investigated. Furthermore, the reinforcing mechanism by which rubber fibers contribute to the micromechanics of sand–rubber mixtures was explored to determine the optimum rubber content in terms of soil mechanical performance. Comparative analysis of the experimental and numerical results demonstrated the applicability and ability of the proposed DEM model and related parameters for modeling sand–rubber mixtures. Through investigation of the constitutive behaviors of sand–rubber mixtures with various rubber contents under triaxial compression, a rubber content of 20% was found to provide the best shear resistance in the critical state. The micromechanics of sand–rubber mixtures, namely particle kinematics, the interparticle coordination number and rubber fiber deformation, were investigated to demonstrate the specific reinforcing mechanism of rubber fibers with respect to improved soil performance. The resulting data strongly support the identified optimum rubber content for sand–rubber mixtures that will provide a valuable guidance to the relevant engineering applications.

Sand Rubber Mixtures under Oedometric Loading: Sand-like vs. Rubber-like Behavior

Each year, the number of scrap tires disposed of in huge piles across the world continuously increases. Consequently, new recycling solutions for these materials have to be proposed. Among them, one possibility consists of shredding tires and mixing the obtained tire chips with sand, which can be used as alternative soils in various geotechnical applications, such as backfilling for retaining structures, slope and highway embankment stabilization, road constructions, soil erosion prevention, and seismic isolation of foundations. Such types of mixtures are highly heterogeneous due to the important difference in elasticity and deformability between the two constituents, which leads to complex mechanical behavior. In this article, the one-dimensional loading/unloading behavior of sand-rubber mixtures is investigated by laboratory strain-controlled experiments performed for different packing densities, particle sizes, rubber contents, and sand/rubber size ratios. After a global analysis of the increase of the packing deformation with the rubber fraction and the stress level, a novel criterion to classify the behavior of the mixture as sand-like or rubber-like was proposed, based on the concavity of the void ratio—log of vertical stress curve. The concavity increased with the stress level and the rubber fraction, up to the limits where the saturation of the voids due to their filling with rubber induces a rubber-like behavior. A simplified phase diagram, limited to the range of this study, is proposed. The one-dimensional confined stiffness and the swelling behavior were also analyzed.

Field Testing on active isolation of vibrating foundations in Middle-frequency range

Open or in-filled trenches are usually used for suppressing disturbing ground vibrations induced by various man-made sources such as construction activities, transportation systems and power plants. However, using a trench to suppress low-frequency excitations, may be either impractical or inefficient. This study evaluates different mitigation strategies to suppress middle-frequency ground vibrations (i.e. between 25 and 40 Hz), generated by a rotating mass vibrator mounted on a shallow foundation in the field. The mitigation strategies encompassed placing isolating materials including sand-rubber mixture (SRM) in bags and block-type EPS geofoam, in sidewalls and bottom of a cubic pit excavated underneath the vibrating foundation and then backfilling the pit. Using EPS geofoam resulted in up to 30% and 20% reduction in ground vibration amplitudes of vertical and horizontal components, respectively. However, SRM-filled bags provided better efficiency which increased with rubber content. For instance, up to 40% and 50% reduction were observed, respectively in vertical and horizontal ground vibrations, when a SRM mixture with 25% rubber content was used. The excavation depth in current study was comparably lower than that of an open trench, for the same vibration reduction level, and thus considerably reduced the earthwork volume.

DEM-based study on the mechanical behaviors of sand-rubber mixture in critical state

This paper presents a numerical method to investigate the critical-state behaviors of the soft-rigid mixture via DEM simulation. First, according to a series of laboratory tests of sand-rubber mixtures, a systematic calibration framework is proposed to acquire the numerical parameters. Then, cubic compression tests are conducted with different rubber contents and confining pressures. The evolution of micro-scale properties, including the internal structure, stress network, and fabric anisotropy, is investigated to reveal the influences of rubber content and confining pressure on the micromechanical behaviors of sand-rubber mixtures. Through the investigation of the macroscopic responses, a unified hypoplasticity constitutive model is established and the relationships between the critical state parameters and rubber content are explored. The results show that the critical state shear strength of sand-rubber mixtures decreases with increasing rubber content and does not correlate with confining pressure. Additionally, the influence of rubber content on shear behaviors of SRMs is highly dependent on confining pressure, e.g., SRMs are more likely to exhibit soft-like behaviors under higher confining pressure. This study lays a foundation for the engineering design of geotechnical structures with an appropriate filling of the sand-rubber mixture. Moreover, this study also paves a viable way for a comprehensive investigation of other soft-rigid mixtures in the critical state.

Cyclic and Postcyclic Interface Characteristics of Geotextile-Embedded Sand-Rubber Composites

A set of 48 cyclic and 12 monotonic large-scale direct shear tests was performed to assess the interface properties of sand–rubber composite along a nonwoven geotextile layer. Rubber content, semiamplitude of the shear displacement, and applied normal stress all were varied to determine the cyclic, postcyclic, and monotonic interface response of the composite system under shear loading. The test results show that adding 40% granulated rubber to pure sand caused approximately 50% reduction in the maximum mobilized interface shear stress as the loading cycles progressed. The addition of granulated rubber to the sand decreased both the damping and the shear stiffness of the interface for all values of displacement amplitude and normal stress; in particular, for the energy dissipation, the observations were associated with the higher linearity of the stress–strain relationship when adding rubber, thereby reversing the typical trend of higher damping at smaller strains or displacements. In addition, an increase in the displacement amplitude value yielded a reduction in the secant shear stiffness, but contrarily increased the damping ratio of the geotextile–composite soil interface. An increasing trend of the hardening factor was observed through the initial cycles of loading for the samples containing 40% granulated rubber, which was ascribed to the increased densification capability of the sand–rubber mixture with the progression of the loading cycles; however, this response was not captured for the pure sand–geotextile interface.

Seismic isolation effect of rubber-sand mixture cushion under different site classes based on a simplified analysis model

The use of rubber-sand mixture (RSM) cushion in geotechnical seismic isolation (GSI) systems is an emerging technique for protecting buildings in earthquake-prone areas. The advantage is that RSM with high shear resistance and low shear modulus improves the foundation soil, allowing seismic energy to be partially dissipated in the cushion before it is transmitted to the structure. However, the isolation effect of the RSM cushion considering site classification has not been recognized due to the complexity of the problem. In this paper, a simplified analysis model is established to study the seismic performance of the RSM cushion, in which 195 ground motion records are obtained from different site conditions according to the Code for Seismic Design of Buildings GB50011-2010, reflecting the influence of site classification. By using the developed theoretical analysis method, the seismic isolation effect of the RSM cushion under different site classes is investigated. The key influencing factors to be considered include the cushion thickness, base pressure and seismic excitation intensity. The results show that: 1) The isolation effect of the underlying RSM cushion on the superstructure is affected by site classification. The harder the site, or more specifically, the shorter the predominant period of the site, the better the isolation effect of the RSM cushion. 2) For the same site classification, the isolation effect increases with increasing cushion thickness, base pressure and seismic excitation intensity. In particular, the robustness of the seismic performance of the RSM cushion deteriorates upon reaching a cushion thickness of 500 mm, and this deterioration in robustness is independent of site classification. Overall, the present study is the first systematic analysis of the effects of ground motion on GSI systems with RSM as the core under different site classes, and the research findings are of great significance for the low-cost seismic design of residential houses in developing countries.

Experimental Investigation on the Compressive Behaviour of Rubber-Sand Mixtures Under Repeated Loading-Unloading

Experimental Investigation on the Compressive Behaviour of Rubber-Sand Mixtures Under Repeated Loading-Unloading

Investigation of Geotechnical Seismic Isolation Bed in Horizontal Vibration Mitigation

Recently, a ground-borne vibration mitigation solution using rigid wave impeding blocks embedded in the foundation bed of buildings/embankments has emerged as a passive vibration isolation mechanism, wherein energy dissipation due to material damping was often ignored. The present study aims to examine the performance of a flexible foundation bed composed of a sand-rubber mixture (SRM) for ground-borne vibration isolation, referred to as geotechnical seismic isolation (GSI) bed, an emerging trend in low-cost earthquake mitigation studies. Field investigation consisting of vibration measurement on a model footing resting on a GSI bed with SRM and SRM-geogrid composite subjected to horizontal sinusoidal vibration of frequency 10 to 30 Hz with acceleration amplitude of 0.18 g to 0.33 g were undertaken. Further, a three-dimensional finite-element analysis of a model footing resting on a GSI bed made of geogrid reinforced SRM composite is presented. The strain-dependent nonlinear response of soil and SRM were accounted for using suitable hypoelastic and hyperelastic constitutive formulations, respectively. For the GSI bed, SRM with 10% to 50% rubber content and biaxial geogrids were studied. The numerical simulation and field study results were found to be comparable with a nominal difference that verifies the adequacy of the developed numerical modeling procedure. It was observed that GSI (30% rubber content) effectively reduced the vibration acceleration amplitude of the model footing above 40% and 55% for without and with geogrid reinforcement, respectively. Overall, the field experimental and numerical results demonstrate the proposed geogrid reinforced GSI bed as an effective ground vibration mitigation solution for typical industrial environments.

A reinterpretation of the mechanical behavior of rubber-sand mixtures in direct shear testing

The mechanical behaviors and properties of rubber-sand mixtures are interesting and of practical importance but are not fully understood yet. In this study, 168 direct shear tests were performed to investigate the shear behaviors and strength of rubber-sand mixtures by considering various rubber content and rubber particle sizes, with an analysis made from the energetic and micromechanical perspectives to illuminate the underlying mechanisms. The experimental results indicate that increasing the rubber content helps reduce the shear strength of rubber-sand mixtures and restrain the mobilization of dilatancy, whereas it aids in promoting the ductility. The role of rubber particle size relies on the rubber content level: increasing the rubber particle size basically weakens the shear strength and dilatancy of rubber-sand mixtures with a relatively high rubber content, but it contributes to a minor increase in the shear strength at large shear displacements, given a low rubber content. The stress-dilatancy behaviors of rubber-sand mixtures can be characterized by a general linear function, in which the dilatancy coefficient ξ and critical state friction angle ϕcs, as two crucial function parameters, are both variables affected by the rubber content, rubber particle size and normal pressure. The energetic and micromechanical analysis based on the idealized conceptual model reveals that the impact of rubber content, rubber particle size, and normal pressure on the critical state shear strength is fundamentally linked with a combined effect stemming from the roughness of shear plane and relative number of particle sliding and rolling behaviors, the variation of which is in essence governed by the deformation of rubber particles.

Dynamic behavior of geocell-reinforced rubber sand mixtures under cyclic simple shear loading

Due to the attributes of low shear modulus and high initial damping, rubber sand mixtures (RSM) can be used as a soil alternative to reduce ground motions when seismic loads are of great concern. However, when RSM is used as a vibration isolation material for geotechnical seismic isolation systems, it suffers from a lack of load-bearing capacity. To overcome this, a three-dimensional interconnected geocell (one type of geosynthetics) is placed within RSM to increase the vertical confinement of the system. In this technical note, to investigate the shear modulus and damping ratio of geocell-reinforced RSM, large-scale cyclic triaxial tests were conducted on specimens prepared with four granulated rubber contents (by weight) and sheared under different cyclic shear strain amplitudes. The results show that Geocell reinforcement can restrict the development of local shear bands in the specimen, weaken the anti-S-shaped characteristics of hysteresis loops and enhance the damping ratio of RSM at large strain amplitudes. The tuck net effect causes an increase in the normal stress of both contact particles, and then leads to the degradation rate of the maximum shear modulus of RSM varying with the rubber content and vertical pressure. The normalized shear modulus degradation curves show the influence range of geocell reinforcement, and demonstrate that a rubber content of 20% for reinforced specimen may be an optimal value from the perspective of the stability of dynamic properties. Additionally, the quantitative analysis of the effect of geocell reinforcement on the mechanical behavior of RSM can provide a reference for subsequent theoretical research and engineering applications.

Geotechnical Seismic Isolation System Based on Rubber-Sand Mixtures for Rural Residence Buildings: Shaking Table Test

The anti-seismic problem of rural residential buildings is the weak link of seismic retrofitting in China. Recently, geotechnical seismic isolation (GSI) technology based on rubber-sand mixtures (GSI-RSM) using rubber-sand mixtures (RSM) between the structural foundation and the foundation soil has been proven to have the possibility of potential applications in rural residential buildings. Many theoretical studies exist on the effectiveness of seismic isolation of the GSI-RSM system, but few studies on either the seismic response test of model buildings placed on the RSM layer or the large-scale shaking table test exist. Therefore, this study considers a large shaking table test performed on a 1/4 single-story masonry structure model with and without a GSI-RSM system by selecting a standard input ground motion and varying input acceleration amplitudes. The test results show that the GSI-RSM system can reduce the seismic response of superstructures. The isolation effect of the GSI-RSM system is low in small earthquakes and increases with increasing earthquake magnitude. Overall, the RSM layer can filter part of the high-frequency components of the earthquake to transmit to the superstructure and consume more seismic energy by generating friction slip in the interaction with the structural foundation.