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Waste tire rubber–soil mixtures feature low density, high energy dissipation, and low shear modulus, which are widely used in geotechnical engineering for vibration attenuation. In this study, the evolution of the small-strain stiffness characteristics of clay-rubber mixture (CRM) is investigated; a resonance column test was carried out to determine the small-strain stiffness characteristics of CRM samples with different confining pressures (σ3), rubber particle contents (Crubber), and rubber particle sizes (Drubber). The test results indicate that σ3 can promote the dynamic shear modulus (G) of CRM and restrain the damping ratio (D). The rubber particles have a great influence on both G and D. Under the same conditions, G decreases significantly with the increase in Crubber and increases slightly with the increase in Drubber, which indicates that rubber particles inhibit the development of G. D increases with the increase in Crubber and Drubber. The results show that the contact area between clay particles and rubber particles increases with the increase in Crubber, resulting in the decreases in G and D. The G–γ curves are analyzed by using the Hardin–Drnevich equation. Based on the fitting results, the maximum dynamic shear modulus (Gmax) is obtained. Therefore, the evolution of Gmax with σ3, Crubber, and Drubber are analyzed, and an equation for the Gmax of CRM considering the effects of σ3, Crubber, and Drubber is proposed. In addition, the D–γ curves can be well described by an empirical equation.

Partial replacement of conventional stabilizers with environmentally-friendly and sustainable materials has recently turned out to be a common approach to enhance the strength and stiffness properties of earthen materials. In this regard, natural zeolite and expanded polystyrene ( EPS ) beads are used in this study to be added to clay samples conventionally stabilized with lime. Accordingly, a systematic survey is conducted to inspect the changes in mechanical strength and shear stiffness of untreated and lime-zeolite treated reconstituted clays (with various proportions of kaolinite and montmorillonite) due to the incorporation of EPS beads. To this end, first, the optimum percentage of lime was obtained from a series of pH tests. Then, the optimum content of lime replacement with zeolite yielding the highest unconfined compressive strength ( UCS ) was estimated which appeared to be 25%. Afterward, all the samples were lightened by adding 0.1% and 0.25% weight ratios of EPS beads to the fine materials ( η ) and the results were compared with similar samples without EPS beads. Several standard Proctor compaction, swelling, UCS , and non-destructive bender element ( BE ) tests were carried out on lightened samples to assess their physical properties, strength characteristics, shear wave velocity ( V s ) and small-strain shear modulus ( G max ). The samples' swelling and compaction properties decreased by incorporating the EPS beads. Strength and stiffness characteristics of lightened composites were observed to be acceptable when 0.1 % EPS beads (denoted as the optimum percentage) were included in the studied mixtures. Furthermore, to interpret microscale phenomena, scanning electron microscopy ( SEM ) micrographs of the interfaces of the typical untreated and treated samples are provided, which demonstrate the interlocking zones, formation of cementitious gels and the considerable volume of the clay medium occupied by deformable EPS beads leading to the significant reduction in the soil weight. Finally, using the group method of data handling ( GMDH )-type neural network ( NN ), several statistical modelings are carried out to predict the UCS , V s , and G max of the studied mix designs, which resulted in highly accurate models.

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.

The shear modulus is an essential parameter that reflects the mechanical properties of the soil. However, little is known about the shear modulus of coral sand, especially under complex consolidation conditions. In this paper, we present the results of a multi-stage strain-controlled undrained cyclic shear test on saturated coral sand. The influences of several consolidation state parameters: effective mean principal stress (p0′), consolidation ratio (kc), consolidation direction angle (α0), and coefficient of intermediate principal stress (b) on the maximum shear modulus (G0), the reference shear strain (γr) and the reduction of shear modulus (G) have been investigated. For a specified shear strain level, G will increase with increasing p0′ and kc, but decrease with increasing α0 and b. However, the difference between G for various α0 and b can be reduced by the increase of shear strain amplitude (γa). G0 shows an increasing trend with the increase of p0′ and kc; on the contrary, with the increase of α0 and b, G0 shows a decreasing trend. To quantify the effect of consolidation state parameters on G0, a new index (μG0) with four parameters (λ1, λ2, λ3, λ4) which is related to p0′, kc, α0, b is proposed to modify the prediction model of G0 in literature. Similarly, the values of γr under different consolidation conditions are also evaluated comprehensively by the four parameters, and the related index (μγr) is used to predict γr for various consolidation state parameters. A new finding is that there is an identical relationship between normalized shear modulus G/G0 and normalized shear strain γa/γr for various consolidation state parameters and the Davidenkov model can describe the G/G0–γa/γr curves. By using the prediction model proposed in this paper, an excellent prediction of G can be obtained and the deviation between measured and predicted G is all within ±10%.

Bio-cementation of natural sand is a prospective solution to improve their engineering properties. The enhancement of strength and low-strain shear modulus is considered to be of high engineering significance for improvement in the performance of sand under both static and dynamic loading. In the present study, bio-cementation effects of bacillus Sporosarcina pasteurii bacteria on standard Ennore sand of India are studied at the microstructure level through scanning electron microscope (SEM) investigation considering microbial-induced calcite precipitation (MICP) technique. The crystallographic structure of the bio-cemented sand is reported through X-ray diffraction (XRD) analyses. Stress–strain behaviour and improvement in the strength of bio-cemented sand with different pore volumes of cementation solution have been investigated through unconfined compression strength (UCS) testing. Finally, the shear wave velocity values of the bio-cemented sand are assessed through bender element testing for different confining pressures, and low-strain shear modulus values have arrived. The study is believed to be helpful in the quantification of improvement of strength and low-strain shear modulus values of bio-cemented sand.

The shear modulus and shear strength of extruded polystyrene foam were obtained by the in-plane shear and asymmetric four-point bending tests. In addition, the test data were numerically analysed, and the effectiveness of these tests was examined. The numerical and experimental results suggest that the shear modulus and shear strength obtained from the in-plane shear test are significantly smaller than those obtained from the asymmetric four-point bending test because the influence of the stress concentration was less significant. Although the in-plane shear test is standardised in ASTM C273/C273M-11, it is considerable to adopt the asymmetric four-point bending test as another candidate for obtaining the shear properties of extruded polystyrene foam.

Rubber asphalt has excellent durability and can maintain excellent performance under harsh service conditions. In order to further promote the application of rubber asphalt, the dynamic rheological shear test was used to test the complex shear modulus G *, rutting factor G */sin δ, fatigue dissipation factor G * sin δ of rubber asphalt under different test temperatures and loading frequencies. The conclusions are as follows: (1) For the dynamic rheological properties of rubber asphalt, the content of rubber powder is an important factor. When the rubber powder content is 30%, the rheological properties of rubber asphalt are optimal. (2) For the rutting factor and fatigue dissipation factor of rubber asphalt, temperature and frequency are the primary influencing factors. The rutting factor and fatigue dissipation factor of rubber asphalt samples in each group decrease with increasing temperature and increases with increasing frequency. (3) Among the three types of rubber powder-mixed rubber asphalt, the 30% rubber asphalt has higher high-temperature performance and fatigue performance, which can meet the performance requirements of the pavement surface layer.

Complex shear modulus imaging (CSMI) is a technique used to determine the elasticity and viscosity of soft tissues; it aids in investigating tissue structure and detecting tumors. CSMI methods can be categorized into quasi-static and dynamic approaches. The dynamic method utilizes force excitation and particle velocity measurements to estimate the Complex Shear Modulus (CSM). However, noise poses a challenge to shear wave estimation, affecting accuracy. Researchers are actively exploring adaptive filtering techniques and signal processing algorithms to address the noise issue and obtain reliable shear wave estimations. By integrating the Algebraic Helmholtz Inversion (AHI) method and the Least Mean Square (LMS) filter, imaging accuracy can be enhanced by mitigating the impact of noise. This study introduces a pioneering advancement in Complex Shear Modulus Imaging (CSMI). A new approach is proposed, using a dual-frequency excitation technique, strategically employing 100 Hz and 150 Hz frequencies. The proposed method is meticulously designed to enhance the overall efficiency of CSMI. Furthermore, a highly effective signal sampling and spectrum estimation procedure is introduced, aimed at elevating the accuracy of Algebraic Helmholtz Inversion (AHI) and significantly mitigating computational complexity in contrast to prior investigations.

To investigate the static and dynamic characteristics of rubber–sand composite soil (RS soil) reinforced with cement, a series of triaxial compression tests and resonant column tests was performed by considering the influence of rubber content (10%, 20%, 30%, 40%, and 50%), cement content (0, 1.5, 2.5, 3.5 and 4.0 g/100 mL), and effective consolidation confining pressure (50, 100, and 150 kPa). Compared with the RS soil, the addition of cement significantly improved the shear strength of a cement–rubber–sand composite soil (RCS soil), based on an undrained shear test. The increase in cement content not only makes the elastic modulus and cohesion of the RCS soil increase but also reduces the internal friction angle of the RCS soil. With the increase in rubber content, the failure of the RCS soil samples changes from strain-softening to hardening, and the prediction equation of the initial elastic modulus of the RCS soil is given herein when the recommended cement content is 3.5 g/100 mL. The effects of rubber content, cement content, and effective confining pressure on the dynamic shear modulus and damping ratio of the RCS soil were studied via the resonant column test. The test results show that the increase in rubber content slows down the modulus attenuation of the RCS soil, but increases its damping ratio. The test results also show that the increase in cement content makes the bonding force between particles greater so that the modulus attenuation of the RCS soil becomes slower and the damping ratio is reduced. At the same time, according to the change rule of the maximum dynamic shear modulus of the RCS soil with the rubber content, when the recommended cement content is 3.5 g/100 mL, an empirical formula and recommended value of the shear modulus Gmax of the RCS soil are proposed.

Phosphogypsum (PG) is a solid waste product of the wet-process phosphoric acid industry that accumulates in large amounts on the ground, forming PG ponds. In recent years, the amount of PG produced and discharged into ponds has increased significantly with the increase in the market demand for phosphate fertilizers. To enrich the basic knowledge of PG properties and provide basic data for the stability analysis of PG dams, a series of laboratory geotechnical tests, including permeability tests, compressibility tests, triaxial shear tests, and dynamic triaxial tests, were conducted in this study. During the preparation of the test samples, solubility and high-temperature dehydration of PG were considered. The results indicated that PG exhibits medium compressibility and medium to weak permeability characteristics. The stress-strain curves of the triaxial shear tests were divided into three typical stages: initial deformation stage, strain hardening stage, and destruction stage. With increasing dry density and consolidation confining pressure, both the shear strength and deformation modulus significantly increased. The relationship between the deformation modulus and confining pressure gradually changed from linear to logarithmic with increasing density. The liquefaction resistance curves ( CSR – N L curves) of PG were expressed by power functions. With increasing dry density, the curves shifted higher and became steeper. Compared with the Hardin–Drnevich model, the Davidenkov model was found to be more suitable for describing the relationship between the dynamic shear modulus ratio and damping ratio of PG and the dynamic shear strain. Furthermore, compared with those of tailings and natural soils, the engineering mechanical properties of PG were relatively poor, which may be related to its uniform particle distribution and neat particle stacking structure.