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Two typical types of gravel.(a) Angular gravels; (b) Magnified view of angular gravels; (c)Round gravels; (d) Magnified view of round gravels.
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![Figure 4.Resonant column device of GZZ-50 type [27,36].](publication/339424369/figure/fig4/AS:861200925597696@1582337709368/Resonant-column-device-of-GZZ-50-type-27-36_Q320.jpg)
![Figure 5.Schematic diagram of the process [27].](publication/339424369/figure/fig5/AS:861200925589515@1582337709472/Schematic-diagram-of-the-process-27_Q320.jpg)
In order to support the dynamic design of subgrade filling engineering, an experiment on the dynamic shear modulus (G) and damping ratio (D) of clay–gravel mixtures (CGMs) was carried out. Forty-two groups of resonant column tests were conducted to explore the effects of gravel content (0%, 10%, 20%, 30%, 40%, 50%, and 60%, which was the mass ratio...
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Context 1
... studies have proved that the particle shape plays a significant role in the dynamic properties of materials. Hence, based on the classification of particle shape by Meidani et al. [17][18][19]32] and the in-site gravels' shape, two typical gravels were selected, including both round and angular shapes, as shown in Figure 3a,c. In this article, the angular gravels were screened from the rocks broken by a jaw crusher, and the round gravels were collected from rivers. ...
Context 2
... this article, the angular gravels were screened from the rocks broken by a jaw crusher, and the round gravels were collected from rivers. As shown in Figure 3b,d, it can be found that the angular gravels have sharp edges and some defects near the edges; in contrast, the round gravels did not have sharp edges and had better completion near the edges. The insufficient breaking of rocks and grinding of small particles or water in rivers can be used to explain the differences in edge characteristics of angular and round gravels, respectively. ...
Context 3
... reason for the greater dynamic shear modulus of CGMr under lower shear strain (<10 −5 ) is because of the better compaction characteristic of CGMr under the same compaction work (shown in Figure 11) and the better completion in the gravel's edges (shown in Figure 3) [16,17,20,35]. The lower reduction tendency of the dynamic shear modulus with shear strain in CGMa can be explained by the better interlock effect between angular gravels when the dynamic shear strain appears in the CGM [2,17]. ...
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... It seems that these have a good relationship with the material properties and confining pressure. The regression laws formulated so far require the initial damping ratio, Dmin (at low strain), e.g., in the Masing model [46] and other authors [47][48][49][50][51]. Instead, Taboada et al. [52] show that Dmin has a weak relation with the confining stress but a greater affinity with Dmax − Dmin through numerous sandy soil tests. ...
Featured Application: The proposed computer-aided algorithm aims to introduce an approach to implement the performance and expand the capability of the downhole method in defining the shear wave velocity and the elastic damping ratio profiles. Abstract: This contribution introduces a computerized semi-automated procedure coupled with a dedicated algorithm to improve shear wave velocity assessment and the on-site elastic damping ratio estimation of ground materials. The standard equipment of the downhole method is integrated with a horizontal geophone (guardian) placed on the field surface. Mask tapering and band multi-filter functions improve first arrival, recognizing and isolating SH-wave trains to estimate damping ratio profiles. These are computed by treating signals using a frequency-time combined approach (frequency-time packets method). The signals are corrected to consider the different source pulse amplitude, the effects of the propagation path, and scattering. The damping ratio profile is statistically computed in terms of the local drift of trend on the amplitude ratio series that would otherwise have a normal distribution centered on zero. These profiles intercept the lithology changes in the test sites and meet the damping values stemming from previous field tests and the laboratory experimental tests available in the literature regarding materials such as the ones investigated here.
... One of the main parameters that has been examined to assess the behavior of composite granular materials is the use of equivalent void ratio in an attempt to quantitatively incorporate the portions of fines and coarse particles [16]. Unlike the static properties, the studies focusing on the dynamic properties of sand-fines mixtures are very limited, especially focusing on the small-strain behavior which is often studied through the assessment of wave propagation parameters (e.g., shear wave velocity, elastic stiffness and damping ratio) [5,[17][18][19][20][21][22][23][24][25][26]. Measuring in the laboratory and modeling the dynamic (and small-strain) properties of granular materials offer, apart from their direct use in practical projects, fundamental insights with respect to the involved multi-scale mechanics understanding in this way the physical behavior of particulate materials [27][28][29][30][31]. Additionally, many computer codes, such as the DEM, utilize laboratory test data from macroscopic experiments, along with grainscale parameters in their calibration process, to provide, based on the numerical output, quantitative understanding of the mechanics of particulate materials, which, for smallstrain analysis, provides links between micro-scale and bulk characteristics of granular materials [32][33][34]. ...
Compacted clay-aggregate composites are extensively utilized or found in various geotechnical engineering projects such as the core of earth embankment dams, the pile foundation of offshore structures, or the impervious blankets in waste disposal landfills. In this study, data from resonant column tests at small shear strains are exploited to examine the dynamic shear modulus and energy dissipation characteristics of compacted clay-sand mixtures and develop empirical expressions for their small-strain dynamic properties. The models incorporate the influences of confining pressure (p'), void ratio (e), aggregate content (AC) and clay plasticity index (PI). Moreover, the application of the equivalent plasticity index (PI*) in the estimation of small-strain dynamic properties is rigorously examined. The level of accuracy of the developed models is inspected with simple comparisons against the experimental data. The proposed empirical correlations can be utilized in geotechnical earthquake engineering problems for the seismic stability analysis of geo-structures containing compacted clay-sand mixtures. These empirical models also comprise a basis to discuss the mechanical behavior of composite granular systems at multi-scales. In this regard, the involved micromechanisms, particularly the contact response of sand-clay systems, are discussed integrating the macroscopic results from the present work with micromechanical-based data previously published in the literature. This analysis highlighted the important role of the formed coating of microparticles on the constitutive behavior of sand grains at their contacts, which in turn, provided some additional insights to explain the macroscopic behavior of clay-sand mixtures as obtained from the element-size experiments.
... In order to ensure a working energy supply, China's coal mining has been gradually promoted to the deep rock strata [1][2][3]. The process of deep coal resource mining will inevitably produce a large mining response. ...
In order to solve the problem of highly brittle shaft lining under dynamic loading, a combination of hybrid fiber concrete mixed with steel and polypropylene fiber is proposed to make shaft lining. C60, the concrete commonly used in shaft lining, was selected as the reference group. The static mechanical properties, dynamic mechanical properties, and crack failure characteristics of the hybrid fiber concrete were experimentally studied. The test results showed that compared to the reference group concrete, the compressive strength of the hybrid fiber-reinforced concrete did not significantly increase, but the splitting tensile strength increased by 60.4%. The split Hopkinson compression bar results showed that the optimal group peak stress and peak strain of the hybrid fiber concrete increased by 58.2% and 79.2%, respectively, and the dynamic toughness increased by 68.1%. The strain distribution before visible cracks was analyzed by the DIC technology. The results showed that the strain dispersion phenomenon of the fiber-reinforced concrete specimen was stronger than that of the reference group concrete. By comparing the crack failure forms of the specimens, it was found that compared to the reference group concrete, the fiber-reinforced concrete specimens showed the characteristics of continuous and slow ductile failure. The above results suggest that HFRC has significantly high dynamic splitting tensile strength and compressive deformation capacity, as well as a certain anti-disturbance effect. It is an excellent construction material for deep mines under complex working conditions.
... There exist many great techniques (in-situ and laboratory) from which stiffness parameters of soil can be derived [26,27]. As a part of the authors' research, several tests were carried out on the RCA properties under dynamic loading with the help of resonant frequency measurements. ...
The construction sector is currently struggling with the reuse of waste originating from the demolition and modernization of buildings and roads. Furthermore, old buildings are gradually being replaced by new structures. This brings a significant increase of concrete debris to waste landfills. To prevent this, many studies on the possibilities of recycling concrete, known as recycled concrete aggregate (RCA), have been done. To broaden the applicability of reused concrete, an understanding of its properties and engineering behavior is required. A difficulty in sustainable, proper management of RCA is the shortage of appropriate test results necessary to assess its utility. For this reason, in the present study, the physical, deformation, and stiffness properties of RCA with gravely grain distribution were analyzed carefully in the geotechnical laboratory. To examine the mentioned properties, an extensive experimental program was planned, which included the following studies: granulometric analysis, Proctor and oedometer tests, as well as resonant column tests. The obtained research results show that RCA has lower values of deformation and stiffness parameters than natural aggregates. However, after applying in oedometer apparatus repetitive cycles of loading/unloading/reloading, some significant improvement in the values of the parameters studied was noticed, most likely due to susceptibility to static compaction. Moreover, some critical reduction in the range of linear response of RCA to dynamic loading was observed.
... With increasing awareness of environmental protection and the continued development of science and technology, the world energy structure is developing toward multipolarization, from traditional fossil fuels to cleaner wind energy, water energy, tidal energy, geothermal energy, etc. [1][2][3][4][5][6]. As a widely distributed resource, the commercial applications of geothermal energy are rapidly expanding [7]. ...
For reducing the initial GSHP investment, the heat transfer efficiency of the borehole heat exchange (BHE) system can be enhanced to reduce the number or depth of drilling. This paper proposes a novel and simple BHE design by changing the cross-sectional shape of the U-tube to increase the heat transfer efficiency of BHEs. Specifically, in this study, we (1) verified the reliability of the three-dimensional numerical model based on the thermal response test (TRT) and (2) compared the inlet and outlet temperatures of the different U-tubes at 48 h under the premise of constant leg distance and fluid area. Referent to the circular tube, the increases in the heat exchange efficiencies of the curved oval tube, flat oval tube, semicircle tube, and sector tube were 13.0%, 19.1%, 9.4%, and 14.8%, respectively. (3) The heat flux heterogeneity of the tubes on the inlet and outlet sides of the BHE, in decreasing order, is flat oval, semicircle, curved oval, sector, and circle shapes. (4) The temperature heterogeneity of the borehole wall in the BHE in decreasing order is circle, sector, curved oval, flat oval, and semicircle shapes. (5) Under the premise of maximum leg distance, referent to the heat resistance of the tube with a circle shape at 48 h, the heat exchange efficiency of the curved oval, flat oval, semicircle, and sector tubes increased 12.6%, 17.7%, 10.3%, and 7.8%, respectively. (6) We found that the adjustments of the leg distance and the tube shape affect the heat resistance by about 25% and 12%, respectively. (7) The flat-oval-shaped tube at the maximum leg distance was found to be the best tube design for BHEs.
... Hence, suitable rock size is important in the analysis of soil-rock mixtures. According to the sample preparation standard (GB/T 50123-1999) and existed references [1,33,34], Kalender et al. [2,8,35,36] concluded that, in soil-rock mixtures, minimum thresholds for soil and rock are suggested to be the minimum value of 2 mm and 0.05 Lc (where Lc is the characteristic length of model), and maximum thresholds are advised to be 0.2 Lc. Based on the advice, Zhang et al. [1] conducted triaxial tests with soil-rock mixtures containing 2-10 mm rocks (samples are 50 mm in diameter and 100 mm in height) and obtained good experimental results. ...
... For better analysis of rock distribution characteristics in soil-rock slopes, 6 groups of soil-rock mixture samples were made consisting of different rock shapes (angular and round) and contents (10%, 30%, and 60%). e specimens were cylindrical in shape with diameter 50 mm and height 100 mm and each layer was compacted 20 [1,34,38], rock size in specimen was defined to be between 2 and 10 mm. CT [39] is a good method to observe the internal structures of objects without any disturbance and has been widely utilized in medicine and engineering. ...
Soil-rock slopes are widely distributed in central or western China. With the development of transportation, many subgrades are being built on mountainsides and therefore, slope stability has to be estimated under high loadings. To obtain better estimation results, a new rock contour establishing algorithm was developed, capable of considering interlock effect between rocks. Then, computed tomography (CT) and unconfined triaxial tests with ring top loadings were conducted. Based on rock distribution characteristics (obtained by CT photos) and the appearance of shear failure surfaces in slopes under ring top loadings, four rock skeleton status and five shear failure surface developing models were introduced. Based on the developed rock contour establishing algorithm, ten groups (twelve models per group) were established and calculated by finite element method (FEM). After this, normalized ultimate loading increasing multiple N, which was the ultimate loading ratio of rock-containing slope to uniform soil slope, was introduced to evaluate the influence of rock distributions on slope stability. The value of N was increased with the increase of rock content due to rock skeleton status. The values of N in slopes with angular rocks were about three times higher than those with round rocks which was due to complex geometric shape and distribution characteristics of angular rocks. Then, considering different slope angles (50°-60°), rock contents (0%-60%), and rock shapes (round and angular), the ultimate loading increasing multiple N of soil-rock slopes under high loadings was calculated and suggested for engineering designs. Finally, based on the failure surfaces of numerical modes, three typical failure modes were developed, which could be reference for designers to deal with slopes.
... In recent years, the concept of sustainable development and ecological environmental protection has become deeply rooted in the hearts of people, and various countries have begun to attach importance to the protection of the natural environment and ecological balance [1][2][3]. In China, in order to protect the natural environment, many areas have implemented prohibit hillside mining prohibitions, which can result in problems for the supply of concrete aggregate for mine support near mountainous areas. ...
In order to study the static and dynamic mechanical characteristics of the coal gangue concrete used in the mine support structure, the compressive strength test, the drop weight impact test, and the Split Hopkinson Pressure Bar (SHPB) test were conducted. The compressive strength, initial and final impacting energy, dynamic strength, and failure characteristic of concrete were obtained of the concrete single-doped with coal gangue coarse aggregate, single-doped with coal gangue fine aggregate, and codoped with coal gangue coarse and fine aggregates. The results show that (1) it is feasible that employing coal gangue to replace natural coarse and fine aggregates in concrete can prepare C30 and C40 concrete; (2) the addition of coal gangue fine aggregate has a positive effect on the impact energy of the initial and final cracks of concrete, while the addition of coal gangue coarse aggregate has a negative effect on it; (3) compared with the static strength, the dynamic strength of concrete is improved no matter whether coal gangue is added to concrete; (4) the incorporation of coal gangue coarse aggregate will make the concrete shear surface smooth; (5) at the given impacting pressure, the concrete with coal gangue coarse aggregate has greater particle breakage and those with coal gangue fine aggregate has less. The research of this study can be a reference for the application of gangue concrete in mine support structures. © 2020 Zhishu Yao et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
A soil–rock slope is a heterogeneous slope composed of soil and rocks that is widely distributed throughout the world. In order to accurately analyze the slope stability of soil–rock mixture, based on a Monte Carlo algorithm (fuzzy-based method), a symmetrical stability analyzing method for soil–rock slopes is proposed, considering the dispersion of strength of soil–rock mixtures. In analyzing it, the numerical model is symmetrical to the real soil–rock slope in geometry and material properties. In addition, the effect of rock content to slope stability was studied by this symmetrical method. The specific work of this paper is as follows: (1) The acquisition method of random number series for the Monte Carlo algorithm and the method of slope stability analysis, using the Monte Carlo method, are introduced. (2) According to in situ samples and remade samples, the strength characteristics of soil–rock mixtures were measured with different rock contents, which proved the scatter of strength of soil–rock mixtures. (3) Based on the measured strength parameters of soil–rock mixtures and the slope landslide, the reliability in analyzing results and superiority in calculating time of using the Monte Carlo method to analyze stability of soil–rock slopes are detailed. (4) The stability of soil–rock slopes with different rock content is discussed with the Monte Carlo method, and it is concluded that with the increase of rock content, the stability of a soil–rock slope decreases first and then increases, and the minimum safety factor is acquired at 20% rock content. (5) Based on a large number of calculation examples, the applied situations of the Monte Carlo method to analyze stability of soil–rock slopes are detailed according to sampling results and rock size.
