Research

25 pages, 8150 KiB

Open AccessArticle

Effects of Freeze–Thaw Cycles on Axial Compression Behaviors of UHPC-RC Composite Columns

by Shuling Gao and Leyu Liu

Materials 2024, 17(8), 1843; https://doi.org/10.3390/ma17081843 - 17 Apr 2024

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Ultra-high performance concrete (UHPC) with excellent durability has broad application prospects in improving the durability of reinforced concrete (RC) structures. To clarify the influence of freeze–thaw cycles on the axial compression performance of UHPC-RC composite columns, axial compression tests were carried out on [...] Read more.

Ultra-high performance concrete (UHPC) with excellent durability has broad application prospects in improving the durability of reinforced concrete (RC) structures. To clarify the influence of freeze–thaw cycles on the axial compression performance of UHPC-RC composite columns, axial compression tests were carried out on composite columns with different cycles (0, 100, 200, 300 cycles) and stirrup spacing (35, 70, 105 mm). The results showed that the UHPC shell did not fall off when the composite column was destroyed, even in the freeze–thaw environment. Under the action of freeze–thaw cycles, the peak load

N_{u, t}

and initial elastic modulus

E

of the composite column decreased, but the ductility coefficient

μ

increased. Increasing the stirrup spacing could significantly improve the ductility of the composite column. After 100 freeze–thaw cycles, the ductility coefficient

μ

of the 35 mm stirrup spacing specimen was 112.6% higher than that of the 105 mm specimen. A prediction model for the bearing capacity of UHPC-RC composite columns under freeze–thaw cycles was established, and the predicted results were in good agreement with the experimental results. This study lays a theoretical and experimental foundation for the application and design of UHPC-RC composite columns in the freeze–thaw environment. Full article

(This article belongs to the Special Issue Advanced Geomaterials and Reinforced Structures)

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14 pages, 4802 KiB

Open AccessArticle

Study on Non-Limited Earth Pressures of Soilbag-Reinforced Retaining Structures with Surcharge Loads

by Changrong Bian, Zhiqiang Lai, Ruonan Liu, Zhongmei Wang and Kewei Fan

Materials 2024, 17(3), 611; https://doi.org/10.3390/ma17030611 - 26 Jan 2024

Viewed by 379

Abstract

The earth pressure acting on soilbag-reinforced retaining structures subjected to surcharge loads under non-limited states is crucial for designing these structures. In this study, mode tests on soilbag-reinforced retaining walls were conducted to the earth pressure of the wall subjected to surcharge loads. [...] Read more.

The earth pressure acting on soilbag-reinforced retaining structures subjected to surcharge loads under non-limited states is crucial for designing these structures. In this study, mode tests on soilbag-reinforced retaining walls were conducted to the earth pressure of the wall subjected to surcharge loads. The findings from these tests reveal a non-linear distribution of lateral earth pressure on the wall when subjected to surcharge loads in non-limited states, with an observed escalation in pressure corresponding to increased surcharge loads. Insights from the tests facilitated the development of a predictive method for estimating lateral pressure on soilbag-reinforced retaining walls under similar conditions, and its performance was fully validated by the model tests. Furthermore, the impact of the geometric dimensions and material properties of the soilbags on the earth pressure distribution was examined using the proposed method. Full article

(This article belongs to the Special Issue Advanced Geomaterials and Reinforced Structures)

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15 pages, 5969 KiB

Open AccessArticle

Interface Mechanics of Double-Twisted Hexagonal Gabion Mesh with Coarse-Grained Filler Based on Pullout Test

by Wenhui Gao, Yuliang Lin, Xin Wang, Tianya Zhou and Chaoxu Zheng

Materials 2024, 17(1), 164; https://doi.org/10.3390/ma17010164 - 28 Dec 2023

Viewed by 512

Abstract

The interface friction mechanics of reinforcement material with filler is an essential issue for the engineering design of reinforced soil structure. The interface friction mechanics is closely associated with the properties of filler and reinforcement material, which subsequently affects the overall stability. In [...] Read more.

The interface friction mechanics of reinforcement material with filler is an essential issue for the engineering design of reinforced soil structure. The interface friction mechanics is closely associated with the properties of filler and reinforcement material, which subsequently affects the overall stability. In order to investigate the interface mechanism of a double-twisted hexagonal gabion mesh with a coarse-grained filler derived from a weathered red sandstone, a large laboratory pullout test was carried out. The pullout force–displacement curve was obtained by fully mobilizing the gabion mesh to reach the peak shear stress at the interface between the gabion mesh and the coarse-grained filler. The change of force–displacement characteristics and the distribution of tensile stress in gabion mesh during the pullout process were obtained. A 3D numerical model was established based on the pullout test model, and the model for analyzing the interface characteristic between the gabion mesh and the coarse-grained filler was modeled using the FLAC3D 6.0 platform. The interface characteristics were further analyzed in terms of the displacement of soil, the displacement of reinforcement, and the shear stress of soil. The strength and deformation behaviors of the interface during the entire pullout process were well captured. The pullout force–displacement curve experiences a rapid growth stage, a development transition stage and a yielding stabilization stage. The critical displacement corresponding to peak pullout stress increases with the increase in normal stress. The normal stress determines the magnitude of shear stress at the reinforcement and soil interface, and the displacement distribution of a gabion mesh is not significantly affected by normal stress when the applied normal stress is within a range of 7–20 kPa. The findings are beneficial to engineering design and application of a gabion mesh-reinforced soil structure. Full article

(This article belongs to the Special Issue Advanced Geomaterials and Reinforced Structures)

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18 pages, 6098 KiB

Open AccessArticle

Evaluating the Potential of Multi-Walled Carbon Nanotube-Modified Clay as a Landfill Liner Material

by Xibin Liu, Zhengfa Chen and Lin Qi

Materials 2023, 16(24), 7705; https://doi.org/10.3390/ma16247705 - 18 Dec 2023

Viewed by 593

Abstract

In this paper, the feasibility of multi-walled carbon nanotube (MWCNT)-modified clay as a landfill liner material is investigated. Experiments were conducted on the modified clay with 0.5%, 1%, and 2% MWCNTs. The effects of the MWCNTs on the compaction characteristics, permeability coefficient, stress–strain [...] Read more.

In this paper, the feasibility of multi-walled carbon nanotube (MWCNT)-modified clay as a landfill liner material is investigated. Experiments were conducted on the modified clay with 0.5%, 1%, and 2% MWCNTs. The effects of the MWCNTs on the compaction characteristics, permeability coefficient, stress–strain curve, peak deviation stress, shear strength parameters (internal friction angle and cohesion), microstructures, and adsorption performance of the clay were analyzed. The results showed that the optimum moisture content (OMC) increased from 16.15% to 18.89%, and the maximum dry density (MDD) decreased from 1.79 g/cm³ to 1.72 g/cm³ with the increase in MWCNTs. The permeability coefficients firstly fell and then gradually rose as the MWCNTs increased; the minimum permeability coefficient was 8.62 × 10⁻⁹ cm/s. The MWCNTs can also effectively increase the peak deviation stress of the clay, and at the maximum level, the peak deviation stress was increased by 286%. SEM images were processed using the Pore and Crack Analysis System (PCAS), and the results showed that the appropriate amount of MWCNTs could fill the pores and strengthen the clay structure. The effect of the MWCNT-modified clay on the adsorption performance of common heavy metal ions Cd²⁺, Mn²⁺ and Cu²⁺ in landfill leachate was analyzed by batch adsorption tests. The maximum adsorption capacities (Q_max) of Cu²⁺, Cd²⁺ and Mn²⁺ in the 2% MWCNT-modified clay were, respectively, 41.67 mg/g, 18.69 mg/g, and 4.97 mg/g. Compared with the clay samples without MWCNTs, the adsorption properties of Cu²⁺, Cd²⁺, and Mn²⁺ were increased by 228%, 124%, and 202%, respectively. Overall, the results suggest that MWCNT-modified clays have the potential to be suitable barrier materials for the construction of landfills. Full article

(This article belongs to the Special Issue Advanced Geomaterials and Reinforced Structures)

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16 pages, 3729 KiB

Open AccessArticle

Combined Influences of Water Content and Coarse Grain Content on Shear Strength of Unsaturated Soil Mixture

by Yu Su, Bo Han, Junyi Duan and Fumin Zhao

Materials 2023, 16(20), 6657; https://doi.org/10.3390/ma16206657 - 11 Oct 2023

Cited by 1 | Viewed by 639

Abstract

An interlayer existed between the ballast layer and subgrade in the conventional railway substructure. Considering that the shear strength τ of the interlayer soil was influenced by the changes in the ballast grain content and water content, this aspect was explored in the [...] Read more.

An interlayer existed between the ballast layer and subgrade in the conventional railway substructure. Considering that the shear strength τ of the interlayer soil was influenced by the changes in the ballast grain content and water content, this aspect was explored in the present study. Monotonic triaxial tests were fulfilled, which considered five coarse grain contents f_v and three water contents of fine soil w_f. The results showed that the growth in f_v contributed to an increment in τ of the soil mixture under both saturation and unsaturation. Conversely, in previous studies, the growth of f_v induced an increment in τ under saturation, but a decline in that under unsaturation. This was explained by the competing influences of f_v and suction ψ: in previous studies, increasing f_v induced a decline in the dry density of the fine soil fraction ρ_d–f, which contributed to a decline in ψ. When the negative influence of declining ψ outweighed the positive influence of the incrementing f_v, the τ of the soil mixture decreased. Meanwhile, modelling of the τ–ψ relationship in the soil mixture with varying f_v was performed. This proposed model was examined using the test results from both the present and previous studies, which shows its reasonably good performance. Full article

(This article belongs to the Special Issue Advanced Geomaterials and Reinforced Structures)

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16 pages, 6791 KiB

Open AccessArticle

Strength Degradation of Foamed Lightweight Soil Due to Chemical Erosion and Wet-Dry Cycle and Its Empirical Model

by Zhen Zhang, Yonggang Zhang, Guanbao Ye, Shenyi Zhang, Honghui Shen and Yonggui Chen

Materials 2023, 16(19), 6505; https://doi.org/10.3390/ma16196505 - 30 Sep 2023

Viewed by 586

Abstract

Foamed lightweight soils (FLS) have been extensively used as backfill material in the construction of transportation infrastructures. However, in the regions consisting of salt-rich soft soil, the earth structure made by FLS experiences both fluctuation of groundwater and chemical environment erosion, which would [...] Read more.

Foamed lightweight soils (FLS) have been extensively used as backfill material in the construction of transportation infrastructures. However, in the regions consisting of salt-rich soft soil, the earth structure made by FLS experiences both fluctuation of groundwater and chemical environment erosion, which would accelerate the deterioration of its long-term performance. This study conducted laboratory tests to explore the deterioration of FLS in strength after being eroded by sulfate attack and/or wet-dry cycling, where the influencing factors of FLS density, concentration of sulfate solution, and cation type (i.e., Na⁺ and Mg²⁺) were considered. An unconfined compressive test (UCT) was conducted, and the corrosion-resistant coefficient (CRC) was adopted to evaluate the erosion degree after the specimens experienced sulfate attack and/or dry-wet cycling for a certain period. The research results show that the erosion of the FLS specimen under the coupling effect of sulfate attack and dry-wet cycling was more remarkable than that only under chemical soaking, and Na₂SO₄ solution had a severe erosion effect as compared with MgSO₄ solution when other conditions were kept constant. An empirical model is proposed based on the test results, and its reliability has been verified with other test results from the literature. The proposed model provides an alternative for engineers to estimate the strength deterioration of FLS on real structures in a preliminary design. Full article

(This article belongs to the Special Issue Advanced Geomaterials and Reinforced Structures)

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16 pages, 8101 KiB

Open AccessArticle

Frost Durability of Self-Compacting Concrete Prepared with Aeolian Sand and Recycled Coarse Aggregate

by Hao Yan, Qing Liu, Fengxia Han, Shan Liu, Tong Han and Bowen He

Materials 2023, 16(19), 6393; https://doi.org/10.3390/ma16196393 - 25 Sep 2023

Cited by 1 | Viewed by 698

Abstract

Aeolian sand (AS) and recycled coarse aggregate (RCA) can be reasonably utilized as green materials for concrete modification. The paucity of natural sand and gravel in the construction industry is anticipated to be remedied by the use of these two eco-friendly concrete ingredients. [...] Read more.

Aeolian sand (AS) and recycled coarse aggregate (RCA) can be reasonably utilized as green materials for concrete modification. The paucity of natural sand and gravel in the construction industry is anticipated to be remedied by the use of these two eco-friendly concrete ingredients. This is incredibly important for environmental protection. Study on the damage law of self-compacting concrete with the addition of AS and RCA (ARSCC) under severely cold conditions is of great significance for the promotion and implementation of this material. In this study, 12 groups of ARSCC specimens were prepared for freeze–thaw cycle experiments, with AS substitution rates of 0, 20%, 40%, and 60% as well as RCA replacement rates of 0, 25%, and 50%. Then, the degradation mechanism of ARSCC freeze–thaw damage was discussed from both macroscopic and microscopic perspectives via mass loss rate (W_n), relative dynamic modulus of elasticity (P_n), bubble spacing factor, and SEM analysis. Finally, the response surface method was utilized to determine the damage variable. A freeze–thaw damage model for ARSCC was developed based on the Weibull distribution and Grey theories. The results showed that the P_n could reflect the evolution law of the internal structure of ARSCC. Appropriate addition of AS to fill the large, harmful pores in RCA would inhibit freeze–thaw damage of ARSCC. The optimum substitution rates of AS and RCA were determined to be 20–40% and 25–50%, respectively. In addition, the values obtained from theoretical damage modeling and experiments were in good agreement. The acquired damage model had the potential to predict ARSCC damage under freeze–thaw cycles. Full article

(This article belongs to the Special Issue Advanced Geomaterials and Reinforced Structures)

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19 pages, 4074 KiB

Open AccessArticle

Hybrid Machine-Learning-Based Prediction Model for the Peak Dilation Angle of Rock Discontinuities

by Shijie Xie, Rubing Yao, Yatao Yan, Hang Lin, Peilei Zhang and Yifan Chen

Materials 2023, 16(19), 6387; https://doi.org/10.3390/ma16196387 - 24 Sep 2023

Cited by 2 | Viewed by 900

Abstract

The peak dilation angle is an important mechanical feature of rock discontinuities, which is significant in assessing the mechanical behaviour of rock masses. Previous studies have shown that the efficiency and accuracy of traditional experimental methods and analytical models in determining the shear [...] Read more.

The peak dilation angle is an important mechanical feature of rock discontinuities, which is significant in assessing the mechanical behaviour of rock masses. Previous studies have shown that the efficiency and accuracy of traditional experimental methods and analytical models in determining the shear dilation angle are not completely satisfactory. Machine learning methods are popular due to their efficient prediction of outcomes for multiple influencing factors. In this paper, a novel hybrid machine learning model is proposed for predicting the peak dilation angle. The model incorporates support vector regression (SVR) techniques as the primary prediction tools, augmented with the grid search optimization algorithm to enhance prediction performance and optimize hyperparameters. The proposed model was employed on eighty-nine datasets with six input variables encompassing morphology and mechanical property parameters. Comparative analysis is conducted between the proposed model, the original SVR model, and existing analytical models. The results show that the proposed model surpasses both the original SVR model and analytical models, with a coefficient of determination (R²) of 0.917 and a mean absolute percentage error (MAPE) of 4.5%. Additionally, the study also reveals that normal stress is the most influential mechanical property parameter affecting the peak dilation angle. Consequently, the proposed model was shown to be effective in predicting the peak dilation angle of rock discontinuities. Full article

(This article belongs to the Special Issue Advanced Geomaterials and Reinforced Structures)

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17 pages, 5169 KiB

Open AccessArticle

Effects of Curing Conditions on Splitting Tensile Behavior and Microstructure of Cemented Aeolian Sand Reinforced with Polypropylene Fiber

by Bo Ruan, Tianyao Zhou, Zhongzheng Yuan, Jenisha Singh, Jidong Teng, Shilong Zheng and Jiasen Zhang

Materials 2023, 16(19), 6347; https://doi.org/10.3390/ma16196347 - 22 Sep 2023

Viewed by 774

Abstract

Aeolian sand is widely distributed in the Takramagan Desert, Xinjiang, China, which cannot be directly used as railway subgrade filling. It is beneficial for environmental protection to use fiber and cement-reinforced aeolian sand as railway subgrade filling. The present work is to explore [...] Read more.

Aeolian sand is widely distributed in the Takramagan Desert, Xinjiang, China, which cannot be directly used as railway subgrade filling. It is beneficial for environmental protection to use fiber and cement-reinforced aeolian sand as railway subgrade filling. The present work is to explore the enhancement of tensile strength in cemented aeolian sand via the incorporation of polypropylene fibers under conditions of elevated temperature and drying curing. The purpose Is to delve into the examination of the temperature’s impact on not only the mechanical attributes but also the microstructure of cemented aeolian sand reinforced with polypropylene fiber (CSRPF). For this, a comprehensive set of tests encompassing splitting tensile strength (STS) assessments and nuclear magnetic resonance (NMR) examinations is conducted. A total of 252 CSRPF specimens with varying fiber content (0, 6‰, 8‰, and 10‰) are tested at different curing temperatures (30 °C, 40 °C, 50 °C, 60 °C, 70 °C, and 80 °C). The outcomes of the NMR examinations indicate that elevating the curing temperature induces the expansion of pores within CSRPF, both in size and volume, consequently contributing to heightened internal structural deterioration. STS tests demonstrate that the STS of CSRPF decreases as the curing temperature increases. Meanwhile, the STS of CSRPF increases with fiber content, with optimal fiber content being 8‰. Regression models accurately predict the STS, with the curing temperature exhibiting the greatest influence, followed by the fiber content according to sensitivity analysis. The research results provide a valuable reference for the use of CSRPF as railway subgrade filling under high temperature and drying conditions. Full article

(This article belongs to the Special Issue Advanced Geomaterials and Reinforced Structures)

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18 pages, 4642 KiB

Open AccessArticle

Experimental Study on the Interface Characteristics of Reinforced Crushed Rock Cushion Layer Based on Direct Shear Tests

by Liangliang Wang, Qianlong Zhu, Yan Jia and Hu Li

Materials 2023, 16(17), 5858; https://doi.org/10.3390/ma16175858 - 26 Aug 2023

Viewed by 983

Abstract

Through indoor large-scale direct shear tests, the interface characteristics of the crushed rock cushions layer reinforced with ParaLink geogrid were studied. The test results indicate that the shear strength of the crushed rock aggregate and the interface strength parameters have a non-linear relationship [...] Read more.

Through indoor large-scale direct shear tests, the interface characteristics of the crushed rock cushions layer reinforced with ParaLink geogrid were studied. The test results indicate that the shear strength of the crushed rock aggregate and the interface strength parameters have a non-linear relationship with the normal stress. The addition of the geogrid reduces the shear strength of the crushed rock aggregate and the interface strength parameters, which is mainly due to the relatively large size, small thickness, and high smoothness of the geogrid. The reinforced geogrid has a significant impact on the deformation and fragmentation characteristics of the crushed rock aggregate. It effectively suppresses the shear contraction and shear dilation effects of the crushed rock aggregate, reducing its peak compression and peak dilation angle. Furthermore, it inhibits the tendency of particle fragmentation in the crushed rock aggregate. Full article

(This article belongs to the Special Issue Advanced Geomaterials and Reinforced Structures)

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18 pages, 5583 KiB

Open AccessArticle

Field Investigation of the Dynamic Response of Culvert–Embankment–Culvert Transitions in a High-Speed Railway

by Ping Hu, Huo Liu, Yi-Zhi Tang and Yu-Liang Lin

Materials 2023, 16(17), 5832; https://doi.org/10.3390/ma16175832 - 25 Aug 2023

Cited by 1 | Viewed by 795

Abstract

The stiffnesses of embankments and culverts differ in the transition sections of high-speed railways (HSRs) due to their different supporting conditions. The dynamic irregularity caused by the different stiffnesses makes this transition area the weakest part of high-speed railways. Graded crushed stone combined [...] Read more.

The stiffnesses of embankments and culverts differ in the transition sections of high-speed railways (HSRs) due to their different supporting conditions. The dynamic irregularity caused by the different stiffnesses makes this transition area the weakest part of high-speed railways. Graded crushed stone combined with 5% cement is typically used to fill the subgrade in these transition areas. Thus, three different particle size ratios of crushed stone were matched and tested regarding the construction parameters to explore the most suitable materials to fill the roadbed in a transition section. Then, field dynamic tests were carried out on the culvert–embankment–culvert transition area where trains run at speeds of 5–360 km/h. A time-domain analysis of the test data was performed to obtain the laws of variation that cause the dynamic characteristics to change with the railway line and roadbed layer and the changes induced by a train’s running speed, operating direction, and axle weight. The results indicate that (i) it is feasible to fill transition section roadbeds with well-graded crushed stone combined with 5% cement with optimal water contents; (ii) extreme dynamic responses in some special sections are observed, suggesting the value of taking special measures at the transition section. For example, the sections 14.5 m and 30 m from the 679 culvert and the bed layer should be specially stabilized; (iii) the train’s axle load and driving direction show a great effect on corresponding sections and layers but present a small effect on the sections and layers nearby; and (iv) 260 km/h is a critical speed. Full article

(This article belongs to the Special Issue Advanced Geomaterials and Reinforced Structures)

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30 pages, 24490 KiB

Open AccessArticle

Influence of Strengthened Nodes on the Mechanical Performance of Aeolian Sand–Geogrid Interface

by Wei Du, Rusong Nie, Yongchang Tan, Jie Zhang, Yanlu Qi and Chunyan Zhao

Materials 2023, 16(13), 4665; https://doi.org/10.3390/ma16134665 - 28 Jun 2023

Cited by 2 | Viewed by 675

Abstract

Node thickening is a way to strengthen the nodes of a geogrid. Increasing the node thickness in conventional biaxial geogrids enhances the interface frictional strength parameters and improves its three-dimensional reinforcement effect. Based on the triaxial tests of aeolian sand, single-rib strip tests [...] Read more.

Node thickening is a way to strengthen the nodes of a geogrid. Increasing the node thickness in conventional biaxial geogrids enhances the interface frictional strength parameters and improves its three-dimensional reinforcement effect. Based on the triaxial tests of aeolian sand, single-rib strip tests of geogrids, and pull-out tests of geogrid in aeolian sand, a three-dimensional discrete element pull-out model for geogrids with strengthened nodes was developed to investigate the mechanical performance of an aeolian sand–geogrid interface. The influences of increasing node thickness, the number of strengthened nodes, and the spacing between adjacent nodes on the mechanical performance of the geogrid–soil interface were extensively studied used the proposed model. The results demonstrated that strengthened nodes effectively optimize the reinforcing performance of the geogrid. Among the three node-thickening methods, that in which both the upper and lower sides of nodes are thickened showed the most significant improvement in ultimate pull-out resistance and interface friction angle. Moreover, when using the same node-thickening method, the ultimate pull-out resistance increase shows a linear relationship with the node thickness increase and the strengthened node quantity. In comparison with the conventional geogrid, the strengthened nodes in a geogrid lead to a wider shear band and a stronger ability to restrain soil displacement. When multiple strengthened nodes are simultaneously applied, there is a collective effect that is primarily influenced by the spacing between adjacent nodes. The results provide a valuable reference for optimizing the performance of geogrids and determining the spacing for geogrid installation. Full article

(This article belongs to the Special Issue Advanced Geomaterials and Reinforced Structures)

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