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Fully grouted rock bolts are widely used in mining, tunneling, and pit support, and thus the study of their anchorage performance is beneficial for optimizing the anchorage system design. In this study, an FDM‐DEM coupled numerical model is established to simulate the whole process of rock bolt pullout test and to investigate the failure mechanism of fully grouted rock bolts. The accuracy of the model is verified by comparison with existing laboratory test results. Virtual experiments are conducted on different models by eliminating the anchor plate, changing the layered rock strata condition, and adding bolts. The results show that the presence of an anchor plate will reduce tensile stress to restrain the rupture of surrounding rock and thus improve the strengthening effect. Due to the different bond strength and tensile strength of the soft and hard rock mediums, the layer sequence of the rock strata affects the maximum pullout force. The upper‐soft and lower‐hard composite rock strata (S‐HCR) exhibits single‐cone damage while the upper‐hard and lower‐soft composite rock strata (H‐SCR) exhibits double‐cone damage. The superposition effect of the anchor group on the stresses and displacements is the reason leading to the reduction of the maximum load‐bearing capacity of the rock bolts. [ABSTRACT FROM AUTHOR]

Mechanically stabilized earth (MSE) walls are widely used to stabilize steep slopes, especially when the crest is subjected to static or dynamic loading. These structures are frequently used in highway and railway structures where they are subjected to dynamic loading and seasonal variation. With rapid urbanization and a growing population, especially in developing countries, the transportation infrastructure is growing at a tremendous speed. Compared with conventional concrete retaining walls, MSE walls emit less carbon dioxide (CO2) and require less area. In addition, the cost of their construction is low, and less earthwork is required. The other advantage of MSE walls in transportation structures is their better performance under dynamic (or seismic) loads and shorter construction time. This paper discusses the pullout behavior of geogrid, which is an important parameter for determining the internal stability of an MSE wall. The internal stability of MSE walls has two major failure types: (1) pullout; and (2) rupture. In this paper, different data-driven algorithms were used to predict the outcome of the geogrid pullout test and to understand the influence of various physical parameters. This paper utilizes statistical models and machine learning (ML) algorithms, for example, correlation analysis, linear regression analysis with one and multiple variables, tree-based ensemble algorithms, artificial neural network (ANN), support vector machine (SVM), and adaptive neuro fuzzy inference systems (ANFIS) for predictive modeling. In total, 201 data sets from geogrid pullout tests were collected from the literature, which considered 12 features. The performance of the developed model was examined using the coefficient of determination (R2) and later compared using a Taylor diagram, Willmott's index of agreement, the root mean square error standard deviation ratio (RSR), and mean absolute percentage error (MAPE). The performance of the ANFIS was superior to any other model. Then, the probabilistic approach was used to perform parametric analysis and evaluate the internal stability performance of a reinforced earth wall using Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

In this study, Recycled Concrete Aggregate (RCA) was employed as a sandwich technique around the geogrid to enhance the pullout resistance of the geogrid in clayey backfills. Large-scale pullout tests were conducted on three configurations: geogrid-reinforced clay, geogrid-reinforced RCA, and geogrid sandwiched between layers of RCA, aimed at investigating pullout resistance and deformation. The experiments encompassed two different geogrid types (designated as G1 and G2), varying normal pressures ranging from 10 to 50 kPa, and RCA layers with thicknesses of 40, 80, 160, and 320 mm. Results from the experiments revealed that the inclusion of RCA layers around the geogrid substantially enhanced pullout resistance, with improvements ranging from 1.5 to 3 times compared to clay specimens. Optimal RCA thicknesses were determined in order to enhance soil-geogrid bonding and pullout resistance. For G1 geogrid, a thickness of 160 mm (equivalent to replacing 25% of clay volume with RCA) was identified as optimal, while for G2 geogrid, an 80 mm thickness (equivalent to replacing 15% of clay volume with RCA) was found to be sufficient. These thicknesses were established to achieve over 80% of the pullout force compared to full RCA specimens. • Large-scale pullout tests were performed on two types of geogrids. • Recycled Concrete Aggregate (RCA) was utilized at various thicknesses within a sandwich technique to enhance geogrid pullout resistance in clayey backfills. • The optimum thickness of RCA layer in sandwich technique was determined. [ABSTRACT FROM AUTHOR]

Carbon fiber–reinforced polymer–steel composite bars (C-FSCBs) and coral sea-sand aggregate seawater concrete (CSSC) are attractive choices as construction materials for island and atoll engineering construction. Understanding the bond behavior between the C-FSCB and CSSC is crucial for evaluating the mechanical properties of C-FSCB-reinforced CSSC structures. In this study, the bond–slip behavior between the C-FSCB and CSSC was experimentally assessed via pullout tests. The influence of various factors on the bond behavior was discussed, and the bond mechanism between the C-FSCB and CSSC was analyzed. The results indicate that, unlike steel bars, the low rigidity of fiber-reinforced polymer caused surface fiber stripping (i.e., shear damage) of the C-FSCB after interface slip, consequently reducing the squeezing fragmentation of concrete between the ribs. As the diameter and bond length of the C-FSCB increased, the bond strength decreased. Compared to specimens with C-FSCBs, the bond strength of specimens with steel bars of the same diameter increased by 17.9%. The degree of coarse aggregate fracture at the CSSC interface in the splitting failure was much higher than that of normal concrete. Based on existing research data, a formula for calculating the bond strength of C-FSCBs in CSSC has been established to determine the anchorage length of C-FSCBs, and the calculated values accurately predicted the test values. [ABSTRACT FROM AUTHOR]

Abstract Coal‐measure strata is a typical layered structure, a better understanding of the bearing characteristics of fully grouted bolts in layered rock mass is of great significance for roadway support. However, limited studies have been conducted to investigate the bearing performance of fully grouted bolts in layered rock mass. In this paper, a numerical model of fully grouted bolt in layered rock mass was established, and a tri‐linear bond–slip model of the anchorage interface was imported into the numerical model by the user‐defined Fish language. The effects of strata sequence, strata thickness, and strata number in layered rock mass on the bearing performance of fully grouted bolts were systematically analyzed. The results show that fully grouted bolts in soft–hard type (SH‐type) layered rock mass has higher bearing capacity. The greater the thickness of the soft rock in the layered rock mass, the more significant the influence of the strata sequence on the bearing performance of fully grouted bolts. The bearing capacity of fully grouted bolts decreases with the increase of the thickness ratio of soft rock to hard rock. The greater the thickness of the hard rock in the layered rock mass, the more beneficial to the bearing performance of fully grouted bolts. With the increase of the strata number, the bearing capacity of fully grouted bolts gradually decreases. For bolt support of layered rock mass, the deep anchoring foundation of fully grouted bolts should be arranged in hard rock or elastic zone rock as much as possible, and rock grouting can be adopted to reduce the difference in mechanical properties between layered rock mass and improve the durability of fully grouted bolts. The research results may provide useful guidance and reference for the support design of fully grouted bolts.

Overall structural integrity and load transfer between concrete and reinforcement enabling composite action relies on the bond between concrete and reinforcement. Bond strength determination of reinforced concrete is an essential task that a pullout test can determine. Experimental pullout behaviour can be affected by various parameters, such as concrete and steel strength, boundary conditions, etc. Therefore, a parametric study on pullout tests is time-consuming. In addition, measurements of internal stress-strain components and damages of constitutive materials are also difficult in experimental endeavours. In this context, finite element (FE) models should be developed to perform a parametric study with cost and time-saving. This study proposes a finite element modeling strategy of reinforced concrete under pullout force by using the expected failure mechanism to predict bond-slip behaviour in ABAQUS. In FE models, surface-to-surface cohesive interaction behaviour was used to assign interaction between reinforcement and concrete. The proposed modelling strategy was validated with available experimental data from four reference specimens, having all possible failures (i.e., pullout, splitting, and splitting-pullout) under pullout loading. The finite element analysis showed that the proposed FE modeling strategy performed well in predicting bond-slip behaviour in elastic regions. Additionally, maximum bond stresses were predicted satisfactorily, except for the splitting failure pattern, using the proposed FE modelling strategy.

This paper presents the results of an experimental study to investigate the effects of two types of graphene, dried (DG) and hydrated graphene (HG), when enhancing the interfacial and tensile mechanical properties of fabric-reinforced cementitious matrix (FRCM) composites. The inclusion of DG and HG could produce an improvement in the tensile strength of the FRCM composites by increasing the tensile strength of the mortar paste and the amount of fibers that participate in load bearing due to the increased penetration of mortar (cement hydrates) into the fiber bundle. The better dispersion of HG produces better results than DG. The maximum increases in the overall tensile strengths of the FRCM composites with DG and HG are 18% and 31%, respectively, with the majority of these improvements coming from the increase in the number of fibers that participate in load bearing. The microstructure images indicate increases of up to 20% and 44% in the mortar penetration thickness into the fiber bundles using DG and HG, respectively. [ABSTRACT FROM AUTHOR]

Portland cement products are extensively used as parent materials in construction projects. However, the production and consumption of these products result in various environmental pollutants, including the emission of carbon dioxide gas and excessive water usage. Geopolymer products have emerged as a promising alternative to Portland cement and its products due to their diverse mechanical and chemical properties. Therefore, in this study, we aim to investigate the potential of geopolymer products as a replacement for Portland cement. To this end, the optimal mixing design was obtained by performing uniaxial compressive strength and flow table tests. Nailing is a commonly used method for stabilizing soil excavations and slopes, often involving the use of Portland cement as grout. Geopolymer is used as a potential replacement for cement grout in this system. Pullout tests were conducted to investigate the interaction between the soil and grout, considering the effect of curing conditions and environmental factors such as temperature, humidity, and overburden pressure for both the geopolymer and cement grouts. The results indicate that, in general, the pullout force of geopolymer samples is lower than that of cement samples. However, raising the temperature in geopolymer samples results in an increase in the pullout force, whereas an increase in temperature in cement samples leads to a decrease in pullout force. It can be concluded that geopolymer samples need to be modified by using an additive, such as sodium silicate, to achieve proper pullout force and suitable interlocking with soil grains. [ABSTRACT FROM AUTHOR]

This study conducts a series of large-scale pullout tests to explore the pullout behavior of the biaxial geogrid-calcareous sand interface. It investigates the effects of normal stress, relative density, and embedded length on the interface pullout behavior of geogrid reinforcement in calcareous sand. In addition, this research examines changes in interface shear strength and the interface friction coefficient. The interface interaction mechanism of geogrid reinforcement in calcareous sand and the evolution of pullout force-clamp displacement curves are determined. The results indicated that the pullout force-clamp displacement curve primarily exhibits softening and hardening behaviors. The passive resistance of the geogrid mesh significantly influences the softening behavior, while shear friction predominantly affects the hardening behavior. The interface friction coefficient ranged from 0.28 to 0.88 for embedded lengths of 300 − 460 mm. The effects of relative density and embedded length on interface cohesion are more pronounced than those on the interface friction angle. When the embedded length increased from 300 to 460 mm, the rise in interface cohesion ranged from 42.0% to 47.7%, whereas the increase in internal friction angle ranged from 9.5% to 14.5%. [ABSTRACT FROM AUTHOR]

This article discusses a numerical study on predicting the bond-slip relationship of reinforced concrete using surface-based cohesive behavior. The study aims to develop a finite element modeling strategy to accurately predict the bond-slip behavior in reinforced concrete. The article provides a comprehensive review of previous research on bond-slip behavior and includes a table of maximum bond stress equations from different literature sources. The document discusses the testing procedure and finite element modeling strategy for studying the bond behavior between concrete and reinforcement in pullout tests. The document also explains the loading and boundary conditions applied in the finite element model and the interaction between reinforcement and concrete. The text discusses the different contact models available in ABAQUS for simulating contact between surfaces. It concludes by discussing the finite element mesh size and solution procedure used in the study. The text discusses the results of finite element analysis (FEM) conducted on reference specimens to predict their failure modes and bond stress-slip behavior. The analysis used different mesh sizes and analytical models to simulate the behavior of the specimens. The results showed that a finer mesh size of 10 mm provided more accurate predictions of failure patterns, while a mesh size of 10 mm or larger could be used to estimate specimen strength. The FEM developed using the analytical model by Strum and Visintin showed the most accurate prediction of maximum bond stress. The failure modes observed in the analysis included pullout failure, splitting followed by pullout failure, and splitting or splitting-pullout failure. The FEM models generally performed [Extracted from the article]

Coal‐measure strata is a typical layered structure, a better understanding of the bearing characteristics of fully grouted bolts in layered rock mass is of great significance for roadway support. However, limited studies have been conducted to investigate the bearing performance of fully grouted bolts in layered rock mass. In this paper, a numerical model of fully grouted bolt in layered rock mass was established, and a tri‐linear bond–slip model of the anchorage interface was imported into the numerical model by the user‐defined Fish language. The effects of strata sequence, strata thickness, and strata number in layered rock mass on the bearing performance of fully grouted bolts were systematically analyzed. The results show that fully grouted bolts in soft–hard type (SH‐type) layered rock mass has higher bearing capacity. The greater the thickness of the soft rock in the layered rock mass, the more significant the influence of the strata sequence on the bearing performance of fully grouted bolts. The bearing capacity of fully grouted bolts decreases with the increase of the thickness ratio of soft rock to hard rock. The greater the thickness of the hard rock in the layered rock mass, the more beneficial to the bearing performance of fully grouted bolts. With the increase of the strata number, the bearing capacity of fully grouted bolts gradually decreases. For bolt support of layered rock mass, the deep anchoring foundation of fully grouted bolts should be arranged in hard rock or elastic zone rock as much as possible, and rock grouting can be adopted to reduce the difference in mechanical properties between layered rock mass and improve the durability of fully grouted bolts. The research results may provide useful guidance and reference for the support design of fully grouted bolts. [ABSTRACT FROM AUTHOR]

Geosynthetics have increasingly been applied to geotechnical engineering works due to their numerous advantages, including cost-effectiveness and their significant role in sustainable development. When geosynthetics are used as reinforcement in earth structures, such as embankments, retaining walls and bridge abutments, soil–geosynthetic interface shear behavior is a critical parameter involved in the design. This paper presents a series of monotonic and cyclic/post-cyclic pullout tests carried out to examine the apparatus scale effect on the pullout response of a geogrid embedded in two different soils. To assess the small-scale equipment feasibility, comparisons were made between pullout test parameters derived from small- and large-scale equipment. The test results indicate that, under a low confining stress of 25 kPa, using a smaller-sized apparatus results in lower values of geogrid pullout resistance and maximum mobilized shear stress, but higher values of confined tensile stiffness at low strains. On the other hand, as the confining stress increases (i.e., 50 kPa and 100 kPa), the difference between the results becomes less significant and similar trends are observed regardless of the equipment type. Adopting small-scale equipment enables obtaining soil–reinforcement interaction parameters using test procedures that are less time-consuming than those associated with large-scale pullout tests. However, proper scale effect correction factors may be considered for more consistent estimates of the interface strength parameters under low normal stress values. [ABSTRACT FROM AUTHOR]

Reinforced concrete structures play a pivotal role in island and reef engineering projects. Given the resource constraints typical of island regions, substituting traditional manufactured sand aggregate with reef limestone not only reduces reliance on river sand but also addresses the issue of disposing of waste reef limestone slag generated during excavation. However, the performance characteristics of reef limestone concrete, particularly its bond strength with reinforcing steel, warrant further investigation. This is particularly true for the bond–slip behavior of the reinforcement. This study aims to elucidate the effects of various parameters on the bond performance between steel and reef limestone concrete through central pullout tests. These parameters include the type and diameter of the reinforcement, bond length, and loading rate. The investigation encompasses the analysis of load–slip curves, bond failure modes, and variations in bond stress. Additionally, using the Abaqus software, a numerical simulation was conducted to analyze the mesoscopic stress characteristics, thereby revealing the mechanisms of bond formation and failure modes between steel reinforcement and reef limestone concrete. The results indicate that the bond–slip curve for reef limestone concrete reinforced with ribbed rebars and Glass Fiber-Reinforced Polymer (GFRP) rebars can be broadly categorized into four phases: minor slip, slip, decline, and residual, with the residual phase exhibiting a wave-like pattern. The predominant failure modes in reef limestone concrete are either pulling out or splitting. The bond stress in reef limestone concrete decreases with an increase in rebar diameter and bond length; conversely, it increases with the loading rate, although the ultimate slip decreases. The mesoscopic failure characteristics of reinforced reef limestone concrete, as simulated in Abaqus, are consistent with the experimental outcomes. [ABSTRACT FROM AUTHOR]

The generalized model and parameter equation for the internal fracture surface of tensile type anchor cable anchorage section are constructed, and the calculation model of ultimate bearing capacity is derived based on the principle of limit equilibrium. The shape of the internal fracture surface in the anchorage section and the expression of its parameter equation are experimentally studied, and the variation law of the parameter equation and fracture range with the diameter of the anchor cable and confining pressure is analyzed. The parameter equation is substituted into the calculation model to realize the calculation and verification of the model. Through theoretical derivation, a calculation model of ultimate bearing capacity of anchor cable is obtained, which comprehensively considers the average shear strength of anchorage section, the shape of fracture surface, fracture range and confining pressure. The tests show that according to the magnitude of the confining pressure on the anchorage section, the internal fracture surface takes on two shapes: cylindrical and trumpet‐shaped, the parameter equation of trumpet‐shaped fracture surface obeys logarithmic distribution approximately. The coefficient a decreases with the increase of confining pressure but increases with the increase of anchor cable diameter, the constant b increases with the increase of confining pressure but decreases with the increase of anchor cable diameter. The ranges of horizontal and vertical fracture decrease with the increase of confining pressure, and increase with the increase of anchor cable diameter. The deviations between the theoretical calculation and the experimental results are less than 6.5%. [ABSTRACT FROM AUTHOR]

Glass fiber-reinforced polymer (GFRP) anchor bolts are a new type of high-performance nonmetallic anchor with significantly higher tensile strength, a lighter weight, better corrosion resistance, and a lower cost than steel bars. Therefore, exploring the durability and bonding performance of GFRP anchor systems is of great importance for the structural design of protective engineering, especially in coastal environments. However, insufficient research has been conducted on the durability of GFRP resin bolts in seawater conditions, with no universal standard on the pullout testing of GFRP bolts. To study the durability and bonding performance of GFRP resin bolts, durability experiments were conducted in this work using artificial seawater, and the pullout tests were conducted using a large-scale concrete platform with different compressive strengths (21.2, 40.8, and 61.3 MPa). The results of the durability experiments indicated that the strength variations of the GFRP rods and epoxy resin materials in artificial seawater environments were less than 5%. Subsequently, indoor pullout tests using steel tubes filled with epoxy resin were conducted, and the test results indicated a critical anchor length value. Pullout tests of the GFRP resin bolts embedded in large-scale concrete blocks were also conducted with different strengths. According to the test results, all GFRP resin bolts embedded in the three concrete blocks with different compressive strengths exhibited rod fracture failure. The failure mode was not controlled via the compressive strength of the concrete blocks due to the high bonding strength between the resin and the rod, as well as between the resin and the concrete. Therefore, this GFRP resin anchor system could fully utilize the tensile strength of GFRP rods. This research offers significant practical value in verifying the safety and reliability of GFRP resin bolts in corrosive marine service environments, and it contributes to the application and development of GFRP materials in the engineering field, serving as a valuable reference for the structural design and further study of GFRP bolts. [ABSTRACT FROM AUTHOR]

A novel application of fiber optic sensing aimed at understanding the tensile behavior of post‐installed reinforcing bars in normal‐strength concrete is presented in this paper. To comply with established assumptions of cast‐in reinforcement, such as the uniform bond stress distribution, the design bond strength of post‐installed configurations is limited. In this study, pull‐out tests in confined conditions were conducted using two high‐performance mortars. Cast‐in‐place anchorages were tested for reference. The proposed fiber optic sensors and post‐processing techniques enable to continually measure and evaluate the bond stress distribution and monitor rebar deformation. Compared to cast‐in rebars, post‐installed rebars exhibit significantly higher bond resistance, particularly due to higher bond stresses at the beginning of the embedment length. These results highlight the potential for reducing the embedment length of post‐installed rebar. Moreover, variations in stiffness and bond stress distribution are found to significantly affect the slip and rebar deformation of both cast‐in‐place and post‐installed rebar. [ABSTRACT FROM AUTHOR]

In Accelerated Bridge Construction (ABC), Ultra-High Performance Concrete (UHPC) is often used for connecting precast concrete bridge components, including deck portions of the Deck Bulb-T girders. An alternative low-cost non-proprietary UHPC has been proposed for use in place of the proprietary UHPC for connecting the precast components. The pullout behavior of steel reinforcing bars in closure pour with typical range for embedment lengths is studied for both proprietary and non-proprietary UHPC materials. [ABSTRACT FROM AUTHOR]

Engineered geopolymer composites (EGC) featuring extraordinary tensile ductility are a potential alternative to engineered cementitious composite. In this study, the local bonding properties of steel bars in EGC were investigated. Monotonic loading tests of the 120 specimens were performed using the pullout test method. The study examined the ultimate tensile strain of EGC, diameter and anchorage length of the steel bar on bond performance. The results showed that the EGC, with an ultimate tensile strain of 4.57%, had the highest peak bond strength. By comparing the test results of rebar to ordinary concrete bond performance provided in several previous literature, it was demonstrated that EGC has superior bond performance with rebar compared to ordinary concrete. Based on this, suggestions were provided for the design of rebar anchorage length in EGC. Finally, a mathematical model suitable for determining the bond–slip curve between EGC and steel bars is proposed. [ABSTRACT FROM AUTHOR]

Accurate deformation monitoring of geotechnical infrastructures using distributed fiber optic sensing requires a strong interfacial bond between strain sensing cables and surrounding soil. Micro-anchors provide a straightforward solution to enhance the interlocking effect at the cable–soil interface, but their anchorage mechanism remains unclear. This paper presents an experimental study on the interfacial behavior of anchored strain sensing cables embedded in soil. A series of pullout tests were conducted to investigate the effect of various factors on interfacial performance, including anchor spacing, anchor diameter, and confining pressure. The test results indicate that the anchor spacing and confining pressure substantially influenced the pullout resistance of anchored cables, while the anchor diameter had a minor effect. In contrast with unanchored cables, anchored cables exhibited strain hardening behavior during the pullout process instead of strain softening. The micro-anchors on cables played a reinforcing role sequentially with increasing pullout displacements, and those closer to the cable head exerted reinforcing effect earlier. Due to the pullout resistance of micro-anchors, the anchored cables have unique step-like strain profiles throughout the pullout tests, and they are not prone to interface decoupling under large deformation conditions. However, for closely spaced micro-anchors, the overlapping of interfacial shear zones led to a loss in the pullout resistance, which becomes insignificant with increasing anchor spacing. This study not only provides improved insight into the interpretation of fiber optic strain measurements but also sheds light on soil–inclusion interaction mechanisms in geotechnical analyses. [ABSTRACT FROM AUTHOR]

The occurrence of cracking, loosening, and other distresses in asphalt pavements is closely related to the failure of asphalt–aggregate adhesion. Studying the effect of asphalt film thickness on asphalt–aggregate adhesion can facilitate an understanding of the mechanism of disease in asphalt pavements. To study the impact of asphalt film thickness on asphalt–aggregate adhesion, this study tested and evaluated the adhesion between asphalt and aggregates at different asphalt film thicknesses from a macromechanical perspective via pullout tests. In addition, based on the surface energy theory, the effects of different film thicknesses on the adhesion of asphalt–aggregate were analyzed from a surface mechanics perspective. Further, the aggregates were subjected to surface property testing to further investigate the differences between the surface mechanics and the macromechanics results. The results showed that for an asphalt film thickness of 400 μm, the failure energy density (FED) and cohesive work (WA) of the asphalt exhibited the same trend, and certain properties of asphalt influenced its adhesion to the aggregate. For an asphalt film thickness of 25 μm, the FED and the asphalt adhesion work (Was) exhibited the same trend, and the combined effect of the asphalt and slag properties influenced the adhesion of asphalt to steel slag. Moreover, with decreasing asphalt film thickness, the adhesion between asphalt and aggregates was reduced owing to the influencing factors of the asphalt, which can effectively reduce the influence of the aging effect on adhesion. [ABSTRACT FROM AUTHOR]

Studying the pullout characteristics of roots can help to gain a deeper understanding of the interaction mechanism between plants and soil, and provide theoretical support and practical guidance for engineering applications. This paper aims to investigate the pulling characteristics of the root–soil interface in expansive soil reinforced by vetiver roots. For this purpose, the study focuses on exploring the correlation between the pullout force (PF) required to extract the roots and the pullout displacement caused by the extraction. The research also examines how the geometry of the roots affects the pulling characteristics of the root–soil using a pullout test. It is found that with increasing root diameter, root length segment (RLS), root volume, and root surface area (RSA), the maximum PF increases. The highest correlation coefficient was found between RSA and maximum PF, which explained 81.4% of the variation in maximum PF. Then, the functional relationship between RLS and PF is established. Using RSA to predict the maximum PF of vetiver root is relatively reasonable. The assessment of PF must consider RSA indicators. The increase in RSA due to a high number of roots results in the improvement of the PF of vetiver root. These findings could assist in enhancing the strength of expansive soils. [ABSTRACT FROM AUTHOR]

Owing to the substantial benefits in environmental protection and resource saving, recycled aggregate concrete (RAC) is increasingly used in civil engineering; among the different types, RAC-filled steel tubes are an efficient structural form utilizing the advantages of concrete and steel tubes. This paper proposed a novel full-bolted beam-to-concrete-filled steel tube (CFST) joint and investigated the anchoring behavior of the steel plates embedded in RAC-filled steel tubes, which represents the behavior of the tensile zone in this joint, to demonstrate the feasibility of utilizing RAC in composite structures. The specimen consisted of a CFST and a connecting plate embedded in the CFST. In total, 18 specimens were tested to study the effects of concrete type (i.e., recycled aggregate concrete and natural aggregate concrete), anchoring type (i.e., plate with holes, notches, and rebars), and plate thickness on the pullout behavior, such as anchorage strength, load–displacement response, and ductility. Based on experimental results, the aggregate type of the concrete does not affect the pullout behavior obviously but the influence of anchoring type is significant. Among the three anchoring methods, the plate with rebars exhibits the best performance in terms of anchorage strength and ductility, and is recommended for the beam-to-CFST joint. In addition, plate thickness obviously affects the behavior of plates with holes and notches, the bearing area of which is proportional to the thickness, whereas the pullout behavior of the plates with rebars is independent of thickness. Finally, design formulas are proposed to estimate the anchorage strength of the connecting plates, and their reasonability is validated using the experimental results. [ABSTRACT FROM AUTHOR]

The shear strength parameter of an anchoring interface is one of the key parameters affecting the design of bolt support. To better realize the design of bolt support, the pullout model of fully grouted bolts was established by FLAC3D numerical software. The commonly used tri-linear bond-slip model of the anchoring interface was selected. The variable controlling method was used to investigate the effects of the shear strength parameters of the anchoring interface on the bearing performance of fully grouted bolts. The results show that, with the increase in the displacement at the peak shear stress, the bearing capacity and the energy absorption of fully grouted bolts decrease and the ability of the fully grouted anchoring system to resist external loads weakens. Meanwhile, the deformation capacity of fully grouted bolts increases, and the durability of the fully grouted anchoring system is enhanced. With the increase in the residual shear stress and the displacement at the residual shear stress, the bearing capacity and deformation capacity of fully grouted bolts both increase, and the energy absorption also increases. Increasing the post-peak bearing properties of the anchoring interface can help improve the bearing performance of fully grouted bolts and enhance the ability of the fully grouted bolts to resist failure. The results may provide guidance for support design and performance enhancement of fully grouted bolts. [ABSTRACT FROM AUTHOR]

Roots anchor plants firmly to the soil, enabling them to effectively resist soil erosion and shear failure. Vegetation restoration has been acknowledged as one of the most useful measures for controlling soil loss; however, which root system characteristics were most beneficial for plant anchoring in the soil remains unclear. In the black soil region of northeastern China, which frequently experiences serious soil erosion, pullout tests were carried out on six species of soil and water conservation woody plants with different growth habits (deciduous shrubs, deciduous trees and evergreen trees), and the root geometry and topology of each species were determined. The results showed that the maximum uprooting force and activation displacement (the displacement at the maximum peak in the relationship curve between pulling force and displacement) of shrubs were significantly greater than those of trees, while deciduous trees were significantly greater than evergreen trees. Therefore, the ability of the whole root system to anchor the soil was the largest for shrubs, followed by deciduous trees, and the smallest for evergreen trees. The uprooting force and activation displacement were mainly affected by the root topological index, total root length and the number of inclined roots. The total root length had the greatest influence on the maximum uprooting force, and the root topology had the greatest influence on the activation displacement, both of which can be used as important predictors of plant root anchorage strength. In addition, the plants with the R-type root structure may have a greater ability to anchor the soi, and can be prioritized for vegetation restoration with black soils. These findings provide references and implications for identifying the effective plant strategies for eroded soil restoration in the black soil region of northeastern China and other areas with similar soil types and bioclimates. [ABSTRACT FROM AUTHOR]

Coating GFRP bars with a layer of carbon fibers containing carbon/glass-hybrid-fiber-reinforced polymer (HFRP) bars has been proven to improved interlaminar shear durability. Thus, the bond performance of the HFRP bar-concrete interface depends on the behavior of the HFRP-reinforced concrete structure. In this context, the study investigates the effects of the compressive strength of concrete and the embedded length of HFRP bars on the bond behavior of the HFRP bar-concrete interface and compares the results with the data on the interfacial bond of GFRP bar to concrete. The results demonstrate that all the specimens fail at the FRP bar–concrete interface under the pullout. The bond strength and bond stiffness of the HFRP bar–concrete composites decrease with an increase in the embedded length of the HFRP bar from 4 to 10 times its diameter. Raising the compressive strength of the concrete enlarges the bond strength and bond stiffness of the HFRP bar–concrete composites. Furthermore, the outer layer of carbon-fiber on the GFRP bar decreases the impact of the embedded length of the HFRP bar on the bond strength and bond stiffness of the HFRP bar–concrete composites. Finally, the improved modified mBPE model can accurately predict the bond stress–slip relationship of GFRP/BFRP/HFRP bar–concrete composites. [ABSTRACT FROM AUTHOR]

In spite of their outstanding properties, FRP reinforcing bars still face a series of drawbacks that should be addressed to widen their applications. For example, straight FRP bars must be used because those bars suffer significant strength degradation when curved. This implies that FRP bars resist the slip nearly solely through their bond strength with concrete. In addition, helically ribbed FRP bars exhibit bond strength twice higher than sand coated bars but develop weaker bond characteristics with concrete than the steel rebar. Anchorages are thus needed to improve the bond strength but may be difficult to realize in narrow spaces like joints. Therefore, this study examines the combined use of helically ribbed FRP bars with connections like lap-splice, epoxy-filled tube, coupler or expanded ribs as mechanical anchorages. A total of 36 pullout specimens considering the types of connection as parameter are tested to investigate the eventual effectiveness of the connections in enhancing the bond behavior. The use of two expanded ribs appears to be the best option. The predictions of the bond stress-slip models of current design codes are compared to the experimental data to examine whether these models can simulate accurately the connections.

Grouted rock bolts subject to axial loading in the field exhibit various failure modes, among which the most predominant one is the bolt-grout interface failure. Thus, mechanical characterization of the grout is essential for understanding its performance in ground support. To date, few studies have been conducted to characterize the mechanical behaviour of fiber-reinforced grout (FRG) in rock bolt reinforcement. Here we experimentally studied the mechanical behaviour of FRG under uniaxial compression, indirect tension, and direct shear loading conditions. We also conducted a series of pullout tests of rebar bolt encapsulated with different grouts including conventional cementitious grout and FRG. FRG was developed using 15% silica fume (SF) replacement of cement (by weight) and steel fiber to achieve high-strength and crack-resistance to overcome drawbacks of the conventional grout. Two types of steel fibers including straight and wavy steel fibers were further added to enhance the grout quality. The effect of fiber shape and fiber volume proportion on the grout mechanical properties were examined. Our experimental results showed that the addition of SF and steel fiber by 1.5% fiber volume proportion could lead to the highest compressive, tensile, and shear strengths of the grout. The minimum volume of fiber that could improve the mechanical properties of grout was found at 0.5%. The scanning electron microscopy (SEM) analysis demonstrated that steel fibers act as an excellent bridge to prevent the cracks from propagating at the interfacial region and hence to aid in maintaining the integrity of the cementitious grout. Our laboratory pullout tests further confirmed that FRG could prevent the cylindrical grout annulus from radial crack and hence improve the rebar's load carrying capacity. Therefore, FRG has a potential to be utilized in civil and mining applications where high-strength and crack-resistance support is required.

Natural roots systems exhibit various tortuous morphologies, which significantly impact the root-soil interaction characteristics. Previous studies often treated root systems as straight, neglecting the deformation characteristics and failure modes of tortuous root systems under tensile loads. In this study, tensile test and pullout test are conducted by using tortuous roots manufactured from 3D printing technology with three different root diameters (2.0, 3.5 and 5.0 mm) and five root tortuosity (1.00, 1.05, 1.10, 1.15, 1.20), and the pullout behaviours of tortuous roots are explored. The results indicate that the tensile properties of root systems are influenced by both the tortuous structure and the material properties. The ultimate tensile force and tensile stiffness decreases with increasing tortuosity but increase with increasing diameter. The peak pull-out force of the root system initially increases and then decreases with tortuosity, reaching a maximum value when tortuosity is equal to 1.15. The peak pull-out displacement shows a similar trend. The tortuous root system forms an engaging effect with the soil by compressing the soil ribs, enhancing the interaction between roots and soil. The tensile force and stiffness of the tortuous fine root system are low, making it more prone to coordinate deformation with the soil to bear tensile loads. The deformation under stress of tortuous root systems differs significantly from that of straight root systems. This study provides theoretical references for the evaluation of soil-reinforcement by root system.

AbstractThe cement-treated dredged mud mixture is suitable for backfill in earthwork projects because of its high water content and flowability. Incorporating geogrid can enhance the mixture’s tensile strength. Constructing with cement-treated mud at greater heights generates curing stress, affecting the interface with geogrid. Pullout tests were performed to analyze the impact of curing stress, water content, and cement content on the interface performance. Results showed similar pullout force-displacement curves regardless of curing stress, indicating strain-softening behavior. Higher water content resulted in decreased pullout forces, while higher cement content led to increased pullout forces. Samples under curing stress exhibited increased peak pullout forces ranging from 2% to 70% compared to samples without curing stress. The rate of increase in pullout force because of curing stress decreased with higher water or cement contents. Curing stress influenced the interface friction angle in specimens with water contents 1.5 and 2 times the liquid limit. It significantly affected the interface cohesion in samples with water contents 2.5 times the liquid limit. Samples subjected to curing stress demonstrated a higher apparent friction coefficient, with an average increase ranging from 4% to 43%, which decreased with higher water content and lower cement content, regardless of curing stress. [ABSTRACT FROM AUTHOR]

The bond strength between reinforcing steel bars and cement concrete plays significant role in the structural performance for civil infrastructure. This work presents the bond performance of steel and concrete as interfacial shear strength, with the inclusion of effects of specimen diameter on embedment length, different aggregate grading and corrosion. The experimental procedure for proposed study includes a series of pullout tests on reinforced concrete cylindrical specimens with embedded steel bar. Cylindrical concrete specimens with varying specimen diameters with respect to different embedment lengths, changing the aggregate grading pattern, i.e., well and gap graded were casted and said effects on bond strength were evaluated through a pullout test. The corrosion effect is also studied through an accelerated corrosion process. The test results revealed that the diameter of the specimen and the embedment length substantially impact the bond strength between reinforcing bars and concrete. Due to the increasing surface area and mechanical interaction between the bar and the surrounding concrete, the bond strength increased as the diameter decreased. The bond performance of well-graded aggregates was effective compared to gap-graded aggregates. Moreover, the study found that as the number of corrosion days increased, the bond strength of corroded reinforcing bars considerably decreased. The results contribute essential insights to the field of reinforced concrete structures and can aid engineers and researchers in designing durable and reliable infrastructure systems. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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This paper investigates the bond behavior between plain steel bars and high-performance concrete (HPC) to study the effect of embedment length and concrete compressive strength on bond performance. A total of 48 concrete specimens were cast and tested under uniaxial load. The main test parameters include the active bond length and concrete compressive strength. Test results show that the ratio of maximum bond stress to concrete compressive strength ranges from 0.12 to 0.17. Moreover, it can be concluded that the maximum bond stress is increased with an increase in concrete compressive strength and is decreased with a longer embedment length of plain steel bars. The adhesive bond stress is approximately 55% of the maximum bond stress. Finally, a new bond stress-slip model was proposed, and good agreement can be achieved between the test research and the theoretical prediction based on the proposed model. [ABSTRACT FROM AUTHOR]

In Accelerated Bridge Construction (ABC), Ultra-High Performance Concrete (UHPC) is often used for connecting precast concrete bridge components, including deck portions of the Deck Bulb-T girders. An alternative low-cost non-proprietary UHPC has been proposed for use in place of the proprietary UHPC for connecting the precast components. The pullout behavior of steel reinforcing bars in closure pour with typical range for embedment lengths is studied for both proprietary and non-proprietary UHPC materials.

Reinforced concrete structures play a pivotal role in island and reef engineering projects. Given the resource constraints typical of island regions, substituting traditional manufactured sand aggregate with reef limestone not only reduces reliance on river sand but also addresses the issue of disposing of waste reef limestone slag generated during excavation. However, the performance characteristics of reef limestone concrete, particularly its bond strength with reinforcing steel, warrant further investigation. This is particularly true for the bond–slip behavior of the reinforcement. This study aims to elucidate the effects of various parameters on the bond performance between steel and reef limestone concrete through central pullout tests. These parameters include the type and diameter of the reinforcement, bond length, and loading rate. The investigation encompasses the analysis of load–slip curves, bond failure modes, and variations in bond stress. Additionally, using the Abaqus software, a numerical simulation was conducted to analyze the mesoscopic stress characteristics, thereby revealing the mechanisms of bond formation and failure modes between steel reinforcement and reef limestone concrete. The results indicate that the bond–slip curve for reef limestone concrete reinforced with ribbed rebars and Glass Fiber-Reinforced Polymer (GFRP) rebars can be broadly categorized into four phases: minor slip, slip, decline, and residual, with the residual phase exhibiting a wave-like pattern. The predominant failure modes in reef limestone concrete are either pulling out or splitting. The bond stress in reef limestone concrete decreases with an increase in rebar diameter and bond length; conversely, it increases with the loading rate, although the ultimate slip decreases. The mesoscopic failure characteristics of reinforced reef limestone concrete, as simulated in Abaqus, are consistent with the experimental outcomes.

Geosynthetics have increasingly been applied to geotechnical engineering works due to their numerous advantages, including cost-effectiveness and their significant role in sustainable development. When geosynthetics are used as reinforcement in earth structures, such as embankments, retaining walls and bridge abutments, soil–geosynthetic interface shear behavior is a critical parameter involved in the design. This paper presents a series of monotonic and cyclic/post-cyclic pullout tests carried out to examine the apparatus scale effect on the pullout response of a geogrid embedded in two different soils. To assess the small-scale equipment feasibility, comparisons were made between pullout test parameters derived from small- and large-scale equipment. The test results indicate that, under a low confining stress of 25 kPa, using a smaller-sized apparatus results in lower values of geogrid pullout resistance and maximum mobilized shear stress, but higher values of confined tensile stiffness at low strains. On the other hand, as the confining stress increases (i.e., 50 kPa and 100 kPa), the difference between the results becomes less significant and similar trends are observed regardless of the equipment type. Adopting small-scale equipment enables obtaining soil–reinforcement interaction parameters using test procedures that are less time-consuming than those associated with large-scale pullout tests. However, proper scale effect correction factors may be considered for more consistent estimates of the interface strength parameters under low normal stress values.

Glass fiber-reinforced polymer (GFRP) anchor bolts are a new type of high-performance nonmetallic anchor with significantly higher tensile strength, a lighter weight, better corrosion resistance, and a lower cost than steel bars. Therefore, exploring the durability and bonding performance of GFRP anchor systems is of great importance for the structural design of protective engineering, especially in coastal environments. However, insufficient research has been conducted on the durability of GFRP resin bolts in seawater conditions, with no universal standard on the pullout testing of GFRP bolts. To study the durability and bonding performance of GFRP resin bolts, durability experiments were conducted in this work using artificial seawater, and the pullout tests were conducted using a large-scale concrete platform with different compressive strengths (21.2, 40.8, and 61.3 MPa). The results of the durability experiments indicated that the strength variations of the GFRP rods and epoxy resin materials in artificial seawater environments were less than 5%. Subsequently, indoor pullout tests using steel tubes filled with epoxy resin were conducted, and the test results indicated a critical anchor length value. Pullout tests of the GFRP resin bolts embedded in large-scale concrete blocks were also conducted with different strengths. According to the test results, all GFRP resin bolts embedded in the three concrete blocks with different compressive strengths exhibited rod fracture failure. The failure mode was not controlled via the compressive strength of the concrete blocks due to the high bonding strength between the resin and the rod, as well as between the resin and the concrete. Therefore, this GFRP resin anchor system could fully utilize the tensile strength of GFRP rods. This research offers significant practical value in verifying the safety and reliability of GFRP resin bolts in corrosive marine service environments, and it contributes to the application and development of GFRP materials in the engineering field, serving as a valuable reference for the structural design and further study of GFRP bolts.

Bioabsorbable polymer implants aid the fracture treatment to overcome the limitations of metallic implants like stress shielding, corrosion, and revision surgeries. The cancellous screw is one of the internal fixation implants more frequently used in fixation procedures. In this work, nano‐hydroxyapatite (nHAp) reinforced polylactic acid cancellous screws were developed for bone fracture treatment. The biocompatibility and mechanical tests were performed before and after in‐vitro hydrolytic degradation studies. The addition of nanofillers (10 wt% nHAp) enhanced the pullout strength, torsional strength, and shear strength by 18%, 48%, and 5%, respectively. The performed thermal studies confirmed that the nanohydroxyapatite facilitates the crystallization process. A mass loss of about 18% in the case of neat PLA and 12% in the case of 10 wt% nHAp was observed for 90 days of in‐vitro hydrolytic degradation studies. So, the developed combination of biocomposite could help fabricate patient‐specific bioabsorbable fixation devices like screws and plates. [ABSTRACT FROM AUTHOR]

The integration of basalt-fiber-reinforced polymer (BFRP) rebars into concrete design standards still remains unrealized due to limited knowledge on the performance of the rebars in concrete, particularly in terms of bond durability in harsh conditions. In this work, we investigated the bond durability characteristics of BFRP rebars in fiber-reinforced self-compacting concrete (FRSCC) structures. To this aim, a number of 24 FRSCC pullout specimens reinforced with either BFRP rebar or glass-fiber-reinforced polymer, GFRP, rebar, which is a commonly used type of FRP, were fabricated. Half of these specimens were submerged in simulated seawater for a two-year span, while the other 12 similar specimens were maintained in standard laboratory conditions for comparative purposes. Subsequently, all 24 specimens underwent monotonic and fatigue pull-out tests. The exploration in this study focused on investigating the influence of the environmental condition, reinforcement type, and loading type on the bond stress versus slip relationship, maximum bond stress, and failure mode of the specimens. Based on the results obtained and by adopting the durability approach of industry standards for prediction of the bond retention of FRP-reinforced concrete, the bond strength retention between BFRP/GFRP and FRSCC after 50 years of exposure to seawater was estimated. The outcomes of the study are expected to enhance engineers' confidence in the use of FRP, especially BFRP, for constructing durable and sustainable reinforced concrete structures in aggressive environments. [ABSTRACT FROM AUTHOR]

An inflatable rockbolt is a steel tube that has been rolled into an omega shape. During installation, water is injected into the tube, which expands the profile of the rockbolt, generating a radial force against the borehole wall. This reinforces the rock mass through the friction at the bolt–rock interface. This study aims to quantify the effects of borehole size, borehole roughness, and installation water pressure on the pull load capacity of the bolt. This was achieved through a series of pull tests under laboratory conditions. The test results showed that the load capacity was higher in boreholes that were either close to the initial profile diameter of the bolt or the fully unfolded diameter of the bolt, that were 26.8 mm and 38.7 mm, respectively, in the study. The load capacity and the radial stiffness of the bolt were lowest in the medium-sized boreholes (33 and 33.5 mm). In small boreholes, the shoulders of the bolt tongue are tightly compressed such that the outward elastic deformation of the bolt tube is locked in after installation. This deformation locking enhances the load capacity of the bolt. In addition, the load capacity was found to be higher in percussively drilled boreholes than in diamond-drilled boreholes. The additional friction angle of the percussive boreholes was back-calculated to be approximately 5.83°. The load capacity was also found to increase as the installation water pressure increases in the range of pressures tested. It was observed that the inflatable bolt was clamped against the borehole in three zones: on the two tongue shoulders and the side of the bolt opposite the tongue. Highlights: The pull load of an inflatable bolt is minimum as the borehole diameter is in the middle of the initial and fully unfolded diameters of the bolt. In small boreholes, the clamping of the shoulders of the tube tongue results in higher contact stress and consequently higher pull load capacities. Borehole roughness is vital in enhancing the pull load capacity of inflatable bolt. The roughness angle of a percussive borehole is around 5.83°. The pull load capacity of the inflatable bolts increased as the installation water pressure increased from 24 to 30 MPa. An installed inflatable bolt contacts the borehole at the two tongue shoulders and in a zone around the opposite of the tongue. [ABSTRACT FROM AUTHOR]

Replacing steel reinforcements with the inclusions of Glass Fiber Reinforced Polymer (GFRP) is one of the most promising solutions not only to overcome corrosion problems, but also to improve soil nail durability as a tool of slopes stabilization and retaining excavations. The present study provides an insightful knowledge regarding the pull-out behaviour of a GFRP nail observed in laboratory from a pull-out test. It is a parametric study, which includes the influence of nail dimensions, the overburden pressure, and the degree of saturation, essentially on the pull-out load of the GFRP nail. Using an experimental working method, based on a full factorial design, the study reveals that the influence of nail dimensions and the overburden pressure on the pull-out load are more significant than that of the degree of saturation. Moreover, the experimental results show that the pull-out behaviour of the GFRP reinforcement is different from the ribbed steel reinforcement, subjected to the same testing condition. The differences between the Young's modulus, the interface properties, and the surface roughness of the bar exhibit the main influence factors. [ABSTRACT FROM AUTHOR]

Owing to the substantial benefits in environmental protection and resource saving, recycled aggregate concrete (RAC) is increasingly used in civil engineering; among the different types, RAC-filled steel tubes are an efficient structural form utilizing the advantages of concrete and steel tubes. This paper proposed a novel full-bolted beam-to-concrete-filled steel tube (CFST) joint and investigated the anchoring behavior of the steel plates embedded in RAC-filled steel tubes, which represents the behavior of the tensile zone in this joint, to demonstrate the feasibility of utilizing RAC in composite structures. The specimen consisted of a CFST and a connecting plate embedded in the CFST. In total, 18 specimens were tested to study the effects of concrete type (i.e., recycled aggregate concrete and natural aggregate concrete), anchoring type (i.e., plate with holes, notches, and rebars), and plate thickness on the pullout behavior, such as anchorage strength, load–displacement response, and ductility. Based on experimental results, the aggregate type of the concrete does not affect the pullout behavior obviously but the influence of anchoring type is significant. Among the three anchoring methods, the plate with rebars exhibits the best performance in terms of anchorage strength and ductility, and is recommended for the beam-to-CFST joint. In addition, plate thickness obviously affects the behavior of plates with holes and notches, the bearing area of which is proportional to the thickness, whereas the pullout behavior of the plates with rebars is independent of thickness. Finally, design formulas are proposed to estimate the anchorage strength of the connecting plates, and their reasonability is validated using the experimental results.

The shear strength parameter of an anchoring interface is one of the key parameters affecting the design of bolt support. To better realize the design of bolt support, the pullout model of fully grouted bolts was established by FLAC3D numerical software. The commonly used tri-linear bond-slip model of the anchoring interface was selected. The variable controlling method was used to investigate the effects of the shear strength parameters of the anchoring interface on the bearing performance of fully grouted bolts. The results show that, with the increase in the displacement at the peak shear stress, the bearing capacity and the energy absorption of fully grouted bolts decrease and the ability of the fully grouted anchoring system to resist external loads weakens. Meanwhile, the deformation capacity of fully grouted bolts increases, and the durability of the fully grouted anchoring system is enhanced. With the increase in the residual shear stress and the displacement at the residual shear stress, the bearing capacity and deformation capacity of fully grouted bolts both increase, and the energy absorption also increases. Increasing the post-peak bearing properties of the anchoring interface can help improve the bearing performance of fully grouted bolts and enhance the ability of the fully grouted bolts to resist failure. The results may provide guidance for support design and performance enhancement of fully grouted bolts.

Roots anchor plants firmly to the soil, enabling them to effectively resist soil erosion and shear failure. Vegetation restoration has been acknowledged as one of the most useful measures for controlling soil loss; however, which root system characteristics were most beneficial for plant anchoring in the soil remains unclear. In the black soil region of northeastern China, which frequently experiences serious soil erosion, pullout tests were carried out on six species of soil and water conservation woody plants with different growth habits (deciduous shrubs, deciduous trees and evergreen trees), and the root geometry and topology of each species were determined. The results showed that the maximum uprooting force and activation displacement (the displacement at the maximum peak in the relationship curve between pulling force and displacement) of shrubs were significantly greater than those of trees, while deciduous trees were significantly greater than evergreen trees. Therefore, the ability of the whole root system to anchor the soil was the largest for shrubs, followed by deciduous trees, and the smallest for evergreen trees. The uprooting force and activation displacement were mainly affected by the root topological index, total root length and the number of inclined roots. The total root length had the greatest influence on the maximum uprooting force, and the root topology had the greatest influence on the activation displacement, both of which can be used as important predictors of plant root anchorage strength. In addition, the plants with the R-type root structure may have a greater ability to anchor the soi, and can be prioritized for vegetation restoration with black soils. These findings provide references and implications for identifying the effective plant strategies for eroded soil restoration in the black soil region of northeastern China and other areas with similar soil types and bioclimates.