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Article

Macro-Mesoscopic Failure Mechanism Based on a Direct Shear Test of a Cemented Sand and Gravel Layer

by
Long Qian
1,2,
Xingwen Guo
1,*,
Qinghui Liu
1,
Xin Cai
1,3 and
Xiaochuan Zhang
1
1
College of Mechanics and Engineering Science, Hohai University, Nanjing 210098, China
2
MCC Huatian Engineering & Technology Corporation, Nanjing 210019, China
3
College of Water Resources and Hydropower Engineering, Hohai University, Nanjing 210098, China
*
Author to whom correspondence should be addressed.
Buildings 2024, 14(12), 4078; https://doi.org/10.3390/buildings14124078
Submission received: 18 November 2024 / Revised: 18 December 2024 / Accepted: 19 December 2024 / Published: 23 December 2024
Browse Figures
Figure 1
<p>Specimen material.</p> "> Figure 2
<p>Experimental procedure flowchart.</p> "> Figure 3
<p>Fabrication process of CSG specimens with no treatment forms.</p> "> Figure 4
<p>Fabrication process of CSG specimens with different interface treatment forms.</p> "> Figure 5
<p>Direct shear test device.</p> "> Figure 6
<p>Shear stress–shear displacement curve.</p> "> Figure 7
<p>Results of interface strength fitting.</p> "> Figure 8
<p>Interface with no treatment.</p> "> Figure 9
<p>Damage pattern of spreading mortar specimens.</p> "> Figure 10
<p>Damage pattern of chiseling specimens.</p> "> Figure 11
<p>Numerical model of the specimen.</p> "> Figure 12
<p>Comparison of numerical simulation results with experimental results for different interfaces of treatment.</p> "> Figure 13
<p>Number of fracture development in the specimen–shear displacement curve.</p> "> Figure 13 Cont.
<p>Number of fracture development in the specimen–shear displacement curve.</p> "> Figure 14
<p>Internal fracture distribution during shearing of the specimen.</p> "> Figure 14 Cont.
<p>Internal fracture distribution during shearing of the specimen.</p> "> Figure 15
<p>Thickness of fracture distribution at the end of specimen shear test.</p> ">
Versions Notes

Abstract

:
In order to explore the influence of different layer treatment methods on the macro- and meso-mechanical properties of cemented sand and gravel (CSG), in this paper, the shear behavior of CSG material was simulated by a three-dimensional particle flow program (PFC3D) based on the results of direct shear test in the laboratory. In shear tests, untreated CSG samples with interface coating mortar and chiseling were used, and granular discrete element software (PDC3D 7.0) was used to establish mesoscopic numerical models of CSG samples with the above three interface treatment methods, in order to reveal the effects of interface treatment methods on the interface strength and damage mechanism of CSG samples. The results show that, with the increase in normal stress, the amount of aggregate falling off the shear failure surface increases, the bump and undulation are more obvious, and the failure mode of the test block is inferred to be extrusion friction failure. The shear strength of the mortar interface is 40% higher than that of the untreated interface, and the failure surface is smooth and flat under different normal stresses. The shear strength of the chiseled interface is 10% higher than that of the untreated interface, and the failure surface fluctuates significantly under different normal stresses. Through the analysis of the fracture evolution process in the numerical simulation, it is found that the fracture of the sample at the mortar interface mainly expands along the mortar–aggregate interface and the damage mode is shear slip. However, the cracks of the samples at the gouged interface are concentrated on the upper and lower sides of the interface, and the damage mode is tension–shear. The failure mode of the samples without surface treatment is mainly tensile and shear failure, and the failure mode gradually changes to extrusion friction failure.

1. Introduction

Cemented sand–gravel (CSG) dams are a novel type of dam that combines the advantages of composite panel rockfill dams and concrete gravity dams [1,2]. These dams are constructed by mixing a small amount of cementitious material, water, and locally available aggregates, such as riverbed gravel or excavated materials from the dam site, in specific proportions to form the CSG material. The mixture is then compacted and poured using high-efficiency earth-moving and compaction machinery. CSG dams minimize environmental impact, making them an environmentally friendly alternative to traditional dam types. Through extensive research conducted by numerous scholars, significant progress has been made in addressing key technical challenges related to cemented sand–gravel materials, including static behavior [3], dynamic characteristics [4], thermodynamic properties [5], creep performance [6], and permeability–corrosion resistance [7].
Studies have shown that the failure of the layers in roller-compacted concrete dams primarily depends on the shear strength and the effects of long-term loading. When the dam is subjected to large shear forces or sustained loads, the layers, which act as relatively weak surfaces, undergo damage and degradation until failure occurs. Similarly to roller-compacted dams, due to the much lower strength and stability of the layer compared to the dam body, the horizontal construction layer of the cemented sand–gravel dam becomes a relatively weak surface [8]. With the increase in construction scale, the dam’s interfaces inside the structure gradually increase, and due to the weak cementation performance of the construction interface, it not only influences the local mechanical properties of the interface, but also becomes a weak part affecting the overall safety of the structure. Therefore, it is necessary to employ appropriate methods to reveal the failure mechanism of the CSG interface, in order to provide a theoretical basis for selecting the suitable interface treatment methods during construction.
According to the “Technical Manual for CSG Dam Construction”, the interval of the CSG interface can be divided into three stages, before the initial setting (0–7.7 h), before the final setting after the initial setting (7.7–14.7 h), and after final setting (after 14.7 h). After the initial setting of CSG, appropriate interface treatment measures are required to ensure the adhesion performance in order to prevent direct contact between the upper layer and the lower layer CSG that has already been set, which leads to the phenomenon of aggregate hollowing. In general engineering, interface treatment methods include spreading mortar, cement net slurry, and chiseling, etc. At present, many scholars have studied the effects of different interface treatment methods and interface interval on the mechanical properties of CSG by indoor direct shear test and explored the relationship between the interface strength characteristics, cohesion, and friction coefficient through the test, which provides a basis for subsequent research [9,10,11].
Research on the damage characteristics and strength evolution mechanism of the interface of CSG materials can draw inspiration from studies on the interface properties of some rock- and roller-compacted concrete dams. Chen et al. [12] investigated the shear performance of iron tailings as fine aggregate rockfill concrete with different layer characteristics and analyzed the effects of different exposure heights, exposure areas, the degree of coarsening, and the stone dust content of rock piles on the test. Li et al. [13] conducted large-scale direct shear tests to study five types of interfaces and examined the coral reef limestone–concrete shear failure characteristics. Peng Xia et al. [14] investigated columnar jointed basalt (CJB) within the dam engineering of the Baihetan Hydropower Station, conducting multiple in situ direct shear tests. The findings reveal that shear strength is correlated with rock-type grade and demonstrates significant anisotropy, as the friction coefficient on the horizontal shear plane exceeds that on the vertical shear plane. Bo Da et al. [15] used superfine cement paste, silicon mortar, and polymer to strengthen the coral surface, and analyzed the failure mode of the coral concrete for different strength grades. Liu et al. [16] studied the shear strength of roller compacted concrete (RCC) interlayer under different time intervals and interlayer treatments and provided a view of the structure on the mesoscopic scale by using test results from a scanning electron microscope.
In fact, CSG can be regarded as a multiphase composite material composed of aggregate, cement, and pore space on a mesoscopic scale [17], and damage of the interface is the process of crack initiation, expansion, and penetration until the formation of macroscopic cracks under the load, which is closely related to the discontinuity and non-uniformity of CSG itself, and its damage behavior is closely related to its meso-structure. Therefore, exploring the internal crack development characteristics from the mesoscopic perspective of a specimen that cannot be obtained by macroscopic tests is an effective method to reveal the performance evolution and damage mechanism of the construction interface in the shear process.
The discrete element method is a numerical simulation method used to reflect the mechanical properties of granular materials and interparticle interactions and is currently widely used in problems such as damage cracking evolution and penetration mechanisms of granular materials [18,19,20]. Lixia Guo et al. [21] employed numerical simulation methods to divide CSG at the mesoscopic level into aggregate units, cement mortar units, and interface units, with aggregates randomly generated. Using laboratory uniaxial compression test results, they inverted the mesoscopic component parameters and verified the validity of the mesoscopic numerical simulation. The study revealed that, at the mesoscopic level, cracks in CSG typically appear on the interface and around the aggregate; with a lower sand ratio and higher aggregate proportion, stress concentration becomes more pronounced, leading to earlier cracking of the test specimens. In addition to the above discrete element simulations on the strength of the material body, researchers have carried out studies on problems at the level or interface. Salazar, A et al. [22] used the three-dimensional discrete element method (DEM) to model direct shear tests, and the results indicate that the stress path can be appropriately reproduced, but the dilatancy was very difficult to replicate. Seyyedan et al. [23] used a combined DEM-XFEM novel approach to simulate the direct shear test of breakable two-dimensional angular particle assemblies, and the results indicated that particle breakage in granular materials reduced the amount of anisotropy, the dilative behavior, and the mobilized friction angle of the sample. Deng et al. [24] used DEM to investigate the micro-mechanical properties of frozen soil during direct shear tests, the simulation results indicated that as the cooling temperature decreased, the cohesion and internal friction angle of the frozen sand samples increased significantly, and the shear dilation tended to increase. Yang et al. [25] used the particle flow code (PFC) to study the shear behavior of concrete–rock joints with similar triangular asperities (STAs). The simulation results showed that the STAs profile exhibited significant plastic behavior after peak, which is likely due to the asynchronous failure of the convexity, rather than the synchronous failure of the RTAs profile causing brittle shear. NM Motlagh et al. [26] used the discrete element method to simulate the mechanical behavior of cementitious materials. The study results indicated that by considering two parameters—cement content and water-to-cement ratio—the bond contact model could capture the main mechanical behaviors of these materials (strain softening and dilation) with reasonable accuracy. Microscopically, it was observed that an increase in cement content and a reduction in the water-to-cement ratio increased the magnitude of the maximum interparticle forces. The cement content and water-to-cement ratio influenced the number of bonds formed between particles at the start and the end of the tests. Aliabadian et al. [27] studied the sprouting, extension, and agglomeration of cracks in rock-like disk specimens containing defects using a particle adhesion model in discrete elements, and the results showed that the discrete element approach was effective in tracking the deformation field and the crack development process in the specimens. Wang et al. [28] conducted numerical shear tests on laminated rocks using PFC and obtained the damage patterns of laminated rocks under different positive stresses, which is a reference value for predicting the damage behavior of rock masses and can be further applied to the study of the damage mechanism of surrounding rocks in engineering. Liu et al. [29] conducted a series of three-dimensional numerical direct shear tests on the unsaturated soil–structure interface under different suction and positive stresses using the discrete element method to investigate the meso-scale mechanical shear properties between the unsaturated soil and the structure during the shear process, including the changes in particle displacement and the magnitude and direction of contact forces. Luo et al. [30] combined tests and PFC to perform compressive and shear tests on fractured rock specimens under four filling conditions, analyzed the strength properties and damage modes of the specimens, and analyzed the crack types and crack merging processes using particle displacement fields. G. Wang et al. [31] explored the shear damage characteristics of filled joints using a combined macroscopic and meso-view approach. The numerical simulations showed that the damage of filled joints is the beginning of the damage process, and the local meso-view displacement of filled joint specimens during shear is significantly limited in the initial stage by the filler adhesion effect. The discrete element method (DEM) is a powerful numerical approach that allows for precise simulation of particle interactions, making it highly suitable for studying granular materials like sand and gravel. Its ability to capture complex behaviors such as friction, bonding, and material failure at the particle level makes it invaluable for understanding microscopic and macroscopic mechanical properties. DEM also offers flexibility in modeling different particle shapes and sizes, and it can handle large deformations. Despite its drawbacks, such as high computational costs, sensitivity to model parameters, and challenges in simulating continuous materials, these issues have not hindered the widespread application of the discrete element method (DEM) in the study of granular materials.
In view of the great advantages of the discrete element method in the study of the meso-mechanics of geotechnical materials, this paper carries out numerical simulations of direct shear of CSG interface based on indoor direct shear tests to study its damage mechanism under different interface treatments, analyze the fracture evolution law from the meso-scale perspective, and compare with the damage phenomenon of indoor direct shear tests to explore the mesoscopic mechanism of deformation damage of the CSG interface.

2. Indoor Interface Direct Shear Test

2.1. Experimental Materials

With regards to reference [32], the primary materials used in this study include cement, fly ash, and gravel. The cement is Conch P.O. 42.5 ordinary Portland cement, produced in Anhui Province, China; the chemical composition of the cement is shown in Table 1. The fly ash is sourced from a coal-fired power plant in Henan Province, China, and is collected from the high-temperature flue gasses in the furnace using dust collection equipment. The physical properties and composition of the crushed stone and medium sand (with a fineness modulus of 2.48) are shown in Table 2. The fine aggregate consists of medium to coarse sand sold in the Nanjing market, while the coarse aggregate is natural pebbles from Liuhe District, Nanjing, as shown in Figure 1. The mass ratio of cement, fly ash, water, and gravel is 1:1:2:48, and the grain size and mass of each aggregate in the gravel are provided in Table 3. It is important to note that in actual engineering projects, the maximum particle size of crushed stone in CSG materials is typically 150 mm. However, due to the requirement to pour the samples in two layers, with a minimum layer size of 75 mm, a particle size limit of 20 mm was set.

2.2. Test Program

In order to study the influence of interface treatment measures on the macroscopic strength and damage mechanism of CSG, this paper considers three interface treatment measures: no treatment, mortar coating, and chiseling. Cubic samples containing 100 kg/m3 of colloidal admixture, an aggregate dry density of 2150 kg/m3, a curing interval of 12 h, and a size of 150 mm were designed and prepared. The experimental process is shown in Figure 2. During the experiment, specimens for each interface treatment were subjected to three direct shear tests under four normal stresses (0.5 MPa, 1.0 MPa, 1.5 MPa, and 2.0 MPa). To minimize large errors introduced by improper operations or other factors, if the deviation of each measured value from the median in a group of test data does not exceed 15% of the median, the average value is taken as the test result. If the deviation of a measured value from the median exceeds 15% of the median, the median is taken as the test result. If the deviation of two measured values from the median exceeds 15% of the median, the test results for that group are considered invalid, and the test is repeated.

2.3. Preparation of CSG Specimens

A special mold was used to pour the CSG specimen into two layers. Before pouring, the lower sealing plate of the mold is assembled, and the oil release agent is applied inside the mold, followed by filling the first layer of CSG into the mold and smoothing the interface after pounding. The specimen interface was treated according to two treatment measures after 12 h resting in the following manner:
(1)
No treatment of interface: After pouring and compacting the lower layer of cement-stabilized macadam material, and allowing it to rest for the corresponding time interval, the upper layer of cement-stabilized macadam material is poured directly without any treatment in between.
(2)
Interface with spreading mortar: Using the brush to clean the scum on the surface and then spreading a layer of 3 mm cement mortar on the surface (the quality ratio of cement, sand, and water is 1:3:0.6), after which pouring the upper layer of CSG.
(3)
Interface with chiseling: Using an iron chisel to remove the mortar on the surface until the large grain size particle is exposed, removing the scum on the interface with a brush, and then wetting the surface and pouring the upper layer of CSG.
The interface treatment process of (1) is shown in Figure 3a, and the interface treatment processes of (2) and (3) are shown in Figure 3b,c. The specimens were de-molded and moved into the curing room after solidification and cured for 90 d under standard conditions (temperature: 25 °C, humidity: 95%). The specimens after drying are shown in Figure 4, the dashed line indicates the Interface of CSG.

2.4. Experimental Equipment and Testing

The equipment used for the test was the YZW-500 microcomputer-controlled hydraulic rock direct shear instrument shown in Figure 5, and the dashed line indicates the location of the cemented sand and gravel interface. The direct shear apparatus comprises a shear box, loading frame, displacement control system, and measurement devices to apply and measure shear forces. It is commonly used to assess the shear strength of soils, rocks, and other materials under controlled laboratory conditions. The specimen was placed in a shear box made of a 3 cm thick steel plate and divided into two parts, and the internal dimensions of a single shear box were 150 mm × 150 mm × 70 mm. During the shear test, the specimen is first subjected to normal loads, with vertical loads of 0.5 MPa, 1.0 MPa, 1.5 MPa, and 2.0 MPa. Each normal load is divided into five equal stages and applied incrementally until the design value is reached. During the test, the normal stress is kept constant. After the specimen was placed, a micrometer was fixed to the shear box to measure the shear deformation. The shear load was loaded at a rate of 0.36 mm/min according to the displacement loading method, until the specimen failed.

2.5. Results and Analysis

2.5.1. Shear Stress–Shear Displacement Curve

The CSG shear stress–shear displacement curves for the interface with no treatment, spreading mortar, and chiseling are shown in Figure 6a–c.
It can be observed that the curve variation patterns of the interfaces treated with mortar spreading and chiseling are roughly similar to the test results of the untreated interface, which can be divided into linear elastic deformation phase (shear displacement of 0–0.3 mm), nonlinear deformation phase (shear displacement of 0.3 mm—shear displacement value corresponding to the peak shear stress) and post-peak residual phase. The drawings were created by Origin 2024.
Compared to the experimental data for the A3 (untreated interface), C3 (mortar-coated interface), and D4 (chiseled interface) groups in [33], the overall patterns of the experimental results are similar. However, there are some differences, primarily due to the fact that in [33], the vertical load was set at 1.6 MPa, and the time interval for the D4 group interface casting was 18 h. In [33], the peak shear load for the A3 group was approximately 0.85 MPa, while in this study, it was around 0.78 MPa. Based on the difference observed in this study, it can be inferred that with a vertical load of 1.6 MPa, the peak shear load would be approximately 0.83 MPa. For the C3 group in [33], the peak shear load was about 1.06 MPa, while in this study, the peak shear load at a vertical load of 1.5 MPa was approximately 1.26 MPa. Interpolation suggests that under 1.6 MPa vertical load, the peak shear load would be about 1.33 MPa. For the D4 group in [33], the peak shear load was about 0.98 MPa, whereas in this study, it was approximately 1.2 MPa at 1.5 MPa vertical load. Interpolation calculations indicate that under 1.6 MPa vertical load, the peak shear load would be around 1.27 MPa.

2.5.2. Interface Strength

The strength of the specimen for each of the three interface treatments was fitted using the Moore–Cullen criterion:
τ f = c ′ + σ tan φ ′
where τf is the shear strength, MPa; σ is the normal stress, MPa; c’ is the cohesion at the interface, MPa; φ’ is the internal friction angle at the interface.
Referring to the test results of the paper [32] with untreated construction interface, the peak shear stress for specimens with three interface treatments at different normal stresses are listed in Table 4, and the corresponding molar coulomb strength fitting curves are shown in Figure 7 by linear fitting of the four stress state points.
Table 5 summarizes the results of shear strength fitting for the three interface treatments. The cohesion of the specimens with spreading mortar increased by 70% and the internal friction angle increased by 22% compared to the specimens with no treatment. The cohesion of the specimens with chiseling was not much different from that of the specimens without treatment, which was reduced by 10%, and the internal friction angle was increased by 15%.
The cohesive force of the CSG interface is mainly provided by the cementing material. The mortar laid on the interface makes the cement between the upper and lower layers increase, and the cementing effect between the particles is more obvious, so the cohesion and the internal friction angle are increased to some extent. The cementitious material between the upper and lower layers was reduced after the interface was chiseled, showing a decrease in cohesion, but the inter-layer aggregate was filled more compactly, resulting in an increase in the bite between the aggregates, and therefore an increase in the internal friction angle.

2.5.3. Exploration of Interface Damage Patterns

The analysis of the shear failure surfaces provides insights into the damage characteristics of the untreated CSG samples under varying normal stresses. As depicted in Figure 8, the shear surface at a normal stress of 0.5 MPa remains relatively smooth. However, with increasing normal stress, the failure surface becomes progressively rougher, with noticeable fluctuations and convexities. At higher normal stresses, the cement structure is observed to deteriorate, and larger pebble particles become dislodged. These particles often interlock, creating protrusions or pits in areas with larger particles. Furthermore, significant white scratches appear in regions with dense aggregate packing on the shear surface, indicating dislocation friction between the aggregates. This observation supports the hypothesis that the shear strength of untreated CSG specimens results not only from friction but also from the interlocking forces between the aggregates. As the normal stress increases, these interlocking forces intensify, and the rougher shear surface contributes to an enhanced shear strength of the test block. This finding highlights the complex interactions between particle interlocking and friction, which play a key role in the overall shear behavior of CSG materials under various loading conditions.
As depicted in Figure 9, the failure behavior of the mortar-coated interface exhibits distinct differences compared to the untreated interface. Under different normal stresses, the shear failure surface of the mortar-coated specimens remains relatively smooth, with minimal damage to the aggregate structure. This indicates that the failure primarily occurs at the interface between the mortar cementation layer and the CSG body, rather than within the aggregates themselves. The presence of hardened mortar and the absence of significant aggregate damage further emphasize the role of the mortar layer in the failure mechanism. Once the bond between the mortar and the CSG body breaks, the specimen undergoes sliding between its layers, resulting in a shear failure surface that is largely flat and perpendicular to the applied shear direction. This suggests that the mortar coating plays a crucial role in the shear strength of the specimen, as its failure initiates sliding and governs the overall shear behavior of the interface.
As depicted in Figure 10, the shear failure behavior of the chiseled specimens reveals a distinct pattern compared to untreated specimens. While the overall failure mode is similar, the chiseled interface exhibits a significantly higher degree of roughness, characterized by more pronounced concavities and convexities. This increased roughness is particularly evident at the upper part of the specimen, where severe spalling leads to a fully penetrated shear failure surface. The jagged appearance of the shear interface, along with the presence of white spots, suggests that the dislodged and misaligned pebble particles enhance the roughness of the shear contact surface. This interlocking effect between the particles contributes to a more intense crushing friction failure under different normal stresses, highlighting the influence of the chiseled interface treatment on the shear behavior of the specimen.
It should be noted that the shear failure interface of the specimen in Figure 8, Figure 9 and Figure 10 shows static characteristics, and the different shear failure characteristics are due to different mechanical behaviors of the aggregates inside the interface under the action of external loads. The specific motion state in the shear process cannot be accurately judged from the phenomena, such as the distribution of abrasion marks and the distribution position of dislodged aggregates observed after the macroscopic test, while the development of cracks inside the interface cannot be observed during the test. Therefore, an in-depth analysis of the failure process of the shear interface requires a comprehensive grasp of the motion of the particles in the entire shear process, and these tasks need to be explored from a mesoscopic viewpoint.

3. Numerical Simulation of Direct Shear Test

3.1. Bonding Model and Failure Criterion

The failure at the interface of CSG is the fracture of the intergranular adhesion leading to the separation and dislocation of the particles. The damage monitoring procedure based on the PFC3D fish function in the numerical simulation monitors the mode of intergranular damage and the process of fracture generation. Drawing on previous research results [32], a linear contact bonded model was used to simulate the interparticle cohesive interaction. The adhesions of the linear contact bonded model can be considered as a pair of springs with constant normal and tangential stiffnesses, with certain tensile strength (σc) and shear strength (τc), and the presence of contact adhesions makes the interparticle shear force limited by the shear strength, independent of the frictional force. When the normal overlap is Un < 0, the contact bond bears the tensile force and the sliding model is activated after the contact bond is broken, and if the bond is not broken, no relative sliding occurs between the particles.
The effect of the forces on the Interparticle adhesion at the beginning of each new time step is calculated by the following equation:
F i n ← F i n n i + Δ F i n
F i s ← F i s n i + Δ F i s
where F i n and F i s represent the normal and tangential components of the contact force, respectively.
The maximum tensile and shear stresses acting on the bonded contact are calculated as follows:
σ max = − F n A
τ max = F s A
When the maximum tensile stress exceeds the normal bonding strength (σmax ≥ σc), tensile failure occurs between particles, and when the maximum shear stress exceeds the tangential bonding strength (τmax ≥ τc), shear damage occurs between particles.

3.2. Mesoscopic Modeling of Different Interface of Processing (Mesoscopic Modeling of Different Interface Treatment Measures)

The numerical simulation was performed using the shear box in the paper [32], keeping the upper shear box fixed during shearing, applying a rightward velocity to the wall of the lower shear box with a velocity of 0.001 m/s, with the time step set to automatic, and stopping the loading when the shear displacement reached 7.0 mm. Referring to the modeling of CSG material in [32], a series of rounded particles were generated using the particle size range in Table 4. The particle flow model without layer treatment in the test is shown in Figure 11a.
The mortar spread treatment in the test was performed by spreading a layer of 3 mm cement mortar on the interface. The numerical modeling corresponds to the test, and the mortar is simulated by adding small particles at the location of the interface. The specific process is as follows: an area with a thickness of 3 mm is taken at the location of the shear interface of the numerical specimen to generate a layer of compact particles all with a radius of 1 mm, and then CSG particles are generated in the remaining space of the shear box according to the way the interface is not treated. The mesoscopic particle model of the CSG interface spread with mortar generated in the numerical simulation is shown in Figure 11b.
The interface with chiseling In the test was performed by removing small particles from the interface until the large-sized pebbles were exposed and then pouring the upper layer of CSG. In the numerical modeling, the interface with chiseling was simulated by removing small particles from the interface area. The specific process is as follows: firstly, the model is simulated in the way of no treatment at the interface, then the fine particles less than 5 mm in the interface area in the lower half of the specimen are deleted, and, finally, the model is cycled to make the upper layer coupled with the lower layer intact. The mesoscopic model of CSG with interface chiseling is shown in Figure 10c.

3.3. Parameter Setting

CSG can be considered a two-phase body consisting of coarse aggregate and mortar. In this paper, a linear contact bonded model is used to give contact between mortar particles, mortar particles, and upper–lower aggregates and filled particles, filled particles, and upper–lower aggregates. The specific meso-parameters are shown in Table 6, with reference to [32] for the meso-parameters in numerical specimens of CSG. The parameters in Table 6 were used to simulate the direct shear of the CSG numerical specimens with a normal stress of 2.0 Mpa for both interface treatments, and the simulation results were compared with the those of indoor test, as shown in Figure 12. It can be seen from the figure that the error between the numerical simulation results and the actual values is within 10%, and the numerical simulation results are in good agreement with the experimental results. The discrepancies between the numerical simulation and experimental results are mainly attributed to the assumptions made in the numerical modeling. For instance, in the numerical simulations, it is assumed that each particle is spherical, which differs from the actual shape of the gravel particles. Additionally, the simulation results are influenced by parameters such as the interparticle friction coefficient and effective modulus. These factors may contribute to the deviations between the numerical predictions and the experimental outcomes in real-world scenarios.

4. Analysis and Discussion

4.1. Analysis of Meso-View Damage Mechanism

Figure 13 obtains the relationship curves of the number of fracture developments inside the specimen with the growth of shear displacement for different interface treatments. According to Figure 13, it can be seen that the development of fractures during shear can be roughly divided into three stages.
(1)
Slow growth stage: When the shear displacement reaches 0.5 mm, the specimen starts to produce cracks, the number of cracks grows slowly, and the crack growth curve at this stage is basically a horizontal straight line; the slow growth stage of cracks corresponds to the shear stress–shear displacement curve in the middle line of the elastic deformation stage. In this stage, the “cementation” between the particles at the interface of CSG resists the shear stress.
(2)
Fracture extension stage: Due to the existence of the interface, the CSG specimen enters the fracture extension stage earlier (between 0.5 and 4.0 mm of shear displacement), which is mainly located in the nonlinear deformation stage of the shear stress–shear displacement curve. In this stage, the fracture inside the specimen expands rapidly, and the macroscopic expression of the shear stress increases slowly, because the cemented material at the interface gradually breaks down and the adhesion of the interface is gradually lost.
(3)
Continuous growth phase: After the shear displacement of 4.0 mm, the increase in fracture continued until the end of the test, and this phase corresponds to the residual phase after the peak in the shear stress–shear displacement curve. In this phase, the adhesion between particles at the interface fails and the roughness of the interface is changed due to the dislodgement of aggregates at the interface, and the magnitude of the shear stress is controlled by the occlusion force between aggregates and the friction force.
As can be seen from Figure 13a, the slope of fracture expansion is the largest and the expansion speed is the fastest. After that, the fracture development speed slows down and tends to be stable, and the entire curve presents an “S” shape. The slope of the rapid growth stage gradually increased, and the number of cracks in the test block was always in a linear growth state from the expansion stage, resulting in almost a straight line between the two stages.
According to Figure 13b, it can be seen that the change (variation) pattern of the number of fracture development–shear displacement curve of the specimen with spreading mortar roughly shows an “S” shape, and the number of shear fractures dominates the whole shear process. In the slow growth stage (shear displacement of 0–0.5 mm), shear fractures accounted for 65% of the total fractures, and the specimen internal shear damage mainly occurred. In the crack expansion stage (shear displacement of 0.5–4.0 mm), the number of cracks continued to rise, and the number of shear cracks was higher than that of tension cracks in this stage, but the growth rate of shear cracks slowed down, and its proportion decreased from 65% to 58%. In the stage of continuous crack growth, the growth slope of shear cracks gradually leveled off, the growth rate of tension cracks accelerated, and the proportion of tension cracks in the total number of cracks in this process increased from 42% to 46%, indicating that the expansion of tension cracks was mostly inside the specimen in the residual stage.
Compare the graph of the number of fracture development–shear displacement for the interface chiseling specimen in Figure 13c. The number of tension fractures inside the specimen dominates during the whole shear process. In the slow growth stage (shear displacement of 0–0.5 mm), the number of cracks is basically zero in this process due to high compaction and less pore space at the interface, and the cracks are more difficult to generate. The specimen has almost a straight line in the crack expansion stage and continuous growth stage, the total crack curve is in a straight line after shear displacement 0.5 mm, the cracks continue to increase until the end of shear, the growth rate of both kinds of cracks in this process is about the same, the number of tension cracks is significantly more than the number of shear cracks, and its proportion in the total number of cracks increases from 0 to 81%. This indicates that the interparticle damage at the fracture extension stage is a mixture of tensile damage dominated by shear damage. Figure 14 shows the distribution of meso-fractures as loading to the fracture extension stage, loading to the rapid growth stage, and loading completed for specimens with different interface treatments. Figure 15 shows the main view of fracture thickness distribution after loading is completed.
According to Figure 14 and Figure 15, when the test block plane is not treated and loaded to the stage of rapid growth, cracks have been spread over the entire shear plane, most of the cracks are concentrated on the four sides of the shear plane, and a small number of intermittent cracks are connected to the center of the plane, forming a basically continuous shear failure plane. The failure plane is almost a plane parallel to the plane at this stage. After the end of loading, the cracks began to spread and distribute along both sides of the plane. With the increase in normal stress, the crack concentration area of the test block becomes thicker, and the crack concentration thickness increases to about 15 mm, showing a zonal distribution. Therefore, with the increase in normal stress, the concentration area of cracks in CSG gradually changes from “plane” to “zone”.
When the specimens with spreading mortar were loaded to the crack expansion stage, shear cracks were observed inside the specimens, indicating that shear damage occurred in the particles inside the specimens, and fewer tension cracks were scattered around the edge of the interface, which was due to the movement of the shear box causing tension damage to the particles around the interface. When loading to the rapid growth stage, a large number of new cracks are generated inside the interface, and the shear cracks cover the whole interface area, during which the shear cracks are fully developed and extend to the center of the specimen. With the increase in shear displacement, the tensile fractures develop rapidly and the whole interface is covered by tensile fractures. After the shear test, the distribution of cracks inside the specimen was observed. The specimen with spreading mortar had a high concentration of cracks, forming a thin band with a regular shape, and its thickness was about 10 mm, which was about 5 times that of the particle size of mortar on the interface.
When the specimens with chiseled interface were loaded to the crack expansion stage, there were more tension cracks and they were distributed in all positions of the specimen interface, and there were fewer shear cracks and they were scattered all around the edge of the interface. When loading to the rapid growth stage, the tensile cracks covered the area of the interface, and a small number of shear cracks were interspersed between the tension cracks; at this time, it was observed from the figure that the cracks had gradually expanded to the upper and lower ends of the interface. With the gradual increase in shear displacement, the number of tension cracks and shear cracks increased dramatically, indicating that the interaction between the aggregate particles on both sides of the interface occurred, and more cracks developed on the upper and lower sides of the interface. The thickness of the specimen crack concentration area is thicker and irregular in shape; observing the distribution position of the cracks after the end of the specimen shear test, the thickness is about 28 mm, which is about 6 times the depth of the chiseled interface.

4.2. Numerical Simulation Results and Discussion

In this study, the damage mechanisms of untreated and treated CSG specimens were investigated through a combination of macroscopic experimental observations and meso-scale numerical simulations. By analyzing the damage phenomena observed in the macroscopic shear tests and the evolution of interparticle fractures at the interface in the numerical simulations, we were able to gain a deeper understanding of the shear behavior and damage modes of CSG under different normal stresses.
The results reveal that under low normal stress, the untreated specimens exhibit tensile failure primarily occurring between particles. During the shearing process, the inter-layer particles tend to shift upwards, with the failure mode dominated by sliding along the plane. As the normal stress increases, the difficulty for the particles to misalign and rotate increases, resulting in simultaneous tensile and shear failure between the particles. Consequently, the failure mode gradually transitions to extrusion friction failure, where the specimen blocks are compressed and shear-induced displacement leads to frictional interaction at the interface.
In the case of specimens treated with mortar, the damage mechanisms evolve differently. The location of interface crack generation and the degree of crack concentration indicate that damage primarily occurs between the mortar particles during the entire shear process. During the elastic deformation stage, shear damage initiates at the interface between the mortar and aggregate particles, with tension damage being induced at the edge of the interface due to the movement of the lower shear box. In the nonlinear deformation stage, the shear strength of the interface is primarily provided by the adhesive effect between the mortar particles. As shear fractures within the interface grow, they rapidly expand towards the center, and the adhesive force between the mortar particles gradually deteriorates. This results in the peak shear stress being reached. In the residual stage, further displacement of the mortar particles causes them to stagger and tumble, leading to increased interparticle tensile damage. Eventually, this damage penetrates the entire interface, forming macro-cracks.
For specimens treated with chiseling, the fine aggregate particles are reduced, and the inter-layer particles become more compact under normal loading, making them less prone to misalignment or overturning. During shearing, the coarse aggregates at the interface experience extrusion misalignment due to the combined action of normal and shear loads. As the contact pressure increases, localized strength at the interface is enhanced, leading to the initiation of tensile damage between the particles. With increasing shear displacement, an “interlocking” effect occurs at the interface, where large particles stagger and tumble, resulting in the pooling and penetration of tension and shear fractures at the top and bottom sides of the interface. This leads to a concentration of cracks and uneven failure of the shear interface.
In conclusion, the shear slip damage occurring along the mortar particle–aggregate interface in mortar-treated specimens contrasts with the tension–shear failure observed in the chiseled specimens, where the aggregate particles experience more interlocking and resistance to misalignment. These findings not only highlight the importance of interface treatments in improving the shear strength of CSG materials but also provide insight into the meso-scale mechanisms of deformation and damage that influence the macroscopic shear behavior of CSG specimens.

5. Conclusions

In this paper, a series of experimental studies on CSG with three types of interface treatment are carried out. Through the comprehensive analysis of the macroscopic test and meso-numerical simulation results, the macroscopic strength and damage characteristics of the CSG interface are revealed in a more comprehensive manner, and the internal property evolution mechanism of the interface under different treatment methods is also investigated from multiple perspectives in meso-view, which can help deepen the understanding of the evolution mechanism and damage mode of the interface properties of CSG and provide a reference basis for engineering practice. The main conclusions are as follows.
(1)
Based on the results of the direct shear test in the laboratory, the expression of the shear strength of the sample at the interface of the untreated layer, the mortar coating, and the chiseled wool is obtained, which can be used as a reference for practical engineering. During the construction of CSG dams, when the exposure time of the layer exceeds the final setting time, surface treatment measures should be adopted to improve the shear strength of the layer.
(2)
The shear plane failure characteristics of the test block under different layer treatment methods were obtained. Based on meso-scale numerical simulations of specimens with different surface treatments during shear, the following conclusions were drawn: In the untreated specimen, under low normal stress, particles mainly experience tensile failure, with interlayer particles becoming suspended, and the failure mode is primarily sliding along the surface. Under high normal stress, both tensile and shear failures occur simultaneously, with the failure mode shifting to compressive and frictional damage. In the mortar-coated specimen, during shear, particles mainly undergo displacement and rotation, with shear strength provided by the bonding between mortar particles. Cracks are concentrated in the surface area, dominated by shear cracks, and the failure mode is a shear-sliding failure of the mortar particles. In the roughened specimen, due to fewer suspended pores and higher surface density, particles are less likely to displace or rotate. During shear, tensile and shear cracks rapidly develop, converging to form thicker crack zones, with the failure mode involving compression and tensile–shear failure between aggregates. The numerical simulation results align well with the macroscopic observations from experiments.
(3)
Based on the meso-scale numerical simulations of specimens with different surface treatments during shear, the particle motion and particle contact characteristics (crack evolution) were analyzed, leading to the following conclusions: In the specimen without surface treatment, under low normal stress, the particles primarily experience tensile failure, and interlayer particles are prone to become suspended, with the failure mode mainly exhibiting sliding along the surface. Under high normal stress, particle displacement and rotation are more difficult, and both tensile and shear failures occur simultaneously, with the failure mode shifting to compressive and frictional damage. In the specimen with a mortar layer, during shear, the particles in the surface area primarily undergo displacement and rotation. The shear strength is provided by the bonding between the mortar particles, with cracks mainly concentrated in the surface area and dominated by shear cracks. The failure mode is characterized by shear-sliding failure of the mortar particles. In the specimen with a roughened surface treatment, due to fewer suspended pores and higher density at the surface, the particles are less likely to experience displacement and rotation. During shear, tensile and shear cracks develop rapidly and converge to form thicker crack zones along both sides of the surface, with the failure mode mainly involving compression and tensile–shear failure between the aggregates. The numerical simulation results are consistent with the macroscopic phenomena observed in the experiments.

Author Contributions

Methodology, L.Q.; Software, X.Z.; Validation, Q.L.; Formal analysis, L.Q. and X.G.; Investigation, X.G.; Data curation, Q.L. and X.Z.; Writing—original draft, L.Q.; Writing—review & editing, L.Q.; Funding acquisition, X.G. and X.C. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Key Research and Development Plan (2018YFC0406804), the National Natural Science Foundation of China (51979094, 51809164), and a project funded by Yunnan Water Conservancy and Hydropower Vocational College (Project No. 2023SZYKL011).

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.

Conflicts of Interest

Author Long Qian was employed by the company MCC Huatian Engineering & Technology Corporation. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

  1. Londe, P. The faced symmetrical hardfill dam: A new concept for RCC. Water Power Dam Constr. 1992, 19–24. [Google Scholar]
  2. Stevens, M.A.; Linard, J. The safest dam. J. Hydraul. Eng. 2002, 128, 139–142. [Google Scholar] [CrossRef]
  3. Cai, X.; Zhang, Y.; Guo, X.; Liu, Q.; Zhang, X.; Xie, X. Functional zoning optimization design of cemented sand and gravel dam based on modified Duncan-Chang nonlinear elastic model. Case Stud. Constr. Mater. 2022, 17, e01511. [Google Scholar] [CrossRef]
  4. Zhang, X.; Li, P.; Huang, H. Dynamic damage constitutive model of cemented sand and gravel material. Mech. Adv. Mater. Struct. 2022, 29, 3324–3333. [Google Scholar] [CrossRef]
  5. Jiang, M.; Cai, X.; Guo, X.; Liu, Q.; Zhang, T. Adiabatic temperature rise test of cemented sand and gravel (CSG) and its application to temperature stress prediction of CSG dam. Adv. Mater. Sci. Eng. 2020, 2020, 3898391. [Google Scholar] [CrossRef]
  6. Cai, X.; Jiang, M.; Guo, X.; Chen, J.; Zhao, Q. Experimental study on the creep behaviour of cemented sand and gravel (CSG) and temperature stress prediction of CSG dam under seasonal temperature change. Adv. Civ. Eng. 2020, 2020, 8289520. [Google Scholar] [CrossRef]
  7. Estekanchi, V.; Aghajani, H.F. Investigating the Strength and Microstructure of Cemented Sand–Gravel Mixtures Subjected to Freeze–Thaw Cycles. J. Cold Reg. Eng. 2024, 38, 04024008. [Google Scholar] [CrossRef]
  8. Ding, Z.; Wang, X.; Xu, L.; Wang, J. Study on the safety of cemented sand and gravel dams based on the profile form of model tests. In Structures; Elsevier: Amsterdam, The Netherlands, 2023; Volume 56, p. 104978. [Google Scholar]
  9. Amini, Y.; Hamidi, A.; Asghari, E. Shear strength–dilation characteristics of cemented sand–gravel mixtures. Int. J. Geotech. Eng. 2014, 8, 406–413. [Google Scholar] [CrossRef]
  10. Chuhan, Z.; Guanglun, W.; Shaomin, W.; Yuexing, D. Experimental tests of rolled compacted concrete and nonlinear fracture analysis of rolled compacted concrete dams. J. Mater. Civ. Eng. 2002, 14, 108–115. [Google Scholar] [CrossRef]
  11. Zhao, X.; He, Y. The permeable character of csg dams and their seepage fields. Complexity 2018, 2018, 6498458. [Google Scholar] [CrossRef]
  12. Chen, F.; Zhang, L.; Zou, C.; Zhu, X.; Fang, Q.; Xu, S. Study on influencing factors of shear characteristics of rock-fill concrete layer of iron tailings as fine aggregate. Constr. Build. Mater. 2022, 345, 128213. [Google Scholar] [CrossRef]
  13. Li, D.J.; Shi, C.; Ruan, H.N.; Li, B.Y.; Li, W.Y.; Yao, X.C. Study on shear behavior of coral reef limestone–concrete interface. Mar. Georesources Geotechnol. 2022, 40, 438–447. [Google Scholar] [CrossRef]
  14. Xia, P.; Hu, X.; Wu, S.; Ying, C.; Xu, C.; Wang, X.; Chen, H. Study on shear strength characteristics of columnar jointed basalt based on in-situ direct shear test at Baihetan hydropower station. J. Earth Sci. 2023, 34, 1280–1294. [Google Scholar] [CrossRef]
  15. Da, B.; Yu, H.; Ma, H.; Tan, Y.; Mi, R.; Dou, X. Experimental investigation of whole stress-strain curves of coral concrete. Constr. Build. Mater. 2016, 122, 81–89. [Google Scholar] [CrossRef]
  16. Liu, G.; Lu, W.; Lou, Y.; Pan, W.; Wang, Z. Interlayer shear strength of Roller compacted concrete (RCC) with various interlayer treatments. Constr. Build. Mater. 2018, 166, 647–656. [Google Scholar] [CrossRef]
  17. Chen, J.; Cai, X.; Lale, E.; Yang, J.; Cusatis, G. Centrifuge modeling testing and multiscale analysis of cemented sand and gravel (CSG) dams. Constr. Build. Mater. 2019, 223, 605–615. [Google Scholar] [CrossRef]
  18. Bahaaddini, M.; Hagan, P.C.; Mitra, R.; Khosravi, M.H. Experimental and numerical study of asperity degradation in the direct shear test. Eng. Geol. 2016, 204, 41–52. [Google Scholar] [CrossRef]
  19. Chiu, C.C.; Weng, M.C.; Huang, T.H. Modeling rock joint behavior using a rough-joint model. Int. J. Rock Mech. Min. Sci. 2016, 89, 14–25. [Google Scholar] [CrossRef]
  20. Salazar, A.; Sáez, E.; Pardo, G. Modeling the direct shear test of a coarse sand using the 3D Discrete Element Method with a rolling friction model. Comput. Geotech. 2015, 67, 83–93. [Google Scholar] [CrossRef]
  21. Guo, L.; Zhang, Y.; Zhong, L.; Wang, M.; Zhu, X. Study on macroscopic and mesoscopic mechanical behavior of CSG based on inversion of mesoscopic material parameters. Sci. Eng. Compos. Mater. 2020, 27, 65–72. [Google Scholar] [CrossRef]
  22. Salazar, A.; Sáez, E.; Pardo, G. Modeling the direct shear test using the Discrete Element Method. In Computer Methods and Recent Advances in Geomechanics: Proceedings of the 14th International Conference of International Association for Computer Methods and Recent Advances in Geomechanics, 2014 (IACMAG 2014); Taylor & Francis Books Ltd.: London, UK, 2015; pp. 1511–1516. [Google Scholar]
  23. Seyyedan, S.M.; Mirghasemi, A.A.; Mohammadi, S. Numerical simulation of direct shear test on granular materials composed of breakable angular particles: A DEM-XFEM approach. Powder Technol. 2021, 391, 450–466. [Google Scholar] [CrossRef]
  24. Chang, D.; Yan, Y.; Liu, J.; Xu, A.; Feng, L.; Zhang, M. Micro-macroscopic mechanical behavior of frozen sand based on a large-scale direct shear test. Comput. Geotech. 2023, 159, 105484. [Google Scholar] [CrossRef]
  25. Yang, K.; Hu, Q.; Zhao, H.; Zhao, M.; Zhou, S. Numerical study on the shear behavior of concrete-rock joints with similar triangular asperities. Comput. Geotech. 2023, 159, 105468. [Google Scholar] [CrossRef]
  26. Motlagh, N.M.; Ardakani, A.R.M.; Noorzad, A. Experimental and numerical studies of a three-dimensional bonded contact model of cemented granular soils. Comput. Part. Mech. 2023, 10, 445–463. [Google Scholar] [CrossRef]
  27. Aliabadian, Z.; Sharafisafa, M.; Tahmasebinia, F.; Shen, L. Experimental and numerical investigations on crack development in 3D printed rock-like specimens with pre-existing flaws. Eng. Fract. Mech. 2021, 241, 107396. [Google Scholar] [CrossRef]
  28. Wang, P.; Ren, F.; Miao, S.; Cai, M.; Yang, T. Evaluation of the anisotropy and directionality of a jointed rock mass under numerical direct shear tests. Eng. Geol. 2017, 225, 29–41. [Google Scholar] [CrossRef]
  29. Liu, X.; Zhou, A.; Shen, S.L.; Li, J.; Arulrajah, A. Modelling unsaturated soil-structure interfacial behavior by using DEM. Comput. Geotech. 2021, 137, 104305. [Google Scholar] [CrossRef]
  30. Luo, X.; Cao, P.; Lin, Q.; Li, S. Mechanical behaviour of fracture-filled rock-like specimens under compression-shear loads: An experimental and numerical study. Theor. Appl. Fract. Mech. 2021, 113, 102935. [Google Scholar] [CrossRef]
  31. Wang, G.; Wu, X.; Zhang, X.; Zhang, Z.; Zhao, Z.; Han, W.; Wang, Y.; Zhao, C. Macro–Microscopic study on the shear characteristics of filled joints with different roughnesses. Arab. J. Sci. Eng. 2020, 45, 8331–8348. [Google Scholar] [CrossRef]
  32. Guo, X.-W.; Zhang, X.-C.; Qian, L.; Cai, X.; Liu, Q.-H. Direct shear test of CSG interface and meso study on failure behavior. Chin. Q. Mech. 2022, 43, 55–56. (In Chinese) [Google Scholar] [CrossRef]
  33. Xiang, Y.; Chen, X.; Zhou, W. Effect of layer Treatment on shear strength of CSG. Water Resour. Power 2018, 36, 136–138. [Google Scholar]
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Figure 1. Specimen material.
Figure 1. Specimen material.
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Figure 2. Experimental procedure flowchart.
Figure 2. Experimental procedure flowchart.
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Figure 3. Fabrication process of CSG specimens with no treatment forms.
Figure 3. Fabrication process of CSG specimens with no treatment forms.
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Figure 4. Fabrication process of CSG specimens with different interface treatment forms.
Figure 4. Fabrication process of CSG specimens with different interface treatment forms.
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Figure 5. Direct shear test device.
Figure 5. Direct shear test device.
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Figure 6. Shear stress–shear displacement curve.
Figure 6. Shear stress–shear displacement curve.
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Figure 7. Results of interface strength fitting.
Figure 7. Results of interface strength fitting.
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Figure 8. Interface with no treatment.
Figure 8. Interface with no treatment.
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Figure 9. Damage pattern of spreading mortar specimens.
Figure 9. Damage pattern of spreading mortar specimens.
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Figure 10. Damage pattern of chiseling specimens.
Figure 10. Damage pattern of chiseling specimens.
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Figure 11. Numerical model of the specimen.
Figure 11. Numerical model of the specimen.
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Figure 12. Comparison of numerical simulation results with experimental results for different interfaces of treatment.
Figure 12. Comparison of numerical simulation results with experimental results for different interfaces of treatment.
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Figure 13. Number of fracture development in the specimen–shear displacement curve.
Figure 13. Number of fracture development in the specimen–shear displacement curve.
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Figure 14. Internal fracture distribution during shearing of the specimen.
Figure 14. Internal fracture distribution during shearing of the specimen.
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Figure 15. Thickness of fracture distribution at the end of specimen shear test.
Figure 15. Thickness of fracture distribution at the end of specimen shear test.
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Table 1. Chemical composition of cementitious materials (%).
Table 1. Chemical composition of cementitious materials (%).
MaterialSiO2Al2O3Fe2O3CaOMgOSO3K2ONa2OTiO2Loss on Ignition
Cement21.967.403.4558.401.301.710.650.100.334.50
Fly Ash46.7538.803.473.610.600.320.560.201.502.75
Table 2. Physical properties and composition of gravel and sand.
Table 2. Physical properties and composition of gravel and sand.
Aggregate TypeSpecific GravityBulk Density (kg/m3)Water ContentClay Content
Gravel2.711650≤0.01%≤0.01%
Sand2.621450≤0.01%≤0.01%
Table 3. Aggregate mass ratio of each particle size.
Table 3. Aggregate mass ratio of each particle size.
Particle size/mm0–33–55–1010–20
Mass ratio/%17.021.027.035.0
Table 4. Peak shear stress at the interface under different normal stresses.
Table 4. Peak shear stress at the interface under different normal stresses.
Interface Processing MethodNormal Stress/MPaPeak Shear Stress/MPa
Interface with no treatment0.50.49
1.00.77
1.51.02
2.01.41
Interface with spreading mortar0.50.74
1.01.06
1.51.38
2.01.89
Interface with chiseling0.50.53
1.00.80
1.51.21
2.01.54
Table 5. Summary of shear strength fitting results.
Table 5. Summary of shear strength fitting results.
Interface Processing MethodCohesion c’/MPaInternal Friction Angle φ’/°
Interface with no treatment0.2029.68
Interface with spreading mortar0.3436.13
Interface with chiseling0.1834.22
Table 6. Meso-parameters of contact model at the interface.
Table 6. Meso-parameters of contact model at the interface.
Contact LocationContact ModelModel ParametersParameter Values
Between coarse aggregateLinear contact bonding modelEffective modulus100 Mpa
Kratio2
Friction coefficient0.2
Bonding strength2.0 Mpa
Between mortar particles and between mortar particles and upper–lower aggregatesEffective modulus100 Mpa
Kratio1
Friction coefficient0.1
Bonding strength2.0 Mpa
Between filled particles and between filled particles and upper–lower aggregatesEffective modulus100 Mpa
Kratio2
Friction coefficient0.3
Bonding strength2.0 Mpa
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MDPI and ACS Style

Qian, L.; Guo, X.; Liu, Q.; Cai, X.; Zhang, X. Macro-Mesoscopic Failure Mechanism Based on a Direct Shear Test of a Cemented Sand and Gravel Layer. Buildings 2024, 14, 4078. https://doi.org/10.3390/buildings14124078

AMA Style

Qian L, Guo X, Liu Q, Cai X, Zhang X. Macro-Mesoscopic Failure Mechanism Based on a Direct Shear Test of a Cemented Sand and Gravel Layer. Buildings. 2024; 14(12):4078. https://doi.org/10.3390/buildings14124078

Chicago/Turabian Style

Qian, Long, Xingwen Guo, Qinghui Liu, Xin Cai, and Xiaochuan Zhang. 2024. "Macro-Mesoscopic Failure Mechanism Based on a Direct Shear Test of a Cemented Sand and Gravel Layer" Buildings 14, no. 12: 4078. https://doi.org/10.3390/buildings14124078

APA Style

Qian, L., Guo, X., Liu, Q., Cai, X., & Zhang, X. (2024). Macro-Mesoscopic Failure Mechanism Based on a Direct Shear Test of a Cemented Sand and Gravel Layer. Buildings, 14(12), 4078. https://doi.org/10.3390/buildings14124078

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