Study on Lateral Erosion Failure Behavior of Reinforced Fine-Grained Tailings Dam Due to Overtopping Breach

Abstract

The overtopping-induced lateral erosion breaching of tailings dams represents a critical disaster mechanism threatening structural safety, particularly in reinforced fine-grained tailings dams where erosion behaviors demonstrate pronounced water–soil coupling characteristics and material anisotropy. Through physical model tests and numerical simulations, this study systematically investigates lateral erosion failure patterns of reinforced fine-grained tailings under overtopping flow conditions. Utilizing a self-developed hydraulic initiation test apparatus, with aperture sizes of reinforced geogrids (2–3 mm) and flow rates (4–16 cm/s) as key control variables, the research elucidates the interaction mechanisms of “hydraulic scouring-particle migration-geogrid anti-sliding” during lateral erosion processes. The study revealed that compared to unreinforced specimens, reinforced specimens with varying aperture sizes (2–3 mm) demonstrated systematic reductions in final lateral erosion depths across flow rates (4–16 cm/s): 3.3–5.8 mm (15.6−27.4% reduction), 3.1–7.2 mm (12.8–29.6% reduction), 2.3–11 mm (6.9–32.8% reduction), and 2.5–11.4 mm (6.2–28.2% reduction). Smaller-aperture geogrids (2 mm × 2 mm) significantly enhanced anti-erosion performance through superior particle migration inhibition. Concurrently, a pronounced positive correlation between flow rate and lateral erosion depth was confirmed, where increased flow rates weakened particle erosion resistance and exacerbated lateral erosion severity. The numerical simulation results are in basic agreement with the lateral erosion failure process observed in model tests, revealing the dynamic process of lateral erosion in the overtopping breach of a reinforced tailings dam. These findings provide critical theoretical foundations for optimizing reinforced tailings dam design, construction quality control, and operational maintenance, while offering substantial engineering applications for advancing green mine construction.

1. Introduction

Tailings ponds, as high-potential-energy artificial debris flow hazard sources, pose severe threats to mining enterprise safety, downstream residents’ lives and properties, and ecological environments through potential dam breach risks [1]. A statistical analysis of the causes of typical tailings dam failures from 2001 to 2020 shows that seepage failure accounts for as much as 50.72% of the incidents, flood overtopping accounts for 34.78%, and dam instability and seismic hazards account for 8.70% and 5.80%, respectively [2]. These data indicate that flood overtopping is one of the major causes of tailings dam failure incidents [3,4].

With the continuous advancement of mineral processing technology, the particle size of tailings has progressively decreased [5]. However, these fine-grained tailings present significant challenges in embankment stability, including poor permeability, difficulties in dissipating excess pore water pressure, extended consolidation periods, and low mechanical strength [6]. To address these challenges in tailings dam construction, strategic reinforcement of tailings embankments can effectively enhance the anti-sliding stability safety factor [7]. Reinforced geogrids, owing to their unique mesh configuration, generate interlocking and occlusal effects on tailings particles, thereby improving the structural stability of reinforced tailings systems [8]. The installation of reinforcement materials further modifies the inherent permeability characteristics of tailings sand through composite formation at reinforcement zones [9]. Feng et al. [10] revealed reinforced geogrid mechanisms through discrete element simulations of direct shear tests. Wang et al. [11] clarified reinforcement material embedment depth and vertical spacing effects on breach discharge and peak discharge.

In recent years, domestic and international scholars have made significant progress in studying tailings dam overtopping erosion failure mechanisms. Through laboratory tests, Zhai et al. [12] systematically analyzed the longitudinal evolution of breach development during overtopping failures and explored erosion rate–shear stress relationships. Yi et al. [13,14] investigated breach formation and expansion processes, proposing a breach-widening model. Li et al. [15] examined breach development patterns, discharge characteristics, downstream flow depth, and final impact distances during dam collapse. Walsh et al. [16] studied dam slope influences on breach development. Alhasan et al. [17] analyzed hydraulic condition–sediment transport relationships through parametric variations including dam material, slope, width, and breach discharge. Wu et al. [18] established a five-stage overtopping stabilization process: minor gully development, multi-level “steep step” formation, large “steep step” emergence, rapid breach expansion, and stabilization. Sun et al. [19], through rainfall-conditioned hydraulic erosion tests, concluded rainfall infiltration drives erosion and deformation instability. Hu et al. [20] conducted rainfall-induced fluidization failure tests revealing underlying mechanisms. Chen et al. [21] studied the erosion rate of reinforced tailings under different hydraulic conditions and established a predictive model. Liu et al. [22] investigated the critical conditions for the initiation of movement of reinforced tailings particles under the action of water flow and developed a formula for the critical flow velocity for the initiation of movement of reinforced tailings particles.

In numerical simulations, Souza et al. [23] found breach inclination angle and width significantly affect tailings discharge. Yao et al. [24] studied particle size influences on overtopping failure processes. Jing et al. [25] established reinforced dam breach width prediction models through displacement and phreatic line measurements. Liu et al. [26], Sun [27], Liu [28], and Zhang et al. [29] demonstrated high model-numerical simulation consistency in initial breach locations, development trends, and final inundation extents through tailings flow evolution studies.

In summary, while existing studies have achieved significant progress in understanding the overtopping failure processes of tailings dams and their influencing factors, the breach formation mechanism during overtopping remains complex due to numerous contributing variables. Notably, reinforced tailings dams exhibit distinct erosion characteristics under overtopping flow scouring compared to conventional tailings dams. To investigate the lateral erosion failure behavior of reinforced fine-grained tailings dams during overtopping (as shown in Figure 1), this study employs a self-developed hydraulic scouring test apparatus. This system enables simulation of lateral flow erosion on fine-grained tailings specimens, effectively replicating the transverse breach development process in reinforced tailings dams under overtopping conditions. Focusing on the lateral erosion failure mechanisms of fine-grained tailings specimens, this research selects reinforced geogrid aperture size and flow velocity as key control variables. Through systematic physical model tests, we comprehensively investigate the lateral erosion patterns of reinforced fine-grained tailings under overtopping flows. The study systematically reveals the interacting mechanisms of “hydraulic scouring-particle migration-reinforcement anti-sliding” during lateral erosion processes and quantitatively analyzes critical influencing factors. FLOW-3D numerical simulation software (https://www.flow3d.com/) was used to investigate the lateral erosion process of the overtopping breach in a reinforced tailings dam, revealing the dynamic process of lateral erosion during overtopping failure. These findings provide scientific insights for the design, construction, and maintenance of reinforced tailings dams, offering technical support for ensuring operational safety in mining engineering and ecological environment protection.

2. Materials and Methods

2.1. Test Facilities

This test employed a purpose-built hydraulic initiation test apparatus (as shown in Figure 2). The specimen box underwent axis-aligned 90° rotation relative to the flow pipe, positioning it laterally to simulate tailings specimen lateral erosion processes. The 2.0 m × 0.6 m × 0.6 m water reservoir connected to an 80 mm × 80 mm internal-dimension horizontal square pipe. The lateral erosion specimen box, equipped with an 80 mm × 50 mm × 80 mm protruding groove, was mounted on the pipe’s lateral surface. The flow control system incorporated a Z45X-16Q soft-seal gate valve and DN65 PTFE-lined electromagnetic flowmeter. Erosion monitoring utilized a high-resolution camera (1920 × 1080-pixel resolution at 50 fps).

2.2. Test Materials

The fine-grained tailings material used in the experiment was sourced from a Class IV tailings dam in Chongqing, China. Material properties include: dry density 1.61 g/cm³, liquid limit 44.65%, plastic limit 36.70%, plasticity index 12.95, and particle size distribution 1.088–8.639 µm (as shown in Figure 3). Per Chinese standard DZ/T 0371–2021 (Classification of tailings for solid mineral resource) criteria for particle size and plasticity index [30], this material is classified as clayey tailings.

Fiberglass mesh was selected as the reinforcement geogrid in the experiment to simulate field conditions. The mesh exhibits tensile strength of 600 N/50 mm and 3% elongation at break, showing no measurable deformation or failure during testing-validating its applicability for scaled reinforced tailings dam modeling. Three fiberglass mesh types (as shown in Figure 4) were implemented: (a) 2 mm × 2 mm aperture, (b) 2.5 mm × 2.5 mm aperture, and (c) 3 mm × 3 mm aperture.

2.3. Test Scheme

To investigate the lateral erosion failure patterns of fine-grained tailings specimens under reinforced geogrid aperture size and flow rate influences, unreinforced specimens and three reinforced geogrid aperture types specimens ((a) 2 mm × 2 mm; (b): 2.5 mm × 2.5 mm; (c): 3 mm × 3 mm) underwent 180 s hydraulic erosion under flow rates of 4.0 cm/s, 8.0 cm/s, 12.0 cm/s, and 16.0 cm/s. A total of 16 groups of tests were conducted, with each group undergoing 5 trials. The average value was taken after discarding any outliers. Test scheme detailed in

Table 1. Hydraulic erosion test scheme for fine-grained tailings specimens.

Tailings Type	Test Number	Reinforced Geogrid Aperture Size (mm × mm)	Erosion Flow Rate (cm/s)
Fine-grained tailings	TN1	Unreinforced	4
	TN2		8
	TN3		12
	TN4		16
	TA1	Reinforced geogrid (a) 2 mm × 2 mm	4
	TA2		8
	TA3		12
	TA4		16
	TB1	Reinforced geogrid (b) 2.5 mm × 2.5 mm	4
	TB2		8
	TB3		12
	TB4		16
	TC1	Reinforced geogrid (c) 3 mm × 3 mm	4
	TC2		8
	TC3		12
	TC4		16

.

2.4. Specimen Preparation

Prior to preparing tailings specimens, pretreatment of raw tailings is necessary. The raw tailings were oven-dried to remove excess moisture. To enhance test data accuracy, the particle size gradation of the tailings was designed to closely mirror an actual tailings reservoir in Chongqing. The raw tailings were sieved into three particle size fractions: 4.5–8.6 µm, 3.0–4.5 µm, and 1.0–3.0 µm. These fractions were then blended at mass percentages of 50%, 37%, and 13% to form a tailings sample. The sample was prepared to achieve 20% moisture content, sealed, and cured for 24 h. This ensured uniform moisture distribution throughout the sample, preventing test errors due to moisture heterogeneity.

According to the test scheme, it is necessary to fabricate unreinforced specimens and three reinforced geogrid aperture types specimens with geometric dimensions of 80 mm × 50 mm × 80 mm. The specific preparation procedure is as follows:

• The tailings sample with 20% moisture content was divided equally into two portions. One portion was transferred into the mold and compacted with a compaction hammer to achieve ≥ 98% compactness. The tailings were compacted to half the mold height, as shown in Figure 5.
• The surface of the underlying tailings was roughened with a spatula to ensure strong bonding with the second portion. After adding the second portion, the tailings were compacted to the full mold height using the compaction hammer. This completed fabrication of the unreinforced specimen.
• The underlying tailings surface was roughened with a spatula. A layer of reinforced geogrid was placed on the tailings surface, positioned at the mid-height of the specimen. The second portion of tailings was then added and compacted to the full mold height with the compaction hammer, completing fabrication of the reinforced specimen, as shown in Figure 6.
• After demolding, specimens were wrapped in plastic film to maintain moisture content, labeled, and stored for subsequent testing.

2.5. Test Procedures

Conduct hydraulic initiation tests according to the test scheme and observe the erosion process and particle migration characteristics of fine-grained tailings. Test procedure is shown in Figure 7.

3. Test Results and Analysis

3.1. Test Study on Lateral Erosion of Reinforced Fine-Grained Tailings

3.1.1. Test Analysis of Erosion Phenomena

• Unreinforced fine-grained tailings specimen

Under constant hydrodynamic conditions (flow rate: 8.0 cm/s), tailings particles disintegrate due to hydraulic action and detach from the specimen surface. They subsequently form a suspended state in the horizontal square pipe at the specimen base (as shown in Figure 8a). Over time, the sustained flow induces microscopic erosion on the specimen surface. This erosion is associated with minor structural damage to the superficial layer, leading to cluster-shaped spalling of tailings. During this phase, some tailings particles slide towards the pipe base, while suspended fine particles migrate along the flow path (as shown in Figure 8b). Prolonged scouring at the constant flow rate results in the progressive development of distinct erosion pits on the specimen surface, with continuous particle migration towards the horizontal square pipe base (as shown in Figure 8c). Importantly, two distinct migration modes are observed in the scoured tailings. While some particles migrate downstream with the flow current, others accumulate via basal sliding, eventually forming a tailings sliding mass (as shown in Figure 8d).

2.

Reinforced fine-grained tailings specimen

Under constant hydrodynamic conditions (flow rate: 8.0 cm/s), the reinforced geogrid exerts a significant regulatory effect on the erosion of fine-grained tailings specimens (as shown in Figure 9). Tailings, with fine particles and low permeability, display distinct erosion phenomena when incorporating reinforced geogrids. During hydraulic scouring on the specimen surface, dislodged tailings slide along the reinforced geogrid, creating localized sliding masses. These micro-sliding masses alleviate erosion on the upper tailings surfaces. Meanwhile, most particles migrate towards the horizontal square pipe, gradually forming macroscopic tailings sliding masses. The formation of these masses alters local flow field characteristics and creates physical barriers, which significantly reduce hydraulic erosion intensity on tailings surfaces.

3.1.2. Analysis of Lateral Erosion Depth Variation Patterns

Under constant hydrodynamic conditions (flow rate: 8.0 cm/s), fine-grained tailings specimens display distinct erosion characteristics under sustained scouring (as shown in Figure 10). The erosion process can be divided into three typical stages:

(1). Initial stage (0–30 s): The specimen absorbs and retains water. Owing to cohesive forces among fine tailings particles, the flow’s scouring effect on the specimen surface is restricted. A few tailings particles slide to the horizontal square pipe’s base, resulting in a slow increase in lateral erosion depth. (2). Accelerated erosion stage (30–90 s): The specimen becomes saturated, reducing cohesive forces between fine tailings particles and making them more prone to hydraulic detachment. Consequently, lateral erosion depth rises sharply, and the sliding mass height at the horizontal square pipe’s base increases rapidly. (3). Stable erosion stage (90–180 s): The sliding mass at the horizontal square pipe’s base serves as a physical barrier, diminishing the flow’s direct scouring effect on the specimen surface. As a result, the erosion rate stabilizes.

Analysis of the three erosion stages reveals that when tailings specimens undergo hydraulic erosion, tailings particles migrate onto the horizontal square pipe, forming a sliding mass. This process intensifies lateral erosion depth. Over successive time intervals, the sliding mass height progressively increases. Consequently, both lateral erosion depth and sliding mass height jointly quantify the erosion severity in reinforced and unreinforced specimens.

In the unreinforced specimen, the final sliding mass height reaches 39.6 mm. In contrast, the reinforced geogrid (a/b/c) specimens exhibit final sliding mass heights of 28.4 mm, 31.2 mm, and 32.8 mm, respectively. Compared to the unreinforced specimen, the reinforced geogrids resist sliding in fine tailings, reducing the final sliding mass height by 6.8–11.2 mm (17.2–28.3% reduction). This indicates that reinforced specimens have significantly lower sliding mass heights than the unreinforced specimen.

Unreinforced specimens display a linear growth trend in lateral erosion depth over time, with the highest erosion rate and a final depth of 24.3 mm. Conversely, reinforced geogrid (a/b/c) specimens show marked nonlinear decreases in lateral erosion depth, reaching final depths of 17.1 mm, 19.8 mm, and 21.2 mm, respectively. The inclusion of reinforced geogrids consistently reduces the final lateral erosion depth by 3.1–7.2 mm (12.8–29.6% reduction). Under other flow conditions (4 cm/s, 12 cm/s, 16 cm/s), reinforced fine-grained tailings specimens demonstrate consistent reductions in final lateral erosion depth compared to unreinforced specimens: 3.3–5.8 mm (15.6–27.4% reduction), 2.3–11 mm (6.9–32.8% reduction), and 2.5–11.4 mm (6.2–28.2% reduction), respectively.

Further analysis indicates that the aperture size of reinforced geogrids is the key parameter affecting reinforcement efficacy. The small-aperture reinforced geogrid (a) effectively restricts particle migration due to its dense structure, maintaining consistently lower lateral erosion depths than other reinforced specimens, thus showing superior erosion resistance. As the aperture size increases, the geogrid’s constraining effect on tailings particles diminishes, resulting in more severe erosion, with large-aperture reinforced geogrid (c) specimens displaying the most pronounced erosion characteristics.

3.2. Test Study on the Effect of Flow Rate on Lateral Erosion of Fine-Grained Tailings

3.2.1. Test Analysis of Erosion Phenomena

Taking the variation process of lateral erosion depth in the reinforced geogrid (c) specimen as an example. Under constant hydrodynamic conditions with a flow rate of 4.0 cm/s, the lateral erosion depth of the fine-grained tailings specimen demonstrated distinct temporal variation characteristics as shown in Figure 11. During the initial test stage, hydrodynamic loading induced microstructural failure on the specimen surface, causing aggregate detachment of tailings particles. Progressive retreat became pronounced as erosion advanced: after 60s of continuous scouring, lateral erosion depth measured 6 mm; at 120s, lateral erosion depth increased to 12 mm; upon test termination at 180s, ongoing structural degradation intensified particle migration and erosion, culminating in a final lateral erosion depth of 18 mm.

Under constant hydrodynamic conditions at a flow rate of 12.0 cm/s, the frictional resistance on the fine-grained tailings specimen surface increased substantially, intensifying erosion. The lateral erosion depth progression is shown in Figure 12. The specimen exhibited distinct progressive retreat under sustained flow: after 60 s of continuous scouring, lateral erosion depth measured 17 mm; at 120 s, significant surface structural degradation caused a sharp erosion rate increase, elevating lateral erosion depth to 25 mm; upon test termination at 180 s, the final lateral erosion depth reached 31 mm.

3.2.2. Analysis of Lateral Erosion Depth Variation Patterns

The effect of different flow rates (4.0 cm/s, 8.0 cm/s, 12.0 cm/s, 16.0 cm/s) on the lateral erosion depth of unreinforced fine-grained tailings specimens is shown in Figure 13a. Test results indicate that at low flow rates (4.0 cm/s), due to relatively low fluid shear stress, the erosion process of tailings specimens progresses gradually. As the flow rate increases, the lateral erosion depth exhibits a distinct accelerating growth trend. At moderate flow rates (8.0 cm/s and 12.0 cm/s), the marked increase in fluid shear stress significantly intensifies the erosion process. At 16.0 cm/s, the specimens display the most pronounced erosion characteristics. After 180 s of systematic observation, the final lateral erosion depths under different flow rates present a clear gradient distribution: 21.2 mm at 4.0 cm/s, 24.3 mm at 8.0 cm/s, 33.5 mm at 12.0 cm/s, and 40.4 mm at 16.0 cm/s. These results confirm a significant positive correlation between lateral erosion depth and flow rate, with increasing flow rate greatly enhancing the erosion effect.

The variation process of lateral erosion depth in the reinforced geogrid (a) fine-grained tailings specimen is shown in Figure 13b. During the initial stage (0–30 s), cohesive forces between fine-grained tailings particles and their structural strength effectively resist flow-induced particle migration, resulting in a slow growth trend in lateral erosion depth. As the test progresses to the 30–90 s stage, the specimen gradually becomes water-saturated. This leads to significantly reduced interparticle cohesive forces and weakened surface anti-scour capacity, causing a marked increase in lateral erosion depth with prolonged scouring duration. When the erosion duration exceeds 90 s, particle sliding occurs on the specimen surface, forming a stable sliding mass above the reinforced geogrid. The structural constraint of the reinforced geogrid effectively inhibits further sliding of the mass. Meanwhile, the sliding mass creates a barrier effect that reduces direct scouring by water flow on the specimen surface. This mechanism significantly decelerated the growth rate of lateral erosion depth compared to the 30–60 s stage, fully demonstrating the dual role of reinforced geogrids in tailings erosion control: restricting particle migration through physical constraints and indirectly reducing erosion rates by altering hydrodynamic conditions.

The variation of lateral erosion depth in reinforced geogrid (b/c) fine-grained tailings specimens exhibits similar patterns to that of reinforced geogrid (a) specimens, as shown in Figure 13c,d. After 90 s of erosion, sliding masses form above the reinforced geogrid and create a barrier effect. This significantly reduces direct shear stress from water flow on the specimen surfaces, leading to a marked decrease in the growth rate of lateral erosion depth compared to the first 90 s. Comparative analysis shows that reinforced geogrids greatly enhance the anti-erosion performance of tailings specimens. Among them, reinforced geogrid (a) specimens show the best erosion resistance. Although all specimens exhibit increased lateral erosion depths with rising flow rates, the reinforced specimens demonstrate significantly better erosion resistance than the unreinforced ones. This conclusively confirms the effectiveness of reinforced geogrids in tailings erosion control. The operational mechanisms are mainly reflected in the following aspects: (1) restricting particle migration; (2) promoting sliding mass formation to alter local flow characteristics; and (3) reducing direct shear stress from water flow on the specimen surfaces.

Further analysis reveals a significant dynamic correlation between flow rate and lateral erosion depth in fine-grained tailings specimens. This is mechanistically attributable to the marked increase in fluid kinetic energy and shear stress induced by elevated flow rates, which enhances tailings particle migration capacity. Hydrodynamic actions on tailings particles are primarily realized through two mechanisms: first, the direct impact of water flow causes particle dispersion and initial migration; second, tailings particles that slide to the bottom of horizontal square pipes are subject to secondary transport by water flow. These hydrodynamic forces can disrupt the original structural integrity of tailings specimens, promoting particle detachment from specimen surfaces and subsequent hydraulic transport. Notably, there is a significant positive correlation between flow rate and tailings particle transport capacity. Increased flow rates enhance both the erosive capacity and particle transport efficiency of water flow. This confirms the pronounced positive correlation between flow rate and lateral erosion depth in fine-grained tailings specimens and demonstrates that flow rate escalation directly exacerbates lateral erosion damage severity.

4. Analysis of Lateral Erosion Mechanisms in Reinforced Fine-Grained Tailings

The erosion processes of reinforced and unreinforced fine-grained tailings specimens show significant differences, as illustrated by the side-view morphological change of specimen erosion as shown in Figure 14. In unreinforced fine-grained tailings tests, water flow erodes the specimen surface at a constant rate. Hydrodynamic forces directly act on particle surfaces, disrupting interparticle cohesion. Tailings particles detach from the specimen surface as clustered aggregates and accumulate at the base of the horizontal square pipe. Under sustained hydrodynamic conditions, the continuous shear stress from water flow gradually forms macroscopic erosion pits on the specimen surface. Tailings particles progressively disintegrate and detach from the surface, starting to migrate along the flow direction. Most particles slide to the base of the horizontal square pipe, forming tailings sliding masses due to combined hydrodynamic action and interparticle interactions. However, these sliding masses remain susceptible to further scouring by water flow and fail to achieve structural stability. Continued flow scouring leads to ongoing particle detachment, ultimately generating larger-scale sliding masses.

In reinforced fine-grained tailings tests, the interaction between tailings particles and the reinforced geogrid forms a relatively stable reinforced composite structure. The reinforced geogrid provides additional physical support and constraint forces to tailings particles, enhancing the overall stability of reinforced specimens. Under constant hydrodynamic conditions, surface particles of reinforced specimens gradually undergo scouring and transport. The mesh structure of the reinforced geogrid effectively intercepts detached particles, causing them to slide onto the geogrid and form small sliding masses. The barrier effect of these masses significantly reduces direct shear stress from water flow on the specimen surface, thereby partially mitigating surface scouring in upper specimen regions. Through its high tensile strength and anti-scour properties, the reinforced geogrid restricts further particle migration and stabilizes sliding mass structures. By reducing applied shear stress and dissipating flow energy, the geogrid decelerates erosion progression. Additionally, the sliding masses obstruct water flow, protecting underlying tailings layers from rapid erosion and reducing backward erosion rates. However, continuous flow action causes progressive accumulation of new particles on existing sliding masses, increasing their volume. Most particles ultimately slide onto the horizontal square pipe, forming final tailings sliding masses.

5. Numerical Simulation

FLOW-3D software differs from other hydraulic software by introducing sediment erosion equations to simulate riverbed sediment scouring. Huang et al. [31] and Li et al. [32] achieved significant advances in tailings dam overtopping failure simulations using FLOW-3D, demonstrating its feasibility for modeling tailings erosion under overtopping conditions. Consequently, this chapter employs Rhino modeling software to construct a simplified 3D tailings dam, imports the geometry in STL format into FLOW-3D, and simulates the dynamic process of lateral erosion during overtopping-induced breach development. By quantifying lateral erosion depth differences between reinforced and unreinforced tailings dams, the influence of reinforced geogrids on breach evolution is analyzed, providing critical references for macroscopic hydraulic erosion characteristics of reinforced tailings dams.

5.1. Simulation Process

5.1.1. Model Development

To investigate lateral erosion depth evolution during overtopping breach development in reinforced tailings dams, a representative geometric model was established. For enhanced observation of reinforced geogrid influences on lateral erosion variation, comparative models of reinforced and unreinforced tailings dams with 10-m crest height ranges were constructed. Geometry specifications: 63 m (L) × 20 m (W) × 10 m (H), downstream slope ratio 1:3.0, upstream slope ratio 1:6.0. The reinforced geogrid was positioned at 8 m height. Post-meshing in FLOW-3D, automated optimization generates curvilinear configurations at dam shoulders, potentially initiating lateral erosion from flanks. To mitigate simulation artifacts, a 1 m × 1 m artificial notch was created at the crest center to direct flow through the dam core, ensuring controlled overtopping failure initiation. The unreinforced tailing dam model in Figure 15a, the reinforced tailing dam model in Figure 15b.

5.1.2. Model Parameter Setting

The upstream inflow boundary was set as a Volume Flow Rate condition with a constant discharge of 10 m³/s. The downstream outlet adopted an Outflow boundary. The upper boundary was configured as a Pressure boundary set to atmospheric pressure. All other surfaces were designated as Wall boundaries. Although reinforced geogrid is a flexible material, negligible deformation occurred during erosion simulations. Consequently, it was modeled as a rigid body module within FLOW-3D.

FLOW-3D employed cubic grids. To accurately resolve the reinforced geogrid geometry while avoiding excessive computational load from uniform meshing, a nested grid scheme was implemented for local refinement. Grid size near the reinforced geogrid measured 0.1 m, while other regions maintained 0.2 m spacing. The FAVOR function verified acceptable mesh quality meeting simulation requirements. A 30 m (L) × 20 m (W) × 5 m (H) water body was initialized on the upstream slope. The simulation period spanned 180 s.

Four physical models were configured: Gravity, Density, Turbulence, and Sediment Scour models. The Sediment Scour model parameters were calibrated using actual tailings dam properties. Critical Shields number, underwater repose angle, bed load coefficient, and carry over coefficient values followed referenced studies [31,32,33], as detailed in

Table 2. Tailings parameters setting.

Median Diameter d50 (mm)	Density (g/cm3)	Critical Shields Number	Underwater Repose Angle	Bed Load Coefficient	Carry Over Coefficient
0.051	1.99	0.05	32°	8	0.018

.

5.2. Simulation Results and Analysis

FLOW-3D’s post-processor FlowSight enabled detailed visualization of lateral erosion dynamics during overtopping breaches for both unreinforced and reinforced tailings dams. This facilitated quantitative analysis of reinforced geogrid effects on lateral erosion depth progression. To facilitate the observation of the lateral erosion dynamics during the overtopping breach of a tailings dam, a half-model perspective of the tailings dam was used to monitor changes on only one side of the breach.

5.2.1. Unreinforced Tailing Dam

Figure 16 illustrates the overtopping breach erosion dynamics process of the unreinforced tailings dam. Within the initial 30 s, upstream flow scoured the breach, initiating lateral erosion at the crest. By 60 s, continuous flow scouring caused topsoil sliding failure on breach flanks, visibly increasing lateral erosion depth in Figure 16b. At 120 s, intensified scouring formed downstream gullies, accelerating lateral erosion progression. By 180 s, the lateral erosion depth exhibited minimal growth compared to 120 s, indicating significantly reduced erosion rates.

5.2.2. Reinforced Tailing Dam

Figure 17 illustrates the overtopping breach erosion dynamics of the reinforced tailings dam. During the first 60 s of overtopping erosion, the process was identical to that of the unreinforced tailings dam. After 60 s of erosion, when the flow reached the installed reinforced geogrid zone, the presence of the reinforced geogrid provided additional physical support and confinement force to the dam body. This restricted the migration of tailings and reduced the erosion rate of tailings, thereby slowing the progression of lateral erosion depth development at the breach. Figure 17a illustrates that during flow through the reinforced geogrid zone, the erosion process exhibited a distinct variation. A gully configuration fundamentally different from that of the unreinforced tailings dam formed, with the dam body developing a stepped appearance due to erosion.

5.2.3. Lateral Erosion Depth Progression at Breach

The variation in lateral erosion depth at the overtopping breach of unreinforced and reinforced tailings dams is shown in Figure 18. Combined analysis with the simulated erosion dynamic process indicates that the variation in lateral erosion depth between the unreinforced and reinforced tailings dams was similar before 60 s; with continuous flow erosion, the lateral erosion depth gradually increased. After 60 s of erosion, the flow reached the installed reinforced geogrid zone. The reinforced geogrid provides additional physical support and confinement force to the dam body, resulting in a reduction in erosion progression. Simulation results indicate that the final lateral erosion depth of the unreinforced tailings dam was 1.28 m, while that of the reinforced tailings dam measured 0.91 m. Due to the presence of the reinforced geogrid, the final lateral erosion depth of the reinforced tailings dam was systematically reduced by 0.37 m (28.9% reduction). Therefore, the reinforced geogrid exhibits a significant mitigating effect during the lateral erosion process.

6. Conclusions and Analysis

This study investigated lateral erosion behavior of fine-grained tailings under varying reinforced geogrid aperture sizes and flow rates through physical model tests and numerical simulations. It analyzed lateral erosion failure patterns of reinforced fine-grained tailings under overtopping flow conditions and elucidated the interaction mechanisms among “hydraulic scouring-particle migration-geogrid anti-sliding” during lateral erosion processes. FLOW-3D numerical simulation software was used to investigate the lateral erosion process of the overtopping breach in a reinforced tailings dam, revealing the dynamic process of lateral erosion during overtopping failure. The main conclusions are as follows:

• Specimens reinforced with varying aperture sizes (2–3 mm) show systematic reductions in final lateral erosion depths compared to unreinforced specimens across flow rates (4–16 cm/s): 3.3–5.8 mm (15.6–27.4% reduction), 3.1–7.2 mm (12.8–29.6% reduction), 2.3–11 mm (6.9–32.8% reduction), and 2.5–11.4 mm (6.2–28.2% reduction). Smaller-aperture geogrids (2 mm × 2 mm) notably enhance anti-erosion performance through superior particle migration inhibition. As aperture size increases (2.5 mm × 2.5 mm and 3 mm × 3 mm), the constraint effect on fine-grained tailings particles diminishes, resulting in significantly greater erosion depths.
• Numerical simulation results show substantial agreement with model tests. The reinforced geogrid demonstrates a significant mitigating effect during the lateral erosion process, particularly after erosion enters the reinforced zone where the erosion rate markedly decreases. Simulations indicate final lateral erosion depths of 1.28 m for the unreinforced tailings dam and 0.91 m for the reinforced tailings dam. Due to the presence of the reinforced geogrid, the final lateral erosion depth of the reinforced tailings dam is systematically reduced by 0.37 m (28.9% reduction). Tests confirm that the lateral erosion depth of reinforced fine-grained tailings specimens is significantly lower than that of unreinforced specimens. The reinforced geogrid provides structural reinforcement and disperses pressure, objectively enhancing the structural stability of tailings specimens and thereby effectively slowing erosion progression.
• Tests confirm a pronounced positive correlation between flow rate and lateral erosion depth. Elevated flow rates substantially increase hydraulic shear stress and kinetic energy, thereby weakening particle erosion resistance and intensifying particle migration and erosion damage. Particularly under high-flow-rate conditions (12.0 cm/s and 16.0 cm/s), specimens exhibit the most substantial erosion depths.

This study investigated the lateral erosion failure behavior under varying reinforced geogrid aperture sizes and flow rates. Due to limitations in experimental conditions, technical methods, and theoretical knowledge, there are some shortcomings in this study: in the future, we will consider enlarging the size of the test model to better simulate the erosion process under actual conditions, thereby enhancing the applicability and universality of the research results; we will consider establishing a prediction model for the lateral expansion of reinforced tailings breaches; and we will also consider integrating the study with practical engineering applications.