Abstract

Tailings reservoirs generally consist of a tailings dam, a tailings conveying system and a drainage system, which are indispensable facilities and provide security and environmental protection for storing tailings and clarifying water in some industries (e.g., metallurgy, non-ferrous building materials, nuclear and chemical industries). Consequently, consolidating seepage prevention and treatment is important. When applied to seepage prevention works for tailings reservoirs, current seepage prevention technologies can cause destruction of the dam and require further construction sites. It is therefore essential to adopt new types of advanced and practical technologies. Aimed at studying the feasibility of the application of non-water reaction polymer grouting technology in seepage prevention of tailings reservoirs and acquiring the properties for practical engineering, an analysis of the environmental impact, chemical resistance and permeability of the polymer material, and the main technical characteristics of the polymer cutoff wall was conducted. The test results showed that the polymer grouting technology applied to seepage prevention works of a tailings reservoir caused little disturbance to the dam, possessed good anti-seepage performance and perfect durability. This study may provide a reference for the seepage control of tailings reservoirs.

INTRODUCTION

As storage places, tailings reservoirs are constructed in a valley mouth or on marsh land to allow tailings and other industrial runoff scum to subside via mineral processing. Tailings reservoirs generally consist of a tailings dam, tailings conveying system and drainage system, which are indispensable facilities and provide security and environmental protection for storing the tailings and clarifying the water in some industries (e.g., metallurgy, non-ferrous building materials, nuclear and chemical industries). Consequently, consolidating the seepage prevention and treatment is important. Tailings reservoirs with a length of service and long-term storage can cause enormous hazards and pollution to the environment. Severe dam failure and tailings leakage can lead to a significant number of casualties, building damage and environmental pollution. To achieve monomer dissociation, minerals are generally shattered owing to the fine particles of some minerals. Tailings slurry from the beneficiation plant is drained into the tailings dam through a piping system. Then, the tailings ores subside in the reservoirs. The cleaning water is drained via a discharge tower. A dry slope section and waters are present in the dam. Tailings dams and dry slope sections with fine particles and low water content result in increasing risks of dust through wind force. Especially in a season with drought, little rain, or strong wind, the tailings mineral powders are more likely to be blown away, which can contaminate the environment. The water resulting from mineral processing contains many mixtures and toxins, which consist of flotation reagents and metal elements in ores, commonly with cyanide, black powder, pine oil, copper ion, lead ion, zinc ion, arsenic and mercury in individual cases during the beneficiation process. Tailings wastewater leaks into surface water, groundwater and soil, which can exacerbate groundwater pollution and land salinization, and result in the reduction of surrounding vegetation and crop yields and the destruction of the ecological environment. Even worse, it can directly threaten the survival of humans and livestock.

China is one of the countries with the largest number of tailings reservoirs and the highest hazard rates in the world. According to a study by the American public hazard assessment group of Clark University, among more than 90 kinds of major disasters in the world, tailings reservoir failure ranks 18th below nuclear explosion, nerve gas, cholera and floods, etc. Once a dam failure occurs, huge damage is inflicted on people's lives, property safety and the ecological environment of the downstream area. According to incomplete statistics, by the end of 2012, China had a total of 12,655 tailings reservoirs. The basic characteristics of tailings dams are shown as follows: (1) large quantities, small-scale and fourth-class reservoirs account for 95%; (2) popularly dams are constructed in the upstream; (3) abnormal reservoirs accounting for almost 40% and tailings dams with low safety; (4) many residents inhabiting the area downstream of tailings and places with more than 100 people taking up 53%; and (5) weak technologies relating to tailings.

The main forms of tailings dam accidents include dam breaks and tailings leakage. Environmental pollution caused by tailings dam accidents cannot be ignored. By the end of 2011, China still had 1,095 defective reservoirs that had not been remedied. Tailings dam seepage control projects are related to the life and property safety of local inhabitants. Strengthening tailings seepage treatment is of significant importance. Some problems exist in the application of the existing seepage prevention technology in tailings dams. When seepage prevention works are applied to tailings reservoirs, the current seepage prevention technologies cause destruction of dams and require construction sites. Therefore, it is necessary to adopt advanced and practical technologies of a new type. Tailings reservoirs operate as a permanent part of mining enterprises. Tailings dam failure bursts or serious damage happen occasionally around the world due to overtopping of floods, dam slope instability, seepage failure, poor foundations, seismic liquefaction, etc. Economic losses caused by dam failures and casualties can affect the public adversely.

Many factors can result in the leakage of tailings dams (e.g., design, construction and management factors, natural, social and technical factors). In tailings dam safety monitoring and management, the main risk factors resulting in tailings reservoir failures directly include too steep tailings dam slopes, saturation line escape, cracks, leakage, landslides, dam slope ditches, insufficient drainage capacity of drainage construction, drainage structures being blocked, drainage structure building dislocation, fracture, collapse, insufficient dry beach length, insufficient safe super elevation, lack of seismic capacity, reservoir leakage, collapse, landslides, earthquakes, etc. The gradient of slope is the ratio of horizontal width and vertical height. The smaller the ratio is, the safer dams are. According to statistical data on dam failure, the causes of various failures are sumarized in Table 1.

Table 1

Analysis of the cause of tailings dam accidents

Cause Flood overflow Dam seepage Foundation seepage Flood discharge project The rest 
Percentage (%) 28 19 22 16 15 
Cause Flood overflow Dam seepage Foundation seepage Flood discharge project The rest 
Percentage (%) 28 19 22 16 15 

As seen from Table 1, the probability of damage caused by flood and seepage failure is relatively large. As for tailings reservoirs draining the tailings, tailings dam failures are mainly caused by flood overtopping, poor slope stability and dam vibration liquefaction. Safety and environmental pollution accidents are often caused by loss of control of potential risk factors. In an analysis of domestic mine tailings, it can be seen that many serious failures have occurred. Therefore, it is significant to eliminate and control the potential risk factors of tailings reservoirs and tailings dams.

In recent years, domestic and international experts and scholars have studied tailings reservoirs with the following results. Zhao (2007) introduced measures for seepage control of tailings dams and ecological restoration, and suggested some problems in their implementation. Rico et al. (2008), collecting tailings dam break information, established the simple correlation between geometric parameters of tailings ponds and release of flood water characteristics caused by release of tailings. Li et al. (2009) established a separate tailings dam risk index system, and applied fuzzy theory to establish a tailings dam risk evaluation model. Through related analysis, the safety of tailings dams, design index of parameters and design indicators were classified. Shuran & Shujin (2011) analyzed the influence of blasting vibration on tailings reservoirs, and discussed the problems of tailings reservoirs' safety management near mining fields. Mei & Wu (2012) discussed a quantitative evaluation method for tailings dam failure risk, used the Monte Carlo model to calculate tailings dam failure probability, established a tailings discharge model after tailings dam break, calculated tailings dam break risk loss degree, and ultimately determined tailings dam break risk degree. Kossoff et al. (2014) analyzed the physical and chemical characteristics of tailings, causes of tailings dam failures, environmental and economic impacts of failures, and proposed remedies.

Shi et al. (2010) and Wang et al. (2011a, 2011b, 2011c, 2014) also studied non-water reaction characteristics of polymer materials. Selecting non-destructive testing technology and polymer grouting technology as the foundation, a set of equipment and a technology were developed for rapid detection and repair of highways according to structural characteristics of domestic pavements and typical failure characteristics. Then, disease treatment technologies were developed (pavement and subgrade disease treatment, rapid repair of tunnel cavity, bridge shunting treatment, underground waterproofing treatment, pipe grouting, emergency bag sealing grouting for levee piping, polymer directional fracturing grouting for levee seepage, levee anti-seepage curtain grouting, polymer grouting impervious wall of levee seepage control applied to roads, tunnels, bridges, dams and reservoirs) showing huge economic and social benefits and significant prospects for development.

Considering the problems, various solutions have been proposed, including fracturing grouting, high pressure jet grouting, curtain grouting and impermeable concrete walls. Impermeable materials are used in these methods, including clay grout, cement-based grout, plastic concrete and reinforced concrete. Reinforced concrete may cause high stress and result in cracking due to its high elastic modulus compared with that of soil while clay grout and plastic concrete have low impermeability and weak durability. This shows that the evident shortcomings of water-tight materials used previously have become the main negative factors impairing the reliability of dams' or dikes' seepage control systems. Therefore, seeking new impermeable materials characterized by good flexibility and excellent durability for dikes and dams has become imperative. Foaming polyurethane materials, which have common attributes including high porosity, light weight, and a good deformation energy absorption capacity, may be ideal substitutes.

With the aim of studying the feasibility of non-water reaction polymer grouting technology application in seepage prevention of tailings reservoirs and acquiring the properties in practical engineering, an analysis of its environment impact, chemical resistance and the permeability of the polymer material, and the main technical characteristics of the polymer cutoff wall were conducted. Based on this, it can be seen that non-water reaction polymer grouting material has various characteristics including environmental protection, safety, quick response, adjustability, good expansion, good performance, and long service life, etc., and is a better grouting material with a comprehensive performance. Polymer grouting technology based on double component polyurethane foam is the leading edge in the field. Furthermore, using polymer grouting technology to solve the problem of tailings reservoir seepage will provide reliable technical support for tailings reservoirs' safe operation and help to prevent environmental pollution.

ENVIRONMENTAL IMPACT PROPERTIES TEST

With the aim of analyzing the influence of polymer materials on the quality of groundwater, a laboratory water quality analysis of the water soaking polyurethane polymer grouting material was carried out.

Polymer material, which was formed under no restriction, was divided into three groups and immersed in distilled water for 24 hours, 72 hours, and 3 months, respectively. The ratio of polymer and distilled water quality was 1:120. Filtration supernatant was collected for water quality analysis after sufficient soaking time.

The results of the polymer water quality test are listed in Table 2, and compared with drinking water sanitary standards.

Table 2

Comparison table of polymers and sanitary standards for drinking water

Test report of polymer soaking water quality
 
Sanitary standard for drinking water
 
Component Soaking water for 24 hours ρ(B)/mg·L−1 Soaking water for 72 hours ρ(B)/mg·L−1 Soaking water for three months ρ(B)/mg·L−1 Component Limit value (mg L−1
Fe <0.05 <0.05 <0.05 Fe 0.3 
Mn <0.05 <0.05 <0.05 Mn 0.1 
Cu <0.05 <0.05 <0.05 Cu 1.0 
Zn <0.05 <0.05 <0.05 Zn 1.0 
Cr <0.05 <0.05 <0.05 Cr 0.05 
As 0.0008 0.0005 0.0003 As 0.05 
Se 0.001 0.0006 0.0004 Se 0.01 
Hg 0.00004 0.00003 0.00002 Hg 0.001 
Cd <0.0001 <0.0001 <0.005 Cd 0.005 
Pb <0.001 <0.001 <0.01 Pb 0.01 
Cl 0.3 0.44 2.3 Cl 250 
 0.1 0.17 1.58  250 
F 0.05 0.11 0.09 F 1.0 
NO3− 0.18 0.24 0.5 NO3− 20 
Al3+ <0.01 <0.01 <0.01 Al3+ 0.2 
pH 5.97 5.72 5.54 pH 6.5–8.5 
CN <0.002 <0.002 <0.002 CN 0.05 
CHCl3 <0.02 <0.02 0.0032 CHCl3 0.06 
CCl4 <0.001 <0.001 0.0018 CCl4 0.002 
Total dissolved solids 16 21 57 Total dissolved solids 1,000 
Smell and taste Null Null Null Smell and taste Null 
Volatile phenols (based on phenol) <0.002 <0.002 <0.002 Volatile phenols (based on phenol) 0.002 
Test report of polymer soaking water quality
 
Sanitary standard for drinking water
 
Component Soaking water for 24 hours ρ(B)/mg·L−1 Soaking water for 72 hours ρ(B)/mg·L−1 Soaking water for three months ρ(B)/mg·L−1 Component Limit value (mg L−1
Fe <0.05 <0.05 <0.05 Fe 0.3 
Mn <0.05 <0.05 <0.05 Mn 0.1 
Cu <0.05 <0.05 <0.05 Cu 1.0 
Zn <0.05 <0.05 <0.05 Zn 1.0 
Cr <0.05 <0.05 <0.05 Cr 0.05 
As 0.0008 0.0005 0.0003 As 0.05 
Se 0.001 0.0006 0.0004 Se 0.01 
Hg 0.00004 0.00003 0.00002 Hg 0.001 
Cd <0.0001 <0.0001 <0.005 Cd 0.005 
Pb <0.001 <0.001 <0.01 Pb 0.01 
Cl 0.3 0.44 2.3 Cl 250 
 0.1 0.17 1.58  250 
F 0.05 0.11 0.09 F 1.0 
NO3− 0.18 0.24 0.5 NO3− 20 
Al3+ <0.01 <0.01 <0.01 Al3+ 0.2 
pH 5.97 5.72 5.54 pH 6.5–8.5 
CN <0.002 <0.002 <0.002 CN 0.05 
CHCl3 <0.02 <0.02 0.0032 CHCl3 0.06 
CCl4 <0.001 <0.001 0.0018 CCl4 0.002 
Total dissolved solids 16 21 57 Total dissolved solids 1,000 
Smell and taste Null Null Null Smell and taste Null 
Volatile phenols (based on phenol) <0.002 <0.002 <0.002 Volatile phenols (based on phenol) 0.002 

Testing polymer material soaked in water proved that polyurethane polymer materials soaked in water over a long period could not be degraded or decayed. The ρ of each component in the filter was far lower than that of the standard. Analysis results of the filter composition showed that no polymer material was contained in the filter. The water quality test results of polymer immersion and drinking water health standards showed that polymer materials caused no damage to the environment considering water quality.

CHEMICAL RESISTANCE TESTS

The polymer materials were immersed in chemical solvents (e.g., oil or grease) in different concentrations, and the volume loss rate of the polymer materials was measured over a period of 30 days. The results were divided into five categories, according to volume loss rate, as shown in Table 3.

Table 3

Evaluation of corrosion resistance of polymer grouting material

Category Loss rate of volume Evaluation result 
Less than 3% Excellent 
3–6% Good 
6–15% Medium 
15–25% Inferior 
Destruction Not recommended for use 
Category Loss rate of volume Evaluation result 
Less than 3% Excellent 
3–6% Good 
6–15% Medium 
15–25% Inferior 
Destruction Not recommended for use 

The volume loss rate of the polymer materials immersed in oil or chemical solvents with different concentrations are listed in Tables 4 and 5.

Table 4

Loss rate of volume of polymer material soaked in acid and basic solution

Solution Loss rate of volume (%) Evaluation grade 
NH4OH (10%) 3.4 Good 
HCl (10%) 4.2 Good 
H2SO4 (10%) 5.6 Good 
NaOH (10%) 1.1 Excellent 
NaOH (dense) 2.6 Excellent 
H2SO4 (dense) Destruction Not recommended 
HNO3 (dense) Destruction Not recommended 
Solution Loss rate of volume (%) Evaluation grade 
NH4OH (10%) 3.4 Good 
HCl (10%) 4.2 Good 
H2SO4 (10%) 5.6 Good 
NaOH (10%) 1.1 Excellent 
NaOH (dense) 2.6 Excellent 
H2SO4 (dense) Destruction Not recommended 
HNO3 (dense) Destruction Not recommended 
Table 5

Loss rate of volume of the polymer material soaked in chemical solution

Chemical solution Loss rate of volume (%) Evaluation grade 
Acetone 21.1 Inferior 
Methyl ethyl ketone 19.7 Inferior 
Methanol 4.1 Good 
Ethanol 3.9 Good 
Kerosene 3.5 Good 
Gasoline 3.6 Good 
Engine oil 2.3 Excellent 
Water Excellent 
Chemical solution Loss rate of volume (%) Evaluation grade 
Acetone 21.1 Inferior 
Methyl ethyl ketone 19.7 Inferior 
Methanol 4.1 Good 
Ethanol 3.9 Good 
Kerosene 3.5 Good 
Gasoline 3.6 Good 
Engine oil 2.3 Excellent 
Water Excellent 

Test results show that polymer materials performed well in the resistance to chemical solvents and oils as evaluated according to volume loss rate. Under ground surface circumstances, polymer materials had good stability in salt, acid or detergent solution, but concentrated sulfuric acid, nitric acid, and concentrated base could lead to chemical degradation, and polar solvents might damage polymer materials; it is hard to experience these conditions in an engineering application.

Based on the analysis, it is shown that high polymer materials have good chemical stability. Polymer materials can be resistant to chemical corrosion in an underground environment over a long period.

PERMEABILITY TEST

Currently, methods of evaluating concrete's permeability mainly include the stable flow method, penetration depth method, and the method of impermeability. The stable flow method is only suitable for the study of high permeability materials. Penetration depth is not easy to measure. Considering the polymer is essentially an impermeable material, permeability resistance of polymer materials was evaluated according to the seepage resistance grade method adopted in the concrete test.

The relationship between material density and initial seepage pressure is shown in Figure 1.

Figure 1

Relationship between density of polymer material and initial seepage pressure.

Figure 1

Relationship between density of polymer material and initial seepage pressure.

It can be seen that permeability resistance of polymer materials increases as the polymer materials' density increases. When polymer material density reached 0.6 g/cm3, initial water seepage pressure reached 1 Mpa, which could withstand a water head of 100 m. According to the method of dividing hydraulic concrete impermeability, the grade of polymer anti-seepage is equivalent to the tenth grade.

In practical water conservancy projects, the density of polymer material grouted in an impervious curtain was not less than 0.1 g/cm3, and initial water seepage pressure reached 0.26 MPa, which could withstand a water head of 26 m. The results show that a double component polymer will usually possess high impermeability.

MAIN TECHNICAL CHARACTERISTICS OF A POLYMER CUTOFF WALL

Polymer grouting mainly splits and compacts soil by self-expansion, and causes penetration and cementation to the soil's interface. A polymer grouting material with non-water reaction in soil generally produces a patchy diffusion. Considering the high risks of flooding and damage caused by tailings dam failure, seepage control and leakage stoppage should be implemented by adopting polymer cutoff wall technology with uniform bonding, the properties of which are shown below:

  • (1)

    Little disturbance to dams: An impervious wall with a thickness of 12 cm in the dam body can be constructed with polymer cutoff wall technology, which is currently the thinnest. Slot mode by static pressure greatly reduces disturbance to the dam. Grouting materials are made of non-water reaction polymer materials. The grouting construction process does not require water and slurry support.

  • (2)

    Excellent impervious performance and high durability: As a flexible cutoff wall, a polymer cutoff wall has elastic modulus approximate to that of soil. It has good coordination of deformation with the soil, and seismic and crack resistance.

  • (3)

    Rapid and convenient construction: Polymer cutoff wall technology has a high construction speed and degree of automation in sealing and continuous grouting operation. Polymer material strength can reach 90% of the maximum in 15 minutes after injection without the requirement of maintenance.

  • (4)

    No impacts on the environment: Polymer grouting materials do not cause pollution to water and soil, and the construction process does not produce sludge wastewater, and therefore has no effect on the surrounding environment.

  • (5)

    Applicable conditions of cutoff wall technology: Polymer cutoff wall technology can only be used in the construction of a cutoff wall in a dam body and dam foundation made of clayey, silty, sand soil, etc. As equipment for holes with static pressure cannot be pressed into the groove plate, a polymer cutoff wall is not applicable for foundations with sand gravel, stone or rock in filling materials. Under the constraints of the construction equipment and technical conditions, polymer cutoff wall technology is only suitable for cut-off walls with a depth of less than 30 m. Polymer materials performed weakly in strong acid resistance, so it is not suitable to be applied in a high concentration and strong acid environment.

ANALYSIS ON THE FEASIBILITY OF POLYMER MATERIALS APPLICATION TO A TAILINGS DAM SEEPAGE CONTROL PROJECT

To ensure that the polymer material can be applied to the tailings dam seepage control project, a series of analyses were conducted.

Material corrosion resistance analysis

According to the test result, a polymer cutoff wall was not applicable for a strong acid environment. Polymer materials performed excellently in basic environment corrosion resistance and could be used to store basic wastewater in a tailings reservoir seepage control layer.

Seepage control effect analysis

Generally, the properties of a tailings dam seepage control layer should be equivalent to the impervious performance of a clay layer with permeability coefficient of 10−7 cm/s and thickness of 1.5 m. In fact, the polymer cutoff wall had a permeability coefficient of 10−8–10−9 cm/s. The anti-seepage performance fully met the tailings dam seepage control requirements.

Stability analysis

A tailings reservoir is an important facility to ensure normal operation of an enterprise and surrounding related units, and is also important for safety and environmental protection. Once the tailings dam breaks, a large amount of tailings waste pours out, which will endanger the surrounding people's lives, property safety and the ecological environment.

Current cutoff wall technologies have an influence on the stability of tailings dams to various extents. For example, as the canal embankment is slotted with the concrete cutoff wall technology, the tailings dam is divided into two parts. Then, concrete wall pouring is conducted by section, while the wall materials and tailings dam soil are separated. This will have an effect on the overall stability of the tailings dam. Vibration rolling with machines causes damage to tailings dams easily, which may cause a rift in the tailings dam. Liquids spray from cracks when being poured. Therefore, effective measures should be taken to reduce the damage to existing tailings dams during construction. Jet grouting cutoff wall technology with high pressure during the process of hole forming or completion may cause damage to the tailings dam. The vibration impact of vibration sinking mold plank wall seepage prevention technology can also cause cracking and a landslide resulting in the destruction of tailings dams.

The polymer cutoff wall has a small slot and through static pressure and anhydrous grouting method reached 90% of the wall strength after 15 minutes and reduced disturbance to the tailings dam greatly. Polymer materials and soil cement as a whole with deformation coordination, enhanced the overall stability of tailings dams.

ANALYSIS OF THE SEISMIC AND CRACK-RESISTANCE PERFORMANCE OF A POLYMER CUTOFF WALL

A polymer cutoff wall is a kind of ultra-thin flexible cutoff wall. Its elastic modulus is very approximate to that of soil. It has deformation coordination with soil and the wall has a width of only 1–3 cm. Whether it is under static conditions or seismic load, tensile stress in the dam is smaller than that of the concrete cutoff wall. A tailings dam can benefit from the flexible seepage cutoff walls in seismic activities.

In order to analyze the static and dynamic characteristics of a polymer cutoff wall under gravity, hydrostatic pressure and seismic load, an earth rock-fill dam project was analyzed and the static characteristics and maximum stress distribution of a polymer cutoff wall, plastic concrete cutoff wall and common concrete cutoff wall were calculated.

The dam is a homogeneous earth dam with a crest length of about 340 m. The dam foundation consists of heavy silt loam, fine sand and mica quartz schist with good geological conditions. A polymer grouting cutoff wall was constructed in a new dam. The polymer grouting cutoff wall's plan is shown as follows: 0.5 m away from upstream axis of the dam and wall thickness of 2 cm, top elevation of 77.15 m, risk section of dam from 1 + 005 to 1 + 220, cutoff wall's length of 215 m.

ALGOR commercial software was used to analyze the mesh generation and calculation of the earth rock dam. The calculation and analysis on the polymer cutoff wall, plastic concrete cutoff wall and common concrete cutoff wall were carried out under two conditions:

  • Condition I: stress analysis on earth rock dam under self-weight and hydrostatic pressure.

  • Condition II: dynamic stress analysis on earth rock dam under seismic load.

In the finite element model analysis, the Duncan-Chang nonlinear model was applied to the dam material. The contact unit was set between the cutoff wall and soil. An El-Centro seismic wave of 0.6 g was applied to time history analysis of seismic acceleration, with damping in accordance with Rayleigh damping. The comparison of the maximum stress in the cutoff wall's interior under the two conditions are shown in Figures 2 and 3.

Figure 2

Comparison of the maximum stress in the diaphragm wall under static load.

Figure 2

Comparison of the maximum stress in the diaphragm wall under static load.

Figure 3

Comparison of maximum stress of anti-seepage wall under seismic load.

Figure 3

Comparison of maximum stress of anti-seepage wall under seismic load.

The calculations showed that with the dam under static and dynamic loads, internal stress of the polymer cutoff wall value was far less than that of the ordinary concrete cutoff wall and plastic concrete cutoff wall. The internal stress of the plastic concrete cutoff wall nearly exceeded the limit, and the polymer cutoff wall still had a large safety margin in condition II generally. The plastic concrete and common concrete cutoff wall exceeded the limit of damage, and the polymer cutoff wall was far from the destruction limit. The calculation results under the two conditions are shown in Table 6.

Table 6

Calculation results with the dam under static and dynamic loads

Condition Stress type Cutoff wall type Stress value/MPa 
Condition I Maximum crushing stress Common concrete 4.39 
Condition I Maximum crushing stress Plastic concrete 2.32 
Condition I Maximum crushing stress Polymer material 0.183 
Condition I Compression limit Plastic concrete 2.5 
Condition I Compression limit Polymer material 1.2 
Condition II Maximum tension stress Common concrete 2.01 
Condition II Maximum tension stress Plastic concrete 0.71 
Condition II Maximum tension stress Polymer material 0.246 
Condition II Tensile limit Common concrete 1.5 
Condition II Tensile limit Plastic concrete 0.3 
Condition II Tensile limit Polymer material 1.2 
Condition Stress type Cutoff wall type Stress value/MPa 
Condition I Maximum crushing stress Common concrete 4.39 
Condition I Maximum crushing stress Plastic concrete 2.32 
Condition I Maximum crushing stress Polymer material 0.183 
Condition I Compression limit Plastic concrete 2.5 
Condition I Compression limit Polymer material 1.2 
Condition II Maximum tension stress Common concrete 2.01 
Condition II Maximum tension stress Plastic concrete 0.71 
Condition II Maximum tension stress Polymer material 0.246 
Condition II Tensile limit Common concrete 1.5 
Condition II Tensile limit Plastic concrete 0.3 
Condition II Tensile limit Polymer material 1.2 

FEASIBILITY OF POLYMER GROUTING'S APPLICATION TO A TAILINGS DAM SEEPAGE CONTROL PROJECT

In view of the threat of tailings dams and the necessity of seepage prevention and reinforcement, combined with the characteristics of polymer grouting material, polymer grouting technology can be used in the following aspects of a tailings dam seepage prevention project.

  • (1)

    Tailings dam foundation seepage control: For a tailings dam with high seepage control requirements, a polymer seepage control layer with a thickness of 1–3 cm is evenly sprayed on the top of the base which is constructed to meet the requirements of flatness, according to the diagram shown in Figure 4. With properties of rapid prototyping of polymer materials, high strength, difficult to puncture and high impervious grade combined closely with soil, a strong, stable and lasting impervious body can be formed, achieving the purpose of seepage control.

  • (2)

    Seepage prevention of tailings dam site: In a sub-dam or accumulation dam in a tailings dam construction, a polymer impermeable layer with a thickness of 1–3 cm on the slope is evenly sprayed to protect the surrounding slope environment from tailings, and is shown in Figure 5. Conducting the construction of spraying concrete slurry above the polymer impermeable layer according to the original design, a solid, stable and durable anti-permeability body is formed, achieving the purpose of seepage prevention.

  • (3)

    Seepage prevention and reinforcement of tailings dam: This is implemented to improve the reliability of safe operation.

    • (a)

      Local seepage prevention and reinforcement of the tailings dam

      • Local leakage polymer grouting: Using grouting pipe, polymer materials are injected into predetermined positions. With the rapid expansion of polymer materials, the gaps between coarse soil and soil are filled, or the contact gaps between soil and buildings are filled. The schematic diagram of local leakage polymer grouting is shown in Figure 6, and thus a solid, stable and durable impervious body is formed, achieving the purpose of seepage control.

      • Rapid film bag polymer grouting: A geotextile bag is strapped in a hollow steel tube and the bag is placed in the piping leakage in the inlet at a certain depth. Then, double component polymer materials are injected into the geotextile bag in the mouth of the piping channel. Materials expand in the volume and cure after reaction, realizing rapid closure to the piping channel inlet, and the results can be found in Figure 7. Further, through duct grouting technology of injecting polymer materials into the piping channel, the piping channel is blocked, strengthening the dam and improving the overall dam stability.

    • (b)

      Continuous seepage prevention and reinforcement of tailings dam

      • Directional splitting polymer grouting: With the static indentation method, a special directional fracturing crack drill is pressed into the soil, forming a symmetric splitting gap columnar borehole. Then, the two-component polymer grouting material is injected into the hole. Polymer materials develop rapid expansion after chemical reaction. The swelling force promotes the round hole of the existing symmetric cracks to expand continuously, and slurry invades the expanding crack, forming an overlapping sheet-like polymer anti-seepage body, which is shown in Figure 8. The purpose of treating a dam's local leakage is achieved.

      • Polymer curtain grouting: Through the grouting pipe, polymer materials are injected into predetermined positions and the interspace in the rock and soil body is filled with rapid expansion and solidification of polymer material; and the dense rock and soil body is compacted forming a strong and stable waterproof layer. Also, according to the determination of dam leakage location and design scheme for seepage prevention, a hole drilling tool of double wing type is pressed in the ballast to the position requiring treatment through static equipment, forming a mutual overlapping narrow slot. Using a grouting pipe to inject grout into the hole, the double component polymer material quickly reacts, expands and flows, filling the hole mold, solidifying and cementing the soil around it. The hole module is in cross or continuous adjacent overlap, forming a thin polymer anti-seepage curtain and achieving the purpose of treating dam leakage. The constructed curtain can be seen in Figure 9.

      • Ultra-thin polymer cutoff wall: According to the design requirements of the dam seepage, in the dam section requiring strengthening, a special drilling tool is pressed into the dam with static pressure equipment, forming a continuous thin hole. Then, two-component polymer materials are injected into the hole through injection pipes. The polymer material presents rapid expansion after chemical reaction, filling the mold of the grouting hole and forming a polymer sheet body. Adjacent molds for holes overlap continuously, forming a continuous thin polymer cutoff wall after grouting to achieve the purpose of improving dam seepage performance, as demonstrated in Figure 10.

Figure 4

Schematic diagram of polymer seepage control of the tailings dam foundation.

Figure 4

Schematic diagram of polymer seepage control of the tailings dam foundation.

Figure 5

Schematic diagram of seepage control of polymer site slope of tailings dam.

Figure 5

Schematic diagram of seepage control of polymer site slope of tailings dam.

Figure 6

Schematic diagram of local leakage polymer grouting.

Figure 6

Schematic diagram of local leakage polymer grouting.

Figure 7

Schematic diagram of rapid film bag polymer grouting.

Figure 7

Schematic diagram of rapid film bag polymer grouting.

Figure 8

Schematic diagram of directional splitting polymer grouting.

Figure 8

Schematic diagram of directional splitting polymer grouting.

Figure 9

Schematic diagram of polymer curtain grouting.

Figure 9

Schematic diagram of polymer curtain grouting.

Figure 10

Schematic diagram of super thin polymer cutoff wall.

Figure 10

Schematic diagram of super thin polymer cutoff wall.

CONCLUSION

Seepage prevention polymer grouting technology of tailings dams is based on the concept of flexible waterproof and non-water reaction swelling polymer grouting materials. It is a new anti-seepage technology, which has the characteristics of little disturbance, fast construction, good impervious performance, good durability, economy, environmental protection, etc.

The new non-water reaction polymer grouting materials cause no pollution to the environment, and have good seepage prevention performance. Their density, expansion ratio and engineering mechanics performance index can be adjusted according to the actual engineering, and can be closely consolidated with the soil body. Compared with existing seepage control technologies, the overall stability of tailings dams and anti-cracking performance of the anti-seepage body are significantly enhanced. Polymer materials have good chemical stability to be resistant to chemical corrosion (e.g., acid and basic environment) in the underground environment over a long period.

Polymer grouting technology can be used in several aspects of a tailings dam seepage prevention project, including tailings dam foundation seepage control, tailings dam site seepage prevention and tailings dam seepage prevention and reinforcement. Local leakage polymer pipe grouting technology, rapid polymer sealing technology of piping, polymer directional splitting grouting technology, polymer curtain grouting technology and ultra-thin polymer cutoff wall grouting technology are applied in the seepage prevention and reinforcement of tailings dams. They show good anti-seepage performance and long durability, and can substitute current techniques for seepage control and effectively avoid the partial rupture caused by leakage.

ACKNOWLEDGEMENTS

The research is supported by the Water Conservancy and Transportation Infrastructure Safety Protection Henan Province Collaborative Innovation Center.

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