At the present, the natural stone used for traditional block rock revetment is becoming increasingly scarce, and other commonly used revetment types also have some problems, such as poor stability, complex fabrication and installation process, and large investment. Therefore, it is imminent to study a new type of reinforcement of dangerous dam banks with both ecological and environmental protection functions to meet the requirement of river flood stability. Combining theoretical calculation with laboratory tests, a new slope protection block of H-type gravity mutual-aid steel slag core concrete (H-type gravity mutual-aid steel slag core concrete block hereinafter), which is composed of an ordinary concrete shell and a steel slag core, is designed as an improvement of revetment reinforcement type and for solid waste utilization and resource saving. The indoor test method shows that the optimal shell thickness of the new block is 6 cm, and the steel slag of a single block can replace the natural aggregate ratio of 25%. The new block has concave and convex structures to enhance the interlocking effect between blocks. The compressive strength of the new block is tested by the drilling core compressive strength test to meet the strength requirement of the revetment works. Moreover, on the basis of the overall stability test platform of the interlocking block and numerical simulation analysis, the H-type gravity mutual-aid steel slag core concrete block was proved to have a better interlocking effect than the traditional blocks and exhibits excellent overall stability.
Revetment works, which are considered the first line of defense for dam safety, play a key role in flood control and discharge and can effectively reduce soil erosion in dam banks. These projects are important for national governance. For a long time, revetment works use slurry block stone, cast-in-place concrete, and bag concrete pavements. Different forms of slope protection play an important role in resisting wind wave impact and preventing rainwater erosion on the slope. However, the traditional bank revetment often suffers from problems and events such as landslides, settlements, and even destruction of roads, and it is easy to lose stability in seismic forces [
The interlocking concrete block revetment has been introduced into China gradually in recent years, and was adopted in Beijing-Hangzhou Canal, Datun Pingyuan Reservoir, and many other projects. The interlocking concrete block possesses qualities like high strength and durability; it can be standardized and mass produced; the construction of it is convenient and fast; and its pavement is simple and does not require large equipment. The revetment made by interlocking concrete is superior to the traditional one, which has a flexible structure with high overall stability and can be applied to all kinds of landforms.
Since the reform and opening, China’s heavy industry-type manufacturing industry has been in a period of rapid development, and the demand for steel is also increasing. However, behind the economic development, it has also brought about a series of negative impacts on ecological environment. Steel slag is solid waste produced after steelmaking and it is difficult to carry out decomposition or transformation, and most of its treatment is only to be landfill as ordinary garbage. Currently, the comprehensive utilization rate of steel slag in China is low at only approximately 22%. The steel slag that has not been utilized is nearly 10 million tons [
Through the unremitting efforts of numerous researchers, the research on block slope protection and steel slag application is deepening. Zhong and Wang [
For the utilization of steel slag, Maslehuddin [
Cox et al. [
At present, local and international studies on slope protection blocks mostly focus on improving external types, and research on steel slag focuses on the properties of steel slag aggregates [
On the basis of the positive effect of steel slag used in concrete production and the severe demand for ecological environmental protection function, a new slope protection block of H-type gravity mutual-aid steel slag core concrete (H-type gravity mutual-aid steel slag core concrete block hereinafter) is designed and studied. Its overall stability is also studied and analyzed. On the one hand, this study enriches the research on the reinforcement of dangerous dam shores. On the other hand, it is important for reclaiming and reusing waste materials and alleviating the pressure of ecological environment suffering from the destruction of steel slag.
The flow chart of the research methodology of this study is presented in Figure
The flow chart of the research methodology of this study.
The P.O 42.5 Portland cement was used in this study. The chemical composition of the cement is shown in Table
Chemical composition of P.O 42.5 Cement (%wt).
Chemical composition | SiO2 | Al2O3 | Fe2O3 | CaO | MgO | TiO2 | Na2O | K2O | SO3 |
---|---|---|---|---|---|---|---|---|---|
Cement (%) | 21.1 | 7.81 | 2.92 | 54.4 | 3.18 | 0.425 | 0.190 | 0.399 | 2.93 |
The designed H-type gravity mutual-aid steel slag core concrete block is a composite structure of a concrete shell and a steel slag core. The abdomen is the main load-bearing part. The thickness of the best concrete shell is selected through indoor testing. The core aggregate is made of 100% steel slag instead of traditional materials to guarantee the compressive strength of the blocks and maximize the economic and environmental benefits of the steel slag instead of the traditional materials.
Table
Mix ratio of C40 ordinary concrete (kg/m3).
Cement | River sand | Natural gravel | Water reducer | Water |
---|---|---|---|---|
480 | 775 | 970 | 11.04 | 165 |
1 | 1.615 | 2.021 | 0.023 | 0.344 |
In the material combination of the steel slag core, 100% steel slag replaces traditional aggregates, 100% steel slag coarse aggregates replace natural crushed stones, and 100% steel slag sand replaces medium-sized river sand. The specific mix proportion is equally substituted in accordance with the
Mix ratio of steel slag concrete (kg/m3).
Cement | Fine steel slag aggregate | Coarse steel slag aggregate | Water reducer | Water |
---|---|---|---|---|
480 | 775 | 970 | 11.04 | 165 |
1 | 1.615 | 2.021 | 0.023 | 0.344 |
According to the
Test block structure size (mm).
Block number | A | B | C | D | E |
---|---|---|---|---|---|
Shell thickness | 40 | 50 | 60 | 70 | 100 |
Steel slag core size | 120 × 120 × 120 | 100 × 100 × 100 | 80 × 80 × 80 | 60 × 60 × 60 | 0 |
In accordance with the mixture ratio and the size shown in Table
According to the requirement of the
Referring to the
This study is based on a hydraulic loading test system that can check the interlocking performance between interlocking blocks (Figure
Loading test platform. (1) Platform frame baffle; (2) horizontal fixed platform; (3) limit bolt; (4) support frame; (5) I-shaped limit plate; (6) horizontal support frame; (7) block limit plate; (8) long strip limit plate; (9) rib plate; (10) jack reaction frame; (11) hydraulic pipe; (12) manual hydraulic pump.
The three blocks are placed neatly on the platform in accordance with their respective locking ways, and the side blocks are applied to the blocks. The block limiting plates and the long strip limiting plates are placed between the ends of the limit bolts and the blocks. The various limiting bolts are adjusted to the tightest state for ensuring full application of the side limit. The load detection and loading devices are installed between the reaction frame and the blocks placed at the middlemost of the platform. The four corners of the block in the middle position on the clockwise direction are marked as A, B, C, and D as shown in Figure
The arrangement of three types of blocks. (a) H-type gravity mutual-aid block. (b) Traditional block 1. (c) Traditional block 2.
The device is closely fitted with the block. After the pressure gauge is opened, the initial pressure value is recorded. The initial displacement value of the block is measured and recorded on the basis of the platform bottom. The jack is slowly loaded after loading. When the pressure gauge reading is no longer changing, the position of the four corners of the central block is measured with the vernier caliper. The pressure and the corresponding displacement are recorded. During the loading process, the changes in the block and block combination surface are carefully observed and recorded until the reading of the pressure gauge is stable.
The test results of compressive strength of steel slag core concrete with different shell thicknesses are shown in Figure
The compressive strength of steel slag core concrete with different shell thicknesses.
The test results show that the shell thickness 6 cm is the safety turning point of the shell thickness-compression strength curve. The average compressive strength at this turning point reaches 47.0 MPa, which is only 4.5% different from that of the ordinary concrete control group. The strength change stabilizes thereafter. Therefore, the optimum shell thickness is selected to be 6 cm to ensure that the composite structure of the concrete shell and the steel slag core meets the requirements of compressive strength, guarantees the consumption of steel slag, and increases the environmental protection effect.
The failure morphology of the specimen after the compressive test is shown in Figure
Failure morphology of the specimen after compression test.
The thickness of the block considerably influences the stability of the revetment surface, whereas the length and width of the block only slightly influence the stability. Therefore, the thickness should be considered when designing the block [
According to the designed wave parameters of the embankment of the key flood detention and control works in the lower Yellow River, the weight and thickness of the block are calculated. Detailed parameters are shown in Table
Wave parameters.
Project | Calculated wind speed (m/s) | Depth of water (m) | Wind area length (m) | Average wave height (m) | Wave height (m) | Wave length (m) | Designed wave height (m) |
---|---|---|---|---|---|---|---|
Data | 19.00 | 7.00 | 12.4 | 0.73 | 1.35 | 21.67 | 1.123 |
The wave parameters in the aforementioned table are substituted in equations (
The appearance design of the block not only can beautify the river environment but also can increase the locking effect between the blocks. The overall stability of the revetment can be substantially improved. Based on the analyses of the best thickness of the concrete shell and the block and the failure mechanism of the block revetment structure, the H-type gravity mutual-aid steel slag core concrete block is designed. And its structure is shown in Figures
Schematic diagram of block structure. (a) Appearance. (b) Perspective. (1) Abdominal structure; (2) flange structure; (3) flange structure; (4) flange I bending hooks; (5) flange II bending hooks; (6) side concave-convex structure; (7) steel slag core.
Three views of block (mm).
It can be seen from Figures
Schematic diagram of block after embedment.
The prism and sharp corner can be hardly avoided in the current block shape design, and it inevitably leads to severe concentration of stresses and the local damage caused by it may invalidate geometric interlocking and threaten the shear and shock resistance of blocks. Considering that, a trapezoid bump was designed on one end surface of this new block and a matching groove on the other end surface, which can raise sheer and shock resistance. The horizontally adjacent blocks were also interlocked to reduce block location error, improve installation quality, and conduce to the integrality and shock resistance of the masonry structure. Moreover, to seek better sheer and shock resistance, the convex projection and concave cavity were designed on the transverse plane of blocks, which makes the concentration of stresses inevitable. However, to minimize stress concentration, the acute angle was designed 72° to achieve the best balance.
From these figures, it can also be observed that the upper and lower sides of flange structure I, flange structure II, flange I side hook, and flange II side hook are plane structures. The left and right sides are of concave-convex structure. Flange structures I and II are folded in the high midline position. Flange structure I is convex upward and concave downward, whereas flange structure II is concave upward and convex downward. The corresponding concave and convex dimensions are the same at the same horizontal height. The concrete shell and the flange and bending hook structures on both sides of the flange are concretely poured. The hooks on both sides of flanges I and II are trapezoidal grooves on the same side. In addition, the hooks on both sides of flanges I and II can be inserted into the trapezoidal groove between both flanges after splicing.
The results of compressive strength of three groups of core specimens are shown in Figure
Core sample compression strength of each group.
As shown in Figure
Compression failure of core sample. (a) Core drilling. (b) Core specimen. (c) Compression failure.
In summary, the designed H-type gravity mutual-aid steel slag core concrete block has the following advantages: The entire structure is H-shaped, and the two sections of the flange have hook structures. Therefore, the interlocking ability of the flange is stronger than that of the traditional interlocking block. On this basis, the concave and convex structures of the left and right flange parts not only can enhance the interlocking between the interlocking blocks but also can provide gravity mutual assistance to the interlocking blocks. Accordingly, the blocks can be prevented from falling off under the wave load. The concave and convex parts are a folding inclined plane, which is convenient for block disassembly and favorable for block installation and repair. When industrial abandoned steel slag is used as material, the ratio of steel slag to traditional aggregate can reach 25% for a single block. As a result, waste utilization can be realized and high consumption and waste of steel slag can be decreased. This material can also solve the shortage of natural stone resources and large investment in traditional slope protection, which have environmental importance. The steel slag concrete core, which is completely replaced by steel slag aggregate, can be easily poured into concrete. Steel slag has the characteristics of high strength and excellent durability. This material also has high strength when cured into blocks and acts with a concrete shell. No mortar masonry is needed during construction. After determining the height of blocks by the specification, the requirements for overall stability can be satisfied only through friction interlocking and gravity mutual assistance. The construction is also convenient and simple.
After loading in accordance with the test procedure, the change in the three kinds of masonry surface and the failure of the single block with H-type gravity interacting steel slag core are shown in Figure
Variations in the surface layers of three kinds of blocks and damage of a single block. (a) Change of H-type block. (b) Change of traditional block 1. (c) Change of traditional block 2. (d) Failure of H-type gravity mutual steel slag core block.
The change in the surface layer of three test blocks is shown in Figures
From Figure
The data of the pressure and vertical displacement of the three blocks at corners A, B, C, and D of the test are plotted as pressure-displacement maps, as shown in Figures
Maximum loading of three types of blocks.
The pressure-displacement curves in Figure
Pressure-displacement curve of 4 corner points of three types of blocks. (a) Pressure-displacement curve of the H-type gravity mutual-aid steel slag core concrete block. (b) Pressure-displacement curve of the traditional block 1. (c) Pressure-displacement curve of the traditional block 2. (d) Three kinds of block pressure-average displacement curve.
According to the experimental results and phenomena, the variation in internal forces of the H-type gravity steel slag-cored concrete block under surface loading is analyzed. In the first half, the central block is subjected to vertical displacement due to force, and the resistance caused by the frictional force and the concave-convex structure causes the surrounding block to slightly shift. The interlocking effect between the blocks is weak, and the pressure is directly proportional to the displacement of the blocks. As the test progresses, the displacement of the central block continues to increase. The surrounding blocks also begin to show evident displacement. The bite force between the blocks begins to take effect, and concrete friction sounds are observed between the blocks. As loading continues, the central block is subjected to the combined effects of friction, gravity, mutual-aid gravity, bite force, and loading force. The loading force and the displacement of the central block and surrounding blocks increase. However, the increase rate is substantially decreased, and the squeak of concrete damage begins to occur due to the increase in bite and squeezing forces. When loading reaches the extreme value, the load suddenly decreases, the surrounding blocks begin to fall, the occlusion between the concave and convex structures of the block is detached, and the interlocking effect is weakened. When loading continues, the displacement of the central block continues to increase and the surface layer is gradually removed. As a result, the interlocking effect is invalid.
The concave-convex structure of the H-type gravity mutual-aid steel slag core concrete block has blocked the blocks to create mutual-aid gravity. Thus, the block has inclined displacement under the action of the loading force. The H-type locking structure starts to occlude the block flange after the inclined displacement of the block. Friction, gravity, mutual-aid gravity, and occlusal force cooperate to resist external loads during the entire process.
Focusing on the bank protection structure under wave loads of the sloping bank revetment of the lower Yellow River, this study conducted numerical modeling to compare the overall stability of the new type block revetment and the tradition one with ABAQUS software. The elevation of the dam base of this revetment 27.61 m, height of the dam crest 32.43 m, slope of the dam 1 : 1.5, and defense water line 31.33 m. The earth filling of the revetment is as following: ① earthwork of the dam foundation, the compactness of it is higher than 0.94 and clay content is more than 3%; ② earthwork of the clay dam tire, the compactness is higher than 0.94 and clay content is more than 20%. The dam body is consolidated soil for years and is with high stability. Since the modeling focuses on the stability of the surface course of revetment, the dam deformation is out of consideration and the dam body is deemed as a rigid body to facilitate calculation. Besides, the key attack zone was located through the wave parameters of flood detention and flood control project design of revetment and was primarily analyzed during the simulation process.
The stability of the revetment composed of the new block and the traditional block is simulated by ABAQUS. The indoor revetment stability test of the H-type gravity mutual-aid steel slag core concrete block is conducted to verify its stability and superiority to the traditional block. The load carried by the concrete block revetment includes gravity, buoyancy, wave pressure, back wave pressure, supporting force, interlocking force, and friction force (defined by the frictional contact). And, the load in simulation mainly consists of the gravity of soil mass and concrete after deducting buoyance, wave pressure, and friction force. Wave pressure is mainly made up of the wind wave and the ship wave, and the back wave pressure originated from a wave is the major force for the failure of interlocking. Therefore, back wave pressure is the most important control factor in the revetment structure design. The most ferocious load for revetment is the coupling of the wind wave load and the ship wave load, and the sum of the back wave pressure of the wind wave and the ship wave was adopted in simulation calculation. Each revetment block layer applies equal wave back pressure on only two interlocking blocks that are vertically oriented at the most intermediate position [
Displacement constraints were imposed on the left and the right side of the surface course of revetment in horizontal and vertical directions and all directions of the dam bottom. The contacts in this model cover contacts between blocks and contacts between the block and the dam body. The contact between blocks means the friction between surfaces, and the friction coefficient is set as 0.4; the contacts between the block and the dam body are also deemed as friction, and the friction coefficient is 0.35.
The simulation results of H-type gravity mutual-aid steel slag-cored concrete block, traditional block 1, and traditional block 2 are shown in Figures
Simulation results of H-type gravity mutual-aid block revetment. (a) Equivalent displacement nephogram. (b) Equivalent stress nephogram.
Cloud diagram of numerical simulation results of traditional block 1 revetment. (a) Equivalent displacement nephogram. (b) Equivalent stress nephogram.
Cloud diagram of numerical simulation results of traditional block 2 revetment. (a) Equivalent displacement nephogram. (b) Equivalent stress nephogram.
The maximum equivalent displacement and stress of three blocks are listed in Table
Numerical simulation results.
Block type | Maximum displacement (cm) | Maximum stress (MPa) |
---|---|---|
New H-type block | 0.734 | 2.429 |
Traditional block 1 | 1.012 | 3.795 |
Traditional block 2 | 1.097 | 2.909 |
Moreover, the numerical simulation results of the stability comparison between the new block and the traditional block are basically consistent with the conclusions of the laboratory tests on the stability of the new block interlocking, which further demonstrates the good performance of stability of the new block.
To address the problems in the existing revetment, this study conducts the indoor test and theoretical calculation to investigate a new type of slope protection blocks blended with steel slag. And the following conclusions can be obtained: The new designed H-type gravity mutual-aid steel slag core concrete block is symmetrical vertically but asymmetrical horizontally. The abdomen structure is composed of a concrete shell wrapping a solid steel slag core. Besides, the concave-convex structure is designed in the blocks to enhance the interlocking effect between them. The optimum shell thickness is selected to be 6 cm by the laboratory test to meet the compressive strength requirement and maximize the environmental protection effect caused by steel slag consumption. The replacement rate of steel slag for traditional aggregate can reach 25% in a single block. The compressive strength of the new revetment block can reach 49.4 MPa, which definitely meets the compressive strength requirement of the bank revetment block. Both the experimental and simulated results proved the H-type gravity mutual-aid steel slag core concrete blocks have better interlocking effect than the traditional blocks and exhibit excellent overall stability.
Individual quality of the main cover block, t
Bulk density of water, kN/m3
Bulk density of artificial block or block stone, kN/m3
Designed wave height, m
Block or block face thickness, m
Armor block or stone layer number
Coefficient when a layer of stone is placed
Slope rate
Stability coefficient
Interlocking coefficient.
The data used to support the finding of this study are included within the article.
The authors declare that they have no conflicts of interest.
The study was supported by the National Natural Science Foundation of China (51908237), the fund of Yellow River Bureau of Shandong Province(1410019006), the Fundamental Research Funds of Shandong University (31560078614117), and the Natural Science Foundation of Shandong Province(ZR2019QEE017).