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Stability Analysis of Geocell Reinforced Embankment Based on Strength Reduction Method

Abstract: In the analysis of reinforced composite embankment, it is difficult to visually see the contribution of the parameters of the reinforcement to the stability of the whole project. In order to better understand the effect of wholesale HDPE geocell reinforcement, the design uses finite element analysis software combined with strength reduction method (strength reduction method), SRM) numerical calculation of a secondary road embankment. Firstly, the SRM calculation is performed on the unreinforced embankment of 3D modeling, and then the limit equilibrium method is used to verify. The conclusions obtained by the two methods are consistent. This indicates that the 3D embankment slope modeling analysis method closer to the actual situation is suitable for use in complex reinforcement conditions. Then, this method is used to analyze the stability of the embankment after laying the high quality HDPE geocell, and the law between the material parameter factors and the slope safety factor is explored by changing the welding distance, depth, height and laying a layer of the HDPE geocell manufacturers. The results show that the low price HDPE geocell material can play an important role in improving the overall stability of the embankment. The reinforcement effect of the HDPE geocell manufacturers with smaller welding pitch and higher height is more obvious. When the multi-layered embankment is destroyed, it will form more The rupture surface of the arc.

Keywords: high quality HDPE geocell; reinforced embankment; stability analysis; strength reduction method; safety factor

With the rise of new geotechnical reinforcement materials, HDPE geocell for sale has been rapidly applied as a flexible structural layer in embankment engineering. This honeycomb-type high-density three-dimensional reinforced material is often used in reinforced retaining wall engineering or laying on the trackbed and the base of the road to achieving the purpose of embankment reinforcement. El-Naggar et al. conducted a series of full-scale tests on the reinforced embankment. And numerical simulation, analysis of the failure mechanism of the reinforced embankment. The results show that reinforcement can improve the filling height of the embankment and effectively improve the plastic zone in the soil. Through a series of model tests, Zhou Jian et al. confirmed that the reinforcement form and arrangement position are the decisive factors affecting the performance of the reinforced foundation. Dash et al. studied the interaction between HDPE geocell manufacturers and gravel by direct shear test, indicating that the high quality HDPE geocell can increase the bite force and friction between the gravel. Zheng Chaoyi et al. carried out several sets of model tests on geogrid-reinforced sand foundations with pure sand foundation and different cell spacing, which proved that wholesale HDPE geocell reinforcement can significantly improve foundation bearing capacity and reduce foundation settlement. Based on the strength reduction method (SRM), Gao Wenhua used FLAC analysis software to compare the lateral displacement and plastic zone of the reinforced and unreinforced slopes under the strip load, and analyzed the factors affecting the slope stability. Zhang Taotao and others based on the strength reduction method, using ABAQUS software to simulate the reinforced foundation. The results show that the H-V (Horizontal-Vertical) reinforcement can greatly improve the bearing capacity of the foundation, and the failure mode of the foundation changes to some extent due to the presence of the reinforcement.

In this study, the ABAQUS software was used to model the two-level highway embankment of the HDPE geocell for sale, and the same boundary constraint and applied load were applied. The safety factor calculated by the post-processing function was used to judge the different grid weld height and height. The influence of the buried depth and the number of layers on the overall bearing capacity and stability of the embankment.

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1. Destruction criteria and verification

1.1 damage judgment criteria
Choosing different slope instability judgment criteria will directly affect the accuracy of slope stability analysis with SRM. At present, there are three main methods for judging slope instability: 1 the value does not converge, that is, within the set analysis step limit after multiple reduction operations, the model operation mid-section does not converge; 2 displacement inflection point, that is, the slope The displacement or strain of a certain feature point suddenly becomes larger; 3 the plastic zone penetrates, that is, the plastic zone starts to communicate with the slope top region from the slope foot region. Starting from the reduction of the model parameters, the cohesive force and the friction angle of the embankment soil become smaller at the same time as the number of operation times of the model increases. The entire damage area gradually expands outward, the sliding surface gradually forms, and the self-stability of the soil body decreases until damage. The area is connected, the embankment gradually loses its bearing capacity, and the simulation process is completed.

1.2 SRM example verification
Considering the symmetry of the embankment along the longitudinal centerline and reducing the amount of calculation and running time, only half of the embankment is taken for analysis, and the longitudinal direction of the slope is 1 m wide. The embankment is simplified to the plane strain problem and a three-dimensional model is established: the slope height H=8. 4m, the soil layer size below the slope is B=2. 4m, L=16. 8m, and the slope height ratio α=1:1. 5. The yield criterion uses the M-C (Mohr-Coulomb) criterion. In the boundary constraint, the displacement constraint in the x-direction is set on the front and rear sides of the slope, the displacement constraint in the z-direction is set on the left and right sides, and the displacement constraint in the x, y, and z directions is set in the bottom. The soil body adopts an eight-node linear hexahedron reduction unit, and the mesh division adopts a sweeping method, and the soil model has a total of 906 units. The wholesale HDPE geocell is simulated by a four-node curved shell reduction unit embedded in the embankment soil in an embedded constrained manner. Figure 1 is a schematic diagram of a model of a non-reinforced embankment after meshing.

According to the relevant specification [14], the numerical model is influenced by gravity and traffic load, and the vertex of the upper right corner of the top surface of the embankment is selected as the feature point. The strength reduction factor Fr takes the value of 0. 50 ∼ 2. 00, and the increase is 0.25. It can be seen from Fig. 2 that if the sudden inflection point of the displacement occurs, the safety factor Fs of the embankment is obtained. If the failure state is determined according to the convergence of the finite element numerical calculation results, that is, if the given number of iterations and the convergence criterion are still not converged, the embankment is considered to be unstable and the model is obtained by the numerical non-convergence criterion to obtain the safety factor of the embankment Fs= 0. 87.

The results of the ABAQUS treatment shown in Fig. 3 show that when Fr = 0.50, the internal friction angle and cohesion of the soil are the set maximum initial values, and only the plasticity appears at the slope area. Zone (see Figure 3(a), where PEMAG is the plastic strain, ie plastic strain magnitude); when Fr = 0.87, the plastic zone gradually extends to the upper part of the embankment, forming a complete connected region (see Figure 3(b) ). At this time, if it is judged by the plastic zone penetration low price HDPE geocell, Fs = 0.87, and if it is calculated by the limit balance method, Fs = 0.84. In summary, the conclusions obtained by the two methods are consistent, indicating that the 3D embankment slope modeling analysis method closer to the actual situation is suitable for use in complex reinforced conditions.

2. Analysis of numerical results of reinforced embankments

In this study, 14 different reinforced forms of embankment conditions were analyzed (see Table 1). The parameters of the simulated materials are shown in Table 2.
Figure 4 is a schematic view of the structure of a reinforced embankment, where q represents the top surface load. The non-reinforced type of working condition 1 is used as a comparison with the working conditions of multiple sets of reinforced embankments. The working condition 2∼4 compares the influence of different grid welding distances on the overall stability of the embankment. Working conditions 5∼7 The relationship between the buried depth of the cell and the bearing capacity of the embankment is studied. The working conditions 8∼11 analyze the contribution of different cell heights to the embankment bearing capacity. Working conditions 12∼14 observe the corresponding embankment by changing the total number of layers. Variety.

2.1 Influence of grid welding distance on embankment stability
In the case where the total length and total width of the high quality HDPE geocell remain unchanged, three wholesale HDPE geocell of different weld distances (see Figure 5) are embedded in the embankment. The boundary constraint of the reinforced model and the applied load are exactly the same as those of the unreinforced embankment. The selected cell thickness z=1mm, buried depth u=1. 2m, height h=5cm.

Fig. 6 is a diagram showing the relationship between the vertical displacement of the apex of the slope and Fr when the HDPE geocell for sale (working condition 2) with the welding pitch d = 30 cm is embedded in the embankment. According to the displacement criterion, the Fs of the single-layer reinforced embankment is 0.95, which is significantly higher than that of the non-reinforced case, Fs=0.85, indicating that the embedding of the cell significantly improves the strength of the embankment soil. From the relationship between the cell gap and Fs shown in Fig. 7, it can be seen that when the grid weld distance becomes larger, that is, when the grid becomes wider, the Fs of the embankment tends to decrease; when the grid weld distanced = 15 cm (condition 4) At the time of the overall instability of the embankment, the soil parameters are reduced to a minimum, that is, the stability is higher than d=20 and 30 cm.

2.2 Influence of cell depth on slope stability
Working conditions 2, 5, 6, and 7 simulate the effects of changing the buried depth of the cell on the stability of the embankment. Since the Fr under different working conditions obtained by the displacement inflection point is roughly consistent, it cannot be judged more intuitively, so it is measured by the Fr corresponding to the non-convergence of the model operation, and the corresponding relationship between the cell depth and the Fs is obtained low price HDPE geocell. Shown. It can be seen that the two are not linearly corresponding. When the buried depth is increased from 1.2m to 2.4m, the overall stability of the slope is decreased. Combined with the vertical displacement variation analysis shown in Fig. 9, the closer the cell depth is to the top surface of the embankment, the more effectively the slope settlement can be controlled. This is because the embankment is affected by the driving load, and the shallower geogrid compartment transmits and disperses the load transmitted by the top surface earlier in the soil reduction calculation. Due to the three-dimensional nature of the cell itself, the lateral and vertical structural systems can limit the transfer of the load further below the stiffened layer, weakening the soil stress below the stiffened layer, thereby better limiting the overall deformation of the soil. Therefore, when designing the buried depth of the cell, the stability of the entire embankment and the requirements of the local maximum vertical displacement should be considered comprehensively.

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2.3 The influence of the height of the cell on the stability of the slope
According to the analysis of the comprehensive working conditions 2,8∼11, the safety factor of the reinforced slope does not show a linear relationship with the height of the cell (see Figure 10). When the height of the cell is changed from h=5.0 cm to 7. 5 cm, the Fs of the reinforced slope decreases; when the cell height continues to increase to h=10. 0 cm, Fs slightly increases; when the cell height increases to When h=15. 0cm, Fs is obviously increased; when h=20. 0cm, Fs is the highest. This shows that in this study, the geogrid reinforcement with the height h=20. 0cm is the best.

The distribution of the plastic zone of the reinforced slope is shown in Fig. 11, where SNEG is the negative normal plane of the shell or membrane. The plastic zone is up from the slope of the foot and develops along the contact surface and the ribs, and begins to spread laterally at the lower part of the rib and the slope of the embankment. The rupture surface is no longer similar to a smooth arc but is constantly deflected toward the slope in the direction of the corresponding reinforced depth, forming a rupture surface similar to a multi-arc. Multi-layer reinforcement expands the overall range of the plastic zone. As can be seen from Fig. 12, the cohesive force and the friction angle of the multi-layer reinforced embankment soil are smaller when the embankment loses the load-carrying capacity as compared with the case of the single-layer reinforcement. This shows that under normal conditions, appropriately increasing the number of layers of the cells helps to improve the overall stability of the embankment. However, the increase in the number of reinforcement layers will increase the construction cost of the project. Therefore, in practical applications, the needs of all parties should be considered comprehensively, and then the optimal reinforcement scheme should be drawn up.

3. Conclusion

(1) Under the same conditions of the buried depth of the HDPE geocell manufacturers, the choice of HDPE geocell for sale with dense mesh and small welding distance can improve the overall stability of the embankment.

(2) The reinforcement of the low price HDPE geocell can greatly improve the bearing capacity of the embankment. Under the condition of single layer reinforcement, as the reinforcement position gradually moves away from the base, the effect of improving the stability of the embankment is gradually weakened, and the effect of controlling the settlement of the embankment is enhanced. Under other conditions, the higher the cell height, the higher the safety factor of the reinforced embankment, but it is not linear, so the economic applicability should be considered comprehensively when selecting the cell parameters.

(3) The addition of low price HDPE geocell changed the failure mode of the embankment. Different from the unreinforced embankment, a smooth arc-shaped sliding surface is formed. The multi-layered reinforced embankment is developed along the contact surface and the ribs and lateral diffusion begins at the lower part of the rib and the embankment slope. And in the corresponding reinforced depth direction, the slope is continuously deflected to form a rupture surface similar to multiple arc segments.

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