Keywords

1 Quotes

Earth and rock dams are widely used in China and are common building in water conservancy projects. However, due to long-term water storage and other reasons, over-saturated, making it a typical soft soil characteristics, resulting in poor foundation-bearing capacity, excessive foundation settlement and uneven settlement problems during construction. These problems have a great impact on the stability of earth and rock dams, and are prone to dam destabilization and damage, so the stability of earth and rock dam foundations is a key concern today.

Numerical simulation analysis has been widely used in engineering projects, such as slope, roadbed and dam construction. Yang Kun, Guo Qing et al.[1,2,3] conducted infiltration as well as stability analysis based on numerical simulation for various working conditions in the field. Zhang Songyun[4] explored the effect of flooding process on the stability of buildings using the embankment of Koster Power Station as an example. Li Sen, Zhang Zhaojun [5, 6] et al. Studied the effect of different parameters on dams based on ANSYS. Feng Wang7 Used the Kriging method to assess the slope safety of earth and rock dams with reliability as the index. Zhang Lijuan and Cheng Ping [8, 9] analyzed and evaluated the permeability and stability of earth-rock dams based on numerical analysis and limit equilibrium theory.

In this paper, we will use a water storage project as the background, and used Geostudio [10] finite element software to numerically simulate the overall slope of the earth and rock dam, to investigate the influence of the growth of the strength of the soft soil layer on the stability of the earth and rock dam under different consolidation coefficients, and to improve the overall stability of the earth and rock dam by adjusting the range of the backpressure platform of the earth and rock dam.

2 Numerical Analysis

2.1 Initial Parameter Selection

In this paper, a typical section is used for analysis, and the section diagram is shown in Fig. 1. According to the field test, where the average value of the consolidation coefficient of layers 2–3 is 1.46 × 10 cm−32/s and the average value of small value is 0.32 × 10 cm−32/s; the average value of the consolidation coefficient of layers 2–4 is 1.01 × 10−3cm2/s and the average value of small value is 0.22 × 10 cm−32/s. Considering that the measured consolidation coefficient in the field is much larger than the measured value in the room, in order to compare the effect of consolidation coefficient on consolidation degree, the consolidation coefficient was enlarged by 5 times, and 0.22 × 10 cm−32/s and 1.1 × 10−3cm2/s were used to calculate the strength growth of 2–3 and 2–4 soil layers, respectively, and the parameters of each soil layer are shown in Table 1.

Fig. 1
A cross-sectional illustration of an earth and rock dam. The 4 layers from the bottom are clay, mucky soil with flow and soft plastic, and loam. A wide peak at the top has 130.00 and 1 is to 3 marked on the on the rising slope, 140.40 on the summit, and 1 is to 2.75 on the downward slope.

Typical cross section of earth and rock dam

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Table 1 Physical and mechanical properties of each layer of soil
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The strength growth is calculated using the following equation.

$$\Delta {\tau }_{f}=\eta \mathrm{U}\Delta {\sigma }_{c}^{^{\prime}}\mathrm{tan}{\varphi }_{cq}$$

where. \(\eta \) is the discount factor, according to the building foundation treatment specification is generally 0.8 ~ 0.85, this paper is taken as 0.825. \(\mathrm{U}\) is the consolidation degree of the dam base soil. \(\Delta {\sigma }_{c}^{^{\prime}}\) is the effective consolidation pressure before shear. \({\varphi }_{cq}\) is the angle of internal friction measured by the consolidation fast shear test. The strength growth at different fill heights is shown in Table 2 and Table 3.

Table 2 Strength growth at different fill heights (Cv = 0.22 × 10–3 cm2 /s)
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Table 3 Strength growth at different filling heights (Cv = 1.1 × 10-3cm2/s)
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2.2 Numerical Analysis Results

In this paper, the SLOPE module in Geo-Studio software is used for analysis, and the hazardous starting arc location is obtained by Bishop method, and the selected model is a homogeneous model, and the hazardous slip surface is determined by specifying the import and export range. The results are shown in Table 4, and the change law of safety coefficient is shown in Fig. 2.

Table 4 Calculation results of safety factor (without reinforcement)
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Fig. 2
2 multiline graphs for C v values of 0.22 and 1.1 times 10 power negative 3 centimeters square per second plot safety factor versus fill depth. The lines for seaside and landside decrease parallelly in the graph on the left, and intersect at around 10 on the x-axis in the graph on the right.

Variation rule of safety factor

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The above calculation results show that the safety coefficient of the earth and rock dam decreases as the filling height rises, and the safety coefficient of the sea side and land side slope is still greater than 1 in a stable state when the filling height is 7 m. When the filling height reaches 12 m, the dam is already in the ultimate stable state and there is a possibility of instability, and the calculation results are in line with the actual situation. At the same time, with different consolidation factors, the safety factor of the dam slope with a consolidation factor Cv of 1.1 × 10−3cm2/s is generally higher than that with a consolidation factor Cv of 0.22 × 10−3cm2/s. This paper concludes that without considering the occurrence of large lateral displacements, a larger consolidation factor will shorten the consolidation time of the foundation soil, increase the average consolidation degree of the foundation soil, and significantly increase the strength of the soft soil layer, thus This paper concludes that a larger consolidation coefficient will shorten the consolidation time, increase the average consolidation of the foundation soil, and increase the strength of the soft soil layer, thus improving the bearing capacity of the foundation and increasing the overall safety factor of the dam slope.

2.3 Program Adjustment

According to the above analysis, the dam body is in the ultimate stable state, the safety factor does not meet the code requirements, and there is a possibility of instability. For this reason, it is necessary to consider adjusting the reinforcement scheme and calculating the length of the additional counterpressure platform required on the original foundation according to the two different soil consolidation factors to make it meet the code requirements. The calculation results of the safety factor are shown in Table 5, and the law of change of the safety factor is shown in Fig. 3.

Table 5 Calculation results of safety factor (with reinforcement)
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Fig. 3
2 multiline graphs for C v values of 0.22 and 1.1 times 10 power negative 3 centimeters square per second plot safety factor versus fill depth. The line for landside decreases below seaside in the graph on the left, while itis above seaside in the graph on the right.

Change law of safety factor after extension

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According to the above calculation results, when the consolidation factor is 0.22 × 10–3 cm2 /s, the length of the additional sea-side ballast platform is 43.3 m and the height is 5 m. The length of the additional land-side ballast is 40.8 m and the height of the counter-pressure is 4.4 m. When the consolidation factor is 1.1 × 10–3 cm2 /s, the length of the additional sea-side ballast is 37.4 m and the height is 5 m. The length of the additional land-side ballast is 35 m and the height is 4.4 m. From the results, it can be seen that the overall slope safety factor is significantly improved by the additional counterpressure platform.

3 Conclusions

  1. (1)

    The pore water discharged is mainly from the soft soil layer due to the poor permeability and high water content of the soil in the soft soil layer, so the consolidation of the soft soil layer is the main reason for the consolidation of the foundation soil. Therefore, the selection of the consolidation coefficient of soft soil layer in the numerical simulation analysis will affect the bearing capacity of the consolidated foundation to a certain extent.

  2. (2)

    According to the comparison of the above calculation results, the foundation strength increases significantly in the calculation process for a larger consolidation coefficient. When the soil consolidation coefficient is larger, the consolidation effect is more obvious, and the safety factor of earth-rock dam is significantly improved. Therefore, it is considered in this paper that when the consolidation coefficient is set as 1.1 × 10-3cm2/s, it is more conducive to the overall stability of earth-rock dam.

  3. (3)

    The overall stability of an earth and rock dam is not only related to the bearing capacity of the foundation, but also to the structural dimensions of the dam itself. The calculation results show that with a significant increase in the bearing capacity of the foundation, the increasing fill height will still reduce the overall safety factor to less than 1. In addition, the ultimate state of stability occurs at the filling height of 12 m. Therefore, additional counter-pressure platforms need to be installed on the seaside and landside. The results show that the additional counter-pressure platform has significantly improved the overall slope safety factor and significantly improved the overall stability of the earth and rock dam.