The stability of high-fill slope has always been a significant technical issue affecting the quality and safety of engineering projects. How to accurately analyze the stability of high-fill slopes and find corresponding reinforcement methods has become a difficult challenge in slope engineering. This paper, through practical examples, analyzes the stability of high-fill slopes and explores reasonable countermeasures to prevent slope instability accidents.
High fill refers to the construction of an area using soil, cement, gravel, or other materials in layers or by compaction to form a design that is higher than the surrounding buildings. A high fill slope is a slope that is raised using the high fill design method. Due to the prominent location of the high fill slope, its stability is not only crucial for the stability of the slope itself but also poses a risk to surrounding buildings and people in the event of collapses or other incidents, thus the stability of the high fill slope cannot be overlooked. In early 2012, I received the design task for the "Wuzhou 220kV Hongling Substation" (now renamed to Jade Substation), responsible for the design of construction drawings for the 'three connections and one leveling' of the project. The 220kV Hongling Substation is the first 3C green intelligent substation in Guangxi. The selected site for this project is located west-south of Wuzhou Railway Station, an area planned to be developed into a logistics park, with the site adjacent to the city's planned road. The southern part of the 220kV Hongling Substation site is a fill section, with the fill soil slope at Hongling Station reaching a maximum height of 26 meters, according to the site leveling elevation (56m-55.75m). Therefore, during the initial design phase of the project, two options were considered: natural slope and Tansa ecological slope. The Tansa ecological slope option saves land, and due to the reinforcement treatment, the layered compaction can effectively control uneven settlement. The amount of backfill is small, requiring less purchased soil, and effectively reduces the costs associated with transporting fill material. After completion, it can blend well with the surrounding environment. Compared to the natural slope option, the natural slope requires an additional 6 acres of land, 6.7 acres of temporary land, an extra 34,000 cubic meters of backfill, and 1,860 cubic meters more of retaining walls. The total project cost for the natural slope option is 1.4 million more than the Tansa option.
Research Status of Analytical Methods and Reinforcement Techniques for High-filled Slope Stability
1.1 Current Research Status of High Filling Slope Stability Analysis Method
Landslides occur frequently in nature and have garnered widespread attention. Initially, people mainly employed qualitative analysis methods to address high embankment slopes, which failed to yield relevant data on their stability, only providing a general determination of whether they were stable. As research and exploration into the stability of high embankment slopes deepened, quantitative analysis methods began to be used, establishing models from various perspectives to study slope stability, thereby providing data support for the results on the stability of high embankment slopes. To date, the analysis of high embankment slope stability primarily involves two methods: qualitative analysis and quantitative analysis. Depending on the type of slope, qualitative analysis can be divided into methods such as natural historical analysis, nomogram method, stereographic projection, engineering analogy, expert systems, and case-based reasoning. Table 1 lists the principles and development trends of these qualitative analysis methods. Quantitative analysis includes deterministic analysis and probabilistic analysis; deterministic analysis encompasses limit equilibrium methods and numerical analysis, with limit equilibrium methods including the Swedish method, Bishop method, Sarma method, Spencer method, Morgenstern-Price method, and transfer coefficient method, while numerical analysis includes finite element method (FEM), finite difference method (FDM), isogeometric element method (IDEM), and numerical manifold method (NMM). Probabilistic analysis includes reliability evaluation methods, artificial neural network analysis (ANN), grey system evaluation, fuzzy evaluation, genetic algorithms, and comprehensive methods.
1.2 Current Status of Research on High Filling Slope Reinforcement Technology
The hazards caused by poor slope stability, such as high fill slope landslides and collapses, can result in economic losses and even irreversible catastrophic disasters. Therefore, researching reinforcement techniques for high fill slope is of significant practical and social importance. As engineers address slopes with varying stability, numerous reinforcement techniques for high fill slopes have been developed to date. The reinforcement techniques for high fill slopes mainly include gravity retaining walls, anti-slide piles, anchored retaining walls with wall shoes, cantilever retaining walls, lattice reinforcement, shotcrete and anchor mesh support, slope drainage methods, grouting reinforcement, suspended retaining walls, and other reinforcement methods. With the variety of existing reinforcement techniques for high fill slopes, it is essential to select the appropriate technique for slopes with different stability levels, rather than making盲目 choices. Additionally, we can innovate or improve existing slope reinforcement techniques for different slopes, making every effort to eliminate potential safety hazards to ensure the safety of humans and property.
2. Stability Analysis of High Filling Slopes
For the project concerning the 220kV Hongling Substation in Wuzhou City with high embankment slopes, we employed a combined approach of quantitative and qualitative analysis to assess its stability: (1) Factors affecting the stability of high embankment slopes; This project conducted qualitative analysis on the geological, hydrological, and slope formation factors influencing the stability of the high embankment slopes at the 220kV Hongling Substation in Wuzhou City, and quantitative analysis on factors such as slope height, area, and economic benefits affecting slope stability. (2) Sensitivity analysis of factors affecting the stability of high embankment slopes; The grey relational degree method is used to study the similarity of changes in the curves of related factors, such as trend, direction, magnitude, and speed. The more similar, the higher the correlation degree, and thus the greater the impact; conversely, the smaller the impact. In this project, the grey relational degree method was used to conduct a primary analysis of the factors identified as affecting slope stability, determining several key factors with relatively high influence. (3) Selection of an appropriate analysis method for high embankment slope stability; For the influencing factors of the high embankment slopes at the 220kV Hongling Substation in Wuzhou City, the qualitative analysis method and the quantitative analysis method, specifically the limit equilibrium method, were selected. (4) Establishing an appropriate model; Determine the boundary conditions, cross-sectional shape, geological attribute data, and bearing capacity of the slope model to establish an appropriate model. (5) Determining the treatment method; Based on the relevant data obtained from the model, determine the treatment of soil and reinforcement materials such as rebar on the contact surface. The high embankment slope at the 220kV Hongling Substation in Wuzhou City adopted the natural slope method, establishing the model first, then filling in soil and other materials for the units, repeating this process until completion.
3. Countermeasures for high-fill slope treatment
If an accident occurs on a high embankment slope due to instability, the consequences may even be unexpected. Once stability issues are identified with high embankment slopes, appropriate remedial measures should be taken to eliminate avoidable safety hazards: 1. Identify alternative solutions to address the stability of high embankment slopes based on environmental and structural factors affecting slope stability. This is a multi-attribute decision-making approach, where solutions can be selected based on the weight and priority of influencing factors. 2. Determine the most optimal choice from the alternatives based on the actual situation. Current remedial measures for high embankment slopes include slope reduction, retaining wall projects, anchoring projects, anti-slide pile projects, slope protection projects, and drainage projects. These can be implemented through a combination of multiple approaches as needed. 3. Conduct an entropy-weighted multi-objective optimization selection for the remedial measures of high embankment slopes from aspects such as feasibility, environmental impact, construction timeline, safety and reliability, economic benefits, and ease of operation, to determine the final remedial measures. 4. Design and implement the remedial measures for the high embankment slope. The Wuzhou 220kV Hongling Substation site is planned to be developed into a logistics park, and the nearby area has been listed in the 2013 Changzhou District land acquisition and relocation plan. It is hoped that the land acquisition will be completed by the end of the year. After coordination between the owner and the Wuzhou City Operation and Maintenance Bureau, the Wuzhou Commercial Trade Logistics Park Management Committee agreed to cooperate with the construction of this project. The excess soil from the excavation of municipal roads near the station site will be backfilled into the ravines near the substation, making the substation further away from the high slope to save on the cost of slope treatment. Therefore, the initial design intake of the station area soil is calculated at 40 meters from the top of the backfilled slope, with a backfill slope ratio of 1:1.5. Three walkways are set up in the middle, each 2.5 meters wide. Both the walkways and the outer edge of the slope are equipped with water-diversion channels. The slope surface is seeded with grass to prevent soil and water erosion. This plan has been approved, and the construction drawings were officially published in August 2012. The slope engineering is currently under construction (see attached figure).
4. Summary
The stability issue of high-filled embankment slopes may seem like just an engineering problem, but if not properly addressed, it could lead to major accidents and significant losses. We should pay close attention to it. For different high-filled embankment slopes, we can choose one or more methods from a variety of stability analysis techniques, and then determine the plan by combining qualitative and quantitative analysis methods based on feasibility, geological hydrology, unit section, and economic benefits, to enhance the stability of the high-filled embankment slopes to the maximum extent possible.
