Anti-slide Pile Research Articles

Slope Stability and Effectiveness of Treatment Measures during Earthquake

Slopes are prone to instability during earthquakes, which will cause geological disasters such as landslides and pose a great threat to people’s lives and property. Therefore, it is necessary to analyze the stability of slopes and the effectiveness of treatment measures during earthquakes. In this study, an actual slope in the creeping slide stage was selected and located in an area where earthquakes occur frequently. Once the slope experiences instability, it will produce great damage. Therefore, a finite difference program, Fast Lagrangian Analysis of Continua in Two Dimensions (FLAC2D), was employed in the numerical simulation to explore the stability of the slope before and after treatment under earthquake action. Different from previous studies, this study explores the effectiveness of various treatment measures on slope stability during earthquake. The computed results show that the stability of the slope is greatly influenced by earthquakes, and the slope displacement under seismic conditions is far larger than that under natural conditions. Three treatment measures, including excavation, anti-slide piles, and anchor cables, can significantly reduce slope displacement and the internal force on anti-slide piles, and improve the stability of a slope during an earthquake. This will provide a valuable reference for the strengthening strategies of unstable slopes. The analysis technique as well as the derived insights are of significance for slope stability and the effectiveness of treatment measures.

Stability analysis of a water-rich slope stabilized by a novel upper-hollow drainage anti-slide pile

Stability analysis of a water-rich slope stabilized by a novel upper-hollow drainage anti-slide pile

Working performance and mechanism of a novel upper-hollow drainage anti-slide pile under the effect of reservoir water fluctuation and precipitation

Working performance and mechanism of a novel upper-hollow drainage anti-slide pile under the effect of reservoir water fluctuation and precipitation

Anti-slide pile structure development: New design concept and novel structure

The anti-slide pile is one of the most used measures in landslide control globally. Following its application, various structures have been developed. In this paper, we analyze the anti-slide pile structure development process and extract two development paths. One path is aimed at improving the applicability. The second path starts from an in-depth study of pile–soil interactions. However, these two paths share a single design concept: The anti-slide pile provides direct resistance to maintain landslide stability, that is, the anti-slide pile and the landslide body are thought to be confrontational sides. We here propose developing and utilizing the landslide body in anti-slide pile design. Accordingly, the confrontation relationship between the anti-slide pile and the landslide body can be changed while shifting away from the view that the landslide body is only a hazard. On this basis, we also design a novel structure: An arm-stretching-type anti-slide pile. The simulation verification results show that this novel structure works well in realizing the proposed design concept. Compared with the commonly used wholly buried pile, the safety factor of the landslide controlled by the novel structure is improved by 43.56%. This study promotes the design concept of anti-slide pile developing from the existing slide–resist single mode to the slide–self-stabilize–resist compound mode.

Study on the Evolution Law of Internal Force and Deformation and Optimized Calculation Method for Internal Force of Cantilever Anti-Slide Pile under Trapezoidal Thrust Load

The evolution law of internal force and deformation of an anti-slide pile affects the slope stability and prevention design in a significant way. Based on the similarity theory, a test system for the bearing characteristics of a cantilever anti-slide pile was constructed, and the physical model test for the bearing characteristics of a cantilever anti-slide pile under trapezoidal thrust load was carried out. The distribution laws of internal force and deformation of a cantilever anti-slide pile were revealed, and the optimized calculation method for internal force of a cantilever anti-slide pile was proposed by taking the elastoplastic characteristics of steel bars and concrete into consideration. Furthermore, a numerical model was employed to conduct a parametric analysis of a cantilever anti-slide pile. The results show that the whole process of stress and deformation of a cantilever anti-slide pile can be classified as the uncracked stage, the cracks emerging and developing stage, and the steel bars yielding–failing stage. In the uncracked stage, the bending moment of the cantilever anti-slide pile calculated by the traditional method is smaller than that calculated by the optimized calculation method established in this paper. The traditional calculation method is no longer applicable in the stage of cracks emerging and developing. The lateral displacement and bending moment of the cantilever anti-slide pile are negatively and positively correlated with the strength of the pile material, respectively, and the influence of the deterioration of steel bars’ strength on the ultimate bearing performance of the anti-slide pile is more obvious than that of the deterioration of concrete strength. The bearing capacity of the anti-slide pile could not be significantly improved by increasing the length of the anchored section when the strength of the rock stratum embedded in anchored section was large enough. As the thrust load behind the pile increased, the difference of the bearing performances of the cantilever anti-slide pile under the uniform load and trapezoidal load increased gradually. The research results can provide guidance for the evaluation of the service performance of the cantilever anti-slide pile and the slope stability.

Deformation characteristics and reactivation mechanism of an old landslide induced by combined action of excavation and heavy rainfall

The reactivation mechanism of old landslides has been extensively studied from building load, erosion of the slope toe, heavy rainfall, and slope cutting for existing research. However, previous research on the reactivation of old landslides pays little attention to the combined action of engineering disturbance and heavy rainfall is rarely studied. This paper describes an old landslide in Wushan County, Chongqing, China, that was reactivated in August 2019 due to engineering disturbance and heavy rainfall. The deformation of the old landslide was first observed in 2007 and 2008, resulting from excavation and rainfall, respectively, and remained stable for about 11 years after treatment. In August 2019, the landslide was reactivated by slope cutting and damaged anti-sliding piles at the toe, and entered a state of imminent sliding due to the concentrated heavy rainfall events that occurred from October 4 to 22, 2019. In order to reveal the deformation features and reactivation mechanism of the landslide, field investigations, drilling activities and monitoring were performed. The results showed that tectonic effects and the stratigraphic lithology were the main reasons for the formation of the old Dashuitian landslide. The cut slope and damaged anti-sliding piles at the toe of the landslide provided the sliding space and reduced the anti-sliding force, and therefore resulted in the reactivation of the landslide. Continuous intense rainfall increased the weight of the landslide, decreased the mechanical properties and increased the pore water pressure of the weak interlayer, which accelerated the deformation rate. Therefore, 1.5 million m3 of rock and soil masses slid along the weak interlayer under the action of gravity, threatening the safety of Wuliu Road, Ring Road, National Road G42 and the Wu-Da Expressway. Our research provides a theoretical basis for reducing the hazard of similar engineering projects involving slopes.

Causes of Landslides in Road Embankment with Retaining Wall and Pile Foundation: A Case Study of National Road Project in Porong-Sidoarjo, Indonesia

This study was conducted to determine the cause of landslides in the toll road embankment of the national road project in the Porong-Sidoarjo area. The landslide was observed only on the north side of the embankment, with a maximum height of 7.8 meters from the subgrade despite the reinforcement with a retaining wall and pile foundation. The land shift and subsidence on the Northside led to a decline in the embankment elevation and the displacement to a maximum depth of 3.50 m. Back analysis through the limit equilibrium method was used to determine the strength of the existing reinforcement against the landslide. The results showed that the heavy rain was indeed one of the causes of landslides in the location, while the main cause was the depth of soft soil, much deeper than those in the surrounding locations. This is why a severe landslide was recorded on one side of the embankment. Moreover, the existing anti-slide pile reinforcement was discovered not to be sufficient due to its shallower length compared to the area of the landslide, and this was associated with the absence of overall stability analysis in this design. The findings showed that it is necessary to conduct a comparative study between the overall stability and the active and passive forces analyses for the soil to produce the safest design required to avoid landslides.

Research on Mechanical Characteristics of Slope Reinforcement by Spatial Arc Crown Beam Composite Supporting Structure

To effectively optimize the mechanical behavior of a traditional anti-slide pile and reduce environmental destruction, a new method for slope reinforcement by a spatial arc crown beam composite supporting structure was proposed. First, a numerical model was validated through lab-scale model test data obtained herein, and then a full-scale numerical model was created for an in-depth understanding of the distribution regularity of displacement along the pile, the soil pressure, the crown beam stiffness, and so on. The results demonstrated that: (1) The spatial arc crown beam is simplified to a two-hinged arch, and the maximum value of the bending moment in the arc crown beam is about one-third of the straight crown beam through theoretical calculation. (2) The spatial arc crown beam redistributes the load sharing among different piles, and the extreme bending moment of other piles varies within 10% along the downhill direction except for the piles at the slope foot. (3) Bending moments are close to zero at the pile end, and the anti-slide pile can be simplified as a vertical beam with one end fixed and the other end hinged. (4) The axial force in the spatial arc crown beam is always presented as pressure, so the crown beam can make full utilization of the compression resistance of concrete. (5) The distribution characteristic of soil pressure in front of the pile at the arch foot is different from that in other positions, and the stable soil at the slope foot provides greater soil resistance for anti-piles. (6) As the crown beam stiffness is above five times the reference value, the axial force of the crown beam tends to be stable, and as the crown beam stiffness increases continually, the maximum value of My is −1013.13 kN·m, and the constraining effect of the crown beam is gradually weakened.

Performance and application of a novel drainage anti-slide pile on accumulation landslide with a chair-like deposit-bedrock interface in the Three Gorges Reservoir area, China

More than 5000 landslides with different kinds of deposit-bedrock interface morphologies developed in Three Gorges Reservoir area (TGR) after its first impoundment. In this paper, the Outang landslide, a typical accumulation landslide with a chair-like deposit-bedrock interface (CLDBI) located in the Three Gorges Reservoir area (TGR) of China, is taken as an example. More than 6 years of multi-technique monitoring data shows that cumulative displacements over time present a step-like pattern, characterized by the gradual increasing of total displacements with altitude. The factors affecting the slope movement at the upper and the lower parts of the landslide are rainfall and reservoir water, separately. In this work a novel drainage anti-slide pile (DASP) is proposed, and the drainage performance of this DASP is verified and studied through physical model test. To this aim, three different environmental scenarios have been simulated by ABAQUS to evaluate the reinforcement effect induced on the landslide when using the proposed DASP. The model revealed that the optimum solution for the stabilization of the slope consists in the construction of single-row DASPs in the upper part of the landslide. These results provide practical experience and enlightenment on common measures to landslide prevent in TGR using the DASPs.

Failure Process Analysis of Landslide Triggered by Rainfall at Volcanic Area: Fangshan Landslide Case Study

The Fangshan landslide was a rainfall-induced landslide that occurred in a volcanic area in the Fangshan scenic spot, Nanjing, Jiangsu, China. On 25 October 2016, after approximately 10 days of continuous rainfall, a shallow landslide rapidly developed, which triggered slow movement of deep mudstone rock. According to the characteristics of the landslide body, measures such as anti-slide piles, anchor cables and drainage were used to reinforce the landslide. Active drainage measures included arranging plant growth zones at the trailing edge of the landslide, and passive drainage measures included arranging pumping wells at the trailing edge of the landslide. It is worth emphasizing that the Fangshan landslide was the first example of a landslide in Jiangsu Province, China that was treated by actively lowering the water pressure. After landslide treatment from 16 May 2017 to 21 January 2018, the Fangshan landslide tended to be stable. However, the stable landslide was reactivated by the rise in groundwater level caused by rainfall and pumping well damage and underwent accelerated downward sliding in July 2020. The Fangshan landslide has caused great damage to the roads and buildings of Fangshan scenic spot, with a direct loss of RMB 6 million and an indirect loss of RMB 95 million. This article discusses the development process of the shallow soil landslide and the underlying deep mudstone rock landslide. The influence of groundwater level variation on the deformation of the shallow soil landslide and deep mudstone rock landslide of the Fangshan landslide are also discussed.

Improved Calculation Method for the Internal Force of h-Type Prestressed Anchor Cable Antislide Piles

An h-type prestressed anchor cable antislide pile is suggested for dealing with large-scale landslide disasters. At present, the internal force calculation of h-type antislide piles includes a great deal of cumbersome and complex calculus and graph multiplication processes, and the research on the action mechanism of prestressed anchor cables is insufficient. To simplify the calculation process, this study proposes an improved calculation method for the internal force and displacement of the h-type prestressed anchor cable antislide pile. A method to simplify the h-type antislide pile into a plane rigid frame calculation model is proposed, and the action of the anchor cable is added to the pile structure in the form of an unchanged tension. Then, the pile is divided into a loaded section and an anchorage section with the sliding surface as the boundary. Based on the engineering case, the results of internal force and displacement obtained through an improved calculation method, numerical simulation method, and graph multiplication method are compared and analyzed to verify the accuracy and applicability of the improved method. Finally, based on the improved calculation method, the internal force and displacement characteristics of piles are analyzed and compared under different support modes, including h-type pile, h-type with single-row anchor cable, and h-type with double-row anchor cables, and the support characteristics of the h-type prestressed anchor cable antislide pile are investigated. The results show that the tension of the anchor cable can effectively reduce the bending moment and displacement of piles. Compared with the h-type antislide pile, adding two prestressed anchor cables can reduce the maximum positive and negative bending moments of the front and rear piles by 14.8%, 14.5%, 9.4%, and 8.7%, respectively, and reduce the horizontal displacement of the top of the rear pile by 21.7%.

Effects of overconsolidation on the reactivated residual strength of remoulded deep-seated sliding zone soil in the Three Gorges Reservoir Region, China

Due to the landslide-prone geological conditions, many landslides have occurred in the Three Gorges Reservoir Region (TGRR), most of which are slow-moving ancient landslides characterized by preexisting shear surfaces. In this study, with the purpose of making full use of reactivated residual strength to prevent and treat the slow-moving landslides, such as designing anti-slide piles, the Huangtupo landslide as a typical reactivated ancient landslide in the TGRR was selected to study the overconsolidation (OCR) effect on the reactivated residual strength of deep-seated sliding zone soil by conducting a series of laboratory ring shear tests. It was found that after a short rest of one day, the reactivated residual strength increased with the increase of OCR under a given normal effective stress, but it was lost after a small shear displacement. The overconsolidation effect on reactivated residual strength at a lower stress was more prominent than that at a higher stress. Very coarse sand with a size of 1–2 mm inside the remoulded deep-seated sliding zone soil sample exerts direct control on the reactivated residual strength, and it significantly influences the overconsolidation effect on reactivated residual strength. The results could provide a reliable scientific basis for improving the stability analysis and reinforcement measures of the slow-moving landslides in the TGRR, as well as can be applied to similar slow-moving landslides in other areas.

Mechanical Characteristics of the Combination System of Medium-Diameter Anti-Slide Piles and Tunnel-Under-Landslide Loading

Landslides have significant impacts on the stress and deformation of existing tunnel that can damage the existing tunnel lining structures and thus affect normal traffic operation. It is of importance to study the mechanical mechanism of tunnel–landslide support systems. However, there are few studies on the mechanical mechanism of existing tunnels in landslide areas. The combination of medium-diameter anti-slide piles (300 mm ≤ D ≤ 800 mm) overcomes the disadvantages of the complex construction process and higher site requirements for large-diameter anti-slide piles (D > 800 mm) and the disadvantage of lower support with micro anti-slide piles (D < 300 mm). In this study, considering the influence of landslides on existing tunnel deformation, a new type of medium-diameter anti-slide pile reinforcement system for existing tunnels is proposed based on the Nanping Tunnel project. In order to study the influence of pile spacing on tunnel support, first, the maximum pile spacing of 12.5 d (25 cm) was calculated by the mathematical geometric method, and then, three physical models were established for experimental comparison and analysis, including three different spacing cases of 7.5 d (15 cm), 10 d (20 cm), and 12.5 d (25 cm). In addition, numerical simulation was used to analyze the landslide and tunnel deformation under three pile spacing working conditions. The following conclusions are reached: As the distance between the combined pile increased, the deformation of the pile body and the tunnel lining structure also increased gradually, and the earth pressure and bending moments acting on the tunnel and the pile body increased progressively. However, when the pile spacing was increased from 7.5 d to 10 d, the increase in tunnel bending moment (52.9% increase in tunnel lining moment) was much more significant than when the pile spacing was increased from 10 d to 12.5 d (28.1% increase in tunnel lining moment). The results showed that if the landslide thrust is small, the pile spacing can be increased to 12.5 d or more in the design of combined medium-diameter anti-slide piles; if the landslide thrust is large, the pile spacing should be reduced to 7.5 d or less. Whether the landslide’s thrust is large or small, the combined medium-diameter anti-slide piles with a 10 d pile spacing are less cost-effective for landslide control. The new combined medium-diameter anti-slide piles have high loading capacity and stability, which can further improve the strength of existing tunnels.

A New Multi-Objective Comprehensive Optimization Model for Homogeneous Slope Reinforced by Anti-Slide Piles: Insights from Numerical Simulation

Abstract Landslides have posed a huge threat to the ecological environment and human society all over the world. As the most conventional reinforcement method, anti-slide piles are widely used in the reinforcement of slopes. Currently, more and more attention has been paid to the low-cost and high-efficiency optimal design of anti-slide piles. However, limitations in the method of the optimization design for slopes reinforced with piles still exist. In this paper, a new multi-objective comprehensive optimization method was proposed for the optimization of the slope reinforced with anti-slide piles. The factor of safety, internal force, and deflection of piles were selected as the optimization indexes, and the optimization index weight was determined by integrating the subjective and objective weights. The influence of pile locations, pile lengths, and pile spacings on the reinforcement effect of a homogeneous slope was analyzed via the numerical simulation. Through the simulation case analysis, the proposed model had achieved good effects on the optimization design of anti-slide piles, which could effectively reduce the engineering costs. The optimization results showed that the best reinforcement effect for the homogeneous slope could be obtained when the anti-slide piles with the critical pile length and small pile spacing were located in the middle of the slope. This provides a new solution for the optimization design of other types of complex slopes and has broad application prospects.

Data Analysis of the Effect of Different Nanomaterials on Antislide Pile Performance in Railway Landslides

Engineering geological conditions in our country are complex and diverse. Many high-rise buildings, bridges, and launch towers are inevitably built on high and steep slopes. Heavy rain, earthquake, human engineering activities, and other factors lead to frequent landslides, soil creep deformation, and overall sliding, resulting in a certain bending moment and flexural deformation of foundation piles, may cause damage to the substructure and foundation pile failure, and then endanger the safety of the superstructure. In the past, bridge pile group foundation was used in bridge pile foundation engineering to improve the impact situation, but the stress environment of bridge pile foundation in landslide is obviously different from that of bridge pile foundation in the flat area. The large deformation of soil in front of the pile will easily cause the phenomenon of soil sliding and peeling, which will increase the technical difficulty of antislide pile construction. Based on this, this study firstly briefly introduces the relevant theories and technologies of railway landslide antislide pile technology and then establishes the static model of railway landslide antislide piles with different nanomaterials. Finally, the reinforcement technology of different nanomaterial antislide piles for railway landslide is expounded, which can provide guarantee for the application of different nanomaterial antislide piles for railway landslide. The results show that the preloading is carried out according to 1/10 of the design load to reduce the void between the soils. After the load is maintained for 2 hours, the load is unloaded to 0, and good skid resistance can be obtained.

Failure Analysis and Treatments of Tunnel Entrance Collapse Due to Sustained Rainfall: A Case Study

Rainfall is a crucial issue affecting the entrance slope stability of mountain tunnels, as it decreases the shearing strength of soil and reduces the stability of tunnel entrance. This paper presents a case history of the collapse failure of a tunnel entrance in Yunnan Province under rainfall conditions, in which the failure mechanism and potential factors and treatment measures were discussed by field investigation, theoretical analysis, and in-situ monitoring. The analysis results show that the decrease of soil shear strength was mainly attributed to the decline of matric suction value of soil caused by the increase of soil water content. The decrease of the soil shear strength reduced the sliding resistance of the entrance slope and then triggered the collapse. Based on the results, three treatment measures to prevent a secondary tunnel entrance collapse due to rainfall are adopted, including anti-slide pile, grouting, and slope reinforcement. Combined with the field monitoring data, the effects of treatment measures were investigated. Lessons in this case study facilitate prevention and treatment of tunnel entrance constructions under rainfall conditions.

Morphological Evolution of Passive Soil Arch in Front of Horizontal Piles in Three Dimensions

The anti-slide pile is a primary method of landslide control. The effect of the passive soil arch in front of the embedded section of piles has a significant effect on the anti-slide pile’s bearing capacity. The upgraded model test scheme was used to conduct model tests with a pile spacing four times the width of the pile and a geometric scale ratio of 1:15. The anti-slide pile stress, pile bending strain, and soil stress in front of the pile were all studied in relation to the loading amount. In addition to the model test, the numerical simulation method was utilized to investigate the three-dimensional morphological change of the passive soil arch in front of the pile. The results indicated that: clearly, the side piles can eliminate the border effect. The distribution of pile bending strain along the pile after loading is referred to as a parabola. Bending failure occurred at a depth of 40 mm, approximately 0.9 m from the pile top. Under the condition that the pile spacing is four times the pile width, a passive soil arch occurs in front of the anti-slide pile’s fixed part, and its development can be split into four stages: formation, development, completion, and destruction. The passive soil arches in front of the piles are generated and destroyed gradually along the buried depth, and the three-dimensional surface of the space drops gradually along the buried depth with the loading amount and advances toward the loading direction until the anti-slide pile system fails. The research findings and experiences can serve as a basis for future research.

An Experimental Study on the Dynamic Evolution Characteristics of Soil Arching and the Rational Spacing of Anti-Slide Piles

In order to analyse the dynamic evolution characteristics of soil arching during sliding processes, we conducted a series of model push-pile and direct shear tests. The tests’ results were used to design a relative displacement monitoring system and to introduce two dimensionless parameters (the push–compaction ratio (e) and the different degrees of push–compaction (t)) to investigate the degree of uneven soil deformation during the sliding processes. This innovative method was used to analyse the rational spacing between adjacent anti-slide piles. The results revealed that there was a push-to-compaction effect in sliding soil during the sliding process. Firstly, in terms of space, the gradual transfer characteristics of the landslide thrust and push-to-compaction effect, rather than a uniform deformation over the entire area, were revealed. In terms of time, the results demonstrated a law for the variation in push-to-compaction ratios: The expansion of e occurred earlier in the rear sliding body than in the front e, while the growth rate of front e was faster than that of e in the rear sliding body. The dynamic evolution process was divided into three stages: an elastic formation stage, a plastic development stage, and a failure stage. Secondly, during the sliding process, the shear strength parameters of the sliding soil did not have constant values but underwent a dynamic process of strengthening, and cohesion responded more efficiently than friction. Finally, the degree of mobilisation of the anti-sliding effect of the sliding soil can be used as a new means of quantitative analysis for rational spacing. The results indicated that the rational spacing between adjacent piles should be five times the width of the pile.

Experimental Investigation of the Influence of the Anchor Cable Inclination Angle on the Seismic Response Characteristics of Anchored Piles

Studies show that prestressed anchor cable antislide piles have good antiseismic characteristics. As an important parameter in the design of anchor-cable piles, the effect of anchor-cable inclination on the seismic response of the anchor-cable pile system has been rarely studied so far. In the present study, the seismic response characteristics of the anchor-pulled pile under different cable inclinations are studied using a large-scale seismic model test platform and numerical methods. The obtained results show that the inclined angle of the anchor cable has a great influence on the seismic response of the pile-anchor system. It is found that under the same seismic conditions, the axial force of the anchor cable becomes smaller as the anchor dip angle increases, while the pile top displacement becomes larger. The dynamic earth pressure behind the pile changes from the sliding surface to the pile top, indicating that the earth pressure near the sliding surface and the pile top is of active and passive earth pressure types, respectively. This pressure decreases with the increase of the anchor dip angle, thereby affecting the performance of the antisliding pile.

Seismic Response Evaluation of High-Steep Slopes Supported by Anti-Slide Piles with Different Initial Damage Based on Shaking Table Test.

In order to study the instability development process of the slope reinforced by anti-slide piles under earthquake conditions, the dynamic response characteristics of the slope are usually taken as the main characteristics, and the model test and numerical simulation are the main research methods. In this paper, a shaking table model test is designed and completed to investigate the influence of anti-slide piles with different initial damage on the failure mode of high and steep slope under earthquake conditions. The changes in velocity, strain and natural frequency during slope vibration are tested in combination with cloud maps when sinusoidal waves of different accelerations with a peak value of 5 Hz are applied. Thus, the differences of slope failure development process and dynamic response characteristics are obtained. The experimental results show that the anti-slide pile with different initial damage has obvious influence on the slope instability process. Under the condition of good anti-slide pile quality, the failure development of the slope behind the pile is limited to soil sliding on top of the slope, slope sliding and overburden sliding; the front slope foot of pile mainly forms shear belt and local sliding. With the decrease in the initial mass of the anti-slide pile, the slope failure develops into topsoil sliding, slope sliding and deep integral sliding; analogously, the failure of the slope in front of the pile develops into a whole slip along the slip belt. The natural frequency cloud map can directly reflect the damage location of the slope, and the frequency change rate is positively correlated with the cumulative shear strain. It shows that the macro-failure characteristics of the model slope change well when the natural frequency is used as the sensitive index to measure the influence of vibration on the model slope. The threshold value of the natural frequency change rate can distinguish different development stages of the slope; 1% is the threshold value of stage II, and 1.5% is the threshold value of stage III.