# Numerical Simulation Analysis of NPR Anchorage Monitoring of Bedding Rock Landslide in Open-Pit Mine

Authors: Kai Zhang; Xiaojie Yang; Xuebin Cui; Yong Wang; Zhigang Tao
Journal: Advances in Civil Engineering
 (2020)

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## Abstract

Nanfen open-pit iron mine is the largest single open-pit mine in Asia. Because of the lag of the extension project, the section has slowly spread in the shape of “V,” and disasters such as landslides occur frequently. In this study, first, the NPR anchor cable monitoring, which shows supernormal mechanical characteristics and can realize the monitoring and early warning target for the whole landslide process and early warning curve of bedding rock “2016-1101 landslide” in the lower wall of Nanfen open-pit mine, was analyzed, revealing the failure process of the bedding rock landslide and the force evolution characteristics of the NPR anchor cable. Then, based on the Fish language in FLAC3D and 3DEC software, the mechanical model of the NPR anchor cable was constructed, and numerical simulation was performed on the whole process of “16-1101 landslide” induced by accumulation of old landslide body. The results of this study indicate that the stress monitoring curves and failure characteristics of the NPR anchor cables in the whole process of landslide by the two numerical simulation methods are basically consistent with the field measurement results, providing a theoretical and practical basis for the mechanistic analysis and numerical simulation of other similar slopes.


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## Body

## 1. Introduction

Under the blasting, rainfall, and human activity, the rock mass of slope weakens, causing a large number of engineering disasters [1–6]. The disaster because of large deformation during a landslide in an open-pit mine not only causes huge economic losses but also seriously threatens the safety of life and property of the staff in the mine. Reducing the casualties and property losses caused by landslides and forecasting them have been a research hotspot. The key to affecting the reliability and authenticity of forecasting results is to timely and accurately monitor and simulate the data. Based on this, the study and development of landslide monitoring methods have become the most basic measure to improve the effectiveness of the prediction results. At present, the monitoring methods widely used include deformation monitoring, physical field monitoring, water monitoring, and external trigger monitoring [7–10]. Allasia et al. proposed a new method called Advanced Displacement Monitoring System for Early Warning for near real-time monitoring of surface displacement caused by landslides [11]; Choon et al. monitored and analyzed the slope displacement of Basel coal mine in Indonesia using a GPS system, and a GIS model combining the fuzzy theory and analytical hierarchy process was established to evaluate the slope instability of open-pit mines [12]. In recent years, satellite remote sensing technology monitoring methods (SAR, INSAR, and D-INSAR) have been widely used in landslide monitoring leading to significant results [13–16]. Based on previous investigation and our experience with Saito's method, an improved Saito curve was drawn with four stages corresponding to the displacement process of the position on the back of the landslide [17]. However, these landslide monitoring methods are basically based on observing the surface displacement, cracks, and settlements. These factors are necessary conditions for the occurrence of landslides rather than sufficient conditions. Therefore, carrying out the advance warning of landslide disasters is impossible. He et al. proposed that “sliding force is greater than the shear strength, and it is the necessary and sufficient condition for landslide generation.” Based on this, they constructed the mechanical model of “sliding force monitoring” and developed an NPR anchor cable with constant resistance characteristics, which can adapt to landslide monitoring in deep deformation conditions [18–21]. On this basis, a wireless sensor network was built based on the GPRS dual-channel platform using Zigbee technology, and a multisource system cloud service platform was established for landslide monitoring to adapt to the complex environment sloping disaster monitoring and early warning system [22–26]. Although they successfully monitored and warned of many dangerous landslides, they neither established the NPR anchor cable numerical calculation model and nor carried out the numerical simulation of the whole process of landslide monitoring and early warning.Similarly, the numerical simulation analysis of landslide geological disasters is also a key method for investigation in the field of slope engineering. At present, a series of numerical methods such as finite difference method and finite volume method for different types of sliding bodies have been developed. Model establishment and control theory include discrete element method (DEM), discontinuous deformation, DAN, smooth particle hydrodynamics, particle flow code (PFC), and tsunami ball. Some numerical simulation software such as FLAC, UDEC, PFC, 3DEC, and Geoslope have emerged. Many researchers carried out a series of simulations on the slope instability and damage by these methods and software achieving significant results. Maihemuti et al. used the three-dimensional rapid Lagrangian analysis program (FLAC3D, 4.0) of geotechnical engineering to numerically simulate the deformation and failure process of the bank slope rock and obtained the deformation mechanism of the E20 bank slope [27]. Li et al. combined C++ programming technology and finite difference method and realized the three-dimensional numerical simulation of slope through the intelligent inversion analysis of the structural parameters of the soil slope [28]. The traditional continuous numerical calculation method has been widely used by the predecessors, and the practicability and effectiveness of the finite element method and boundary element method have been fully confirmed [29–32]. At the same time, Munjiza et al. combined the finite element method suitable for the analysis of continuous problems with the discrete element method suitable for transient, contact detection, contact interaction, and other discrete problems [33]. Some scholars explored the integrated continuity and discontinuity methods, known as the finite element-discrete element method for the numerical simulation of material cracking and fracture after slope instability [34–37]. However, the NPR anchor cable monitoring, numerical modeling, and simulation analysis in the whole process of landslides are rarely investigated. Based on the monitoring data and the engineering geological conditions of “2016-1101 landslide,” in this study, we established the NPR anchor cable numerical calculation model and carried out numerical simulation on the monitoring of “2016-1101 landslide” through the Fish language in FLAC3D and 3DEC software. The whole process of monitoring and early warning of Newtonian force of typical landslide in Nanfen open-pit mine was established, laying a good theoretical foundation for the layout of the monitoring points of the Newtonian force and slope stability analysis in Nanfen open-pit mine in the future.


## 2. Structural Composition and Static Tensile Mechanical Properties of the NPR Anchor Cable

### 2.1. Structural Composition of the NPR Anchor Cable

The NPR anchor cable is different from the traditional PR anchor cable and has improved constant resistance and large deformation mechanical characteristics. Figure1 shows the structural composition of the NPR anchor cable, mainly including mechanical sensors, anchor cables (steel strands), constant resistance bodies, constant resistance bushings, top covers, backing plates, filling new materials, and other equipment.Figure 1
Structure diagram of constant resistance large deformation anchor cable.Normally, the force applied on the anchor cable is offset by the static friction between the constant resistance body and the constant resistance casing. When the load applied to the anchor cable is larger than the constant resistance design load value, the body begins to move along the inner wall of the casing and absorbs the load energy through the structural deformation, leading to constant resistance and large deformation.


### 2.2. The Mechanical Model for NPR Anchor Cable

The constant resistance body is the core part of the constant resistance and large deformation anchor cable, and its structure is shown in Figure2 [18].Figure 2
Analysis of the axial stress of the constant resistance device.Among them,α is the angle of constant resistance body, h is the effective length of constant resistance body, a is the inner radius of constant resistance casing, b is the outer radius of constant resistance casing, u is the radial deformation, V is the elongation of anchor cable bundle, P0 is the external load, M is the mass of constant resistance body, δz is the inner wall deformation of constant resistance casing of A−B section at z from the top of constant resistance body, p′ is the acting stress of constant resistance body to constant resistance casing, and p′z is the action stress of A−B profile constant resistance casing to constant resistance body. The mechanical model of the rheostat is as follows [18]:(1)P0=2πfIsIc,Is=Eb2−a2tanαaa2+b2−μb2−a2,Ic=ah22cosα+h33sinα,where P0 is the constant resistance (kN), f is the static friction coefficient, Is is the elastic constant of the constant resistance sleeve, IC is the geometric constant of the constant resistance body, E is the elastic modulus of the material, and μ is Poisson’s ratio of the material.The constant resistance value of the NPR anchor cable is related to the material size of the constant resistance body and the external load.


### 2.3. Extraordinary Statics and Its Test

#### 2.3.1. Testing System

In order to verify and investigate the supermechanical properties such as tensile properties, negative Poisson’s ratio (NPR) characteristics, and constant resistance specialty of the anchor cables in this study, we used “the static tensile test system of HWL-2000 NPR anchor cables,” developed by the State Key Laboratory of Deep Geotechnical Mechanics and Underground Engineering, China University of Mining and Technology (Beijing). The anchor cables are numbered as “MS-01-01,” “MS-01-02,” and “MS-01-03,” and their physical parameters are listed in Table1.Table 1
Anchor cable parameters.
Anchor cable number
Anchor cable lengthL1 (mm)
Constant resistance sleeve lengthL2 (mm)
Constant resistance body lengthL3 (mm)
MS-01-01
2854
2005
150
MS-01-02
2856
2007
150
MS-01-03
2860
2010
150The test system mainly includes a data acquisition and processing system, a liquid crystal display system, a hydraulic power system, and an anchorage and tension system. The maximum tensile force is 2,000 kN; the resolution of the tensile force is 3.3 × 10−6; and the strain rate and tension are in the ranges 0–200 mm/min and 30–5000 mm, respectively. Figure 3 shows the schematic diagram of the static stretching system.Figure 3
Schematic diagram of the static stretching system.Figure 4
Static tensile test curve of the anchor cable.


#### 2.3.2. Result Analysis

(1)
Tensile properties and constant resistance characteristics of the constant resistance and large deformation anchor cables
Figure4 shows the static tensile test curve of the test piece anchor cable, indicating the following:(a)
From the beginning of the tension to the failure of the anchor cable, it has an average elongation of 1960 mm, showing an extraordinarily large deformation capacity.(b)
During the static tension, the axial force of the anchor cable rises to the maximum constant resistance (850 kN) in a short time and then becomes constant at 850 kN, exhibiting a remarkable constant resistance characteristic.
(2)
Negative Poisson’s ratio effect of the constant resistance large deformation anchor cable structureThe cable structure with a constant resistance and large deformation under axial elongation also undergoes radial structural expansion. Figure5 shows the NPR anchor cable resistor used in the experiment.Figure 5
NPR anchor cable resistor.The outer diameters of the cross sections 1-1 and 2-2 in two vertical directions were measured using a Vernier caliper. The interval is 100 mm, and the length of the casing is read. Figures6(a) and 6(b) show the diameters of the three groups of the constant resistance casing in 1-1 and 2-2 directions, respectively.(1)
The initial average diameters before and after the test in the 1-1 direction are 121.42 mm and ∼125.42 mm, respectively. The expansion in the 1-1 direction before and after the test is ∼4 mm.(2)
The initial average diameters before and after the test in the 2-2 direction are 121.50 and ∼125.66 mm, respectively. The expansion in the 2-2 direction before and after the test is ∼4.16 mm.In summary, the large deformation anchor cable with a constant resistance has supernormal tensile properties, NPR characteristics, and constant resistance characteristics.(3)
Geological conditions, landslide monitoring system, and distribution characteristics of monitoring point.Figure 6
Diameter variation of constant resistance casing before and after the test: (a) diameter variation of 1-1 section; (b) diameter variation of 2-2 section.
(a)
(b)


### 3.1. Topography, Geomorphology, and Stratigraphic Lithology

Nanfen open-pit iron mine (Figure7) of the Benxi Steel Group is located 25 km south of Benxi City, Liaoning Province. Its terrain undulates greatly. The relative elevation difference is generally 300–400 m, and the maximum elevation is 500 m. The overall topography is high in the east and low in the west, and the mountain trend is close to the east and west. It is a middle-high mountain area with a denudation structure. The orebody is a monoclinic structure. The east and west sides of the stope are the lower and upper walls of the monoclinic structure, respectively.Figure 7
Mine mining site shape and landform.The strata in the stope are relatively complex. First, the Anshan group (mainly composed of mica quartz schist, epidote amphibolite schist, magnetite quartz, quartz chlorite schist, mica quartz schist, and gneissic migmatite) was widely developed, followed by the Liaohe group of the Proterozoic (mainly composed of quartzite, phyllite, and marble), sinian strata (mainly composed of quartzite and shale), and the quaternary strata of the Cenozoic (lithologically including sand, gravel, clay soil, and gravel).


### 3.2. Geological Structure and Hydrometeorological Characteristics

The geological structure in the mining is the fold structure and fault structure dominated by the inverted anticline (the inverted dome structure of the Heibeishan mountain, the inverted anticline of the open-pit mine, and the F1 fault structure). The core drilling data show obvious inverted anticline morphology and fault structure (Figure8).Figure 8
Reverse anticline shape and fault structure in the mining area.The mining area belongs to the north temperate monsoon climate. The annual average rainfall and the maximum daily rainfall are close to 900 and 300 mm, respectively. Rainfall mainly concentrates in the summer. Besides, the annual temperature difference is relatively large; the extreme minimum temperature in the winter is close to –33°C, while the extreme maximum temperature in the summer is close to 38°C; and the annual average temperature is 8.2°C. Groundwater also plays an important role in the region. The ice and snow melt in the rainy and winter-spring alternating seasons. The water seriously affects the stability of the landslide body, thus increasing the difficulty in mining operations.


### 3.3. Distribution Characteristics of Monitoring Point

#### 3.3.1. Monitoring System

The landslide observation system is divided into indoor and outdoor monitoring systems.The indoor landslide monitoring system (Figure9) mainly consists of a GPRS data receiver, a BeiDou satellite signal receiver, an automatic data analysis and processing system, a 3D automatic search system, and a liquid crystal display system.Figure 9
Indoor monitoring system.The outdoor landslide monitoring system (Figure10) mainly consists of a signal transmission system, a power supply system, a mechanical transmission device, and a mechanical signal acquisition and conversion device. Among them, the power supply system contains 100a colloidal battery overcharge, a 85 W monocrystalline silicon solar panel, and a dedicated controller, guaranteeing 24 h of working status. The mechanical transmission devices include mechanical sensors. The signal transmission system includes a BeiDou machine and an antenna. There are also anchored piers, poles, and other equipment.Figure 10
Outdoor system equipment: 1, power supply (12 V); 2, power supply (9 V); 3, solar controller; 4, communication node; 5, GPRS-DTU; 6, switch; 7, solar battery; 8, data acquisition device.Data transmission and aggregation in the monitoring area are mainly based on the data transmission topology (Figure11).Figure 11
Data transmission topology.


#### 3.3.2. Mechanism of Large Deformation Control

NPR anchor cable plays an important role in controlling the large deformation of the slope:(1)
Before the slope slides (Figure12(a)): assembly of a new anchor cable equipment and application of prestressBefore excavation, the slope is in equilibrium. According to the survey and construction design, holes are drilled in the design depth, the anchor cable is extended into the tunnel, and the anchorage section is grouted and reinforced; besides, the free end is molded, and the installation of equipment is completed, followed by applying the prestressing force.(2)
Slope sliding (Figure12(b)): energy absorption process of the “NPR structure”When the slope is about to slip or begin to slip, the original mechanical equilibrium state between the slope and NPR anchor cable will be destroyed, causing slip. As the slip exceeds a certain limit, the constant resistance body will absorb energy with increasing deformation in the casing, effectively increasing or avoiding the breaking of the anchor cable, thus avoiding the sudden collapse of the slope and the failure of the monitoring equipment.(3)
After the slope slides (Figure12(c)): controlling the sliding bodyIn the case of large deformation, the elastic energy is released, the deformation energy inside the slope is less than the design constant resistance P of the resistor, the axial force F of the anchor cable is less than the friction force, and the soil body reaches a new equilibrium and stable state.Figure 12
Process of interaction between NPR anchor and slope: (a) before the slope slides; (b) slope sliding; (c) after the slope slides.
(a)
(b)
(c)Therefore, the anchor cable can not only realize the monitoring and early warning of the slope landslide but also reinforces the slope.


#### 3.3.3. Distribution Characteristics of the Monitoring Point

With the continuous exploitation of deep mineral resources, landslides, rolling stones, and other geological disasters occur frequently. In June 2015, nine new NPR anchor monitoring points were introduced in the 478–502 m platform range of the stope working face. The buried depth is in the range 55–84 m, the angle of incidence is 45°, and the azimuth angle is 84°. As shown in Figure13(a), the red marking dots are the new monitoring points, and the A-A′ section of the monitoring area is shown in Figure 13(b).Figure 13
Monitoring point distribution: (a) added monitoring point distribution characteristics; (b) section A-A′ of the monitoring area.
(a)
(b)


## 2.1. Structural Composition of the NPR Anchor Cable

The NPR anchor cable is different from the traditional PR anchor cable and has improved constant resistance and large deformation mechanical characteristics. Figure1 shows the structural composition of the NPR anchor cable, mainly including mechanical sensors, anchor cables (steel strands), constant resistance bodies, constant resistance bushings, top covers, backing plates, filling new materials, and other equipment.Figure 1
Structure diagram of constant resistance large deformation anchor cable.Normally, the force applied on the anchor cable is offset by the static friction between the constant resistance body and the constant resistance casing. When the load applied to the anchor cable is larger than the constant resistance design load value, the body begins to move along the inner wall of the casing and absorbs the load energy through the structural deformation, leading to constant resistance and large deformation.


## 2.2. The Mechanical Model for NPR Anchor Cable

The constant resistance body is the core part of the constant resistance and large deformation anchor cable, and its structure is shown in Figure2 [18].Figure 2
Analysis of the axial stress of the constant resistance device.Among them,α is the angle of constant resistance body, h is the effective length of constant resistance body, a is the inner radius of constant resistance casing, b is the outer radius of constant resistance casing, u is the radial deformation, V is the elongation of anchor cable bundle, P0 is the external load, M is the mass of constant resistance body, δz is the inner wall deformation of constant resistance casing of A−B section at z from the top of constant resistance body, p′ is the acting stress of constant resistance body to constant resistance casing, and p′z is the action stress of A−B profile constant resistance casing to constant resistance body. The mechanical model of the rheostat is as follows [18]:(1)P0=2πfIsIc,Is=Eb2−a2tanαaa2+b2−μb2−a2,Ic=ah22cosα+h33sinα,where P0 is the constant resistance (kN), f is the static friction coefficient, Is is the elastic constant of the constant resistance sleeve, IC is the geometric constant of the constant resistance body, E is the elastic modulus of the material, and μ is Poisson’s ratio of the material.The constant resistance value of the NPR anchor cable is related to the material size of the constant resistance body and the external load.


## 2.3. Extraordinary Statics and Its Test

### 2.3.1. Testing System

In order to verify and investigate the supermechanical properties such as tensile properties, negative Poisson’s ratio (NPR) characteristics, and constant resistance specialty of the anchor cables in this study, we used “the static tensile test system of HWL-2000 NPR anchor cables,” developed by the State Key Laboratory of Deep Geotechnical Mechanics and Underground Engineering, China University of Mining and Technology (Beijing). The anchor cables are numbered as “MS-01-01,” “MS-01-02,” and “MS-01-03,” and their physical parameters are listed in Table1.Table 1
Anchor cable parameters.
Anchor cable number
Anchor cable lengthL1 (mm)
Constant resistance sleeve lengthL2 (mm)
Constant resistance body lengthL3 (mm)
MS-01-01
2854
2005
150
MS-01-02
2856
2007
150
MS-01-03
2860
2010
150The test system mainly includes a data acquisition and processing system, a liquid crystal display system, a hydraulic power system, and an anchorage and tension system. The maximum tensile force is 2,000 kN; the resolution of the tensile force is 3.3 × 10−6; and the strain rate and tension are in the ranges 0–200 mm/min and 30–5000 mm, respectively. Figure 3 shows the schematic diagram of the static stretching system.Figure 3
Schematic diagram of the static stretching system.Figure 4
Static tensile test curve of the anchor cable.


### 2.3.2. Result Analysis

(1)
Tensile properties and constant resistance characteristics of the constant resistance and large deformation anchor cables
Figure4 shows the static tensile test curve of the test piece anchor cable, indicating the following:(a)
From the beginning of the tension to the failure of the anchor cable, it has an average elongation of 1960 mm, showing an extraordinarily large deformation capacity.(b)
During the static tension, the axial force of the anchor cable rises to the maximum constant resistance (850 kN) in a short time and then becomes constant at 850 kN, exhibiting a remarkable constant resistance characteristic.
(2)
Negative Poisson’s ratio effect of the constant resistance large deformation anchor cable structureThe cable structure with a constant resistance and large deformation under axial elongation also undergoes radial structural expansion. Figure5 shows the NPR anchor cable resistor used in the experiment.Figure 5
NPR anchor cable resistor.The outer diameters of the cross sections 1-1 and 2-2 in two vertical directions were measured using a Vernier caliper. The interval is 100 mm, and the length of the casing is read. Figures6(a) and 6(b) show the diameters of the three groups of the constant resistance casing in 1-1 and 2-2 directions, respectively.(1)
The initial average diameters before and after the test in the 1-1 direction are 121.42 mm and ∼125.42 mm, respectively. The expansion in the 1-1 direction before and after the test is ∼4 mm.(2)
The initial average diameters before and after the test in the 2-2 direction are 121.50 and ∼125.66 mm, respectively. The expansion in the 2-2 direction before and after the test is ∼4.16 mm.In summary, the large deformation anchor cable with a constant resistance has supernormal tensile properties, NPR characteristics, and constant resistance characteristics.(3)
Geological conditions, landslide monitoring system, and distribution characteristics of monitoring point.Figure 6
Diameter variation of constant resistance casing before and after the test: (a) diameter variation of 1-1 section; (b) diameter variation of 2-2 section.
(a)
(b)


## 2.3.1. Testing System

In order to verify and investigate the supermechanical properties such as tensile properties, negative Poisson’s ratio (NPR) characteristics, and constant resistance specialty of the anchor cables in this study, we used “the static tensile test system of HWL-2000 NPR anchor cables,” developed by the State Key Laboratory of Deep Geotechnical Mechanics and Underground Engineering, China University of Mining and Technology (Beijing). The anchor cables are numbered as “MS-01-01,” “MS-01-02,” and “MS-01-03,” and their physical parameters are listed in Table1.Table 1
Anchor cable parameters.
Anchor cable number
Anchor cable lengthL1 (mm)
Constant resistance sleeve lengthL2 (mm)
Constant resistance body lengthL3 (mm)
MS-01-01
2854
2005
150
MS-01-02
2856
2007
150
MS-01-03
2860
2010
150The test system mainly includes a data acquisition and processing system, a liquid crystal display system, a hydraulic power system, and an anchorage and tension system. The maximum tensile force is 2,000 kN; the resolution of the tensile force is 3.3 × 10−6; and the strain rate and tension are in the ranges 0–200 mm/min and 30–5000 mm, respectively. Figure 3 shows the schematic diagram of the static stretching system.Figure 3
Schematic diagram of the static stretching system.Figure 4
Static tensile test curve of the anchor cable.


## 2.3.2. Result Analysis

(1)
Tensile properties and constant resistance characteristics of the constant resistance and large deformation anchor cables
Figure4 shows the static tensile test curve of the test piece anchor cable, indicating the following:(a)
From the beginning of the tension to the failure of the anchor cable, it has an average elongation of 1960 mm, showing an extraordinarily large deformation capacity.(b)
During the static tension, the axial force of the anchor cable rises to the maximum constant resistance (850 kN) in a short time and then becomes constant at 850 kN, exhibiting a remarkable constant resistance characteristic.
(2)
Negative Poisson’s ratio effect of the constant resistance large deformation anchor cable structureThe cable structure with a constant resistance and large deformation under axial elongation also undergoes radial structural expansion. Figure5 shows the NPR anchor cable resistor used in the experiment.Figure 5
NPR anchor cable resistor.The outer diameters of the cross sections 1-1 and 2-2 in two vertical directions were measured using a Vernier caliper. The interval is 100 mm, and the length of the casing is read. Figures6(a) and 6(b) show the diameters of the three groups of the constant resistance casing in 1-1 and 2-2 directions, respectively.(1)
The initial average diameters before and after the test in the 1-1 direction are 121.42 mm and ∼125.42 mm, respectively. The expansion in the 1-1 direction before and after the test is ∼4 mm.(2)
The initial average diameters before and after the test in the 2-2 direction are 121.50 and ∼125.66 mm, respectively. The expansion in the 2-2 direction before and after the test is ∼4.16 mm.In summary, the large deformation anchor cable with a constant resistance has supernormal tensile properties, NPR characteristics, and constant resistance characteristics.(3)
Geological conditions, landslide monitoring system, and distribution characteristics of monitoring point.Figure 6
Diameter variation of constant resistance casing before and after the test: (a) diameter variation of 1-1 section; (b) diameter variation of 2-2 section.
(a)
(b)


## 3.1. Topography, Geomorphology, and Stratigraphic Lithology

Nanfen open-pit iron mine (Figure7) of the Benxi Steel Group is located 25 km south of Benxi City, Liaoning Province. Its terrain undulates greatly. The relative elevation difference is generally 300–400 m, and the maximum elevation is 500 m. The overall topography is high in the east and low in the west, and the mountain trend is close to the east and west. It is a middle-high mountain area with a denudation structure. The orebody is a monoclinic structure. The east and west sides of the stope are the lower and upper walls of the monoclinic structure, respectively.Figure 7
Mine mining site shape and landform.The strata in the stope are relatively complex. First, the Anshan group (mainly composed of mica quartz schist, epidote amphibolite schist, magnetite quartz, quartz chlorite schist, mica quartz schist, and gneissic migmatite) was widely developed, followed by the Liaohe group of the Proterozoic (mainly composed of quartzite, phyllite, and marble), sinian strata (mainly composed of quartzite and shale), and the quaternary strata of the Cenozoic (lithologically including sand, gravel, clay soil, and gravel).


## 3.2. Geological Structure and Hydrometeorological Characteristics

The geological structure in the mining is the fold structure and fault structure dominated by the inverted anticline (the inverted dome structure of the Heibeishan mountain, the inverted anticline of the open-pit mine, and the F1 fault structure). The core drilling data show obvious inverted anticline morphology and fault structure (Figure8).Figure 8
Reverse anticline shape and fault structure in the mining area.The mining area belongs to the north temperate monsoon climate. The annual average rainfall and the maximum daily rainfall are close to 900 and 300 mm, respectively. Rainfall mainly concentrates in the summer. Besides, the annual temperature difference is relatively large; the extreme minimum temperature in the winter is close to –33°C, while the extreme maximum temperature in the summer is close to 38°C; and the annual average temperature is 8.2°C. Groundwater also plays an important role in the region. The ice and snow melt in the rainy and winter-spring alternating seasons. The water seriously affects the stability of the landslide body, thus increasing the difficulty in mining operations.


## 3.3. Distribution Characteristics of Monitoring Point

### 3.3.1. Monitoring System

The landslide observation system is divided into indoor and outdoor monitoring systems.The indoor landslide monitoring system (Figure9) mainly consists of a GPRS data receiver, a BeiDou satellite signal receiver, an automatic data analysis and processing system, a 3D automatic search system, and a liquid crystal display system.Figure 9
Indoor monitoring system.The outdoor landslide monitoring system (Figure10) mainly consists of a signal transmission system, a power supply system, a mechanical transmission device, and a mechanical signal acquisition and conversion device. Among them, the power supply system contains 100a colloidal battery overcharge, a 85 W monocrystalline silicon solar panel, and a dedicated controller, guaranteeing 24 h of working status. The mechanical transmission devices include mechanical sensors. The signal transmission system includes a BeiDou machine and an antenna. There are also anchored piers, poles, and other equipment.Figure 10
Outdoor system equipment: 1, power supply (12 V); 2, power supply (9 V); 3, solar controller; 4, communication node; 5, GPRS-DTU; 6, switch; 7, solar battery; 8, data acquisition device.Data transmission and aggregation in the monitoring area are mainly based on the data transmission topology (Figure11).Figure 11
Data transmission topology.


### 3.3.2. Mechanism of Large Deformation Control

NPR anchor cable plays an important role in controlling the large deformation of the slope:(1)
Before the slope slides (Figure12(a)): assembly of a new anchor cable equipment and application of prestressBefore excavation, the slope is in equilibrium. According to the survey and construction design, holes are drilled in the design depth, the anchor cable is extended into the tunnel, and the anchorage section is grouted and reinforced; besides, the free end is molded, and the installation of equipment is completed, followed by applying the prestressing force.(2)
Slope sliding (Figure12(b)): energy absorption process of the “NPR structure”When the slope is about to slip or begin to slip, the original mechanical equilibrium state between the slope and NPR anchor cable will be destroyed, causing slip. As the slip exceeds a certain limit, the constant resistance body will absorb energy with increasing deformation in the casing, effectively increasing or avoiding the breaking of the anchor cable, thus avoiding the sudden collapse of the slope and the failure of the monitoring equipment.(3)
After the slope slides (Figure12(c)): controlling the sliding bodyIn the case of large deformation, the elastic energy is released, the deformation energy inside the slope is less than the design constant resistance P of the resistor, the axial force F of the anchor cable is less than the friction force, and the soil body reaches a new equilibrium and stable state.Figure 12
Process of interaction between NPR anchor and slope: (a) before the slope slides; (b) slope sliding; (c) after the slope slides.
(a)
(b)
(c)Therefore, the anchor cable can not only realize the monitoring and early warning of the slope landslide but also reinforces the slope.


### 3.3.3. Distribution Characteristics of the Monitoring Point

With the continuous exploitation of deep mineral resources, landslides, rolling stones, and other geological disasters occur frequently. In June 2015, nine new NPR anchor monitoring points were introduced in the 478–502 m platform range of the stope working face. The buried depth is in the range 55–84 m, the angle of incidence is 45°, and the azimuth angle is 84°. As shown in Figure13(a), the red marking dots are the new monitoring points, and the A-A′ section of the monitoring area is shown in Figure 13(b).Figure 13
Monitoring point distribution: (a) added monitoring point distribution characteristics; (b) section A-A′ of the monitoring area.
(a)
(b)


## 3.3.1. Monitoring System

The landslide observation system is divided into indoor and outdoor monitoring systems.The indoor landslide monitoring system (Figure9) mainly consists of a GPRS data receiver, a BeiDou satellite signal receiver, an automatic data analysis and processing system, a 3D automatic search system, and a liquid crystal display system.Figure 9
Indoor monitoring system.The outdoor landslide monitoring system (Figure10) mainly consists of a signal transmission system, a power supply system, a mechanical transmission device, and a mechanical signal acquisition and conversion device. Among them, the power supply system contains 100a colloidal battery overcharge, a 85 W monocrystalline silicon solar panel, and a dedicated controller, guaranteeing 24 h of working status. The mechanical transmission devices include mechanical sensors. The signal transmission system includes a BeiDou machine and an antenna. There are also anchored piers, poles, and other equipment.Figure 10
Outdoor system equipment: 1, power supply (12 V); 2, power supply (9 V); 3, solar controller; 4, communication node; 5, GPRS-DTU; 6, switch; 7, solar battery; 8, data acquisition device.Data transmission and aggregation in the monitoring area are mainly based on the data transmission topology (Figure11).Figure 11
Data transmission topology.


## 3.3.2. Mechanism of Large Deformation Control

NPR anchor cable plays an important role in controlling the large deformation of the slope:(1)
Before the slope slides (Figure12(a)): assembly of a new anchor cable equipment and application of prestressBefore excavation, the slope is in equilibrium. According to the survey and construction design, holes are drilled in the design depth, the anchor cable is extended into the tunnel, and the anchorage section is grouted and reinforced; besides, the free end is molded, and the installation of equipment is completed, followed by applying the prestressing force.(2)
Slope sliding (Figure12(b)): energy absorption process of the “NPR structure”When the slope is about to slip or begin to slip, the original mechanical equilibrium state between the slope and NPR anchor cable will be destroyed, causing slip. As the slip exceeds a certain limit, the constant resistance body will absorb energy with increasing deformation in the casing, effectively increasing or avoiding the breaking of the anchor cable, thus avoiding the sudden collapse of the slope and the failure of the monitoring equipment.(3)
After the slope slides (Figure12(c)): controlling the sliding bodyIn the case of large deformation, the elastic energy is released, the deformation energy inside the slope is less than the design constant resistance P of the resistor, the axial force F of the anchor cable is less than the friction force, and the soil body reaches a new equilibrium and stable state.Figure 12
Process of interaction between NPR anchor and slope: (a) before the slope slides; (b) slope sliding; (c) after the slope slides.
(a)
(b)
(c)Therefore, the anchor cable can not only realize the monitoring and early warning of the slope landslide but also reinforces the slope.


## 3.3.3. Distribution Characteristics of the Monitoring Point

With the continuous exploitation of deep mineral resources, landslides, rolling stones, and other geological disasters occur frequently. In June 2015, nine new NPR anchor monitoring points were introduced in the 478–502 m platform range of the stope working face. The buried depth is in the range 55–84 m, the angle of incidence is 45°, and the azimuth angle is 84°. As shown in Figure13(a), the red marking dots are the new monitoring points, and the A-A′ section of the monitoring area is shown in Figure 13(b).Figure 13
Monitoring point distribution: (a) added monitoring point distribution characteristics; (b) section A-A′ of the monitoring area.
(a)
(b)


## 4. Numerical Simulation and Analysis of “16-1101 Landslide” NPR Monitoring

### 4.1. Characteristic Analysis of “16-1101 Landslide”

At 8:30 on September 14th, 2016, the No. 478-3 curve rose to point D, and the system issued a “long-term warning”; at 10:20 on October 1st, 2016, because of a working shovel under 430 m steps, the sliding force curve of No. 478-3 suddenly rose to point F, and the system issued a “medium-term warning.” The mine leaders asked all large machinery and extension workers to evacuate; at 23:52 on October 31st, 2016, the curve suddenly appeared. On November 1st, 2016, at 3:40, the monitoring system reported the occurrence of the landslide, producing a loud noise. The broken rock and soil mass rolled down along the slope and piled up on the 430 m step. The failure characteristics of the slope top behind the landslide are shown in Figure 14.Figure 14
Characteristics of the “16-1101 landslide.”


### 4.2. Numerical Simulation Analysis of the “16-1101” Landslide

In this section, the field monitoring data of “16-1101 landslide” in Nanfen open-pit iron mine was calculated by FLAC3D and 3DEC numerical simulation software to realize the recurrence of the landslide process. The numerical analysis model of the NPR anchor cable was constructed by Fish language in numerical simulation software. The model was analyzed, and the calculation was performed for the 16-1101 landslide to investigate the similarities and differences between the simulation and the actual monitoring results.


#### 4.2.1. Principle of Large Deformation Design of NPR Anchor Cable in Numerical Simulation Software

The NPR anchor reinforcement unit is generally defined by geometric parameters, material parameters, and anchorage agent characteristics. The axial stiffness of the boltK is expressed by(2)K=AEL,where A is the cross-sectional area of the reinforcement, E is the elastic modulus of the bolt, and L is the length of the bolt.Conventional anchor cables do not have large deformation characteristics. For the NPR anchor cables, with constant resistance and large deformation characteristics, it is necessary to set the end of the anchor section with conventional anchorage strength and the end of the free section as the rigid contact with the rock mass through Fish language in the modeling process. The principle of large deformation is as follows: applying axial force at the end of the NPR anchor cable, when the axial force reaches the design constant resistanceP, the anchor cable will produce axial deformation, until the maximum deformation is reached, the failure of anchorage agent will be judged, and the anchor cable unit will be released to achieve the effect of large deformation.


#### 4.2.2. Numerical Model Establishment of the 16-1101 Landslide

Calibration of model boundary and elevation: the maximum width of the old landslide body and “16-1101 landslide body” is 50 m, and the elevation limits are in the ranges 502–550 m and 430–502 m. Because the width of the model boundary is 2.5 times larger than the width of the target body, the height range of the model is 277–634 m, and the strike direction length is 200 m. In order to simulate the spatial relationship between the upper and lower sliding bodies and the interface characteristics of the sliding body during the start-up process, setting the interface elements between the sliding body and the rock foundation is necessary. The back, bottom, and both sides of the landslide body have a fixed boundary, and the upper and front parts have a free boundary.


#### 4.2.3. Landslide Numerical Simulation Based on FLAC3D

The NPR anchor cable model was constructed by FLAC3D software, as shown in Figure15. The static tensile mechanical properties are shown in Figure 16.Figure 15
The NPR anchor cable model.Figure 16
The static tensile mechanical properties.(1) Insertion of the NPR Anchor Cable Model. The parameters of the NPR anchor cable model were determined by the coordinates of the monitoring points of the deep sliding force and buried depth of the NPR anchor cable: inclination angle, 30°; length, 75 m; preload force, 40 kN; and constant resistance value, 85 kN. The excavation length of the 430 platform shovel is set to 70 m. The rock mechanical parameters are as follows (Table 2).Table 2
Parameters of rock mechanics.
Rock mass name
Bulk weight(kg/m3)
Bulk modulus (GPa)
Shear modulus (GPa)
Cohesion (kPa)
Friction angle (°)
Tensile strength (MPa)
Basement
2873
20
10.9
420
36
1.5
Sliding mass
2580
5.2
2.10
70
27
0.2Figure17 shows the double-sliding body model.Figure 17
Construction of double-sliding body model.Figure 18
Displacement contour of the old landslide after stabilization.Figure 19
“16-1101 landslide” instability displacement contour.(2) Analysis of Simulation Results
(i)
Numerical simulation analysis of the old landslide (Figure18)
Principles of simulation:(a)
When the maximum unbalance forceF is <1e − 5, the software determines the landslide as stable.(b)
When the calculation exceeds 10,000 steps and the model is still unstable, the calculation is stopped, and the model is considered to be in a plastic flow state.(c)
Observe the strain increment contour of the sliding surface. When the sliding surface passes through, the software determines the sliding surface instability and stops calculation.
According to these three principles, the maximum displacement of the old landslide after stabilization is ∼1.3 m. The landslide body is basically located at the set position of the contact surface of the model. When the slope slides, the strength of the contact surface is set as the actual strength of the sliding surface and then slides until reaching the stable state.
(ii)
Numerical simulation analysis of “16-1101 landslide” (Figure19)The numerical simulation of “16-1101 landslide” was carried out by setting both the velocity and deformation of the old landslide in the calculation as zero.After the appearance of “16-1101 landslide,” the old landslide body “resurrected” and then slipped, and the 502 m step appeared staggered. The direct cause of the ultimate instability of the whole slope is the transfixion of the sliding surface, and the antisliding force is less than the sliding force. Therefore, in practical calculation, the strength of the contact surface (sliding surface) should also be decreased in stages to investigate the rock mass instability. The strength of the contact surface should be divided into stages from the stable state to the final sliding state, as listed in Table3.Table 3
Strength degradation stages criteria.
Stage classification
Normal stiffness (GPa)
Tangential stiffness (GPa)
Cohesive strength (kPa)
Friction angle (°)
First stage
10
10
148
21
Second stage
10
10
36
20
Third stage
10
10
25
19
Fourth stage
10
10
18
18The axial force variation in the NPR anchor cables located at 478 m steps in the landslide body is also divided into four stages, as shown in Figure20.Figure 20
Stairs of axis force change of NPR anchor cables.The four stages shown in Figure20 are as follows:Stage 1 (shovel excavation at the foot of the slope): the axial force of the NPR anchor cable increases gradually because of the disturbance of shovel excavation on the 430 m steps.Stage 2 (old sliding body revival): with the excavation of the electric shovel, the sliding force of the slope increases, the old sliding body revives, the strength of the weak interlayer of the sliding surface decreases gradually, and the axial force of the NPR anchor cable increases sharply; however, the sliding surface does not produce relative displacement.Stage 3 (relative displacement of 16-1101 slip surface): the slope has reached the safety threshold because of the shovel excavation, microcracks appear in the rock mass, relative displacement of the slip surface begins to appear, and the axial force of the NPR anchor cable increases suddenly.Stage 4 (16-1101 landslide facing slip warning): the sliding surface completely losses its stability and sends out early warning information.In summary, the actual monitoring results and simulation results are in close agreement, providing a theoretical and practical basis for the mechanistic analysis and numerical simulation calculation of other similar slopes.


#### 4.2.4. Landslide Numerical Simulation Based on 3DEC

The NPR anchor cable model was constructed by 3DEC software, and the static tension and mechanical characteristics were simulated, as shown in Figure21.Figure 21
NPR anchor cable model and its static tensile properties.The boundary of the old landslide body and “16-1101 landslide body” and the boundary of the excavation area of the shovel are shown in Figure22.Figure 22
Model building and meshing.The NPR anchor parameters are listed in Table4.Table 4
Parameters of anchor cable.
Anchor cable
Length (m)
Inclination (°)
Preload (kN)
Value of consistence (kN)
75
30
400
850The rock mechanical parameters are listed in Table5.(1)
The double-sliding model is shown below (Figure23).Table 5
Parameters of rock mechanics.
Rock mass name
Bulk weight(kg/m3)
Bulk modulus (GPa)
Shear modulus (GPa)
Cohesion (kPa)
Friction angle (°)
Tensile strength (MPa)
Basement
2900
40
18
420
36
1.5
Sliding mass
2500
20
8
70
27
0.2Figure 23
Double-sliding model created by 3DEC.(1) Analysis of the Simulation Results
(i)
The Mohr–Coulomb elastic-plastic model was used to observe the displacement contours of the slip surface, settlement curve, and NPR cable axial force curve.
(ii)
The sign of the stability of the slope is that the subsidence curve does not change, but the calculation is continued.
As shown in Figure24, the maximum displacement of the old landslide is 1.2 m after stabilization. The landslide body is basically located at the set position of the contact surface of the model. When the landslide starts, the strength of the contact surface is set to the actual strength of the sliding surface and then slides to the stable state. Because of the reinforcement of multiple anchor cables with constant resistance and large deformation, the 16-1101 sliding body does not slip and disintegrate as a whole, but only emerges from the tongue. In the present extrusion failure mode, tension fracture occurs in the middle and rear edges.
(iii)
Numerical simulation analysis of “16-1101 landslide”Figure 24
Displacement contour after landslide stabilization.The speed and deformation of the old landslide body set to zero to fully consider the effect of the accumulated load caused by the old landslide body. The numerical simulation of the “16-1101 landslide” started, and the typical three-step process was used to reproduce the entire landslide instability process.The “16-1101 landslide” started as a second landslide after the instability of the old landslide body in the upper part. Figure25 shows the displacement change contour (intercepting steps 9401, 22401, and 29401), and the final displacement contour of the landslide more intuitively shows the whole process of the “16-1101 landslide” instability. The direct cause of the ultimate instability of the whole slope is the penetration of the sliding surface, and the antisliding force is less than the sliding force, gradually deteriorating the strength of the old landslide body. Therefore, in practical calculation, the strength of the contact surface (sliding surface) should be weakened to decrease the rock mass instability. The strength of the contact surface should be divided into stages from the stable state to the final sliding state, as listed in Table 6.Figure 25
16-1101 landslide instability displacement contour.Table 6
Criteria of strength degradation stages.
Stage classification
Normal stiffness (GPa)
Tangential stiffness (GPa)
Cohesive strength (kPa)
Friction angle (°)
First stage
9
14
148
21
Second stage
9
12
36
20
Third stage
9
10
25
19
Fourth stage
9
8
18
18After the start of “16-1101 landslide,” the axial force variation characteristics of the NPR anchor cable, the elongation variation curve of the anchor cable, the vertical relative displacement curve of monitoring point 1 on the upper edge of the old landslide body, and the vertical relative displacement curve of monitoring point 2 on the upper edge of “16-1101 landslide” are shown in Figure26.Figure 26
Monitoring curve of 16-1101 landslide by 3DEC software: (a) anchor cable force; (b) anchor cable elongation; (c) vertical relative displacement of monitoring point 1; (d) vertical relative displacement of monitoring point 2.Figure27 shows the monitoring point 1 of the subsidence at the upper edge of the old landslide body and monitoring point 2 of the subsidence at the upper edge of the “16-1101 landslide.”Figure 27
Layout of the landslide settlement.The four stages shown in Figure26 are summarized as follows:Stage 1 (shovel excavation at the foot of the slope): the slope body is affected by the disturbance of shovel excavation on 430 m steps. The axial force of the NPR anchor cable increases from 400 kN to 530 kN, and its elongation reaches 0.3 m. The sliding distance is 0.6 m.Stage 2 (revival of the old sliding body): with the excavation of the electric shovel, the sliding force of the slope rock mass increases and then the old sliding body revives, the strength of weak sliding surface decreases gradually, and the axial force of the NPR anchor cable increases sharply; the curve of the axial force monitoring increases rapidly to 680 kN, the elongation of the anchor cable reaches 0.64 m, and the relative displacement of sliding surface is 1.54 m.Stage 3 (relative displacement of the 16-1101 slip surface): the slope reached the safety threshold because of shovel excavation. There are microcracks in the rock mass. The slip surface begins to displace relatively. The axial force of the NPR anchor cable rises rapidly to 770 kN, the elongation of the anchor cable reaches 0.84 m, and the slip body generates a relative displacement of 1.87 m along the potential slip surface.Stage 4 (16-1101 slope near landslide warning): the axial force of the NPR anchor cable continues to rise to a constant resistance of 850 kN. When the relative displacement of the sliding surface reaches 2.54 m, the sliding surface completely losses stability, the anchor cable fails, the axial force suddenly drops to 18 kN, and the anchor cable extends to 1.45 m, eventually sending out warning information.According to the landslide process, three typical steps are selected in the displacement slice contour to reproduce the landslide process, as shown in Figure28.Figure 28
Key point displacement slice contour.The slope failure simulated by 3DEC is in close agreement to the field investigation parameters: “16-1101 landslide” has an actual settlement of 3.5 m at the top; the slope of the middle part is broken, and the crack zone appears; the sinking amount is 12 m; a compression deformation zone is formed at the bottom, and a settlement is in the range 2-3 m. It is accumulated at a height of 430 m platform at the bottom. Figure29 shows that the simulation results are consistent with the actual field situation.Figure 29
Comparison of simulation results with field conditions.The NPR anchor cables built at 478 m steps in the landslide body were further selected, and numerical simulation was performed on the whole process of landslide. The change in the axial force curve was observed (Figure30), indicating that the curves were significantly consistent with the field monitoring curves, providing a theoretical and practical basis for the analysis of landslide mechanism and numerical simulation calculation of other similar slopes.Figure 30
Comparison of numerical simulation curve and monitoring curve.


### 4.3. Comparison of the Simulation Results Obtained by FLAC3D and 3DEC Software

The whole landslide process was simulated and analyzed by FLAC3D and 3DEC software. The monitoring curve characteristics and the landslide displacement distribution contour obtained by the two software were compared as follows.


#### 4.3.1. Comparison of the Monitoring Curves

The axial force changes in the NPR anchor cables were monitored by FLAC3D and 3DEC software. The comparison shows that both have four different degrees of cracks, with identical curve trend and characteristics. As shown in Figure31, the curves of the axial force variation of the anchor cables were simulated by FLAC3D and 3DEC software in Figures 31(a) and 31(b), respectively.Figure 31
Comparison of the axial force variation curve of the NPR anchor cable.
(a)
(b)


#### 4.3.2. Comparison of Landslide Displacement Contour

The landslide instability process was also simulated by FLAC3D software and 3DEC software, as shown in Figure32. Figure 32(a) is simulated by FLAC3D, and the maximum deformation is ∼5 m; Figure 32(b) is simulated by 3DEC, and the maximum displacement is ∼6 m, showing a very small difference.Figure 32
Comparison of displacement distribution contour after the landslide instability process.
(a)
(b)


## 4.1. Characteristic Analysis of “16-1101 Landslide”

At 8:30 on September 14th, 2016, the No. 478-3 curve rose to point D, and the system issued a “long-term warning”; at 10:20 on October 1st, 2016, because of a working shovel under 430 m steps, the sliding force curve of No. 478-3 suddenly rose to point F, and the system issued a “medium-term warning.” The mine leaders asked all large machinery and extension workers to evacuate; at 23:52 on October 31st, 2016, the curve suddenly appeared. On November 1st, 2016, at 3:40, the monitoring system reported the occurrence of the landslide, producing a loud noise. The broken rock and soil mass rolled down along the slope and piled up on the 430 m step. The failure characteristics of the slope top behind the landslide are shown in Figure 14.Figure 14
Characteristics of the “16-1101 landslide.”


## 4.2. Numerical Simulation Analysis of the “16-1101” Landslide

In this section, the field monitoring data of “16-1101 landslide” in Nanfen open-pit iron mine was calculated by FLAC3D and 3DEC numerical simulation software to realize the recurrence of the landslide process. The numerical analysis model of the NPR anchor cable was constructed by Fish language in numerical simulation software. The model was analyzed, and the calculation was performed for the 16-1101 landslide to investigate the similarities and differences between the simulation and the actual monitoring results.


### 4.2.1. Principle of Large Deformation Design of NPR Anchor Cable in Numerical Simulation Software

The NPR anchor reinforcement unit is generally defined by geometric parameters, material parameters, and anchorage agent characteristics. The axial stiffness of the boltK is expressed by(2)K=AEL,where A is the cross-sectional area of the reinforcement, E is the elastic modulus of the bolt, and L is the length of the bolt.Conventional anchor cables do not have large deformation characteristics. For the NPR anchor cables, with constant resistance and large deformation characteristics, it is necessary to set the end of the anchor section with conventional anchorage strength and the end of the free section as the rigid contact with the rock mass through Fish language in the modeling process. The principle of large deformation is as follows: applying axial force at the end of the NPR anchor cable, when the axial force reaches the design constant resistanceP, the anchor cable will produce axial deformation, until the maximum deformation is reached, the failure of anchorage agent will be judged, and the anchor cable unit will be released to achieve the effect of large deformation.


### 4.2.2. Numerical Model Establishment of the 16-1101 Landslide

Calibration of model boundary and elevation: the maximum width of the old landslide body and “16-1101 landslide body” is 50 m, and the elevation limits are in the ranges 502–550 m and 430–502 m. Because the width of the model boundary is 2.5 times larger than the width of the target body, the height range of the model is 277–634 m, and the strike direction length is 200 m. In order to simulate the spatial relationship between the upper and lower sliding bodies and the interface characteristics of the sliding body during the start-up process, setting the interface elements between the sliding body and the rock foundation is necessary. The back, bottom, and both sides of the landslide body have a fixed boundary, and the upper and front parts have a free boundary.


### 4.2.3. Landslide Numerical Simulation Based on FLAC3D

The NPR anchor cable model was constructed by FLAC3D software, as shown in Figure15. The static tensile mechanical properties are shown in Figure 16.Figure 15
The NPR anchor cable model.Figure 16
The static tensile mechanical properties.(1) Insertion of the NPR Anchor Cable Model. The parameters of the NPR anchor cable model were determined by the coordinates of the monitoring points of the deep sliding force and buried depth of the NPR anchor cable: inclination angle, 30°; length, 75 m; preload force, 40 kN; and constant resistance value, 85 kN. The excavation length of the 430 platform shovel is set to 70 m. The rock mechanical parameters are as follows (Table 2).Table 2
Parameters of rock mechanics.
Rock mass name
Bulk weight(kg/m3)
Bulk modulus (GPa)
Shear modulus (GPa)
Cohesion (kPa)
Friction angle (°)
Tensile strength (MPa)
Basement
2873
20
10.9
420
36
1.5
Sliding mass
2580
5.2
2.10
70
27
0.2Figure17 shows the double-sliding body model.Figure 17
Construction of double-sliding body model.Figure 18
Displacement contour of the old landslide after stabilization.Figure 19
“16-1101 landslide” instability displacement contour.(2) Analysis of Simulation Results
(i)
Numerical simulation analysis of the old landslide (Figure18)
Principles of simulation:(a)
When the maximum unbalance forceF is <1e − 5, the software determines the landslide as stable.(b)
When the calculation exceeds 10,000 steps and the model is still unstable, the calculation is stopped, and the model is considered to be in a plastic flow state.(c)
Observe the strain increment contour of the sliding surface. When the sliding surface passes through, the software determines the sliding surface instability and stops calculation.
According to these three principles, the maximum displacement of the old landslide after stabilization is ∼1.3 m. The landslide body is basically located at the set position of the contact surface of the model. When the slope slides, the strength of the contact surface is set as the actual strength of the sliding surface and then slides until reaching the stable state.
(ii)
Numerical simulation analysis of “16-1101 landslide” (Figure19)The numerical simulation of “16-1101 landslide” was carried out by setting both the velocity and deformation of the old landslide in the calculation as zero.After the appearance of “16-1101 landslide,” the old landslide body “resurrected” and then slipped, and the 502 m step appeared staggered. The direct cause of the ultimate instability of the whole slope is the transfixion of the sliding surface, and the antisliding force is less than the sliding force. Therefore, in practical calculation, the strength of the contact surface (sliding surface) should also be decreased in stages to investigate the rock mass instability. The strength of the contact surface should be divided into stages from the stable state to the final sliding state, as listed in Table3.Table 3
Strength degradation stages criteria.
Stage classification
Normal stiffness (GPa)
Tangential stiffness (GPa)
Cohesive strength (kPa)
Friction angle (°)
First stage
10
10
148
21
Second stage
10
10
36
20
Third stage
10
10
25
19
Fourth stage
10
10
18
18The axial force variation in the NPR anchor cables located at 478 m steps in the landslide body is also divided into four stages, as shown in Figure20.Figure 20
Stairs of axis force change of NPR anchor cables.The four stages shown in Figure20 are as follows:Stage 1 (shovel excavation at the foot of the slope): the axial force of the NPR anchor cable increases gradually because of the disturbance of shovel excavation on the 430 m steps.Stage 2 (old sliding body revival): with the excavation of the electric shovel, the sliding force of the slope increases, the old sliding body revives, the strength of the weak interlayer of the sliding surface decreases gradually, and the axial force of the NPR anchor cable increases sharply; however, the sliding surface does not produce relative displacement.Stage 3 (relative displacement of 16-1101 slip surface): the slope has reached the safety threshold because of the shovel excavation, microcracks appear in the rock mass, relative displacement of the slip surface begins to appear, and the axial force of the NPR anchor cable increases suddenly.Stage 4 (16-1101 landslide facing slip warning): the sliding surface completely losses its stability and sends out early warning information.In summary, the actual monitoring results and simulation results are in close agreement, providing a theoretical and practical basis for the mechanistic analysis and numerical simulation calculation of other similar slopes.


### 4.2.4. Landslide Numerical Simulation Based on 3DEC

The NPR anchor cable model was constructed by 3DEC software, and the static tension and mechanical characteristics were simulated, as shown in Figure21.Figure 21
NPR anchor cable model and its static tensile properties.The boundary of the old landslide body and “16-1101 landslide body” and the boundary of the excavation area of the shovel are shown in Figure22.Figure 22
Model building and meshing.The NPR anchor parameters are listed in Table4.Table 4
Parameters of anchor cable.
Anchor cable
Length (m)
Inclination (°)
Preload (kN)
Value of consistence (kN)
75
30
400
850The rock mechanical parameters are listed in Table5.(1)
The double-sliding model is shown below (Figure23).Table 5
Parameters of rock mechanics.
Rock mass name
Bulk weight(kg/m3)
Bulk modulus (GPa)
Shear modulus (GPa)
Cohesion (kPa)
Friction angle (°)
Tensile strength (MPa)
Basement
2900
40
18
420
36
1.5
Sliding mass
2500
20
8
70
27
0.2Figure 23
Double-sliding model created by 3DEC.(1) Analysis of the Simulation Results
(i)
The Mohr–Coulomb elastic-plastic model was used to observe the displacement contours of the slip surface, settlement curve, and NPR cable axial force curve.
(ii)
The sign of the stability of the slope is that the subsidence curve does not change, but the calculation is continued.
As shown in Figure24, the maximum displacement of the old landslide is 1.2 m after stabilization. The landslide body is basically located at the set position of the contact surface of the model. When the landslide starts, the strength of the contact surface is set to the actual strength of the sliding surface and then slides to the stable state. Because of the reinforcement of multiple anchor cables with constant resistance and large deformation, the 16-1101 sliding body does not slip and disintegrate as a whole, but only emerges from the tongue. In the present extrusion failure mode, tension fracture occurs in the middle and rear edges.
(iii)
Numerical simulation analysis of “16-1101 landslide”Figure 24
Displacement contour after landslide stabilization.The speed and deformation of the old landslide body set to zero to fully consider the effect of the accumulated load caused by the old landslide body. The numerical simulation of the “16-1101 landslide” started, and the typical three-step process was used to reproduce the entire landslide instability process.The “16-1101 landslide” started as a second landslide after the instability of the old landslide body in the upper part. Figure25 shows the displacement change contour (intercepting steps 9401, 22401, and 29401), and the final displacement contour of the landslide more intuitively shows the whole process of the “16-1101 landslide” instability. The direct cause of the ultimate instability of the whole slope is the penetration of the sliding surface, and the antisliding force is less than the sliding force, gradually deteriorating the strength of the old landslide body. Therefore, in practical calculation, the strength of the contact surface (sliding surface) should be weakened to decrease the rock mass instability. The strength of the contact surface should be divided into stages from the stable state to the final sliding state, as listed in Table 6.Figure 25
16-1101 landslide instability displacement contour.Table 6
Criteria of strength degradation stages.
Stage classification
Normal stiffness (GPa)
Tangential stiffness (GPa)
Cohesive strength (kPa)
Friction angle (°)
First stage
9
14
148
21
Second stage
9
12
36
20
Third stage
9
10
25
19
Fourth stage
9
8
18
18After the start of “16-1101 landslide,” the axial force variation characteristics of the NPR anchor cable, the elongation variation curve of the anchor cable, the vertical relative displacement curve of monitoring point 1 on the upper edge of the old landslide body, and the vertical relative displacement curve of monitoring point 2 on the upper edge of “16-1101 landslide” are shown in Figure26.Figure 26
Monitoring curve of 16-1101 landslide by 3DEC software: (a) anchor cable force; (b) anchor cable elongation; (c) vertical relative displacement of monitoring point 1; (d) vertical relative displacement of monitoring point 2.Figure27 shows the monitoring point 1 of the subsidence at the upper edge of the old landslide body and monitoring point 2 of the subsidence at the upper edge of the “16-1101 landslide.”Figure 27
Layout of the landslide settlement.The four stages shown in Figure26 are summarized as follows:Stage 1 (shovel excavation at the foot of the slope): the slope body is affected by the disturbance of shovel excavation on 430 m steps. The axial force of the NPR anchor cable increases from 400 kN to 530 kN, and its elongation reaches 0.3 m. The sliding distance is 0.6 m.Stage 2 (revival of the old sliding body): with the excavation of the electric shovel, the sliding force of the slope rock mass increases and then the old sliding body revives, the strength of weak sliding surface decreases gradually, and the axial force of the NPR anchor cable increases sharply; the curve of the axial force monitoring increases rapidly to 680 kN, the elongation of the anchor cable reaches 0.64 m, and the relative displacement of sliding surface is 1.54 m.Stage 3 (relative displacement of the 16-1101 slip surface): the slope reached the safety threshold because of shovel excavation. There are microcracks in the rock mass. The slip surface begins to displace relatively. The axial force of the NPR anchor cable rises rapidly to 770 kN, the elongation of the anchor cable reaches 0.84 m, and the slip body generates a relative displacement of 1.87 m along the potential slip surface.Stage 4 (16-1101 slope near landslide warning): the axial force of the NPR anchor cable continues to rise to a constant resistance of 850 kN. When the relative displacement of the sliding surface reaches 2.54 m, the sliding surface completely losses stability, the anchor cable fails, the axial force suddenly drops to 18 kN, and the anchor cable extends to 1.45 m, eventually sending out warning information.According to the landslide process, three typical steps are selected in the displacement slice contour to reproduce the landslide process, as shown in Figure28.Figure 28
Key point displacement slice contour.The slope failure simulated by 3DEC is in close agreement to the field investigation parameters: “16-1101 landslide” has an actual settlement of 3.5 m at the top; the slope of the middle part is broken, and the crack zone appears; the sinking amount is 12 m; a compression deformation zone is formed at the bottom, and a settlement is in the range 2-3 m. It is accumulated at a height of 430 m platform at the bottom. Figure29 shows that the simulation results are consistent with the actual field situation.Figure 29
Comparison of simulation results with field conditions.The NPR anchor cables built at 478 m steps in the landslide body were further selected, and numerical simulation was performed on the whole process of landslide. The change in the axial force curve was observed (Figure30), indicating that the curves were significantly consistent with the field monitoring curves, providing a theoretical and practical basis for the analysis of landslide mechanism and numerical simulation calculation of other similar slopes.Figure 30
Comparison of numerical simulation curve and monitoring curve.


## 4.2.1. Principle of Large Deformation Design of NPR Anchor Cable in Numerical Simulation Software

The NPR anchor reinforcement unit is generally defined by geometric parameters, material parameters, and anchorage agent characteristics. The axial stiffness of the boltK is expressed by(2)K=AEL,where A is the cross-sectional area of the reinforcement, E is the elastic modulus of the bolt, and L is the length of the bolt.Conventional anchor cables do not have large deformation characteristics. For the NPR anchor cables, with constant resistance and large deformation characteristics, it is necessary to set the end of the anchor section with conventional anchorage strength and the end of the free section as the rigid contact with the rock mass through Fish language in the modeling process. The principle of large deformation is as follows: applying axial force at the end of the NPR anchor cable, when the axial force reaches the design constant resistanceP, the anchor cable will produce axial deformation, until the maximum deformation is reached, the failure of anchorage agent will be judged, and the anchor cable unit will be released to achieve the effect of large deformation.


## 4.2.2. Numerical Model Establishment of the 16-1101 Landslide

Calibration of model boundary and elevation: the maximum width of the old landslide body and “16-1101 landslide body” is 50 m, and the elevation limits are in the ranges 502–550 m and 430–502 m. Because the width of the model boundary is 2.5 times larger than the width of the target body, the height range of the model is 277–634 m, and the strike direction length is 200 m. In order to simulate the spatial relationship between the upper and lower sliding bodies and the interface characteristics of the sliding body during the start-up process, setting the interface elements between the sliding body and the rock foundation is necessary. The back, bottom, and both sides of the landslide body have a fixed boundary, and the upper and front parts have a free boundary.


## 4.2.3. Landslide Numerical Simulation Based on FLAC3D

The NPR anchor cable model was constructed by FLAC3D software, as shown in Figure15. The static tensile mechanical properties are shown in Figure 16.Figure 15
The NPR anchor cable model.Figure 16
The static tensile mechanical properties.(1) Insertion of the NPR Anchor Cable Model. The parameters of the NPR anchor cable model were determined by the coordinates of the monitoring points of the deep sliding force and buried depth of the NPR anchor cable: inclination angle, 30°; length, 75 m; preload force, 40 kN; and constant resistance value, 85 kN. The excavation length of the 430 platform shovel is set to 70 m. The rock mechanical parameters are as follows (Table 2).Table 2
Parameters of rock mechanics.
Rock mass name
Bulk weight(kg/m3)
Bulk modulus (GPa)
Shear modulus (GPa)
Cohesion (kPa)
Friction angle (°)
Tensile strength (MPa)
Basement
2873
20
10.9
420
36
1.5
Sliding mass
2580
5.2
2.10
70
27
0.2Figure17 shows the double-sliding body model.Figure 17
Construction of double-sliding body model.Figure 18
Displacement contour of the old landslide after stabilization.Figure 19
“16-1101 landslide” instability displacement contour.(2) Analysis of Simulation Results
(i)
Numerical simulation analysis of the old landslide (Figure18)
Principles of simulation:(a)
When the maximum unbalance forceF is <1e − 5, the software determines the landslide as stable.(b)
When the calculation exceeds 10,000 steps and the model is still unstable, the calculation is stopped, and the model is considered to be in a plastic flow state.(c)
Observe the strain increment contour of the sliding surface. When the sliding surface passes through, the software determines the sliding surface instability and stops calculation.
According to these three principles, the maximum displacement of the old landslide after stabilization is ∼1.3 m. The landslide body is basically located at the set position of the contact surface of the model. When the slope slides, the strength of the contact surface is set as the actual strength of the sliding surface and then slides until reaching the stable state.
(ii)
Numerical simulation analysis of “16-1101 landslide” (Figure19)The numerical simulation of “16-1101 landslide” was carried out by setting both the velocity and deformation of the old landslide in the calculation as zero.After the appearance of “16-1101 landslide,” the old landslide body “resurrected” and then slipped, and the 502 m step appeared staggered. The direct cause of the ultimate instability of the whole slope is the transfixion of the sliding surface, and the antisliding force is less than the sliding force. Therefore, in practical calculation, the strength of the contact surface (sliding surface) should also be decreased in stages to investigate the rock mass instability. The strength of the contact surface should be divided into stages from the stable state to the final sliding state, as listed in Table3.Table 3
Strength degradation stages criteria.
Stage classification
Normal stiffness (GPa)
Tangential stiffness (GPa)
Cohesive strength (kPa)
Friction angle (°)
First stage
10
10
148
21
Second stage
10
10
36
20
Third stage
10
10
25
19
Fourth stage
10
10
18
18The axial force variation in the NPR anchor cables located at 478 m steps in the landslide body is also divided into four stages, as shown in Figure20.Figure 20
Stairs of axis force change of NPR anchor cables.The four stages shown in Figure20 are as follows:Stage 1 (shovel excavation at the foot of the slope): the axial force of the NPR anchor cable increases gradually because of the disturbance of shovel excavation on the 430 m steps.Stage 2 (old sliding body revival): with the excavation of the electric shovel, the sliding force of the slope increases, the old sliding body revives, the strength of the weak interlayer of the sliding surface decreases gradually, and the axial force of the NPR anchor cable increases sharply; however, the sliding surface does not produce relative displacement.Stage 3 (relative displacement of 16-1101 slip surface): the slope has reached the safety threshold because of the shovel excavation, microcracks appear in the rock mass, relative displacement of the slip surface begins to appear, and the axial force of the NPR anchor cable increases suddenly.Stage 4 (16-1101 landslide facing slip warning): the sliding surface completely losses its stability and sends out early warning information.In summary, the actual monitoring results and simulation results are in close agreement, providing a theoretical and practical basis for the mechanistic analysis and numerical simulation calculation of other similar slopes.


## 4.2.4. Landslide Numerical Simulation Based on 3DEC

The NPR anchor cable model was constructed by 3DEC software, and the static tension and mechanical characteristics were simulated, as shown in Figure21.Figure 21
NPR anchor cable model and its static tensile properties.The boundary of the old landslide body and “16-1101 landslide body” and the boundary of the excavation area of the shovel are shown in Figure22.Figure 22
Model building and meshing.The NPR anchor parameters are listed in Table4.Table 4
Parameters of anchor cable.
Anchor cable
Length (m)
Inclination (°)
Preload (kN)
Value of consistence (kN)
75
30
400
850The rock mechanical parameters are listed in Table5.(1)
The double-sliding model is shown below (Figure23).Table 5
Parameters of rock mechanics.
Rock mass name
Bulk weight(kg/m3)
Bulk modulus (GPa)
Shear modulus (GPa)
Cohesion (kPa)
Friction angle (°)
Tensile strength (MPa)
Basement
2900
40
18
420
36
1.5
Sliding mass
2500
20
8
70
27
0.2Figure 23
Double-sliding model created by 3DEC.(1) Analysis of the Simulation Results
(i)
The Mohr–Coulomb elastic-plastic model was used to observe the displacement contours of the slip surface, settlement curve, and NPR cable axial force curve.
(ii)
The sign of the stability of the slope is that the subsidence curve does not change, but the calculation is continued.
As shown in Figure24, the maximum displacement of the old landslide is 1.2 m after stabilization. The landslide body is basically located at the set position of the contact surface of the model. When the landslide starts, the strength of the contact surface is set to the actual strength of the sliding surface and then slides to the stable state. Because of the reinforcement of multiple anchor cables with constant resistance and large deformation, the 16-1101 sliding body does not slip and disintegrate as a whole, but only emerges from the tongue. In the present extrusion failure mode, tension fracture occurs in the middle and rear edges.
(iii)
Numerical simulation analysis of “16-1101 landslide”Figure 24
Displacement contour after landslide stabilization.The speed and deformation of the old landslide body set to zero to fully consider the effect of the accumulated load caused by the old landslide body. The numerical simulation of the “16-1101 landslide” started, and the typical three-step process was used to reproduce the entire landslide instability process.The “16-1101 landslide” started as a second landslide after the instability of the old landslide body in the upper part. Figure25 shows the displacement change contour (intercepting steps 9401, 22401, and 29401), and the final displacement contour of the landslide more intuitively shows the whole process of the “16-1101 landslide” instability. The direct cause of the ultimate instability of the whole slope is the penetration of the sliding surface, and the antisliding force is less than the sliding force, gradually deteriorating the strength of the old landslide body. Therefore, in practical calculation, the strength of the contact surface (sliding surface) should be weakened to decrease the rock mass instability. The strength of the contact surface should be divided into stages from the stable state to the final sliding state, as listed in Table 6.Figure 25
16-1101 landslide instability displacement contour.Table 6
Criteria of strength degradation stages.
Stage classification
Normal stiffness (GPa)
Tangential stiffness (GPa)
Cohesive strength (kPa)
Friction angle (°)
First stage
9
14
148
21
Second stage
9
12
36
20
Third stage
9
10
25
19
Fourth stage
9
8
18
18After the start of “16-1101 landslide,” the axial force variation characteristics of the NPR anchor cable, the elongation variation curve of the anchor cable, the vertical relative displacement curve of monitoring point 1 on the upper edge of the old landslide body, and the vertical relative displacement curve of monitoring point 2 on the upper edge of “16-1101 landslide” are shown in Figure26.Figure 26
Monitoring curve of 16-1101 landslide by 3DEC software: (a) anchor cable force; (b) anchor cable elongation; (c) vertical relative displacement of monitoring point 1; (d) vertical relative displacement of monitoring point 2.Figure27 shows the monitoring point 1 of the subsidence at the upper edge of the old landslide body and monitoring point 2 of the subsidence at the upper edge of the “16-1101 landslide.”Figure 27
Layout of the landslide settlement.The four stages shown in Figure26 are summarized as follows:Stage 1 (shovel excavation at the foot of the slope): the slope body is affected by the disturbance of shovel excavation on 430 m steps. The axial force of the NPR anchor cable increases from 400 kN to 530 kN, and its elongation reaches 0.3 m. The sliding distance is 0.6 m.Stage 2 (revival of the old sliding body): with the excavation of the electric shovel, the sliding force of the slope rock mass increases and then the old sliding body revives, the strength of weak sliding surface decreases gradually, and the axial force of the NPR anchor cable increases sharply; the curve of the axial force monitoring increases rapidly to 680 kN, the elongation of the anchor cable reaches 0.64 m, and the relative displacement of sliding surface is 1.54 m.Stage 3 (relative displacement of the 16-1101 slip surface): the slope reached the safety threshold because of shovel excavation. There are microcracks in the rock mass. The slip surface begins to displace relatively. The axial force of the NPR anchor cable rises rapidly to 770 kN, the elongation of the anchor cable reaches 0.84 m, and the slip body generates a relative displacement of 1.87 m along the potential slip surface.Stage 4 (16-1101 slope near landslide warning): the axial force of the NPR anchor cable continues to rise to a constant resistance of 850 kN. When the relative displacement of the sliding surface reaches 2.54 m, the sliding surface completely losses stability, the anchor cable fails, the axial force suddenly drops to 18 kN, and the anchor cable extends to 1.45 m, eventually sending out warning information.According to the landslide process, three typical steps are selected in the displacement slice contour to reproduce the landslide process, as shown in Figure28.Figure 28
Key point displacement slice contour.The slope failure simulated by 3DEC is in close agreement to the field investigation parameters: “16-1101 landslide” has an actual settlement of 3.5 m at the top; the slope of the middle part is broken, and the crack zone appears; the sinking amount is 12 m; a compression deformation zone is formed at the bottom, and a settlement is in the range 2-3 m. It is accumulated at a height of 430 m platform at the bottom. Figure29 shows that the simulation results are consistent with the actual field situation.Figure 29
Comparison of simulation results with field conditions.The NPR anchor cables built at 478 m steps in the landslide body were further selected, and numerical simulation was performed on the whole process of landslide. The change in the axial force curve was observed (Figure30), indicating that the curves were significantly consistent with the field monitoring curves, providing a theoretical and practical basis for the analysis of landslide mechanism and numerical simulation calculation of other similar slopes.Figure 30
Comparison of numerical simulation curve and monitoring curve.


## 4.3. Comparison of the Simulation Results Obtained by FLAC3D and 3DEC Software

The whole landslide process was simulated and analyzed by FLAC3D and 3DEC software. The monitoring curve characteristics and the landslide displacement distribution contour obtained by the two software were compared as follows.


### 4.3.1. Comparison of the Monitoring Curves

The axial force changes in the NPR anchor cables were monitored by FLAC3D and 3DEC software. The comparison shows that both have four different degrees of cracks, with identical curve trend and characteristics. As shown in Figure31, the curves of the axial force variation of the anchor cables were simulated by FLAC3D and 3DEC software in Figures 31(a) and 31(b), respectively.Figure 31
Comparison of the axial force variation curve of the NPR anchor cable.
(a)
(b)


### 4.3.2. Comparison of Landslide Displacement Contour

The landslide instability process was also simulated by FLAC3D software and 3DEC software, as shown in Figure32. Figure 32(a) is simulated by FLAC3D, and the maximum deformation is ∼5 m; Figure 32(b) is simulated by 3DEC, and the maximum displacement is ∼6 m, showing a very small difference.Figure 32
Comparison of displacement distribution contour after the landslide instability process.
(a)
(b)


## 4.3.1. Comparison of the Monitoring Curves

The axial force changes in the NPR anchor cables were monitored by FLAC3D and 3DEC software. The comparison shows that both have four different degrees of cracks, with identical curve trend and characteristics. As shown in Figure31, the curves of the axial force variation of the anchor cables were simulated by FLAC3D and 3DEC software in Figures 31(a) and 31(b), respectively.Figure 31
Comparison of the axial force variation curve of the NPR anchor cable.
(a)
(b)


## 4.3.2. Comparison of Landslide Displacement Contour

The landslide instability process was also simulated by FLAC3D software and 3DEC software, as shown in Figure32. Figure 32(a) is simulated by FLAC3D, and the maximum deformation is ∼5 m; Figure 32(b) is simulated by 3DEC, and the maximum displacement is ∼6 m, showing a very small difference.Figure 32
Comparison of displacement distribution contour after the landslide instability process.
(a)
(b)


## 5. Conclusions

In this study, numerical simulation was carried out on the whole process of large deformation and failure of 16-1101 landslide, and the following conclusions were obtained:(1)
Based on the theory of Cataclysm mechanics, a large deformation numerical calculation model of the NPR anchor cable was constructed, and the simulated curve has a significant constant resistance effect, confirming that the large deformation can be achieved without damage.(2)
The numerical analysis model of the NPR anchor cable with constant resistance large deformation was constructed by Fish language in the finite element numerical simulation software FLAC3D, and it is embedded in the “2016-1101 landslide,” achieving the numerical simulation of monitoring and warning of Newtonian force. The comparison between the numerical simulation results and the field measurement results shows good agreement between the simulation monitoring curve and the field monitoring curve and proves that this model can be used to monitor the landslide model of Nanfen open-pit mine.(3)
The numerical calculation model of the NPR anchor cable was constructed by the discrete element software 3DEC. The numerical simulation monitoring curve of the anchor cable force shows four times of rise and one time of decline, coinciding with the field monitoring curve. The numerical simulation calculation of the whole process monitoring and early warning target of 16-1101 landslide in Nanfen open-pit iron mine was realized, indicating that the model can be used in Nanfen open-pit mine.(4)
The numerical simulation results of the landslide by FLAC3D and 3DEC software were compared and analyzed, indicating a significant consistency between them. The characteristic cracks are relatively consistent, and the trend of landslide also coincides. The maximum deformation is in the range 5-6 m, with a small difference, thus providing a theoretical and practical basis for the mechanistic analysis and numerical simulation of other similar slopes.



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*Source: 8241509-2020-01-06.xml*