Slope Rock Mass Research Articles

Freeze-Thaw Effects on Stability of Open Pit Slope in High-Altitude and Cold Regions

The cycle of the freeze-thaw action must be taken into account in the stability analysis of an open pit slope in the high-altitude and cold regions, because the natural process of freeze-thaw poses a significant effect on mechanical properties of the rock mass. To achieve this purpose, a linear relationship between the geological strength index (GSI) and the Tianshan slope rock mass rating (TSMR) system is established considering the effect of the freeze-thaw action by introducing a freeze-thaw correction coefficient δ. The GSI value is modified for rock mass in high-altitude and cold regions. The improved Hoek-Brown criterion considers the influences of the freeze-thaw action and steep and gentle slopes. The research outcome is applied in the No. 4 minefield open pit coal mine in the Muli mining area. Numerical calculations are performed by inputting rock mass mechanical parameters obtained in traditional and modified criterions, to discuss the influences of the freeze-thaw action on the stabilities of both the present mining slope and the final slope at the end of the designed mining. The results show that the safety factors of the original slope are 2.33 and 1.67, respectively, while after the modification, they are 2.14 and 1.61, respectively. In terms of the No. 4 minefield open pit coal mine, the slope stability meets the design requirement, although taking the freeze-thaw cycle into account.

The Failure Mechanism and Stability of the End Slope of Inclined Composite Coal Seam

In view of the inclined occurrence of coal seam in Heishan open-pit coal mine, in the longitudinal exploitation process of the first mining area, the height of the slope at the west end is increasing, and the occurrence of weak interlayer in the slope is in production. The failure mechanism and stability of the end slope of the inclined composite coal seam, which is typical of the West end slope of Heishan open-pit mine, are studied by means of field investigation, theoretical analysis, limit equilibrium analysis, and numerical simulation. The factors affecting the stability of the western side slope and the potential landslide mode are analyzed. The residual thrust method and simplified Bishop method were used to study the stability of two potential landslide modes on the western slope, and the landslide mode, final slope angle, and slope morphology were determined. FLAC3D was used to simulate the western end of the slope, reveal its landslide mechanism, and clarify the evolution law of the slope rock mass displacement. The results show that the landslide mode at the west end of the first mining area is the combined sliding mode of “cutting and bedding.” With the decrease of longitudinal mining depth, the final slope angle functions from 40° to 37°. The stress and strain are concentrated at the weak layer of the coal floor of the western side slope 13-2 and at the foot of the slope. Meanwhile, the failure also occurs inside the slope. The internal cracks connect through the weak layer of the coal floor and slide along the weak layer of the coal floor 13-2. The displacement evolution law of the slope monitoring point shows that the deformation of the slope is mainly horizontal displacement, the maximum displacement deformation is at the foot of the slope, and the degree of displacement deformation of the slope surface is obviously greater than that of the inside of the slope.

Experimental Study on Vibration Reduction Technology of Hole-by-Hole Presplitting Blasting

In order to effectively reduce the disturbance of the precrack blasting vibration on slope rock mass, except paying attention to the damping effect of the precrack, it is also necessary to optimize the blasting parameters and initiation mode of the precrack itself. Based on the blasting theory and empirical formula, the parameters of presplitting blasting such as the hole diameter, hole spacing, charge decoupling coefficient, and line charge density were determined, and field tests of conventional pre-splitting blasting and presplitting blasting with precise delay and hole-by-hole initiation were carried out on the west slope of Buzhaoba. Regression analysis was carried out on the vibration monitoring data, and the blasting vibration attenuation regularity of slope particles was obtained. By comparing the monitored vibration velocity of the two presplitting blasting tests and the forecast results of theoretical calculation, the average reduction rate of the conventional same row blasting vibration is 26.40%, while that of the hole-by-hole blasting vibration can reach 41.45% with a half hole rate of 80.7% and an irregularity of about 130 mm. Results show that the effect of precise delay initiation between preholes based on the digital electronic detonator is better than that of the simultaneous initiation of preholes. Therefore, it is suggested that the hole-by-hole presplitting blasting technology should be applied in the excavation of boundary slope and the treatment of high and steep slope.

Rock mass classification and rock mass slope failures along Bang Pa-In to Nakhon Ratchasima intercity motorway (M6) Project, Thailand

This research intends to use the Rock Mass Rating (RMR) and the Slope Mass Rating (SMR) systems to evaluate the rock mass classes of the road cut slope in the construction of the Bang Pa-In-Nakhon Ratchasima intercity motorway (M6) project, sections 19, 20, and 21. The study area consists of a mountain and plain landform with limestone, sandstone interbedded with shale, and structural control. Drill and blast techniques were utilized to excavate and develop the slope face as well. Kinematic analysis was also used to classify potential slope failure and estimate the adjustment factors. The result found that three sections of the study area have the potential failures of the wedge, toppling, and planar. In section 19, the SMR class is normal to good and stable to a partial stable of slope that is a failure with toppling and wedge on the right and wedge on the left side. Section 20 is normal and partially slope stable, with three types of failure on the left side, but a wedge and toppling on the right side. Section 21 is a good class, and the slope is stable, but slightly wedged and toppling failure on some blocks on the right side and only wedged on the left site as indicated.

Influence Factors of the Slope Rockmass Deformation Characteristics based on in-situ tests

The Sanhekou reservoir arch dam (145m) is one of the highest in the world. It is founded on metamorphic sandstones and crystalline limestone. This work conducted an in-situ deformation test on various lithology and weathering degree rock developed in slope adits on dam abutment, under same loading paths and maximum pressure as that acting on the abutment rockmass. In the tests, factors of deformation behavior of slope rockmass were extracted and variation range of deformation parameters of different rockmass were evaluated. Results show that the three of factors (weathering degree, integrity degree and anisotropy) are the main ones influencing the deformation performance of slope rockmass.

The formation and failure process of Yigong landslide in Tibet Plateau

Yigong landslide is located in Zhamunong gully, Yigong Township, Bomi County, Linzhi region in Tibet, the volume of which is 3×108m3. Firstly, we analyse the formation mechanism of Yigong landslide in 2000, based on the field investigation and data collection. Secondly, we analyse the failure mechanism of Yigong landslide in 2000, combined with the mechanical test results of granite rock and stability calculation results of slumped mass (BH01). Under the combined effect of rapid incision and seismic activity in Yigong Lake zone, the basic factor of landslide formation is that the rock mass structure for controlled slope rock mass evolution has entered a stage of progressive failure in Zhamunong gully, and precipitating factors of landslide are excess melt-water and continuous rainfall under the temperature rise before landslide hazard happens, according to the results of the study. The formation process of landslide can be divided into 4 stages. (i) Trailing edge fracture of slope rock mass is in rapid development stage due to the effect of fast incision in the valley. (ii) The frequent seismic activities in Yigong Lake district facilitate the development and evolution of granite rock mass’s structural plane; (iii) The combined effect of excess melt-water and continuous rainfall at the prophase of the disaster makes the high angle fissure in trailing edge of BH01 rock fall body further develop. (iv) The high-speed rock fall block of BH01 rock fall body triggers the liquefaction of detrital accumulation materials at the source of gully, which forms landslide and finally transforms into high-speed granular mass flows. The stability-losing distruction mechanism of landslide is as follows. Under the combined effect of many conditions, such as fast incision of valley in Yigong district, earthquakes, temperature change, and continuous rainfall and so on, the high angle fissure in trailing edge of BH01 rock fall body develops quickly, and continuous creeping deformation occurs in rock fall body along weak structural plane or fracture surface, forming mid ‘locking section’. When the depth of cracking segment in trailing edge of BH01 rock fall body Hcr >363m or the length of rock mass’s locking section L<455m, sudden brittle failure occurs in the mid locking section of BH01 rock fall body, and rock fall occurs in rock fall body.

Computational tools for the analysis of circular failure of rock slopes

Among other types of failure in slopes created by excavation or filling, circular (also referred to as rotational) type of failure plays an important role in the design and stability analysis of high rock slopes, such as those encountered in deep open pit mines. When a rock slope of significant height involves predominantly one type of jointed rock mass, the scale of the problem is frequently such that the rock mass (intact rock and rock discontinuities) can be regarded as a homogeneous isotropic material. In such case, if the rock slope is unstable and collapse occurs, circular (or rotational) failure as in failed slopes in soils is also observed for the rock slope. One main goal in practical design of deep open pit mines is to determine safe inclination angles for the pit faces to be excavated to avoid failure. Computational tools for quick assessment of the stability conditions, in particular determination of factor of safety and location of the critical circular failure surface, are useful during the preliminary stages of open pit design. Among others, such tools allow the engineer to gain insight in the role that the different variables controlling the problem have in defining the stability conditions for the rock slope. This paper provides first an overview of typical numerical techniques used to assess the stability of high rock slopes. For the case of slopes in rock masses that are assumed to obey the Mohr-Coulomb or the Hoek-Brown failure criteria, the paper discusses how application of transformation rules leads the criteria to be re-casted in dimensionless form, so when these are applied to the solution of slope problems, the results (factor of safety and coordinates that define the location of the critical circular failure surface) can be summarized in dimensionless compact forms. The paper presents then computational tools in the form of dimensionless charts and computer spreadsheets for stability analysis. These are developed from numerical limit equilibrium models that use the mentioned transformation rules. Among others, the computational tools allow the concept of mechanical similarity of rock slopes to be naturally introduced. Finally, the paper presents various rock slope examples that illustrate the use of the computational tools. In these examples, results from limit equilibrium models are also compared with results obtained with full numerical analysis, in particular with finite difference models implementing the shear strength reduction technique.

Numerical Investigation on Dynamic Response Characteristics and Deformation Mechanism of a Bedded Rock Mass Slope Subject to Earthquake Excitation

In order to systematically reveal the dynamic response characteristics of rock mass slopes subject to seismic excitation, time-domain and frequency-domain analyses are used to investigate the dynamic response of a bedded rock slope from multiple perspectives, using the two-dimensional numerical dynamic analyses. Based on the numerical simulation results, the influence of the weak bedded structural planes on the propagation characteristics of seismic waves in the slope is analyzed. The time-domain analysis suggests that the topographic and geological conditions have an influence on the dynamic response of the slope. The effects of ground motion direction on the dynamic response characteristics of the slope are identified. In addition, according to the frequency-domain analysis, the impacts of slope surface, elevation, and structural plane on the seismic response characteristics of the slope are also clarified. The intrinsic characteristics of the slope are investigated by using Fourier spectral analysis and modal analysis, and the deformation response characteristics of the slope are clarified. The relationship between different natural frequencies of the slope, the predominant frequency of the seismic wave, and the dynamic response characteristics of the slope is discussed. Moreover, the dynamic failure mechanism of the slope is analyzed. This work provides a reference for the seismic analysis of this type of slope.

Stability mechanism recognition and failure risk assessment on a high slope by synthesizing different analysis methods

The studied slope is located in the middle reach of the Yalong River in the eastern margin of Qinghai-Tibet Plateau in Southwest China. A large hydropower station is planning to be built near the slope. Understanding the stability mechanism of the slope is important for dam site design. Under a combination of tectonic activity, unloading and weathering, the bedrock mass was fractured. On the basis of field investigation, the GSI classification system and Barton criterion were introduced to determine the strength of the rock mass. The kinematic, limit equilibrium and discontinuum modeling methods were carried out to comprehensively understand the stability of the slope. The kinematic analyses show that only wedge mode is possible for large rock mass failure. However, limit equilibrium analyses show that both wedge failure and circular slip are not expected for rock mass. The slope rock mass is now in the surface rebalance stage. The potentially unstable part is the covering deposit. The 40 million m3 surface deposit is now nearly in a limit equilibrium state. The possibility of failure reaches 41%. Mitigation measures must be put into effect on the deposit to assure the stability of the slope. The results indicated that the failure mechanism of the slope was not controlled by the discontinuities in the rock mass at present but depended on the stability of the surface deposit.

Stability Assessment of High and Steep Cutting Rock Slopes with the SSPC Method

The stability of high rock slopes has become a key engineering geological problem in the construction of important projects in mountainous areas. The original slope stability probability classification (SSPC) system, presented by Hack, has made obvious progress and been widely used in rock slope stability analysis. However, the selection and determination of some evaluation indexes in the original SSPC method are usually subjective, such as intact rock strength and weathering degree. In this study, the SSPC method based on geological data obtained in the prospecting tunnels was presented and applied. According to the field survey and exploration of the prospecting tunnels, the weathering degree of the slope rock mass was evaluated. The empirical equation for the maximum stable height of the slope was applied to the slope stability evaluation in the presented SSPC method. Then, the slope stability probability of numerous cutting slopes in the sandstone unit was evaluated using the presented system. Results of the Geostudio software based on the limited equilibrium analysis of the investigated slopes were compared with the results obtained by the SSPC method. The results indicate that the SSPC method is a useful tool for the stability prediction of high and steep rock slopes.

Numerical characterization of slope rock mass through considerations of hydraulic and mechanical properties

In this paper, the slope rock mass is numerically characterized by considering hydraulic and mechanical properties using two distinct element models. The flow rate and permeability are calculated from localized fluxes through rock masses with varied fracture orientations and scales. Flow models suggest that rock mass permeability is predominantly controlled by fracture size. High rock mass permeability is simulated when the fractures are enlarged. Hydraulic anisotropy is captured when the difference in the fracture size is amplified. The mechanical properties of the slope rock mass are characterized through numerical shearing tests. In general, high permeability corresponds to low shearing resistance of the rock mass. The fractures obliquely distributed to shearing direction lead to additional shearing resistance. Enlarged fractures reflect high conductivity of the rock mass structure and decrease the shearing resistance. Mechanical anisotropy of the rock mass is also captured and attributed to the difference in the fracture size. The relations between hydraulic and mechanical properties are examined, and negative exponential relations are fitted between rock mass cohesion and permeability. The research introduces permeability as reference to slope rock mass characterization and provides reliable methods to this challenging issue.

Assessment of rock slope stability using slope stability probability classification (SSPC) system, around AlemKetema, North Shoa, Ethiopia

This research was conducted in an area around AlemKetema, North Showa, central Ethiopia; with a general objective of conducting a rock slope stability assessment on the selected natural rock slope sections. To achieve this objective, slope stability probability classification was followed to determine the stability probability conditions of slope rock mass in the study area. These classification systems mainly depend on the primary data collected from field works. As a reason, systematic and extensive fieldwork was conducted. However, secondary data was also required to characterize the general conditions of the study area and to have a deep understanding of the subject matter. In the SSPC system, ratings for the degree of weathering, intact rock strength, method of excavation, roughness condition, and infill material were given according to standards. The slope stability probability classification (SSPC) system practices three-step classification systems. These steps are exposure rock mass, reference rock mass, and slope rock mass. Following these steps, slope rock mass stability probability classifications have been carried out for 92 natural rock slope sections. The stability of slope rock mass was determined by two different approaches namely orientation-dependent and orientation independent stability. Orientation dependent stability is linked with the orientation of the discontinuities and characterized by toppling and sliding criteria, while orientation independent stability is linked with the strength of slope rock mass. Accordingly, the overall assessment indicated that 80.4% of rock slope sections showed less than 5% stability probability, 10.9% of rock slope sections showed from 5 to 49%, 6.5% showed from 50 to 95%, and the rest 2.2% of rock slope sections showed greater than 95% stability probability. All these results were compared with the visual stability assessment results. Accordingly, different stability probability maps were produced.

Prediction of Deep Rock Mass Quality and Spatial Distribution Law of Open-pit Gold Mine Based on 3D Geological Modeling

Changshanhao open-pit gold mine in Inner Mongolia is the largest gold heap leach mine in North China. Recently, the mining depth and scale have increased, due to depletion of shallow resources. Since deep mining and steep slope mining have begun at Northeast stope of Changshanhao gold mine, landslides and instabilities of different scales occurred at many areas, constituting severe threat to both personnel and equipment. In order to comprehensively evaluate the slope stability of the Northeast stope and provide guidance for the division of dangerous areas in the stope, the 3D geological model of the Northeast stope of Changshanhao open-pit gold mine was established by using 3D digital modeling technology. Following, the rock quality designation (RQD) value of deep rock in the stope was estimated, based on RQD sample data of deep rock extracted from borehole and geostatistics method, while the distribution characteristics in three-dimensional space of rock mass quality of the open-pit slope were revealed. Ultimately, through the comparative analysis of the integrity investigation results outcrop rock mass and the prediction results of deep rock mass, the feasibility of three-dimensional geological modeling method and the reliability of the calculation results based on geostatistics method were verified, providing reference for safe mining of the high and steep slope within the open pit. The comparative analysis results indicated that: (1) the overall rock mass quality grade of current slope at the Northeast mining area was poor; (2) the rock mass at the north side of the upper part of the east U-shaped mouth was quite fractured, further reinforcement, monitoring and prevention are needed; (3) in the final state of design, the influence of mining disturbance will further degrade the quality of slope rock mass.

Geotechnical monitoring during construction in difficult soil conditions

One of the common and at the same time most difficult problems that developers may face is unstable soil layer at the base of a future building. This paper describes problems of construction on weak, subsidence and heaving soils in engineering and geological conditions of Kursk city. Real problem of construction property safety is shown with the example of one of the demanding geomorphological and lithological conditions of urban areas. The paper offers a description of geologic and hydrogeological features of the slope rock mass in the right bank of the Tuskar river. Groundwater level lies at 8.7 m. depth. It is possible to predict an increase in the level of groundwater in building maintenance because this area is potentially flooded. Various engineering and geological processes and such phenomena as ground subsidence, Karst, suffosia, landslides, flooding, etc., can also be found in the studied territory. Initially an insufficient engineering-geomorphological, hydrogeological, ecological and engineering-geological study of hazardous areas in the city of Kursk have led to its problematic development, which illustrates the situation with residential real estate in the studied territory. To predict dangerous engineering-geological processes and ensure the reliability of the construction fund, specific proposals have been developed for the organization of a geotechnical monitoring system based on the optimal integration of geomorphological, geodesic, engineering-geological, hydrogeological and environmental construction methods in complex engineering-geological conditions.

The failure mechanism of gentle incline rock slope during the process of rock cell retreating

The main inducement for collapse disaster of gentle incline rock slope is differential weathering, and for rock breakage of it is rock cell. On the study of gentle incline rock slope in this paper, we established the mechanics mode of arbitrary rock in gentle incline rock slope, analyzed the failure mechanism of gentle incline rock slope during the process of rock cell retreat, and established the distinguish method of its stability based on fracture mechanics. Then, taking the rock mass slope of JIMINGSHAN in CHENGKOU as an example, analyzed the stability change law of each rock block during the process of rock cell retreated. The study result of this essay can provide certain theoretical foundation for the prevention of disaster of gentle incline rock slope.

Investigation of the seismic response characteristics of a rock mass slope containing weak structural planes under seismic excitation based on multi-domain coupling analysis

Because of the complexity of interactions between seismic waves and rock masses, the dynamic response of slopes has typical multi-domain characteristics. To fully consider the multi-domain characteristics of ground motion, the dynamic response of a rock slope containing weak structural planes was systematically investigated in the time domain, frequency domain, and time-frequency domain. Two-dimensional dynamic analyses were carried out on two numerical models, including the homogeneous slope- and slope-containing structural planes. The results show that slopes containing structural planes have dynamic topographic and geological amplification effects. Based on the frequency-domain analysis, the relationship between the frequency of waves and the dynamic response of slopes was further studied. The geological structure influences the high-frequency components of waves in slopes containing structural planes. The analyses of the marginal spectrum show that seismic energy is mainly concentrated in the frequency band of waves (7–10 Hz). In addition, the seismic failure mechanism of slopes containing structural planes was explored. Structural planes have an important effect on the seismic failure mode of slopes containing structural planes. Multi-domain coupling analysis can reveal the seismic response characteristics of slopes more comprehensively and provide a reference for the seismic design of rock slopes.

Energy Catastrophe of Jointed Rock Slope Considering Spatiotemporal Variability of Strength

The spatiotemporal variability of rock mass strength for jointed rock mass is crucial for the stability of open-pit mine slopes. The Dagushan Open-pit Iron Mine was taken as the background to systematically study the unloading damage and energy evolution of high slope jointed rock mass. Through a field survey of mixed rock slope and fuzzy C-means clustering optimization analysis, the random distribution parameters of two dominant joint sets of rock mass were determined, and a three-dimensional joint network of rock mass was reconstructed. Additionally, a numerical analysis method is proposed for the energy evolution of jointed rock mass considering the spatiotemporal variation of strength, and the variation trends of gravity potential energy, elastic strain energy, and dissipation energy of jointed rock slope were analyzed. Moreover, based on the cusp catastrophe theory, an energy criterion was established for jointed rock mass slope instability. Furthermore, the energy evolution mechanism of deformation and failure of jointed rock slope under mining was elucidated. The slope safety factor obtained from the energy cusp catastrophe dissipation energy cusp catastrophe is the same as that obtained from the limit equilibrium Janbu method.

The characteristics of blasting vibration frequency bands in jointed rock mass slope

High-slope and rock mass joint development are the factors for predicting and controlling blasting vibrations under open pit mining. Blasting vibration adversely affects the stability of jointed rock slopes, thus studying the characteristics of blasting vibration frequency bands in jointed rock masses slope is an important task to ensure the safety of blasting operations. In the present study, vibratory ground motions were measured during blasting excavation in open-pit mining, and the blasting vibration frequency band characteristics of jointed rock masses and high slope were studied through the wavelet transform and response spectrum method. The results demonstrated that the amplification effects of the peak particle velocity (PPV) and energy between different frequency bands exhibited distinguishing characteristics. It was found that, with the increase in elevation, the PPV and energy amplification effects were the most obvious in the 0–16 Hz band, while they were attenuated in the 32–64 Hz band. Furthermore, the distribution of dominant frequency bands of vibration signals observed to be low and narrow, and the average frequency had been reduced. In the development of joints in rock masses, the PPV and energy in each frequency band were attenuated, and the distribution of the dominant frequency bands of vibration signals was high and wide. Also, the average frequency had been increased and the multi-modal characteristics of the responses to blasting vibrations were more obvious. The rock mass structures had displayed different amplification effects on the frequency components of the blasting seismic waves. Finally, as the effects of jointed rock masses on the blasting load responses could not be simply considered as reducing vibrations, they must be analyzed using vibration theory and actual situations.

Characteristics of wave propagation through rock mass slopes with weak structural planes and their impacts on the seismic response characteristics of slopes: a case study in the middle reaches of Jinsha River

Time-frequency joint analysis was used to investigate the seismic response of rock slopes containing weak structural planes. Four three-dimensional finite element models containing infinite element boundaries were modelled: homogeneous slope, anti-dip slope, bedding slope, and block slope models. The material of the models was elastic material. The influence of the structural planes on the seismic responses of the slopes was systematically analyzed. The results of time-frequency joint analysis show that the structural planes impact the propagation characteristics of the waves and the dynamic amplification effect of the slopes. The wave propagation characteristics and peak ground acceleration distribution of the block slope model are more complex than those of the other models. The influence of structural planes on the amplification effect of the slopes is discussed. Additionally, according to frequency-domain analysis, structural planes have a small impact on the natural frequencies and the peak Fourier spectrum amplitude distribution of the slope but have a significant influence on its dynamic deformation characteristics. The natural frequencies of slopes can be obtained by using modal analysis and Fourier spectrum analysis. The relationships between the natural frequencies of the slopes and their dynamic deformation characteristics were analyzed; in particular, the impacts of low-order and high-order natural frequency on the deformation of the surficial slope were investigated. The applicability of the energy spectrum in the evaluation of the dynamic deformation characteristics of slopes was discussed. The effects of structural planes on the seismic failure mode of the slopes are identified according to the analyses of the dynamic responses of the slopes.

Model test and numerical simulation on the dynamic stability of the bedding rock slope under frequent microseisms

Shake table testing was performed to investigate the dynamic stability of a mid-dip bedding rock slope under frequent earthquakes. Then, numerical modelling was established to further study the slope dynamic stability under purely microseisms and the influence of five factors, including seismic amplitude, slope height, slope angle, strata inclination and strata thickness, were considered. The experimental results show that the natural frequency of the slope decreases and damping ratio increases as the earthquake loading times increase. The dynamic strength reduction method is adopted for the stability evaluation of the bedding rock slope in numerical simulation, and the slope stability decreases with the increase of seismic amplitude, increase of slope height, reduction of strata thickness and increase of slope angle. The failure mode of a mid-dip bedding rock slope in the shaking table test is integral slipping along the bedding surface with dipping tensile cracks at the slope rear edge going through the bedding surfaces. In the numerical simulation, the long-term stability of a mid-dip bedding slope is worst under frequent microseisms and the slope is at risk of integral sliding instability, whereas the slope rock mass is more broken than shown in the shaking table test. The research results are of practical significance to better understand the formation mechanism of reservoir landslides and prevent future landslide disasters.