Rock Mass Deterioration Research Articles

A photographic method to identify reservoir geohazards induced by rock mass deterioration of hydro-fluctuation belt

Potential geohazards triggered by the rock mass deterioration (RMD) of the hydro-fluctuation belt (HFB) in the Three Gorges Reservoir area (TGRA) severely threaten the lives and property of people, it is necessary and urgent to timely identify this kind of potential geohazard. Aiming at this issue, several typical evolution modes of potential RMD-induced geohazards were generalized, and an unmanned aerial vehicle (UAV) photographic method integrating the orthophotography, three-dimensional multi-angle oblique photography and high-precision digital elevation model (DEM) was proposed to early recognize the newly formed potential RMD-induced geohazards. By resolving the problem of poor precision in the orthophotographic images of high steep bank slopes, the proposed method improved the recognition reliability of potential reservoir geohazards in the HFBs. Taking the bank slopes from Zigui County to Badong County as the study area, 116 new potential RMD-induced geohazard sites were identified by the presented approach, including 64 and 52 sites on the left and right bank, respectively. Through field verifications, 17 and 19 sites on the left and right bank were found to be consistent with existing hazards, indicating the effectiveness of the proposed approach in avoiding the false and missing recognitions of potential RMD-induced reservoir geohazards at current levels of knowledge and technology. The study can provide a valuable reference for the early identification of RMD-induced geohazards in reservoir areas.

A numerical method to consider the interaction between multiple fractures in frozen rocks based on XFEM

The initiation, propagation, and coalescence of fractures in frozen rocks plays an important role in determining the deterioration and stability of the geotechnical engineering structure in cold regions. This study proposes a numerical method to consider the interaction of multiple fractures in frozen rock based on the volumetric expansion theory and extended finite element method (XFEM). The effective expansion coefficient is adopted in this paper to describe the volume change of ice-water mixture. To accurately determine the magnitude of frost-heaving pressure during the deformation and propagation of fractures, two iterative methods have been proposed. The correctness of the numerical method is verified by the analytical solution of frost-heaving pressure within a single fracture. In addition, the secant method shows the higher efficiency in solving the problems considering the fracture interaction. The evolution of frost-heaving pressure and cracking behavior under different geometric conditions were studied by the proposed method. The numerical results suggest that stress interference may promote the propagation of fractures and accelerate the deterioration of rock mass when the fractures are located in the favorable zone. After considering the multi-fracture interaction, the configuration of two fractures has a significant influence on the evolution of the frost-heaving pressure.

Extrusion 3D printing circular and horseshoe tunnel physical models: A comparative study of deformation and brittle failure

The instability of high-stress hard rock tunnels mainly presented with the deformation and brittle failure, the tunnel brittle failure’s location and range are dissimilar under different stress and shape conditions. In this study, similar 3D printing materials are developed according to the brittleness index of the hard rock in an underground cavern. The physical models of circular and horseshoe tunnel with the equal area are printed, and overloading tests are carried out. The test results reveal that the horseshoe tunnel’s peak strength and residual strength are decreased by 17.2% and 6.6% compared with that of the circular tunnel, the circular tunnel’s vertical displacement is greater than the horseshoe tunnel’s, and the depth and range of brittle failure in the circular tunnel are bigger than the horseshoe tunnel’s. The circular tunnel brittle failure is mainly in the middle of both sides’ walls, while the horseshoe tunnel brittle failure is mainly in the bottom of both sides’ walls. The location and range of the tunnels’ brittle failure can be well simulated by using the rock mass deterioration model (RDM) combined with the rock fracture degree (RFD) index, and the numerical simulation results are consistent with the physical simulation experiment results. According to the results of laboratory physical model experiment and numerical simulation, the brittle failure evolution model of hard rock tunnel is proposed, which can provide a reference for the excavation and support design of hard rock tunnel under high stress.

Multi-source monitoring data helps revealing and quantifying the excavation-induced deterioration of rock mass

There exist many high-steep rock slopes in Southwest China due to the construction of large-scale hydropower projects. The study on excavation-induced damage of high rock slopes is vital for disaster prevention and mitigation. Due to the complexity of high-steep rock slopes, assessing the excavation-induced deterioration of rock mass is often challenging. This study used the space-borne Interferometric synthetic aperture radar (InSAR) and multipoint displacement meters to monitor the slope displacements before and after the excavation. Based on the multi-source monitoring data and the parameter estimation method, we evaluated the changes in rock mass properties due to slope excavation. We employed an improved particle swarm optimization algorithm with dynamic topology and adaptive parameter adjustment and a neural network-based surrogate model in the parameter estimation. The degradation of rock mass strength and stiffness coincides with the increased sensitivity of slope deformation to rainfall infiltration. An in-depth analysis indicates that the absence of vegetation protection and excavation-induced deterioration of rock masses are responsible for the noticeable slope deformation during the rainy season. As slope excavation profoundly influences slope stability and deformation, we should pay closer attention to the excavation way and support style. This study also demonstrates the benefits of using multi-source monitoring data in slope deformation analysis. The findings can aid in comprehending the deformation evolution and instability mechanisms of rock slopes excavated at the hydropower sites, thereby contributing to the prevention and mitigation of landslide disasters.

Experimental study on the reasonable proportions of rock-like materials for water-induced strength degradation in rock slope model test

Water-induced strength deterioration of rock mass is a crucial factor for rock slope instability. To better show the degradation process of rock slope water–rock interaction, we used bentonite as a water-sensitive regulator to build a new rock-like material that matches the features of water-induced strength degradation based on the cement-gypsum bonded materials. Twenty-five schemes of the material mixture proportion were designed using the orthogonal design method considering four factors with five variable levels, and a variety of experiments were conducted to obtain physico-mechanical parameters. In addition, one group of rock-like material proportion was selected and applied to the large-scale physical model test. The experiment results reveal that: (1) The failure mode of this rock-like material is highly similar to that of natural rock masses, and the physico-mechanical parameters vary over a wide range; (2) The bentonite content has a significant influence on the density, elastic modulus, and tensile strength of rock-like materials; (3) It is feasible to obtain the regression equation based on the linear regression analysis to determine the proportion of rock-like material; (4) Through application, the new rock-like material can effectively simulate or reveal the startup mechanism and instability characteristics of rock slopes under water-induced degradation. These studies can serve as a guide for the fabrication of rock-like material in the other model tests.

Deterioration Effect of Sandstone Tensile Strength and Its Mesoscopic Mechanism under Dry-wet Cycles

The rock mass in the hydro-fluctuating zone of the reservoir bank slope is under dry-wet cycles for a long time, which will cause the deterioration of rock mass and induce geological disasters. In this study, a series of dry-wet cycle tests on the argillaceous quartz sandstone in the Three Gorges Reservoir area was carried out. Then, after different dry-wet cycles, the sandstone specimens were used to conduct the Brazilian splitting, scanning electron microscope, and 3D laser scanning tests. Herein, we provided detailed physical and microscopy image data to analyze the deterioration effect of tensile strength and mesostructure deterioration process of sandstone. With the increase of dry-wet cycles, the tensile strength of sandstone initially decreases rapidly, and then the decline rate tends to slow down. The evolution laws of fractal dimension and porosity are also significantly consistent with the deterioration of tensile strength. Moreover, further mesostructural analysis has revealed the repeated “absorption and swelling-dehydration and contraction” of clay minerals. This results in the breakage of framework mineral quartz and the expansion and connectivity of internal cracks, which ultimately deteriorates sandstone’s tensile strength.

Study on Calculation Method of Stability of Damaged Sliding Dangerous Rock on Reservoir Bank

The rapid destruction of dangerous rock produces a large amount of energy, causing heavy casualties and economic losses every year. There are various failure modes and stability calculation methods of dangerous rock. The common failure modes of dangerous rock are tipping mode, sliding mode and falling mode. For large tower pillar dangerous rock with degraded foundation, it is unreasonable to use conventional stability calculation methods to calculate the stability of dangerous rock. This paper takes Jianchuandong dangerous rock in Wushan County as the research background, considering the expansion of rock cavity of damaged dangerous rock base and the deterioration of rock mass in the base of large tower column reservoir bank, and establishes the stability calculation method of dangerous rock suitable for the damage deterioration of the base. It is innovative on the basis of the traditional stability calculation method of dangerous rock, which has important practical significance and theoretical basis for the calculation of the stability of unconventional dangerous rock.

Study on the deterioration trend of the rock mass on the reservoir banks under dry-wet cycles

The deterioration of rock mass under dynamic mechanical state is difficult to determine, especially when evolution trends of micro-fractures are considered. Taking the limestone from Wuxia section of the Three Gorges Reservoir area as studying case, cross-scale tests and theoretical analysis were adopted to study the influence of dry-wet cycles on rock deterioration. The weakly acidic condition (pH = 6) and the dry environment at 105°C were together constituted the two extreme mechanical states of the dry-wet cycles. Meanwhile, the number of dry-wet cycles and soaking time were used as the main variables to analyze the deterioration trend. After introducing the damage mechanics, the quantitative relationship between the mechanical parameters and changing mechanical states was obtained. Combined with the microstructure obtained by scanning electron microscope (SEM), it can be found that with the increase of dry-wet cycles and soaking time, the morphology of mineral particles changed, the number of secondary pores gradually increased, the surface structure became looser, and the microcracks gradually increased, causing the decrease of macro strength. The related method proposed in this paper could provide significant references to determine the mechanical parameters of rocky reservoir bank.

Investigation on the dynamic cumulative damage mechanism and stability of bedding rock slope under the deterioration of rock mass in the hydro-fluctuation belt

Investigation on the dynamic cumulative damage mechanism and stability of bedding rock slope under the deterioration of rock mass in the hydro-fluctuation belt

Numerical Simulation of Long-Term Deterioration of Rock Mass Supported by Shotcrete Lining

The deterioration of rock mass and shotcrete lining has major consequences on the long-term performance of tunnels in the weak rock mass. In this study, the long-term behavior of rock mass and shotcrete in tunnels was simulated by using the three-dimensional finite difference method, considering the nonlinear deterioration mechanism. The degradation of rock mass was simulated by weakening the mechanical parameters, while the deterioration of shotcrete was modeled by decreasing the thickness. The support pressure, internal force, and displacement of the secondary lining were monitored with the gradual degradation of rock mass and shotcrete. As a consequence, the factor of safety (FoS) evolution with time was discussed. The results indicated that 1) the deterioration of both rock mass and shotcrete would significantly increase the rock pressure on the secondary lining, leading to an increase in the displacement (0–14 mm). The FoS of the secondary lining was reduced by 85%. 2) The influence of shotcrete’s deterioration on the secondary lining was relatively less, and the rock pressure on the secondary lining increased from 0 kPa to 13.8 kPa. The long-term safety of the tunnel is remarkably affected by the deterioration of rock mass, depending on the deterioration characteristics of the rock mass. Therefore, the deterioration characteristics of rock mass should be fully considered in tunnel maintenance.

Damage Characteristics of Argillaceous Quartz Sandstone Mesostructure under Different Wetting-drying Conditions

Extensive water–rock interaction in the Three Gorges Reservoir area of the Yangtze River leads to rock mass deterioration along the reservoir banks. However, mineral evolution behavior and its effect on the mesostructure deterioration of rocks under the wetting–drying cycle condition remain unknown. So, the wetting–drying cycle tests were conducted on peculiar argillaceous quartz sandstone in TGRA under neutral (pH = 7) and alkaline (pH = 10) water environments. Here, we provided detailed physical and microscopy images data to determine the control mechanism of mineral behavior on the evolution of sandstone’s mesostructure. Under the neutral condition, repeated “absorption and swelling–dehydration and contraction” of clay minerals leads to the repeated physical action of “squeezing–unloading” in the interior of a rock. This results in the initiation and gradual expansion of cracks in the framework mineral quartz, exhibiting failure mode from the interior to the exterior. In contrast, under the alkaline condition, the dissolution on the surface of quartz particles leads to the expansion and connection of pores, implying that the sandstone exhibits failure mode from the exterior to the interior. Moreover, the internal mechanical analysis indicates the minerals are at high pressure because of the expansion of clay minerals in the neutral solution. However, in an alkaline water environment, the extrusion pressure of framework mineral quartz decreases significantly and is not easily broken due to increased porosity. Thus, the evolution behavior of minerals in different water environments plays an important role in the damage of the rock.

Rock mass deterioration model of bank slope based on high-precision 3D multiperiod point clouds in the Three Gorges Reservoir, China

Karst bank slopes are widely developed in the Three Gorges Reservoir area. Potential bank slope instability caused by the deterioration of rock masses has aroused considerable attention. This paper describes an attempt to use high-precision 3D laser scanning point cloud technology to reveal the deterioration law of a rock mass from a meso-/macroscale perspective and to preliminarily establish the relationship between the characteristics of the rock mass deterioration and 3D point cloud response. The main conclusions are as follows. The point cloud response characteristics of rock mass deterioration can be divided into three types: crack manifestation–extension, collapse-block falling, and translation-rotation. The crack manifestation–extension type can be further subdivided into three subcategories: crack extension, crack widening and crack deepening. These three subclasses of point cloud response characteristics of crack manifestation–extension all exhibit strip-like erosion-induced extensions, but the deformation forms and locations are slightly different. The point cloud response of collapse-block falling shows irregular sheet erosion. The point cloud response characteristics of translational rotation are similar, but associated erosion deformation often presents regular isosurface deformation characteristics. The C2C and M3C2 algorithms are used to calculate the deterioration and deformation, and the difference between recording points at the same location is small, except where the local normal vector N → changes greatly or the point cloud is sparse, where there are large differences. Based on 3D point clouds, the deterioration rate formula D e = n / N for a rock mass is proposed for the first time, where n is the number of degraded and deformed point clouds, and N is the total number of point clouds in the test area. According to the deterioration rates D e corresponding to different deformation thresholds, the deterioration degree and state of a rock mass can be described and judged.

Predicting the excavation damaged zone within brittle surrounding rock masses of deep underground caverns using a comprehensive approach integrating in situ measurements and numerical analysis

Excavation Damaged Zone (EDZ) scope is important for optimizing excavation and support schemes in deep underground caverns. However, accurately predicting the full EDZ scope within the surrounding rock masses of deep underground caverns during excavation remains a pressing problem. This study presents a comprehensive EDZ scope prediction approach (CESPA) for the brittle surrounding rock masses of deep underground caverns by coupling numerical simulation with quantitative analysis of borehole wall images and ultrasonic test results. First, the changes in both P-velocity (Vp) and joint distribution of the surrounding rock masses before and after excavation damage are captured using ultrasonic tests and borehole digital cameras. Second, the quality Q-parameters of the surrounding rock mass before and after excavation damage are preliminarily rated with the rock mass descriptions provided by borehole wall images, and the rock mass Vp-parameter values are determined according to the Vp–borehole depth curves. Third, the Q-parameter ratings are further finely adjusted by updating the related Q-values to be similar with the Q-values estimated by Vp-parameter values. Fourth, the initial and residual mechanical parameters for the rock mass deterioration model (RDM) are estimated by the adjusted Q-parameter ratings based on the modified Q-based relations, and the elastic modulus deterioration index (EDI) threshold to describe the EDZ boundary is determined with the Vp-parameter values. Finally, EDZ scope is predicted using the elastoplastic numerical simulation with RDM and EDI based on the mechanical parameter estimates and EDI threshold. Analyses of applications in Sub-lab D1 in Jinping II project show that CESPA can provide a reliable and operable solution for predicting full EDZ scopes within the brittle surrounding rock masses of deep underground caverns.

Time-dependent damage mechanism of rock deterioration under freeze–thaw cycles linked to alpine hazards

The unique natural environment of the alpine terrains along the Tianshan highway has led to the frequent occurrence of hazards. The typical hazards in this area, such as sliding collapse, have obvious time-dependent deformation characteristics, and the extreme climatic change causes rock mass deterioration under freeze–thaw cycles, which serves as an important factor that indirectly triggers hazards, while the relationship between the time-dependent characteristics of hazards and the damage characteristics of rock mass deterioration triggering hazards remains uncertain. A series of microscopic examination and macroscopic mechanical experiments were conducted on quartz sandstone from the Tianshan highway to study the mechanism. The experimental results show that the cyclic freeze–thaw action changed the microstructure of quartz sandstone and weakened its mechanical performance. The weakening effect on the long-term mechanical characteristics is much more remarkable than that on the short-term characteristics, and the failure modes become more complicated after long-term loading. Based on the experimental phenomenon, the mechanism was analyzed, and a new constitutive model was established to reflect the long-term mechanical characteristics of rock with freeze–thaw cycles and predict the deformation of an unstable rock mass during collapse. These results can provide a reference for alpine hazard prevention.

Deterioration of non-persistent rock joints: A focus on impact of freeze–thaw cycles

Existing research on rock freeze-thaw mainly focuses on a single freeze-thaw process, while little attention is paid to the cumulative effect of cyclic freeze-thaw on rock mass joints. However, the accumulated freeze-thaw effects are precisely the leading cause of rock mass deterioration and damage in severe cold regions. This study aims to investigate the use of a novel laboratory testing method, i.e., membrane pressure sensors in the joint, to demonstrate the impact of cyclic frost-thaw on jointed rocks. With the sensors, the change of frost-heaving pressure in the joint under cyclic process is continuously monitored. The measurements indicate that under freeze-thaw cycles, the initiation of frost-heaving pressure is critical, which is followed by an explosion, stability, and ablation stages. In these stages, the maximum frost-heaving pressure is observed to emerge at the early stage of the freeze-thaw cycle. Based on the experimental observations, frost-heaving pressure evolution law and damage mechanism of jointed rock masses are analyzed. For example, the peak frost-heaving pressure increases exponentially with the decrease of temperature and decreases exponentially with the increase of freeze-thaw cycles. Also, the pressure has a positive linear relationship with the geometric size of the joint. In essence, the deterioration of freeze-thaw cycles on jointed rock masses is mainly due to crack propagation caused by the frost-heaving pressure.

Weathering Characteristics of Heterogeneous Permian-Age Siltstone and Mudstone Sediments from Serbia

This paper presents the results of an investigation of weathering characteristics of heterogeneous mudstone and shale sediments encountered during corridor X motorway construction, crossing Republic of Serbia. Red Permian braided river deposits are prone to weathering after exposure to natural climatic conditions. As a consequence of deterioration the cuttings suffered from over ten instabilities, along 12km long motorway section. In order to investigate the slaking properties of studied rock material slake durability indices along with disintegration ratio were determined. Five cycles of slake durability tests were performed. Disintegration ratio was determined in laboratory and field conditions. Field samples were exposed to natural climatic conditions during the period of one year. Slake durability index after second and fifth cycle has values between 95% < Id(2) <98% and 92% < Id(5) < 97%, respectively. Disintegration ratio determined after second and fifth cycle has values between 0.92 < DRL < 0.98 and 0.88 < DRL < 0.97, respectively. Field value of disintegration ratio of representative samples J-1(7), J-2(12) and J-3(2) after 2, 5 and 12 months of exposure amounts to 98-96-96, 92-91-86 and 92-82-70, respectively. Laboratory testing showed that material has high resistance to disintegration, thus could not be matched with field rate of slaking. Weathering of samples exposed to natural climatic conditions showed somewhat better agreement with weathering of exposed cut slopes. Observations of deterioration of samples during one year exposure gave better understanding of mechanical processes involved in rock mass deterioration.

Numerical modelling of multistage caving processes: insights from multi‐seam longwall mining‐induced subsidence

SummaryEvaluating the induced subsidence is a critical step in multi‐seam longwall mining. Numerical modelling can be a cost‐effective approach to this problem. Numerical evaluation of longwall mining‐induced subsidence is much more complicated when more than one seam is to be extracted. Only a few research works have dealt with this problem. This paper discusses the essential requirements of a robust numerical modelling approach to simulation of multi‐seam longwall mining‐induced subsidence. In light of these requirements, the previous works on this topic are critically reviewed. A simple yet robust FEM‐based modelling approach is also proposed that is capable of simulating caving process, rock mass deterioration and subsidence around multi‐seam excavations. The effectiveness of this approach in comparison with two other conventional FEM approaches is demonstrated through numerical examples of two different multi‐seam mining configurations. Results show that the proposed numerical modelling approach is the only robust method, which is capable of simulating multi‐seam subsidence in both demonstrated cases. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Characterization of failure modes and planned stabilization measures for the Ajanta caves in India

The Ajanta caves are classified as a UNESCO World-heritage monument, where ancient Buddhist rock-cut caves from the Second Century BC to 6th Century AD are found. The caves were carved manually in Basaltic rock mass in the Deccan trap basaltic flow of the Ajanta Formation of the Sahyadri Group in the Upper Cretaceous age. In the Ajanta caves, the hillside slopes are predominantly covered by surface boulders. Boulder dislocations caused by long-term rock mass deterioration, distressing, water percolation and weathering for a strike length of 600m, and a height of 75m; are a major concern when considering the safety of both visitors and site personnel, as well as with regard to the preservation of the historic UNESCO World Heritage site. This study was carried out to assess and characterize the formation of boulders with possible stabilization measures to be planned of a boulder field and slope surface is described and discussed herewith. The possible geological mode of development of the boulder field, rock mass characterization of slope, boulder stabilization philosophy is presented herewith along with planned various stabilization measures considering the esthetic value of the World Heritage site at Ajanta.

Numerical Simulation of Advanced Small Pipe in Tunnels during Excavation by Steps

Advanced small pipe support is one of the advanced support patterns in tunnel engineering construction for weak and fractured surrounding rock. The support effect cannot be predicted because of depending on engineering experiences. Efforts are made to study and analyze the support mechanism of advanced small pipe in the excavation of soft - fracture wall rock. By the numerical simulation of FLAC3D of Dawangou tunnel based on rock mass deterioration model (RDM), the plastic zone, displacement and stress filed of the surrounding rock are simulated with and without the advanced small pipe support. The support effect of advanced small ducts in tunnels during excavation by steps is presented.

Research on the Stability of Surrounding Rock in Shallow Tunnel under Unsymmetrical Pressure Based on RDM

Reasonable evaluation for weak surrounding rock of shallow tunnel under unsymmetrical pressure is very important for the design and construction of tunnel project. The evolvement rule and space distribution characteristic of surrounding rock under different thickness of side covering soil were gained, which include the stress field and plastic zone by adopting rock mass deterioration model, to reveal the instability and failure mechanisms of surrounding rock. And then through analyzing and calculating the measured data in site, the stress characteristics of surrounding rock and supporting structure were gained. The conclusion can be a reference for the design and construction of Hongshigou Tunnel and other similar engineering projects.