Rock Damage Research Articles

Investigating the Impact of Pores on Rock Damage during Thermal Spalling Drilling

Numerous microcracks and pores in geological rock formations cause early flaws. High temperatures increase these fractures and pores, thermally damaging reservoir rocks and changing the rock failure mechanism. However, research on pores' high-temperature thermal spalling and fragmentation effects on heterogeneous rocks is sparse. This study built a finite element numerical model of heterogeneous granite rock thermal damage with pores based on rock thermal fracture theory and the Voronoi method and explored the mechanism under varied pore settings. The research's findings indicate that the application of high temperatures to local heterogeneous porous rocks results in a higher proportion of tensile damage. The proportion of shear damage and tensile damage constantly varies due to the changing position and shape of the pores. The rock's porosity has the effect of decreasing temperature in the direction of heat transfer while increasing the extent of temperature transfer along the pore parallel to the heating surface. The potential degree of damage increases as the density of pores increases, the distances between them decrease, and the pore lengths increase. The thermal damage resulting from heating in the vicinity of the pore is primarily localized in the area between the pore and the heated surface. This effect becomes more significant as the distance between them decreases. The findings of this study can serve as a theoretical framework for understanding the impact of rock pores on rock thermal fracturing and fragmentation in the thermal spalling-assisted development of deep oil and gas resources.

Optimization of Accurate Spacing for Gas Extraction from Damaged Coal Seams Based on a Dual-Penetration Model

In order to develop precise hole placement technology for gas extraction, this paper combines industrial testing, the evolution law of coal rock damage permeability, and the coal double-pore double-permeability model; establishes a coupling model of the coal damage deformation field and matrix-fracture double diffusion seepage field; and determines precise hole placement spacing for a coal seam gas by using the COMSOL Multiphysics 5.6 numerical simulation software. This study shows that the effective radius of gas extraction is 4.8 m after 180 d of extraction, which is a power function of the extraction time. The permeability of the coal body is affected by matrix adsorption, and contraction and effective stress, and the influence range between the boreholes under multi-hole extraction increases with the increase in spacing; at the same time, we took into account the positive effect of the permeability change on the extraction effect and ultimately determined the optimal spacing of boreholes in Dashucun Mine to be 6 m, which was arranged in the square area. The extraction effect was good after the on-site test, and the results of this study can provide guidance for the optimal arrangement of the spacing of boreholes in the underground areas of coal mines.

A new constitutive model for salt rock under cyclic loadings based on state variables

Underground salt rock caverns are ideal for national strategic energy storage, compressed air energy storage, and CO2 storage. Operation periods of salt cavern storage can be affected by periodic injection of gases during production/charging and discharging activities, thus causing fatigue damage to surrounding rock. It is therefore necessary to establish a model that can accurately characterize the evolution process of fatigue damage in salt rock under cyclic loading. This is a necessary input into the design of salt cavern storage systems and for the evaluation of their operation and safety. Relying on the rheological properties and cracks of salt rock and their effects on the bearing capacity of materials, this paper establishes a fatigue damage constitutive model of salt rock, using the rheological characteristics of rock and the deformation–crack expansion relationship. First, the time-varying state variable is introduced through the classical Norton model to characterize the degree of hardening; this is in order to modify the relationship between the stress deformation rate and the correlation of the historical path of loading and unloading of salt rock. Then, based on the relationship between crack damage and effective stress development under deformation conditions, a fatigue damage constitutive model of salt rock is established. Finally, using cyclic loading and unloading data of salt rock under different stress ratios or confining pressures, we verify and compare the model parameters. The results show that: (1) The model can accurately predict the fatigue deformation characteristics of salt rock under different cyclic loading and unloading paths and can better characterize the interaction between deformation and stress path; (2) In this model, parameter a affects stage II while parameter b affects stage I of salt rock fatigue deformation. This can be understood as the factor representing the relationship between stress and deformation rate of salt rock; (3) Parameter d0 characterizing the initial nucleation area and parameter μd representing crack growth rate factor jointly affect/modify the stress–strain relationship in the critical failure stage or stage III of the model.

Analyzing the Stability of Rock Surrounding Deep Cross-Tunnels Using a Dynamic Velocity Field

With the increasing number of deep rock engineering projects, many different types of tunnels have emerged, such as cross-tunnels. These tunnels intersect with each other in rock, which causes potential safety hazards. We must analyze the stability of the surrounding rock, to ensure worker safety. This article presents a method for dynamically assessing the stability of the surrounding rock in deep-buried cross-tunnels. The method consists of two main analysis steps: (1) P-wave velocity field inversion; and (2) Stability analysis of the surrounding rock. The P-wave velocity field inversion involves inverting the S-wave velocity field by Rayleigh wave and inverting the P-wave velocity field by adjoint state traveltime tomography. Then, a method of stability analysis is proposed which is used to update the mechanical properties of the rock (based on the continuously updated wave velocity field). The elastic modulus of the surrounding rock is approximated throughout the excavation process. CASRock V1.0 (Cellular Automation Software for engineering Rockmass fracturing processes) is used to assess rock damage via the equivalent plastic shear strain and local energy release rate. The new method is used to analyze the stability of a new tunnel excavated in Jinping (in China). The results reveal the severity and spatial distribution of the damage caused. The yield depth is concentrated near the sidewalls, while the top and bottom of the tunnel exhibit a smaller depth. The yield depths present a particular pattern of change (high–low–high–low) with increasing distance from tunnel #2. Finally, this research enriches our understanding of excavating deep cross-tunnels and makes an important contribution to improving worker safety in deep cross-tunnels.

Study on the evolution law and quantitative characterization of micro-crack propagation in the compressive failure process of rocks

Quantitative characterization of the evolution law of micro-crack propagation in rocks is important for understanding the rock failure mechanism. This study aims to establish a theoretical method for quantitatively characterizing the evolution of micro-crack propagations during the compressive failure of rocks. Mechanical properties and failure characteristics of carbonaceous mudstone were investigated by triaxial compression tests. In order to study the evolution law of crack propagation morphology and quantity, numerical simulations of micro-crack propagation in rocks during triaxial compression were performed using the particle flow code (PFC). Based on the phenomenological theory, we proposed to define the rock damage increment by crack propagation quantity. The evolution law of crack quantity was characterized using the Logistic growth model. Furthermore, an equation for the evolution of micro-crack propagation quantity during compressive failure was established, and the rationality of the equation was verified. The results show that micro-cracks initiate in weak areas of rocks and develop and converge around existing cracks, eventually leading to localized failure through propagation and connection. The number of micro-cracks grows in an “S-shaped” pattern, accelerating before the peak stress, reaching a maximum growth rate at the peak stress, and decelerating in the post-peak stage. As the confining pressure increases, the number of rock micro-cracks increases, the propagation morphology becomes more complex, and the failure localization weakens. The proposed equation accurately characterizes the evolution of micro-crack propagation quantity in the rock failure process. In addition, the calculation results are in good agreement with the numerical analysis results, verifying the rationality of the equation.

Rock damage evolution in the production process of the enhanced geothermal systems considering thermal-hydrological-mechanical and damage (THM-D)

Hot dry rocks (HDRs) geothermal relies mainly on enhanced geothermal systems (EGS) for production. During production, the evolution of rock stress distribution will cause damage to the rock, especially near fractures. The application of damage mechanics in the geothermal field has mostly focused on the process of hydraulic fracturing, with limited reports on damage research related to long-term water injection development. According to previous experimental studies, the effect of rock damage is significant and cannot be ignored. Therefore, based on a thermal-hydrological-mechanical and damage (THM-D) coupling model, it studies the rock damage evolution features and its role in changes in rock physical properties. It also analyzed the effects of the initial temperature, injection flow, fracture curvature/number, and stress difference on damage evolution. Results indicate that the damage area and degree continue to increase with time, but the growth rate becomes slower. There are two methods of damage evolution: the new damage caused by the expansion of the low-temperature region is throughout the process, and the original damage is aggravated in the later stages. Damage will cause changes such as reduced Young's modulus (negative feedback) and increased permeability (positive feedback) of the rock matrix, which in turn affect the damage evolution. More, damage increases with the initial rock temperature, injection mass flow, and stress difference increase, and the impact of the fracture curvature is small. The damage of complex fracture reservoirs is more pronounced than that of single fracture reservoirs. This study provides a tool for analyzing the impact of damage on the production performance of HDRs. The investigation of relevant patterns is expected to offer guidance for production strategies.

Frost-heaving characteristics and formation mechanism of saturated sandstone under unidirectional freezing conditions

In this study, a series of frost-heaving experiments were conducted on saturated sandstone at varying cooling rates under unidirectional freezing conditions. The frost-heaving strain in the freezing process was examined using a novel laboratory testing methodology. The results showed that the frost-heaving behavior of the saturated sandstone was significantly affected by the freezing direction and rate. Specifically, the rapid freezing of sandstone parallel to the freezing direction resulted in a more pronounced frost-heaving strain than that perpendicular to the freezing direction. The rock freezing rate had a positive correlation with the peak frost-heaving strain parallel to the freezing direction, and a negative correlation with that perpendicular to the freezing direction. A microstructure-based conceptual model is proposed to determine the frost-heaving pressure. The conceptual model showed that the ice pressure, determined by the pore-water pressure and capillary force, resulted from the crystallization of the pore water within the pore structure. A nonlinear relationship was observed between the ice pressure and crystallization rate. Capillary forces were more significant for slow crystallization processes, resulting in a larger difference between ice and water pressures. At high crystallization rates, the hydraulic pressure acted on the pore structure before the capillary forces become significant, leading to a smaller difference between the water and ice pressures. Rapid crystallization processes resulted in the uneven distribution of ice pressure within the pore structure, with subsequent re-equilibration occurring with the migration of unfrozen water. The proposed conceptual model presents a new perspective for obtaining an improved understanding of the microscopic frost-heaving mechanism involved in the freeze-thaw damage of porous rocks. It provides an evaluation method for the behavior of rocks during weathering by frost heave in cold regions.

Real-Time Recognition Method for Key Signals of Rock Fracture Acoustic Emissions Based on Deep Learning.

The characteristics of acoustic emission signals generated in the process of rock deformation and fission contain rich information on internal rock damage. The use of acoustic emissions monitoring technology can analyze and identify the precursor information of rock failure. At present, in the field of acoustic emissions monitoring and the early warning of rock fracture disasters, there is no real-time identification method for a disaster precursor characteristic signal. It is easy to lose information by analyzing the characteristic parameters of traditional acoustic emissions to find signals that serve as precursors to disasters, and analysis has mostly been based on post-analysis, which leads to poor real-time recognition of disaster precursor characteristics and low application levels in the engineering field. Based on this, this paper regards the acoustic emissions signal of rock fracture as a kind of speech signal generated by rock fracture uses this idea of speech recognition for reference alongside spectral analysis (STFT) and Mel frequency analysis to realize the feature extraction of acoustic emissions from rock fracture. In deep learning, based on the VGG16 convolutional neural network and AlexNet convolutional neural network, six intelligent real-time recognition models of rock fracture and key acoustic emission signals were constructed, and the network structure and loss function of traditional VGG16 were optimized. The experimental results show that these six deep-learning models can achieve the real-time intelligent recognition of key signals, and Mel, combined with the improved VGG16, achieved the best performance with 87.68% accuracy and 81.05% recall. Then, by comparing multiple groups of signal recognition models, Mel+VGG-FL proposed in this paper was verified as having a high recognition accuracy and certain recognition efficiency, performing the intelligent real-time recognition of key acoustic emission signals in the process of rock fracture more accurately, which can provide new ideas and methods for related research and the real-time intelligent recognition of rock fracture precursor characteristics.

Rate-dependent strength and crack damage thresholds of rocks at intermediate strain rate

To investigate the rate dependence on the mechanical behaviours of rocks under intermediate strain rate, three types of rock were loaded by using a newly developed servo-controlled dynamic triaxial apparatus. In this study, the dynamic strength and crack damage thresholds of rocks under different confinements were investigated at the strain rate range of 10−3∼100s−1, which is of significance to understand the rock damage subjected to earthquakes or far-field blasts. The results indicate that the apparatus could ensure the rock samples being loaded under a stable strain rate without causing prominent disturbance on the confining stress. In addition, the strength and damage thresholds are dependent on the strain rate, i.e., the increasing strain rate would result in the increase of dynamic strength and crack damage thresholds. The increase of confinement leads to a higher failure strength, the crack initiation and damage stresses are also positively correlated to the confining pressure under dynamic loads. Based on the theory of fracture mechanics that considers the crack growth velocity, it is found that the dynamic stress intensity factor exhibits a negative correlation with both the strain rate and confining pressure, whilst the fracture toughness presents an inverse trend. Therefore, the larger axial stress is required to initiate the cracks, which might further induce the variation of crack initiation stress.

Volumetric Structure of the Bachat Earthquake (Kuzbass) Aftershock Area and Stress State of Rock Mass under Open-Pit Mine

Abstract —The Bachat earthquake (M = 6.1) with the epicenter coordinates of 54.29° N, 86.17° E occurred on June, 18 2013 near the Bachatsky coal strip mine, is the world’s largest earthquake induced while mining solid minerals. More than 5000 aftershocks were registered and the spatial volumetric structure of the aftershock area was investigated. The Bachat coal field is located in the Salair zone of the Kuznetsk Depression and is represented by a brachysynclinal fold of a very complex structure characterized by the damage and fracturing behaviors of rocks. The main event is confined to the coal-mine pit wall, with the greatest density of aftershocks observed in its middle portion. In the cross section, aftershocks form a wide area with its deepened portion shifted towards the Kuznetsk Depression, while large faults bounding the depression dip down under the Salair Ridge. In the exposed pit wall, at a depth of 4 km, the activated area resembles a rhombus whose horizontal diagonal line runs across the entire length of the mine pit and decreases both in upward and downward directions. The area is seismically activated to a depth of 6 km, with more intense activation of rock mass observed within the 1–3 km depth interval. Results of the study of the mechanisms of aftershock sources revealed a disagreement between the stress state of rock mass of the Bachatsky open-pit coal mine modeled from the mechanisms of aftershocks, and the mainshock mechanism of the Bachat earthquake.

Flow–solid coupling analysis of underground reinforced concrete forked pipe enclosing rock and structure

The stability of the surrounding rock for the construction excavation and the reinforcement of the lining structure during operation in the water-rich area is a difficult problem for the design of high-head underground turnout pipes. Firstly, according to the mechanism of excavation load release and surrounding rock damage evolution, the seepage effect of excavation in the construction of the forked caves is coupled to the surrounding rock stress damage, and an iterative method of numerical simulation of the coupled mutual feedback effect of excavation surrounding rock stress and seepage is proposed. Then, based on the cracking characteristics of the high internal water pressure reinforced concrete turnpike lining, a numerical analysis method of the coupling interaction between lining cracking and internal water seepage is proposed by coupling internal water seepage to stress damage in the lining by cracking the forked pipe structure. Applying the aforementioned method to a forked pipe project, the results show that: during the construction period, there is a significant increase in the damage zone, stress, and displacement of the rock around the cavern after considering the coupled iterations; during the operation period, with the increase in internal water pressure, the lining structure accelerates cracking due to the external infiltration of internal water; after the internal water is applied, the surrounding rock bears the main internal water pressure and the reinforcement bears only part of the circumferential force. The method provides theoretical support for the analysis and calculation of the reinforcement of similar underground high-pressure tunnels for rock support and lining structures and has certain theoretical and engineering significance.

The time-dependent deformation and damage constitutive model of rock based on dynamic disturbance tests

Abstract In the deep rock excavation process, the rock will produce deformation and damage under multiple dynamic disturbances, while there is also unrecoverable time-dependent deformation. In order to research this deformation characteristic, a sine wave disturbance triaxial loading test was carried out on red sandstone to simulate the failure process of deep underground rock mass under dynamic disturbance loads with low confining pressure. Based on the results that the deformation of the rock increases suddenly during dynamic disturbances and varies with the number of disturbances, a novel disturbance damage model relating the number of disturbances to the deformation of the disturbances is created to describe the deformation and damage accumulation of the rock under multiple disturbances and an operator is developed to ensure that the model works. In order to describe the time-dependent deformation of rocks, the elasticity model in the traditional Bingham model was improved to a nonlinear elasticity model that varies with time, and its viscous and plasticity models were retained. The time-dependent deformation and damage constitutive model is obtained by combining the improved Bingham model with the disturbance damage model. The model parameters were identified according to the test data, and the finite-element calculation of the model was realized with the secondary development program. The results show the strain of rock increases suddenly under multiple disturbances, and the main reason for rock damage is the action of dynamic disturbances. The fitted curves and finite-element results are consistent with the experimental results. The time-dependent deformation and damage constitutive model of rock not only reflects the decaying rheological and steady-state rheological properties of rock under static loading but describes the characteristics of strain surge and disturbance damage accumulation caused by dynamic disturbances. This article contributes to the characteristics of the deformation of deep rock mass.

Viscoelastic Strains of Palaeozoic Shales under the Burger’s Model Description

This article presents the results of creep studies of Palaeozoic shales from the Baltic Basin in which the exploitation of shale gas in Poland was planned. Knowledge of instantaneous and long-term properties investigated in triaxial stress conditions is important from the point of view of exploitation techniques related to hydraulic fracturing. Rheological phenomena also play an important role in the analysis of the initial stress in shales, the knowledge of which is indispensable in the hydraulic fracturing process. The tests were carried out on samples representing four siltstone–claystone lithostratigraphic units occurring in the Baltic Basin. The studies and analyses were aimed at determining the character of creep in shales, selection of the appropriate rheological model for the analyzed rocks, and determination of the threshold of the linear creep under triaxial compression conditions. An original approach together with analysis results are presented here, which enable the separation and monitoring of shear and volume creep effects, and on this basis, the determination of the significance of the contribution of volume creep in the entire creep process. A relatively simple methodology for determination of the parameters of the Burgers model using this division is presented. The original value of the article is also due to the test results themselves and the parameter values of the analyzed model for triaxial creep of shales, which are not numerous in the literature. The investigations were performed at various loading levels in relation to the triaxial strength of the shales. Depending on the load, at its low values up to 0.7 (σ1 − σ3)max, creep had a determined character and did not show features of progressive creep. The linear creep threshold was also analyzed in this range. The loading level of 0.7 (σ1 − σ3)max was the limit of linear creep. Exceeding this load resulted in the loss of the linear character of creep, which in consequence lead to the subsequent third creep phase ending with rock damage. Parameters of the Burger’s model for gas shales from the Baltic Basin (northern Poland) were identified. There are significant differences in the behavior of shales depending on the lithostratigraphic unit from which the samples were collected. The mineral composition of the shales also influenced their behavior.

Investigating Pore-Throat Blockage in Tight Rocks: The Role of Colloidal Particles in Treated and Untreated Produced Water

Colloidal particles in produced water used for hydraulic fracturing can block pore throats in tight reservoir rocks through three main mechanisms. The blockage of these pore throats damages the permeability of the reservoir, leading to low productivity and higher operational cost. However, the characterization of these particles in produced water used for hydraulic fracturing is understudied. This study investigates the size distribution of these particles in produced water and the resulting pore plugging mechanisms potentially operating on typical 0.1, 0.2, and 0.4-micron-wide siltstone reservoir rock pore throats caused by primary, aggregate, and agglomerate particles in such produced waters. The siltstone pore throat diameters and particle diameters from untreated and treated produced water from McClean, McKenzie, Williams, and Mountrail Counties were compared and used to calculate the jamming ratios from which the main pore throat plugging mechanisms in those rocks were inferred. The results show that bridge blockage, and single pore blocking through straining are the main pore throat blocking mechanisms contributing to formation damage in these reservoir rocks. The bridge blocking mechanism is more prevalent when untreated produced water is used as the base fluid for hydraulic fracturing, while single pore blocking through straining is more prevalent in treated water. The size of the particles also affects the pore plugging mechanisms, with smaller particles causing damage through bridging and larger particles causing damage through single pore blockage and straining. These findings have important implications for the management of produced water in the oil and gas industry, as they may provide clues to minimize formation damage.

Study on the deterioration characteristics and mechanism of physical and mechanical properties of natural gypsum rock under freeze–thaw action

The physical and mechanical properties, microstructure degradation characteristics, and damage mechanism of natural gypsum rock under 15, 30, and 45 freeze–thaw cycles were studied by using a self-developed program-controlled freeze–thaw experimental device. The results show that compared with natural gypsum, with the increase in freeze–thaw cycles, the mass of the sample increases first and then decreases, Poisson's ratio increases, the density decreases, and the longitudinal wave velocity, the uniaxial compressive strength, and the elastic modulus decrease. Indexes decrease greatly in the early stage of freeze–thaw and slowdown in the later stage. With the increase in freeze–thaw cycles, the slope of the pre-peak stage of the stress–strain curve decreases, the compaction stage is significantly prolonged, and the brittleness of the post-peak failure process decreases. Failure cracks of the specimens after freeze–thaw cycles are mainly inclined shear failure and axial tensile cracks. The analysis shows that the freeze–thaw damage of gypsum rock is caused by the superposition and mutual promotion of water-rock softening and pore frost heave. The specific performance is the damage of crystal particles and the loose pore structure at the mesoscale. On this basis, the cracks gradually develop and expand, which is consistent with the macroscopic test results of the sample. The research results have reference significance for the construction scheme design and frost damage prevention of gypsum surrounding rock tunnels in cold regions.

Analysis of Cement Sheath–Rock Damage Mechanism—A Case Study on Water Injection Wells

In the field of water injection wells within oilfields, comprehending the intricate mechanics of water channeling and the resulting rock damage on the external cemented surface holds paramount significance for the efficient management of reservoirs. This paper presents a comprehensive study aimed at illuminating the complex nature of rock damage on the external cemented surface of casings and deciphering the underlying mechanisms that underpin water channeling occurrences. To this end, a robust constitutive model is established and refined to capture the multifaceted interactions inherent in rock damage on the cemented surface. This model introduces a modified bonding force approach to enhance shear stress precision and thoughtfully accounts for the profound effects of elastic–plastic behavior, cracking damage, and elastic-cracking coupling damage on damage progression. Subsequently, the refined model is employed to investigate rock damage on the external cemented surface of water injection wells, encompassing variations in confining pressure, rock width on the cemented surface, and the ratio of Young’s modulus between the cement sheath and the rock. The research findings emphasize the interplay between cracking and elastic damage as the catalyst for rock damage on the cemented surface. Impressively, the accuracy of the refined constitutive model for the cemented surface has advanced by over 5% compared to prior studies. The manipulation of confining pressure and the Young’s modulus ratio enhances peak fracture water pressure, signifying substantive strides in comprehending damage propagation mechanics. Furthermore, the study discerns the negligible influence of rock width on the cemented surface regarding damage patterns. These findings have important implications for the effective management of water injection wells, providing insights for the restoration of water channeling wells and proactive measures against water channeling phenomena. They also contribute to the refinement of well cementing practices and the proficient management of water channeling and water flooding in oilfields. The research findings have profound implications for the domain of water injection wells, offering novel insights into the restoration of water channeling wells and the implementation of preemptive measures against water channeling phenomena. These findings hold the potential to guide the refinement of well cementing practices and the adept management of water channeling and water flooding wells within the studied oilfield.

Rock fracture mechanism of air-deck charge blasting considering the action effect of blasting gas

This paper primarily focuses on examining the impact of blasting gas, studying the rock fracture mechanism of air-deck charge blasting, and analyzing the evolutionary characteristics of blasting stress, the law of damage distribution, and the fracture characteristics in rock specimens. Firstly, indoor blasting model experiments are conducted and analyzed by combining the computed tomography (CT) scanning method, three-dimensional (3D) reconstruction technology, and fractal damage theory. The experimental results indicate that the distribution characteristics of rock damage in air-deck charge blasting are mainly determined by factors such as charge segment position, air-deck length, and position. Next, a numerical simulation method based on the coupling analysis of Lagrangian finite element and Euler finite volume is proposed to enable the numerical simulation of rock blasting fracture while considering the action effect of blasting gas. The analysis of the numerical simulation results reveals that the rock failure near the blasthole, under the influence of blasting gas, is primarily due to tensile failure, whereas the rock failure in the distant area is predominantly caused by shear failure. Furthermore, during the process of rock fragmentation by blasting gas, the initial interaction between the blasting gas and rock is the main controlling factor for rock damage and failure, whereas the subsequent reflection and transmission of blasting gas have a relatively minor impact on rock damage and failure.

Study on the evolutionary mechanisms driving deformation damage of dry tailing stack earth–rock dam under short-term extreme rainfall conditions

Study on the evolutionary mechanisms driving deformation damage of dry tailing stack earth–rock dam under short-term extreme rainfall conditions

Degradation of physico-mechanical properties and damage mechanisms of sandstone under the combined action of freeze–thaw cycles, chemical solution, and compressive stress

Rocks in cold regions subjected to freeze–thaw cycles are often affected by the surrounding hydro-chemical solutions and external load. In this study, the evolution of physical and mechanical characteristics and the damage mechanism of sandstone under the combined action of freeze–thaw cycles, chemical solution, and compressive stress were investigated. A series of quick cyclic freeze–thaw tests in different chemical solutions and stress levels were conducted. The dry mass, wave velocity, and compressive strength decrease as the number of freeze–thaw cycles increases. The variations in dry mass, wave velocity, and rock appearance indicate that lower stress levels (<0.5σ0, σ0 is the saturated uniaxial compressive strength of the original specimen) can limit the effect of repeated freeze–thaw cycles and chemical corrosion, whereas higher stress levels (>0.5σ0) can exacerbate the combined effect on rock damage. In addition, a modified decay model is proposed that incorporates the initial properties and residual integrity of the rock to describe the evolution of rock strength and wave velocity. Both the residual strength and wave velocity of sandstone are constants that are independent of stress level and chemical solution. The degradation rate of compressive strength increases abruptly at higher stress, whereas that of wave velocity generally decreases with increasing stress level. The continuous action of the cyclic frost-heaving force, hydrolysis and chemical corrosion, and external compressive stress promote generation and propagation of pores and microcracks, causing deterioration of the mass, wave velocity, and compressive strength.

Dam Surface Deformation Monitoring and Analysis Based on PS-InSAR Technology: A Case Study of Xiaolangdi Reservoir Dam in China

The Xiaolangdi Dam is a key project for the control and development of the Yellow River. It bears the functions of flood control, controlling water and sediment in the lower reaches, ice prevention, industrial and agricultural water supply, power generation, and so on. Its safety is related to people’s life and property safety and local economic and social development. It is of great significance to carry out comprehensive and regular deformation monitoring for dams since the deformation is an important evaluation index for dam safety. Interferometric Synthetic Aperture Radar (InSAR) technology has been a rapidly evolving technology in the field of space geodesy in recent years. It offers advantages such as high monitoring precision, extensive coverage, and high monitoring point density, making it a powerful tool for monitoring deformations in hydraulic engineering projects. Based on Sentinel-1 data covering the Xiaolangdi Dam from September 2020 to November 2022, the PS-InSAR technique was used to obtain the surface deformation of the Xiaolangdi Dam, and reservoir water level data on image acquisition dates were obtained for joint analysis. The results show that there is a large deformation in the center of the dam crest of the Xiaolangdi Dam, while both sides of the slope and downstream dam foot are relatively stable. The time series deformation of the dam body is closely related to the reservoir water level change. When the water level increases, the dam body tends to deform downstream; when the water level decreases, the dam body tends to deform upstream. The deformation and water level of the Xiaolangdi Dam exhibit a clear negative correlation. There is no significant cumulative deformation on the dam slopes or at the base of the dam. However, cumulative deformation occurs over time in the central area of the dam’s crest. The deformation process at the central area of the dam’s crest follows a continuous and non-disruptive pattern, which is consistent with the typical deformation behavior of the Xiaolangdi earth–rock dam structure. Therefore, it is judged that the current deformation of the Xiaolangdi Dam does not impact the safe operation of the dam. InSAR technology enables the rapid acquisition of high-precision, high-density deformation information on the surfaces of reservoir dams. With an increasing number of radar satellites in various frequency bands, such as Sentinel-1 and TerraSAR-X, there is now an ample supply of available data sources for InSAR applications. Consequently, InSAR technology can be extended to routine monitoring applications for reservoir dam deformations, especially for small and medium-sized reservoirs that may not be equipped with ground measurement tools like GNSS. This holds significant importance and potential for enhancing the safety monitoring of such reservoirs.