Dam Site Area Research Articles

Research on orthotropic anisotropy characteristics of thick bedded limestone based on in situ deformation tests

The orthotropic anisotropy of sedimentary rocks has a significant impact on the force and deformation behavior of the project. In this paper, radial pressurization tests were carried out in the borehole in a typical northern karst area to obtain the deformation properties and orthotropic anisotropy of the rock masses. The test results showed that the deformation modulus and elastic modulus of the limestone rocks in the dam site area obeyed normal distribution. The deformation modulus was basically larger than the proposed deformation modulus of Class II rocks (10 GPa). The deformation behavior and anisotropy degree of the limestone showed a weak correlation with the elevation, but a strong correlation with the development density of the rock joints. The larger development density of the rock in the right bank test section leads to a larger degree of orthotropic anisotropy and frequency of occurrence.

Failure analysis of arch dam under fault action based on inter-generational coordination

Complex geological faults play a crucial role in the site selection and construction of dams. In this paper, considering the intergenerational coordination theory and addressing the complex geological fault conditions of the LCGX hydropower project, the entire life cycle of the arch dam is divided into four stages: initial state, dam foundation excavation, arch dam casting, and reservoir operation. Improved multiple linear regression with modified boundary conditions is employed for the inversion of initial stress, considering the unloading effects caused by dam foundation excavation and the temperature differentials arising from concrete hydration during arch dam casting, and considering the effective stress principle during the water storage operation stage. Based on the above considerations, the whole life cycle of LCGX arch dam from initial state to excavation and casting operation and maintenance is analyzed, including the impact of faults in the LCGX dam site area on the arch dam. The water pressure overload method is employed to evaluate the safety of the arch dam. And the concrete grid backfill replacement is carried out by the combination of open excavation and hole excavation. The results indicate that faults have varying degrees of influence across different stages of intergenerational coordination, with f119 and F115 showing more pronounced effects. In the overload calculation, the f119 fault, along with the hazardous rock mass formed by cutting the foundation surface, and the f124 fault, cause the arch dam to undergo displacement, thus the arch dam occurs shear failure, the reinforcement greatly improves the safety of arch dam. This study systematically investigates the arch dam and slope displacement caused by complex geological faults in the LCGX hydroelectric project dam site area. It explores the specific impact of faults on the arch dam, providing essential references for structural safety during dam maintenance.

Experimental and Numerical Investigation of Rock Failure Process under Hydromechanical Coupling Action

Abstract In order to study the initiation mechanism of rocks under hydromechanical coupling, hydromechanical coupling triaxial tests and acoustic emission tests were carried out on basalt in the Xiluodu hydropower station dam site area in southwestern China. The test results indicate that the basalt displays typical hard brittle behavior, and its peak strength increases as confining pressure rises. Conversely, the peak strength decreases gradually as the initial water pressure increases, which leads to decreased hardness. Meanwhile, tensile failure is the main crack initiation mode under hydromechanical coupling action. During the stable crack growth stage, tensile failure is predominant, complemented by shear failure, with failures mainly occurring in the rock middle position. Contrary to this, during the unstable stage, the rock failure is mainly due to shear failure. The critical pore water pressure failure criterion of rock crack initiation under hydromechanical coupling conditions is derived based on the test results and introduced into the numerical simulation. The hydromechanical coupling failure process and pore water pressure distribution law of basalt are analyzed, and the rationality of the critical pore water pressure failure criterion is verified. These findings are significant for understanding the rock failure process under hydromechanical coupling action and provide a valuable reference for future research.

Shear creep characteristics and creep constitutive model of bolted rock joints

The shear creep behavior of bolted rock joints is closely related to the long-term stability of bolt-reinforced high slopes and underground caverns. To investigate the controlling effect of bolts on rock joint shear creep, limestone samples from the Wudongde dam site area in southwest China were collected and processed, and multistep shear creep tests were conducted on both bolted an unbolted rock joints. The results show that the shear creep of bolted rock joints includes the instantaneous strain stage, transient creep stage and steady-state creep stage, yet the accelerating creep typically occurs instantaneously and is unobservable. By comparing the shear creep process of bolted and unbolted rock joints, it is observed that the presence of bolts decelerates the deterioration of joint surfaces, resulting in a shorter duration of transient creep and lower creep rate. Furthermore, the bolt alters the creep failure mode of the rock joint from brittle failure to plastic failure. Based on experimental results, the reinforcement effect of the bolt through joint creep is analyzed, and the stress evolution during creep is divided into three stages, i.e., the stress-compatibility stage, the stress-compensation stage, and the stress-limitation stage. We summarize how the bolt compensates for stress loss caused by joint surface deterioration through increased shear and axial forces, thereby reducing the creep rate and creep deformation of the rock joint. Based on the stress compensation mechanism of the bolt, a B-Q-N (Burgers-shear force Qo-axial force No) creep constitutive model for bolted rock joints is proposed. When the creep behavior of the unbolted rock joint and the anchorage parameters are known, the B-Q-N model can describe the shear creep behavior of bolted rock joints without experimental data for parameter identification, as well verified by our tests.

A Numerical Method for Evaluating the Collapse of High-Steep Scarp Slopes Based on the Bonded Block Model–Discrete Fracture Network Model

Geotechnical engineering works in deep-incised valleys or open-pit mining areas often encounter high-steep scarp slopes with a slope angle greater than 75°. This type of slope directly threatens the safety of construction personnel, so assessing their stability is essential to ensure construction safety. The natural geometry of high-steep scarp slopes possesses complexity in terms of geometric morphology, structural features of rock mass, and occurrence mechanisms of collapse. There is little research and less emphasis on the evaluation of the collapse risk of high-steep scarp slopes. In particular, the fracture of intact rock or rock bridges is generally ignored in the analysis of collapse processes. A bonded block model (BBM)–discrete fracture network (DFN) coupling characterization model for the high-steep scarp slope is proposed based on a high-steep scarp slope containing dominant joint sets on the left bank of the dam site of the Huangzangsi Water Conservancy Project (Qinghai Province, China). By using the model, the complex geometric forms of the surface of the high-steep scarp slope are quantified, and the fracture process of falling rock masses as well as the controlling effect of dominant joints on the collapse of the scarp slope are revealed. A strength reduction method based on the BBM–DFN model is constructed, and the safety factor of the collapse-prone scarp slope is evaluated. The research results show that (1) the BBM–DFN model can be used to describe the local collapse process; (2) the occurrence of dominant joints plays an important part in controlling the collapse process; (3) there are differences in the safety factor of the scarp slope with different coupling methods; the collapse and failure modes also differ. For safety considerations, the safety factor of the scarp slope on the left bank of the dam site area is determined to be 1.85. The research findings can be used to guide the safety assessment of high-steep scarp slopes and the formulation of both collapse risk prevention and control measures to ensure construction safety in high-steep scarp slope areas.

Investigating the hydrodynamic and biogeochemical evolutions of the hyporheic zone due to large-scale reservoir impoundment

The impact of large reservoir construction on the basin water cycle, ecological environment, and engineering safety needs to be studied urgently, especially, the evolution of the hyporheic zone in the dam site area connecting the basin SW-GW. Few hyporheic zone research investigates the evolution of SW-GW interaction in a certain period of large reservoirs. The Xiluodu Reservoir, located in the Yangtze River's upper reaches, has a dam height of 285.5 m and covers a basin area of 454,400 km2. The isotope balance calculation of water samples demonstrates that following impoundment, the upper boundary, lower boundary, and extension width of the hyporheic zone expands from 370–395 m, 320–330 m, and 125 m to 560–600 m, 370–390 m, and 200 m, respectively. Meanwhile, the upstream increment is bigger than downstream increment. Both temperature tracing and hydrodynamic methods show that the hyporheic flow velocity increases about three times during the initial impoundment cycle and then gradually fallbacks. The hydrochemistry of hyporheic zone water, which changed significantly, was strongly related to the season, depth of burial, and distance perpendicular to river but not to distance along river. The biological activities in the hyporheic zone strengthened after impoundment and gradually changed from the initial impoundment nitrification-dominated to denitrification-dominated. The SW-GW interaction shifts from alternating upwelling and downwelling to continuous downwelling according to the computation of increasing NO3- flux. The study helps better understand scientific and technical concerns such as the evolution of the hyporheic zone, river valley contraction, and dam foundation leakage in the Xiluodu reservoir. Meantime, the thoughts and approaches would also be useful to other large reservoirs.

Seismic hazard analysis for engineering sites based on the stochastic finite-fault method

Seismic hazard analyses are mainly performed using either deterministic or probabilistic methods. However, there are still some defects in these statistical model-based approaches for regional seismic risk assessment affected by the near-field of large earthquakes. Therefore, we established a deterministic seismic hazard analysis method that can characterize the entire process of ground motion propagation based on stochastic finite-fault simulation, and we chose the site of the Xiluodu dam to demonstrate the method. This method can characterize earthquake source properties more realistically than other methods and consider factors such as the path and site attenuation of seismic waves. It also has high computational efficiency and is convenient for engineering applications. We first analyzed the complexity of seismogenic structures in the Xiluodu dam site area, and then an evaluation system for ground motion parameters that considers various uncertainties is constructed based on a stochastic finite-fault simulation. Finally, we assessed the seismic hazard of the dam site area comprehensively. The proposed method was able to take into account the complexity of the seismogenic structures affecting the dam site and provide multi-level parameter evaluation results corresponding to different risk levels. These results can be used to construct a dam safety assessment system of an earthquake in advance that provides technical support for rapidly and accurately assessing the post-earthquake damage state of a dam, thus determining the influence of an earthquake on dam safety and mitigating the risk of potential secondary disasters.

Sensitivity Analysis of Fracture Geometry Parameters on the Mechanical Behavior of Rock Mass with an Embedded Three-Dimensional Fracture Network

The existence of fractures has a significant influence on the mechanical properties of a rock mass. The sensitivity of the rock mass’s mechanical properties to the fracture’s geometric parameters is conducive to improving the measurement accuracy of fractured rock mass engineering. Firstly, the fracture geometric parameters in the dam site area of Lianghekou Hydropower Station were counted using the ShapeMetriX3D system. Then, the effect of the fracture’s geometric parameters on the deformation characteristics, failure mode, and mechanical parameters of the rock mass were investigated based on the RFPA3D under the uniaxial compression test. The results showed that the stress–strain curves of the fractured rock mass mainly exhibited elastic-brittle characteristics. The failure pattern of the fractured rock mass was mainly defined by a compressive-shear composite. Additionally, the influence of the fracture’s geometric parameters on the uniaxial compressive strength (UCS) was greater than that of elastic modulus. The sensitivity of the UCS to fracture trace length was more significant.

Inversion method of hydraulic conductivity for steady-state problem based on reduced-order model constructed by improved greedy sampling method

To solve the time-consuming parameter inversion problem based on swarm evolution algorithm, this study proposes an improved greedy sampling method (GSM) (IGSM) based on model reduction technology to rapidly estimate the hydraulic conductivity of steady-state seepage problem. Different from the traditional GSM, IGSM neither needs to estimate the posterior error bound of the reduced-order model (ROM) nor does it require a training sample set to train the ROM. Instead, the observation data are directly applied to the training process of ROM. Each iterative process of IGSM includes a parameter inversion process to obtain the parameters that best match the observation information and use it to update the current ROM. The improved differential evolution algorithm (e.g., MMRDE) is used as the search algorithm, and the resulting algorithm is denoted as IGSM-MMRDE. After comparative testing, IGSM-MMRDE was found to have higher accuracy and lower calculation cost than GSM-MMRDE. In addition, IGSM-MMRDE is also capable of high-dimensional parameter inversion problems and parameter inversion with a wider search range. After applying IGSM-MMRDE to the inversion of the rock mass hydraulic conductivity of the natural seepage field in the dam site area of a hydropower station, IGSM-MMRDE converges quickly and takes much less time than ADINA-MMRDE based on the full-order model (approximately 0.31% of ADINA-MMRDE). The performance results are even better than the ADINA-MMRDE using the fixed evolutionary generation. Therefore, the advantages of using IGSM in the rapid inversion of the initial seepage field of large-scale projects are extremely evident.

Development and verification of three-dimensional equivalent discrete fracture network modelling based on the finite element method

The discrete fracture network (DFN) method is essential for estimating the mechanical properties of naturally fractured rock masses. A three-dimensional (3D) equivalent DFN model was proposed and thoroughly validated for fractured rock masses. In the equivalent DFN modelling, the Monte Carlo method and 3D rock failure process analysis (RFPA3D) software were used. Additionally, the fracture and its spatial distribution were described explicitly, and the strength and deformability of complex fractured rock masses were investigated. A case study was conducted at the dam site area of Lianghekou Hydropower Station's the left bank slope. The ShapeMetriX3D system was used to acquire the geometric parameters and probability distribution of fractures via digital photogrammetry. Additionally, a series of numerical models were created by combining the proposed equivalent DFN method with the fracture geometry information from the case study. Based on the concept of scale effect and anisotropy, the representative element volume (REV) and mechanical parameters of fractured rock masses were determined. The mechanical parameters of slope rock masses obtained by the proposed DFN modelling and generalized Hoek Brown strength criterion were compared. Furthermore, the applicability and reliability of the proposed model were validated using site data and numerical verifications. The proposed 3D equivalent DFN modelling can analyze the scale effect and anisotropy of mechanical properties of fractured rock masses effectively. Finally, the influence of water head on the hydraulic characteristics of fractured rock masses was analyzed based on the proposed model. Results showed that fractures were the main pathway of water.

Numerical simulation of in-situ stress field characteristics about the dam site area of Baihetan Hydropower Station

In order to study the geological history of the rock mass in the Baihetan dam site area, this paper carries out a numerical simulation study on the in-situ stress field in the dam site area of Baihetan Hydropower Station. With the help of numerical simulation technology, the macro distribution law of the in-situ stress field is discussed. The results show that the in-situ stress value in the dam site area belongs to medium ∼ high stress level. The large principal stress value of the powerhouse on the left and right bank will be close to or even greater than 25 MPa, furthermore the stress state are not good. The horizontal large principal stress is close to the horizontal small principal stress. The results of the paper reproduce the load action history of the rock mass in the dam site area, which provides a preventive theory for the safety of the dam construction of Baihetan Hydropower Station.

Study on Progressive Failure of Hard Rock Tunnel After Excavation Under High Stress

The analysis and simulation of brittle failure of hard rock tunnels under high stress is essential for understanding and mastering the brittle failure characteristics of rock masses and for analyzing and regulating the stability of surrounding rocks in underground projects. The rupture and deformation of hard brittle basalt in the dam site area is one of the key problems faced by Baihetan Hydropower Station. In the paper, the spalling characteristics of the surrounding rock on the right bank of the exploratory tunnel are summarized. CDEM (continuum‐based discrete element method) is used to carry out the numerical simulation and the fracture energy model considering cohesive force weakening and friction angle strengthening is adopted. The indoor test simulations are conducted first to verify the effectiveness of the model. Then the simulation of the right bank exploratory tunnel is conducted to study the brittle failure of the surrounding rock. The results are compared with the field exposure, and the stress and displacement of characteristic points of the surrounding rock are analyzed. The numerical results are in good agreement with the damage situation in the field and reflect the brittle failure characteristics of basalt under high‐stress conditions, which helps to reasonably grasp the damage situation of the surrounding rock and take corresponding support measures, and also proves the superiority of CDEM method in solving hard rock fracture, providing a technical reference for similar hard rock brittle failure problems in engineering.

Study on creep models and parameter inversion of columnar jointed basalt rock masses

Taking the Baihetan hydropower station in Southwest China as an example, creep models and parameter inversion of the columnar jointed basalt rock mass were investigated in this study. Based on the large in situ flexible double pillow bearing plate compression creep tests, the applicability of empirical creep models, such as the power function model, the logarithmic model and the exponential model, for the creep characteristics of columnar jointed basalt rock masses in the dam site area was analyzed first. Then, the compression creep formula of the measuring points in the middle of the flexible double pillow pressure plate was derived based on the generalized Kelvin model. Finally, three optimization algorithms, including the traditional least squares method (LSM), particle swarm optimization algorithm with a compression factor (CFPSO), and particle swarm optimization algorithm with a compression factor based on the simulated annealing algorithm (SA-CFPSO), were used to identify the creep parameters of the generalized Kelvin model. The results confirmed that the generalized Kelvin model based on the flexible double pillow pressure plate outperforms the traditional empirical models, and the performance of the proposed SA-CFPSO algorithm is superior to that of the LSM and CFPSO algorithms in identifying the creep parameters of the generalized Kelvin model.

Field test on engineering characteristics of karst breccia

Karst breccia is a special kind of rock related to karst action with wide distribution. The karst breccia in the dam site area of a hydropower station in the Three Gorges reservoir is very representative. Field tests are carried out on the karst breccia at the dam site of the hydropower station, including in-situ deformation test, direct shear test, triaxial compressive test, large density test and particle analysis test. The test results show that the engineering characteristics of karst breccia in the dam site area is close to that of soil, and moisture content, gravel content and lateral pressure are important factors affecting deformation modulus. Water content has a weakening effect on the mechanical properties of karst breccia, and the higher the water content is, the lower the deformation modulus of the same kind of lithology is. The shear strength parameters of karst breccia determined by triaxial compression test are higher than that of the direct shear test.

In-situ rock tests for fault gouge zone：A case in Fengman hydropower station, China

The existence of faults in the dam site area threatens the stability and safety of large-scale hydropower projects in China. The fault argillaceous zone is the worst kind of fault fracture zone, and the determination of its deformation and strength parameters is the key point of rock engineering investigation. In this study, the in-situ bearing plate test and direct shear test were carried out on the gouge zone of F67 fault in the dam site of Fengman Hydropower Station. The test results show that the deformation and shear law of each test point is good, which is basically consistent with the actual condition of the measured rock mass. However, due to the limited number of measurements, the results are limited in terms of macroscopic representation. The experimental results provide scientific basis for subsequent engineering design and further enhance the understanding of mechanical properties of fault gouges.

Constitutive Model of Stress-Dependent Seepage in Columnar Jointed Rock Mass

Columnar jointed rock mass (CJRM) is a highly symmetrical natural fractured structure. As the rock mass of the dam foundation of the Baihetan Hydropower Station, the study of its permeability anisotropy is of great significance to engineering safety. Based on the theory of composite mechanics and Goodman’s joint superposition principle, the constitutive model of joints of CJRM is derived according to the Quadrangular prism, the Pentagonal prism and the Hexagonal prism model; combined with Singh’s research results on intermittent joint stress concentration, considering column deflection angles, the joint constitutive model of CJRM in three-dimensional space is established. For the CJRM in the Baihetan dam site area, the Quadrangular prism, the Pentagonal prism and the Hexagonal prism constitutive models were used to calculate the permeability coefficients of CJRM under different deflection angles. The permeability anisotropy characteristics of the three models were compared and verified by numerical simulation results. The results show that the calculation results of the Pentagonal prism model are in good agreement with the numerical simulation results. The variation of permeability coefficient under different confining pressures is compared, and the relationship between permeability coefficient and confining pressure is obtained, which accords with the negative exponential function and conforms to the general rule of joint seepage.

Deformation and Reinforcement Monitoring Analysis of Tail Water Outlet Slope in a Hydropower Station

The slope stability situation surrounding the dam site area is very important to each correlative department during constructing hydroelectric power station. So it is important to enforce the high slope rock deformation monitoring, and to process and analyze the measuring data timely. Surface displacement of different height of slope were tracked and monitored based on the field investigation of a hydroelectric power station in Jinsha river. Deformation and the static stability of high slope were analyzed by utilizing rock deformation monitoring data. Taking the left-bank tailrace outlet slope of underground power station for example, we analyzed the slope stability by numerical simulation to obtain the characteristics of deformation and failure of slope. The time and space deformation distribution regularity of rock mass were summarized, the deformation, stress and failure of the studied slope were simulated. The results intuitively show the displacement distribution characteristics and slope plastic failure.

Meticulous simulation and evaluation of seepage control effects at right bank dam foundation and underground powerhouse of Jinping I hydropower station

This case study presents a systematic performance assessment of the seepage control system at the right bank abutment of Jinping I Hydropower Station. By utilizing the in-situ measurements of seepage field, the characteristics of groundwater flow behaviors in the dam foundation and around the underground powerhouse were analyzed. Based on an equivalent continuum method, an anisotropic seepage tensor model of the fractured rock mass in the dam site area was established. Considering the features of topography, geological settings and hydraulic structures, a three-dimensional finite element mesh with complex seepage control structures was generated. A numerical method combining a substructure technique, a variational inequality formulation of Signorini’s type and an adaptive penalized Heaviside function (short for SVA method) is adopted to simulate the three-dimensional seepage field at the dam site. On this basis, the distribution of seepage field during the operation period was predicted, and the performance of the seepage control system was evaluated. Besides, the influence of critically oriented fractures along the direction of NWW on the seepage control effect was also discussed. The methodology presented in this study is useful for understanding the groundwater flow behavior and the performance of the seepage control system in hydraulic engineering.

An Approach to Predict Debris Flow Average Velocity

Debris flow is one of the major threats for the sustainability of environmental and social development. The velocity directly determines the impact on the vulnerability. This study focuses on an approach using radial basis function (RBF) neural network and gravitational search algorithm (GSA) for predicting debris flow velocity. A total of 50 debris flow events were investigated in the Jiangjia gully. These data were used for building the GSA-based RBF approach (GSA-RBF). Eighty percent (40 groups) of the measured data were selected randomly as the training database. The other 20% (10 groups) of data were used as testing data. Finally, the approach was applied to predict six debris flow gullies velocities in the Wudongde Dam site area, where environmental conditions were similar to the Jiangjia gully. The modified Dongchuan empirical equation and the pulled particle analysis of debris flow (PPA) approach were used for comparison and validation. The results showed that: (i) the GSA-RBF predicted debris flow velocity values are very close to the measured values, which performs better than those using RBF neural network alone; (ii) the GSA-RBF results and the MDEE results are similar in the Jiangjia gully debris flow velocities prediction, and GSA-RBF performs better; (iii) in the study area, the GSA-RBF results are validated reliable; and (iv) we could consider more variables in predicting the debris flow velocity by using GSA-RBF on the basis of measured data in other areas, which is more applicable. Because the GSA-RBF approach was more accurate, both the numerical simulation and the empirical equation can be taken into consideration for constructing debris flow mitigation works. They could be complementary and verified for each other.

Optimization of Seepage Prevention of Ma Erdang Hydropower Station

Base on the design of seepage control, the three-dimensional non-steady saturated - unsaturated seepage finite element analysis program CNPM3D is used to establish the three-dimentional finite element seepage model of junction area during operating period. The seepage field of dam site area is studied under the different anti-seepage curtain arrangement scheme. Specifically, the seepage gradient and the seepage discharge of the panel, major material zone, foundation curtains and two sides abutment curtains are analyzed to evaluate the stability of the major district of dam area, in order to provide suggestions for choosing the seepage control standard in the next deepen design stage.The calculation results show that the panel and the impervious curtain anti-seepage effect is remarkable.Impervious curtain can greatly reduce the total seepage flow of the dam and its foundation.However the curtain deepened to 1Lu has little effect on seepage discharge. It is showed that the seepage prevention standards of 3 lu should be proposed in the deepen design stage for both security and economic benefit. The achievement and experience of this seepage prevention design should be taken into consideration for other similar projects.