Deep Overburden Research Articles

Study on the Effect of Liquefiable Overburden Foundations of Rockfill Dams Based on a Pore Pressure Model

China’s southwestern region boasts abundant hydropower resources. However, the area is prone to frequent strong earthquakes. The areas surrounding dam sites typically have deep overburden, and the liquefaction of saturated sand foundations by earthquakes poses significant safety risks to the construction of high dams in the southwest. The effects of liquefaction and reinforcing measures on the foundations of rockfill dams on liquefiable overburden under seismic action are currently the subject of somewhat unsystematic investigations. The paper utilizes the total stress and effective stress methods, based on the equivalent linear model, to perform numerical simulations on the overburden foundations of rockfill dams. The study explores how factors such as dam height, overburden thickness, liquefiable layer depth, liquefiable layer thickness, ground motion intensity, and seismic wave characteristics affect the liquefaction of the overburden foundations. Additionally, it examines how rockfill dams impact the dynamic response, considering the liquefaction effects in the overburden. The results show that although the total stress method, which ignores the cumulative evolution of pore pressure during liquefaction, can reveal the basic response trend of the dam, its results in predicting the acceleration response are significantly biased compared to those of the effective stress method, which comprehensively considers the cumulative changes in liquefaction pore pressure. Specifically, when the effect of soil liquefaction is considered, the predicted acceleration response is reduced compared to that when liquefaction is not considered, with the reduction ranging from 4% to 30%; with increases in the thickness and burial depth of the liquefiable layer, the effective stress method considering liquefaction significantly reduces the predicted peak acceleration; the effect of liquefiable soil on the attenuation of the speed response is more sensitive to the low-frequency portion of the seismic wave. The study’s findings are a significant source of reference for the planning and building of rockfill dams on liquefiable overburden.

Study on the seismic wave input method for earth-rock dam on overburden foundation with dynamic nonlinearity based on nonlinear artificial boundary

Accurately obtaining the seismic response of earth-rock dams on overburden foundations is crucial for seismic safety assessment and design, and a reasonable seismic input method is necessary. The seismic wave input method based on artificial boundaries is widely used in elastic foundations. However, the overburden with obvious dynamic nonlinearity is an insurmountable obstacle for the traditional method. In this research, relying on a specific earth-rock dam project, the essence of the seismic wave input method for nonlinear foundations is analyzed in detail from equivalent loads and viscous boundaries, respectively. The mechanism of inapplicability of the traditional seismic wave input method is illustrated, and an effective modified method is validated and presented. The research indicated that equivalent loads for the nonlinear dynamic response of the overburden foundation can be accurately acquired with the shear box model. The dynamic parameters of soil can be captured dynamically by the nonlinear viscous coupling boundary. The states of the lateral boundary of the overburden foundation are consistent with the free field precisely with the modified seismic wave input method by combining the shear box model and the nonlinear viscous coupling boundary. A large error will be caused by neglecting the dynamic nonlinear behavior of the overburden foundation, where the maximum deviation of peak acceleration may be over 55 % or more. A numerical model with a relatively small lateral range of overburden foundation will be obtained when the modified seismic wave input method is engaged. Moreover, the computational accuracy is enhanced remarkably, with a maximum deviation of no more than 5 %. This study provides effective theoretical support for seismic analysis and safety assessment of earth-rock dams on deep overburden foundations.

Random dynamic response analysis of an asphalt concrete core wall dam on deep overburden with double random factors

The spatial variability of material parameters and the randomness of ground motion are factors that influence the seismic response of a dam. To obtain more reliable seismic response results, it is crucial to study the influence of various uncertain factors on the response to earthquakes. In this paper, the K-L series expansion method and LH sampling technique are combined to characterize the spatial correlation of material parameters using a Gaussian autocorrelation function. This allows for the simulation of random fields of material parameters. By improved the Clough-Penzien power spectrum model and incorporating the concept of a random function, it becomes possible to generate nonstationary random ground motion that accurately reflects the site conditions. Taking an asphalt concrete core dam on deep overburden as an example, a random dynamic response analysis was conducted, considering various random factors. Statistical analysis and distribution testing were conducted on the horizontal acceleration and vertical permanent deformation responses. The process of the evolution of the probability density of the horizontal acceleration at the top of the dam was determined using the generalized probability density evolution method. This method helps to reveal the influence of various random factors on the response of the dam body. The research results show that among the spatial variability of material parameters and the randomness of ground motions, the randomness of ground motions is the main influencing factor of the random response results of the dam body. The mean response of two random factors is significantly larger than that of a single random factor. When considering dual random factors simultaneously, the complexity of the random factors increases, resulting in statistical properties that differ from those of single random factors. Therefore, to obtain more reliable random seismic response results, it is necessary to consider both the spatial variability of material parameters and the randomness of ground motions.

Lithological and Structural Factors Affecting Groundwater Occurrence in Eruwa, South West Nigeria

The subsurface Lithological and Structural framework was investigated to understand its effects on groundwater aquiferous occurrence in this study, underlined by the Precambrian Basement Complex of Nigeria, with granite, gneiss, and schist occurring as the dominant rock types. To successfully map the subsurface, fifty-two (52) Vertical Electrical Sounding points were probed to a depth of current electrode spacing of 100m depth to obtain the variation in the resistivity measurement of the underlying weathered basement and basement rock in the subsurface. Apparent resistivity values and current electrode spacing are plotted on a bi-logarithm plot and correlated to standard curves to estimate subsurface layers' depth, thickness, and resistivity values. WinResist software uses a mathematical algorithm to estimate further the geoelectric parameters to find the best-fit model that matches the observed data. Golden Surfer software was used to represent the geoelectric parameters to aid in geospatial representation. Results show 3-5 lithological layers, which include Topsoil, Clay, Laterite, Sand, Sandy Clay, and Fresh Basement with resistivity value range 82.1Ωm - 2648.2Ωm, 21.8Ωm - 98.4Ωm, 102.3Ωm -167.5Ωm, 404.6Ωm - 2468.2Ωm and 606.8Ωm - 20,535.90Ωm indicating a weathered and fresh unweathered basement rocks layers with H, KH, HA, HKH, KHKH, QH and A geophysical curve which are also typical geometry of weathered material and limited or no fractures basement rock layer. Basement rock resistivity, Overburden thickness, Reflection coefficient, longitudinal conductance, Anisotropy coefficient range (606.8Ωm-20535.9Ωm, 2.6m - 35.6m, 0.3-1.0, 0.01-0.86 and 0.7-3.3) respectively which a typical value of shallow to deep overburden layer with limited or no-detected fracture basement rock). Incorporating the geoelectric parameters value obtained and calculated reveal limited structural deformation of the basement rocks to yield fracture capable of creating secondary porosity in the area while the lithology of the weathered layers becomes the exploitable source for groundwater recovery in the study area.

Analysis of Stress and Deformation Characteristics of Different Dam Heights in Deep Overburden

Relying on an actual project, this paper carries out the application analysis and prediction research of the dam height 150m-200m concrete-faced rockfill dam on deep overburden. Through the finite element calculation results, the stress and deformation of the dam and the structural design of the seepage control system are analyzed. Several preliminary standards have been adopted to control its safety and provide a reasonable basis and technical support for the construction of a 150m-200m high dam on deep overburden.

Study on Mechanism and Main Influencing Factors of Rockburst under Complex Conditions of Hard and Deep Overburden

Xinzhuang Coal Mine is a typical kilometer-deep rockburst mine in the Ningzheng mining area of China Huaneng Group, which is still in the capital construction period. At present, there are a few studies on the rockburst mechanism and prevention of this mine. In order to explore the occurrence mechanism and main influencing factors of rockburst under the complex geological conditions of large buried depth, thick topsoil, and hard overburden in Xinzhuang Coal Mine, this paper, based on the analysis of the basic geological data of the mine, deeply explores the comprehensive disaster factors of Xinzhuang Coal Mine; then, uses the analytic hierarchy process to carry out quantitative analysis of each disaster factor, and finally, it obtains the impact type and occurrence mechanism of the mine. Through research, it is found that the main disaster factors of Xinzhuang Coal Mine are mining depth, coal seam thickness, coal seam thickness change, tectonic stress field, hard overburden, roadway layout, bottom coal reservation, and tunneling activities. The key to the process of the rockburst disaster in Xinzhuang Coal Mine is the superimposed effect of static and dynamic loads on the roadway surrounding the rock system. The potential rockburst type during excavation and mining is the “high static and dynamic load disturbance” type.

Study on seismic wave propagation regularity and dam-foundation interaction characteristics of earth-rock dam on deep overburden

Many dams have to be constructed on deep overburden in meizoseismal areas, so it is vital to understand the seismic performance of these dams. Current research primarily focuses on the whole seismic response of dams, in which the analysis can be relatively imprecise. Nevertheless, an in-depth understanding of the propagation regularity of seismic waves in earth-rock dams on deep overburden, as well as the interaction characteristics between the dam and overburden, is critical. In this paper, based on a planning soil core wall dam with over 500 m of overburden, the seismic wave input method is employed to conduct a detailed and in-depth study from the perspectives of the spatial distribution of seismic acceleration and the Fourier spectra of acceleration time history. The results indicate that the spatial distribution of the peak acceleration of the dam is significantly inconsistent. The horizontal peak acceleration of the upstream side of the dam is greater than that of the downstream side because the dynamic modulus of the dam is significantly inconsistently distributed. In addition, the amplification behaviours of the seismic wave are different in the overburden and dam body, and the low-frequency and high-frequency components are amplified. The dynamic interaction between the dam body and the overburden significantly reduces the acceleration response at the dam-foundation interface by 44 % and 50 % in horizontal and vertical accelerations, respectively, because of the absorption of seismic wave energy by the dam body and the inconsistency of the dynamic modulus distribution of the overburden. The findings of this study provide robust theoretical support for evaluating the seismic performance and designing measures for the seismic resistance of earth-rock dams on deep overburden.

A meshfree large-deformation analysis method for geotechnical engineering based on the RBF field variable mapping technology

In this paper, a practical meshfree large deformation method (MFLDM) is proposed for numerical analysis in geotechnical engineerings, including: soil foundation, slop, dam, etc. The MFLDM leverages both the flexible nodal distribution in the meshfree method and the high stability in the arbitrary Lagrangian–Eulerian (ALE) framework. In each calculation step, two sets of Gauss points, fixed and moving Gauss points, are generated in the background mesh. In addition, the radial basis function (RBF) is used to map field variables, including stress, stain, and constitutive variables, between the fixed and moving Gauss points to achieve the field variable redistribution during the large-deformation analysis. The proposed MFLDM, which is written in C++ using the object-oriented programming approach, can be completely integrated into the self-development calculating system named GEODYNA and coupled with the finite element method (FEM) at the matrix level, which significantly broadens its practical application. The proposed model is verified by several numerical examples and compared with different constitutive models, including the linear elasticity model, ideal elastic–plastic model, and generalized elastic–plastic model. The comparison results verify the high accuracy, fast convergence, and good robustness of the proposed MFLDM. Finally, the proposed MFLDM is applied to a local large deformation analysis between the cut-off wall and the core wall on a deep overburden.

Evaluation of Seismic Potential in a Longwall Mine with Massive Sandstone Roof Under Deep Overburden: an Update

Evaluation of Seismic Potential in a Longwall Mine with Massive Sandstone Roof Under Deep Overburden: an Update

Numerical investigation of seepage dissolution evolution of the bottom expansion cutoff wall in deep overburden

The bifurcation defect at the bottom of the cutoff wall in the deep overburden leads to a sharp increase in the local seepage gradient of the adjacent overburden at the bottom of the cutoff wall, which affects the evolution process of seepage dissolution of the cutoff wall. This study presents a novel type of bottom expansion cutoff wall to alleviate the problem that the seepage gradient of adjacent strata at the bottom of the cutoff wall far exceeds its allowed value. Considering the effects of the pore, aggregate, and convection on the calcium ion diffusion coefficient of concrete, we propose a coupling analytical model of seepage dissolution for two cutoff wall schemes, including the bifurcation defect schemes and bottom expansion schemes, to investigate the evolution of calcium ion concentration, porosity, and seepage characteristics, and to reveal the influence mechanism of the bottom bifurcation defect and bottom expansion of the cutoff wall on the seepage dissolution of the cutoff wall in deep overburden. The results indicate that subjected to the bottom bifurcation defect, the calcium ion concentration of the cutoff wall decreases faster, and the porosity increases faster with the increase of service life compared to the conventional cutoff wall when subjected to the bottom bifurcation defect. With a bifurcation height of 24 m at the bottom of the wall, the service life of the cutoff wall is reduced by 6.64%. In contrast, the novel type of bottom expansion cutoff wall is used to reveal that the concrete porosity increases slowly with the increase of the expansion radius over the same service life. The seepage gradient of the adjacent overburden at the bottom of the cutoff wall is significantly reduced. The service life of the cutoff wall is extended by 47.33% due to its 5 m bottom expansion radius. This study can provide a theoretical basis for the evolution of long-term service performance of the cutoff wall of an earth-rock dam on deep overburden.

Seismic response and fragility evaluation of circular tunnels in the Himalayan region: Implications for post-seismic performance of transportation infrastructure projects in Jammu and Kashmir

The expanding infrastructural projects together with the prior historical records of significant earthquakes including the deadliest 2005 Kashmir earthquake in the Himalayan region, urge to assess the seismic vulnerability and risk of Jammu and Kashmir. This paper attempts to assess the seismic vulnerability of circular tunnels using the fragility function for various seismic environments. To accomplish this, the seismic performance of tunnels is quantified for each hazard zone with a diverse typology and seismic scenario. Microzonation results aided in defining the four hazard zones based on seismic severity. Zone A, B, C, and D are seismic zones with severe, high, moderate ad low Seismic Hazard Indexing (SHI). Tunnel performance is evaluated for each hazard zone, and empirical correlations for damage indices are defined. For Zone A, the fragility curves presented for minor, moderate, and extensive damage states for both shallow and deep tunnels appear to be extremely catastrophic. For various slippage conditions, the variation of flexibility and racking ratios for tunnels with shallow and deep overburden depths is significant. The proposed fragility curves are used to evaluate the seismic risk of a roadway network that includes A, B, and C routes that pass through Jammu. The risk matrices and probability function revealed that all tunnels on Route A are extremely vulnerable to damage. Extensive portal collapse and tunnel lining failure will render this route inoperable during the post-seismic phase. The developed empirical correlations, fragility curves, and risk matrices will serve as a ready-to-use tool for tunnel design engineers working on any Himalayan infrastructure project.

Fracture features of brittle coal under uniaxial and cyclic compression loads

Under the effects of complex geological and stress environments, burst hazards continue to be a major challenge for underground space utilization and deep resources exploration as its occurrence can lead to personnel causalities, equipment damage and structural collapse. Considering the stress path experienced by in-situ coal body, cyclic loading appears in quite various forms for instance shearer cutting, overlying strata breakage, hydro-fracturing and blasting, during tunnel, mining and underground space utilizing process. The stability of the underground coal body subject to periodic loading/unloading stress is extremely important for maintain the function of designed engineering structure for waste storage, safe mining, roadway development, gas recovery, carbon sequestration and so on. The mechanical properties of hard rock subject to cyclic fatigue loads has been intensively investigated by many researchers as the rock burst induced by supercritical loads has long been a safety risk and engineering problems for civil and tunneling engineering under deep overburden. More recently, the mechanical properties of coal samples under cyclic fatigue loads is investigated from the aspect of hysteresis, energy dissipation and irreversible damage as the burst hazards of brittle coal is rising in many countries. However, the crack propagation and fracture pattern of brittle coal need more research to understand the micro mechanism of burst incubation subject to cyclic fatigue loads as brittle coal can store more elastic strain energy and rapidly release the energy when its ultimate strength once reached. This research studied the internal crack status corresponding to different cyclic fatigue loading stage of brittle coal samples. The AE monitoring was applied during the uniaxial and cyclic loading process of brittle coal samples to record the crack intensity of samples at different loading stages. The damage evolution curve corresponding to loading status was then determined. The fracture pattern of coal samples determined by micro-CT scan was observed and discussed. It has been found by this paper that brittle coal of uniaxial compression tests demonstrated sudden failure caused by major splitting fracture while that of cyclic fatigue tests experienced progressive failure with mixture fracture network.

Study on the seepage control of ultra-deep in situ test wells in deep overburden of riverbeds

Study on the seepage control of ultra-deep in situ test wells in deep overburden of riverbeds

Simulation experiment study on the activity law of deep overburden with large mining

Simulation experiment study on the activity law of deep overburden with large mining

Model Test on Mechanical and Deformation Property of a Geomembrane Surface Barrier for a High Rockfill Dam

The cushion of a geomembrane surface barrier of a high rockfill dam built on deep overburden is prone to crack and fail because of excessive flexural deformation. This study proposes a geomembrane surface barrier for a high rockfill dam on deep overburden. The proposed geomembrane surface barrier uses polyurethane bonded aggregates as the cushion material. The loading and deformation performance of the barrier system under uniform water pressure was investigated using a self-developed structure model test device. The mechanical and deformation property of each layer of the barrier, and the interaction mode between adjacent layers, were obtained through external videos and internal sensor monitoring. The results demonstrated that the polyurethane bonded aggregate cushion exhibited good adaptability to flexural deformation during the entire loading process and maintained good contact and coordinate deformation with the upper protective and the lower transition layers. The geomembrane surface barrier created using polyurethane bonded aggregates as the cushion material can adapt to the flexural deformation of a high rockfill dam surface on deep overburden.

Multifield Coupling Numerical Simulation of the Seepage and Stability of Embankment Dams on Deep Overburden Layers

Multifield Coupling Numerical Simulation of the Seepage and Stability of Embankment Dams on Deep Overburden Layers

Estimating Deformation Modulus and Bearing Capacity of Deep Soils from Dynamic Penetration Test

The dynamic penetration test (DPT) and the Menard pressuremeter test (PMT) have been widely used in geotechnical survey of deep soils for megadam foundations in western China. The DPT measures are not well utilized due to the lack of correction factors and of empirical relationships for deep soils. This study investigates the relationships between the corrected DPT blow counts ( N 120 ′ ), pressuremeter modulus (EPMT), limit pressure (pL), deformation modulus (E0), and bearing capacity (fak) derived from the PMT results. Meanwhile, a nonlinear regression model is developed to predict the DPT correction factor (a) based on the raw DPT blow counts (N120) and the rod length (L) by integrating the available correction factors for shallow gravelly soils suggested by the code provisions and the deep soil data in this work. It is concluded that the proposed DPT correction factors match well with the code suggestions and the new compiled dataset, and the corrected DPT blow counts can be used to reasonably predict the engineering properties of deep sand and clay soils. Although the proposed correlations need to be tested among different soil types and regions, the results shed the light on in situ geotechnical tests and data utilization for deep and thick overburden.

A binary-medium-based constitutive model for artificially cemented gravel-silty clay mixed soils

In situ soils of deep overburden layer of dam foundation are widely distributed in Southwest China, which are mixtures of gravel and silty clay in varying proportions and have cementation feature between soil particles. Based on a series of triaxial compression tests carried out on artificially cemented mixed soils (CMS) and remolded mixed soils (RMS) at confining pressures of 50, 100, 200 and 400 kPa with fine contents (silty clay) of 13%-70% in mass, a binary-medium constitutive model for artificially cemented mixed soils is proposed within framework of breakage mechanics theory for geological materials and homogenization theory. This model was formulated by regarding the soils as a binary medium consisting of bonded blocks (idealized as bonded elements) and weakened bands (idealized as frictional elements), whose deformation properties are described by the modified Duncan-Chang model and the Lade-Duncan elastoplastic model, respectively. The non-uniform distribution of stress and strain within a representative volume element can be given by introducing the structural parameters of breakage ratio and local stress coefficient. Comparisons of computed results with test results demonstrate that the binary-medium constitutive model can reflect mechanical properties of artificially cemented mixed soils well.

Seismic response analysis of earth-rock fill dam on deep overburden under viscoelastic boundary condition

The dynamic response characteristics of an earth-rock fill dam on a deep overburden are the focus of seismic research. In particular, evaluating the influence of the earthquake safety of the dam. A dynamic response analysis of earth-rock fill dam on a deep overburden based on viscoelastic boundary conditions was used to study the influence of boundary conditions (including fixed boundary conditions and viscoelastic boundary conditions). The results show that the fixed boundary condition greatly improves the dynamic response level of the dam during an earthquake and has no obvious influence on the distribution of the acceleration response in the dam and the foundation. The difference in the calculation results under the two boundary conditions is related to the seismic input characteristics and dynamic deformation characteristics of the soil material. An analysis of the acceleration response spectrum shows that the influence of the boundary conditions on the calculation results is limited to the magnitude level of the acceleration response, while the spectral characteristics of the vibration of the dam and the foundation do not have a significant impact.

Effect of slope with overburden layer on the bearing behavior of large-diameter rock-socketed piles

Pile foundation is a typical form of bridge foundation and viaduct, and large-diameter rock-socketed piles are typically adopted in bridges with long span or high piers. To investigate the effect of a mountain slope with a deep overburden layer on the bearing characteristics of large-diameter rock-socketed piles, four centrifuge model tests of single piles on different slopes (0o, 15o, 30o and 45o) were carried out to investigate the effect of slope on the bearing characteristics of piles. In addition, three pile group tests with different slope (0o, 30o and 45o) were also performed to explore the effect of slope on the bearing characteristics of the pile group. The results of the single pile tests indicate that the slope with a deep overburden layer not only accelerates the drag force of the pile with the increasing slope, but also causes the bending moment to move down owing to the increase in the unsymmetrical pressure around the pile. As the slope increases from 0o to 45o, the drag force of the pile is significantly enlarged and the axial force of the pile reduces to beyond 12%. The position of the maximum bending moment of the pile shifts downward, while the magnitude becomes larger. Meanwhile, the slope results in the reduction in the shaft resistance of the pile, and the maximum value at the front side of the pile is 3.98% less than at its rear side at a 45o slope. The load-sharing ratio of the tip resistance of the pile is increased from 5.49% to 12.02%. The results of the pile group tests show that the increase in the slope enhances the uneven distribution of the pile top reaction and yields a larger bending moment and different settlements on the pile cap, which might cause safety issues to bridge structures.