Experimental and Numerical Investigation of Seepage and Seismic Dynamics Behavior of Zoned Earth Dams with Subsurface Cavities

Structural design of the vertical displacements and shear strains in the earth fill (EF) dams has great importance in the structural engineering problems. Moreover, far fault earthquakes have significant seismic effects on seismic damage performance of EF dams like the near fault earthquakes. For this reason, three dimensional (3D) earthquake damage performance of Oroville dam is assessed considering different far-fault ground motions in this study. Oroville Dam was built in United States of America-California and its height is 234.7 m (770 ft.). 3D model of Oroville dam is modelled using FLAC3D software based on finite difference approach. In order to represent interaction condition between discrete surfaces, special interface elements are used between dam body and foundation. Non-reflecting seismic boundary conditions (free field and quiet) are defined to the main surfaces of the dam for the nonlinear seismic analyses. 6 different far-fault ground motions are taken into account for the full reservoir condition of Oroville dam. According to nonlinear seismic analysis results, the effects of far-fault ground motions on the nonlinear seismic settlement and shear strain behaviour of Oroville EF dam are determined and evaluated in detail. It is clearly seen that far-fault earthquakes have very significant seismic effects on the settlement-shear strain behaviour of EF dams and these earthquakes create vital important seismic damages on the swelling behaviour of dam body surface. Moreover, it is proposed that far-fault ground motions should not be ignored while modelling EF dams.

As a significant geological hazard in large–scale engineering construction, deep subsurface voids demand effective and precise detection methods. Cross–hole radar tomography overcomes depth limitations by transmitting/receiving electromagnetic (EM) waves between boreholes, enabling the accurate determination of the spatial distribution and EM properties of subsurface cavities. However, conventional inversion approaches, such as travel–time/attenuation tomography and full–waveform inversion, still face challenges in terms of their stability, accuracy, and computational efficiency. To address these limitations, this study proposes a deep learning–based imaging method that introduces the concept of travel–time fingerprints, which compress raw radar data into structured, low–dimensional inputs that retain key spatial features. A large synthetic dataset of irregular subsurface cavity models is used to pre–train a UNET model, enabling it to learn nonlinear mapping, from fingerprints to velocity structures. To enhance real–world applicability, transfer learning (TL) is employed to fine–tune the model using a small amount of field data. The refined model is then tested on cross–hole radar datasets collected from a highway construction site in Guizhou Province, China. The results demonstrate that the method can accurately recover the shape, location, and extent of underground cavities, outperforming traditional tomography in terms of clarity and interpretability. This approach offers a high–precision, computationally efficient solution for subsurface void detection, with strong engineering applicability in complex geological environments.

This study employs GeoStudio software to analyze a zone earth dam model seepage behavior, slope stability, and dynamic response under seismic loading. Seepage behavior, pore water pressure distribution, displacement, and safety factors are factors to be analyzed. The presence of cavities in the dam foundation significantly compromises the dam’s stability. Increasing seepage flow rate through both the dam body and foundation due to the formation of cavities leads to a serious risk of structural failure. In addition to normal cavities, elliptical and irregular shape cavities will be studied. Based on the simulation results, flow rate seepage for different locations of cavities (upstream, core, and downstream), measured displacement due to the applied earthquake, and the safety factor will be analyzed. The impact of increment in the cavities’ diameter on the earth dam model safety will be summarized according to the design guidelines of USACE (2003). These findings provide valuable insights into the long-term resilience of any plans to construct a zone earth dam and contribute to the broader field of dam safety engineering under complex geotechnical and seismic conditions.

Climate change with extreme hydrological conditions, such as drought and flood, bring new challenges to seepage behavior and the stability of earthfill dams. Taking a drought-stricken earthfill dam of China as an example, the influence of drought-flood cycles on dam seepage behavior is analyzed. This paper includes a clay sample laboratory experiment and an unsteady finite element method seepage simulation of the mentioned dam. Results show that severe drought causes cracks on the surface of the clay soil sample. Long-term drought causes deeper cracks and induces a sharp increase of suction pressure, indicating that the cracks would become channels for rain infiltration into the dam during subsequent rainfall, increasing the potential for internal erosion and decreasing dam stability. Measures to prevent infiltration on the dam slope surface are investigated, for the prevention of deep crack formation during long lasting droughts. Unsteady seepage indicators including instantaneous phreatic lines, equipotential lines and pore pressure gradient in the dam, are calculated and analyzed under two assumed conditions with different reservoir water level fluctuations. Results show that when the water level changes rapidly, the phreatic line is curved and constantly changing. As water level rises, equipotential lines shift upstream, and the pore pressure gradient in the dam’s main body is larger than that of steady seepage. Furthermore, the faster the water level rises, the larger the pore pressure gradient is. This may cause internal erosion. Furthermore, the case of a cracked upstream slope is modelled via an equivalent permeability coefficient, which shows that the pore pressure gradient in the zone beneath the cracks increases by 5.9% at the maximum water level; this could exacerbate internal erosion. In addition, results are in agreement with prior literature that rapid drawdown of the reservoir water level is detrimental to the stability of the upstream slope based on embankment slope stability as calculated by the Simplified Bishop Method. It is concluded that fluctuations of reservoir water level should be strictly controlled during drought-flood cycles; both the drawdown rate and the fill rate must be regulated to avoid the internal erosion of earthfill dams.

Abstract. Earthfill dams are man-made geostructures which may be especially damaged by seismic loadings, because the soil skeleton they are made of suffers remarkable modifications in its mechanical properties, as well as changes of pore water pressure and flow of this water inside their pores, when subjected to vibrations. The most extreme situation is the dam failure due to soil liquefaction. Coupled finite element numerical codes are a useful tool to assess the safety of these dams. In this paper the application of a fully coupled numerical model, previously developed and validated by the authors, to a set of theoretical cross sections of earthfill dams with impervious core, is presented. All these dams are same height and have the same volume of impervious material at the core. The influence of the core location inside the dam on its response against seismic loading is numerically explored. The dams are designed as strictly stable under static loads. As a result of this research, a design recommendation on the location of the impervious core is obtained for this type of earth dams, on the basis of the criteria of minor liquefaction risk, minor soil degradation during the earthquake and minor crest settlement.

Uncontrolled seepage through earth-fill dams may cause of dam failure. Seepage analysis, therefore, is an essential study required before construction for a safe and sustainable dam operation. In this study, numerical analysis of seepage through a theoretical case of an earth-fill dam was applied using SEEP/W program. Five different dam models, two with homogenous and three with zoned cross sections, have been studied. The study consists normal and maximum reservoir water levels, different drainage lengths and thicknesses, different percentages of permeability between shell and core. Total of 26 tests were conducted and the best model based on seepage behavior was chosen. Seepage analysis acknowledged that with availability of required soil quantity, the homogeneous model that has medium length of drainage with thickness of 0.5 m is the most appropriate model for the case study. Otherwise, zoned model with core at the centre with 1:0.5 (H:V) slope is recommended

First impounding of the earth-fill dams is considered as one of the most critical stages of these earth structures during their lifespan such that it demands careful monitoring of the dam’s safety. In this study, behavior of Siahoo dam, an earth-fill dam in Iran, is evaluated by numerical modeling at the stage of first impounding to (1) back-analysis and calibration of the numerical model using data of instrumentation measurements, gathered during the dam construction. (2) Determine the optimized plan of the dam’s first impounding so that the dam safety is secured against hydraulic fracturing. (3) Predict the displacements of the dam in the future under seepage and consolidation using the calibrated numerical model. (4) Analyze the dam under seismic loading condition. The material properties were chosen through a two-step procedure based on numerical simulation of laboratory tests in the software and calibration between the stress–strain analysis of the dam and instrumentation measurements at the end of construction stage, so that the real behavior of the dam can be represented. To find the maximum rate of dam’s first impounding in safe condition, a sensitivity analysis was performed assuming eight number of impounding scenarios. Having performed the steady-state seepage analysis, seismic loading was applied using the equivalent linear method and the permanent displacements were predicted using the method of Newmark sliding blocks. Liquefaction analysis was also performed to recognize liquefiable zones of the foundation. Finally, stress redistribution analysis was carried out to estimate the post-earthquake displacements.

Karst problems often result in unexpected additional building costs and the proper understanding of karst terrains is therefore important for geotechnical engineer. The karst terrain is developed from the dissolution of carbonate rock. Groundwater flow through carbonate rock enhances the dissolution of carbonate minerals which can cause the development of subsurface cavities or voids. The subsurface cavities and uneven depth of bedrock make foundation design very difficult in karst terrain. A subsurface characterization and grouting case study are presented for the Yongweol-ri site, South Korea. In the project area, mortar was injected into subsurface cavities for consolidation and/or grouting purposes. The subsurface cavities were imaged using electrical resistivity and borehole camera (BHTV) before and after mortar injection. In addition, the resistivity changes of mortar specimens were studied in the laboratory simulating various field conditions. The injected mortar was imaged as anomalies exhibiting lower resistivity than the surrounding rocks. A comparison of the pre- and post-grouting resistivity provided detailed information of the subsurface cavities plus the areas which have been occupied by the mortar after consolidation. Also, BHTV field test confirmed the presence of the mortar in the subsurface cavities. The results obtained from this study showed that electrical resistivity imaging can be a useful tool for detecting and evaluating changes in subsurface resistivity due to the injection of the mortar. From the laboratory analysis, it is confirmed that mortar is a good material for grouting and ground stability hazard management.

Automated hybrid singularity superposition and anchored grid pattern BEM algorithm for the solution of inverse geometric problems

Mollasadra dam is an earth fill dam with a clayey core and a height of 72 m from river bed, constructed on Kor River. pore water pressure in the dam was investigated following its construction and first and second impoundments. The dam was modeled by a finite element mesh. After the first and second dam impoundments, the overall trend in monitored pore water pressure was well modeled by the transient analysis. The result showed the six month time period between impoundments was long enough for the pore water pressure to reach equilibrium everywhere throughout the core, except where considerable initial constructioninduced pore water pressure was observed. High values of construction-induced pore water pressure at elevation2050 m did not dissipate completely during the 6 month period of almost constant reservoir level (el. 2098.3 m) and the pore pressures were still at the transient state throughout the core. Therefore, it was concluded that porepressures in the core of earth fill dams may not achieve steady state conditions even several months after the dam construction and impoundments.

Problem statement: A number of tailings earthen dams have failed during past earthquakes. The failure of tailings dam ultimately results into the release of the stored tailings waste deposit in the surrounding locality. To reduce such damage of tailings earthen dam, a detail method of seismic analysis is very much essential which can be used reliably for the design and construction. Approach: To establish a detail method of static and seismic analysis for a tailings earthen dam, in this study both the static and seismic analysis were performed for a typical section of tailings earthen dam. The whole analysis was performed using various software packages like FLAC3D, TALREN 4, SEEP/W and SLOPE/W. Results: After FLAC3D analysis it was observed that under the seismic loading condition the maximum displacement of the dam is about 66.7 cm, whereas by using the Makdisi-Seed method the maximum displacement was obtained as 57 cm. FLAC3D analysis showed that the base level input acceleration gets amplified with the height of the dam and at the crest level the amplification is about three times. After slope stability analysis under seismic loading it was found that the factor of safety is 0.89, but under the static loading condition the minimum value of factor of safety was obtained as 1.22. Conclusion/Recommendation: From this analysis it was clear that the dam was unsafe under the seismic loading.

The embedded cantilever retaining walls are often required for excavation to construct the underground facilities. Significant numbers of numerical and experimental studies have been performed to understand the behavior of embedded cantilever retaining walls under static condition. However, very limited studies have been conducted on the behavior of embedded retaining walls under seismic condition. In this paper, the behavior of a small scale model embedded cantilever retaining wall in dry and saturated sand under seismic loading condition is investigated by shake table tests in the laboratory and numerically using software FLAC2D. The embedded cantilever walls are subjected to sinusoidal dynamic motions. The behaviors of the cantilever walls in terms of lateral displacement and bending moment are studied with the variation of the two important design parameters, peak amplitude of the base motions and excavation depth. The variation of the pore water pressures within the sand is also observed in the cases of saturated sand. The maximum lateral displacement of a cantilever wall due to seismic loading is below 1% of the total height of the wall in dry sand, but in case of saturated sand, it can go up to 12.75% of the total height of the wall.

Three-dimensional (3D) kinematic limit analysis of unsaturated hillslopes is presented in this paper. Different from the traditional two-dimensional (2D) mechanism based on the infinite slope model, the 3D failure mechanism is more rational for its advantage in taking the out-of-plane geometries and soil properties into consideration. The soils in engineering practice are mostly unsaturated in nature and are commonly characterized with an arbitrary distribution of the moisture content, i.e., the matric suction, and therefore the formation of the work balance equation becomes much more elaborated using traditional methods. To tackle the nonlinear features of matric suction, a semi-analytical method is presented and is validated through comparisons with the benchmark solutions. The hillslope stability under seismic and pore water pressure conditions are both numerically studied. The results are presented in forms of graphs for a practical range of parameters, indicating the significance in accounting for the influences of 3D constraints, seismic loads and pore water pressures in hillslope stability assessments.

This paper reports on the potential performance of earthfill and tailings dams, and other saturated earthen structures, subjected to blast vibrations. Relationships between explosive-induced residual pore pressure increase and crest settlement versus peak particle velocity are presented. Eight explosive tests, conducted on a 2.25-m-high dam constructed of loose dilative sand, showed that significant increases in residual pore pressure (PPR > 0.1) occurred when peak particle velocity exceeded 0.015 m/s at shallow depths to 0.035 m/s at greater depths. Limited crest settlement occurred when the peak particle velocity exceeded 0.025 m/s. Results of this research, previous research, and the field behavior of full-scale earthfill and tailings dams indicate that peak particle velocity below 0.025 m/s and 0.10 m/s are reasonable thresholds to limit pore pressure buildup in full-size earthfill and tailings dams sensitive and not sensitive to vibrations, respectively.

Impact of soil deformation on phreatic line in earth-fill dams