Dam Abutment Research Articles

Calibration of seepage analysis sections based on observation well monitoring data: a case study on Darian dam abutments–Kermanshah province, Iran

Water seepage, after impounding, is among the main problems encountered in dam construction projects. Assessment and prediction of the amount of seepage water can be useful in preventing such incidents. Darian dam has been constructed on Sirvan River in Kermanshah province in west of Iran. This dam, which is currently in impounding state, was built for flooding control and electricity generation purposes. No seepage problem was observed in this dam, but the water level recorded in observation wells in right and left abutments indicated a significant difference with water levels predicted through designing step by numerical analysis using software of SEEP/W. In this study, iso-piezometric map of dam area and its abutments was produced using data obtained from 27 observation wells. Using this map, the actual phreatic line (underground water level) along the seepage analysis sections at design time was extracted. Then, the actual curve of water level was compared with the curve of water level obtained from the SEEP/W. Using the actual curve of underground water and geological features, rock masses in the seepage analysis sections were divided into hydrogeological sub-units. The main objective of the study was to overlap the computed phreatic line and actual underground water level on the basis of observation wells by changing the permeability of the hydrogeological sub-units in the software of SEEP/W, and to compare the permeability of the units relative to each other in real situation and design time. In this regard, in the right abutment, the permeability of all units was expressed as a proportion of permeability of unit Li (k/kli). Similarly, in the left abutment the ratio k/klml was calculated for all units. This relative expression allow calibrating of seepage analysis section by using the data from underground water level, even when the amount of seepage in rock masses is not known.

Validation and modification of extensometer results in Karun-4 double-curvature arch concrete dam

ABSTRACTThe present study was conducted to investigate and modify the extensometer results in double-curvature arch dams. To evaluate extensometer results of Karun-4 dam, first, the distinct element 3DEC-DP 5.00 software was used to model Karun-4 dam through a numerical model consisting of discontinuities, dead loads (dam weight) and piezometric pressure in the rock–concrete contact. Next, this numerical model was calibrated using 30 extensometer results in the dam foundation and abutments and 5 Direct Pendulum results in dam body. As the results show the base rod has a displacement due to the loads applied to the foundation and abutments and located outside the range of effect zone (disturbance zone), and thus it cannot be used as the base rod. Since no point has zero displacements in the numerical modeling and obtaining such a point is almost impossible, the accuracy of the electrical transducers was employed; the point in the numerical modeling with the lower displacement than the accuracy of transducers was selected as the base rod location. Next, the distance at which displacement of the base rod is zero was identified and the absolute deformation of each extensometer was determined.

An approach using Dempster–Shafer evidence theory to fuse multi-source observations for dam safety estimation

Considering the limitations existing in the single-effect quantity analysis method of dam service behavior reasoning, the dam service behavior multi-effect quantities fusion reasoning model is built and implemented based on the study of improved methods about classic Dempster–Shafer (D–S) evidence fusion technologies. Focusing on the problems that classic D–S evidence fusion rules fail or the reasoning results are contrary to the intuition and convention due to the high-conflict evidences, the calculation methods of compatibility coefficient measurement matrices between any two basic probability assignment functions of evidences (E-BPAF) and between any two basic probability assignment functions of focal elements (FE-BPAF) are provided, respectively, based on the compatibility analysis of any two E-BPAFs and any two FE-BPAFs. The weight matrices about any two E-BPAFs and any two FE-BPAFs for initial BPAFs are defined, respectively, through compatibility coefficient matrices. Then, the comprehensive weight matrix for initial BPAFs is introduced to unify weight matrices. By analyzing and comparing some examples and existing study results, the performance test of the proposed method is conducted and the correctness and rationality are also verified. Finally, combining with an instance of a gravity arch dam project, the proposed method is utilized to fuse the multi-information from measuring points on the dam abutment, and the reasonable reasoning results are obtained about the dam service behavior.

Surface and borehole geophysics for the rehabilitation of a concrete dam (Penne, Central Italy)

In this paper, surface and borehole geophysical surveys are employed to improve the effectiveness of a rehabilitation intervention (cut-off wall) to be executed on the right abutment of a leaking concrete dam (Penne, Central Italy). In a first step, surface geophysical measurements (electrical resistivity and P-wave velocity data), were collected to provide a geophysical model to be compared to the preliminary geological model available before the geophysical survey. Because significant differences emerged between the geophysical and the preliminary geological models, a second phase of borehole investigations was planned to validate the geophysical reconstruction obtained from surface data. The final geological model resulting from the geophysical results differs significantly from the preliminary model available at the time of the geophysical survey. Therefore, the planned cut-off wall needs to be extended both laterally and in depth beyond the position estimated before the geophysical campaign, so that the low-permeability bedrock is intercepted at a depth equal or lower than the critical one. At the end, the low-cost geophysical campaign (1.5% of the entire costs of the intervention) was highly beneficial to this project, minimizing subsurface geological uncertainty to design an effective anti-seepage intervention and stressing the importance of a representative geological model for engineering design.

Dynamic Stability Analysis of Arch Dam Abutment Based on Strength Reduction Method

Dynamic stability analysis of dam abutment is related to safety, reliability and rationality, which gives significant consideration on arch dam development. This paper aims at an engineering project, using static and dynamic combined method, firstly to slove the static forces from dam body to dam abutment; Then using strength reduction method combined with seismic load got from response spectrum with the same strength reduction factor to get the dynamic safety factor. The result s provide design basis for the projects.

Impulsive forces distribution along the sediment storage dam upstream face for different mud–rock flow unit weight

Because of the huge damage caused by mud-rock flow for the downstream life and property, engineering prevention must be given. It is one of fast and effective measures to build sediment storage dams in the formation zone to the circulation area. Due to the undercutting, scour and impact effect of mud-rock flows to sediment storage dam foundation or the unreasonable reconnaissance design, sediment storage dams possibly cause damage in the design period. However, the impulsive forces of mud-rock flow are the main reason to lead the engineering control structures (sediment storage dams, drainage grooves and block structure of pipe group) to damage. It is very important to study the law of mud-rock flow impulsive forces, and it is of great significance to prevent the damage of sediment storage dam and provide data support and technical support for the construction of sediment storage dam. First, the distribution rules of the maximum and mean value of the impulsive forces of mud-rock flow for the sediment storage dam upstream surface were studied for four mud-rock flow slurry unit weight as the experiment variable. The mud-rock flow impulsive forces value was collected by a numerical collection device that connected eight pressure sensors positioned in various locations, which received the mud-rock flow impact signal. Then, the distribution roles of the maximum and mean impulsive forces value imparted by water or water-rock flows were compared. The results indicate that (1) due to the randomness of particle impacts, the distribution law of the maximum impulsive forces is not obvious, and the maximum mud-rock flow impulsive forces of 99.277 kPa occur in A(1)B(3)C(7) (for a range of particle sizes of 2-4.5 cm); (2) the mud-rock flow impulsive forces mean value first increases and then decreases as the unit weight of the mud-rock flow increases; and (3) the mud-rock flow impulsive forces mean value gradually decreases along the height direction of the sediment storage dams' upstream surface and gradually decreases as the direction changes to the overflow section toward the dam abutments.

An Improved Computing Method for 3D Mechanical Connectivity Rates Based on a Polyhedral Simulation Model of Discrete Fracture Network in Rock Masses

Based on a 3D model of a discrete fracture network (DFN) in a rock mass, an improved projective method for computing the 3D mechanical connectivity rate was proposed. The Monte Carlo simulation method, 2D Poisson process and 3D geological modeling technique were integrated into a polyhedral DFN modeling approach, and the simulation results were verified by numerical tests and graphical inspection. Next, the traditional projective approach for calculating the rock mass connectivity rate was improved using the 3D DFN models by (1) using the polyhedral model to replace the Baecher disk model; (2) taking the real cross section of the rock mass, rather than a part of the cross section, as the test plane; and (3) dynamically searching the joint connectivity rates using different dip directions and dip angles at different elevations to calculate the maximum, minimum and average values of the joint connectivity at each elevation. In a case study, the improved method and traditional method were used to compute the mechanical connectivity rate of the slope of a dam abutment. The results of the two methods were further used to compute the cohesive force of the rock masses. Finally, a comparison showed that the cohesive force derived from the traditional method had a higher error, whereas the cohesive force derived from the improved method was consistent with the suggested values. According to the comparison, the effectivity and validity of the improved method were verified indirectly.

3D transient numerical flow simulation of groundwater bypass seepage at the dam site of Dongzhuang hydro-junction

Hydrogeological conditions at the Dongzhuang Hydro-Junction site are complex and include underground water divides, a hanging river and hydraulic drops along faults. The site suffers from seepage because of its location in karst terrain. This study addresses dam bypass leakage at the Dongzhuang site and deficiencies in the regional groundwater seepage model. A hydrological conceptual model is generated, as well as a regional numerical simulation of groundwater flow based on analysis of the geology and hydrogeology of the dam site and surrounding area. From the analysis, a detailed 3D model of the groundwater flow field at the dam site is established, in which permeability and precipitation infiltration parameters are corrected using the inversion method. Leakage quantities are calculated for three different conditions: natural state, regular dam impoundment with an impervious curtain, and regular dam impoundment without an impervious curtain. The results show that underground water flows from west to east during all three conditions. The leakage quantity bypassing the dam region without anti-seepage treatment is 220,000m3/d, with seepage concentrated around the dam foundation, dam abutments and the river bend of the reservoir head. Leakage in these areas accounts for 72% of the total leakage in the study area. However, when an impervious curtain is included in the model, the total leakage quantity is reduced to 51,000m3/d and seepage concentrates along the banks of the reservoir. The 3D numerical model of regional groundwater flow is promising in that it can simulate complex hydrogeological conditions, and the accuracy and confidence levels improve when a detailed 3D model of groundwater flow at the dam site is added to the regional model.

Mechanisms of Interaction Between an Arch Dam and Abutment Slope Using Physical Model Tests

In southwestern China, the stability of high-steep slopes in large-scale hydropower projects has become a key technical challenge that constrains the safety of construction and operation. Based on a geological survey of the large-scale rock block in the Jinping-I Hydropower Station left bank, the entire system of the dam and its abutment slope is defined as the study subject. The mechanisms of interaction between the arch dam and the abutment slope during the construction stage, the impoundment stage and the structural plane strength-weakening stage are investigated using physical model tests. (1) During the excavation stage, the early-stage excavation has a significant impact on the huge rock block, whereas the impact of later-stage excavation is relatively small. (2) During the impoundment stage, the dam foundation is under hydraulic load. Therefore, the huge rock block moves away from the slope due to the arch thrust. (3) During the structural plane strength-weakening stage, both sides of the structural planes develop a relative displacement, and the massive rock block slips slightly. Moreover, the strain of the dam is slightly different from the situation in the normal impoundment stage. The majority of the downstream plane is under tension, indicating that a decline in the bedrock strength of the left bank dam abutment results in deformation of the dam towards the mountain body, the riverbed and the top part of the dam crest.

Development of a Risk-based Methodology for Rock Slope Analysis

The objective of this research is to develop a geotechnical risk assessment methodology to concurrently identify and quantify important risk elements in rock slopes. Thus, important geotechnical issues affecting a high rock slope were categorized into three major critical risk groups after a comprehensive literature review and field observation program. A set of knowledge-based fuzzy inference rules were established to set up membership functions and calculate risk index (RI) for each critical risk element (CRE). The CREs were ranked on the basis of the calculated RI. The developed risk algorithm was employed to assess the geotechnical risks associated with the right abutment slope of Vanyar dam, Iran. The analysis results showed that the presence of high water level (RI 4.47), shear strength of discontinuities (RI 4.27), and presence of shear or fault zones in the slope (RI 4.01) were the most critical elements which affected the slope stability, respectively. According to calculated risk indices the engineers should pay more attention to the underground water level in the dam abutments. The proposed method could provide scientific decision-making basis for varying risk levels associated with rock slope engineering and can be used as an aid in corresponding risk control measures. The obtained results indicated that the developed algorithm is beneficial in providing guidelines for design and remedial measures to improve slope construction and performance. The present study proposes a methodology based on a combination of project management, risk modelling, and geotechnical engineering.

Wedge Instability on the Abutment of a Gravity Dam in Italy

This paper describes a wedge instability occurred during excavation of the right abutment slope in a granite rock mass at the Cumbidanovu dam site in Italy. The dam is a 72.7 m high concrete gravity dam, presently under construction. The slopes are characterized by the presence of a granite rock mass, rather complex geologic features (shear/fault zones), multiple rock joint sets, and significant differences in rock mass quality. The rock mass conditions are briefly illustrated based on systematic geological and discontinuity mapping during excavation of the abutment slopes, from the top down. Also briefly described are the rock mass characterization studies, including the results of laboratory and in situ testing. The results of three-dimensional stability studies with limit equilibrium and finite element analyses are illustrated. The main purpose has been to back-analyze the rock wedge instability based on the available data and the geological mapping performed, in view of the stabilization measures to be adopted, including a reshaping of the abutment slope.

Stability analysis of arch dam abutments due to seismic loading

Abutments of concrete arch dams are usually crossed by several joints which may create some rock wedges. Abutment stability analysis and controlling the probable wedge movements is one of the main concerns in the design procedure of arch dams which should be investigated. For decades, the quasi-static method due to its simple approach is used by most of dam designers. In this study the dynamic method is presented and the obtained time history of sliding safety factors are compared to the quasi-static results. For this purpose, all three components of Kobe 1979 and Imperial Valley 1940 earthquakes are applied to the wedge, simultaneously and the magnitude and direction of wedge displacements are calculated based on Newmark method which is not possible in the quasi-static approach. A 3-D finite element model of Luzzone dam including dam-foundation-reservoir interactions is used to compute the thrust forces. The obtained results indicate that quasi static method is more conservative. The importance of uplift pressure effects on the abutment stability is investigated as well. It is shown that the uplift pressure can play a key role in the abutment stability analysis and it is necessary to control the uplift pressure and seepage in arch dam foundations.

Whose “Fault” Is This? Overcoming Faulting and Ancient Landslides in a Dam Abutment

Whose “Fault” Is This? Overcoming Faulting and Ancient Landslides in a Dam Abutment

Spectral prediction and control of blast vibrations during the excavation of high dam abutment slopes with millisecond-delay blasting

In hydropower projects in Southwest China, large-scale, high-intensity blasts are required to excavate high rock slopes. In these cases, traditional prediction and control methods for blast vibrations are invalid. Thus, a method to predict the time history of blast vibrations on high slopes is proposed, and a blast vibration spectral control scheme based on this method is presented. Additionally, a case study for the abutment slope excavation of the Xiluodu hydropower project is presented. The results indicate that if the delay interval is <20ms or >50ms, a large amount of energy is distributed in the resonant frequency band of the slope; with optimized delay interval of 20–25ms and 45–50ms, the low-frequency compositions of blast vibrations are considerably fewer, and spectral control can be implemented more effectively. Delay intervals of 25 and 50ms are adopted in practice considering the detonator limitation.

Uncertainty Instability Risk Analysis of High Concrete Arch Dam Abutments

The uncertainties associated with concrete arch dams rise with the increased height of dams. Given the uncertainties associated with influencing factors, the stability of high arch dam abutments as a fuzzy random event was studied. In addition, given the randomness and fuzziness of calculation parameters as well as the failure criterion, hazard point and hazard surface uncertainty instability risk ratio models were proposed for high arch dam abutments on the basis of credibility theory. The uncertainty instability failure criterion was derived through the analysis of the progressive instability failure process on the basis of Shannon’s entropy theory. The uncertainties associated with influencing factors were quantized by probability or possibility distribution assignments. Gaussian random theory was used to generate random realizations for influence factors with spatial variability. The uncertainty stability analysis method was proposed by combining the finite element analysis and the limit equilibrium method. The instability risk ratio was calculated using the Monte Carlo simulation method and fuzzy random postprocessing. Results corroborate that the modeling approach is sound and that the calculation method is feasible.

Performance of the reinforced right abutment slope of Zipingpu Dam during magnitude 8.0 earthquake, Wenchuan, China

On 12 May 2008, an earthquake of magnitude 8.0 on the Richter scale occurred at Wenchuan in China. Zipingpu dam also experienced the earthquake. The maximum ground acceleration near the top of the 156 m high rockfill dam exceeded 2 g . The right dam abutment slope, which accommodates all the discharge facilities, remained intact after this severe earthquake. However, the natural slopes on the opposite side of the reservoir were severely damaged. It has been found that the reinforcement provided by more than 1000 prestressed cables in the right abutment slope helped to stabilize it. Measurements from multipoint extensometers and load cells installed in the slope showed that there were sudden changes in displacement and stress during the earthquake. This is clear evidence that reinforcement with anchored cables can be successfully used to stabilize a slope.

Analysis on stability of an Arch Dam with interlayer shear zones

This paper focuses on the stability of arch dam abutment with interlayer shear zones, presents the experimental analysis on Lizhou Arch Dam, and implements comprehensive method by combining geo-mechanical model test with the finite element method to analyze the impact of interlayer shear zones on the stability of dam abutment. Firstly, 3D geo-mechanical model test is conducted and the model shows the impact of interlayer shear zones on stability of arch dam. According to the deformation behaviors and eventual failure form of rock mass and structure planes in dam abutment and dam foundation, the impact of interlayer shear zones unstable failure on the safety coefficient of arch dam is analyzed. Secondly, the FEM (Finite Element Method) is used for supplementary verification. As a conclusion of the analysis: Interlayer shear zones fj1 - fj4 are developing towards riverbed in the rock mass of the dam abutment of Lizhou Arch Dam, cutting through the rock mass of dam abutment and forming a bottom slide face. In the dam abutment, fault f5 and fracture Lp285 have developed and formed a side fracture plane by intersecting the interlayer shear zone. Under the effect of the resultant force of the arch abutment, with the interlayer shear zone of inferior properties as the bottom slide face, the rock mass of dam abutment slides out in the form of steps or drawers, and the stability of the dam and the foundation is influenced.

A Comparative Study of Rock Wedge Stability of an Arch Dam Abutment Subjected to Static and Seismic Loading

In the present paper, the stability evaluation of a rock wedge in an arch dam abutment under static and seismic loading is studied via the finite element (FE) method and a conventional method. The Luzzone arch dam in Switzerland is selected as a case study in which response of the potential wedge at the left abutment is investigated. In the FE models, the reservoir's water is assumed compressible and the coupled system is solved simultaneously. Also, the foundation is studied for two different cases; massless and massed medium via viscous boundary on the far-end truncated boundary. In addition, the effect of modeling joint between the wedge and the remaining foundation medium on the wedge displacements is considered. The results of the FE models are compared with those obtained from the traditional method in which wedge stability is evaluated utilizing the Londe method. The results reveal that the traditional method overestimates the wedge displacement in comparison with the finite element technique.

Seismic stability assessment of an arch dam-foundation system

A seismic stability assessment of arch dam-foundation systems is presented using a comprehensive approach, in which the main factors that significantly influence the seismic response of an arch dam-foundation system are considered. A large scale finite element model with over 1 million degrees of freedom is constructed for the Baihetan arch dam (289 m high), which is under construction in the Southwest of China. In particular, the complicated geological conditions with faults intersecting interlayer shear weakness zones at the dam base and the dam abutment resisting force body is modeled in the analysis. Three performance indices are adopted to assess the seismic stability of the arch dam. The results demonstrate that the opening of the joints of the Baihetan arch dam is small and the water stop installed between the joints would not be torn during a design earthquake. The yielding formed in the interface between the dam and foundation does not reach the grouting curtain that would remain in an elastic state after an earthquake. The yielding zones occurring on the upper portion of the dam faces extend 1/8 thickness of block section into the dam body and thus cantilever blocks need not be concerned with sliding stability. The faults and interlayer shear weakness zones in the near field foundation exhibit severe yielding, and a potential sliding surface is penetrated. Although the factor of safety against sliding of the surface fluctuates with a decreased trend during an earthquake, the minimum instantaneous value reaches 1.02 and is still larger than 1.0. Therefore, a conclusion is drawn that the Baihetan arch dam-foundation system will remain stable under the design earthquake.

Rock Slope Stability Problems in Wadi Quaz-Dam Site No. 2, Jeddah-Saudi Arabia

The present investigation deals with the engineering geological studies of soil and rock masses in the Wadi Quaz area-Dam No. 2, East of Jeddah. Wadi Quaz area-Dam No. 2, East of Jeddah, Saudi Arabia often faces floods during rainy seasons, so it is so urgent to investigate the area before building any dam or preventing water from flow. Preventing water from flow will produce new dangerous factors such as uplift force which may cause the dam failure. To have a better understanding of the factors that may affect the slope stability, many rock slope locations are observed in detail to assess the effect of discontinuities formed in the rock masses. Fieldwork and Laboratory tests were carried out on soil and rocks. Soils included identification of soil type using unified soil classification system, permeability, water content and field density were done for soils. Rocks include identification of physical and mechanical properties such as: rock type, degree of weathering, rock strength, RQD, joint spacing measurements, and geometric properties (Dip, and Dip direction). Different methods were used to evaluate the potential failure in the studied area depending on rock mass rating and slope stability analysis. The well-known classification of rock masses titled Rock Mass Rating system [1] was used for categorizing the rock masses in the studied area besides slope mass rating [2] which would help to estimate the rock stability. The kinematical analysis was applied to investigate the potential failure mode which might occur in the dam abutments. This paper will provide the stability of dam abutments in both summer season and winter season besides general estimation of the seepage problems related to the soil and according to its permeability.