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Dam engineers frequently utilize the Hoek–Brown failure criterion for estimating foundation parameters of highly jointed rock masses. An integral component of this criterion, the disturbance factor, is used to assess the effects of blasting and stress relief on rock masses. Defining this strength reduction parameter has been a long-running issue in dam engineering practices. While some preliminary guidelines for determining disturbance factors in open-pit mining, tunnels, and slope applications are available in existing literature, clear guidance specific to dam foundations, where conventional mechanical excavation or controlled blasting techniques are employed, remains limited. In this paper, it is (1) investigated the effects of disturbance on dam foundations, highlighting deviations from other engineering practices, (2) developed a comprehensive dataset that establishes correlations between rock mass properties, disturbance types, and assigned disturbance factors in many dams, and (3) evaluated the influence of disturbance factors on dam design through a classical stability analysis. Incorporating these findings with field observations of disturbance effects on dam foundations, a preliminary guideline is proposed for dam engineers to identify an appropriate range of disturbance factors for their projects. [ABSTRACT FROM AUTHOR]

Water seepage from dam foundations causes reservoir water loss and raises the risk of dam instability. One method of remediation for controlling instability and leakage of these rock foundations is grouting. Since a considerable portion of the costs for dam construction is allocated to grouting, as a result, study of the influencing factors of cement take in grouting jobs is of paramount importance for each site. The most dominant parameters which play a decisive role in the efficiency of grouting are rock mass strength and permeability, grouting pressure, water-to-cement ratio, and properties of jointed rock mass such as joint aperture, roughness, and spacing. In this paper, the relationship between cement take and Q-system, aperture and spacing of joints, Lugeon number, depth of grouting, and grouting parameters such as grouting pressure and water-to-cement ratio is investigated via statistical analysis and artificial neural networks for two large concrete dam sites, Bakhtiari and Karun 4, located in southwest Iran. Karun 4 has been constructed while Bakhtiari is still under construction with respective heights of 230 and 325 m. The mentioned parameters, the relationships of which are found in relation to cement take, are determined based on engineering geology reports for all the 5-m segments of the trial grouting boreholes. Bivariate statistical analyses showed that the highest correlation (R = 0.64) exists between cement take and Q-system by a logarithmic relationship. In addition, statistical investigations based on multivariate analyses between cement take and all the mentioned variables show a poor correlation (R = 0.48) which encouraged the authors to use neural networks for finding a relationship between cement take and the influencing variables. This resulted in a higher correlation (R = 0.77, RMSE = 9.2) with respect to the statistical method. [ABSTRACT FROM AUTHOR]

The Secondary Permeability Index (SPI) is a permeability-based rock mass classification, which when complemented with the degree of jointing can be employed as an approximation to the ground treatment design. However, when the grout mix and success of the grout operation are known, a back-analysis can be conducted to infer the degree of jointing. The aim of this paper is to back-analyse and verify the ground treatment as proposed by the SPI from water pressure tests conducted in primary production grout boreholes, at the De Hoop Dam in South Africa. The calculated SPI class, together with information obtained from detailed mapping of the foundation rock mass, is compared to the mix, the take, and the success of each of the primary production grout boreholes. Based on the success of the grout, a degree of jointing is assumed, which is evaluated and validated against the RQD values obtained from the exploratory investigation boreholes. Overall, the degree of jointing inferred from the success of the grout mix showed that most of the compared boreholes validated the ground treatment as suggested by the SPI. Successful thin mixes coincide with minor fault zones with or without dolerite intrusions, as well as very closely jointed gabbro bedrock, whilst unsuccessful thin mixes are associated with the contacts of dolerite intrusions, which are generally highly weathered and fractured. This is highlighted by the success of thick mixes when applied to these intrusions. Unsuccessful thick mixes are mostly attributed to major fault zones. [ABSTRACT FROM AUTHOR]

The state of the art of blasting techniques for dam foundation excavation in China is introduced in this paper. Firstly, contour blasting techniques used for high rock slopes and dam abutments, including presplit blasting and smooth blasting, are introduced as well as the optimization of contour excavation procedures under confined rock condition. Secondly, blasting techniques for horizontal dam foundation and protective layer (PL), including layered blasting excavation (LB), horizontal presplit blasting (HPB), horizontal smooth blasting (HSB) and bench blasting with bottom cushion-deck (BC), are introduced and assessed. Thirdly, the test and onsite application of a newly developed foundation excavation technique, i.e. bench blasting with shock wave-reflecting block and bottom cushion-deck (BSRC) are displayed. Meanwhile, the control of blast-induced damage, excavation shaping quality and construction speed of different blasting techniques are compared and evaluated. Engineering practices in Baihetan Hydropower Station, China, demonstrated that BSRC could be a prospective method for horizontal dam foundation excavation. Finally, some remarks and future research aspects for dam foundation excavation are presented. [ABSTRACT FROM AUTHOR]

Abstract Several investigators have attempted to quantify the Geological Strength Index (GSI) chart, with the latest modification of the chart (2013) utilizing RQD as a measure of blockiness. This approach has limitations where discontinuity spacing is wide (typically greater than 0.3 m) and RQD alone cannot adequately characterize the degree of blockiness, since it remains static at 100%. This paper introduces a new approach to quantifying widely spaced jointed rockmasses that is not dependent on RQD alone. At the core of the approach is a bias free volumetric fracture count (VFC) parameter (fractures/m3), that is integrated into the newly defined GSI chart as an aid to alleviate scalability and bias concerns related to the use of RQD in the quantification process. While the new GSI chart builds on the work of many, it is unique in the sense that not only is it fully quantifiable for a full range of block sizes, including block sizes much larger that possible with RQD alone, but it provides a unique approach linking the VFC parameter with P 32 , a parameter frequently used in DFN modelling. The correlation of VFC with P 32 in particular, is possible because the VFC parameter has no constraints of a limited number and/or assumed orthogonality of discontinuity sets or rectilinear block shapes or the need for block shape correction factors. The new chart also includes correlated scales on both the vertical and horizontal axis using both the RMR and the Q-systems, providing a unified approach that is both scalable and easily quantifiable and allows for the use of all three major rock mass classification systems along with P 32 within one chart, something not attempted before. Data from a dam foundation rockmass in the Lesotho Highlands are introduced and are used to validate the quantification process for the overall GSI ratings for the foundation rock mass. These ratings have been used to estimate strength and deformability parameters for the foundation rock mass using the Hoek-Brown empirical failure criteria equations and then they were compared to the large-scale in-situ test results to validate the use of the V-GSI chart and system as a new tool for use in rock engineering. [ABSTRACT FROM AUTHOR]

It is essential to determine rockmass mechanical parameters in stability assessment. The structural z is the main factor in this regard, and we know little about the relationship between mechanical parameters and multiple structure planes. In this paper, we have conducted a series of numerical tests to obtain mechanical parameters for a dam foundation in Southwest China. The biaxial numerical test was performed based on the discrete element method. This numerical test considers the spacing, types, dip angles, and size effect. We established a relationship of mechanical parameters between small size lab samples and large size field samples. We forecasted the strength parameters for a spillway slope in Southwest China. The dip angle has a significant effect on the slope strength and stability. In this case, the rockmass fracture stress-dip angle curve forms a U-shaped distribution. The X-shaped double structure plane demonstrates severe strength weakening relative to a single structure plane. As structure plane spacing reaches a certain level, its influence on rockmass strength diminishes. The elementary volume of the rockmass for dam foundation analysis is about 4 m × 4 m × 4 m. [ABSTRACT FROM AUTHOR]

Under complicated geological conditions, the vibration in the dam foundation caused by blasting can lead to further deterioration of the foundation rock mass and adversely affect the safety of foundation. In order to effectively control the vibration in dam foundation rock mass, a new bench blasting technique with shock-reflection device is proposed. It introduces a shock-reflection device consisting of high wave impedance block and cushion material, which is placed at the bottom of vertical borehole. This shock-reflection device can effectively reflect the explosion shock wave from vertical direction to horizontal direction after detonation, which can make blasting energy concentrated on the rock mass above dam foundation, so the vibration in the foundation can be controlled. Field blasting experiment was carried out to contrast the blasting induced vibration in foundation rock by bench blasting with shock-reflection device and conventional bench blasting. The results indicate that the vibration in the foundation rock can be reduced by 30%~57%. In addition, the vibration at the bottom of the borehole is also demonstrated by numerical simulation, with results similar to the field experiments. The production experiment results show that the new blasting technique can replace the conventional excavation method of dam foundation in complicated geological conditions, and the new blasting technique has been successfully applied to the Baihetan dam foundation excavation. [ABSTRACT FROM AUTHOR]

Grouting plays a crucial role in dam safety. Due to the concealment of grouting activities, complexity of fracture distribution in rock masses and rheological properties of cement grout, it is difficult to analyze the effects of grouting. In this paper, a computational fluid dynamics (CFD) simulation approach of dam foundation grouting based on a 3D fracture network model is proposed. In this approach, the 3D fracture network model, which is based on an improved bootstrap sampling method and established by VisualGeo software, can provide a reliable and accurate geometric model for CFD simulation of dam foundation grouting. Based on the model, a CFD simulation is performed, in which the Papanastasiou regularized model is used to express the grout rheological properties, and the volume of fluid technique is utilized to capture the grout fronts. Two sets of tests are performed to verify the effectiveness of the Papanastasiou regularized model. When applying the CFD simulation approach for dam foundation grouting, three technical issues can be solved: (1) collapsing potential of the fracture samples, (2) inconsistencies in the geometric model in actual fractures under complex geological conditions, and (3) inappropriate method of characterizing the rheological properties of cement grout. The applicability of the proposed approach is demonstrated by an illustrative case study—a hydropower station dam foundation in southwestern China. [ABSTRACT FROM AUTHOR]

Grouting methods are known to effectively remediate the dam foundation or the abutment. However, remediation grouting of the deteriorated embankment earth-core itself has rarely been performed or studied. In this study, low-pressure permeation grouting is adopted to remediate the deteriorated central core layers of five aging dams. Technical features of each dam's deterioration are described, such as sinkholes, slope failures, fluidized clay cores, and wet zones on the downstream surface induced by excessive seepage. This study suggests several empirical standards for the application of permeation grouting to the improvement of core permeability, including grout mix, injection period per stage, injection rate, and maximum fluid pressure to prevent hydraulic fracturing. The results of this empirical case study can be applied to effectively remediate degraded dam embankment cores to decrease their permeability and minimize the risk of hydraulic fracturing, without requiring a reduction in the reservoir water level. [ABSTRACT FROM AUTHOR]

Background: We examined seven landslide dams and their changes over time in the Peace River region of Canada. These landslides had subchannel rupture surfaces in glacial and glaciolacustrine sediments. We assessed the stability of the dams using 6 separate, morphometric-based stability indices (with a total of 10 stability thresholds). Results: The landslides caused the streambeds to be elevated from 4 to 30 m forming the dams. The landslide lakes diminished in size over one to several years through stream incision into the dams and sediment infilling. The longest-lived dam persisted for up to 20 years. For two dams, incision into the dams lowered the lake levels by about half of the total depth, while the remainder of the water in the basins was displaced by sediment infilling. After the lakes drain, the sediment accumulations behind the dams can persist for decades. The stability analyses overpredicted unstable conditions which is inconsistent with the observed longterm persistence of the dams. Conclusions: The landslide dams in our study were relatively stable. Their lakes persisted for up to 2 decades and diminished over time through a combination of slow incision and basin infilling. The stability indices we assessed overpredicted unstable conditions and thus would require modification for these particular types of dams in this regional setting. [ABSTRACT FROM AUTHOR]

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 220,000 m 3 /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 51,000 m 3 /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. [ABSTRACT FROM AUTHOR]

This study focused on the dam foundation rock quality evaluation. Six evaluation indicators involving saturated uniaxial compressive strength， structural plane spacing， RQD， integrality coefficient， acoustic longitudinal wave velocity and ground stress correction coefficient were taken into consideration. Based on the component weighting method and cloud model， the Jinsha Xulong dam foundation rock mass was taken as a case. The optimal sequence diagram method and entropy value method were combined by the preference coefficient method to overcome the disadvantages of using subjective and objective weighting method alone. The rock mass quality evaluation indicators clouds were established based on the digital characteristic values. Then the certainty of each indicator was calculated. The corresponding quality degree is the rock mass quality degree. The cloud model results were compared with traditional BQ method results and the extension theory results. The cloud model has stronger controllability and higher classification accuracy， which is able to express the comprehensive uncertainty of rock quality. [ABSTRACT FROM AUTHOR]

Fractured seepage is an important factor affecting the interface stability of rock mass. It is closely related to fracture properties and hydraulic conditions. In this study, the law of seepage in a single fracture surface based on modified cubic law is described, and the three-dimensional discrete element method is used to simulate the dam foundation structure of the Capulin San Pablo (Costa Rica) hydropower station. The effect of construction joints and developed structure on dam stability is studied, and its permeability law and sliding stability are also evaluated. It is found that the hydraulic-mechanical coupling with strength reduction method in DEM is more appropriate to use to study the seepage-related problems of fractured rock mass, which considers practical conditions, such as the roughness of and the width of fracture. The strength reduction method provides a more accurate safety factor of dam when considering the deformation coordination with bedrocks. It is an important method with which to study the stability of seepage conditions in complex structures. The discrete method also provided an effective and reasonable way of determining seepage control measures. [ABSTRACT FROM AUTHOR]

An analytical solution is obtained for 2-D steady Darcian flow under and through a cutoff wall partially obstructing a homogeneous isotropic foundation of a dam. The wall is leaky; that is, flow across it depends on the ratio of hydraulic conductivity of the wall and the wall thickness that results in the third-type (Robin) boundary condition along the wall, as compared with the Terzaghi problem for an impermeable wall. The Laplace equation for the hydraulic head is meshlessly solved in a non-standard flow tube. A Fredholm equation of the second kind is obtained for the intensity of leakage across the wall. The equation is tackled numerically, by adjusted successive iterations. Flow characteristics (total Darcian discharge and its components through the wall and the window between the wall top and horizontal bedrock, stream function, head distribution, and Darcian velocity along the wall and tailwater bed) are obtained for various conductivity ratios, head drops across the structure, thicknesses of the foundation, and the degree of its blockage by the wall. Comparisons with the Terzaghi limit of an impermeable wall show that for common wall materials and thicknesses, the leakage may constitute tens of percent of the discharge under the dam. The through-flow hydraulic gradients on a vertical wall face (Robin's boundary condition) as well as the exit gradients along a horizontal tailwater boundary (Dirichlet's boundary condition) acting for decades have deleterious impacts on dam stability because of potential heaving, piping, and mechanical-chemical suffusion. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The explicit formulation of a small displacement model for the coupled hydro-mechanical analysis of concrete gravity dam foundations based on joint finite elements is presented. The proposed coupled model requires a thorough pre-processing stage in order to ensure that the interaction between the various blocks which represent both the rock mass foundation and the dam is always edge to edge. The mechanical part of the model, though limited to small displacements, has the advantage of allowing an accurate representation of the stress distribution along the interfaces, such as rock mass joints. The hydraulic part and the mechanical part of the model are fully compatible. The coupled model is validated using a real case of a dam in operation, by comparison of the results with those obtained with a large displacement discrete model. It is shown that it is possible to assess the sliding stability of concrete gravity dams using small displacement models under both static and dynamic conditions. [ABSTRACT FROM AUTHOR]

One of the main causes of lining damage in stilling basins and at the toe of chute spillways is the global instantaneous uplift forces due to the difference in pressure acting on the upper and the lower surface of protection slabs or rock elements. Spillway stilling basin linings can be built according to two different techniques: using sealed joints or unsealed joints. In the case of sealed joints, the pressure underneath the slab is constant and the uplift force results from the pressure fluctuations acting on the slab. In the case of unsealed joints, the pressure propagation at the lower surface of the slab, being transferred through the joints, should also be considered. The aim of the paper is to study, define, and compare the design criteria in these two cases. In the present study, the pressure field on the slab is evaluated according to a recent method based on the Taylor hypothesis, whereas the pressure propagation under the slab is computed by a new 3D model based on unsteady flow analysis of seepage through porous media. By this approach, it is possible to consider the effect of finite thickness foundation layers, typical in the case of weirs for run-of-river power plants, earth dams, and rock-fill dams. Furthermore, to complete the presented design criteria, the dynamic behavior of anchored slabs is experimentally investigated with reference to the sealed joint case due to a lack of studies in the literature. [ABSTRACT FROM AUTHOR]

Response sensitivity analysis (RSA) is an important component in various gradient-based methods, e.g., structural optimization, reliability analysis, system identification, and finite element (FE) model updating. The direct differentiation method (DDM) is efficient and accurate, providing an ideal solution to RSA. This paper extends the DDM significantly for performing RSA of realistic coupled concrete dam-reservoir-foundation systems, in which the material nonlinearity, the solid fluid interaction, the dam-foundation interaction, and the truncation boundary conditions of the water and rock foundations are considered. The response sensitivities for various elements and materials used to simulate the complicated coupled system are derived and implemented into an existing DDM framework in a generalpurpose nonlinear finite element analysis program, OpenSees. A realistic dam-reservoir-foundation system subject to dynamic loading conditions is taken as application example. The newly developed response calculation algorithms are verified by commercial FE software, ABAQUS, and the DDM algorithms are validated by finite difference method (FDM). In addition, as application of the DDM, the calculated response sensitivities are used to compare the relative importance of various material parameters regarding the dynamic responses of the systems. It is demonstrated that the DDM is accurate and efficient, providing an excellent solution to the RSA of complicated nonlinear concrete dam-reservoir-foundation systems. [ABSTRACT FROM AUTHOR]

Debris flow can cause serious damage, and it is & part of the study of fluid-structure interaction (FSI). FSI analysis was established on the interaction between unsteady flow and the slit-trap dam's vibration, with a coupling bench which can transfer fluid pressure and structure displacement. Debris flow can be seen as the Bingham body of incompreesible. Based on ANSYS and CFX softwares, unidirectional and bidirectional coupling methods were used to study the transient interaction between debris flow and dam. The comparison between lateral fluid preesure states under different velocities and the equivalent streeses of the dam under different coupling conditions was made. The result shows that fluid-structure coupling becomes ssronger with the increase of flow velocity. The maximum equivalent stress appears at the dam foundation, while the minimum equivalent strees appears at the dam abutment. With the increase of height, the fluid preesure decreases. The fluid pressure based on unidirectional FSI analysis is larger than that based on bidirectional FSI analysis and the maximum appears on the joint of the dam foundation and channel. The maximum equivalent slress of the dam based on the former is lus than that based on the latter. [ABSTRACT FROM AUTHOR]

Betone werden in Dichtwänden aufgrund ihrer geringen Durchlässigkeit und ihrer Beständigkeit bei großen hydraulischen Gradienten oftmals in Staudämmen oder in deren Untergrund als Abdichtungsmaßnahme eingesetzt. Normalbeton weist im Vergleich zu anderen Materialien einen vergleichsweise hohen Elastizitätsmodul auf, sodass insbesondere bei einer dynamischen Beanspruchung wie Erdbebeneinwirkung Probleme hinsichtlich des spröden Materialverhaltens auftreten können. Diesem Problem kann man begegnen, indem der Betonmischung ein bestimmter Prozentsatz an Feinmaterial beigegeben wird. Der Elastizitätsmodul wird dadurch verringert und es kommt zu einer höheren Duktilität des Materials. Als Zugabematerial bieten sich Tone sowie Bentonite an. In dem vorliegenden Beitrag werden bodenmechanische Versuche an einer als Tonbeton bezeichneten Mischung vorgestellt. Für Proben mit unterschiedlichem Probenalter werden einaxiale Druckfestigkeiten, Biegezugfestigkeiten, Scherfestigkeitsparameter in Triaxialversuchen sowie Wasserdurchlässigkeitsbeiwerte ermittelt. Laboratory investigations on the material behaviour of plastic concrete Concrete cut‐off walls are often used as a water barrier in earth dams or their foundation due to the low permeability and resistance to large hydraulic gradients. Regular concrete has in comparison to other materials a relatively high modulus of elasticity. Due to the brittle material behavior this may cause problems in particular under dynamic loading during seismic action. This drawback can be handled by adding a certain percentage of fine‐grained material into the concrete mix, thus reducing the elastic modulus and increasing the ductility of the material. Suitable additives are clay powders or bentonites. In the present paper soil mechanical tests on a mixture known as plastic concrete are presented. Unconfined compressive strength, flexural strength, shear strength parameters under triaxial compression and water permeability coefficients are assessed in dependency on the specimen age. [ABSTRACT FROM AUTHOR]

Not only should dams be evaluated for seismic shaking, but their capability to survive potential fault displacement in their foundations should also be assessed. Safety reviews of existing dams suggest that geological-seismic evaluation of some dam sites has failed to recognize the existence of possibly active faults. In this study, the nonlinear seismic behavior of concrete gravity dams, due to relative fault dislocation occurring in foundations, has been investigated. Two types of fault movement, including normal-slip and reverse-slip, have been considered. These two types, combined with the location of fault lines, with respect to the toe, middle, and heel of the dam base, angle of fault, and water elevation in reservoirs, which result in 36 types of model, have been considered. Results show that each type of fault can cause propagation of specific crack patterns, and the angle and location of the fault beneath the dam have a great effect on the amount of damage induced. The water pressure of the reservoir can also have increasing or even decreasing effects on the crack propagation rate. The existence of foundation fault movement beneath concrete gravity dams, depending on the condition of the problem, can cause rapid crack propagation in the dam body, jeopardize stability, and significantly change the dam's dynamic response. [ABSTRACT FROM AUTHOR]

In 1986-1989, Jackson Lake Dam, Wyoming, was removed after standard penetration tests indicated that the foundation soil was subject to liquefaction. Part of a subsequent research program involved measuring lateral in situ stresses at various depths in the foundation soil by use of the Stepped Blade, a device that introduces a stepwise lateral displacement of soil so contact pressures can be extrapolated to give the hypothetical pressure on a zero-thickness step. The foundation soil was cohesionless mix of alluvial and deltaic silts and sands with some sharp-edged gravel. The lateral stress measurements established relationships between the four topics in the title of this paper. A normal consolidation state, meaning that a soil is in equilibrium with its own weight, can be established when is constant with depth and lateral effective stresses extrapolate to zero at the ground surface. On this basis, three stress zones were identified: (1) Based on limited data, an uppermost zone, to a depth of 4 m (13 ft) underneath the dam, was identified as being normally consolidated under the weight of the dam. This is as expected and probably occurred during construction. Underneath the upper zone was (2) a transition zone, 4 to 5.5 m (13 to18 ft) in depth, and under that (3) a lower zone, 5.5 to 10 m (18 to 33 ft) in depth. The lower zone was determined to be normally consolidated without the weight of the dam. without the weight from the dam was determined to be 0.5, and lateral effective stresses extrapolate to zero at the predam ground surface. Note that the value of was measured and not derived from empirical correlations. Nevertheless, it is consistent with normal consolidation and a friction angle of 30 degrees reported for this deposit. Despite having been characterized as cohesionless, the soil deep underneath the dam had resisted consolidation for over 60 years, and the depth to the underconsolidated layer is consistent with observations that liquefaction can be deep-seated. The existence of such a layer calls into question the use of a temporary surcharge for site preparation for cohesionless soils, or a reliance on measurements that settlement has stopped. A similar situation can be anticipated under existing structures such as dams and highway embankments that are located on the geologically young but historically old granular soil deposits of floodplains and deltas. The weight of the dam reduced in the lower zone soil from 0.5 to 0.35. This can happen only if the soil has developed sufficient strength to resist consolidation and can be attributed to aging. Mohr circles drawn from the lateral stress measurements indicate a gain in cohesion of the order of 34 kPa (4.9 psi or 700 psf) from aging. The gain also may be explained by an increase in the friction angle from dilatancy attributed to cementation rims at grain contacts. The site was treated by deep dynamic compaction that increased to 1.0, but with considerable variability. That value indicates a temporary liquid condition, and may have been preserved by seepage forces when pore water pressure supported the entire weight of the soil column. The replacement dam reduced the average from 1.0 to about 0.5, which should be sufficient prevent future liquefaction. However, the cap on of 1.0 during ramming can restrict the amount of additional load if the final is to be no lower than the normal consolidation value. [ABSTRACT FROM AUTHOR]

Structural reliability analysis is not widely used for the design and assessment of concrete dams. In this paper, the system reliability of a spillway structure consisting of two monoliths is calculated. Limit state functions are defined from the failure modes sliding in the concrete rock contact, sliding in the rock mass, and adjusted overturning. Random variables in the limit state functions are defined by stochastic distributions. These are defined based on site investigations and laboratory tests from samples taken at the dam. Simulations and information from the literature are used for the remaining variables. The safety index is calculated by the first-order reliability method for each failure mode and monolith, and the system reliability is approximated by direct integration of the bivariate normal distribution. The output is the safety index including associated sensitivity values at the single failure mode, monolith, and system levels. The results show that the system safety is governed by a persistent rock joint beneath one monolith. A system reliability analysis is found to be a useful tool in the dam risk management process as it can be used to calculate the probability of failure and to identify important failure modes and variables. [ABSTRACT FROM AUTHOR]

Cataclastic rocks and fault gouge present highly variable properties, from those of soil-like materials to those of competent rock mass. In most cases, the entire rock mass, or internal major shear zones, can be represented as a block-in-matrix rock (bimrock), i.e., rock fragments of different shape and size, embedded in a finer matrix. In this paper, a tectonized metamorphic rock mass at the site of a planned gravity dam is investigated. The dam foundation is crossed by numerous major discontinuities, often grouped to form wider shear zones and characterized by high persistency, waviness, and abundant cataclastic filling. Systematic measurements of local orientation and filling thickness along the discontinuity traces made a detailed morphological analysis possible. The most frequent type of filling is a lightly cemented matrix-supported gouge. Undisturbed sampling of filling materials was successful only in some special cases. Laboratory tests, as well as in-situ mechanical tests, were therefore difficult and not exhaustive. Micromechanical distinct-element method (DEM) modeling was instrumental in obtaining a more comprehensive framework of deformation and failure mechanisms of cataclastic materials. The mechanical properties of the particulate model were first analyzed by numerical simulation of biaxial and direct shear tests. The relationship between the overall constitutive parameters and micromechanical properties, such as interparticle friction, contact stiffness, cement bond strength, volumetric block proportion, and block shape, was determined. The complex interplay between the geometric features of a major discontinuity (joint-wall roughness and waviness) and the properties of the infilling bimrock was then investigated, and finally, the overall strength of the infilled discontinuity was analyzed. [ABSTRACT FROM AUTHOR]

This paper describes the results of engineering geological investigations and rock mechanics studies carried out at the proposed Chamshir dam site. It is proposed that a 155 m high solid concrete gravity-arc dam be built across the Zuhreh River to the southeast of the city of Gachsaran in south-western Iran. The dam and its associated structures are mainly located on the Mishan formation. Analysis consisted of rock mass classification and a kinematic analysis of the dam foundation's rock masses. The studies were carried out in the field and the laboratory. The field studies included geological mapping, intensive discontinuity surveying, core drilling and sampling for laboratory testing. Rock mass classifications were made in line with RMR and DMR classification for the dam foundation. Dam foundation analysis regarding stability using DMR classification and kinematic analysis indicated that the left abutment's rock foundation (area 2) was unstable for planar, wedge and toppling failure modes. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: A hybrid simplex artificial bee colony algorithm (HSABCA) which combines Nelder–Mead simplex method with artificial bee colony algorithm (ABCA) is proposed for inverse analysis problems. The proposed algorithm is applied to parameter identification of concrete dam-foundation systems. To verify the performance of HSABCA, it is compared with the basic ABCA and a real coded genetic algorithm (RCGA) on two examples: a gravity dam and an arc dam. Results show that the proposed algorithm is an efficient tool for inverse analysis and it performs much better than ABCA and RCGA on such problems. [Copyright &y& Elsevier]

Suffusion is the process by which finer soil particles are moved through constrictions between larger soil particles by seepage forces. Soils susceptible to suffusion are described as internally unstable. This technical note describes a method for assessing the potential of internal instability of silt-sand-gravel or clay-silt-sand-gravel soils based on their particle size distribution based on laboratory tests carried out by the writers and results published by others. It is shown that some commonly used methods are conservative for these soils. [ABSTRACT FROM AUTHOR]

Alibey Dam is located near Istanbul in Turkey on the Alibey Stream, 4.5 km north of its point of confluence with Golden Horn, an ancient submerged river mouth. It was constructed as an earthfill dam over 30-m-thick soft valley sediments. Before the construction of the dam, field and laboratory tests were performed to determine the geotechnical characteristics of the foundation soils. During the construction and many years after the construction of the earthfill embankments, including the cofferdams and the intermediate fills, the response of the foundation soils was monitored by extensive field instrumentation generating a unique long-term (over 25 years) database. With proper instrumentation and careful monitoring of the collected data, field construction rates could be adjusted and the earth dam was safely constructed on the thick soft deposits. Approaches to settlement prediction were evaluated in a historical context, starting with the simplified one-dimensional approach available at the time of construction to more sophisticated analyses including the employment of modern numerical methods, in terms of the recorded data. Standard subsurface exploration and field testing supplemented with conventional laboratory testing provided the relevant material parameters that were used in the finite element method. The only exception to this was the overall hydraulic conductivity of the deposit, which controlled the rate of consolidation. Early field observations were used to assign the appropriate hydraulic conductivity. An elastoplastic soil model in a coupled analysis of consolidation was employed in the analysis that yielded realistic predictions of field behavior in response to the complex construction history. The accurate prediction and monitoring of the behavior of soft and thick soil layers subjected to staged construction, as in the case of Alibey Dam, is very important for planning of the construction as well as the expected behavior after construction. [ABSTRACT FROM AUTHOR]

Earthquake-induced liquefaction is a major concern for embankment dam safety. Many liquefaction-induced earth embankment failures or near failures have been reported around the world during various earthquakes. Such embankment damages were particularly destructive when the underlying saturated granular soils liquefied, resulting in cracking, settlement, lateral spreading, and slumping of the embankment. Through a series of four highly instrumented geotechnical centrifuge model tests, seismic behavior of a zoned embankment dam with saturated sandy soil foundation was studied under moderate earthquake conditions. The beneficial effects of foundation densification were investigated. Valuable insights into the dynamic behavior of the employed embankment–foundation systems are provided. Test results suggest that there may be an optimum depth of densification treatment beneath an earth dam beyond which the reduction of the earthquake-induced deformations are relatively minor and that relatively small and isolated zones (e.g., at depth) of loose material within a densified volume of soil may not impair the overall effectiveness of treatment and do not necessarily result in damaging displacements. [ABSTRACT FROM AUTHOR]

A series of four dynamic centrifuge model tests was performed to investigate the effect of foundation densification on the seismic performance of a zoned earth dam with a saturated sand foundation. In these experiments, thickness of the densified foundation layer was systematically increased, resulting in a comprehensive set of dam-foundation response data. Herein, Class-A and Class-B numerical simulations of these experiments are conducted using a two-phase (solid and fluid) fully coupled finite element code. This code incorporates a plasticity-based soil stress–strain model with the modeling parameters partially calibrated based on earlier studies. The physical and numerical models both indicate reduced deformations and increased crest accelerations with the increase in densified layer thickness. Overall, the differences between the computed and recorded dam displacements are under 50%. At most locations, the computed excess pore pressure and acceleration match the recorded counterparts reasonably well. Based on this study, directions for further improvement of the numerical model are suggested. [ABSTRACT FROM AUTHOR]

Pontesei Dam is a major concrete dam built after World War II across the canyon of Maè Creek (Valle di Zoldo) in the Italian Eastern Alps. Just upstream from the dam, a gully discharges water from steep mountains. The only road serving the dam and the entire valley upstream of the dam runs along the mountainside and crosses the gully. In 1959, an exceptionally rainy season caused a flood, which destroyed the bridge. A temporary Bailey bridge was subsequently built by the army, but in 1990 it was decided to design a new bridge. The main challenges posed to the designer included building the new deck and the abutments underneath the Bailey bridge without disrupting traffic, hoisting the deck just to the bottom of the Bailey bridge, and finally substituting the new deck for the Bailey bridge in one day. Other problems included the instability of the rock mass at the abutments and the gravitative convergence of the two sides of the gully. This paper describes the design, construction, and testing of the bridge replacement and the bridge abutments. [ABSTRACT FROM AUTHOR]

In this Technical Note, the adaptive block element method of rock masses is formulated, in which the elastoplastic characteristics of both rock blocks and discontinuities are taken into account. The concept of an overlay element is illustrated first; then the displacement fields of rock blocks are expressed as functions of so-called general degree of freedoms using the shape functions of the hierarchical finite element method; the governing equations of the rock block system are deduced on the basis of the virtual work principle; and the p-version adaptive algorithm based on the energy norm error estimation of each block element is proposed. The method is applied to the deformation and stability study of a gravity dam, and the parallel laboratory physical test is used to check the validity and ability of the method. [ABSTRACT FROM AUTHOR]

Sliding in a dam foundation along potential sliding paths is generally caused by two kinds of external factors: one is the overloading of the designed upstream hydrostatic load due to flooding; and the other is the gradual degradation of the shear strength of joints due to seepage, deformation, damage, and geochemical reactions between water and joint surface minerals. Based on the conceptualized geomechanical model of the Three-Gorges Dam, described in the Part I paper, in this Part II paper the limit equilibrium method and finite element method are used to study the effects of gradual degradation of the shear strength of joints on the stability of the dam foundation. The numerical modeling focuses on the stability conditions of the no. 3 powerhouse-dam section which are estimated to be the most critical. The constraint influences from the adjacent no. 2 and no. 4 powerhouse-dam sections are also included. The failure mechanisms, factors of safety and critical displacements of these dam sections are derived numerically as the measures for stability evaluation. The factor of safety is defined as the ratio between the combined shear strength of joints and intact rock bridges, and the mean shear stress along potential sliding path required for limit equilibrium under the designed external loads. All the results obtained from these different numerical models, together with the results of physical model tests as presented in Part I, are compared in this paper. The comparisons show that both the numerical modeling and physical modeling results support each other and demonstrate the stability of the Three-Gorges Dam foundation as designed. Nevertheless, considering the overall engineering and social–economical importance of the Three-Gorges Dam complex, some additional treatment and reinforcement measures are recommended in this paper. [Copyright &y& Elsevier]

Proposes a performance-mode (PM)-based evaluation procedure to determine the probability of unsatisfactory performance (UP) for two-dimensional and three-dimensional (3-D) systems involving pile-supported dams. Ductile behavior of individual piles; Three-dimensional effects on the bounds for series-parallel systems; Narrower bounds of probability of UP for the ductile behavior than for brittle behavior.

Summary: The displacement at arbitrary point in the dam is composed of two parts: One is the elastic deformation of dam body and the other that is due to the constrained deformation of foundation. The two parts should be separated to obtain reliable information reflecting the different characteristics of dam body and foundation. A simplified simulation method for gravity dam foundations is proposed that reflects the constrained deformation of foundation in a rational manner while taking into account the complex and diverse mechanical properties. Only the effects of the foundation on dam is investigated in the proposed model, and they are considered either centralized constraints or distributed constraints. The solution of the global foundation deformation is based on the monitoring displacements at measuring points in the gravity dam section using the hybrid partition finite element–interface boundary element approach. The reaction of the foundation on dam can be reflected by the global foundation deformation and the constrained force at dam bottom. On the basis, the whole dam response under a given load combination can be estimated using finite element theory. Three analyses have been performed on a typical gravity dam section to verify the feasibility of simplified simulations for different foundations as well as to allow for discussions regarding the differences among the simulations. An example analysis based on the proposed method is performed on a prototype gravity dam, and the results, which compared with actual measurements for discussions, show that the proposed method is reasonable and practical. [ABSTRACT FROM AUTHOR]

Evaporative rocks are known to have a high susceptibility to dissolution in fresh water. Substantial evidence all over the world has shown that the dissolution of evaporative rocks in the foundations of dams and basins can lead to unfortunate disasters. In a basin located in Iran, owing to dissolution of evaporative rock in the foundation on the south side, some hazardous events, such as unexpected subsidence, ground collapse, and water escape from the reservoir, have been reported. Comprehensive geological and geophysical surveys along with detailed geotechnical investigations were performed in order to assess the reasons. By analyzing the site investigation results, it is recognized that even though the foundation of the basin is composed of impervious marl layer, the dissolution of thin streaks of gypsum embedded inside the marl layer provides interconnected paths for the flow of water into the lower depths of the foundation in order to reach to halite layer located inside the marl. The geophysical survey results indicate that the zone with defects is limited to the specific area of the basin where the halite layer is located relatively near the ground surface. However, if the reservoir is filled completely again, the dissolution front may advance to other zones of the basin, and more area of the basin ground may be affected by subsidence and other relevant phenomena. [ABSTRACT FROM AUTHOR]

Discusses methods and numerical procedures in the assessment of complexity of seismic forces, as well as dams and foundation conditions during the time of the quake. Field observation as the best guidance in the performance of real structures under real loading conditions; Useful estimates of earthquake-induced displacement through the Makdisi-Seed method; Review on the real response of La Vilita Dam in 1985.

Cases of damages experienced in stilling basins and on the toe of chute spillways are recognized to be due to global instantaneous uplift force resulting from imbalance between the instantaneous pressure distribution both above and below slabs. The latter is due to pressure fluctuation propagation forced though unsealed slab joints. In the past, several theoretical approaches were developed to estimate the uplift contribution due to pressure transmission underneath the slabs. In the paper, a model is presented, based on unsteady flow analysis of seepage through porous media, that shows that the propagation models proposed in literature are particular cases of this more comprehensive formulation. In addition, the use of the unsteady seepage model makes it possible to account for finite thickness foundation layers, typical in the cases of earth dams, rock-fill dams, and in other dam types, whenever the slabs are posed on alluvial substrates. Experimental results obtained in laboratory facilities, as reported in literature, might underestimate the stable slab thickness due to limits in accurately reproducing the foundation layer. [ABSTRACT FROM AUTHOR]