Rock Slope Stability and Water tightness Assessment of Arjo Didesa Dam site, Western Ethiopia

Arjo Didesa dam is an earth and rock fill dam which is under construction on the Didesa River in western Ethiopia. However, the dam encountered engineering geological problems that affected the water tightness and slope stability of the dam abutments and reservoir area. To solve these problems, different methods such as discontinuity survey, packer test, sampling and laboratory tests were applied to evaluate the engineering geological conditions of materials along the dam abutments and reservoir area on slope stability and water tightness. Slope stability analyses were performed by kinematic, limit equilibrium and finite element methods using laboratory and in-situ tests. Kinematic analyses revealed that both the left abutment slope 1(LAS1) and the right abutment slope 1(RAS1) sections were unstable for planar mode of failures. Further stability analyses using deterministic methods indicated that both sections were unstable only during saturated conditions. Similarly, stability analysis using limit equilibrium and finite element method revealed that both the left abutment slope 2(LAS2) and the right abutment slope 2(RAS2) sections were unstable under saturated conditions. This study also analyzed the permeability of soils and rock masses and the result showed that the permeability values range from 2.693*10− 7cm/s − 6.687*10− 5cm/s and 3.19*10− 5cm/s − 1.3*10+ 1cm/s for soils and rock masses respectively. Integration of surface hydraulic conductivity and subsurface packer permeability tests showed the presence of potential leakage through the dam abutments. Remedial measures such as rock bolts, anchors and shotcrete for slope stabilization and grouting and clay blanketing are recommended to control this leakage.

Grout Curtain Construction At Bolivar Dam, Ohio

Bolivar Dam, located in eastern Ohio, is an embankment dam constructed by the U.S. Army Corps of Engineers in 1937 as part of the Muskingum River Basin Project for flood control. As a result of seepage concerns observed at the dam during several flood events over the life of the project, seepage reduction measures, including a partial-depth seepage barrier wall through the embankment and a grout curtain in the left abutment, were designed and constructed. These dam safety modifications were constructed between 2014 and 2016. During flood events, Bolivar Dam experiences excessive seepage through the glacial outwash foundation as well as through a network of open joints within the left bedrock abutment. Seepage in the bedrock abutment could erode/scour the dam embankment at the bedrock contact, potentially leading to dam failure. To lower this potential risk of dam failure in the left abutment, a grout curtain was constructed between the new seepage barrier wall and an existing grout curtain across the emergency spillway. The new grout curtain is designed to impede groundwater seepage, resulting in reduced groundwater velocity/energy downstream of the grout curtain, thereby decreasing its potential to scour or transport fine-grained embankment material. The double-line grout curtain is approximately 65 ft (19.8 m) deep and 400 ft (121.9 m) long and was completed in November 2015 as part of a major dam safety modification project. Two thin limestone units encountered during drilling proved to be problematic and posed various challenges during construction. It was common during drilling to lose water circulation within the vicinity of these limestone units, which then required the use of downstaged grouting methods. The majority of the grout volume for the project was placed within these downstaged intervals. This article presents the risk-informed decisions that were made during both design and construction of the grout curtain and includes various lessons that were learned during this process.

Using the modified scalar product approach for testing the direction of seepage through the earth-fill dam in Pieczyska

Currently, the problems related to the development of seepage are emerging more and more frequently. For this reason, there is a constant need to improve the existing methods, and to develop new ones, for determining the direction and intensity of the development of seepage processes occurring in earth-fill dams and their foundations. The analysed earth-fill dam is located in Pieczyska in the Kujawy-Pomerania province at 49.115 km from the river mouth of the Brda River. The catchment area is 4.109 km2. The article aims to verify the non-invasive, non-subjective method for examining the direction of seepage through earth-fill dams using the modified scalar product approach, which allows to determine the direction and intensity of the seepage process. A proper analysis of this process can greatly reduce the repair costs (injections or other methods of sealing), and significantly increase the safety of the existing earth-fill dams. In the case of the dam in Pieczyska, in 2010–2015, the two piezometers (located on the left abutment of the dam and denoted as P15A and P60) exhibited a direct hydraulic connection with the upstream water level (the scalar product approach). For the study dam, the “source” piezometer (to which all the piezometers in its surrounding exhibited similar changes in water levels) turned out to be the piezometer P15A. This fact was confirmed both by the number of connections between the individual piezometers and the resulting system of equipotential lines for the dam.

GEOLOGICAL AND GEOTECHNICAL BEHAVIOUR OF EVINOS DAM FOLLOWING THE IMPOUNDMENT

The Evinos dam built between 1993 and 1997. The period of construction followed a period of rest until 2001. The impoundment of the Evinos Dam and the subsequent 3rd operational period took place between 2001 and 2005. The 4th period of operation commenced in February 2005 and concerns the period of regular operation of Dam Evinos after completion. During this period, sufficient data have been gathered for the evaluation of the geotechnical behaviour of both Evinos Dam itself and the stabilization works on the two landslides that occurred (Landslide of the left abutment ’93, Landslide of Ag.Demetrios-Arahova country road). Specialized personnel of the Department of the Evinos Dam of the Athens Water Supply and Sewage Company S.A are responsible for the in-situ collection of instrumental readings. On the other hand specialized personnel of the Division of Raw Water Intake of Athens Water Supply and Sewage Company S.A are assigned to evaluate the dam’s behaviour. The infiltration of water within the Dam’s core is continuously monitored together with the horizontal movement and settlement upstream and downstream the dam’s body through a considerable number of vibrating wire piezometers, earth pressure cells, extensiometers, inclinometers and surface monumental stations. The behaviour of the stabilization interventions in the landslide area’s are evaluated through measurement of topographic monuments ,open piezometers and drainage measurements. The evaluation of the instrumental measurerements confirms the expected behavior of the dam and the satisfactory performance of the stabilization interventions in the landslide area’s

Effect of Foundation Nonlinearity on Seismic Response of an Existing Arch Dam

In the present paper, the effect of foundation nonlinearity on the seismic response of an existing arch dam is investigated. Luzzone arch dam in Switzerland is selected as a case study. The foundation nonlinearity is originated from opening/slipping of joints between a potential wedge at the left abutment and remaining foundation. Reservoir's water is assumed compressible and the coupled system is solved simultaneously. Also, the foundationis assumed massed medium via viscous boundary on the far-end truncated boundary. Two cases are considered in the analyses; the system applying reservoir pressure on the foundation; the system with no reservoir pressure applied on the foundation. The results reveal that the ignoringreservoir pressure on the foundation overestimates the response of the dam body. Finally, based on the conducted analyses, considering foundation nonlinearity has no significant effect on the results in the considered case due to special design of the body shape.