Parametric stress-strain analysis for upstream slope of the asphaltic concrete core rockfill dams in static state

In this study, the effects of various geometric parameters of a dam in 2D static analysis of stress-strain on the upstream slope of the asphaltic concrete core rockfill dams were investigated. For this purpose, first the geometric characteristics of a large number of world's dams were collected and assessed, then by geometric modeling of these dams, many numerical models were developed for static analysis using GeoStudio software in eight height classes, three cases of upstream and downstream slopes, three different shape and thickness of the asphaltic concrete core under different Impounding states including "Full Reservoir", "Half full Reservoir", "End of construction and "Rapid Drawdown on a rigid type of foundation. The results of this study demonstrated that in four different construction and impounding states and in three different cases of slopes, Increasing the height parameter, causes increasing the Maximum total stress, Maximum total strain, Shear strain and Maximum shear stress for all construction and impounding states. The Maximum total stress decreased for all operating situations as the upstream slope reduced. According to the obtained results from the static stress-strain analysis, increasing both vertical and inclined asphaltic concrete core thicknesses, leads to decreasing the Maximum shear stress in Full Reservoir state but it increases in other state of impoundment. Moreover, by comparing the displacements related to specified points on the upstream slopes, increasing the height parameter, leads to increasing both horizontal and vertical displacements, the volumetric strain, deviator strain and deviator stress for all impounding conditions. In the following, the additional results were provided along with diagrams for further analysis.

SLOPE STABILITY ASSESSMENT OF THE UPSTREAM SLOPE OF THE DRY MOUNTAIN FLOOD CONTROL RESERVOIR DURING THE FLOOD

The flood control is one of the priority goal for successful economic activity on the areas that are periodically suffer from floods. Such areas are the mountainous regions of the Ukrainian Carpathian Mountains. Floods on the mountain rivers are repeated several times each year, and are characterized by the sudden water level rise with almost the same rapid decrease of the water level. Active flood protection measures include dry mountain flood control reservoirs, the principle of which is to transform part of the flood runoff and to accumulate water for the short time in the the artificial reservoir, with followed rapid emptying to the minimum level. The complex hydraulic regime is formed in the body of the dam which forms the flood control reservoir during the flood, that is different from the operation of the water permanent reservoir. The design of the flood control structures is car-ried out in accordance with Ukrainian building codes for the construction of the water reservoirs with constant water level, and require testing the stability of the downstream slope for the maximum water levels under steady state seepage conditions and assessment the upstream slope stability during the water level decreasing from the maximum level calculated in the steady state condition, these calculations do not correspond to the real seepage processes in the body of the dam of the dry flood control reservoir. Therefore, the purpose of this work is to determine the necessary boundary conditions of the flood control reservoir operation and upstream slope stability assessment by the limit equilibrium method. In the article the operation of the dry mountain flood control reservoir was analysed and found that the dam was characterized by two states: dry reservoir with water minimum water level and variable position of the seepage curve in the core and the upstream prism during the flood. The main factors influencing the upstream slope stability are the physical and mechanical properties of the soil, the laying of the slope, the period of time when the high-water level is maintained and the intensity of water level dropping. The upstream slope stability was evaluated by the Morgenstern & Price and Ordinary methods on the Slope/w software package. After the first 25 hours of the flood (period of high-water levels and the next water level dropping) the Safety Factor evaluated by limit equilibrium methods began to decrease, and reached the minimum value during the greatest seepage curve gradients at the time between 45 and 50 hours. Slope stability calculations by the limit equilibrium method were compared with the results of calculations performed by the SRM method, the values ​​of the Safety Factor and the way of their change during the flood evaluated by Ordinary and SRM methods almost coincide, which indicates the reliability of the results obtained by different methods of slope stability analysis

The Influence of Damage to the Geomembrane Layer on the Seepage Pattern and Discharge at the Homogeneous Embankment Dam

Placing the geomembrane layer on the upstream slope can control the seepage in homogeneous dams. Poor geomembrane design, construction and maintenance caused damage to the geomembrane that caused a leak through the dam body. This study discusses the effect of damage on the geomembrane layer at the homogeneous embankment dam on the seepage pattern and discharge. The study location is in the Sianjo Anjo dam, Aceh Singkil district, a homogeneous dam with a geomembrane layer located in the dam body's upstream part. The damage of the geomembrane layer is assumed caused by the various defect of locations and size. The results show that the seepage pattern (phreatic line) tends to be weak in the geomembrane layer without damage. Meanwhile, if the geomembrane layer is damaged, the larger the defects' width, the higher the phreatic line. However, the seepage pattern that occurs shows insignificant or almost the same. The seepage discharge increases with increasing defect width and decreasing defect location

Assessment of the Upstream Slope Stability of Darbandikhan Rockfill Dam during Drawdown

Earth and rockfill dams face a variety of loading conditions during lifetime. One of the most critical loading conditions is the rapid drawdown of water level after steady state conditions. Rapid drawdown may cause instability of upstream slope of the dam. The present work examines the stability of a rockfill dam under different drawdown rates in terms of factor of safety for the upstream slope of the dam. For this purpose, a computer software named GeoStudio 2012 SEEP/W and SLOPE/W has been used for the numerical analysis. The results showed that the drawdown rate has a significant effect on stability of rockfill dam in which increasing the drawdown rate from 1 m/day to 10 m/day decreases the stability of the dam by 33%. Based on the outcomes, for the studied case the drawdown rate (1 m/day) can be recommended.

The dam slope stability under the transient condition during an extreme flood

Mountain Flood Control Reservoir (MFC Reservoir) is used to reduce the flood level in the mountainous area and protect settlements downstream. The special feature of this MFC Reservoir is the fast filling during 1-2 days, short storage time at the maximum level and speed falling of the water level. Simulation of the MFC Reservoir operation was carried out on the software Midas GTS NX. Two rockfill dam models were developed: with the core and with the screen. The fluctuation of the water level in the MFC Reservoir was taken as the transformed flood from 1% to 10% probability. The fast water level change in the MCF Reservoir creates the transient seepage condition during the flood. During the water level rising in the MFC Reservoir, the upstream slope stability gradually increases because of hydrostatic pressure. After the water level begins to fall with rate of 0.7 m/hour, the slope stability decreases. The core or screen location significantly affects the stability of the upstream dam slope. The simulation showed that the upstream slope of the dam with the core was more stable. Due to the high hydraulic conductivity, the upstream dam prism with the berm significantly dampens the pore pressure in the dam and increases the stability of the upstream slope.

Experimental and numerical study of upstream slope stability in an earth dam reservoir under rapid drawdown conditions

The rapid ‎drawdown of the dam reservoir is one of the most common situations occurring in the lifetime of a dam. For this reason, one of the main factors in the design of the upstream slope is the rapid drainage of the reservoir. In this case, the upstream slope is in a critical condition and the slope may be unstable. When the water surface in the reservoir is drawdown suddenly, the water level in the dam body does not decrease at the same time as the reservoir water level. The analysis of seepage from the earth dam body and calculation of the water loss play an important role in calculating the amount of pore water pressure, and, consequently, the stability analysis of the dam body. In addition, any seepage analysis is dependent on the hydraulic properties of the dam materials. In order to investigate the effect of hydraulic conductivity on the rapid drawdown of water level and the seepage, an experimental model was constructed of an earth dam. By accurate measurement of hydraulic parameters of the materials in saturated and unsaturated media, the flow through this model was modeled using a disk penetrometer by seep/w software. The results were then compared with the observed data.