Generally, the safety of a dam is not only related to its design and construction, but also to the complete characterization of its performance during the first dewatering and operation period, as well as regular service during the life of the dam. In this study, the vertical and horizontal displacements of the Eyvashan Dam were analyzed using actual instrument results in an eight-year period in three steps of construction, first dewatering and operation period. The numerical model of the largest section of the dam was prepared by Geostudio and Plaxis software and examined with respect to the behavioral model of Mohr– Coulomb. According to the results of the instrumentation, the settlement of the dam core has increasing trend and sometimes after the construction, it reaches almost constant. The maximum settlement of the dam core at the end of construction phase was 809 mm which is equal to 1. 2% of the dam height at the middle level. The horizontal displacements in the longitudinal direction of dam upstream are completely influenced by the reservoir water level and hydrostatic forces. The maximum horizontal displacement in the upper crust of Eyvashan dam is 75. 6 mm. After reservoir filling, the amount of settlement from the lower levels to the higher levels (crest of the dam) have had an increasing trend. In order to adapt the observational and predictive data, multivariate regression and determination coefficient were used which showed a consistency result of about 85 percent between observation and prediction data. This indicates that the maximum settlements and their location are agreed well with the technical specifications, revealing the proper operation of the dam in terms of settlement.

IntroductionStability analysis of earthen slopes is important for the investigation of road embankments, river walls and upstream and downstream slopes of earthen dams. The sloping earthen walls of the river are always subject to instability and failure caused by various factors such as floods, variations of the water level in the river. In investigating the stability of the earthen sloping walls of rivers, the role of hydraulic and geotechnical variables and their correlations are important as factors of creating uncertainty in the analyzes. The aim of current research is to investigate the effect of water level changes on the stability of the soil slopes of the river wall under the conditions of applying the correlation of effective random geotechnical variables with the use of copula functions. Also, comparing the performance of copula functions used in combination with limit equilibrium methods is another goal of this research.MethodologyThe uncertainty and correlation of the random soil properties including the internal friction angle and the cohesion of the river sloping wall were investigated at four cross-sections of Shalmanrood river in Guilan province of Iran. To this end, a computer code was developed in MATLAB and five copula functions were applied to the soil properties and the calculated correlations and distributions were compared using Akaike and Bayesian information criteria to determine the best copula. Then in GeoStudio software, using three limit equilibrium methods including Bishop, Spencer and Morgenstern-Price the slope stability was approximated. The distributions of factor of safety were obtained for three scenarios of water level including the maximum observed level and the water level decline by 20 and 40 %. Results and discussionFor the maximum water level in the river cross-section 1, the distribution of factor of safety was obtained in the range of 1.4-3.6 using the limit equilibrium method. By decreasing the water level by 20%, the factor of safety changes to 1.2-1.9 and declining the water level by 40% , the range is obtained 1.06-2.8. The same trends of decreasing the factor of safety by the water level decline in the river are observed in three other cross-sections. For the maximum river water level in cross-section 1, the maximum error of normal and GEV distributions were obtained equal to 7.8 and 11.4%, respectively. In addition, the error of normal and GEV distributions for water level decline by 20% were13.4% and 13.6% respectively. Finally, the error of 9% and 14.5% were obtained for the water level decline by 40% for the normal and GEV, respectively. It is observed that normal distribution offers better performance for all water levels and the errors of both distributions increase with water level decline. This trend is also observed in the all studied cross-sections.ConclusionsThe performance of the Morgenstern-Price method compared to other limit equilibrium methods is not affected by the variations of the water level in the river and always offers acceptable results. Three limit equilibrium methods used (Bishop, Spencer, and Morgenstern-Price) provide similar results at lower values of the factor of safety (with lower cumulative probability, CDF). Frank copula is the best function to model the correlation of random variables affecting the studied sloping walls of the river. The highest rate of change in factor of safety is observed for the water level decline by 20%.

The study utilizes the Limit Equilibrium Method (LEM) to investigate slope movements. These movements were initially generated by construction activities at the slope's base, and subsequent events were driven by seismic activities, as the study studied area lies within the Main Karakoram Thrust (MKT) and Main Mantle Thrust (MMT) zones. Soil samples, characterized by a moisture content of 13% and a dry unit weight of 18.14 kN/m³ were analyzed. The study revealed that an increase in saturation caused by rainwater infiltration, resulted in a reduction in unconfined compression strength, decreasing from 712 kPa to 349 kPa. The shear strength and deformation parameters (cohesion, angle of internal friction, and deformation modulus) were also examined with varied degrees of saturation. The results revealed a decrease in these parameters as the percentage of saturation increased from 30% to 90%. The slope stability study revealed that the Factor of Safety (FOS) reduced from 1.85 to 0.86 as the saturation of the material raised from 30% to 90%. To assess the influence of unit weight, cohesion, and angle of internal friction on the FOS, multiple cases were considered. The analysis revealed that the FOS increased with higher cohesion and angle of internal friction, while an increase in unit weight resulted in a lower factor of safety. Furthermore, stability of the slope was evaluated by modifying the slope geometry such as lowering the height. According to the GeoStudio investigation, the slope remained steady even at saturation levels exceeding 80%.