The geomorphological feature of the valley's asymmetry is described in the Western Zagros in Iraqi Kurdistan; in terms of facing of the valley sides relative to the position of the sun. The asymmetry is represented by steeper northwest facing valley sides; as compared to the southeast facing sides. This feature shows clear valley's asymmetry in cross section is a new geomorphological characteristic for the Western Zagros Mountain Belt. The asymmetry of valleys, in the present study, is proved to exist in different rock types and areas, which is developed by more chemical weathering of one facing sides relative to the other side. The weathering is attributed to the remaining of the moisture for longer time than the southeastern sides, which are stroke by sun radiation for longer time and are dried more rapidly. A simple method was established for indicating the steeper side of the valleys. The method consists of drawing two parallel lines across the photo of the valley, then connecting the bottom of the valley with the left and right deflection points on the inter-valleys ridges by lines. Finally the angles between the lower horiozontal line and inclined lines are measured, which indicates the asymmetry of the valleys.
Seasonal freezing and thawing can have significant effects on tailings management. Tailings delivery, depositional schemes and water treatment are examples of activities that must be dealt with extra concern in sub-zero temperatures. Changes in mechanical properties, drainage possibilities or embedded frozen tailings layers are effects that can arise in poorly managed facilities. To avoid such consequences, a good understanding of the seasonal effects on the tailings deposit is needed. To get a better understanding of the geothermal regime in tailings, this paper presents a case study with geothermal modelling performed for the Laiva tailings facility in Finland, where major seasonal freezing and thawing periods are present. Ground temperatures and frost lines were predicted via one-dimensional modelling using air temperatures and snow cover depths from adjacent weather stations, and basic soil properties from the facility. Simulated results were compared to data obtained from thermal instruments in the field. The snow cover and its estimated thermal properties were shown to have large influence on the results. The model was able to accurately predict the thermal regime measured in the field. Strong agreement was shown, both in terms of ground temperatures and frost front positions. The methodology presented is useful for tailings management schemes in cold regions.
Behavior of tailings dams are often controlled in dam surveillance programs where horizontal deformation is one of the key aspects. When evaluating field data, there is a necessity for comparison with anticipated deformations in order to relate field behavior to dam stability. With numerical modeling, these predictions can be made. This paper presents a case where horizontal deformations in a tailings dam have been simulated for a six-year period, using two-dimensional finite element modeling. Yearly dam raises have been simulated as staged constructions according to activities at site. Tailings materials have been simulated with an elasto-plastic constitutive model with isotropic hardening, called Hardening Soil and the conventional linear-elastic, perfectly plastic Mohr-Coulomb model. Soil parameters used for input were calibrated to laboratory data. Results from simulations were compared with data obtained in situ by a slope inclinometer. Results obtained by the Hardening Soil model indicate good agreement with respect to field measurements. However, this was not reached with the Mohr-Coulomb model. The results presented indicate benefits by using an advanced constitutive model for tailings in order to estimate in situ deformations in a tailings dam. The methodology presented can be used for prediction of future deformations, in order to relate the dam behavior to its stability. This is important in dam safety assessment, and will lead to a better understanding of the dam safety, being of great importance for the dam owner and the society in general.
In dam safety operations for tailings dams, instrumentation has a major role. High pore-water pressure or large deformations can both be observed with good monitoring programs, and are covered in many dam safety guidelines. A key aspect when evaluating field data is the way to compare values with expected dam behavior (including a certain safety margin). This is needed in order to determine the safety of a dam, but there is lack of methods for this in the dam industry. With the use of finite element modeling, the behavior and stability of tailings dams can be simulated. Simulated behavior can be used in dam safety operations, where field data is compared with numerical results. In this paper, a case study is presented where a method for instrumentation alarm-level set-up is proposed.
Deposition of mine tailings in a cold climate requires precautions as temporary sub-zero temperatures can imply considerable consequences to the storage due to creation of permafrost. The risk of creating man-made permafrost lenses due to tailings deposition exists even in regions with no natural permafrost, as material being frozen during winter might not fully thaw by the following summer. When such frozen layers thaw during later longer warmer periods, excess pore water pressure and large settlements might develop. Such implications close to the dam structure have to be avoided and therefore the risk of generating permafrost should be reduced. This paper describes a geothermal model for one-dimensional heat conduction analysis. The model is able to simulate the temperature profile in tailings where the surface elevation is constantly increased due to deposition. At the tailings surface, the boundary condition is the air temperature changing over time during the year. Air temperatures, tailings deposition schedule and tailings properties are given as input to the model and can easily be changed and applied to specific facilities. The model can be used for tailings facilities in cold regions, where the effects of tailings deposition on the temperature regime are of interest. Findings can improve tailings management by explaining man-made permafrost generation. The model can also aid in setting up appropriate deposition schedules and to prevent generation of permafrost layers.
Managing tailings deposition in cold climate requires specific measures not to create permafrost. The risk of generating permafrost due to tailings deposition exists even in regions where permafrost would naturally not occur. Material being frozen during winter might not fully thaw in the following summer due to added height of the tailings on the surface. Such embedded layers of permafrost should be avoided especially close to tailing dams. Main reasons are to prevent impermeable layers in tailings facilities, and to reduce the risk of having implications if such layers thaw during warmer summers causing increase in pore water pressure, reduced effective stress, and increased water content.
This paper presents a numerical study on the effects of tailings deposition in cold regions in relation to the potential formation of permafrost. Various deposition rates, schedules and tailings properties were evaluated. One-dimensional heat conduction analyses were performed with a temperature scenario representing a mine district in northern Sweden. Results show, that the thickness of permafrost layers increase with increased deposition rate and with increased water content. It was also shown that wet and loose tailings must be deposited in short periods during summer to avoid permafrost generation. In the case of dry and dense tailings more time is available for deposition in order not to cause aggradation of permafrost in the deposit.
These findings can help mining operation to set up deposition schedules for tailings facilities in cold climate. For known tailings properties, results can be used to identify periods of the year when, and how much, tailings can be deposited in critical areas of a deposit in order to avoid permafrost formation.
In Scandinavia, a lot of manholes and gullies, designed for the drainage of rain water, get damaged during winter due to frost action mainly because of the heave of frost susceptible backfill. The concrete rings are pulled apart and the joints between the rings are opened. When thawing starts, water and soil flows into the gullies through the opened joints and the inflowing material prevents the rings from returning to their original positions. In order to study the behavior of manholes and gullies with and without a newly invented rubber sleeve mounted over the joints, a field test was performed during the winter 1980/81 in Lulea, Sweden. The paper describes the instrumentation installed as well as the results obtained
Avhandlingens första del behandlar en teoretisk beräkningsmodell för tjällyftning samt studier av dess noggranhet i olika situationer. Tjällossningsförloppet analyseras och studeras genom noggranna mätningar av porvattentryckens fördelning i tid och rum. Porvattentrycksutvecklingen kopplas till läget av islinserna i jorden, som detekteras med hjälp av röntgenteknik. Avhandlingens andra del belyser hur frusen jord kan packas och vad deformationerna i sådan jord blir då den tinar. Beräkningar av kompressionen i samband med upptining jämförs med resultat från såväl laboratorieförsök som uppföljningar i fält. Strukturella förändringar i jorden till följd av frysning och tining belyses också.
The hydropower embankment dam in Suorva, Sweden, is located in north of the Arctic Circle. The region is known for cold winters and severe wind conditions. The construction was completed in 1972 and has since then been exposed to a wide temperature range and low annual mean temperatures, leading to the presumption that the fine-grained frost susceptible moraine core of the embankment was exposed to cyclic freezing and thawing. The aim of this project was to find indications for freezing processes that affect the structure of the soil. The project included field investigations and a theoretical thermal analysis carried out with a commercial finite element program. Results from this analysis showed that the freezing plane advances to a maximum depth of 5 m from the top of the core. Hence, it may be possible that frost action affects the construction in its function as hydraulic barrier. Softening due to freeze/thaw can form initial soft part where internal erosion may be initiated thus causing weak points in the dam structure.
Since older embankment dams have a tendency to gradually display an increased degree of leakage it is interesting to find out if this phenomenon can be captured by an inverse modelling approach. Numerical tests with a model system will hopefully lead to a better understanding of the decomposition of material in dams and enhance the knowledge about the long term effects in order to forsee potential problems in the future.These embankment dams typically consist of a central core of moraine that is surrounded by a filter, a transition layer and a fill material. Ideally the seepage through the dam is relatively small and the effect on the dam from the flow is negligible. However, in reality there are several situations that promote a fatal failure of the dam including overtopping at high flood discharges, internal erosion and seepage problems in the embankment and the foundation. The status of embankment dams are generally examined by in-situ measurement of one or several of the following quantities: pore pressure, inclination and settlement, temperature, resistivity, self-potential, seepage rate, turbidity of the seepage water, ground penetration radar and bore hole tomography. These indirect and/or discrete methods give indication of the condition of the dam leaving the real situation for the imagination. Hence, when there are alterations to measured values great efforts are often spent on reinforcing dams in order to keep a high safety level. An increased knowledge of the composition of material in dams would enable the usage of focused measures reducing the costs and increasing the safety.