Study On Crack Problems Of Gravity Dams With Temperature Change Effects

Due to the brittleness and large volume of concrete gravity dams,micro-cracks inevitably occur in the dam due to the influence of temperature change and others during the construction.The existence of initial micro-cracks could significantly reduce the safety of the dam.During the operation,with the increase of the reservoir water level and the change of the external temperature,the tensile stress of the dam heel area increases.The above-mentioned initial micro-cracks will cause the dam heel to crack and affect the safety of the dam.According to the results in recent works,except for self-weight,water pressure,earthquake,etc,temperature stress is also one of the important components affecting the stress distribution of gravity dams.Because of the difference between the external and internal temperature of the dam,the stress concentration at the crack front is caused by the temperature gradient.It is of great significance to study the crack problems of gravity dams under the effect of temperature change.Using the ABAQUS platform,two types crack models are investigated where the straight line and crescent cracks are located at 20 m,40m,and 60 m up from the bottom of the dam to the upstream surface,respectively.Two different climatic conditions,of the 48 h cold wave in January and the daily temperature change in July 24 h,are considered to carriy out the finite element simulation of the non-overflow dam section of the Liujiaxia Hydropower Station.Under,crack shapeand crack positions,the obtained results are compared with the working conditions that do not consider the temperature field.The influences of cracks on the stress and strain of the dam under various temperature fields are analyzed.The obtained results can be used to understand operational safety and life estimation of the dam.The main findings are given as follows:(1)Under the influence of temperature,although the range of temperature change is limited to the surface layer of concrete,the existence of cracks increases the surface area of concrete of the dam body,making the temperature field of the dam body under the influence of external temperature change range.The more close to the crack position is to the top of the dam,the more obvious the influence of temperature field is.It is worth noting that in July the initial crack at 60 m position has been exposed to the air.Compared with the crack under water,the temperature variation amplitude of the concrete surface of the dam in direct contact with the air temperature is larger than that of the interior of the dam.(2)Under the influence of temperature field,the maximum stress values in X and Y directions of each crack tip are tensile stress.With the decrease of temperature,the maximum tensile stress of dam heel increases and the maximum compressive stress of dam toe decreases.Compared with the condition without considering the temperature change,the compressive stress at the crack tip in the X direction is smaller.The compressive stress in Y direction is higher in January and lower in July.(3)Compared with different crack shapes,the crescent-shaped cracks are more consistent with the crack propagation path of the upstream side of the dam when the dam body is inclined to the downstream due to the change of external load,so the maximum tensile and compressive stresses of crescent-shaped cracks are greater than those of linear cracks.For the stress field of the crack tip,the change amplitude of the crack tip stress and its variation amplitude of the crescent crack are larger than that of the linear crack.(4)Comparing different crack positions,the higher the crack position,the closer to the water surface: the smaller the compressive stress near the crack;the influence range of the crack on the stress distribution of the dam body gradually decreases,and the maximum tensile stress in the X direction is determined by the dam body The downstream surface transfers to the vicinity of the crack,the maximum compressive stress at the dam site in the Y direction does not change much,and the maximum tensile stress at the top of the dam gradually increases;for the stress state of the crack tip,the compressive stress at the crack tip is constantly decreasing,and the temperature The amplitude of change caused by the change also gradually decreases.