| In the process of dam construction,the orifice structure is often the key part of temperature control and crack prevention.The high-grade concrete is usually used at the opening of the dam,the hydration heat,the autogenous volume deformation and the elastic modulus are large,which lead to the rapid increase of the early stress,while the low-grade concrete is often used in the surrounding dam body,the material characteristics are different,as a result,the surface cracks are easy to occur at the orifice.If not handled properly,the surface cracks often develop into harmful cracks,endangering the orifice and even the safety of the dam.Therefore,in view of the special structure of the dam,it is very important to study its temperature development course and adopt appropriate temperature control measures.Therefore,the author has carried out the surface temperature monitoring tests on the bottom slab of the orifice and the side wall of the concrete in the 19 #-030 Bin and 19 #-032 bin of the typical section of the Baihetan Dam,and has sorted out the temperature monitoring data of the concrete at the bottom slab and side wall,and from the highest temperature,cooling water,environmental temperature,internal and external temperature differences and other aspects of analysis.Based on the temperature data obtained from the monitoring,the BP neural network-genetic Algorithm is used to inverse the thermal parameters of different concrete according to the complex characteristics of the material parameters of the concrete with openings,on the basis of considering solar radiation heat,the temperature field of concrete at the orifice is calculated by simulation method,and the calculated concrete temperature is in good agreement with the measured value.Then,using the 3D finite element model with high accuracy,the temperature control effect of different temperature control measures at the orifice was analyzed,and the factors such as the distance of cooling water pipes,the thickness of insulating layer and the temperature of cooling water supply were analyzed respectively,the maximum temperature,temperature difference between inside and outside,cooling rate of bottom plate and side wall under different working conditions are studied.The results show that the maximum temperature of concrete at different depths from the top of the bottom slab of the runner and the side wall of the runner is about 2 days,and the depth of concrete affected by the external temperature is within 60 cm,in the high temperature season,the solar radiation has a great influence on the temperature of concrete,especially in the early stage of concrete.The equivalent temperature of solar radiation can be added to 11.62 °C.The arrangement of 1 m × 1.5 m cooling water pipe is helpful to reduce the maximum temperature of concrete and the difference between inside and outside temperature.At the same time,the 3 cm insulating layer is covered under the principle of economic safety,at the beginning of pouring,the cooling water temperature of 10 ～ 13 °C has the same cooling effect on the concrete at the orifice.Finally,combined with the technical standard of temperature control construction,aiming at the first cooling stage,taking the maximum temperature of 27 °C and the cooling rate of 0.5 °C / d as The control index,the temperature control measures are recommended as follows: adopting the pouring temperature of 12 °C and arranging the cooling water pipe of 1 m × 1.5 m,covering 3 cm of insulation layer,through 10 °C water temperature,the flow rate of the first-stage temperature control and cooling stage of the bottom plate is 25 L/ min and 15 L/ min respectively,and the flow rate of the side wall in the first-stage temperature control and cooling stage is 33L/ min and 25L/ min respectively. |
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