CN103603312B - A kind of concrete dam ideal temperature control curve model and utilize its intelligent control method - Google Patents

Abstract

This application discloses a kind of concrete dam ideal temperature control curve model, use Finite Element Simulation Analysis method, on the basis of existing specification and temperature control practical experience, study the temperature field of various dam type, the temperature stress regularity of distribution, obtain different parts by simulation calculation, concrete desirable temperature control curve model that different materials subregion, Various Seasonal are built, its middle ideal temperature control curve model temperature stress when equal Winkler's foundation is minimum。It addition, additionally provide the intelligent control method utilizing this concrete dam ideal temperature control curve model。

Description

A Concrete Dam Ideal Temperature Control Curve Model and Its Intelligent Control Method

technical field

The invention belongs to the technical field of concrete structure monitoring and construction in water conservancy and hydropower projects, in particular relates to a concrete dam ideal temperature control curve model, and also provides an intelligent control method using the model.

Background technique

The crack problem in the dam concrete construction period is one of the problems that have not been effectively solved. The main reason is that in addition to the complex site construction conditions in the construction stage, the implementation of many temperature control measures during the construction process is inevitably interfered by human factors. Another important reason is that its actual anti-cracking effect cannot reach the expected effect. Many concrete dams with cracks are due to the failure of the internal temperature to cool or protect the surface according to the design requirements, so that the anti-cracking safety reserve of the dam concrete during the construction period is insufficient, and the stress exceeds the standard, resulting in cracks.

In previous engineering practice, the control of water pipe cooling was mainly done manually. Whether the water flow control is good or bad depends entirely on the experience of the on-site management personnel. Because there are often hundreds of water pipes passing through the dam at the same time. , relying only on manual methods to deal with so many water pipeline controls, the result is that it is difficult to avoid the situation that there are many human errors and the temperature drop process deviates from the design guide curve. This traditional water control management mode brings the greatest The problem is that the cost of water passage is high, the temperature drop process is relatively random, and the risk of cracking is often in an uncontrolled state. Therefore, on the basis of the existing theoretical research and engineering practice, make full use of modern scientific and technological means, research and develop relevant intelligent water flow analysis software and control equipment, reduce the interference of human factors, and realize the intelligence of the whole process of internal temperature drop of concrete. Control appears to be very necessary.

Contents of the invention

The technical problem of the present invention is: to overcome the deficiencies of the prior art, to provide a concrete dam ideal temperature control curve model, which can promote the internal temperature to cool down along the model as much as possible in different stages of temperature drop, so that the concrete The risk of cracking can be controlled within the allowable range throughout the process.

The technical solution of the present invention is: the ideal temperature control curve model of the concrete dam, using the finite element simulation analysis method, on the basis of existing specifications and temperature control practice experience, to study the temperature field and temperature stress distribution of various dam types The ideal temperature control curve model of concrete poured in different parts, different material partitions, and different seasons is obtained through simulation calculations. The ideal temperature control curve model has the smallest temperature stress under the same temperature control standard conditions.

An intelligent control method using the ideal temperature control curve model of the concrete dam is also provided, and according to the ideal temperature control curve model of the concrete dam, the temperature change process is controlled by adjusting the water flow rate during the construction period.

Through this ideal temperature control curve model of concrete dams, using the finite element simulation analysis method, on the basis of existing specifications and practical experience in temperature control, the temperature field and temperature stress distribution of various dam types are studied, and the calculation of different parts and different The ideal temperature control curve model of concrete poured in different seasons and material partitions, in which the ideal temperature control curve has the smallest temperature stress under the same temperature control standard conditions, so in different stages of temperature drop, the internal temperature can be urged to follow the model as much as possible The temperature is lowered so that the risk of concrete cracking can be controlled within the allowable range throughout the process.

Description of drawings

Fig. 1 shows a preferred embodiment of the ideal temperature control curve model of a concrete dam according to the present invention.

Fig. 2 shows another preferred embodiment of the ideal temperature control curve model of a concrete dam according to the present invention.

detailed description

This ideal temperature control curve model of concrete dam uses the finite element simulation analysis method to study the temperature field and temperature stress distribution law of various dam types on the basis of existing specifications and practical experience in temperature control, and obtain different parts through simulation calculation. , The ideal temperature control curve model of concrete poured in different material zones and in different seasons, wherein the ideal temperature control curve model has the smallest temperature stress under the same temperature control standard conditions.

Preferably, the determination of the ideal temperature control curve includes the determination of the maximum temperature and the temperature drop rate, wherein the determination of the maximum temperature is related to the base temperature difference, and the base temperature difference is obtained through specification or finite element simulation calculation analysis; wherein the temperature drop rate is obtained through finite element simulation Obtained by calculation and analysis, and controlled according to the temperature difference between inside and outside, the temperature difference between top and bottom, and allowable stress.

Preferably, the ideal temperature control curve includes five stages: first-stage temperature control, first-stage temperature reduction, mid-stage temperature reduction and temperature control, second-stage temperature reduction, and second-stage temperature control.

An intelligent control method using the ideal temperature control curve model of the concrete dam is also provided, and according to the ideal temperature control curve model of the concrete dam, the temperature change process is controlled by adjusting the water flow rate during the construction period.

Through this ideal temperature control curve model of concrete dams, using the finite element simulation analysis method, on the basis of existing specifications and practical experience in temperature control, the temperature field and temperature stress distribution of various dam types are studied, and the calculation of different parts and different The ideal temperature control curve model of concrete poured in different seasons and material partitions, in which the ideal temperature control curve has the smallest temperature stress under the same temperature control standard conditions, so in different stages of temperature drop, the internal temperature can be urged to follow the model as much as possible The temperature is lowered so that the risk of concrete cracking can be controlled within the allowable range throughout the process.

Preferably, the change process of controlling temperature is divided into the following stages:

(1) Warehouse temperature control, if the outlet temperature is higher than the design value, and the ambient temperature is higher than the outlet temperature, control the warehouse entry by strengthening surface insulation and reducing the temperature of various ingredients before concrete mixing Temperature; if the ambient temperature is lower than the outlet temperature and the design value, the temperature of the concrete to the warehouse surface will be reduced by heat dissipation;

(2) Pouring temperature control, controlling the pouring temperature by reducing the covering time of the germ layer;

(3) Concrete cooling stage: In the first stage of temperature control, if the pouring temperature exceeds the standard, control it by moderately reducing the cooling water temperature or increasing the water flow rate. If the pouring temperature is lower than the design value, delay the water flow Or use high water temperature and low flow to control; in the first stage of cooling, control by reducing the water flow rate or increasing the cooling water temperature; in the mid-term cooling and temperature control, if the concrete does not reach the target temperature at the beginning of the mid-term cooling, Then increase the daily water flow rate. If the concrete mid-term cooling starts lower than the mid-term cooling start temperature, then reduce the daily water flow rate. If there is a water stop phenomenon, then when re-cooling, the cooling water temperature will first increase and then decrease. The cooling water temperature and flow rate are controlled gradually from small to small; in the second-stage cooling, if the concrete does not reach the target temperature at the beginning of the second-stage cooling, then increase the daily water flow. If it is lower than the starting temperature of the second-stage cooling, then reduce the daily water flow. If there is a water stop, then when the water is re-circulated, the flow will be reduced first and then gradually increased, and the water temperature will be gradually reduced; In the second stage of temperature control, the method of reducing the water flow rate is used to control the temperature, and the intermittent water flow method is avoided.

Preferred embodiments of the present invention will be specifically described below.

(1) Control model and determination method of ideal temperature process lines of different dam types

1) Control types of ideal temperature process lines for different dam types

The so-called ideal temperature process line refers to a cooling curve followed by the dam concrete during the cooling process. If the temperature is lowered according to this curve, the cracking risk of the dam concrete due to temperature changes is relatively minimal, and the selected cooling scheme is relatively optimal. .

Generally speaking, according to the type of dam and the need for joint grouting, the types of ideal temperature process lines mainly include the following types:

(1) Roller compacted concrete gravity dam: This type of dam generally does not require joint grouting, and there is only one stage of cooling during the construction period. If necessary, before winter or before water storage, in order to reduce the temperature difference between the inside and outside of the dam concrete, the internal temperature of the dam body will be reduced. A mid-term cooling is added to the relatively high area, and the cooling process is generally shown in Figure 1, which mainly includes three stages: first-stage temperature control, first-stage cooling, and mid-term cooling.

(2) Normal concrete gravity dam: This type of dam generally has longitudinal joints, and joint grouting is required. The concrete cooling period is divided into first, middle and second phases. The typical temperature drop curve is shown in Figure 2, mainly including the first phase control There are five stages: temperature reduction, first-stage cooling, mid-term cooling (possibly including mid-term temperature control), second-stage cooling, and second-stage temperature control.

(3) Roller compacted concrete arch dams without arch sealing grouting requirements: This type of dam is generally equipped with induced joints. During the construction period, there is usually a first-stage cooling and a mid-term cooling. There is no mandatory second-stage cooling, and the temperature is often not cold enough to the arch sealing temperature The dam began to store water, and then cooled freely. The cooling process line is similar to that shown in Figure 1, mainly including three stages: first-stage temperature control, first-stage cooling, and mid-term cooling.

(4) Normal concrete arch dam and roller compacted concrete arch dam with grouting requirements: This type of dam generally has transverse joints, which require arch sealing and grouting, and the internal temperature of the concrete needs to be cooled to the temperature of arch sealing and grouting. The typical temperature drop curve is shown in the figure As shown in 2, it mainly includes five stages: first-stage temperature control, first-stage cooling, mid-term cooling (possibly including mid-term temperature control), second-stage cooling, and second-stage temperature control.

2) How to obtain the ideal temperature process line

The acquisition of the ideal temperature process line generally considers the temperature control characteristics of mass concrete, uses the finite element simulation analysis method, and studies the temperature field and temperature stress distribution law of various dam types on the basis of existing specifications and practical experience in temperature control. The ideal temperature control curve model of concrete poured in different parts, different material partitions and different seasons is proposed. The ideal temperature control curve has the characteristics of the minimum temperature stress under the same temperature control standard conditions.

The determination of the ideal temperature process line is mainly determined by two key indicators: one is the maximum temperature, and the other is the temperature drop rate. The determination of the maximum temperature depends on the base temperature difference (the difference between the maximum temperature and the stable temperature). For any dam, its final stable temperature (or joint grouting temperature) is basically fixed, and the value of the base temperature difference determines What is the maximum temperature. Generally, the base temperature difference can be obtained through specification or finite element simulation calculation and analysis.

The acquisition of temperature drop rate is also mainly obtained through finite element simulation calculation and analysis. At the same time, it is controlled according to three indicators: internal and external temperature difference, upper and lower temperature difference, and allowable stress. The control standard of temperature drop rate needs to be based on the overall temperature and stress inside the dam concrete. Considering the distribution of different dam types, different parts, different materials and concrete poured in different seasons, the temperature drop rate has different requirements.

(2) Analysis of the main influence and control factors of the concrete cooling process

For dam projects, there are many methods of on-site temperature control, and the main factors affecting the cooling process include: cement hydration reaction (generally expressed by the adiabatic temperature rise formula), water pipe layout, cooling water temperature, water flow, water pipe Several key factors such as differential pressure.

Among the above-mentioned factors, the hydration reaction characteristics of cement (adiabatic temperature rise) are generally relatively stable, and once the cooling water pipe is buried in concrete, its layout will not change. Therefore, these two factors are basically fixed factors. ;Theoretically speaking, the water pipe pressure difference can also be adjusted. This adjustability depends on the configured power of the refrigeration unit. Generally speaking, starting from the premise of reducing faults and improving the life of the unit, after deducting the resistance loss along the way, the pressure The difference is generally kept relatively fixed, and the change of the pressure difference does not directly affect the change of the temperature, but its influence is reflected in the influence on the flow rate. Therefore, adjusting the pressure difference of the water pipe is equivalent to adjusting the flow parameter; the cooling water temperature is different according to the specific project. There are many choices for different cooling requirements. For dams with general seamless grouting requirements, such as roller compacted concrete dams, river water is sometimes used for cooling. At this time, if you want to control the concrete temperature along the ideal process line, you can only control it by adjusting the water flow; for concrete dams with joint (or arch sealing) grouting requirements, the water temperature of the cooling unit is generally relatively low Fixed, for example, the water temperature in the first cooling temperature control stage and the second cooling stage may be basically the same, with a lower water temperature, and a relatively higher water temperature for the mid-term cooling water temperature.

Based on the above analysis, among several factors affecting the temperature drop process, the most convenient, direct and effective way is to control the temperature change process by adjusting the water flow rate during the construction period. Of course, there is room for adjustment of the cooling water temperature when necessary.

(3) Measures and methods of intelligent control of the ideal temperature process line in stages

The boundary conditions of the dam concrete construction site are very complex. The temperature process line obtained under the ideal state is often affected by many external factors after arriving at the construction site. How to make the temperature of the concrete change along the ideal process line as much as possible is the key to realizing intelligent water flow. The key to control. For this reason, this part focuses on solving the problems that may occur in the temperature control process of each stage in the actual project, and proposes appropriate countermeasures and methods.

According to the actual control needs, the concrete temperature control process is divided into the following stages for discussion:

(1) The first stage: Warehousing temperature control

The temperature when the concrete comes out of the mixing building is called the outlet temperature, and it is transported to the warehouse surface by belt conveyor or cable conveyor, and the temperature when it reaches the warehouse surface is called the warehouse entry temperature. In this process, the concrete generally does not start to release heat from the hydration reaction. Therefore, the change of the concrete temperature is mainly caused by the heat exchange with the outside air temperature. If the ambient temperature is higher than the concrete temperature, there will be heat backflow, and the concrete The temperature will increase, and vice versa, the temperature of concrete entering the warehouse will decrease. The measures to control temperature changes at this stage are mainly surface protection. If the outlet temperature is higher than the design value, and the ambient temperature is higher than the outlet temperature, then the only way to prevent the warehouse entry temperature from exceeding the standard is to strengthen the surface insulation. Measures should be taken to reduce the temperature of the various ingredients before concrete mixing; if the ambient temperature is relatively low, the temperature of the concrete when it reaches the warehouse surface can be moderately reduced by heat dissipation (without surface protection). It should be controlled within the allowable range of the design as much as possible.

(2) The second stage: pouring temperature control

After the concrete is transported to the warehouse surface, until it is covered by the upper layer of concrete, the specification stipulates that the concrete temperature within 5-10cm from the surface is called the pouring temperature. Past engineering experience shows that the pouring temperature has a great influence on the maximum temperature of concrete. Generally, under the premise of water pipe cooling, if the pouring temperature increases by 1°C, the maximum temperature will increase by about 0.4-0.6°C. Therefore, if you want to increase the concrete temperature If the temperature changes along the ideal temperature process, then the pouring temperature should be controlled within the allowable range of the design as much as possible, otherwise, other temperature control measures need to be adjusted to control.

The most effective way to control the pouring temperature is to reduce the covering time of the germ layer. When the temperature is high, the surface of the germ layer should be protected, and if necessary, measures such as spraying on the warehouse surface should be added to reduce the phenomenon of heat backflow; when the temperature is too low, appropriate measures should also be taken. Good surface protection work to avoid the phenomenon of too low concrete pouring temperature, otherwise the actual temperature curve may deviate from the ideal process line.

(3) The third stage: concrete cooling stage

At this stage, the interior of the concrete is mainly affected by three factors, including: hydration temperature rise, surface heat dissipation and water pipe cooling.

Hydration temperature rise is an inherent characteristic of concrete. In the case of little difference in climatic conditions, the hydration reaction process and its own temperature are related, but generally speaking, the difference will not be too large. The influence coefficient of this factor on the temperature change process is basically constant;

The same is true for the influence of surface heat dissipation on the temperature change process, which is mainly related to whether insulation measures are taken on the surface, the thickness of the insulation material used, and the surface heat dissipation coefficient. Once determined, the influence weight of this factor on the temperature process is basically determined;

The third key influencing factor is water pipe cooling. The water pipe cooling effect is mainly related to the water flow rate, cooling water temperature and water pipe layout. It has been analyzed before that once the concrete is poured, the layout of the water pipes is basically the same influencing factor. It can be seen that the control of the concrete temperature drop process is mainly realized by changing the water flow rate and cooling water temperature.

After the concrete enters the actual cooling stage, it can be seen from the two types of ideal process lines that the first-stage cooling includes two stages of temperature control and temperature drop, and also includes mid-term cooling (medium-term temperature control), second-stage cooling and second-stage temperature control Wait a few stages. For the two types of ideal processes, the temperature control measures at the same stage are basically the same. Therefore, the following mainly analyzes the selection of temperature control measures at each stage of the second type of ideal temperature drop curve as an example.

①Temperature control in the first phase: The main purpose of the temperature control phase is to cut the peak, so that the maximum temperature inside the concrete is controlled within the allowable range of the design (or below the maximum temperature value of the ideal temperature curve). At this stage, if the pouring temperature exceeds the standard, the maximum temperature must be controlled as much as possible by adjusting other measures or parameters on the basis of the control measures and parameters corresponding to the ideal cooling curve. Control the water temperature or increase the water flow. Generally speaking, the effect of lowering the cooling water temperature on the maximum temperature is more significant than that of increasing the water flow rate. Therefore, lowering the cooling water temperature is a relatively better choice. If there is little room for adjustment of the water temperature, then both measures need to be combined consider.

If the pouring temperature is significantly lower than the design requirements, it can be controlled by appropriately delaying the water flow, or using high water temperature and low flow rate. Since the adjustment of the water temperature during the construction period may be required by the refrigeration unit and system water use, it should be optimized at this time. Consider low flow or delayed water control.

②Phase 1 cooling: The purpose of the first phase cooling of concrete is to reduce the internal temperature and reduce the temperature difference between inside and outside, so as to avoid cracks in early-age concrete due to the large temperature difference between inside and outside. The control of the temperature process at this stage can be mainly controlled by reducing the water flow rate or increasing the cooling water temperature. The specific choice can be determined according to the actual situation on site and combined with real-time feedback analysis.

Handling of abnormal temperature drop in the first phase: If the temperature exceeds the standard after taking all possible preliminary temperature control measures during the construction period, it is necessary to control the rate of temperature drop. If it exceeds 1°C, according to the engineering practice experience in recent years, the daily cooling can generally be controlled at no more than 0.5°C/day, and the first cooling time can be extended appropriately until the concrete re-intersects with the ideal process line, and then along the ideal process line Take control.

③ Mid-term cooling: The main purpose of mid-term cooling is to reduce the temperature difference between inside and outside or reduce the cooling range of the second cooling in the later stage. Generally, the cooling time is longer. The daily reference cooling range can be interpolated according to the difference between the target temperature of the first cooling and the target temperature of the intermediate cooling. Obtained, generally not more than 0.3 ℃ / day. If the concrete has not reached the target temperature when the mid-term cooling begins, the daily water flow can be appropriately increased, and can be controlled at no more than 0.5°C/day. If the beginning of the mid-term cooling of the concrete is already lower than the starting temperature of the mid-term cooling, the flow rate can be moderately reduced, for example, controlled according to the standard of 0.1-0.2°C/day. It should be noted that the concrete should avoid water cut-off as much as possible in the later stage, so as to reduce the risk of cracking caused by low-temperature water cold shock after re-flowing the water. If there is a water cut-off phenomenon, the cooling water temperature should be appropriately higher when re-cooling , and then slowly reduce the cooling water temperature, and the flow rate should also be controlled in a way that gradually increases from small to small.

④ Second-stage cooling (later cooling): The main purpose of the later cooling is to cool the concrete to the temperature of the arch closure. Since the stress of the concrete in the later stage of cooling is relatively large, the temperature drop rate should not be too high. The daily reference cooling range can be based on the target temperature of the first cooling. The difference with the target temperature of the intercooler is obtained by interpolation according to time, and generally does not exceed 0.3°C/day. If the concrete has not reached the target temperature at the beginning of the second-stage cooling, the daily water flow can be appropriately increased, and can be controlled at no more than 0.5°C/day.

If the start of the second-stage cooling of concrete is lower than the start temperature of the second-stage cooling (the target temperature of the mid-term cooling), the flow rate can be moderately reduced, for example, controlled at no higher than 0.2°C/day.

For the second-stage cooling, it is necessary to avoid intermittent water supply as much as possible to reduce the risk of cold shock cracking. flow, and then gradually increase the flow, and the water temperature should also be gradually reduced.

⑤Second phase temperature control:

After the concrete reaches the target temperature of the second-stage cooling, there will generally be a temperature control period of about 7-15 days before the joint (arch closure) is grouted. The purpose of temperature control is to prevent the temperature from rising later and reduce the opening and closing of the joint. Thus affecting its pourability. During the second-stage temperature control period, the rate of dissipation of the residual heat of hydration of concrete is relatively small. Therefore, in this case, it is generally better to control the temperature by reducing the flow rate of water, and intermittent water flow should be avoided. Water way.

The above are only preferred embodiments of the present invention, and are not intended to limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention are still within the scope of this invention. The protection scope of the technical solution of the invention.

Claims (1)

1. A kind of intelligent control method utilizing concrete dam ideal temperature control curve model, it is characterized in that: According to the ideal temperature control curve model of the concrete dam, the temperature change process is controlled by adjusting the water flow during the construction period; The control temperature change process is divided into the following stages: (1) Warehouse temperature control, if the temperature at the exit of the machine is higher than the design value, and the ambient temperature is higher than the temperature at the exit, the entrance of the warehouse is controlled by strengthening the surface insulation and reducing the temperature of various ingredients before concrete mixing Temperature; if the ambient temperature is lower than the outlet temperature and the design value, the temperature of the concrete to the warehouse surface will be reduced by heat dissipation; (2) Pouring temperature control, controlling the pouring temperature by reducing the covering time of the germ layer; (3) Concrete cooling stage: In the first stage of temperature control, if the pouring temperature exceeds the standard, control it by moderately reducing the cooling water temperature or increasing the water flow rate. If the pouring temperature is lower than the design value, delay the water flow Or use high water temperature and low flow to control; in the first stage of cooling, control by reducing the water flow rate or increasing the cooling water temperature; in the mid-term cooling and temperature control, if the concrete does not reach the target temperature at the beginning of the mid-term cooling, Then increase the daily water flow rate. If the concrete mid-term cooling starts lower than the mid-term cooling start temperature, then reduce the daily water flow rate. If there is a water stop phenomenon, then when re-cooling, the cooling water temperature will first increase and then decrease. The cooling water temperature and flow rate are controlled gradually from small to small; in the second-stage cooling, if the concrete does not reach the target temperature at the beginning of the second-stage cooling, then increase the daily water flow. If it is lower than the starting temperature of the second-stage cooling, then reduce the daily water flow. If there is a water stop, then when the water is re-circulated, the flow will be reduced first and then gradually increased, and the water temperature will be gradually reduced; In the second stage of temperature control, the method of reducing the water flow rate is used to control the temperature, and the intermittent water flow method is avoided.