A method for monitoring concrete temperature at the bottom hole of an arch dam in high temperature season

Abstract

The present invention provides a method for monitoring the temperature of concrete at the bottom hole of an arch dam in a high temperature season, comprising: step 1, selecting a location for burying optical fibers; step 2, designing a temperature gradient monitoring test plan; step 3, selecting a distributed optical fiber warehouse layout plan that meets the actual situation of the arch dam bottom hole casting warehouse, and designing a warehouse surface optical fiber layout plan; step 4, burying optical fibers according to the test plan; step 5, determining the location of the temperature gradient monitoring test measurement points and the location of the warehouse fiber measurement points; step 6, after obtaining multiple groups of data through the temperature gradient monitoring test, combining the maximum temperature and cooling rate of the concrete, analyzing the monitoring data rules of the bottom plate and the side wall, and evaluating the temperature control effect and measures of the bottom hole. The monitoring method can monitor the concrete temperature and temperature change trend of the bottom hole of the arch dam in real time during the high temperature season, provide a reference for the formulation of concrete temperature control measures, and effectively prevent the cracking of the concrete at the bottom hole of the arch dam.

Description

Technical Field

[0001] The invention relates to a concrete temperature monitoring method, in particular to a concrete temperature monitoring method at a bottom hole of an arch dam in a high temperature season. Background Art

[0002] During the construction process, concrete dams are affected by various definite and uncertain factors such as materials, air temperature, and water flow, which can easily cause concrete cracking. The bottom hole of the arch dam is the weak link of the entire dam. High-grade impact-resistant and wear-resistant concrete is usually used, and the stress of the bottom hole structure is concentrated and the heat dissipation area is large, which makes the bottom hole very easy to crack, thereby affecting the overall safety of the dam. The Baihetan Hydropower Station Project is located in the southwest of my country. The summer is hot, the temperature difference between day and night is large, the solar radiation is strong, and the light energy resources are abundant. The temperature effect of the early poured concrete is greatly affected, making the determination of the temperature boundary attributes during the construction period more complicated, and the risk of cracking of the bottom hole is greater. Therefore, it is particularly important to grasp the temperature change history of the concrete at the bottom hole of the arch dam during the construction period in the high temperature season. Distributed optical fiber has the advantages of high sensitivity, long life, long transmission distance, and real-time monitoring. It is one of the commonly used concrete temperature monitoring methods in dam projects. The present invention utilizes the advantages of the distributed optical fiber temperature measurement system, carries out temperature gradient monitoring tests during the construction period in the high temperature season at the bottom hole, and buries the pouring bin through the bin to obtain the temperature data of the bottom hole of the arch dam at the initial pouring stage. By obtaining temperature data at different distances from the flow channel bottom plate, different distances from the flow channel side wall, and temperature data at different positions on the warehouse surface, the temperature of the concrete at the bottom hole and the temperature change law are analyzed. In view of the complexity of the concrete material parameters at the bottom hole, based on the temperature data obtained by monitoring, a reference is provided for the formulation of concrete temperature control measures, which effectively prevents the cracking of the concrete at the bottom hole of the arch dam. Summary of the invention

[0003] The technical problem to be solved by the present invention is to propose a method for monitoring the concrete temperature of the bottom hole of an arch dam in the high temperature season. The method can effectively monitor the concrete temperature and temperature change trend of the bottom hole of the arch dam in real time during the high temperature season, provide a reference for the formulation of concrete temperature control measures, and effectively prevent cracking of the concrete at the bottom hole of the arch dam.

[0004] In order to solve the above technical problems, the present invention proposes the following technical solution: a method for monitoring the concrete temperature of the bottom hole of an arch dam in a high temperature season, comprising the following steps:

[0005] Step 1: Select the optical fiber embedding position according to the bottom hole structure of the arch dam;

[0006] Step 2: Design a temperature gradient monitoring test plan for selected locations of the arch dam bottom hole;

[0007] Step 3: Select a distributed optical fiber warehouse layout plan that meets the actual situation of the arch dam bottom hole casting warehouse, and design the warehouse surface optical fiber layout plan;

[0008] Step 4: Complete the preparation work before burying the optical fiber and bury the optical fiber according to the test plan;

[0009] Step 5: Determine the location of the temperature gradient monitoring test measurement points and the location of the optical fiber measurement points for the warehouse;

[0010] Step 6: After obtaining multiple sets of data through the temperature gradient monitoring test, analyze the monitoring data patterns of the bottom plate and side walls in combination with the maximum temperature and cooling rate of the concrete, evaluate the temperature control effects and measures at the bottom hole, and provide reference for subsequent temperature control measures.

[0011] In a preferred embodiment, the step 1 is performed as follows:

[0012] Step 1-1, select the bottom hole for optical fiber burial according to the arch dam construction progress;

[0013] Step 1-2, select the side wall of the bottom hole and the flow channel bottom plate as the optical fiber embedding position, select the casting bin including the side wall of the bottom hole and the flow channel position to carry out the temperature gradient test and optical fiber embedding through the bin.

[0014] In a preferred embodiment, the step 2 is performed as follows:

[0015] Step 2-1, design a temperature gradient monitoring test plan for the casting bin at the bottom plate of the flow channel, select a monitoring position, which is the middle position of the upper and lower reaches of the flow channel bottom plate, lead the optical fiber along the starting point of the lead-in line to the monitoring position, and lay 3 to 5 layers of optical fibers at different positions from the surface on the surface of the middle part of the flow channel bottom plate, with a spacing of 0.1 to 0.3 m between each layer of optical fibers;

[0016] Step 2-2, design a temperature gradient monitoring test plan for the casting bin at the side wall. The monitoring position is the middle position of the diversion bottom hole along the river. The side wall temperature gradient test optical fiber is arranged in the middle of the two layers of cooling water pipes in the vertical direction. 3 to 5 layers of optical fibers at different positions from the side wall surface are arranged along the transverse seam direction. The distance between each layer of optical fibers is 0.1 to 0.3 m.

[0017] Step 2-3: The design of the test scheme for monitoring the temperature gradient of the flow channel bottom plate and side wall adopts double-stranded optical fiber, and the special monitoring optical fiber for the temperature gradient of the bottom plate is attached to the steel mesh of the casting bin at the bottom plate. The auxiliary steel bars and transverse steel bars at the side wall are arranged alternately, and the special monitoring optical fiber for the temperature gradient of the side wall is attached under the transverse steel bars.

[0018] Step 2-4: Determine the buried length of the optical fiber according to the optical fiber layout plan, and draw the plane layout schematic diagram and cross-sectional diagram of the optical fiber for monitoring the surface temperature gradient at different parts of the arch dam bottom hole.

[0019] In a preferred embodiment, the operation steps of step 3 are as follows:

[0020] Step 3-1: The warehouse layout plan is selected as double-strand "I" type, "L" type or "Z" type;

[0021] Step 3-2, determine the optical fiber burial elevation, the optical fiber burial elevation is equal to the optical fiber burial layer top elevation minus 0.25m, the optical fiber burial layer is selected as the middle layer, and the optical fiber line is drawn from upstream to downstream along the river according to the warehouse layout plan.

[0022] In the preferred scheme, in step 3-2, the starting and ending points of the "I" type or "L" type or "Z" type buried from the upstream surface are 3 to 5 meters away from the upstream and downstream surfaces, and the "I" type or "Z" type buried from the upstream surface is 3 to 5 meters away from the nearest transverse joint; if the "Z" type starts from the transverse joint surface, the starting and ending points of the burial are no more than 3 meters away from the transverse joint surface, and the inflection point is 3 to 5 meters away from the upstream and downstream surfaces.

[0023] In the preferred scheme, in step 4, before opening the warehouse, the reserved experimental optical fiber is tied to the specific welded steel mesh, and the optical fiber is buried starting from the upstream surface or the downstream surface, and buried in sequence. After the steel mesh and the optical fiber are completely covered by the upper layer of concrete, the temperature gradient monitoring test is completed.

[0024] In a preferred embodiment, the operation steps of step 5 are as follows:

[0025] Step 5-1: Name the optical fiber measurement points starting from the bottom layer of optical fiber close to the transverse seam of the dam section, corresponding to the typical measurement points in the scheme, and name the upper layer of optical fiber in the same way after turning the corner;

[0026] Step 5-2: Determine the spatial position of each measuring point according to the actual position of the buried optical fiber measured on site, so as to determine the position of the bottom plate and top plate temperature gradient monitoring test measuring point;

[0027] Step 5-3: Use distributed optical fiber to monitor the temperature of the warehouse surface, with the starting point, turning point and end point as feature points;

[0028] Step 5-4: Divide the temperature measuring optical fiber into sections according to the characteristic points. The number of measuring points on the upstream surface parallel to the dam axis and the number of measuring points on the downstream surface parallel to the dam axis do not include the inflection points. The number and position of the measuring points in each section of the optical fiber are used as the number and position of the optical fiber measuring points in the whole warehouse.

[0029] In a preferred embodiment, the test data analysis steps in step 6 are as follows:

[0030] Step 6-1, select the temperatures of the measuring points at 0.2m, 0.45m, and 0.7m from the top surface of the flow channel bottom plate and the measuring points at 0.1m, 0.2m, 0.4m, 0.6m, and 0.8m from the flow channel side wall surface, take the average value of the temperature at each distance as the final temperature measurement data, and draw the concrete temperature duration curves at different depths from the top surface of the bottom plate and the flow channel side wall;

[0031] Step 6-2, select the temperatures of the measuring points at 0.2m, 0.45m, and 0.7m from the top surface of the flow channel bottom plate and the measuring points at 0.1m, 0.2m, 0.4m, 0.6m, and 0.8m from the flow channel side wall surface, draw a curve of the temperature variation at different positions versus time, and obtain the variation law of the daily cooling rate of concrete;

[0032] Step 6-3: In combination with the technical standards for temperature control during construction, evaluate the temperature control effect of the maximum concrete temperature and cooling rate in steps 6-1 and 6-2 on the bottom hole to provide a reference for subsequent construction.

[0033] The present invention provides a method for monitoring the temperature of concrete at the bottom hole of an arch dam in the high temperature season. By utilizing the advantages of a distributed optical fiber temperature measurement system, the temperature of concrete at the bottom hole of an arch dam in the high temperature season is monitored in real time, online, comprehensively and effectively, and the temperature change trend of concrete is clearly displayed. On the basis of obtaining the temperature and temperature change trend of concrete at the bottom hole of the arch dam, the temperature change law and influencing factors of concrete at the bottom hole during the construction period are analyzed, providing an effective reference for the formulation of temperature control measures for concrete at the bottom hole during the subsequent construction period. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a three-dimensional schematic diagram of the bottom hole;

[0035] Figure 2 Fiber layout diagram for temperature gradient monitoring test;

[0036] Figure 3 This is a schematic diagram of the layout of the "I" type warehouse;

[0037] Figure 4 This is a schematic diagram of the "L" type warehouse layout plan;

[0038] Figure 5 This is a schematic diagram of the "Z" type warehouse layout plan 1;

[0039] Figure 6 This is a schematic diagram of the second "Z" type warehouse layout plan;

[0040] Figure 7 This is a schematic diagram of the material division of the 4# diversion bottom hole of the 19# dam section;

[0041] Figure 8This is the optical fiber plane layout diagram of the special monitoring scheme for the temperature gradient of the bottom plate of warehouse 19#030;

[0042] Fig. 9 This is a schematic diagram of the optical fiber longitudinal section layout of the special monitoring solution for the temperature gradient of the bottom plate of warehouse 19#-030;

[0043] Fig.10 This is the optical fiber plane layout diagram of the special monitoring scheme for the temperature gradient of the side wall of warehouse 19#-032;

[0044] Fig.11 This is a schematic diagram of the optical fiber buried on the side wall of the diversion bottom hole of the 19#-032 warehouse;

[0045] Fig.12 This is the schematic diagram of the distributed optical fiber layout and the optical fiber buried cross-section diagram of warehouse 19#-030;

[0046] Fig.13 This is the schematic diagram of the distributed optical fiber layout and the optical fiber buried cross-section diagram of warehouse 19#-032;

[0047] Fig.14 This is a schematic diagram of the locations of typical optical fiber measurement points in the 19#-032 warehouse side wall temperature gradient monitoring test;

[0048] Fig.15 It is the curve diagram of concrete temperature development at different depths from the top surface of the flow channel bottom plate;

[0049] Fig.16 It is the temperature course curve of concrete at different depths from the side wall surface;

[0050] Fig.17 The curve of daily cooling rate of concrete at different positions of the bottom plate as a function of age;

[0051] Fig.18 This is a curve of the daily cooling rate of concrete at different locations on the side wall changing with age.

[0052] In the figure: bottom plate 1, side wall 2, bottom plate distributed optical fiber layout 3, side wall distributed optical fiber layout 4. DETAILED DESCRIPTION

[0053] Embodiment 1:

[0054] A method for monitoring the concrete temperature of the bottom hole of an arch dam in a high temperature season, the specific steps are as follows:

[0055] Step 1: The surface area of ​​the bottom hole casting bin of the arch dam is large, and the temperature changes dramatically due to factors such as solar radiation heat and air temperature in the high temperature season. The bottom hole of the arch dam usually uses high-grade concrete, which has a larger hydration heat than ordinary concrete, and the temperature inside the bin changes slowly, with a large temperature gradient. The risk of cracking of the bottom hole is greater than that of other casting parts. Therefore, the present invention needs to monitor the temperature of the bottom hole, select key monitoring parts according to the structural characteristics of the bottom hole, and conduct a temperature gradient test of the surface concrete of the bottom hole and bury the optical fiber through the bin.

[0056] The detailed steps of step 1 are:

[0057] Step 1-1: Select the appropriate bottom hole according to the actual construction progress of the arch dam. In order to meet the requirements of diversion and flood discharge during the construction and operation periods, the arch dam is usually designed with multiple bottom holes. According to the construction progress of the arch dam, the casting bin containing the bottom hole is selected, and the optical fiber is buried and arranged at the casting site of the selected casting bin.

[0058] Step 1-2: Select the bottom hole temperature monitoring location. The bottom hole of the arch dam consists of an inlet section, a flow channel, and an outlet section. The inlet section is mostly in a bell-mouth shape, and the flow channel consists of a bottom plate, a top plate, and a side wall. The bottom hole structure is as follows: Figure 1 As shown. The bottom plate and side walls are both thin-walled concrete structures. The length of the thin-walled concrete structure is significantly larger than the thickness, and it is more susceptible to factors such as external temperature, solar radiation heat, and water flow to produce penetrating cracks. In addition, the bottom plate and side wall parts use more concrete and have a larger hydration heat. Therefore, the side wall and flow channel bottom plate of the typical bottom hole selected in step 1-1 are used as the optical fiber burying parts, and the casting bin containing the bottom hole side wall and flow channel parts is selected for the temperature gradient test.

[0059] Step 2: Design a test plan for monitoring the temperature gradient of the concrete on the bottom hole surface for the concrete pouring bins on the side walls and bottom plate of the typical bottom hole selected in step 1. The fiber optic cables for the temperature gradient monitoring test are laid as follows: Figure 2 shown.

[0060] The detailed steps of step 2 are:

[0061] Step 2-1: Design a temperature gradient monitoring test plan for the casting bin at the bottom plate of the flow channel, select the starting point of the lead and the monitoring position, the lead position is determined according to the location of the optical fiber placement room and the monitoring room, and the monitoring position is the middle position of the upper and lower reaches of the flow channel bottom plate. The optical fiber is led from the starting point of the lead to the monitoring position, and the optical fiber lead and path are planned. According to the needs of the temperature gradient test, 3 to 5 layers of optical fibers at different positions from the surface are generally laid on the surface of the middle of the bottom plate, and the distance between each layer of optical fibers is 0.1 to 0.3m.

[0062] Step 2-2: Design a temperature gradient monitoring test plan for the casting bin at the side wall, select the lead-in starting position and monitoring position, the lead-in position is determined according to the position of the optical fiber placement room and the monitoring room, and the monitoring position is the middle position of the diversion bottom hole along the river. In order to prevent the optical fiber from being squeezed and broken during casting and avoid interference from the cooling water pipe, the optical fiber for the side wall temperature gradient test is arranged in the middle of the two layers of cooling water pipes in the vertical direction. Generally, 3 to 5 layers of optical fibers at different positions from the side wall surface are arranged along the horizontal seam direction, and the distance between each layer of optical fibers is 0.1 to 0.3m.

[0063] Step 2-3: The design of the flow channel bottom plate and side wall temperature gradient monitoring test schemes both use double-stranded tied optical fibers to improve the survival rate of buried optical fibers. In order to fix the optical fiber position and ensure that each layer of optical fiber is parallel to the warehouse surface, the bottom plate temperature gradient special monitoring optical fiber is attached to the bottom plate casting warehouse steel mesh, the auxiliary steel bars and transverse steel bars at the side wall are staggered, and the side wall temperature gradient special monitoring optical fiber is attached below.

[0064] Step 2-4: Determine the buried length of the optical fiber according to the optical fiber layout plan, and draw the plane layout schematic diagram and cross-sectional diagram of the optical fiber for monitoring the surface temperature gradient at different parts of the arch dam bottom hole.

[0065] Step 3: Select a distributed optical fiber warehouse layout plan that meets the actual situation of the arch dam bottom hole casting warehouse, and design the warehouse surface optical fiber layout plan.

[0066] The detailed steps of step 3 are:

[0067] Step 3-1: Considering the size and shape of the casting bin at the bottom hole of the arch dam, combined with the temperature gradient test plan, select one of the double-strand "I" type, "L" type or "Z" type to design the through-bin layout plan.

[0068] Step 3-2: The “I” type through-warehouse layout scheme is applicable to the situation where the warehouse surface size in the foundation area is large but the wiring is affected by the foundation corridor, and it is arranged in a straight line along the upstream and downstream directions; the “L” type through-warehouse layout scheme is applicable to the situation where the warehouse surface size is large and through-warehouse wiring can be achieved, starting from the transverse seam surface and turning to half of the warehouse surface width, and arranged along the upstream and downstream surfaces; the “Z” type through-warehouse layout scheme is applicable to the situation where the warehouse surface size is small in the non-foundation area and through-warehouse wiring can be achieved. There are two types of “Z” type layout schemes: Scheme 1: Starting from the upstream surface, Scheme 2: Starting from the transverse seam surface, both are arranged in a “Z” shape. The three through-warehouse layout schemes are as follows: Figures 3 to 6 shown.

[0069] Step 3-3: Determine the fiber optic buried elevation, which is equal to the fiber optic buried layer top elevation minus 0.25m. The fiber optic buried layer is generally selected as the middle layer, which can better reflect the temperature characteristics of the casting bin. Draw the fiber optic line from upstream to downstream along the river according to the scheme selected in the previous step.

[0070] For "I" type, "L" type and "Z" type of Scheme 1, the burial starting point and end point are 3 to 5 meters away from the upstream and downstream surfaces, and "I" type and "Z" type are 3 to 5 meters away from the nearest transverse joint; for "Z" type of Scheme 2, the burial starting point and end point are no more than 3 meters away from the transverse joint surface, and the inflection point is 3 to 5 meters away from the upstream and downstream surfaces.

[0071] Step 4: Complete the preparation work before burying the optical fiber and bury the optical fiber according to the test plan.

[0072] The detailed steps of step 4 are:

[0073] Step 4-1: Arrange a dedicated person to follow up the progress of concrete pouring on the warehouse surface before the fiber optic laying construction.

[0074] Step 4-2: Before opening the warehouse, tie the reserved experimental optical fiber to the welded specific steel mesh. Reserve 1m of optical fiber at the corner of each layer of steel mesh to avoid damage to the optical fiber at the corner due to the small turning radius.

[0075] Step 4-3: During the optical fiber burial process, the optical fiber burial shall be carried out strictly in accordance with the concrete temperature gradient test plan and the warehouse surface burial plan. The optical fiber burial can start from the upstream surface or the downstream surface and be buried in sequence, depending on the completion of the concrete pouring and vibration of the upstream and downstream surfaces.

[0076] Step 4-4: During burial, prevent mechanical operations or manual vibration from causing damage to the optical fiber.

[0077] Step 4-5: After the steel mesh and optical fiber are completely covered by the upper layer of concrete, the temperature gradient monitoring test is completed.

[0078] Step 5: Determine the location of the temperature gradient monitoring test measurement points and the location of the optical fiber measurement points laid through the warehouse.

[0079] The implementation process of step 5 is:

[0080] Step 5-1: Start naming the optical fiber measurement points from the bottom layer of optical fiber close to the transverse seam of the dam section, corresponding to the typical measurement points in the scheme, and name the upper layer of optical fiber in the same way after turning the corner.

[0081] Step 5-2: Determine the spatial position of each measuring point based on the actual position of the buried optical fiber measured on site, thereby determining the position of the bottom plate and top plate temperature gradient monitoring test measuring points.

[0082] Step 5-3: Use distributed optical fiber to monitor the warehouse surface temperature, with a spatial resolution of 1m. The starting point of the optical fiber is taken at 5m from the upstream or downstream surface, and the starting point, turning point and end point are used as characteristic points. When selecting characteristic measuring points, try to choose points that best reflect the temperature characteristics of concrete. For example, when secondary concrete is used locally in the warehouse, try to avoid its influence range when selecting points to prevent the average temperature value obtained from monitoring from being "abnormal".

[0083] Step 5-4: Divide the temperature measuring optical fiber into sections according to the characteristic points. The number of measuring points on the upstream surface parallel to the dam axis and the number of measuring points on the downstream surface parallel to the dam axis do not include the inflection points. The number and position of the measuring points in each section of the optical fiber are used as the number and position of the optical fiber measuring points in the whole warehouse.

[0084] Step 6: After obtaining multiple sets of data through the temperature gradient monitoring test, analyze and process the data to conduct real-time monitoring of the temperature distribution at the bottom hole of the arch dam:

[0085] Step 6-1: Select the temperature of the measuring points at 0.2m, 0.45m, 0.7m from the top surface of the runner bottom plate and 0.1m, 0.2m, 0.4m, 0.6m, 0.8m from the runner side wall surface, take the average of the temperature at each distance as the final temperature measurement data, and draw the concrete temperature history curve at different depths from the top surface of the bottom plate and the runner side wall. Analyze the monitoring data in combination with the highest temperature of concrete development.

[0086] Step 6-2: Select the temperatures of the measuring points at 0.2m, 0.45m, and 0.7m from the top surface of the flow channel bottom plate and 0.1m, 0.2m, 0.4m, 0.6m, and 0.8m from the flow channel side wall surface, and draw a curve of the temperature variation at different positions versus time to obtain the changing pattern of the daily cooling rate of concrete.

[0087] Step 6-3: In combination with the temperature control technical standards, evaluate the temperature control effect of the maximum concrete temperature and cooling rate in Step 6-1 and Step 6-2 on the bottom hole to provide a reference for subsequent construction.

[0088] It is very important to monitor the concrete temperature and temperature changes at the bottom hole of the arch dam during the high temperature season. The present invention provides a method for monitoring the concrete temperature at the bottom hole of the arch dam during the high temperature season. The present invention utilizes the advantages of the distributed optical fiber temperature measurement system to monitor the temperature of the concrete at the bottom hole of the arch dam in real time, online, comprehensively and effectively during the high temperature season, and clearly shows the trend of concrete temperature changes. On the basis of obtaining the temperature and temperature change trend of the concrete at the bottom hole of the arch dam, the temperature change law and influencing factors of the concrete at the bottom hole during the construction period are analyzed, which provides an effective reference for the formulation of temperature control measures for the bottom hole concrete during the subsequent construction period.

[0089] Embodiment 2:

[0090] The following is combined with Figures 1 to 10 The present invention provides a detailed description of an embodiment of a method for monitoring the temperature of concrete at the bottom hole of an arch dam during high temperature seasons. The main purpose of this embodiment is to conduct a temperature gradient test on the side walls and bottom plate of the diversion bottom hole of the arch dam, and to arrange an "L"-shaped through-bin in the corresponding bin, so as to monitor the temperature and temperature change trend of the concrete at the bottom hole of the arch dam during high temperature seasons. By analyzing the temperature change law and influencing factors, a reference is provided for the formulation of temperature control measures for the concrete at the bottom hole of the arch dam during the construction period. This embodiment includes the following specific steps:

[0091] Step 1: Select the fiber optic embedding location based on the arch dam bottom hole structure:

[0092] Step 1-1: The inner edge of the hole in the dam body is exposed to the air, which is the weak link of the overall structure of the arch dam. It is greatly affected by the external temperature. In addition, the casting material uses concrete of different graded concretes, which is prone to concrete cracking. This is one of the key points of the dam temperature control and crack prevention research. The Baihetan Dam has a total of 6 diversion bottom holes, which are arranged in the 16#~20# dam section and the 22# dam section. This embodiment selects the 4# diversion bottom hole in the 19# dam section for temperature gradient testing and fiber optic burial on the warehouse surface. The bottom hole material division is as follows: Figure 7 shown.

[0093] Step 1-2: According to the actual pouring conditions on site, the flow channel bottom plate and flow channel side wall of the diversion bottom hole of the dam section were finally selected for the temperature gradient special monitoring test and the warehouse layout plan, among which 19#-030 warehouse (EL.628m~631m) is the warehouse where the bottom hole flow channel bottom plate is located, and 19#-032 warehouse (EL.634m~637m) is the warehouse where the side wall is located.

[0094] Step 2, design a test plan for monitoring the temperature gradient of the bottom hole of the arch dam. In this embodiment, the 19#-030 warehouse of Baihetan is selected to carry out a special monitoring test on the temperature gradient of the flow channel bottom plate, and the 19#-032 warehouse is selected to carry out a special monitoring test on the temperature gradient of the flow channel side wall surface. The specific plan is as follows:

[0095] Step 2-1: In the 19#-030 warehouse flow channel bottom plate temperature gradient special monitoring test plan, select the lead-in starting point and the monitoring starting point, lead the optical fiber along the lead-in starting point to the upstream surface steel mesh, and then lead it along the bracket steel mesh and the flow channel bottom plate steel mesh to the monitoring position, such as Figure 8 Three layers of optical fiber are arranged for the special monitoring of the temperature gradient of the corridor bottom plate. The optical fiber is attached to the three layers of steel mesh on the flow channel bottom plate along the dam axis. Each layer of steel mesh is arranged with a 6m long temperature measurement optical fiber, which is slightly longer than the bottom hole size (5.5m). The three layers of optical fiber are respectively 0.20m, 0.45m, and 0.70m away from the top of the flow channel bottom plate. The effective temperature measurement optical fiber is buried for 20m. Fig. 9 .

[0096] Step 2-2: In the special monitoring test plan for the temperature gradient on the side wall of the flow channel in the 19#-032 warehouse, the starting point of the lead wire and the starting point of the monitoring are selected. The optical fiber is buried in the warehouse and then led to the monitoring starting point. Fig.10 In the middle of the diversion bottom hole (EL.635.50m), five layers of 4m long distributed optical fibers are laid along the river. The five layers of optical fibers are 0.10m, 0.20m, 0.40m, 0.60m, and 0.80m away from the side wall surface of the flow channel, and 48m of effective temperature measurement optical fiber is buried. Fig.11 .

[0097] Step 3: Select a distributed optical fiber warehouse layout plan that meets the actual situation of the arch dam bottom hole casting warehouse, and design the warehouse surface optical fiber layout plan:

[0098] In this embodiment, Baihetan 19#-030 warehouse and 19#-032 warehouse were selected to carry out the distributed optical fiber through-warehouse layout scheme. Considering the large shapes and sizes of the two casting warehouses, and the lack of special structures such as corridors to hinder the laying of optical fibers through the warehouses, the "L"-shaped through-warehouse layout scheme was finally selected. The burial starting points of the two "L"-shaped layout schemes are 3m away from the upstream and downstream surface templates and 0.5m away from the nearest transverse seam. Fiber lines are drawn from upstream to downstream along the river, and the fiber lengths are both 54m. The thickness of warehouses 030 and 032 is 3m (divided into 6 blanks), and the optical fiber is buried in the third blank. The burial elevation is equal to the top elevation of the fiber burying blank layer minus 0.25m, that is, 1.15m. The fiber optic layout of warehouse surfaces of warehouses 19#-030 and 19#-032 is as follows: Fig.12 , Fig.13 .

[0099] Step 4: Complete the preparations before fiber optic burial and bury the fiber optic according to the test plan:

[0100] Step 4-1: Arrange a dedicated person to follow up the concrete pouring progress of the warehouse surface before the fiber optic laying construction.

[0101] Step 4-2: Before opening the warehouse, tie the reserved experimental optical fiber to the welded specific steel mesh. Reserve 1m of optical fiber at the corner of each layer of steel mesh to avoid damage to the optical fiber at the corner due to the small turning radius.

[0102] Step 4-3: During the fiber optic burial process, the fiber optic burial shall be carried out strictly in accordance with the concrete temperature gradient test plan and the warehouse surface layout plan. The fiber optic burial can start from the upstream surface or the downstream surface and be buried in sequence, depending on the completion of the concrete pouring and vibration of the upstream and downstream surfaces.

[0103] Step 4-4: During burial, prevent damage to the optical fiber caused by mechanical operations or manual vibration.

[0104] Step 4-5: After the steel mesh and optical fiber are completely covered by the upper layer of concrete, the temperature gradient monitoring test is completed.

[0105] Step 5: Determine the location of the temperature gradient monitoring test measurement points and the location of the optical fiber measurement points for the warehouse:

[0106] Step 5-1: Naming the optical fiber measuring points from the bottom layer of optical fiber close to the transverse seam of the dam section, corresponding to the typical measuring points in the scheme, and naming the upper layer of optical fiber in the same way after turning the corner; in this embodiment, when determining the position of the temperature gradient monitoring test measuring point of the flow channel bottom plate of the 19#030 warehouse, the optical fiber measuring points are named starting from the bottom layer of optical fiber close to the 19# transverse seam. The bottom layer is named as 01 to 07 measuring points, corresponding to A to G in the scheme, respectively. After turning the corner, the second layer is named as 08 to 14 measuring points, corresponding to H to N typical measuring points in the scheme, respectively. After turning the corner again, the third layer is named as 15 to 21 measuring points, corresponding to O to U typical measuring points in the scheme, respectively. The spatial position diagram is as follows: Fig. 9 ,The specific information of the measuring points is shown in Table 1.

[0107] Step 5-2: Determine the spatial position of each measuring point based on the actual position of the buried optical fiber measured on site, so as to determine the position of the bottom plate and top plate temperature gradient monitoring test measuring point. The specific spatial position information of each measuring point is shown in Table 2. When determining the position of the measuring point of the 19#032 warehouse flow channel side wall temperature gradient monitoring test, the schematic diagram of the spatial position of the typical measuring point of the flow channel side wall temperature gradient monitoring test is as follows: Fig.14 The measurement point numbers in the temperature measurement system corresponding to the relevant measurement points are shown in Table 3, and the spatial position coordinate information is shown in Table 4.

[0108] Step 5-3: Use distributed optical fiber to monitor the warehouse surface temperature with a spatial resolution of 1m. The starting point of the optical fiber is taken at 5m from the upstream or downstream surface, and the starting point, turning point and end point are taken as feature points.

[0109] Step 5-4: Divide the temperature measurement optical fiber into sections according to the characteristic points. The number of measurement points on the upstream side parallel to the dam axis and the number of measurement points on the downstream side parallel to the dam axis do not include the inflection point. The number and position of the optical fiber measurement points in each section are used as the number and position of the optical fiber measurement points in the warehouse. See the number and position of the measurement points in warehouse 19#030 and warehouse 19#032 for details. Fig.12 , Fig.13 The number of measuring points on the upstream surface parallel to the dam axis is 1, the number of measuring points on the downstream surface parallel to the dam axis is 0, and the number of measuring points in the middle section is 5.

[0110] Table 1 Typical measurement point information table of the special monitoring program for the temperature gradient of the flow channel bottom plate

[0111]

[0112] Table 2. Spatial position coordinate information table of the measurement points of the special monitoring scheme for the temperature gradient of the flow channel bottom plate

[0113]

[0114]

[0115] Table 3 Typical measurement point information of the flow channel side wall surface temperature gradient monitoring scheme

[0116]

[0117] Table 4. Spatial position coordinate information of measuring points on the flow channel side wall surface temperature gradient monitoring scheme

[0118]

[0119] Step 6: After obtaining multiple sets of data through the temperature gradient monitoring test, analyze and process the monitoring data of the bottom plate and side wall, and evaluate the temperature control effect and measures of the concrete at the diversion bottom hole. The specific process is as follows:

[0120] Step 6-1: Select the temperature of the measuring points at 0.2m, 0.45m, and 0.7m from the top surface of the flow channel bottom plate and the measuring points at 0.1m, 0.2m, 0.4m, 0.6m, and 0.8m from the flow channel side wall surface, take the average of the temperature at each distance as the final temperature measurement data, and draw the concrete temperature history curve at different depths from the top surface of the bottom plate and the flow channel side wall. Analyze the monitoring data in combination with the highest temperature developed by the concrete. The temperature development process curves at different positions of the flow channel and the side wall are shown in Fig.15 and 16 The maximum temperatures at different depths of the flow channel and side wall are shown in Tables 5 and 6.

[0121] Table 5 Maximum temperature and appearance age of measuring points at different depths from the top surface of the flow channel bottom plate

[0122] Measuring point location Maximum temperature / ℃ Age of appearance / d 0.2m from the top surface of the flow channel bottom plate 28.03 2.28 0.45m from the top of the flow channel bottom plate 26.96 1.75 0.7m from the top of the flow channel bottom plate 23.34 2.08

[0123] Table 6 Maximum temperature and appearance age of measuring points at different depths from the flow channel side wall

[0124] Measuring point location Maximum temperature / ℃ Age of appearance / d 0.1m from the flow channel side wall 35.30 1.75 0.2m from the flow channel side wall 34.94 1.92 0.4m from the flow channel side wall 35.31 2.33 0.6m from the flow channel side wall 34.78 2.33 0.8m from the flow channel side wall 33.26 2.83

[0125] Combined with Table 5, Table 6, Fig.15 and Fig.16 The following conclusions can be drawn:

[0126] (1) The ages at which the concrete reaches the highest temperature at 0.7m, 0.45m, and 0.2m from the top surface of the flow channel bottom plate are 2.08d, 1.75d, and 1.67d, respectively; the ages at which the concrete reaches the highest temperature at 0.8m, 0.6m, 0.4m, 0.2m, and 0.1m from the flow channel side wall surface are 2.83d, 2.33d, 2.33d, 1.92d, and 1.75d, respectively. The greater the depth from the flow channel side wall, the longer the age at which the highest concrete temperature appears.

[0127] (2) The age at which the highest temperature of concrete appears at all positions is basically around 2 days, except for the position 0.2 m from the top surface of the bottom plate, which is earlier than the age at which the highest temperature of concrete appears in the dam body bin. The reason is that high-grade concrete is used at the orifice, and the hydration heat is higher, so the concrete in this position reaches the highest temperature earlier. The highest temperature of concrete at the position away from the top surface of the bottom plate appears at the age of 5.58 days, which is considered to be affected by the external ambient temperature.

[0128] (3) The maximum temperature of concrete at 0.2m from the top surface of the flow channel bottom plate is 1.07℃ higher than that at 0.45m from the top surface, while the maximum temperature of concrete at 0.7m from the top surface is 3.62℃ lower than that at 0.45m from the top surface; the maximum temperatures of concrete at 0.1m, 0.2m, 0.4m, and 0.6m from the flow channel side wall surface are not much different, while the maximum temperature of concrete at 0.8m is about 2℃ lower.

[0129] (4) The concrete temperature at different distances from the bottom plate to the concrete surface is between 23℃ and 27.02℃, and the concrete temperature at different distances from the side wall to the surface is between 33℃ and 36℃.

[0130] Step 6-2: Select the temperature of the measuring points at 0.2m, 0.45m, and 0.7m from the top surface of the flow channel bottom plate and the measuring points at 0.1m, 0.2m, 0.4m, 0.6m, and 0.8m from the flow channel side wall surface, and draw a curve of the temperature variation at different positions over time to obtain the variation law of the daily cooling rate of concrete. The daily cooling rate of concrete at different positions of the bottom plate is shown in Fig.17 The daily cooling rate of concrete at different locations on the side wall is shown in Fig.18 The temperature drop control information of dam concrete at each stage is shown in Table 7.

[0131] Table 7 Dam concrete temperature drop control information at each stage

[0132] Cooling stage Temperature drop / ℃ Target temperature / ℃ Cooling rate / (℃ / d) Cooling time / d Phase I 6～8 21、23 ≤0.5 ≥21 Mid-term 3～4 17、20 ≤0.3 ≥28 Phase II 3～4 13、14、16 ≤0.3 ≥30

[0133] Combination Figure 17-Figure 18 And from the analysis of Table 7, we can get:

[0134] (1) In the first cooling stage, the cooling rate must be ≤0.5℃ / d. At 0.7m, 0.45m, and 0.2m from the top of the bottom plate, the maximum cooling rates are 1.11℃ / d, 1.41℃ / d, and 1.50℃ / d, respectively. The corresponding ages are the 10th, 5th, and 1st day after the highest temperature is reached. The first cooling target of the diversion bottom hole is 21℃. At the age of 21 days, the concrete temperatures at 0.7m, 0.45m, and 0.2m from the top of the bottom plate are 20.5℃, 22.13℃, and 23.18℃, respectively. The temperature drop ranges are 3.24℃, 4.18℃, and 3.79℃, respectively. In the mid-term temperature control stage (21-40d), the temperature change needs to be kept within 1°C. During this period, the concrete temperature changes at 0.7m, 0.45m, and 0.2m from the top of the bottom plate are 3.42°C, 1.98°C, and 1.50°C respectively. In the intermediate cooling stage, the cooling rate needs to be ≤0.3°C / d. The maximum cooling rates of the concrete temperatures at 0.7m, 0.45m, and 0.2m from the top of the bottom plate are 1.87°C / d and 0.71°C / d respectively. / d, 0.43℃ / d; in the secondary temperature control stage of mid-term cooling, the concrete temperature is required to reach the mid-cooling target temperature of 17℃. When the mid-term secondary cooling begins, the concrete temperatures at three locations are 21.89℃, 22.52℃, and 22.81℃ respectively. At the same time, this stage requires that the concrete temperature change range is within 1℃. During this period, the concrete temperature changes at 0.7m, 0.45m, and 0.2m from the top surface of the bottom plate are 0.78℃, 0.58℃, and 0.65℃ respectively.

[0135] (2) In the first cooling stage, the cooling rate must be ≤0.5℃ / d. At 0.8m, 0.6m, 0.4m, 0.2m, and 0.1m from the side wall surface, the maximum cooling rates are 1.18℃ / d, 1.61℃ / d, 1.94℃ / d, 2.09℃ / d, and 2.09℃ / d, respectively. The corresponding ages are the 3rd, 2nd, 2nd, and 2nd days after the highest temperature is reached. On the 3rd day, the target temperature of the diversion bottom hole was 21℃. At the age of 21 days, the concrete temperatures at 0.8m, 0.6m, 0.4m, 0.2m and 0.1m away from the side wall surface were 25.66℃, 26.2℃, 26.57℃, 26.67℃ and 26.75℃ respectively, and the temperature reduction ranges were 7.35℃, 8.32℃, 8.38℃, 7.25℃ and 7.17℃ respectively. In the mid-term primary temperature control stage (21-40d), the temperature change needs to be kept within 1°C. During this period, the concrete temperature changes at 0.8m, 0.6m, 0.4m, 0.2m and 0.1m away from the side wall surface are 3.49°C, 3.4°C, 3.19°C, 2.96°C and 2.87°C respectively. In the intermediate cooling stage, the cooling rate needs to be ≤0.3°C / d. The maximum cooling rates of the concrete temperatures at 0.8m, 0.6m, 0.4m, 0.2m and 0.1m away from the side wall surface are 0.43°C / d, 0.29°C / d, 0.35°C / d, 0.61℃ / d, 0.74℃ / d; in the secondary temperature control stage of mid-term cooling, the concrete temperature is required to reach the mid-cooling target temperature of 17℃. When the mid-term secondary cooling begins, the concrete temperatures at five locations are 23.1℃, 23.36℃, 23.75℃, 24.07℃, and 24.25℃ respectively. At the same time, this stage requires that the concrete temperature change range is within 1℃. During this period, the concrete temperature changes at 0.8m, 0.6m, 0.4m, 0.2m, and 0.1m away from the side wall surface are 1.15℃, 1.49℃, 2.06℃, 2.69℃, and 2.95℃ respectively.

[0136] Step 6-3: Combined with the temperature control technical standards, evaluate the temperature control experimental data of steps 6-1 and 6-2 to provide reference for subsequent construction. By analyzing the acquired orifice data, the following conclusions can be drawn:

[0137] (1) The greater the depth from the top surface of the flow channel bottom plate, the longer the age at which the maximum temperature of the concrete appears; the greater the depth from the flow channel side wall, the longer the age at which the maximum temperature of the concrete appears.

[0138] (2) During the first cooling stage of the concrete at the bottom plate and side wall, the temperature drop amplitude at the bottom plate was within the standard requirements, but the temperature drop rate exceeded the standard, with a maximum exceeding the standard requirement of 1.0°C / d. The temperature drop amplitude at the side wall exceeded the standard, with a maximum exceeding the standard requirement of 2.38°C. The temperature drop rate exceeded the standard, with a maximum exceeding the standard requirement of 1.59°C / d. During the mid-term temperature control stage, the temperature change amplitude of the concrete at the bottom plate exceeded the standard, with a maximum exceeding the standard requirement of 2.42°C. The temperature change amplitude of the concrete at the side wall exceeded the standard requirement of 2.49°C. During the intermediate cooling stage, the temperature drop rate of the concrete at the bottom plate exceeded the standard requirement of 1.57°C / d, and the temperature drop rate of the concrete at the side wall exceeded the standard requirement of 0.44°C / d. During the secondary temperature control stage, the temperature change amplitude of the concrete at the bottom plate was within the temperature control standard requirements, and the temperature change amplitude of the concrete at the side wall exceeded the temperature control construction technical standard requirement of 1.95°C.

[0139] Later, combined with the "Technical Requirements for Temperature Control Construction of Baihetan Arch Dam" (Second Edition), the temperature control effect and measures of the concrete at the diversion bottom hole were evaluated, and the relevant conclusions are as follows:

[0140] (1) The maximum temperature of the concrete in the side wall exceeds the standard by 7.95℃.

[0141] (2) The maximum daily cooling rate of concrete in the bottom plate and side wall exceeded the standard requirements by 1°C / d and 1.59°C / d.

[0142] (3) The reasons for the maximum concrete temperature and cooling rate exceeding the standard are: the pouring temperature of the side wall exceeds the standard requirement of 12°C, the water temperature and flow rate deviate from the standard requirements, and the insulation measures are not implemented in accordance with the temperature control standard requirements.

Claims

1. A method for monitoring the concrete temperature of the bottom hole of an arch dam in high temperature season, characterized in that: The following steps are involved: Step 1: Select the optical fiber embedding position according to the bottom hole structure of the arch dam; Step 2: Design a temperature gradient monitoring test plan for selected locations of the arch dam bottom hole; The step 2 is performed as follows: Step 2-1, design a temperature gradient monitoring test plan for the casting bin at the bottom plate of the flow channel, select a monitoring position, which is the middle position of the upper and lower reaches of the flow channel bottom plate, lead the optical fiber along the starting point of the lead-in line to the monitoring position, and lay 3 to 5 layers of optical fibers at different positions on the surface of the middle surface of the flow channel bottom plate, with a spacing of 0.1 to 0.3 m between each layer of optical fibers; Step 2-2, design a temperature gradient monitoring test plan for the casting bin at the side wall. The monitoring position is the middle position of the diversion bottom hole along the river. The side wall temperature gradient test optical fiber is arranged in the middle of the two layers of cooling water pipes in the vertical direction. 3 to 5 layers of optical fibers are arranged at different positions from the side wall surface along the transverse seam direction. The distance between each layer of optical fibers is 0.1 to 0.3 m. Step 2-3: The design of the test scheme for monitoring the temperature gradient of the flow channel bottom plate and side wall adopts double-stranded optical fiber, and the special monitoring optical fiber for the temperature gradient of the bottom plate is attached to the steel mesh of the casting bin at the bottom plate. The auxiliary steel bars and transverse steel bars at the side wall are arranged alternately, and the special monitoring optical fiber for the temperature gradient of the side wall is attached under the transverse steel bars. Step 2-4: Determine the buried length of the optical fiber according to the optical fiber layout plan, and draw the optical fiber plane layout schematic diagram and cross-sectional diagram of the surface temperature gradient monitoring test at different parts of the arch dam bottom hole; Step 3: Select a distributed optical fiber warehouse layout plan that meets the actual situation of the arch dam bottom hole casting warehouse, and design the warehouse surface optical fiber layout plan; Step 4: Complete the preparation work before burying the optical fiber and bury the optical fiber according to the test plan; Step 5: Determine the location of the temperature gradient monitoring test measurement points and the location of the optical fiber measurement points for the warehouse; Step 6: After obtaining multiple sets of data through the temperature gradient monitoring test, analyze the monitoring data patterns of the bottom plate and side walls in combination with the maximum temperature and cooling rate of the concrete, evaluate the temperature control effects and measures at the bottom hole, and provide reference for subsequent temperature control measures.

2. A method for monitoring concrete temperature at the bottom hole of an arch dam in high temperature season according to claim 1, characterized in that , the step 1 is operated as follows: Step 1-1, select the bottom hole for optical fiber burial according to the arch dam construction progress; Step 1-2, select the side wall of the bottom hole and the flow channel bottom plate as the optical fiber embedding position, select the casting bin including the side wall of the bottom hole and the flow channel position to carry out the temperature gradient test and optical fiber embedding through the bin.

3. The method for monitoring concrete temperature at the bottom hole of an arch dam in high temperature season according to claim 1 is characterized in that: The operation steps of step 3 are as follows: Step 3-1: The warehouse layout plan is selected as double-strand "I" type, "L" type or "Z" type; Step 3-2, determine the optical fiber burial elevation, which is equal to the top elevation of the optical fiber burial layer minus 0.25m. The optical fiber burial layer is selected as the middle layer. According to the warehouse layout plan, draw the optical fiber line from upstream to downstream along the river.

4. The method for monitoring concrete temperature at the bottom hole of an arch dam in high temperature season according to claim 3 is characterized in that: In step 3-2, for "I" type or "L" type or "Z" type buried from the upstream surface, the starting point and end point of the burial are 3 to 5 meters away from the upstream and downstream surfaces, and the "I" type or "Z" type buried from the upstream surface is 3 to 5 meters away from the nearest transverse joint; if the "Z" type starts from the transverse joint surface, the starting point and end point of the burial are no more than 3 meters away from the transverse joint surface, and the inflection point is 3 to 5 meters away from the upstream and downstream surfaces.

5. The method for monitoring concrete temperature at the bottom hole of an arch dam in high temperature season according to claim 1 is characterized in that: In step 4, before opening the warehouse, the reserved experimental optical fiber is tied to the specific welded steel mesh, and the optical fiber is buried starting from the upstream surface or the downstream surface, and buried in sequence. After the steel mesh and the optical fiber are completely covered by the upper layer of concrete, the temperature gradient monitoring test is completed.

6. The method for monitoring concrete temperature at the bottom hole of an arch dam in high temperature season according to claim 1 is characterized in that: The operation steps of step 5 are as follows: Step 5-1: Name the optical fiber measurement points starting from the bottom layer of optical fiber close to the transverse seam of the dam section, corresponding to the typical measurement points in the scheme, and name the upper layer of optical fiber in the same way after turning the corner; Step 5-2: Determine the spatial position of each measuring point according to the actual position of the buried optical fiber measured on site, so as to determine the position of the bottom plate and top plate temperature gradient monitoring test measuring point; Step 5-3: Use distributed optical fiber to monitor the temperature of the warehouse surface, with the starting point, turning point and end point as feature points; Step 5-4: Divide the temperature measuring optical fiber into sections according to the characteristic points. The number of measuring points on the upstream surface parallel to the dam axis and the number of measuring points on the downstream surface parallel to the dam axis do not include the inflection points. The number and position of the measuring points in each section of the optical fiber are used as the number and position of the optical fiber measuring points in the whole warehouse.

7. The method for monitoring concrete temperature at the bottom hole of an arch dam in high temperature season according to claim 1 is characterized in that: The steps for analyzing the test data in step 6 are as follows: Step 6-1, select the temperatures of the measuring points at 0.2m, 0.45m, and 0.7m from the top surface of the flow channel bottom plate and the measuring points at 0.1m, 0.2m, 0.4m, 0.6m, and 0.8m from the flow channel side wall surface, take the average value of the temperature at each distance as the final temperature measurement data, and draw the concrete temperature duration curves at different depths from the top surface of the bottom plate and the flow channel side wall; Step 6-2, select the temperatures of the measuring points at 0.2m, 0.45m, and 0.7m from the top surface of the flow channel bottom plate and the measuring points at 0.1m, 0.2m, 0.4m, 0.6m, and 0.8m from the flow channel side wall surface, draw a curve of the temperature variation at different positions versus time, and obtain the variation law of the daily cooling rate of concrete; Step 6-3: In combination with the technical standards for temperature control during construction, evaluate the temperature control effect of the maximum concrete temperature and cooling rate in steps 6-1 and 6-2 on the bottom hole to provide a reference for subsequent construction.

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