CN101799430A - Built-in anti-seepage geomembrane damage monitoring method based on optical fiber temperature-measurement principle - Google Patents

Abstract

The invention relates to a solution for quickly locating damage of a geomembrane inside an anti-seepage engineering, and belongs to the technical field of water conservancy engineering (civil engineering)-anti-seepage. This method is to combine the continuous optical fiber and the geomembrane into one, the optical fibers are evenly arranged in the shape of a snake on the geomembrane, and the distance between the optical fibers is less than or equal to twice the temperature sensitive distance of the optical fiber; the geomembrane is used as the anti-seepage material, and Make the optical fiber optical path of the entire anti-seepage area open; lead the end point of the optical fiber to the optical fiber temperature measurement and detection device, and cover the protective layer of the geomembrane; according to the layout design of the anti-seepage project, establish the relationship between the length L of the optical fiber and the XY coordinate value of the anti-seepage surface The conversion between the two uses an optical fiber temperature measurement device to monitor the temperature of each part of the geomembrane, and the area where the temperature contrast is abnormal is judged to be the leakage site, and the most abnormal temperature is the center of the geomembrane damage. The method solves the problem of damage location of the geomembrane, and can obviously improve the safety performance of the dam with the geomembrane as the anti-seepage body.

Description

A built-in anti-seepage geomembrane damage monitoring method based on the principle of optical fiber temperature measurement

technical field

The invention relates to a method for locating a damaged geomembrane inside an anti-seepage engineering, and belongs to the technical field of water conservancy engineering (civil engineering)—anti-seepage

Background technique

Seepage damage is the most important cause of dam collapse disasters. Among the constituent materials of the anti-seepage body, geomembrane is cheap, has good anti-seepage effect, and has the obvious advantage of adapting to the deformation of the dam body and foundation. It is almost the preferred material in earthquake-prone areas, especially in karst landform areas. Since the relevant technology was introduced into my country in the 1970s, a complete set of standards and procedures for geomembrane production, inspection, anti-seepage body design, construction quality control, and acceptance has been formed, and the overall life span has also been significantly improved—life expectancy It has been nearly a hundred years. All countries in the world are strongly recommending geomembrane as an anti-seepage material in various design specifications and construction specifications. my country's former Economic and Trade Commission and the Ministry of Water Resources have organized more than 50 demonstration projects in order to promote its application scope as soon as possible. However, the tensile and shear strength of the geomembrane is low. Once the geomembrane in the dam is damaged by the environment, water and soil organisms, and external force of the liner, its major defect of "difficult to determine the cracking position" will immediately appear. Due to the rapid diffusion of seepage water in the soil after passing through the geomembrane, it is impossible to determine the damage site even if the monitoring instrument is embedded in the embankment. This shortcoming makes the short-term emergency repair opportunity in the early stage of cracking lose, which leads to the rapid expansion of tearing and seepage damage, which seriously threatens the safety of the embankment. Therefore, the application of geomembrane in dams, especially medium and high earth-rock dams has been greatly restricted.

The statistics of the relevant departments show that because the geomembrane in the dam is difficult to be detected in time and repaired after being damaged, most projects (even small projects) are reluctant to use geomembrane, preferring to carry out a large-scale repair at a doubled cost. Grout seepage prevention. Many areas in my country are earthquake-prone areas. Although the magnitude or damage intensity is usually not large, the anti-seepage body formed by grouting is thin and brittle, and has poor affinity with the dam body material, so it is bound to break when the dam is deformed by earthquakes. Or contact zone segregation. As a result, a vicious cycle of grouting-leakage-re-grouting-re-leakage has appeared in many places. The grouting of millions to tens of millions of dollars each time can only make the seepage index of the dam within 2 to 5 years meet the corresponding standards. Take the Longlin Reservoir in Dayao County, Yunnan, which the applicant undertook to appraise as an example: the dam grouting was completed in May 2001, and the seepage index in the flood season of that year passed the inspection; immediately after the earthquake in July 2003, a larger seepage than before the grouting was found, and There is a dangerous situation of flowing soil, and it is identified as a three-type dangerous dam by safety appraisal. More than 2 million yuan of national debt funds have only "reinforced" this small (one) type reservoir dam for two years, and the cost of irrigation water has increased sharply to an unacceptable 3000-5000 yuan/m ³ .

In contrast, geomembrane is a flexible material, which has a strong adaptability to the deformation of the dam foundation. Its aging speed can meet the economic life requirements of most water conservancy projects without being pierced or torn by external forces. It is especially suitable for It is used as a cheap and high-quality anti-seepage blanket in earthquake-prone areas and karst areas. For example, Kunming Jindian Reservoir area and Cuihu Lake and other places used to leak a lot of water for a long time. Concrete plugs, backfilling concrete, filling grouting, etc. were used many times to solve the problem. Finally, geomembrane was used as a basin-type bedding to stop the leakage. anti-seepage target. During the national flood season in 1998, geomembrane was also the most commonly used measure for anti-seepage and emergency rescue in various places. Once the problem of "damage location" of the geomembrane is solved, the safety performance of the geomembrane will be improved, the cost-effectiveness of the anti-seepage body will be improved, and the cost of the dam will be significantly reduced; and valuable repair time will be gained for the dam after the geomembrane is damaged, effectively To prevent disasters caused by dam failure.

Data retrieval shows that domestic and foreign research on geomembrane-related fields mainly focuses on two aspects: ① research on the laying process, such as the screening, layer, thickness of the cushion, and the relationship between water pressure, corner water interception measures, etc.; ②Research on material modification, such as trying to increase the toughness and plasticity of the geomembrane, changing the thickness, prolonging the life and anti-aging, etc. However, in terms of "determination of the damaged part of the built-in geomembrane", no research or achievement information has been retrieved.

"Distributed optical fiber temperature measurement technology" has matured and is especially suitable for projects that require large-scale intensive monitoring. It has been successfully applied to the monitoring of hydration heat of concrete dams and the temperature monitoring of high-voltage cables. Temperature can be transmitted through saturated or unsaturated soil, and the change of temperature in the formation is continuous. Water is most dense at 4°C, so the water temperature at the bottom of the reservoir is usually cooler; the temperature distribution in the formation is just the opposite, with a steady increase in temperature with increasing depth. Many studies have proved that the abnormal low temperature found in the dam or dam foundation is related to the concentrated leakage of reservoir water, so the temperature can be used to detect the concentrated leakage caused by the damage of geomembrane. In addition, the "reinforcing" effect of the flexible optical fiber can also significantly improve the performance of the geomembrane.

Contents of the invention

The technical problem solved by the invention is to provide a method for monitoring the damage of the built-in anti-seepage geomembrane and quickly determining the location of the damage. The method is mature and reliable in principle, easy to operate, and quick in quantitative analysis and calculation.

The solution adopted to solve the technical problem of the present invention is: combine the continuous optical fiber and the geomembrane into one, the optical fibers are evenly arranged in a serpentine shape on the geomembrane, and the distance between the optical fibers is less than or equal to twice the temperature sensitive distance of the optical fibers; Use geomembrane as the anti-seepage material, and make the optical fiber optical path in the entire anti-seepage area conduct; lead out the end point of the optical fiber to the optical fiber temperature measurement and detection device, and cover the protective layer of the geomembrane; according to the layout design of the anti-seepage project, establish the length L of the optical fiber The conversion formula between the XY coordinate value of the anti-seepage surface, the temperature of each part of the geomembrane is monitored by an optical fiber temperature measurement device, and the area where the temperature contrast is abnormal is judged as the leaking part, and the place with the largest temperature anomaly is the geomembrane Broken central location.

Concrete technical scheme of the present invention also includes:

The diameter of the optical fiber is 4 μm to 50 μm, and the arrangement distance between the optical fibers is ≤1m. The optical fiber can be sandwiched in the geomembrane or pasted on one side of the geomembrane, or the optical fiber will be arranged in a temperature sensitive area near the geomembrane; The geomembrane is laid along the axis of the dam. It is not advisable to cut the optical fiber at the side. Instead, the geomembrane with excess width is embedded and laid toward the anti-seepage boundary (dam crest, dam foundation, etc.).

At the edge of each geomembrane, a 0.2m~0.5m non-optical fiber overlapping area should be reserved for mutual welding or bonding, and the optical fiber head and tail joints of each geomembrane should be welded by connecting optical fibers outside the membrane to form a Fully-conducted optical path.

As the anti-seepage main body of the water-retaining building, the damaged part of the geomembrane will have concentrated leakage. Repeated experiments at various ambient temperatures and ambient humidity have proved that the flow of water in the damaged part of the geomembrane will inevitably lead to a significant difference in temperature between the location before the damage and the nearby undamaged parts. Therefore, the damaged location of the geomembrane can be determined by temperature comparison. The error of optical fiber temperature measurement is ≤0.03℃, and the positioning error of built-in geomembrane damage is ≤0.3m. The above indicators are sufficient to meet the needs of anti-seepage engineering safety and reinforcement.

The function of each important composition of the present invention is:

(1) Optical fiber geomembrane: The geomembrane is used as the anti-seepage main body in the water retaining project; the optical fiber geomembrane uses the distributed optical fiber as a dense sensor to monitor the temperature change of each point in the geomembrane, and "temperature contrast abnormal "As the basis for judging the rupture of geomembrane.

(2) Judging that the temperature contrast is abnormal: the damaged part of the geomembrane will have concentrated leakage, and the flow of the water body will cause the temperature here to be significantly different from that before the damage and from the nearby undamaged parts. The error of optical fiber temperature measurement is ≤0.03°C, and the location of geomembrane damage is determined by abnormal temperature comparison.

(3) Optical fiber temperature measurement system: Using optical fiber as a sensor, the temperature value of each measuring point in the geomembrane is collected repeatedly, and automatically compared with the previous temperature of the point and the temperature of nearby measuring points, and abnormal temperature exceeding the threshold is found It will automatically alarm with sound and light, and display the length L of the optical fiber corresponding to the abnormal point. Existing optical fiber temperature measurement equipment such as Raman spectroscopy can be used.

(4) Coordinate conversion of abnormal points: Based on the construction design of geomembrane laying at each construction site, the length L of the optical fiber from the abnormal point of temperature comparison to the origin is converted into the XY coordinate value of the anti-seepage surface, so that the positioning data and engineering and technical personnel Consistent practice allows for quick and accurate location of geomembrane damage.

Working principle of the present invention:

(1) Anti-Stokes light intensity is closely related to temperature

Monochromatic (single frequency) light will undergo molecular scattering in the optical fiber, thereby producing a Raman spectrum with a "different frequency" from the source light. Among them, the component with a frequency lower than the source light is also called Stokes light, and the component with a frequency higher than the source light is also called anti-Stokes light; the spectral lines on both sides with a large frequency difference from the source light are called Dala Mann spectrum. The light intensity quotient of anti-Stokes light and Stokes light in the Raman spectrum is closely related to the vibration energy level of the molecule - temperature, and there are already mature theories and calculation formulas.

(2) The scattering and speed of light are closely related to the optical fiber

The material and microscopic structure of the optical fiber have a direct impact on the Raman spectrum and propagation speed. As long as the speed of light in the optical fiber is calibrated on site, the interval of the measuring points is set, and the length of the optical fiber at each measuring point can be easily calculated according to the propagation time of the Raman spectrum.

(3) Optical fiber temperature measurement technology has matured

There are successful applications of optical fiber temperature measurement technology in many fields. For example: in the power grid system, use optical fiber temperature measurement to monitor the abnormal temperature of ultra-high voltage transmission lines; Locating the location of mesoscopic leak channels; and the list goes on.

(4) The temperature change of each measuring point of the built-in geomembrane is significantly related to the concentrated leakage

The damaged part of the geomembrane will have concentrated leakage, and the flow of the water body will cause the temperature here to be significantly different from that before the damage and from the nearby undamaged parts. The temperature measurement error of the optical fiber is ≤0.03°C, and the location of the geomembrane's damage can be determined through the abnormal temperature comparison.

The beneficial effects of the present invention are:

(1) Provides a positioning method for the damaged location of the built-in geomembrane

After the geomembrane in the dam is damaged, it is difficult to detect and fix it. This shortcoming will lose the repair time, lead to the rapid expansion of seepage damage and even dam failure. Therefore, the application of geomembrane has been greatly restricted all over the world. The invention introduces the mature "optical fiber temperature measurement" principle into the anti-seepage technology of geomembrane, combines the innovation of optical fiber geomembrane and the practice of anti-seepage laying, and fundamentally solves the problem that the built-in geomembrane of the anti-seepage project cannot be located after it is damaged. Tests show that the positioning error of the invention is lower than 0.3m, which is sufficient to meet the requirements of engineering safety and reinforcement.

(2) Promote the use of geomembrane, save engineering cost, reduce and prevent disasters

Seepage damage is the most dangerous situation of dams and the main cause of collapse. Geomembrane is a flexible and cheap anti-seepage material recommended by national regulations. Its expected life can meet the requirements of engineering economic life. In earthquake-prone areas, especially in karst landforms Area is almost the preferred material, and the Ministry of Water Resources has organized several demonstration projects to promote it. my country is the country with the largest number of dams and dangerous projects in the world. The government allocates tens of billions of funds every year for the reinforcement of water conservancy projects. Since this invention solves the key problem of "damage location of built-in geomembrane", as a cheap and high-quality anti-seepage body, the application scope of geomembrane will be rapidly expanded, gradually replacing filling grouting, curtain grouting, and even high-pressure rotary jetting High-priced structures such as grouting and anti-seepage walls, thus generating significant economic benefits under the premise of ensuring safety. This technology is of great significance for improving the safety performance of the geomembrane, improving the cost performance of the anti-seepage body, increasing the stability of the dam slope, and obviously saving the cost of reinforcement of the dam. The repair time can effectively reduce the occurrence of dam collapse disasters.

(3) Proposed the innovation of "optical fiber geomembrane"

Thanks to the rapid development of the communication field, the diameter of the optical fiber has reached 4μm, and the transparency is sufficient. There has been an example of using the G652 optical fiber to successfully measure the temperature of 30km in length and 0.5m in the surrounding area. The flexibility also fully meets the "fiber" attribute. The serpentine implantation of optical fiber into various geomembranes not only arranges dense monitoring sensors, but also has the effect of "reinforcement" to improve the mechanical properties of traditional geomembranes.

Description of drawings

Fig. 1 is the structural representation of fiber optic geomembrane of the present invention;

Fig. 2 is a schematic diagram of the laying state of the geomembrane of the present invention.

In the figure: geomembrane 1, optical fiber 2, anti-seepage boundary 3, overlapping welded film area 4, external connecting optical fiber 5, dam crest 6.

Detailed ways

(1) Manufacture of fiber optic geomembrane

Referring to FIG. 1 , in the production process of a traditional geomembrane 1 , an optical fiber 2 is arranged in a serpentine manner, thereby obtaining an "optical fiber geomembrane". Let the width of the geomembrane be B, and leave δ (recommended 0.25m) at the edge of the geomembrane as the area without overlapping welding (bonding) of optical fibers, then the single length of the optical fiber Γ ₁ = B-2δ; the optical fiber is 0.5 to both sides The temperature change within m is more sensitive, so the distance between temperature-measuring optical fibers Γ ₂ ≤1m (recommended 0.6m).

(2) laying optical fiber geomembrane

Referring to Fig. 2, during the construction process of the anti-seepage project, the above-mentioned optical fiber geomembrane 1 is used as the anti-seepage material, and the construction is carried out according to the current specification. In order to avoid too many optical fiber joints and cumbersome positioning calculations, it is recommended to lay along the axis of the dam; it is not suitable to cut the optical fiber 2 on the side, and it is recommended to embed the geomembrane with excess width to the anti-seepage boundary 3 (dam crest, dam foundation, etc.).

(3) Connect the light path between the spectral sensor and the device

After the laying is completed, according to the specification of the communication optical fiber, use the external connecting optical fiber 5 to weld the head and tail of the optical fiber 2 of each geomembrane 1 to form a fully conductive optical path. Referring to Fig. 2, it is assumed that the lengths of the external connecting optical fibers 5 are S ₁ , S ₂ , . . . respectively. Lead out the starting point of the optical fiber, connect the optical path to the Raman spectroscopy temperature measurement system, and then cover the protective layer of the geomembrane (dam shell soil material, dam slope protection stone material, etc.) according to the current specifications.

(4) Establish coordinate transformation formula

Referring to Figure 2, according to the layout design of the anti-seepage project, the conversion formula between the optical fiber length L and the XY coordinate value with the entrance of the temperature measurement system as the origin O is derived by applying conventional mathematical transformation.

(5) Temperature monitoring

Set the measuring point interval on the optical fiber (recommended 0.01m), and calibrate the project using the speed of light in the optical fiber. Use an optical fiber temperature measurement system (Raman spectroscopy, etc.) to automatically monitor the temperature change of each measuring point of the optical fiber in the geomembrane, and automatically compare it with the previous temperature of the point and the temperature of nearby measuring points; If the temperature is abnormal, it will automatically sound and light alarm, and display the length L of the optical fiber from the abnormal point to the entrance of the temperature measurement system. Suggested temperature abnormal threshold: 0.5min interval, ≥±0.6°C compared with the same measuring point, ≥0.2°C compared with nearby measuring points.

(6) Coordinate transformation of positioning value

Based on the conversion formula established in step (4), the length L of the optical fiber at the maximum abnormal point in the temperature contrast area is converted into the XY coordinate value of the geomembrane damage position.

For example, suppose point H in Figure 2 is perforated by the geomembrane and the temperature exceeds the threshold, the optical fiber temperature measurement system alarms and displays that the L values of the two optical fiber abnormal points are L ₁ =1089.00m and L ₂ =1095.10m respectively, and the abnormal temperature increases The quantities are ΔT ₁ =0.58°C and ΔT ₂ =1.89°C, respectively. Then the coordinates of the damaged geomembrane in the dam can be determined through the following calculations.

① Assume that it is known from the design and construction records: geomembrane width B = 6m; edge overlapping area without optical fiber δ = 0.25m; 5 pieces of geomembrane (from top to bottom) are respectively long C ₁ = 120m, C ₂ = 113m , C ₃ =103m, C ₄ =89m, C ₅ =70m; the lengths of connecting optical fibers outside the film (from top to bottom) are S ₁ =16m, S ₂ =16m, S ₃ =9m, S ₄ =19m. The distance between optical fibers in the film is Γ ₂ =0.6m, and the single fiber length Γ ₁ =B-2δ=5.5m.

② Completion acceptance calculation: the length D of the optical fiber in each geomembrane (from top to bottom)

D ₁ =(C ₁ -2δ)/Γ ₂ ×(Γ ₁ +Γ ₂ )+Γ ₁ =1220.42m

D ₂ =(C ₂ -2δ)/Γ ₂ ×(Γ ₁ +Γ ₂ )+Γ ₁ =1149.25m

D ₃ =(C ₃ -2δ)/Γ ₂ ×(Γ ₁ +Γ ₂ )+Γ ₁ =1047.58m

D ₄ =(C ₄ -2δ)/Γ ₂ ×(Γ ₁ +Γ ₂ )+Γ ₁ =905.25m

D ₅ =(C ₅ -2δ)/Γ ₂ ×(Γ ₁ +Γ ₂ )+Γ ₁ =712.08m

③Coordinate transformation of abnormal points in optical fiber monitoring: L ₁ <L ₂ <D ₁ , so the two temperature abnormal points are located in the geomembrane with length D ₁ .

Because int[L ₁ /(Γ ₁ +Γ ₂ )]=178, int[L ₂ /(Γ ₁ +Γ ₂ )]=179, the remainders are all 0.52<Γ ₁ , which has no effect on X value. Therefore X ₁ =int[L ₁ /(Γ ₁ +Γ ₂ )]×Γ ₂ =106.80m

X ₂ =int[L ₂ /(Γ ₁ +Γ ₂ )]×Γ ₂ =107.40m

Because the number of fiber intervals corresponding to L ₁ and L ₂ is an even number of 178 and an odd number of 179, the remainder 0.52 will affect the Y value from top to bottom: Y ₁ = 0.52m; Y ₂ = Γ ₁ -0.52 = 4.98m .

④ Calculate the coordinates of the geomembrane perforation point H: the distance from point H to the abnormal temperature point of the optical fiber on both sides is approximately inversely proportional to the increment ΔT of the abnormal temperature.

(H _X -X ₁ ): (X ₂ -H _X )≈ΔT ₂ :ΔT ₁ ; (H _Y -Y ₁ ):(Y ₂ -H _Y )≈ΔT ₂ :ΔT ₁

Bringing in the data obtained earlier, the coordinates of the geomembrane perforation point H can be solved as follows: H _X ≈ 107.26m, H _Y ≈ 3.93m.

Claims (3)

1. A built-in anti-seepage geomembrane damage monitoring method based on the principle of optical fiber temperature measurement, which is characterized in that: continuous optical fibers and geomembrane are combined into one, the optical fibers are evenly arranged in a snake shape on the geomembrane, and the distance between the optical fibers Less than or equal to twice the temperature sensitive distance of the optical fiber; use the geomembrane as the anti-seepage material to conduct the optical path of the optical fiber in the entire anti-seepage area; lead the end point of the optical fiber to the optical fiber temperature measurement and detection device, and cover the protective layer of the geomembrane; press the anti-seepage For the layout design of the seepage project, establish the conversion formula between the length L of the optical fiber and the XY coordinate value of the anti-seepage surface, monitor the temperature of each part of the geomembrane with an optical fiber temperature measurement device, and judge the area where the temperature contrast is abnormal as the leaking part , locate the center of the geomembrane damage where the temperature anomaly is the largest. 2. The built-in anti-seepage geomembrane damage monitoring method based on the principle of optical fiber temperature measurement according to claim 1, characterized in that: the diameter of the optical fiber is 4 μm to 50 μm, the arrangement distance between the optical fibers is ≤ 1m, and the optical fiber is sandwiched In the geomembrane or pasted on one side of the geomembrane, or arranged in the temperature-sensitive area near the geomembrane; the geomembrane is laid along the axis of the dam, and the excess width of the geomembrane is embedded in the anti-seepage boundary at the anti-seepage boundary. . 3. The built-in anti-seepage geomembrane damage monitoring method based on the principle of optical fiber temperature measurement according to claim 2, is characterized in that: a non-optical fiber overlapping area of 0.2m～0.5m should be reserved at the edge of each piece of geomembrane, And the optical fiber connected outside the membrane is used to weld the optical fiber head and tail joints of each geomembrane.

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