A watertightness test is performed on structures that contain water to determine if there are any undetected or incidental defects that may lead to water leakage. The outcome of the test depends on several factors, such as the type and location of the linings used, as well as the ambient temperature.
Various variables can influence the results of the test, including structural deflection, water absorption, temperature, precipitation, and evaporation. It is important to take these factors into account and adjust the test results if necessary.
To ensure accurate results, the watertightness test is carried out after the water-containment structure has been filled with water for at least three days. This helps to eliminate the impact of water absorption and structural deflection on the test results. After this period, the effect of temperature, precipitation, and evaporation on the test results is analyzed.
The test is designed to continue until there is a decline of 12.7 mm in water level due to leakage occurring at the maximum permissible rate. The test method described in this article is suitable for cast-in-place reinforced concrete structures used for containing water, such as tanks, reservoirs, basins, and conduits.
Test Preparations and Precautions
To ensure the integrity of a water-containment structure during testing, several precautions should be taken. First, it is important to avoid any loss of water during the test. Additionally, the structure must be structurally sound and able to withstand the hydrostatic pressure of the test water. To observe any leakage, it is recommended to avoid having backfill material around the structure and to ensure that the groundwater level is below the structure’s floor.
During the test, it is important to monitor the flow of the underdrain line located close to the containment structure. All temporary bulkheads, cofferdams, pipe blind flanges, and closed valves should be checked to ensure that they form a complete seal at these outlets. If possible, these outlets should also be observed during the test.
Before filling the structure with water, all piping, channels, and conduits must be sealed. Once the structure has gained adequate strength to support water pressure, it can be filled with water. During this process, it is important to inspect all joints for any visible leakage, monitor outlets for watertightness, and observe the underdrain outlet for any increase in the flow.
If any visible leakage or other issues are observed, they should be addressed before the test begins. Finally, retesting of the structure should be allowed in case the results of the initial test become unreliable due to external factors such as unusual precipitation.
Factors Affecting Watertightness Test Result
1. Water Absorption
Water-containment structures, particularly new ones or those that have not been drained for a long period, tend to absorb water during and after the filling process. This can negatively impact the watertightness test results. To mitigate the effects of water absorption, it is advisable to wait for at least three days after filling the structure with water before starting the test. This waiting period will allow the structure to stabilize and reach a state of equilibrium, which can help to produce more accurate test results.
This recommendation is particularly relevant for conventional concrete water-containment structures. However, for more stringent test criteria, it may be necessary to extend the waiting period beyond three days, up to seven days or more. This will ensure that the structure has reached a state of stability and can be tested under the most rigorous conditions possible.
In summary, waiting for a few days after filling a water-containment structure with water before conducting the watertightness test can help to reduce the effects of water absorption on the test results. The duration of the waiting period may vary depending on the type of structure and the test criteria, but a minimum of three days is generally recommended.
2. Structural Deflection
When a water-containment structure is filled with water, it tends to deflect or bend due to the pressure exerted by the water. This deflection can vary from the initial to the final state of the structure due to various factors like microcracking, creep, and relaxation. These factors can alter the stresses and strains experienced by the concrete used in the structure, which ultimately affects the deflection.
To obtain accurate and reliable test results, it is recommended to wait for a three-day interval between the time the water-containment structure is filled with water and the start of the test. This waiting period is necessary to remove the effect of structural deflection on the test, which can result in misleading outcomes.
Moreover, while filling the water containment structure with water, it is advisable to limit the maximum rate of filling to 1.2 meters per hour. This slow filling rate allows the air to escape freely from the structure, preventing any air pockets from forming, which could negatively impact the structure’s stability and accuracy of test results.
3. Temperature
When a water-containment structure is filled with water, it undergoes deflection or bending due to the pressure exerted by the water. This deflection can be affected by factors such as microcracking, creep, and relaxation, and can vary from the initial to the final state of the structure. These factors can change the stresses and strains experienced by the concrete in the structure, ultimately affecting the deflection. To ensure reliable test results, it is recommended to wait for a three-day interval between filling the water-containment structure with water and starting the test. This waiting period helps remove the effect of structural deflection on the test, which can lead to misleading outcomes.
To prevent any negative impact on the structure’s stability and the accuracy of the test results, it is advisable to limit the maximum rate of filling the water containment structure with water to 1.2 meters per hour. This slow filling rate allows the air to escape freely from the structure, preventing any air pockets from forming. Such air pockets could otherwise affect the structure’s stability and accuracy of the test results.
5. Evaporation and Precipitation
In semiarid or arid regions, water containment structures that have been uncovered and properly vented may experience significant fluctuations in water levels due to evaporation and precipitation. As a result, when conducting watertightness tests, it is important to account for any changes in water level resulting from these factors.
One way to measure this difference is by using a transparent, floating, open container that has been calibrated and partially filled. It should be positioned in the water containment structure away from the sides and any overhead obstruction that may block or shade the container.
The container should have enough freeboard to handle the precipitation from normal rainfall and avoid being overtopped by waves caused by wind. By monitoring the water level in this container, it is possible to determine the impact of evaporation and precipitation on the overall water level in the structure and make any necessary adjustments to the results of the watertightness test.
Watertightness Test Procedure
To test the water-containment structure, there are several steps that need to be taken. First, the level of water in the structure needs to be measured at two points that are 180 degrees apart or at four points that are 90 degrees apart from each other. Additionally, the temperature of the water needs to be recorded at around 45 cm below the water surface. If the leakage criteria are strict, the temperature should also be measured and recorded at a 1.5 m depth interval.
To measure evaporation and precipitation, a calibrated, partially filled open container should be placed in the uncovered water-containment structure. The water level in the container should be recorded at 24-hour intervals. The exterior of the structure should also be examined for any visible leakage.
The test should be continued until there is a 12.7 mm drop in water surface based on the maximum permissible rate of leakage. At the end of the test, the water level should be measured and recorded at the same locations where the first measurements were taken, as well as in the evaporation and precipitation container.
To determine if the structure has failed the test, there are certain criteria that must be met. If the leakage rate surpasses the values provided in Table-1, the structure has failed the test. Additionally, if flowing water is observed from positions other than the underdrain system, the structure has failed. Finally, if moisture can be transferred to a dry hand from the exterior surfaces, except from precipitation or condensation, the structure has also failed the test. If necessary, the leakage measurements should be corrected for evaporation, precipitation, and temperature.
Table-1: Watertightness Test Criteria
| Type of structure | Side water depth, m | Maximum leakage rate, percent of the water volume in 24 h |
| Unlined water-containment concrete structure | 7.62 or less | 0.1 |
| Concrete water-containment structures with lined wall | 9.14 or less | 0.06 |
| Concrete water-containment structures with lined floor | 9.14 or less | 0.04 |
| Fully lined concrete water-containment structure | – | 0.025 |
Note:
When it comes to concrete water-containment structures with side water depths exceeding those listed in Table-1, determining the allowable leakage rate requires the use of engineering judgment. This means that careful consideration must be given to the specific circumstances of the structure in question, particularly with regard to the tank floor and the type and location of concrete joints.
It is important to recognize that these structures may require unique considerations that are not accounted for in standard tables or guidelines. As such, a thorough analysis of the factors that may impact the potential for leakage is necessary to determine an appropriate allowable rate.
One key area of focus when evaluating the leakage rate for such structures is the tank floor. Given the increased water depth, there may be additional stress on the floor that could impact the overall integrity of the containment system. Additionally, the type and placement of concrete joints can also have a significant impact on the potential for leaks.
Given the importance of properly assessing the allowable leakage rate for concrete water-containment structures with greater side water depths, it is essential that engineering judgment be employed to ensure the safety and reliability of the structure. By taking into account all relevant factors and employing sound engineering principles, an appropriate allowable rate can be determined that mitigates the risk of leaks and ensures the long-term functionality of the system.
FAQs
Why are reinforced concrete structures tested for watertightness?
In order to verify that water is not able to seep through incidental defects and joints, reinforced concrete structures undergo watertightness testing. This process aims to ensure that the structure is able to withstand water pressure without allowing any water to pass through it. The testing is conducted to ensure that the concrete structure is able to fulfill its intended function without any compromise in its integrity. By detecting any water leakage, the testing can identify potential areas of weakness or damage that may require repair or maintenance to prevent any further deterioration.
What are the factors that influence watertightness test?
- The absorption of water by concrete structures is a common concern in construction. When water seeps into the concrete, it can cause a range of problems, such as degradation, cracking, and corrosion of the reinforcing steel. Therefore, it is important to understand the water absorption properties of concrete and take measures to prevent or mitigate its effects.
- Concrete structures are often subjected to pressure from water, such as in the case of flooding or water storage. This can cause deflection, or bending, of the structure, which can lead to structural failure if not properly addressed. It is important to test the deflection of concrete structures under the pressure of water to ensure their safety and stability.
- Temperature is a critical factor in the behavior of concrete structures. Extreme temperatures, such as those experienced in hot or cold climates, can cause the concrete to expand or contract, leading to cracking or other forms of damage. Proper consideration of temperature effects is essential for the design and maintenance of concrete structures.
- Evaporation and precipitation can also have significant effects on concrete structures. In hot and dry conditions, water can evaporate from the surface of the concrete, leading to shrinkage and cracking. On the other hand, excessive precipitation can cause water to penetrate into the concrete, leading to swelling and degradation. It is important to consider these factors in the design and maintenance of concrete structures to ensure their durability and longevity.
When should reinforced concrete structure be retested for watertightness?
The need to retest a reinforced concrete structure for watertightness arises if there are external factors that may have affected the reliability of the previous test results. This includes instances where there has been unusual precipitation, which can have a significant impact on the ability of the structure to prevent water infiltration.
In such cases, it is important to conduct a retest to ensure that the structure is indeed watertight and that it can effectively protect against water damage. The presence of external factors can cause the previous test results to be inaccurate or unreliable, which can have serious consequences if not addressed promptly. Therefore, it is essential to perform a retest to confirm the integrity of the structure and to identify any potential issues that may need to be addressed.
How many days are required to wait between the time the structure is filled with water and the beginning of testing?
It is recommended to wait for at least three days before beginning the testing process after filling a structure with water. This waiting period is essential as it allows time for the structure to settle and stabilize after being filled with water. If the testing process were to begin immediately after filling the structure with water, it could potentially lead to inaccurate results. This is because the water may cause the structure to shift or settle, which could impact the testing process’s accuracy. Therefore, it is crucial to wait for a minimum of three days to ensure the structure is stable and ready for testing.
When do concrete structures fail watertightness test?
When conducting a watertightness test on a concrete structure, there are certain conditions that indicate a failure. One of these is when the test results exceed the maximum allowable leakage rate. Another indicator of failure is when water flows from areas of the structure other than the underdrain system. Additionally, if moisture is transferred to a dry hand from exterior faces of the structure, apart from condensation and precipitation, this is also a sign of failure.
Concrete water tank structures require joints to accommodate movements caused by temperature changes, shrinkage, and settlement. These joints can be classified into two categories: working joints and construction joints. Working joints are intended to accommodate movements that occur during the service life of the structure, while construction joints are used to join new concrete to previously placed concrete. Proper spacing of these joints is important to ensure the overall stability and longevity of the structure.