Ensuring Water Integrity in Concrete Structures: A Practical Guide

Water leakage in structures designed to contain water can be a real headache, causing damage and raising concerns about safety. To avoid these issues, a thorough watertightness test is crucial. Let’s delve into the details of how you can conduct such tests on reinforced concrete structures.

Understanding Watertightness

In essence, a watertightness test seeks to uncover potential defects that may lead to water leakage in water-containment structures. Factors such as the type of linings, the location of the structure, and the ambient temperature all play a role in determining the watertightness of the structure.

Factors Influencing Test Results

Several factors can affect the outcome of the watertightness test. These include structural deflection, water absorption, temperature variations, precipitation, and evaporation. It’s essential to consider these variables and make necessary corrections to the test results.

The Testing Process

Before we jump into the testing process, it’s important to ensure the structure is ready. Here are some preparatory steps and precautions to keep in mind:

Test Preparations and Precautions

1. Zero Water Loss: Ensure that the testing procedure doesn’t lead to any water loss in the structure.
2. Structural Integrity: The water-containment structure must be structurally sound and capable of withstanding the hydrostatic pressure from the test water.
3. Visible Inspection: Optimize visibility by avoiding backfill material around the structure.
4. Groundwater Level: Ensure that groundwater is below the floor of the structure.
5. Monitoring Outlets: Keep an eye on outlets, underdrain lines, and closed valves for any potential issues.
6. Sealing: Seal all piping, channels, and conduits before starting the test.

Filling and Inspection

1. Structure Strength: Fill the structure with water once it has gained sufficient strength to support water pressure.
2. Seal Inspection: Check joints for visible leakage during the filling process.
3. Observation: Monitor outlets for watertightness and underdrain outlets for any increase in flow.
4. Immediate Action: If any leakage or issues are observed, address them before initiating the test.
5. Retesting: Allow for retesting if external factors like unusual precipitation compromise the initial test results.

Factors Affecting Watertightness Test Result

1. Water Absorption

New or long-unused water-containment structures tend to absorb water during and after filling. To mitigate this, wait for at least three days after filling before starting the test. For more stringent criteria, consider extending this waiting period to seven days or more.

2. Structural Deflection

As water is introduced into the structure, it deflects under the water pressure. To account for this, wait for three days after filling to allow the structure to settle. Fill the structure at a maximum rate of 1.2 m/hour to let air escape freely.

3. Temperature

Water volume changes with temperature fluctuations. Regularly measure and record water levels to account for temperature variations during the test.

4. Evaporation and Precipitation

In uncovered structures in semiarid or arid regions, evaporation and precipitation can impact water levels. Correct test results for these effects by using a calibrated, partially filled container.

Watertightness Test Procedure

1. Water Level Measurement: Measure water levels at specific points, either 180 degrees apart or 90 degrees apart from each other.
2. Temperature Recording: Record water temperatures at designated depths.
3. Evaporation and Precipitation Monitoring: Use a calibrated container to measure evaporation and precipitation.
4. Visual Inspection: Examine the exterior for visible leakage.
5. Test Duration: Continue the test until a 12.7 mm drop in water surface is observed.
6. Post-Test Measurements: Measure water levels again and calculate leakage, correcting for evaporation, precipitation, and temperature.

Criteria for Test Results

The structure fails the test if:

• The leakage rate exceeds the values provided in Table-1.
• Water is observed flowing from positions other than the underdrain system.
• Moisture, excluding precipitation or condensation, can be transferred to a dry hand from exterior surfaces.

Watertightness Test Criteria (Table-1)

Type of Structure	Side Water Depth (m)	Maximum Leakage Rate (% of Water Volume in 24h)
Unlined Concrete	7.62 or less	0.1
Lined Wall	9.14 or less	0.06
Lined Floor	9.14 or less	0.04
Fully Lined	–	0.025

Note: Adjust allowable leakage rate for structures with greater side water depths using engineering judgment, with special consideration for tank floor and concrete joints.

By adhering to these guidelines, you can conduct a thorough watertightness test on reinforced concrete water-containment structures, ensuring the integrity and longevity of these essential constructions.