Hokkaido Poracon Co. Ltd.

Validity of on-site percolation test

The nature of the soil is a key factor in calculating the necessary scale of infiltration facilities.
We use a simple test and analysis method devised by Public Works Research Institute of Ministry of Land, Infrastructure, Transport and Tourism (so-called PWRI method).
Since 1984, we have experiences in more than 500 sites including public properties.
By conducting on-site percolation tests, accidents caused by risky designs or overdesigns can be avoided, which results in cost reduction.
Infiltration coefficient can be obtained only by analysis in this method. When this coefficient is used, infiltration capacity tends to be bigger than permeability coefficient.

Test by “PWRI method”

Test method to make water permeate the bottom of a cylinder with a diameter of 30 cm

• Infiltration coefficient and permeability coefficient can be obtained through analysis.
• Infiltration surface can be easily inspected and maintained.
• The method can be used in all kinds of soil.
• The coefficient can be converted to water depth of infiltration facilities.
• The test can be conducted on a site where the canonical structure of the facility is not yet completed.
• Permeability of infiltration trench can be calculated.
• Coefficients obtained by the analysis (PWRI method)

Other Test Methods

Borehole Method has been used as a test method in soil engineering field. However, this method uses a auger hole and a water-impermeable film can be formed on the hole wall or the hole bottom during the excavation and the permeability coefficient may be undercalculated. This method cannot be used in the sand and the gravel ground as the hole wall may be destroyed in boring. The structure of this experiment is not always suitable for designing infiltration facilities, and much care is needed as the test method and the analysis method is applicable to not all the cases.

Fixed Water Level Method

Water is injected into a cylinder up to the set water level, and the amount of injected water is adjusted so that the water level does not change. The amount of injected water is measured at regular intervals, and injection is continued until the amount of injected water becomes stable.
The problems regarding this method are as follows; a large amount of water is required; a device to measure the amount of injected water is required; it needs to be monitored continuously.

Flexible Water Level Method

Water is injected into a cylinder up to the set water level, and the level of water reduction after the stop of injection is measured.

Other Test Methods

Quasi Fixed Water Level Method

1. Water is injected into a cylinder up to a set water level.
2. Water injection is stopped and water level after a certain interval is measured.
3. After the water level is measured, water is injected again up to the set water level.
4. The second and third process is repeated.

Fixed Amount Injection Method

A fixed amount of water is injected into a cylinder for a long period of time, And the water level is measured when it becomes stable.