Double loop water injection test device for Beijing water conservancy and hydropower engineering test pit

Double loop water injection test device for water conservancy and hydropower engineering test pits

Double ring method for measuring field permeability coefficient

1、 Experimental purpose and significance

Trial pit double loop water injection test deviceIt is a commonly used and simple method for determining the permeability coefficient of unsaturated loose rock layers in the field, and the experimental results are closer to the actual situation. It is very important to use this experimental data to study regional water balance, as well as the leakage of reservoirs, irrigation areas, and channels.

2、 Experimental methods

The commonly used methods for determining the permeability coefficient of unsaturated loose rock layers in the field are the test pit method, single ring method, and double ring method. The double ring method has high accuracy.

3、 Experimental principle

Within a certain hydrogeological boundary, water is injected into loose rock layers on the surface to stabilize the amount of infiltration, that is, when the amount of infiltration per unit time is approximately equal, the permeability coefficient (K) value is then calculated using the principle of Darcy's law.

Two iron rings with a height of about 20cm and diameters of 0.25m and 0.5m are embedded at the bottom of the pit. During the experiment, water is injected into both the inner and outer iron rings simultaneously, and the water column of the inner and outer rings is kept at the same height, preferably 0.1m. Due to the constraint effect of the outer ring permeability field, the water in the inner ring can only infiltrate vertically, thus eliminating the error of lateral seepage,

This method has higher accuracy than both the trial pit method and the single ring method.

4、 Experimental instruments

Double ring, shovel, ruler, bucket, tape, rubber pipe

5、 Experimental steps

(1) It is better to choose a testing site where the diving depth is greater than 5m. If the diving depth is less than 2 meters and the measured permeability coefficient is not accurate due to the short infiltration path, do not use the infiltration test.

(2) Install the testing device according to the schematic diagram of the double ring method water seepage test.

(3) Inject water into the inner and outer iron rings, and keep the water column of the inner and outer rings at the same height, preferably 0.1m.

(4) Observe the amount of infiltration water at regular intervals. At the beginning, due to the large amount of infiltration, the observation interval should be short. Later, observations can be made at certain time intervals, such as every 10 minutes, until the amount of infiltration per unit time reaches a relatively stable level, and then continue for 2-4 hours to end the experiment.

6、 Precautions

(1) Keep the water column of the inner and outer rings at the same height of 0.1m at all times.

(2) When filling the water supply bottle with water, do a good job in converting the water volume