PERMEABILITY TEST: FALLING HEAD METHOD

 

Equipment

1.) Permeameter with its accessories: The permeameter is made of non-corrodible material with a capacity of 1000 ml, with an internal diameter of 100±0.1 mm and effective height of 127.3± 0.1 mm.

2.) Standard soil specimen, 3.) Deaired water, 4.) Balance to weigh up to 1 gm,

5.) I.S sieves 4.75 mm and 2 mm, 6.) Mixing pan, 7.) Stop watch, 8.) Measuring jar,

9.) Meter scale, 10.) Thermometer, 11.) Container for water, 12.) Trimming knife etc.

 

Experimental Procedure

1.        Prepare the soil specimen as specified.

2.        Saturate the specimen preferably by using Deaired water.

3.        Assemble the permeameter in the bottom tank and fill the tank with water.

4.        Inlet nozzle of the mould is connected to the stand pipe. Allow the water to flow until steady flow is obtained.

5.        Note down the time interval ‘t’ for a fall of head in the stand pipe ‘h’.

6.        Repeat step 5 three times to determine ‘t’ for the same head.

7.        Find ‘a’ by collecting ‘q’ for the stand pipe. weigh it correct to 1 gm and find ‘a’ from q/h=a.

 

Observation and Recording:

                Sample No. …………………                                               Moulding water content: ………………..

                Dry Density: ……………….                                               Specific Gravity: ………………………..

                Void ratio ………………….

 

 

 

1st set

2nd set

3rd set

1.

Area of stand pipe (dia. 5 cm)                 

a (cm)

 

 

 

2.

Cross sectional area of soil specimen     

A (cm2)

 

 

 

3.

Length of soil specimen                          

L (cm)

 

 

 

4.

Initial reading of stand pipe                      

h1 (cm)

 

 

 

5.

Final reading of stand pipe                      

h2 (cm)

 

 

 

6.

Time                                                          

t (sec)

 

 

 

7.

Test temperature                                      

T (oC)

 

 

 

8.

Coefficient  of permeability at …….. oC 

     k = 2.303.a.L.(log10 h1/h2) / (A.t)

k (cm/sec)

 

 

 

9.

Average Permeability, kt

kt (cm/sec)

 

10.

­Coefficient of permeability at 27o C  :
            k27 = kt x ht / h27                (See Table IV)

k27 (cm/sec)

 

                               

General Remarks:

1.        During test there should be no volume change in the soil, there should be no compressible air present in the voids of soil i.e. soil should be completely saturated. The flow should be laminar and in a steady state condition.

2.        Coefficient of permeability is used to assess drainage characteristics of soil, to predict rate of settlement founded on soil bed.

3.        Magnitudes of permeability:

High permeability:                k > 10-1 cm/sec

Medium permeability:          k » 10-1 cm/sec

Low permeability: k < 10-1 cm/sec