PERMEABILITY TEST: CONSTANT HEAD METHOD

 

Equipment

1.        Permeameter mould of non-corrodible material having a capacity of 1000 ml, with an internal diameter of 100 ±0.1 mm and internal effective height of 127.3± 0.1 mm.

2.        The mould shall be fitted with a detachable base plate and removable extension counter.

3.        Compacting equipment: 50 mm diameter circular face, weight 2.76 kg and height of fall 310 mm as specified in I.S 2720 part VII 1965.

4.        Drainage bade: A bade with a 12 mm thick porous disc having its permeability 10 times of that for soil.

5.        Drainage cap: A porous disc of 12 mm thick having a fitting for connection to water inlet or outlet.

6.        Constant head tank: A suitable water reservoir capable of supplying water to the permeameter under constant head.

7.        Graduated glass cylinder to receive the discharge.

8.        Stop watch to note the time, and a meter scale to measure the head differences and length of specimen.

 

Test Procedure

1.        For the constant head arrangement, the specimen shall be connected through the top inlet to the constant head reservoir.

2.        Open the bottom outlet.

3.        Establish steady flow of water.

4.        The quantity of flow for a convenient time interval may be collected.

5.        Repeat three times for the same interval.

 

Observation and Recording

The flow is very low at the beginning, gradually increases and then stands constant. Constant head permeability test is suitable for cohesionless soils. For cohesive soils falling head method is suitable.

 

PRESENTATION OF DATA

The coefficient of permeability is reported in cm/sec at 27o C. The dry density, the void ratio and the degree of saturation shall be reported.The test results should be tabulated as below:

 

Permeability Test Record

Project:  ………                                                                                     Tested By: ……..

Location: ……..                                    Boring No. : ……..                                                Depth: ………                      

Details of sample

Diameter of specimen ………………. cm                                          Length of specimen(L)  …..…………… cm

Area of specimen (A) ………….…….cm2                                         Specific gravity of soil Gs ……………..

Volume of specimen (V) …………….cm3                                          Weight of dry specimen (Ws) …………. gm

Moisture content, w …..………..…… %                                          Dry density, rd = Ws / V = …………….. gm/cc

Void Ratio, e = Gs.rw / rd  - 1 = ………..                                           Saturation, S = Gs.w / e = ……………… %

 

Experiment No.

 

1

2

3

Discharge

Q (cm3)

 

 

 

Time t

(sec)

 

 

 

Height of water

h (cm)

 

 

 

Temperature

(oC)

 

 

 

Coefficient of Permeability at …… oC
                  k = Q.L / (A.h.t)

cm/sec

 

 

 

Average Permeability, kt

cm/sec

 

Permeability at 27 oC: k27 = kt x ht / h27      (See Table IV)

cm/sec