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II
Falling Head
Permeability Test in Sand
Introduction
The procedure for conducting the constant head penneability tests in sand were discussed in the preceding chapter. The falling head penneability test is another experimental procedure to detennine the coefficient of penneability of sand.
Equipment
- Falling head penneameter
- Balance sensitive to 0.1 g
- Thennometer
- Stop watch
Falling Head Permeameter
A schematic diagram of a falling head penneameter is showb. in Fig. 11-1. This consists of a specimen tube essentially the same as that used in the constant head test. The top of the specimen tube is connected to a burette by plastic tubing. The specimen tube and the burette are held vertically by clamps from a stand. The bottom of the specimen tube is connected to a plastic funnel by a plastic tube. The funnel is held vertically by a clamp from another stand. A scale is also fixed vertically to this stand.
Procedure
Steps 1 through 9: ·Follow the same procedure (Le., Steps 1 through 9) as described in Chapter 10 for the preparation of the specimen.
75
76 Soil Mechanics Laboratory Manual
Water supply
Scale r^ L^ '- ------ - - - - - -- ---- ----- (^) ~ , , Burette
''" - ---- ----:-------- ~
l
h' ,
Plastic tube
S
"'- (^) Glass
land^ \\I^ ~^ tube
......': -,^ ':.":^ ~.
f
',",^ L ::s~i(:.' I--Specimen
- "'~
. ...... tube
,'J ... "::..~ ..
unnel L~ ~ '- [--Glass tube
t
Pinch c~ck^ ~. L·~ .I- (^) Plastic tut e
Figure 11-1. Schematic diagram of falling head permeability test setup.
Sland
- Supply water using a plastic tube from the water inlet to the burette. The water will flow from the burette to the specimen and then to the funnel. Check to see that there is no leak. Remove all air bubbles. II. Allow the water to flow for some time in order to saturate the specimen. When the funnel is full, water will flow out of it into the sink.
- Using the pinch cock, close the flow of water through.the specimen. The pinch cock is located on the plastic pipe connecting the bottom of the specimen to the funnel.
- Measure the head difference, hI (cm) (see Fig. II-I).
Note: Do not add any more ~a1:e'r to the burette.
- Open the pinch cock. Water will flow through the burette to the specimen and then out of the funnel. Record time (t) with a stop watch until the head difference is equal t6 h2 (cm) (Fig. II-I). Close the flow of water through the specimen using the pinch cock.
78 Soil Mechanics Laboratory M;mual
Table 11-1. Falling Head Permeability Test
Determination of Void Ratio of Specimen
Description of soil--'U""'fJ.!!.iifl.""Q:u.rm'-'-"sa"'n.<>dL.-__-,-____ Sample No. ___ _
Location _________________--~ _
Length of specimen, L. /3.2 cm Diameter of specimen, 0 -,6"".3""'5,,,-_ cm
Tested by _-'-______~______- Date^ _______^ _
Volume of specimen, V = 1t D2 L (cm 2 )
418. 4 Specific gravity of soil solids, Gs 2.
Mass of specimen tube with fittings, WI (g) 238.
Mass of tube with fittings arid specimen, W 2 (g) 965.
Dry density of specimen, Pd = W, ~ W; (g 1 cm 3 ) (^) 1.
Void ratio of specimen, e = Gsp w - Pd 0.
(Note: Pw=
Soil Mechanics Laboratory Manual 79
Table 11-2. Falling Head Permeability Test Determination of Coefficient of Permeability
Test No. 1
Diameter of specimen, D (cm) 6.
Length of specimen, L (cm) /3.
Area of specimen, A (cm^2 ) 3/.
Beginning head difference, hi (cm) 85.
Ending head difference, h2 (cm) 24.
Test duration, t (s) /5.
Volume of water flow through the specimen, V w (cm 3 ) 64
k = 2.303Vw^ L I og--hI ( cm / s')
(hI - h, )tA h, 0. .
Averagek = 0.037 (^) cm/s
k 20 • C = (^) kpc --I1^ T•C^ = CO. QJZ)(.O. 8.8'1,) - 0.033 cm 112O"C
2 3
6.35 6.
/3.2 /3.
3/.67 3/.
76.0 65.
20.0 (^) 20.
/5.3 /4.
58 47
0.038 0.
