Geotecnica engineering ( Constant Head and Falling Head Permeability Test in Sand )

Lab 6. Constant Head and Falling Head Permeability Test in Sand (Lab13 and Lab14 in 9th, Lab 10 in 8th ) Lab reports for the remaining experiments will be due within one week of your lab section. Lab report #6 due for Group A, B and C is on May 2, 2017 for Group D, E and F is on May 9, 2017 Lab #7 for all groups will be held on May 9, 2017 The rate of flow of water through a soil specimen of cross-sectional area A

can be determined as 𝑞 = 𝑘𝑖𝐴

where q = flow in unit time, k=coefficient of permeability, i = hydraulic gradient k is defined as a measure of material’s capacity to transmit water k can be determined in the lab by

Constant head test (for coarse grain) Falling head test (for coarse or fine grain soils)

Constant Head Test Measure Q flowing through the sample over a period of time (t) under a steady state head condition (h)

Falling Head Test Allow water flowing through the sample and measure the time (t) to drop from the upper (h

0 ) to the lower head (h

1 )

𝑞 = 𝑘𝑖𝐴 then 𝑘 = 𝑞𝑖𝐴 =

𝑄𝐿 ℎ𝐴𝑡

due to 𝑞 = 𝑄 𝑡 and 𝑖 = ℎ 𝐿

Assembly a permeameter Bottom porous stone 2/3 of compacted sandy soil Top porous stone Spring Fix the specimen tube

Data Recording for constant head

Use data sheet for Constant-Head Permeability Test : Determination of Coefficient of Permeability in p.309 (9th).

Determine Q with the constant collection time t

Data Recording for falling head

Use data sheet for Falling-Head Permeability Test : Determination of Coefficient of Permeability in p.309.

Take a reading Vw from burette Read h1 and h2 from ruler Record time t from h1 to h2

Calculation

Ignore Table 13-4 and 14-1 determination of void ratio of specimen

Calculate k and k20ºC for constant-head method

𝑘 = 𝑄𝐿 𝐴ℎ𝑡

𝑘20℃ = 𝑘𝑇℃ 𝜂𝑇℃ 𝜂20℃

Calculate k and k20ºC for falling-head method

𝑘 = 2.303𝑉𝑤𝐿 (ℎ1 − ℎ2)𝑡𝐴

log ℎ1 ℎ2

𝑘20℃ = 𝑘𝑇℃ 𝜂𝑇℃ 𝜂20℃

Lab Report (see section 13.7 and 14.7 in your textbook)

– Results section should include data tables and sample calculations for both permeability tests.

– Discuss the variation of k between two test methods.

– Discuss any sources of error