Estimation of Soil Permeability Using an Acoustic Technique Jin Won - PowerPoint PPT Presentation

Estimation of Soil Permeability Using an Acoustic Technique Jin Won Kim and Chung R. Song Department of Civil Engineering The University of Mississippi University, MS 38677

Concepts The propagation of elastic waves in saturated soils causes the coupled motion between solid particles and pore water. l d ti b t lid ti l d t Characteristic Frequency The coupled behavior involves the permeability of soils. By measuring the characteristic frequency of elastic waves in saturated soils, the permeability of soils is estimated . The University of Mississippi Civil Engineering

Theory : Characteristic Frequency and permeability Characteristic Frequency and permeability (Biot, 1956) (Biot, 1956) tion Attenuat : Characteristic Frequency f c = frequency at Maximum q y Specific (specific) Attenuation f f Frequency (Hz) Frequency (Hz) c • Characteristic frequency is related to the viscosity of the fluid and pore size (and eventually to the permeability of soils). y p y ) • When the frictional loss is maximum, the attenuation is maximum. φ φ ⋅ g g = π k ⋅ 2 f The University of Mississippi c Civil Engineering

Specific Attenuation Specific Attenuation Amp.:A1 A e α − − = Amp.: A2 A A2 ( ( r r ) ) A 2 1 2 1 r r 1 2 α = attenuation coefficient Underwater actuator • Specific attenuation Specific attenuation α − = c 1 Q Q π f The University of Mississippi Civil Engineering

Experimental Set Up Experimental Set Up ( To capture ) ( To capture ) f c Wave generator Digital oscilloscope Amplifier Receiver 2 Underground Actuator Receiver 1 The University of Mississippi Civil Engineering

Measured Signal Measured Signal Frequency : 400 Hz x 1 x 1 Receiver 1 x 2 Receiver 2 Receiver 2 Amplitude : X 1 ≈ X 2 Very little attenuation: not the characteristic frequency The University of Mississippi Civil Engineering

Measured Signal Measured Signal Frequency : 3000 Hz Receiver 1 X 1 X 2 Receiver 2 Amplitude : X 1 < X 2 V Very high attenuation: hi h tt ti Characteristic frequency The University of Mississippi Civil Engineering

Comparison of Dry and Saturated Conditions Saturated Condition : w = 23.14 (%) Dry Condition : w = 0.098 (%) y ( ) 1 Dry Soil Saturated Soil 0.5 Q -1 0 0 500 1000 1500 2000 2500 3000 3500 4000 4500 -0.5 Frequency (Hz) The University of Mississippi Civil Engineering

Field Testing Field Testing The University of Mississippi Civil Engineering

General General P Properties of roperties of S Soils for Field Tests oils for Field Tests γ n Gs W 3 ( / t m ) (%) d Sardis Lake 2.65 24.15 1.616 0.390 Tillatoba River 2.67 25.90 1.364 0.489 C S S B T C T B 0 0 2 0 1 3 1 2 1 2 2 0 0 2 1 0 1 3 2 0 2 2 1 3 0 3 1 2 4 1 4 2 l i a a Baton Rouge 2.68 45.56 1.210 ( ( 0.550 5 . . . 4 . . 1 . . . . . . . 5 t l e r t % . 5 4 6 4 3 6 . 3 6 6 . 4 2 . 6 d o / ) l d o a l ) / a 5 8 5 1 9 7 9 6 1 5 8 6 6 100 8 5 1 m rcent Finer i n r a 80 2 5 9 6 0 0 0 0 4 5 0 60 6 0 t s ) 40 C o R C R o 20 20 Per 0 o b r L 10.000 1.000 0.100 0.010 0.001 0.000 u e a a Grain Size, D(mm) k e k g Tillatoba River Baton Rouge Sardis Lake k R e e i

Field Test at the Sardis Lake (Sandy Soil) Field Test at the Sardis Lake (Sandy Soil) 0.6 0.4 0.2 Q -1 0 -0.2 0 1000 2000 3000 4000 5000 6000 7000 -0.4 0 4 -0.6 Frequency (Hz) Frequency (Hz) Acoustic Tech.: 2.02 × 10 -4 m/sec Field Perm. Test: 3.65 × 10 -4 m/sec The University of Mississippi Civil Engineering

Tillatoba River (Sandy Silt) Tillatoba River (Sandy Silt) 0.6 0.4 0.2 Q -1 0 -0.2 0 2000 4000 6000 8000 10000 12000 -0.4 Frequency (Hz) Frequency (Hz) Acoustic Tech.: 1.73 × 10 -4 m/sec Field Perm. Test: 3.70 × 10 -5 m/sec The University of Mississippi Civil Engineering

LSU Lake, Baton Rouge, Louisiana (Silty Clay) LSU Lake, Baton Rouge, Louisiana (Silty Clay) 0.6 0.4 0.2 Q -1 0 -0.2 0 2000 4000 6000 8000 10000 12000 -0.4 -0.6 -0.8 -1 -1.2 Frequency (Hz) Acoustic Tech.: N/A Field Perm. Test: 8.82 × 10 -6 m/sec Expected f c =900 kHz The University of Mississippi Civil Engineering

Conclusions Conclusions • Laboratory tests showed the existence of Biot’s characteristic frequency characteristic frequency. • Field tests for sandy soils and silty soils showed clear characteristic frequencies which can be used to compute the h t i ti f i hi h b d t t th permeability of soils according to Biot (1956) theory. • Field tests for silty soils did not show the good agreement with the field permeability test data. • Field tests for clayey soils did not provide the characteristic frequency because of the limitation of the equipment. The University of Mississippi Civil Engineering

Thank you for your attention. Any Questions ? The University of Mississippi Civil Engineering

• Checking system compliancy Checking system compliancy Lab. test with water only 5 4 3 3 0.92 m 2 1 0 0 2000 4000 6000 8000 10000 12000 14000 frequency (Hz) 0.47 m Errors from incorrect alignment The University of Mississippi Civil Engineering

5 4 3 Ratio A2/A1 2 1 0 0 2000 4000 6000 8000 10000 12000 14000 Frequency (Hz) 5 4 3 Attenuation 2 coefficient 1 0 0 2000 4000 6000 8000 10000 12000 14000 -1 System characteristic frequency is approximately 10000 Hz System characteristic frequency is approximately 10000 Hz Frequency (Hz) Frequency (Hz) The University of Mississippi Civil Engineering

• Checking Near Field Effect Checking Near Field Effect Near field ( Fresnel zone) : the amplitude with distance does not follow the geometric attenuation Hunter and Bolt (1955) ; Kinsler et al. (1982) 2 R ≈ ≈ π π λ x x R : radius of the source λ : wavelength 7 kHz 200 Hz mplitdue (mV) plitude (mV) 6000 6000 4000 4000 2000 2000 amp am 0 0 0 0 0 2 4 6 8 10 12 0 2 4 6 8 10 12 distance (cm) distance (cm) near far near far The University of Mississippi Civil Engineering

• Hvorslev Equation (1951) Hvorslev Equation (1951) π ⎛ ⎞ + ⎜ ⎜ ⎟ ⎟ D L ⎝ ⎝ ⎠ ⎠ ln h h 11 D : the diameter of a stand pipe = 1 k − L : the length of a sample t t h 2 1 2 h h h h 2 1 L L D The University of Mississippi Civil Engineering