REFERENCES�

ULTRASONIC WAVES THROUGH AGRICULTURAL SOILS TO DETERMINE THEIR COMPACTION AND POROSITY LEVEL�

Compaction is one of the major causes of the physical degradation of agricultural soils. The traffic of more and more heavy machines leads to a decrease of the porosity at both the topsoil and subsoil levels. This has negative impacts in agricultural and environmental contexts such as the reduction of soil fertility and water infiltration. This project aims at characterizing in a fast and non-destructive way the state of compaction of an agricultural soil at a local scale using ultrasonic wave propagation. Acoustic signatures of soil samples will be correlated to their compaction level and their porosity distribution.  As a result, this methodology could assist in taking restrictive measures such as load limitation of agricultural engines and implementing remedial methods�

QUESTIONS�

EXPERIMENTAL SETUP �

PERSPECTIVES�

SPEE

D OF

ULTR

ASON

IC WA

VES M

/S�

5T � 10T� 15T �DISTANCE (PERPENDICULAR TO DRIVING DIRECTION) FROM THE CENTER (CM)[1]�

Depth

(cm)�

•  Experimental results will be supported by modelling�

Triaxial cell�Vertical �pressure�

Later

al pr

essu

re�

Soil s

ample�

Is acoustic spectrum linked to size of pores?�

ACOUSTIC SPECTRUM �

2μm�

20μm� Pore size�

Input signals as pulse, sinusoid and chirp are generated and amplified. Sensors make contact with the sample through ultrasonic gel. The ultrasonic transducer sends the input signal through the sample. The attenuated signal is received by the opposite piezoelectric sensor. Finally, the signal received is amplified and digitized. All the acquisition is controlled with labview. Output signals are treated and postprocessed using Matlab.�

Mercury porosimeter characterizes soil’s porosity by applying various levels of pressure to a sample immersed in mercury. �

•  Integration of a triaxial cell in device to take into account the confining pressure and the hydraulic behavior of the soil �

[1] Destain, M.-F., Barbieux, S., Rosière, C. 2013. Rapport final de la convention « Evaluation des risques de compaction des sols en Wallonie » financée par le SPW (DGARNE), ULg, 110p�[2] Lu Z., Hickey C.J., Sabatier J.M. 2004. Effects of compaction on the acoustic velocity in soils, Soil Science Society of America Journal, 68:7-16.�[3] Louwagie, G., Gay, S.H., Burrell, A. 2009. Addressing soil degradation in EU agriculture: relevant processes, practices and policies. Report on the project ‘Sustainable Agriculture and Soil Conservation (SoCo)’. �[4] Cheeke D. 2002. Fundamentals and Application of Ultrasonic Waves. CRC Press. �[5] Lee J., Santamarina J. 2005. Bender Elements: performance and signal interpretation. Journal of Geotechnical and Geoenvironmental Engineering, 1063-1070. �[6] Leong E., Cahyadi J., Rahardjo H. 2009. Measuring shear and compression wave velocities of soil using bender-extender elements. Canadian Geotechnical Journal, 46:792-812. �

•  Correlate signal propagation signature through agricultural soil to water content, microbian life, roots pattern… �

Vertical stress σ (kPa) �

Do ultrasonic waves propagate faster in more compacted soil?�

0 �20 �40 �60 �80 �100 �120�140�160 �70 50 30 10 -10 -30 -50 -70 �

J. Luong, B. C. N. Mercatoris, M.-F. Destain - Precision Agriculture / Environmental Sciences and Technologies Dept - Faculty of Gembloux Agro Bio Tech - University of Liège�Passage des Déportés, 2 – 5030 Gembloux�

? � ? �

Controlled:��①  Granulometry�

②  Compaction level �(uniaxial compression /� Water content fixed) �

③  Porosity �

INPUT�

UNIMODAL � BIMODAL �INCR

EMEN

TAL I

NTRU

SION

DENS

ITY�

INCR

EMEN

TAL I

NTRU

SION

DENS

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%Figure'1:'Measurement'chain'

%Input%signals%as%pulse,%sinusoid%and%chirp%are%applied%to%the%National%Instrument%(NI)%acquisition%board%PXI%1031%(1)%that%generates%signal%through%the%AWG%(Arbitrary%Wave%Generator%P%2)%card%PXI%5421.High%Voltage%Amplifier%from%Falco%System%(3)%multiplies%the%incoming%signal%by%50.%The%transducer%A314S%from%Panametrics%(4)%emits%a%150V%signal.%After%passing%through%the%soil%sample%the%attenuated%signal%is%receipted%by%the%opposite%piezoelectric%sensor.%The%natural%frequency%of%the%sensors%is%1%MHz%and%its%bandwidth%is%0.35%MHz.%Sensors%make%contact%with%the%sample%through%ultrasonic%gel%that%presents%an%acoustic%impedance%close%to%the%water%acoustic%impedance.%The%air%acoustic%impedance%act%as%a%barrier%and%prevent%the%wave%from%penetrating%the%soil%sample.%The%ultrasonic%preamplifier%(5)%from%Panametrics%filters%the%signal,%thus%the%noise%is%reduced.%Finally,%the%PXI%2122%card%from%National%Instrument%digitizes%the%signal%received.%All%the%acquisition%is%controlled%with%a%labview%program.%%%The%black%arrows%show%the%circulation%of%the%electric%signal%for%the%ultrasonic%waves%acquisition.%%As%the%attenuation%is%strong%in%the%compacted%soil,%the%preamplifier%is%not%suficient%to%obtain%a%good%reading%of%the%measurements.%Repeated%signals%are%applied%and%the%average%of%those%signals%is%calculated%with%the%labview%program,%until%the%signal%to%noise%ratio%(SNR)%is%high%enough%to%have%an%accurate%reading.%Thus%the%weight%of%the%noise%in%the%signal%is%reduced%and%the%signal%without%noise%predominate.%Output%signals%are%treated%and%postprocessed%using%Matlab.%% %

12

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=Amplification�

Frequency�domain �

Spectrum�Pore size �

Time �domain � Velocity�

OUPUT�