| Popis: |
The effects of rainfall on one type of buried container has been investigated at a test site near the University of Mississippi. Simulated and natural rainfall experiments were carried out over a three-year time period. The measurements allow for weathering effects on the buried container seismic to acoustic ratio detection contrast. The container was a filled 20 l plastic fuel container buried 30 cm in the natural loess soil. Six containers were buried, two were controls, two were exposed to the natural weather and two were used for simulated rainfall experiments. A loudspeaker was used to excite vibrations in the ground and a co-located vertical component geophone and a microphone measured the out of plane seismic/acoustic ratio in the vicinity of the containers. The rain induced wetting phase causes the container’s acoustic-to-seismic coupling contrast to increase and resonant frequency to decrease. The water drying phase restores the original frequency responses of smaller amplitude and higher resonant frequency. The phenomenon is cyclical. The capillary pressure in the pore spaces of soil grains reduces with wetting and increases with drying. These pore pressure changes are controlling the soil stiffness and acoustic response of the buried container.The effects of rainfall on one type of buried container has been investigated at a test site near the University of Mississippi. Simulated and natural rainfall experiments were carried out over a three-year time period. The measurements allow for weathering effects on the buried container seismic to acoustic ratio detection contrast. The container was a filled 20 l plastic fuel container buried 30 cm in the natural loess soil. Six containers were buried, two were controls, two were exposed to the natural weather and two were used for simulated rainfall experiments. A loudspeaker was used to excite vibrations in the ground and a co-located vertical component geophone and a microphone measured the out of plane seismic/acoustic ratio in the vicinity of the containers. The rain induced wetting phase causes the container’s acoustic-to-seismic coupling contrast to increase and resonant frequency to decrease. The water drying phase restores the original frequency responses of smaller amplitude and higher resonan... |
