Project Number: 6408-13000-022-00
Start Date: Mar 11, 2012
End Date: Mar 10, 2017
1. Developing methodology and protocols for the rapid assessment of earthen embankments using non-invasive geophysical techniques will extend the application of geophysical methods by investigating the simultaneous use of seismic and electrical resistivity tomography to detect compromised zones within earthen embankments. Design and install a remote monitoring system of geophysical and geotechnical sensors in an earth embankment dam. The goal is to design and install the first remote real time continuous monitoring system in an earthen dam. The acoustic interaction with the soil medium depends upon mechanical and hydraulic properties of the soil surface that also influence soil surface erodibility. Therefore, acoustically measured properties can be used as a proxy for estimating soil surface erodibility. The first step in testing the hypothesis of this objective is to determine the experimental configuration and optimal range of acoustic frequencies. A numerical model based on existing theories of sound interaction with soil will be used to predict the acoustic response. The parameter space for the model will be constrained based upon typical soil characteristic (porosity, shear modulus, permeability, bulk density, elasticity) for a realistic range of erodibilities. 2. A design effort to advance the state of the art in the use of ultrasonic backscatter and attenuation to measure suspended sediment flux, developing a technique to evaluate the concentration and particle sizing of fines (0.1–100 µm) suspended in water, could be achieved by using either a single frequency acoustic system utilizing attenuation from forward propagation in conjunction with back-scattered signals or utilizing backscatter from multiple high (2-20 MHz) frequencies. Also, a design effort will be made to advance the state of the art in the use of kinetic energy impact plates instrumented with geophones or accelerometers to monitor bedload movement of gravel or sand. Under a parallel research effort, the NCPA has been working with the BOR to instrument a set of kinetic energy plate impact sensors to monitor bedload gravel movement as part of the Elwha River dam removal in the Olympic National Park in Washington State. The effort provides an opportunity to expand the state of the art for monitoring gravel bedload movement across other watersheds that are of interest to the USDA. 3. A seismic technique known as the multi-channel analysis of the surface wave (MASW) method has been developed at NCPA to obtain soil profile data at depths from a few centimeters to a couple of meters. A lab-scale test will be conducted. The MASW procedure consists of an acoustic/seismic excitation, a stepper motor controlled LDV for multi-points surface vibration measurement, a spectrum analysis to convert collected time-domain signals into the frequency-phase velocity domain, and an inversion process. Applying the MASW method to field soil, time/climate-related variations will be used for calculating the infiltration rate. Additional testing will consist of two parts: (1) lab tests with an acoustic transmission method and (2) field tests using MASW setup and dynamic move-out technique.