PARAMETER-ESTIMATION FOR DETERMINING HYDRAULIC-PROPERTIES OF A FINE SAND FROM TRANSIENT FLOW MEASUREMENTS

A cone penetrometer method for measuring hydraulic conductivity of uns aturated soils at depth is under development. Successful advancement o f this method hinges on using parameter estimation to obtain hydraulic parameter values from pore water pressure and flow rate data. A finit e element model is employed to predict flow responses, and objective f unctions describe differences between ''true'' and simulated responses . Contour plots in parameter space show the relative sensitivity of ob jective functions to field-saturated hydraulic conductivity, K-fs, fie ld-saturated moisture content, theta(fs), and the van Genuchten hydrau lic parameters, alpha and n. Principal curvatures and directions in pa rameter space describe the nature of objective functions near ''true'' parameter values. An objective function based on flow rate and pore w ater pressures does not provide better parameter sensitivity than one based on pore water pressures alone. It appears possible to obtain est imates of K-fs and alpha but unlikely that the other parameters will b e identifiable.