Recently there has been interest in using the velocity of elastic waves to deduce soil physical properties. We wanted to validate the suggestion that the small strain shear modulus has a relatively simple linear relationship with penetrometer resistance. We were also interested in testing published equations for predicting shear wave velocity with an independent data set. Three soils were investigated in this study: a loamy sand soil and two silty clay loam soils. The soils were packed into cores with vertical axial stresses of 30, 200, or 1000 kPa. Following saturation, they were drained to a range of matric potentials between −10 and −500 kPa. After equilibration, we measured the velocities of shear (S wave) and compression (P wave) waves as well as the penetrometer resistances. Our data confirmed a previous proposal that the penetrometer resistance was an approximately linear function of the small strain shear modulus but tested the relationship by direct measurement. The relationships were found to have some sensitivity to soil type. Nevertheless, we show for the first time that there is considerable potential for using S wave velocity to deduce penetrometer resistance with a calibration that is relatively insensitive to soil type. Although estimation of the matric potential with either shear or compression wave velocity was found not to be very accurate, the possibility for estimating the matric potential from an elastic wave velocity given a priori knowledge of the void ratio is an interesting opportunity.

The acoustic, thermal, and mechanical performances of sawdust-reinforced polyurethane (PU) foam are investigated for different thicknesses and varying mesh sizes. Acoustic properties are explored using a combination of impedance tube testing and mathematical modeling with the Johnson–Champoux–Allard–Lafarge (JCAL) model, a simplified JCAL model and a model of non-uniform cylindrical pores with a log-normal radius distribution (NUPSD). Thermal Insulation and mechanical properties are determined by measuring the effective thermal conductivity (K_eff) and by tensile strength tests, respectively. Compared with pure PU foam, the presence of sawdust matches noise reduction coefficients (NRC) and increases sound absorption averages (SAA) by nearly 10%. Increasing thickness and width of backing air gap have the usual effects of improving low- and mid-frequency absorption and shifting resonance peaks toward lower frequencies. As well as superior acoustic performance, samples with Mesh 16 sawdust reinforcement provide both useful insulation (K_eff = 0.044 W/mK) and tensile strength (~0.06 MPa), confirming their multifunctionality. Although the JCAL model provides reasonable fits to the sound absorption data, some of the fitted parameter values are unphysical. Predictions of the NUPSD model are relatively poor but improve with sample thickness and after fiber addition.

Analytical approximations for the acoustical properties of a rigid-porous matrix perforated by labyrinthine slits are developed using classical theories for sound propagation in tortuous slits and for sound absorption by double porosity materials. Predictions of enhanced low-frequency absorption result from a combination of pressure diffusion and labyrinth tortuosity if there is a high permeability contrast between the matrix and the labyrinthine slit. Additional insight into the predicted influence of the properties of the porous matrix is gained by considering the matrix porosity to be provided by inclined micro-slits. Extra tortuosity can be introduced by alternating the width of the labyrinthine slit. An alternating-width vertical-wall labyrinth perforation is predicted to lead to low-frequency absorption peaks in a relatively low-flow-resistivity and low-porosity matrix. Example predictions, even when using underestimates of labyrinth tortuosity, demonstrate the potential of labyrinthine slit perforations for achieving narrowband deep sub wavelength absorption peaks from thin hard-backed porous layers.