Use of Shear Wave Velocity to Estimate Settlement Potential in Mine Spoils

Mine spoils are crushed rock fragments resulting from mountaintop removal mining. Mine spoils are typically placed in valleys as fill, but are susceptible to large amounts of differential settlement. Settlement mechanisms in mine spoil are different than those in soil, and include 1) stress-induced settlement due to particle crushing under increased confinement, and 2) hydrocompression due to wetting of the material. Herein, a method has been developed to quantitatively predict settlement in mine spoils by measuring the effect of confining stress and wetting on void ratio in reconstituted laboratory specimens. Settlement potential was found to be much more severe for dry specimens that had not been previously wetted. Upon wetting, the dry specimens experienced almost instant volume change corresponding to vertical strains of around 8%. Resonant column testing revealed that wetted specimens had lower shear wave velocities (v_s) than specimens that had not been wetted. Thus, v_s can be used to indicate whether or not spoils have been previously wetted, and settlement potential can be estimated based on deformation observations made in the laboratory specimens. With this method, mine spoil sites can be screened, and sites less susceptible to excessive amounts of settlement can be identified.