Estimating the surface density of fissures in clay soil from deterministic parallel sections

In much clay soil the pore space consists of 3-D networks of narrow, approximately planar fissures. The density of the interface between fissures and solid soil is important; a method for its estimation from the horizontal and vertical cuboid samples that are taken conventionally is described here. Undisturbed samples are impregnated with resin containing a fluorescent dye. Parallel plane faces are cut, and the exposed surfaces are photographed under u.v. light. Pairs of superimposed photographic negatives are projected onto a screen, and the lateral displacement of each interface from one section to the next is measured at points of intersection of the interface with linear probes through the soil. These distances are used to infer the local orientation of the interfaces, which are then used with the point counts to estimate the interface areas. The method was applied to subsoil of the Windsor series. The interface density was estimated to be 9.69cm²/cm³ from one horizontal and one vertical sample. Point-counting with isotropic uniform random linear probes applied to five randomly orientated samples from the same site gave an estimate of 8.78cm²/cm³. It seems probable that the error associated with the new method is no greater than that associated with the standard method.