Instrumentation to Measure Soil Subsidence and Water Content in a Single Borehole

Abstract

Errors associated with current methods for measuring in situ vertical soil shrinkage related to water loss are associated with measurements being spatially disconnected, which introduces unknown spatial variability and excessive soil disturbance during installation. To minimize these errors, a method was developed to measure changes in thicknesses of multiple soil layers in a single borehole. Soil layer thickness was measured by tracking the location of magnets in the sidewall of the borehole using a probe with a magnetic field sensor. The sensor was capable of submillimeter repeatability for measurements of soil layer thickness. Soil water content was measured with a neutron moisture meter in the same borehole. Measurements made on two soils showed that, compared with spatially separated measures, the single borehole method improved the observed relationship between soil shrink-swell and water content change, increasing r2 from 0.73 to 0.90.