INFLUENCE OF SOIL JOINTS ON PERMEABILITY OF GLACIAL TILL

Soil joints can significantly control the engineering and hydraulic behavior of soil masses similar to the manner in which rock joints control the behavior of rock masses. To investigate how soil joints can affect permeability of glacial till, 3 study sites were selected along the Lake Erie shoreline where glacial till is well exposed in the form of jointed bluffs. Field investigation consisted of detailed line survey of joints, and in-situ permeability and dye tests. Laboratory investigations focused mostly on how different aspects of joints (spacing, aperture, type of infilling material) and the properties of till itself (intact vs. disintegrated till, till with different water content) influence its permeability.

Field data analysis showed the existence of 3 mutually perpendicular prominent sets of joints. The studied glacial till falls into CL-ML category with up to 5% clay. The spacing and aperture of joints was expressed as open area/m² of the bluff and was about 40 cm² / m². In-situ measured water flow velocity varied from 7x10^-2–8.23 cm/s. Lab tests showed that intact till permeability varied from 2x10^-8 – 1.60x10 ^-7 cm/s where the permeability of disintegrated saturated till was within the range of 1.44x10^-6 – 3.41x10 ^-5 cm/s. Permeability of glacial till also proved to be time dependant. In case of seepage, permeability is strongly influenced by till water content and the type of joint infilling material, where aperture is not very significant. In the case of turbulent water flow, field tests indicated that the aperture of joints plays significant role in the overall permeability of glacial till masses.